WO2017112694A1 - Adaptation of cyclic prefix duration to delay spread whilst maintaining symbol duration - Google Patents

Abstract

Methods, apparatuses, systems, devices, and computer program products directed to adapting cyclic prefix (CP) duration to delay spread, e.g., CP adaptation with constant OFDM symbol duration, are provided. Pursuant to new methodologies and/or technologies provided herein, adaptive CP may be carried out, e.g., to enhance spectral efficiency. In an embodiment, a CP duration may be made proportional or otherwise adapted (collectively "adapted") to a delay spread without adjusting symbol duration. Adapting the CP duration may include adjusting a clocking rate of digital-to-analog conversion and/or a clocking rate of analog-to-digital conversion according to the CP duration. Alternatively, adapting the CP duration may include performing fractional sampling rate conversion.

Description

ADAPTATION OF CYCLIC PREFIX DURATION TO DELAY SPREAD WHILST MAINTAINING SYMBOL DURATION

CROSS REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 62/263,592, filed 4-Dec-2015, which is incorporated herein by reference.

BACKGROUND

[0002] Field

[0003] This application is related to wireless communications.

[0004] Related Art

[0005] To meet the high data rate required for the next generation of cellular communication systems, the wireless industry and academia have been exploring ways to leverage the large bandwidths available at above-6 GHz frequencies, e.g., at centimeter wave (cmW) and millimeter wave (mmW) frequencies. The large bandwidth available at these frequencies may provide enormous capacity improvement for user-specific data transmission.

[0006] One challenge of using the above-6 GHz frequencies may be characteristics related to their propagation that may be unfavorable for wireless communication, especially in an outdoor environment. For example, higher frequency transmissions may experience higher free space path loss. Rainfall and atmospheric gasses, e.g., oxygen, may add further attenuation and foliage may cause attenuation and depolarization.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A more detailed understanding may be had from the detailed description below, given by way of example in conjunction with drawings appended hereto. Figures in such drawings, like the detailed description, are examples. As such, the Figures and the detailed description are not to be considered limiting, and other equally effective examples are possible and likely. Furthermore, like reference numerals ("ref ") in the Figures indicate like elements, and wherein:

[0008] FIG. 1 A is a system diagram of an example communications system in which one or more disclosed embodiments may be implemented;

[0009] FIG. IB is a system diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1 A;

[0010] FIGs. 1C, ID and IE are system diagrams of example radio access networks and example core networks that may be used within the communications system illustrated in FIG.

1A;

[0011] FIG. 2 illustrates an example communications system in which embodiments may be practiced or implemented; [0012] FIG. 3 is a block diagram illustrating an example of adaptive cyclic prefix ("CP");

[0013] FIG. 4 is a block diagram illustrating an example architecture of a system configured to carry out CP adaptation;

[0014] FIG. 5 is a block diagram illustrating an example architecture of a system configured to carry out CP adaptation;

[0015] FIG. 6 is a block diagram illustrating an example architecture of a system configured for fractional sampling rate conversion;

[0016] FIG. 7 is a block diagram illustrating a polyphase implementation for fractional sampling rate conversion;

[0017] FIG. 8 is a block diagram illustrating an example Farrow structure implementation of fractional sampling rate conversion;

[0018] FIG. 9 is a graph illustrating example Farrow filtering with frequency shifting;

[0019] FIG. 10 is a graph illustrating simulation results for Farrow filtering with frequency shifting;

[0020] FIG. 1 1 illustrates mutual interference between multiple users for (a) adaptive cyclic prefix, and (b) for zero-tail orthogonal frequency division multiplexing (OFDM);

[0021] FIG. 12 is a block diagram illustrating an example architecture of a transmitter configured for filtered OFDM for users of different CP lengths;

[0022] FIG. 13 is a block diagram illustrating an example architecture of a receiver configured for filtered-OFDM for users of different CP lengths;

[0023] FIG. 14 is a block diagram illustrating an example architecture of a receiver configured for filtered-OFDM for users of different CP lengths;

[0024] FIG. 15 is a block diagram illustrating an example architecture of a transmitter configured for filtered-OFDM for users of different CP lengths;

[0025] FIG. 16 is a block diagram illustrating an example architecture of a transmitter configured for group based CP length assignment with filtering;

[0026] FIGs. 17-22 are flow diagram illustrating representative procedures for supporting adaptation of cyclic prefix duration to delay spread; and

[0027] FIG. 23 is a graph illustrating an example performance evaluation of adaptive CP for DFT-spread-OFDM.

DETAILED DESCRIPTION

[0028] In the following detailed description, numerous specific details are set forth to provide a thorough understanding of embodiments and/or examples disclosed herein. However, it will be understood that such embodiments and examples may be practiced without some or all of the specific details set forth herein. In other instances, well-known methods, procedures, components and circuits have not been described in detail, so as not to obscure the following description. Further, embodiments and examples not specifically described herein may be practiced in lieu of, or in combination with, the embodiments and other examples described, disclosed or otherwise provided explicitly, implicitly and/or inherently (collectively "provided") herein.

[0029] Example Communications System

[0030] The methods, apparatuses and systems provided herein are well-suited for communications involving both wired and wireless networks. Wired networks are well-known. An overview of various types of wireless devices and infrastructure is provided with respect to FIGs. 1A-1E, where various elements of the network may utilize, perform, be arranged in accordance with and/or be adapted and/or configured for the methods, apparatuses and systems provided herein.

[0031] FIG. 1 A is a diagram of an example communications system 100 in which one or more disclosed embodiments may be implemented. Example communications system 100 is provided for the purpose of illustration only and is not limiting of the disclosed embodiments. The communications system 100 may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system 100 may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems 100 may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like.

[0032] As shown in FIG. 1A, the communications system 100 may include wireless transmit/receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d may be configured to transmit and/or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like.

[0033] The communications systems 100 may also include a base station 114a and a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the core network 106, the Internet 110, and/or the networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like. While the base stations 114a, 114b are each depicted as a single element, it will be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and/or network elements.

[0034] The base station 114a may be part of the RAN 104, which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and/or the base station 114b may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, i.e., one for each sector of the cell. In another embodiment, the base station 114a may employ multiple-input multiple output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell.

[0035] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0036] More specifically, as noted above, the communications system 100 may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA) and/or High- Speed Uplink Packet Access (HSUPA). [0037] In another embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and/or LTE- Advanced (LTE-A).

[0038] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 IX, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0039] The base station 114b in FIG. 1A may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 via the core network 106.

[0040] The RAN 104 may be in communication with the core network 106, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in FIG. 1A, it will be appreciated that the RAN 104 and/or the core network 106 may be in direct or indirect communication with other RANs that employ the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may be utilizing an E-UTRA radio technology, the core network 106 may also be in communication with another RAN (not shown) employing a GSM radio technology. [0041] The core network 106 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and/or other networks 112. The PSTN 108 may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) in the TCP/IP internet protocol suite. The networks 112 may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks 112 may include another core network connected to one or more RANs, which may employ the same RAT as the RAN 104 or a different RAT.

[0042] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities, i.e., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0043] FIG. IB is a system diagram of an example WTRU 102. Example WTRU 102 is provided for the purpose of illustration only and is not limiting of the disclosed embodiments. As shown in FIG. IB, the WTRU 102 may include a processor 118, a transceiver 120, a transmit/receive element 122, a speaker/microphone 124, a keypad 126, a display/touchpad 128, non-removable memory 106, removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and other peripherals 138. It will be appreciated that the WTRU 102 may include any sub-combination of the foregoing elements while remaining consistent with an embodiment.

[0044] The processor 1 18 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit/receive element 122. While FIG. IB depicts the processor 118 and the transceiver 120 as separate components, it will be appreciated that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0045] The transmit/receive element 122 may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, the transmit/receive element 122 may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element 122 may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element 122 may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element 122 may be configured to transmit and/or receive any combination of wireless signals.

[0046] In addition, although the transmit/receive element 122 is depicted in FIG. IB as a single element, the WTRU 102 may include any number of transmit/receive elements 122. More specifically, the WTRU 102 may employ MTMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit/receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0047] The transceiver 120 may be configured to modulate the signals that are to be transmitted by the transmit/receive element 122 and to demodulate the signals that are received by the transmit/receive element 122. As noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers for enabling the WTRU 102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example.

[0048] The processor 118 of the WTRU 102 may be coupled to, and may receive user input data from, the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker/microphone 124, the keypad 126, and/or the display/touchpad 128. In addition, the processor 118 may access information from, and store data in, any type of suitable memory, such as the non-removable memory 106 and/or the removable memory 132. The non-removable memory 106 may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SFM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as on a server or a home computer (not shown).

[0049] The processor 118 may receive power from the power source 134, and may be configured to distribute and/or control the power to the other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like.

[0050] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to, or in lieu of, the information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0051] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like.

[0052] FIG. 1C is a system diagram of the RAN 104 and the core network 106 according to an embodiment. As noted above, the RAN 104 may employ a UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106. As shown in FIG. 1C, the RAN 104 may include Node-Bs 140a, 140b, 140c, which may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. The Node-Bs 140a, 140b, 140c may each be associated with a particular cell (not shown) within the RAN 104. The RAN 104 may also include RNCs 142a, 142b. It will be appreciated that the RAN 104 may include any number of Node-Bs and RNCs while remaining consistent with an embodiment.

[0053] As shown in FIG. 1C, the Node-Bs 140a, 140b may be in communication with the RNC 142a. Additionally, the Node-B 140c may be in communication with the RNC 142b. The Node-Bs 140a, 140b, 140c may communicate with the respective RNCs 142a, 142b via an Iub interface. The RNCs 142a, 142b may be in communication with one another via an Iur interface. Each of the RNCs 142a, 142b may be configured to control the respective Node-Bs 140a, 140b, 140c to which it is connected. In addition, each of the RNCs 142a, 142b may be configured to carry out or support other functionality, such as outer loop power control, load control, admission control, packet scheduling, handover control, macrodiversity, security functions, data encryption, and the like.

[0054] The core network 106 shown in FIG. 1C may include a media gateway (MGW) 144, a mobile switching center (MSC) 146, a serving GPRS support node (SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0055] The RNC 142a in the RAN 104 may be connected to the MSC 146 in the core network 106 via an IuCS interface. The MSC 146 may be connected to the MGW 144. The MSC 146 and the MGW 144 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices.

[0056] The RNC 142a in the RAN 104 may also be connected to the SGSN 148 in the core network 106 via an IuPS interface. The SGSN 148 may be connected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide the WTRUs 102a, 102b, 102c with access to packet- switched networks, such as the Internet 110, to facilitate communications between and the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0057] As noted above, the core network 106 may also be connected to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0058] FIG. ID is a system diagram of the RAN 104 and the core network 106 according to another embodiment. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106.

[0059] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MFMO technology. Thus, the eNode-B 160a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a. [0060] Each of the eNode-Bs 160a, 160b, and 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown in FIG. ID, the eNode-Bs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0061] The core network 106 shown in FIG. ID may include a mobility management gateway (MME) 162, a serving gateway 164, and a packet data network (PDN) gateway 166. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0062] The MME 162 may be connected to each of the eNode-Bs 160a, 160b, and 160c in the RAN 104 via an SI interface and may serve as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 162 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0063] The serving gateway 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 via the SI interface. The serving gateway 164 may generally route and forward user data packets to/from the WTRUs 102a, 102b, 102c. The serving gateway 164 may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing contexts of the WTRUs 102a, 102b, 102c, and the like.

[0064] The serving gateway 164 may also be connected to the PDN gateway 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP- enabled devices.

[0065] The core network 106 may facilitate communications with other networks. For example, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the core network 106 may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network 106 and the PSTN 108. In addition, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0066] FIG. IE is a system diagram of the RAN 104 and the core network 106 according to another embodiment. The RAN 104 may be an access service network (ASN) that employs IEEE 802.16 radio technology to communicate with the WTRUs 102a, 102b, and 102c over the air interface 116. As will be further discussed below, the communication links between the different functional entities of the WTRUs 102a, 102b, 102c, the RAN 104, and the core network 106 may be defined as reference points.

[0067] As shown in FIG. IE, the RAN 104 may include base stations 170a, 170b, 170c, and an ASN gateway 172, though it will be appreciated that the RAN 104 may include any number of base stations and ASN gateways while remaining consistent with an embodiment. The base stations 170a, 170b, 170c may each be associated with a particular cell (not shown) in the RAN 104 and may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the base stations 170a, 170b, 170c may implement MTMO technology. Thus, the base station 170a, for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a. The base stations 170a, 170b, 170c may also provide mobility management functions, such as handoff triggering, tunnel establishment, radio resource management, traffic classification, quality of service (QoS) policy enforcement, and the like. The ASN gateway 172 may serve as a traffic aggregation point and may be responsible for paging, caching of subscriber profiles, routing to the core network 106, and the like.

[0068] The air interface 116 between the WTRUs 102a, 102b, 102c and the RAN 104 may be defined as an Rl reference point that implements the IEEE 802.16 specification. In addition, each of the WTRUs 102a, 102b, and 102c may establish a logical interface (not shown) with the core network 106. The logical interface between the WTRUs 102a, 102b, 102c and the core network 106 may be defined as an R2 reference point, which may be used for authentication, authorization, IP host configuration management, and/or mobility management.

[0069] The communication link between each of the base stations 170a, 170b, and 170c may be defined as an R8 reference point that includes protocols for facilitating WTRU handovers and the transfer of data between base stations. The communication link between the base stations 170a, 170b, 170c and the ASN gateway 172 may be defined as an R6 reference point. The R6 reference point may include protocols for facilitating mobility management based on mobility events associated with each of the WTRUs 102a, 102b, 102c. [0070] As shown in FIG. IE, the RAN 104 may be connected to the core network 106. The communication link between the RAN 104 and the core network 106 may defined as an R3 reference point that includes protocols for facilitating data transfer and mobility management capabilities, for example. The core network 106 may include a mobile IP home agent (MTP- HA) 174, an authentication, authorization, accounting (AAA) server 176, and a gateway 178. While each of the foregoing elements are depicted as part of the core network 106, it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator.

[0071] The MTP-HA 174 may be responsible for IP address management, and may enable the WTRUs 102a, 102b, and 102c to roam between different ASNs and/or different core networks. The MIP-HA 174 may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The AAA server 176 may be responsible for user authentication and for supporting user services. The gateway 178 may facilitate interworking with other networks. For example, the gateway 178 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. In addition, the gateway 178 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired or wireless networks that are owned and/or operated by other service providers.

[0072] Although not shown in FIG. IE, it will be appreciated that the RAN 104 may be connected to other ASNs and the core network 106 may be connected to other core networks. The communication link between the RAN 104 the other ASNs may be defined as an R4 reference point, which may include protocols for coordinating the mobility of the WTRUs 102a, 102b, 102c between the RAN 104 and the other ASNs. The communication link between the core network 106 and the other core networks may be defined as an R5 reference, which may include protocols for facilitating interworking between home core networks and visited core networks.

[0073] FIG. 2 illustrates an example communications system 200 in which embodiments may be practiced or implemented. The communications system 200 is provided for the purpose of illustration only and is not limiting of disclosed embodiments. As shown in FIG. 2, the communications system 200 includes a base station 202 and WTRUs 204a, 204b. As would be understood by a person of skill in the art, the communications system 200 may include additional elements not shown in FIG. 2. [0074] The base station 202 may be any of the base stations 114 (FIG. 1A), Node-Bs 140 (FIG. 1C), eNode-Bs 160 (FIG. ID) and base stations 170 (FIG. IE), for example. The base station 202 may include functionality similar to, and/or different from, the base stations 114, Node-Bs 140, eNode-Bs 160 and base stations 170, as well. For example, the base station 202 may include functionality to support features of 5G and to implement the procedures, techniques, etc. included herein.

[0075] The base station 202 may be configured for small cell operation and/or deployment. The base station 202 may be configured to support any of centimeter wave (cmW) and millimeter wave (mmW) operation. For simplicity of exposition, the term "xmW" may be used herein to refer to any of cmW and mmW. The base station 202 may be additionally and/or alternatively configured to support various (e.g., all or some) functionality and/or features for small cell operation and/or deployment as specified in 3GPP Release 12. In this regard, the base station 202 may be capable of operating an xmW air interface in parallel, simultaneously and/or otherwise in connection with an LTE, LTE-A or like-type (collectively "LTE") air interface. The base station 202 may be equipped with at least one of various advanced antenna configurations and beamforming techniques, such as those that may allow the base station 202 to simultaneously transmit LTE downlink channels in a wide beam pattern and xmW channels in one or more narrow beam patterns. The base station 202 may also be configured to utilize an LTE uplink configuration adapted with features and procedures (e.g., those detailed herein) to support WTRUs that lack, or do not use their, xmW uplink transmission capabilities.

[0076] Each of the WTRUs 204a, 204b may be any of the WTRUs 102 (FIGs. 1A-1E), for example. Each of the WTRUs 204a, 204b may include functionality similar to, and/or different from, the WTRUs 102, as well. The WTRUs 204a, 204b may include functionality to support features of 5G and to implement the procedures, techniques, etc. included herein. For simplicity of exposition, when "WTRU 204" is used herein, it may refer to any of the WTRUs 204a, 204b.

[0077] Each of the WTRUs 204a, 204b may be configured to support xmW operation. The WTRUs 204a, 204b may be further configured to support various (e.g., all or some) functionality and/or features for user equipment operation and/or deployment as specified in 3 GPP Release 12. Each of the WTRUs 204a, 204b may be capable of operating LTE and xmW air interfaces in parallel, simultaneously and/or otherwise in connection with each other. Each of the WTRUs 204a, 204b may have two sets of antennas and accompanying RF chains; one configured for operating in a LTE band and the other configured for operating in a xmW frequency band. However, the present disclosure is not limited thereto, and a WTRU may have any number of sets of antennas and accompanying RF chains. Each of the WTRUs 204a, 204b may include one or more baseband processors, and the baseband processors may include separate, or at least partially combined, functionality for baseband processing of the LTE frequency band and the xmW frequency band. The baseband processing functions may share hardware blocks for the xmW and LTE air interfaces, for example.

[0078] Introduction

[0079] Cyclic prefix (CP) has been widely used in practice to mitigate inter-symbol interference (ISI) for OFDM and/or OFDM-based transmissions. For example, CP is used for OFDM transmissions in LTE downlink and in IEEE 802.11a/g/n/ac, and for DFT-spread- OFDM in the LTE uplink. To eliminate ISI, a CP should have a duration ("CP duration" or, equivalently, "CP length") that is at least as long as a delay spread of a communications channel. For spectral efficiency reasons, excess duration of the CP duration over the delay spread, if any, may be minimized.

[0080] Delay spread may vary significantly from user to user, and from cell to cell. Recognition of this leads to a conclusion that multiple CP lengths may be used. In LTE, for example, two CP lengths were adopted, namely, a normal CP and an extended CP. The normal CP is 4.7 microseconds (" /s") and the extended CP is 16.7 μs. The extended CP is intended for use (and may be used) in environments of extensive delay spread (e.g., in large cells) and/or in a Multicast/Broadcast over Single Frequency Network (MBSFN). A MBSFN may have a large effective delay spread. This delay spread may be due to difference in propagation delays from different base stations, for example. Both the normal and extended CPs were adopted over other possible CP lengths for various reasons, including not having an acceptable spectral efficiency. Although the normal and extended CPs may have acceptable spectral efficiency (at least for LTE), they provide course granularity.

[0081] Recent measurement studies show that for millimeter-wave wireless channels at 28 gigahertz ("GHz") and/or at 73 GHz, a maximum root-mean-square (RMS) delay spread (e.g., the RMS of the power delay profile) might be tens of times greater than an average RMS delay spread and hundreds of times greater than a minimum RMS delay spread. For the millimeter wave, the symbol duration may be short. If a fixed (predefined) CP length is used, then, to prevent ISI, the fixed CP length has to be long enough to accommodate the maximum RMS delay spread. Using such fixed CP length may result in very inefficient use of the transmission time. As an example, consider an environment where the maximum RMS delay spread may be 200.3 nanoseconds ("ns") and the average RMS delay spread may be 12.1 ns at 73 GHz, such as set forth in Table 2 of S. Sun, T. S. Rappaport, R. W. Heath, A. Nix, and S. Rangan, "MIMOor millimeter -wave wireless communications: beamforming, spatial multiplexing, or both? " IEEE Communications Magazine, pp. 110-121, Dec. 2014, which is incorporated herein by reference. Assuming a subcarrier spacing of 0.5 megahertz ("MHz"), 2 /s of symbol duration is attributable to a data portion of a symbol (e.g., an OFDM symbol). Under these conditions and assuming that the CP length is a multiple, say, six times, of the maximum RMS delay spread, 99.7% of the delay lines may be covered by the CP (assuming the delay lines follow a Gaussian distribution). In this example, the fixed CP length is 6 x 200.3 ns, which amounts to an overhead of 37.5%. If, however, the CP length is set to 6 x an actual RMS delay spread, then the overhead may be as low as 3.5% on average.

[0082] For simplicity of exposition, "OFDM symbol" may refer to a symbol generated using any of OFDM, DFT-spread-OFDM, and like-type OFDM waveforms. An OFDM symbol includes a CP and a data portion, and has a duration attributable to the data portion and the CP appended to the data portion. In legacy systems, the symbol duration is dependent on CP length; different CP lengths result in different symbol durations. Different symbol durations, e.g., on a symbol by symbol basis, make it difficult to use a fixed-length frame structure (an important part of numerology) without compromising spectral efficiency.

[0083] In practice, a fixed subframe duration may be desirable for synchronous communication systems, such as LTE. The fixed subframe duration may facilitate inter-cell interference management, for example, by expressing a use of a resource (time) of a cell in a form that is understandable to its neighboring cells without communicating much information. The fixed subframe duration may facilitate backward computability with legacy systems that allocate a network resource (e.g., to a user) in terms of a unit of time. This unit of time may be, for example, a transmission time interval (TTI), such as used in HSPA and/or LTE.

[0084] Alternatives to CP -based waveforms that provide cyclic redundancy exist. These alternatives may include, for example, zero-tail discrete Fourier transform (DFT) spread OFDM ("zero-tail DFT-spread-OFDM") waveform that has a "zero" tail. In practice, the tails are not exactly zeros and are data dependent, and as a result, exact cyclic convolution is not achieved. Not achieving exact cyclic convolution may lead to poor bit error rate (BER) performance at high SNR. Additionally, to make the tail almost zero in an IFFT output at a transmitter, subcarrier mapping may be restricted to be contiguous or localized. Unique Word (UW) DFT- spread-OFDM is an alternative for mitigating ISI for OFDM. In principle, it can be made to adapt to delay spread. A redundant signal is added in the frequency-domain signal to generate a zero tail in the time-domain signal, and then a unique word is superposed on the zero tail. At a receiver, a channel-transformed unique word needs to be subtracted, and that requires an accurate estimate of the channel, which is hard to be met in practice. [0085] Overview

[0086] This disclosure is drawn, inter alia, to methods, apparatuses, systems, devices, and computer program products directed to adapting CP duration to delay spread, e.g., CP adaptation with constant OFDM symbol duration. Pursuant to new methodologies and/or technologies provided herein, a CP duration may be made proportional or otherwise adapted (collectively "adapted") to a delay spread without adjusting symbol duration. In various embodiments, this adaptive CP may be carried out to enhance spectral efficiency.

[0087] In an embodiment, making the CP length proportional to a delay spread without adjusting symbol duration may include adjusting a clocking rate of digital-to-analog conversion (DAC) and/or a clocking rate of analog-to-digital conversion (ADC) according to the CP length. In an embodiment, adjusting the clocking rate of digital-to-analog conversion (DAC) and/or the clocking rate of analog-to-digital conversion (ADC) may allow for use of efficient FFT/IFFT signal processing.

[0088] In an embodiment, making the CP length proportional to a delay spread without adjusting symbol duration may include performing fractional sampling rate conversion. In an embodiment, performing fractional sampling rate conversion may allow for use of efficient FFT/IFFT signal processing.

[0089] In an embodiment, making the CP length proportional to a delay spread without adjusting symbol duration may include performing mixed radix computation of DFT/IDFT with consideration of desired data duration.

[0090] In an embodiment, MAC-layer scheduling may be used to enhance multiple user performance in view of different users being assigned different CP lengths. In embodiment, per-channel filtered transmissions may be used for multiple user support where the CP length adaptation is performed on a per user basis or a per user group basis.

[0091] Example Cyclic Prefix Adapted OFDM Symbols

[0092] FIG. 3 is a block diagram illustrating an example of adaptive CP 300, which is sometimes referred to herein as "CP adaptation" and/or "CP adaptation with constant symbol duration". Pursuant to adaptive CP, a CP duration of an OFDM symbol is adapted (e.g., made proportional) to delay spread without adjusting symbol duration of such OFDM symbol.

[0093] As shown, the symbol duration ("OFDM-symbol duration"), T , is a combination of (i) a duration ("data-portion duration"), T_d , associated with a data portion of a OFDM symbol, and (ii) a duration ("CP duration"), T_c . for a CP appended to the data portion of such OFDM symbol. As also shown, the CP duration , T_c , increases with increasing delay spread, and resultantly, the data-portion duration, T_d , decreases in proportion to the increase in CP duration, T_c . As described herein in more detail, the OFDM-symbol duration, τ = T_c + T_d , is constant, such that, for any CP duration, T_c , the data-portion duration, T_d , is determinable from

T„ = T - T_C .

[0094] The OFDM symbol duration, T , is constant in that each OFDM symbol generated and/or transmitted for a given time period (e.g., a defined period for a fixed length frame structure) has the same duration. The OFDM symbol duration, T , may be any duration that provides reasonably high efficiency (e.g., T T being greater than or equal to 75%) and that satisfies other criteria, such as, controlling carrier-frequency offset and having a channel impulse response (CIR) that can be considered as a constant during T . With adaptive CP, adapting CP duration with fine granularity to the delay spread while meeting a constraint of a fixed subframe duration can be carried out (which others in the filed have considered as infeasible).

[0095] Example Architecture

[0096] FIG. 4 is a block diagram illustrating an example architecture of a system 400 configured to carry out CP adaptation. The system 400 may include a transmitter 401 and a receiver 403. The transmitter 401 may include an M-point DFT module 402, a subcarrier mapping module 404, an N-point IDFT module 406, a CP insertion module 408, a CP length adapter 409 and a digital-to-analog converter (DAC) 410. The receiver 403 may include an analog-to-digital converter (ADC) 414, a channel impulse response (CIR) estimation module 415, a CP removal module 416, an N-point DFT module 418, a subcarrier de-mapping module 420, an equalizer 422 and an M-point IDFT module 424.

[0097] The M-point DFT module 402 may include an input, M outputs and an M-point DFT, where Mis an integer. The input of M-point DFT module 402 may receive modulated symbols in blocks of length M. The modulated symbols may be modulated in accordance quadrature amplitude modulation (QAM) or another modulation scheme. Each block of symbols may be represented as "u", where u = (u₀ , u₁, - - - , u_M_^^T , and ^T stands for transpose. The M-point DFT module 402 may use using the M-point DFT to transform the symbols into a vector of M coefficients. The vector of M coefficients may be represented as " U", where

U = DFT (u) = (E/₀, E/₁, - , E/_i,-₁)^r , U_k =∑^;₀u_ne-^j2°"^klM , and k = 0,1, -, - 1 . The M-point

DFT module 402 may output the vector of M coefficients via the M outputs. [0098] The subcarrier mapping module 404 may include N inputs, N output and a include an N x N permutation matrix, P, for carrying out subcarrier mapping. The subcarrier mapping module 404 may receive the vector of M coefficients, U, on M of the N inputs. The subcarrier mapping module 404 may receive on the remaining {N-M) inputs a 1 x (N -M) vector with all entries being 0. The l x (N - ) vector may be represented as 0_lx(jV_ ₎ . The subcarrier mapping module 404 may perform subcarrier mapping on the input vector of M coefficients and 1 x (N -M) vector using the N x N permutation matrix, P, and may output a vector of N coefficients via the N outputs. The vector of N coefficients may be represented as "D", where the N-vector D = P(V^T , _lx(N__M))^T .

[0099] The N-point IDFT module 406 may include N inputs, an output and an N-point IDFT, where N is an integer. The N-point IDFT module 406 may receive the vector of N coefficients, "D", output from the subcarrier mapping module 404 on the Ninputs. The N-point IDFT module 406 may transform the N coefficients using the N-point IDFT. The N-point IDFT module 406 may provide from the output a signal, d, such as d = IDFT(D) = (d₀,d_l,- - - ,d_N__l)^T , where

[0100] The CP insertion module 408 may receive the signal, d, output from N-point IDFT module 406. The CP insertion module 408 may generate a CP based on a CP length provided by the CP length adapter 409. The CP may be K samples long, assuming a channel impulse response (CIR) is K+\ samples long. The CP insertion module 408 may insert (add) the CP to the received signal, d. The combination of the signal, d, and the CP of K samples may be output from CP insertion module 408 as a signal, x. The signal x may be represented as x = (d_N._K , d_N__K+1, - , ά^, άο , ά,, - , ά_Ν_,)^τ of length (N + K) .

[0101] The signal, x, may be fed to an input of the DAC 410, output from the DAC 410, carrier modulated, and transmitted across continuous-time channel.

[0102] A signal received by the receiver 403 from the channel may be carrier demodulated and then fed to an input of the ADC 414. The ADC 414 may covert the signal. The converted signal may be fed to an input of the CP removal module 416. The CP removal module 416 may remove the CP, and output a signal, y. The signal, y may include a channel induced discrete- time CIR h on the signal, x. The signal, y, for example, may be y = h ®d + z , where ® stands for circular convolution and z for noise.

[0103] The N-point DFT module 416 may include an input, Ν outputs and an N-point DFT. The input of the -point DFT module 416 may receive the signal, y. The N-point DFT module 416 may use the N-point DFT to transform the signal, y, into a vector of N coefficients, F. The vector of N coefficients, F may be represented as as Y = DFT(y) . The N-point DFT module 416 may provide the vector of N coefficients, F, from the N outputs.

[0104] The subcarrier demapping module 420 may include N inputs, N outputs and an N x N permutation matrix, P^'1 , for carrying out subcarrier demapping. The permutation matrix, P^'1 , may be an inverse of the Nx N permutation matrix, P . The N inputs of the subcarrier demapping module 420 may receive the vector of N coefficients, F, provided from the N outputs of the N-point DFT module . The subcarrier de-mapping module 420 may de-map the vector of N coefficients, F, and may output Y equal to elements 1 through M of ^_1Y , where P^'1 is the inverse permutation.

[0105] The equalizer 422 may include M inputs andMoutputs. The Minputs of the equalizer 422 may receive the vector of M coefficients output from the subcarrier de-mapping module

420. The equalizer 422 may provide from the M outputs an equalization vector, U .

[0106] TheM-point IDFT module 424 may include M inputs, an output and anM-point IDFT.

TheMinputs of theM-point IDFT module 424 may receive The equalization vector, U , output from equalizer 422. The -point IDFT module 424 may use theM-point IDFT to transform the equalization vector, U , and may output demodulated (e.g., QAM) symbols, ύ .

[0107] The architecture shown in FIG. 4 may be modified to support OFDM, e.g., by removing DFT precoding (i.e., removing the M-point DFT module 402 and the IDFT module 424 and setting M = N ).

[0108] Example Adaptive CP Methodologies and Technologies

[0109] Pursuant to various procedures herein for carrying out adaptive CP, a CP duration, T_c , may be determined, a corresponding CP length representative of the CP duration, T_c , may be determined, a data-portion duration, T_d , may be determined, and a data portion may be adapted to in accordance with the data-portion duration, T_d .

[0110] Adapting the CP duration, T_c , to the delay spread may be carried out as follows (and described with reference to FIG. 4, for convenience). The receiver 403 may measure or otherwise determine a statistic about the delay spread. The statistic may be, for example, a RMS delay spread, τ . The statistic may be fed back from the receiver 403 to the transmitter 401. The transmitter 401 may determine the CP duration, T_c , based on the fed back statistic. For example, the transmitter 401 may set the CP duration, /^ , as a multiple of, or more generally a function of, the RMS delay spread, τ .

[0111] The discrete-time signal x may enter the DAC 410 one sample per time, 7 , where ("clocking period"), T_s, is a period of a clocking signal of the DAC 410. As such, the transmitter 401 may determine (e.g., convert the CP duration, T_c , to) the CP length in samples, ^ , based on, T_c = KT_S or:

K = T T_S . ₍₁₎

[0112] To maintain the same numerology (e.g., subframe duration), the OFDM symbol duration, T = T_c + T_d may be kept constant. As such, the transmitter 401 may determine a window size, N, of the IDFT based on, T -T_c = NT_S , or:

N = (T -T_C)IT_S. ₍₂₎

[0113] To maintain the orthogonality among subcarriers, the transmitter 401 may determine the subcarrier spacing according to Δ ^" = l/(T - T_c) . The bandwidth, B, (in Hertz) of the D/A converted signal may be determined from:

B = NAf = N/(T -T_c) = l/T_s. ₍₃₎

[0114] It follows from (3) and (2) that the window size, N, is proportional to T - T_c , if the bandwidth, B, and the clocking period, T_s, are left unchanged. The transmitter 401 may send the determined CP length in samples, K , determined window size, N, and determined subcarrier spacing, Af , to the receiver 403. The receiver 403 may use the received parameters in connection with receiving OFDM symbols transmitted from the transmitter 401.

[0115] In one embodiment, the receiver 403 may determine the delay spread. The delay spread may be directly measured at the receiver 403, for example. Alternatively, the delay spread may be inferred, for example, via a method set forth in M. Krondorf and G. Fettweis, "Throughput enhancement for MIMO OFDM using frequency domain channel length indicator and guard interval adaptation " Proceedings of the 3rd International Symposium on Wireless Communication Systems (ISWC). IEEE, 2006, pp. 195-199; which is incorporated herein by reference. The receiver 403 may determine the delay spread in other ways, as well. The delay spread may be based on a reference signal sent from the transmitter 401 for the purpose of measuring or inferring the delay spread. [0116] The receiver 403 may calculate or otherwise determine a statistic of the delay spread ("delay-spread statistic"). The statistic may be, or be based on, a RMS of a delay power profile. The receiver 403 may report (send) of delay-spread statistic to the transmitter 401. Alternatively, the receiver 403 may quantize the delay-spread statistic and report the quantized delay-spread statistic to the transmitter 401. As another alternative, the receiver 403 may map the quantized delay-spread statistic to an index, and report such index to the transmitter 401.

[0117] The transmitter 401 may receive one or more of the reported delay-spread statistic, quantized delay-spread statistic or delay-spread-statistic index. The transmitter 401 (e.g., the CP length adapter 409) may calculate or otherwise determine the CP duration, /^ , based on, e.g., as a function of, the reported delay-spread statistic, the reported quantized delay-spread statistic or the reported delay-spread-statistic index. For example, the CP duration, /^ , may be determined as a multiple (e.g., 6 times) the delay spread using a function, the reported delay- spread statistic, quantized delay-spread statistic or delay-spread-statistic index, and/or lookup tables. The transmitter 401 may convert the CP duration, T_c , to, or otherwise determine, the CP length in samples, K, according to K = T T_S . The determined CP length may be provided to the CP insertion module 408, and may be used by the CP insertion module 408 to adapt the CP (set the CP duration, /^ ) of one or more OFDM symbols. The transmitter 401 may determine the window size, N, of the IDFT according to N = (T - T_C)IT_S . The window size, N, may be provided to the N-point IDFT module 406, and may be used by the N-point IDFT module 406 in connection with generating one or more OFDM symbols.

[0118] The transmitter 401 may determine the subcarrier spacing according to Af = \/(T - T_c)

. The transmitter 401 may send the determined CP length in samples, K, determined window size, N and/or determined subcarrier spacing, Af , to the receiver 403. The receiver 403 may receive the determined CP length in samples, K, determined window size, Nand/or determined subcarrier spacing, Af , and may use these parameters in connection with receiving OFDM symbols transmitted from the transmitter 401.

[0119] A complexity of the system of FIG. 4 comes from the use of the DFT and the IDFT, which have complexity 0(m²) , where m is the size of the DFT or IDFT. The complexity might be prohibitive when m is large, for example, m = 2048 as in LTE. As an alternative, low complexity FFT and IFFT may be used instead of the -point DFT and the -point IDFT. One example of a low complexity FFT (IFFT) that may be used is an efficient implementation radix-

2 FFT (assuming m is a power of 2). The efficient implementation radix-2 FFT may have substantially lower complexity, e.g., C nlog^m) , than theM-point DFT and theM-point IDFT of FIG. 4. To facilitate the use of such low complexity FFT(IFFT), Mmay be set to a power of 2 for the blocks of length M fed to the system.

[0120] The M-point DFT and the M-point IDFT of FIG. 4 may be configured to have low complexity by setting Mas a product of the powers of small primer numbers. If N is a power of 2, then the N-point DFT and the N-point IDFT of FIG. 4 may have low complexity, e.g., Nlo¾N .

[0121] FIG. 5 is a block diagram illustrating an example architecture of a system 500 configured to carry out CP adaptation. The system 500 of FIG. 5 is similar to the system 400 of FIG. 4, except that system 500 includes N+O -point IFFT and an N+O -point FFT, instead of an N-point IDFT and an N-point DFT.

[0122] The system 500 may include a transmitter 501 and a receiver 503. The transmitter 501 may include an M-point FFT module 502, a subcarrier mapping module 504, an N+OJ-point IFFT module 506, a CP insertion module 508 and a DAC 510. The subcarrier mapping module 504 may include an Nx N permutation matrix, P, for carrying out subcarrier mapping.. The receiver 503 may include an ADC 514, a CP removal module 516, an N+O -point FFT module 518, a subcarrier de-mapping module 520, an equalizer 522 and an M-point IFFT module 524. The subcarrier de-mapping module 520 may include an N x N permutation matrix, , P^'1 , for carrying out subcarrier demapping. The permutation matrix, P^'1 , may be an inverse of the N x N permutation matrix, P . .

[0123] The N+ -point IFFT module 506 and N+OJ-point FFT module 518 may implement a radix-2 or other low complexity IFFT and FFT, respectively. The transmitter 501 and receiver 503 may employ zero padding (of length Q) at the (N+Q)-po t IFFT module 506 and (N+Q)- point FFT module 518, respectively, if Nis not a power of 2.

[0124] Example ADC DAC Clocking Rate Adjustment

[0125] When N is not a power of 2, a window size of the (N+O -point IFFT module 506 and/or the (N+O -point FFT module 518 may be set by appending a vector of length Q (integer) such that N = N + Q is a power of 2 and that the output of the (N+O -point IFFT module 506 is N samples, regardless of the value of N. The output of the DAC 510 may be a waveform of duration NT_S . By setting NT_S = T— T_c , the CP duration, T_c , may be adapted by adjusting the clocking period, T_s . The waveform output from the DAC 510 may be generated based on the following. [0126] Define d(t) as a sum of NFSK signals according to:

[0127] d(t) may be represented in the digital domain as, d(ri) , such that the output of the (N+Q) -point IFFT module 506 are the samples of d(t) according to:

N-1

d(n) = d(t) \_t=nT =∑D_ke ^NTs \_t=nT ,0<n<N-\,

(5)

[0128] d(n) may be used to reconstruct d(t) without loss of information through the DAC

510 (e.g., using the Sampling Theorem). If Nis not a power of 2, Q zeros may be appended to Nto form a length- (N+Q) vector:

D = (D^rAx_e)^r ₍₆₎ such that N+Q is a power of 2. The \ength-(N+Q) vector may be applied to the inputs of (N+Q)- point (e.g., radix-2) IFFT module 506, as shown. Set a new sampling time interval as T_s . The output of the (N+Q)-point IFFT module 506 may be: d(n) = d(t)\_t___n¥, <n<N + Q-\,

/) where:

N-1 jl - ^b

d(t) =∑D_ke ^(N+Q)T 0≤t≤T-T_c,

k=o (8) from equation (6). Set:

(N+Q)f_s=T-T_c, ₍₉₎ and with N+Q being a constant, the CP duration, T_c , may be adapted by changing the sampling time interval, T_s . For example, by setting the CP length in samples to K, then T {T -T_c) = K/(N + Q) ; which together with equation (9) yields:

[0129] With equation (9), the DAC 510 may convert sequences d{ri) and d{ri) to respective analog signals d(t) and d(t) , which are identical. The zero padding at the (N+Q)-^ t IFFT module 506 does not change an equivalent lowpass signal, and in turn, the signal transmitted over the air. The total bandwidth B may be represented as:

B = N/(T - T_C) = N/((N + Q)T_S), (11) which may be controlled by adjusting N for a given (value of the) CP duration, T_c .

[0130] The system 500 of FIG. 5 may be configured to carry out adaptive CP to handle various operational criteria, including any of (i) a constant data (e.g., QAM) symbol rate, and (ii) a constant total bandwidth.

[0131] Example Configuration for Constant Data Symbol Rate.

[0132] The data (e.g,. QAM ) symbol rate may be defined as a number of data symbols that can be sent across the system per second. Given a OFDM symbol duration, T , is fixed (at least for a defined duration), N is constant for a constant data symbol rate (regardless of the zero padding). When the CP duration, T_c , changes, the clocking periods T_s and T_s along with the total bandwidth may change according to equations (3) and (11).

[0133] Example Configuration Constant Total Bandwidth.

[0134] Without zero padding, it follows from equation (3) that, for the total bandwidth, B, to remain unchanged without adjusting the clocking period, T_s, N may be adjusted by the transmitter and/or receiver in proportion to a change in T -T_c , With zero padding, it follows from equation (11) that, for the total bandwidth B to reamin unchanged, Nmay be adjusted by the transmitter and/or receiver in proportion to a change in T - T_c , and the sampling period,

T_s , may change with the adjusted N.

[0135] Example Clocking Rate Adjustment

[0136] The output of the (N+OJ-point IFFT module 506, d(n) , may be fed to the DAC 510 at a clocking rate F_s = \IT_s = (N + Q)/(T - T_c ) , where equation (9) is used. Given that N+Q may be considered as a constant, the clocking rate, F_s may change as the CP duration, T_c , adapts to the delay spread. Each of the tranmitter and receiver may employ a programmable frequency synthesizer to carry out changes in the clocking rate, F_s . The programmable frequency synthesizer may use at least one phase-locked loop (PLL). [0137] The PLL may be configured to operate according to various metrics, including PLL lock time. The PLL lock time may be defined as a perod of time that it takes a voltage-controlled oscillator (VCO) output to match a PLL reference clock signal in both frequency and phase. In some embodiments, the PLL lock time may be on the order of tens of microseconds or less. Although the channel might change significantly on an order of milliseconds, a delay spread may change very little over a much longer time interval as the delay spread is primarily determined by the objects in the reflection and/or scattering environment within a beam. Under this assumption, the clocking rate of the DAC 510 (ADC 514) may be changed infrequently, and loss of efficiency due to changes in clocking rate may be made negligible. If the delay spread changes frequently, then two PLLs may be used; one providing the clocking signal for a current communication, and the other to be turned on to provide a new clocking rate some time (greater than the PLL lock time) before the desired change in clocking rate.

[0138] To account for limited granularity of the clocking rate provided by the frequency synthesizer, a set of L available clocking rates T_s ^m , T_s ⁽²⁾ T_s ^(L) may be provided (e.g., stored in memory), from which one is selected to determine the CP duration, /^ , by equation (9), K by equation (10), and B and Nby equation (11).

[0139] When changing the clocking rate, the transmitter 501 and the receiver 503 may coordinate so that a clocking rate ("DAC clocking rate"), F_DAC, used at the DAC 510 is the same as a clocking rate("ADC clocking rate"), F_ADC, used at the ADC 514. In some embodiments, the ADC clocking rate, F_ADC, may be greater than DAC clocking TaXe, F_DAC, to perform oversampling at the receiver 504. The ADC clocking rate, F_ADC, may be based on the DAC clocking Tate, F_DAC, so that receiver 503 can sample the output of the oversampling based processing at the correct rate. The transmitter 501 may send the DAC clocking rate, F_DAC, to the receiver 503. Alternatively, the DAC clocking rate, F_DAC, may be communicated as an index that is representative a particular allowable value of the DAC clocking rate, F_DAC . The transmitter 501 and the receiver 503 may agree upon a set of indices and the mapping from indices to clocking rates.

[0140] Alternative Example Operation

[0141] In an embodiment, the transmitter 501 may send a reference signal for the receiver to directly measure or infer the length of the channel impulse reponse (CIR). The receiver 503 may directly measure or infer the CIR length based on the reference signal sent from the transmitter 501. The receiver 503 may report the CIR length and/or indication of the CIR length to the transmitter 501. The indication of the CIR length may be a quantized CIR length or an index mapped to the quantized CIR length, for example. The transmitter 501 may determine the CP length and the clocking rates to the ADC 514 and DAC 514 according to equation (11). The transmitter 501 may send the determined CP length and the clocking rate(s) to the reciever 503.

[0142] In an embodiment, the transmitter 501 may send a reference signal for the receiver 503 to directly measure or infer the CIR length. The receiver 503 may directly measure or infer the CIR length based on the reference signal sent from the transmitter. The receiver 503 may determine the CP length and the clocking rate to the ADC 514 and DAC 510 according to equation (11). The receiver 503 may send the determined CP length and the clocking rate to the transmitter 501. The receiver 503 may also report the CIR length and/or indication of the CIR length to the transmitter 501.

[0143] Example Sampling Rate Conversion

[0144] FIG. 6 is a block diagram illustrating an example architecture of a system 600 configured for (digital) fractional sampling rate conversion. The system 600 may include a transmitter 601 and a receiver 603. The system 600 of FIG. 6 is similar to the system 500 of FIG. 5, except that system 600 employs sampling rate conversion at the transmitter 601 and the receiver 603. The transmitter 601 may include an M-point FFT module 602, a subcarrier mapping module 604, an (N+Q)-pomt IFFT module 606, a sampling rate conversion module 607, a CP insertion module 608 and a DAC 610. The subcarrier mapping module 604 may include an JV x JV permutation matrix, P . The receiver 603 may include an ADC 614, a CP removal module 616, a sampling rate conversion module 617, an (N+Q)-po t FFT module 618, a subcarrier de-mapping module 620, an equalizer 622 and an M-point IFFT module 624. The subcarrier de-mapping module 620 may include an N x N permutation matrix, P .

[0145] In an embodiment, the clocking rate F_s of the DAC 610 (and ADC 614) may be the same as the clocking rate F_s . But to make sure that d(t) is of length T - T_c , converting d(n) , which oversamples d(t) , into a shorter sequence d(n) may be performed via sampling rate conversion with a fraction N/(N + Q) . The complexity is low if N/(N+ Q) is a fraction in which both the numerator and the denominator are small numbers. The value of N may be selected from a set of values for N that offer low complexity. The selected value of N may be one that gives a reasonably low value for T T while satisfying equation (1 1).

[0146] An efficient way of performing fractional sampling rate conversion is using polyphase filters. The fraction N/(N + Q) may be simplified to I/D, i.e., N/(N + Q) = 1 1 D where / and D are relatively prime (the greatest common divisor is 1). Then, a fractional I/D sampling conversion is performed.

[0147] FIG. 7 is a block diagram illustrating a polyphase filter implementation 700 for fractional sampling rate conversion. In FIG. 7, the commutator rotates counterclockwise and

P ) = g + ^nI \ i = 0 , 1 , I- I , n = 0 ,1 , ...,L 1 where Li = Mi/I, and Mi is the length of the lowpass filter g(n) that would be used in the direct- form realization of the fractional sampling frequency conversion with the following frequency response

[0148] An alternative (or alternate) way of performing fractional sampling rate conversion includes using a Farrow filter. The Farrow filter may make the system more flexible to the values of I and D and reduce overall hardware complexity. The Farrow filter has an advantage of simplicity in hardware implementation when the fraction (in sampling rate conversion) changes over time. At a high level, the effect of sampling rate conversion is to introduce a fractional delay (in samples) to the output samples relative to the input samples, and the desired fractional delay filter is decomposed into multiple FIR filters and the outputs are weighted by the polynominals of a control varaible which represents the time-varying factional delay.

[0149] Using the sampling interval of the input signal d[i] as the time unit, the fractional delay of the output sample d[i] may be

A [i] = i—— n (13) where n =

[0150] Let the desired fractional delay filter be approximated by f_r(A[i]), r = 0, 1, ... , R. A parametric approach is taken to expressing each filter tap, which is a polynomial in Δ[ί] with parameters b [r], I = 0, 1, ... , L, to be determined:

[0151] The conversion yields

where Vi [n] =∑^=o M d n — r) .

[0152] FIG. 8 is a block diagram illustrating an example Farrow structure 800 implementation of fractional sampling rate conversion. As shown, Bi(z) is the Z-transform of bi[r], where 1=0, 1, L, and r=0, 1, R. a benefit of the Farrow structure is that the structure remains the same, and the only parameter that needs to be changed is the fractional delay Δ[ί], which changes on a output sample basis. The parameters bj [r], I = 0, 1, ... , L, may be solved by minimizing the error between the ideal fitler and f_r(A[i]), r = 0, 1, ... , R, for example, via Lagrange interpolation.

[0153] One procedure to use the Farrow filter to calcualte an arbitrary-size IDFT is as follows.

Np

Choose a constant integer p and solve for q =— . Note that q may not be an integer. Then use lower order polynomials to approximate successive fragments of an original lowpass filter. Then ^λ decimate' the output of the polyphase filters in strides of q, corresponding to a step size of AT in seconds, where F_s is the sampling rate corresponding to the IFFT output.

P^Fs

[0154] A special treatment can simplify the design. The original lowpass filter g(n) is symmetric in the frequency domain, but the spectrum of the output of the IFFT module 606 is asymmetric with a support of [o,^ j in relative frequency, where N = N + Q, resulting in a zero-interpolated signal with asymmetric spectrum with support = + ^], i = 0, ±1, ±2, as illustrated at plot 901 of FIG. 9. To resolve this mismatch, shift the spectrum of the IFFT output by multiplying d(n) with a phasor exp(—jnnN /N) . This phase shift makes the spectrum of the interpolated signal symmetric in the frequency domain as shown in plot 903 of FIG. 9. The resulting Farrow filter output is shown in plot 905 of FIG. 9. An inverse phase shift exp jnnN /N) is applied to the output of the Farrow filter 800.

[0155] The polynomial approximation can result in very good performance, as illustrated in the FIG. 10 for the first 100 data points of the IDFT/IFFT output. The dashed line with circles is the IDFT using the direct computation method, and the dotted line with crosses is the IDFT using the Farrow approximation method. The two curves almost overlap. The relative MSE is -44.4dB, well below the effect of noise in a typical operating environment. [0156] The Farrow approximation offers attractive complexity reduction. Assume that the original lowpass filter has a length L, and the polynomials are of order a. Then, each polyphase filter has a length - . Using Horner's rule, the evaluation of a polynomial requires multiplications. There are 2 multiplications for phase shifts for each sample. The total complexity is about (a + 1) ^ + 2 + ^{LN l}°^^{2 N} multiplications per input sample, as opposed to

N in the direct IDFT/DFT approach. For the example in FIG. 10, L = 231, p = 9, a = 4. The Farrow approximation method may use 146 multiplications per sample for, as opposed to 1543 multiplications in the direct IDFT computation method.

[0157] The a psuedocode for carrying out the procedure is provided below. There are several tecnquiues used to ensure the accuracy of the filtering process. One is how to ensure the continuity of the polynomial fitted segments of the orignal lowpass filter g(n). Another one is how to take care of the tail of the incoming data d(n).

/* phase shift */

for i=l:( N - 1)

d(n) = d(n) exp (- ^)

end

/* get lowpass filter g(ri) */

For example, use the Parks-McClellan optimal equiripple FIR filter design method L=length of g(ri)

/* get polyphase filters or subfilters */

num_sub = - p

zero-pad g(n) to get h(ri) so that the latter's length is a multiple of num_sub M=length of filter h( )

subfilter i is: h^ri) = h(i + np), i = 1, 2, ... , num_sub

length_sub = M/num_sub

for i=l:num_sub

sub_filters(i,:)= h(i:num_sub:end); /* subfilter i picks h(i), h(i+num_sub), ...*/ end

/* polynomial approximation of segments of the original lowpass filter g(ri) */

/* to store polynomial coefficients of segments of g(n) */ for i= l:length_sub

col_0 = sub_filters(:, i)

if i<length_sub

/* to make sure continuity between adjacent segments */

col = [col_0; sub_filters(l,i+l)]; /* add the first element of the next column */

else

col = [col_0; 0]

end

X = 0:(l/num_sub) : l; /* time offset relative to an input sample interval of d(n) V

P(i,:) =polyfit(X, col^T, a); /* polynomial fitting */

end ^{w =} ®lxlength_sub

delay = (L-l)/2

delayl = floor(delay/p)

delay2=delay/p - delayl

w(l:delayl)= d(delayl:- l: l)

ptr=delay2 /* initialize the pointer */

m=l

v ⁼ ®lxN

stride = N/N for k=(delayl+l) :length(d_t) /* iterate on input signal on a per sample basis */ w = [d (k) w(l:end-l)]; /* shift in a new sample */

while ptr < 1

/* apply polynomial approximation */

filter_poly = 0_{lx len5t/l}__suiJ

for n=l:length

filter_poly(n) = polyval(P(n,:), ptr) /* evaluate the polynomial at value ptr

7

/* Horner's rule may be used */ end

v(m) = sum(input_in_window .* filter_poly) /* filter output */

ptr = ptr + stride

m=m+l;

end

ptr=ptr -1; /* will move to the next sample interval */

end

/*handle the tapering tail of input signal */

for k=l:length_sub

w = [0 w(l:end-l)]; /* shift in a zero */ while ptr < 1

filter_poly = 0_lxi_ength_sub

for n=l:length_sub

filter_poly(n) = polyval(P(n,:), ptr);

end

v(m) = sum(input_in_window * filter_poly);

ptr = ptr + stride;

m=m+l;

end

ptr=ptr -1;

end

v = v(l:N) /* choose the first N elements only */

/* inverse phase shift */

for i=l:( N - 1)

d(n) = v(n) exp (^ )

end

[0158] Pursuant to a Farrow filter implementation, a phase shift of the IFFT output signal to center it at the zero frequency may be applied, and the inverse phase shift may be carried out when Farrow filtering is completed. In addition, polynomial approximated segments of the original lowpass filter may be made continuous. [0159] Example Mixed-Radix Implementation of DFT

[0160] Direct computation of DFT/IDFT has high computational complexity. If the size of the DFT/IDFT can be factorized into the powers of small prime numbers, computational complexity can be reduced. The value of Nmay be set by choosing the powers of prime numbers such that the value is closest to the desired value for N. The following is an example for prime numbers 2, 3, 5:

[0161] Mixed Transmiter Receiver Architecture

[0162] For simplicity of exposition, the transmitters and receivers shown and described herein have complementary architectures; e.g., the receivers are configured to invert operations carried out by the corresponding transmitters. Those having skill in the art will recognize that the transmitters and receivers need not have complementary architectures and may be configured to (and may) carry out adaptive CP using different techniques. For example, in one embodiment, a transmitter may be configured to (and may) carry out adaptive CP using an adjustable DAC clocking rate technique, and a corresponding receiver may be configured to (and may) carry out adaptive CP using a fractional sampling rate conversion technique.

[0163] Example Architecture and Procedures for Mitigating Mutual Interference

[0164] Multiple users on disjoint subsets of subcarriers with different CP lengths may interfere with each other during simultaneous transmissions. An example of this is illustrated in FIG. 11(a). As shown, two simultaneous transmissions may be received at user 2. One of them may be intended for user 1 and the other may be for user 2. The ISI impacting the head of the DFT window of user 2 may be different from what would be caused by the superposed tails of the two symbols, causing interference. This problem exists with many other approaches. Mutual interference may occur between users may occur any time CPs, zero-tails, or UWs of simultaneous transmissions are of different lengths. An example of this is illustrated in FIG. 11(b). As shown, two simultaneous zero-tail OFDM transmissions may be received at user 2; one of them may be intended for user 1 and the other may be for user 2. The difference in duration of the data segments en and e₁₂ breaks cyclicity of the received signal in the DFT window of user 2. [0165] The CIRs shown in FIGs. l l(a)-(b) are those that may be seen by user 2. For the transmission intended for user 1, the CIR seen by user 2 might be longer than what is seen by user 1 and might be longer than the zero tail for user 1 (as shown in FIG. 11(b)).

[0166] FIG. 12 is a block diagram illustrating an example architecture of a transmitter 1200 configured for filtered-OFDM for users of different CP lengths. The transmitter 1200 may be suitable as a transmitter of a base station as it supports simultaneous transmissions to multiple users in a cellular downlink, for example. The transmitter 1200 may include multiple transmitter structures 1201a, 1201b ... 1201k (each "a transmitter structure 1201 "). The transmitter structures 1201a, 1201b ... 1201k may be configured for transmission of data to respective users. Each transmitter structure 1201 may include an N-point IFFT module 1206, a parallel- to-serial converter (P/S) 1207, a CP insertion module 1208, a CP length adapter 1209, an up- sampler 1211, a sub-channel filter 1213 and a DAC 1210. The N-point IFFT module 1206, P/S 1207, CP insertion module 1208, CP length adapter 1209 and DAC 1210 may be configured, and may operate, as described previously in connection with FIGs. 4-11.

[0167] The sub-channel filters 1213a-k may be used along with frequency upconverters 1217a-k to select a desired frequency range for each intended receiver before doing the DFT. Each sub-channel filter 1312 may be configured to filter on subcarriers or groups of subcarriers, and may be based, for example, on like type filtering used for filtered OFDM, Filter Bank Multicarrier and resource block filtered OFDM.

[0168] Data for different users may be generated by the transmitter structures 1201a, 1201b ... 1201k in disjoint spectrum blocks, and the resulting signals may be added together by adder 1212 and then transmitted using one or more RF chains (not shown). Eahc spectrum block may be a subcarrier, or a contiguous block of subcarriers (including the special case of 12 contiguous subcarriers, or one resource block (RB) in LTE/LTE-A), or any contiguous block of spectrum. Vector si[n] = (si,o[n], Si,i[n], .. . , si,Mi[n]) may be the data to be sent to user i, where i=0, 1, K, and Mi may be the length of the vector si[n]. The CP length adapters 1208a-k may performed CP length adaption on a per user basis. The CP length adapters 1208a-k mayuse methodologies and/or techniques described herein, including changing the clocking rate or fractional sampling rate conversion to perform the CP length adaption. Although FIG. 12 illustates CP length adaptation using a changing the clock rate methodology and/or technique, a fractional sampling rate conversion methodology and/or technique will be apparent to those skilled in the art from the foregoing descriptions.

[0169] For any transmitter structure 1201, the IFFT output with the CP appended (added) may be upsampled by the upsampler 1211. The upsampler 1211may upscale it by a factor of Qi=L/Ni, where L is the desired OFDM symbol duration in samples and z=0, 1, ... , K. The spectrum of the signal of user i may be shaped by using a filter fa(n) of the sub-channnel filter 1312, where z=0, 1, ... , K. The signal may be up-converted by a user specific frequency where

7=0, 1, ... , .

[0170] There may be a number of ways to design the filters. One way is to make all of the filters h(n) the same. This may simplify the design while limiting the use of spectrum among different users. Another way is to design the filters on a per user basis. The per user design may allow for more flexibility in using the spectrum. For example, with a wider filter one user may use twice as much spectrum as another user does. Additionally, different out of band (OOB) emission can be achieved for different users. For example, when a user's spectrum chunk (called channel in the sequel) is close to another user's, a window (e.g., Blackman) with low side lobes may be incorporated into the filter. In contrast, when a user's channel is far apart from any other user's, a less complex window may be chosen.

[0171] The transmitter shown in FIG. 12 may be configured to support DFT-spread-OFDM, e.g., by adding, to each transmitter structure 1201, an M-point DFT module and a subcarrier mapping module configured to feed the Ni-point IFFT module 1206, where i=0, 1, ... , K.

[0172] FIG. 13 is a block diagram illustrating an example architecture of a receiver 1300 configured for filtered-OFDM for users of different CP lengths. The receiver 1200 may be suitable as a receiver of a base station as it supports simultaneous reception from multiple users in a cellular uplink. The receiver 1200 may include multiple receiver structures 1303a, 1303b ... 1303k (each "a receiver structure 1303 "). The receiver structures 1303a, 1303b ... 1303k may be configured for reception of data from respective users. Each receiver structure 1303 may include an ADC 1314, a sub-channel filter 1315, a down-sampler 1319, a CP removal module 1316, a serial -to-parallel converter (S/P) 1321, anN-point FFT module 1320 and a FDE module 1322. Each receiver structure 1303 may perform a reverse of the operations carried out by a transmitter structure configured in accordance with a transmitter structure 1201 of FIG. 12. For example, a received signal may converted to digital, and then frequency translated by o, fi... /κ, for user 0, user 1, user *, resepctively.

[0173] The receiver 1300 may be configured to support DFT-spread-OFDM, e.g., by adding, to each receiver structure 1303, a subcarrier demapping module and an M-point IDFT module following the FDE block, where i=0, 1, K.

[0174] FIG. 14 is a block diagram illustrating an example architecture of a receiver 1400. The receiver 1400 may be suitable for use in a mobile terminal i, where i=0, 1, ... , K. [0175] The receiver 1400 may receive transmissions from the transmitter 1200 of FIG. 12. The receiver 1400 is similar to a receiver structure 1303 of FIG. 13. The receiver 1400 may include an ADC 1414, a sub-channel filter 1415, a down-sampler 1419, a CP removal module 1416, an S/P 1421, an N-point FFT module 1420 and a FDE module 1422. The receiver 1400 may perform a reverse of the operations carried out by a transmitter structure configured in accordance with a transmitter structure 1201 of FIG. 12.

[0176] The frequencies the downsampling factor Qi and the filter coefficients h(n) may be communicated from the transmitter 1200 to the receiver 1400. Alternatively, such parameters may be mapped to indices, and the indices may be communicated from the transmitter 1200 to the receiver 1400, where the indices may be mapped back to the respective parameters. The receiver 1400 may be configured to support DFT-spread-OFDM, e.g., by adding a subcarrier demapping module and an M-point IDFT module following the FDE module 1422, where i=0, Ι, . , . , Κ.

[0177] FIG. 15 is a block diagram illustrating an example architecture of a transmitter 1500. The transmitter 1500 may be suitable for use in a mobile terminal /^', where i=0, 1, . . . , K. The transmitter 1500 may transmit transmissions to the receiver 1300 of FIG. 12. The transmitter 1500 is similar to a transmitter structure 1200 of FIG. 12. The transmitter 1500 may include an N-point IFFT module 1506, a P/S 1507, a CP insertion module 1508, a CP length adapter 1509, an up-sampler 151 1, a sub-channel filter 1513 and a DAC 1510.

[0178] The transmitter 1500 may be configured to support DFT-spread-OFDM, e.g., by adding an M-point DFT module and a subcarrier mapping module configured to feed the Appoint IFFT module 1506, where i=0, 1, K.

[0179] The delay spread may be communicated from the transmitter 1500 to the receiver 1300 by sending any of a quanitzed delay spread or an index mapped to the quantized delay spread. The number of subcarriers N may be communicated from the transmitter 1500 to the receiver 1300. The transmitter 1500 and the receiver 1300 both may calculate the amount of spectrum according to Equation (3), and may consult a pre-defined lookup table to find parameters, such as upsampling/downsampling factor Qi and filter coefficients h[n], where i=0, 1, . . . , K.

[0180] The filtering approach may have low complexity when the number of spectrum chunks is small. For example, if a channel coherent bandwidth is large relative to the total bandwidth, then the total bandwidth input may be partitioned into a small number of spectrum chunks, and the filtering approach can be applied.

[0181] FIG. 16 is a block diagram illustrating an example architecture of a transmitter 1600 configured for group based CP length assignment with filtering. The transmitter 1600 may be suitable as a transmitter of a base station as it supports simultaneous transmissions to multiple users in a cellular downlink, for example. The transmitter 1600 may include multiple transmitter structures 1601a, 1601b ... 1601k (each "a transmitter structure 1601 "). The transmitter structures 1601a, 1601b ... 1601k may be configured for transmission of data to respective groups of users. Each transmitter structure 1601 may include an N-point IFFT module 1606, a P/S 1607, a CP insertion module 1608, a CP length adapter 1609, an up-sampler 1611, a subchannel filter 1613 and a DAC 1610.

[0182] The transmitter 1660 may be configured to exploit scheduling flexibility to support multiple users. The transmitter 1600, for example, may configure the same CP lengths for users of similar delay spreads, and may schedule only users of the same CP length for simultaneous transmissions. As an example, the transmtter 1600 may configure the CP lengths as follows:

[0183] 1. Partion a range [to, tmax] of all possible values of delay spread into N intervals: [to, ti], [ti, t₂], [tN-2, tN-i], [tN-i, tmax], with CP lengths LengthCP[0], LengthCP[l], LengthCP[N-2], LengthCP[N-l], respectively.

[0184] 2. For any user i, find an interval from above, e.g., the kth interval, such that del ay spread [i] is included in that interval. User i is then configured to set its CP length to LengthCP[k].

[0185] The transmitter 1600 may perform resource allocation as follows:

[0186] 1. If there is a single user (e.g., user i) whose traffic can fill out all the subcarriers, then allocate all the subcarriers to that user.

[0187] 2. If not, look for other users which have been configured with the same CP lengths, and schedule them for simultaneous transmissions or receptions. Other users may include users in a beam where user i resides.

[0188] 3. If such other users cannot be found, then find users with greater or lesser CP lengths, and schedule one or more such users with the user, setting the CP lengths to the maximum of the CP lengths of all users being scheduled.

[0189] The base station may send a CP reconfiguration command to the user(s) of which the common CP length used for multi-user simultaneous transmission/receiving differs from the determined CP length.

[0190] As an alternative, the transmitter 1600 may be configured to exploit scheduling flexibility and use filtering to support multiple users transmitting in part of the entire spectrum. Using this configuration multiple groups of users may be simultaneously transmitting, and each group may use the same CP length. Resource allocation may be carried out as follows. [0191] 1. The transmitter 1600 may partition the whole spectrum into multiple channels. The partition may depend on Quality of Service (QoS) requirements of the traffic waiting for transmission, for example.

[0192] 2. On each channel, the transmitter 1600 may assign users to disjoint groups, e.g, by using the above resource alloaction procedure. The users in a group may be scheduled for receiving on a same channel. Filtering may be performed on each channel (i.e., on a per group basis) such that transmissions from different groups do not interfere with (or limited interferene to) one another.

[0193] 3. The determination of the CP length and the number of subcarriers for each user in a group may be communicated from the transmitter 1600 to the receivers.

[0194] As another alternative, the transmitter 1600 may be configured to use CP adaptation algorithm, metholodolgy and/or technology other than shown in FIG. 16 for determining the length of the CP. A suitable CP adaptaiton algorithm is one in which the length of the CP is adapted to delay spread and the length of the data portion of the OFDM symbol (or DFT-spread- OFDM symbol) is fixed; an example of whihc may be found in M. Krondorf and G. Fettweis, "Throughput enhancement forMIMO OFDM using frequency domain channel length indicator and guard interval adaptation " Proceedings of the 3rd International Symposium on Wireless Communication Systems (ISWC). IEEE, 2006, pp. 195-199.

[0195] The assignment of the users into different groups may take QoS into account. For example, assume that all users have the same delay spread and there are three QoS levels, e.g., the required packet loss rates are different. Three different groups, i.e., K=2, may be created with CP lengths, such that LengthCP[0] > LengthCP[l] > LengthCP[2]. Users with the least required packet loss rate may be assigned to group 0 with CP length equal to LengthCP[0], users with the moderate packet loss rate may be assigned to group 1 with CP length equal to LengthCP[l], and users with the highest required packet loss rate to group 2 with CP length equal to LengthCP[2]. The assignment may be sent in the downlink control channel.

[0196] To measure the delay spread and determine the appropriate CP duration, a base station may configure a dedicated time interval for measuring the delay spread. During the time interval the base station may transmit an impulse and a WTRU may measure the delay spread and report the delay spread which may be represented in the form of an index to minimize control overhead.

[0197] FIG. 17 is a flow diagram illustrating a representative procedure 1700 for supporting adaptation of cyclic prefix duration to delay spread in a communications network that supports multiple access. The representative procedure 1700 may be implemented in a transmitter and an accompanying receiver, such as the transmitter of FIG. 12 or FIG. 16 and the receiver of FIG. 13. The representative procedure 1700 may be carried out by other transmitters and receivers, as well.

[0198] Referring to FIG. 17, the transmitter 1200 may generate a first OFDM symbol based on a configured OFDM symbol duration and a first CP duration based on a first CIR (1710). The first OFDM symbol may be mapped to a first sub-channel of a channel. The first CIR may be associated the first sub-channel. The transmitter 1200 may apply a first sub-channel filter to the first OFDM symbol (1712). The transmitter 1200 may use the first sub-channel filter to filter one or more spectral components from the first OFDM symbol. The filtered spectral components may correspond to one or more frequencies not within the first sub-channel. The first sub-channel filter may include one or more coefficients corresponding to one or more frequencies within the first sub-channel.

[0199] The transmitter 1200 may generate a second OFDM symbol based on the configured OFDM symbol duration and a second CP duration based on a second CIR (1714). The second OFDM symbol may be mapped to a second sub-channel of the channel. The second CIR may be associated with the second sub-channel. The transmitter may apply a second sub-channel filter to the second OFDM symbol (1716). The transmitter may use the second sub-channel filter to filter one or more spectral components from the second OFDM symbol. The filtered spectral components may correspond to one or more frequencies not within the second subchannel. The second sub-channel filter may include a set of coefficients corresponding to one or more frequencies within the second sub-channel. The first and second sub-channels may be adjacent sub-channels with or without a guard band between them.

[0200] The transmitter may simultaneously transmit the first and second filtered OFDM symbols on the first and second sub-channels, respectively (1718). The transmitter, for example, may transmit the first and second OFDM symbols during a common symbol time period. In an embodiment, the transmitter may combine the first and second OFDM symbols into a frequency division multiplexing (FDM) OFDM symbol, and may then transmit the FDM-OFDM symbol during the common symbol time period.

[0201] In an embodiment, the transmitter may generate first and second symbols having respective durations. The first and second durations may be different, and each may be based on, e.g., a difference between, the symbol duration and its corresponding CP duration. The transmitter may use a single waveform generator to generate the first and second symbols. Alternatively, then transmitter may use separate waveform generators, such as shown in FIGs. 12 and 16. The transmitter may generate and/or further process the first and second symbols simultaneously or offset in time.

[0202] After generating the first symbol, the transmitter may generate a first CP based on the first symbol and the first CP duration. After generating the first CP, the transmitter may append the first CP to (or insert the CP into) the first symbol. The transmitter may map the first symbol to the first sub-channel when generating it and/or thereafter, such as after CP insertion. The transmitter may thereafter further process and/or convert the first symbol to the first OFDM symbol. The mapping to the first sub-channel may be maintained when processing the first symbol into the first OFDM symbol. Alternatively, the first OFDM may be mapped or remapped to the first sub-channel during and/or after formation. For example, the first OFDM may be mapped or re-mapped to the first sub-channel prior to, or in connection with, the application of the first sub-channel filter (1712).

[0203] The transmitter may further process the second symbol so as to form the second OFDM symbol. The further processing of the second symbol may be carried out in the same or similar way as described above for the first symbol, and as such is not described herein for simplicity of exposition.

[0204] Although not shown in FIG. 17, the transmitter may obtain the first and second CIRs via the accompanying receiver. The first and second CIRs may be generated by first and second receivers, respectfully, and may be transmitted to and/or received by the accompanying receiver. Additionally, the transmitter may send, to the first receiver, information (e.g., signaling) indicating any of the first CP duration and a filter configuration corresponding to the first sub-channel filter. Alternatively, the transmitter may send to the first receiver information (e.g., signaling) indicating a first CP configuration. The first CP configuration may include the first CP duration and a first filter configuration corresponding to the first sub-channel filter. The transmitter may send, to the second receiver, information (e.g., signaling) indicating any of the second CP duration and a second filter configuration corresponding to the second sub-channel filter. Alternatively, the transmitter may send to the second receiver information (e.g., signaling) indicating a second CP configuration. The second CP configuration may include the second CP duration and a second filter configuration corresponding to the second sub-channel filter.

[0205] FIG. 18 is a flow diagram illustrating a representative procedure 1800 for supporting adaptation of cyclic prefix duration to delay spread in a communications network that supports multiple access. The representative procedure 1800 may be implemented in a receiver and, optionally, and an accompanying transmitter. The receiver and accompanying transmitter may be, for example the receiver of FIG. 13 or FIG. 14 and the transmitter of FIG. 15. The representative procedure 1700 may be carried out by other receivers and transmitters, as well.

[0206] Referring to FIG. 18, the receiver may receive information and/or signaling (collectively "information") indicating any of a CP duration and a filter configuration (1810). The receiver may configure a sub-channel filter based on the received filter configuration (1812). The receiver may receive a signal during a configured symbol time (1814). The signal may include one or more FDM-OFDM symbols. The receiver may filter an OFDM symbol from the received signal using the sub-channel filter (1816). The receiver, for example, may filter one of the OFDM symbols from the FDM-OFDM symbols. The receiver may remove a CP from the OFDM symbol based the CP duration (1818) so as to form a CP-less OFDM symbol. Although not shown, the receiver may further process the resulting CP-less OFDM symbol into one or more modulation symbols.

[0207] The representative procedure 1800 may be carried out in conjunction with the representative procedure 1700 (FIG. 17). For example, the signal received during the configured symbol time (1814) may correspond to the first and second OFDM symbols simultaneously transmitted on the respective sub-channels (1718). Additionally and/or alternatively, the information indicating any of a CP duration and a filter configuration received by the receiver (1810) may correspond to the any of the first or second CP duration and any of the first or second filter information signaled by the transmitter (not shown).

[0208] Prior to carrying out the representative procedure 1800, the receiver may receive reference symbols, and may determine a CIR based on the reference symbols. The reference symbols may be transmitted from the transmitter that transmits the signal (1814). The accompanying transmitter may send the CIR to a receiver accompanying that transmitter.

[0209] As an alternative to receiving information indicating the CP duration, the receiver may determine the CP duration based on the CIR and/or a set of rules. An advantage of this alternative is a reduction in signaling overhead.

[0210] FIG. 19 is a flow diagram illustrating a representative procedure 1900 for supporting adaptation of cyclic prefix duration to delay spread in a communications network that supports multiple access. The representative procedure 1900 may be implemented in a transceiver, including a receiver and a transmitter such as disclosed herein and/or illustrated in FIG. 14 and FIG. 15, respectively. The representative procedure 1900 may be carried out by other transceivers, as well.

[0211] Referring to FIG. 19, the transceiver may receive information indicating a CP duration and a filter configuration (1910). The information may be received from second transmitter, e.g., the transmitter of FIG. 12 or FIG. 16, or transceiver (collectively "second transceiver/transmitter"). The CP duration may correspond to one of various CP durations determined at the second transceiver/transmitter based on an earlier signaled CIR for a channel or a sub-channel associated with the transceiver (i.e., associated with any of the transmitter and the receiver). The received filter configuration may correspond to a sub-channel filter employed at the second transceiver/transmitter in connection with a sub-channel assigned to the transceiver. The transceiver may configure a sub-channel filter based on the received filter configuration (1912). The configured sub-channel filter may include a set of coefficients corresponding to one or more frequencies within the assigned sub-channel.

[0212] The transceiver may generate an OFDM symbol based on a configured OFDM symbol duration and the received CP duration (1914). The OFDM symbol may be mapped to the assigned sub-channel. The transceiver may apply the sub-channel filter to the OFDM symbol (1916). The transceiver may use the sub-channel filter to filter one or more spectral components from the OFDM symbol. The filtered spectral components may correspond to one or more frequencies not within the assigned sub-channel. The transceiver may transmit the filtered OFDM symbol on the assigned sub-channel (1918).

[0213] In an embodiment, the transceiver may generate a symbol having a duration based on, e.g., a difference between, the configured OFDM symbol duration and the signaled CP duration. After generating the symbol, the transceiver may generate a CP based on the symbol and the CP duration, and may append the CP to, or insert the CP into, the symbol. The transceiver may map the symbol to the assigned sub-channel when generating it and/or thereafter, such as after CP insertion. The transceiver may further process and/or convert the symbol to the OFDM symbol. The mapping to the assigned sub-channel may be maintained when processing the symbol into the OFDM symbol. Alternatively, the OFDM may be mapped or re-mapped to the assigned sub-channel during and/or after formation; e.g., prior to, or in connection with, the application of the sub-channel filter (1916).

[0214] Although not shown in FIG. 19, the transceiver may receive a grant for the subchannel; e.g., indicating an assignment of any of time, frequency, code and spatial resources. The representative procedure 1900 may be carried out in conjunction with the representative procedure 1700 (FIG. 17). For example, the information indicating any of a CP duration and a filter configuration received by the transceiver (1910) may correspond to the first or second CP duration and the first or second filter information signaled by the second transceiver/transmitter.

[0215] FIG. 20 is a flow diagram illustrating a representative procedure 2000 for supporting adaptation of cyclic prefix duration to delay spread in a communications network that supports multiple access. The representative procedure 2000 may be implemented in a transceiver, including a receiver and a transmitter such as disclosed herein and/or illustrated in FIG. 14 and FIG. 15, respectively. The representative procedure 2000 may be carried out by other transceivers, as well.

[0216] Referring to FIG. 20, the transmitter may determine a CP duration based on a CIR (2010). The transmitter may perform fractional sampling rate conversion using a farrow filter to generate a symbol having a duration based on a configured OFDM symbol duration and the determined CP duration (2012). The transmitter may generate a CP based on the symbol and the determined CP duration (2014). The transmitter may append the CP to, or insert the CP into, the symbol (2016). The transmitter may convert or otherwise process the symbol into an OFDM symbol having the determined CP duration and the configured OFDM symbol duration (2018). The transmitter may transmit the OFDM symbol on a sub-channel of a channel (2020).

[0217] Although not shown in FIG. 20, the transceiver may receive a grant for the subchannel; e.g., indicating an assignment of any of time, frequency, code and spatial resources. The representative procedure 2000 may be carried out in conjunction with the representative procedure 1800 (FIG. 18). For example, the CIR used to determine the CP duration (2010) may correspond to the CIR sent prior to carrying out the representative procedure 1800.

[0218] FIG. 21 is a flow diagram illustrating a representative procedure 2100 for supporting adaptation of cyclic prefix duration to delay spread in a communications network that supports multiple access. The representative procedure 2100 may be implemented in a transceiver, including a receiver and a transmitter such as disclosed herein and/or illustrated in FIG. 13 (14) and FIG. 12 (15), respectively. The representative procedure 2100 may be carried out by other transceivers, as well.

[0219] Referring to FIG. 21, the transceiver may determine a CP duration based on a CIR and one or more quality of service parameters (2110). The transmitter may generate an OFDM symbol having the determined CP duration and a configured symbol duration (2112). The transmitter may transmit the OFDM symbol on a sub-channel of a channel (2114).

[0220] When generating the OFDM symbol, the transmitter may adjust a clocking rate used for digital-to-analog conversion according to the CP duration. Alternatively, the transmitter may perform fractional sampling rate conversion to generate a symbol having a duration based on the symbol duration and the determined CP duration. The transmitter may use any of polyphase decomposition and fractional delay with a Farrow structure to perform the fractional sampling rate conversion. The transmitter may generate a CP based on the generated symbol and the determined CP duration. The transmitter may append the CP to (or insert the CP into) the symbol, and/or further process the symbol into the OFDM symbol.

[0221] Although not shown in FIG. 21, the transmitter may receive the CIR from a receiver. In an embodiment, the transmitter may send, to the receiver, information indicating a clocking rate to use for analog-to-digital conversion. Alternatively, the transmitter may send to the receiver information indicating the CP duration and/or one or more parameters to use for performing fractional sampling rate conversion.

[0222] FIG. 22 is a flow diagram illustrating a representative procedure 2200 for supporting adaptation of cyclic prefix duration to delay spread in a communications network that supports multiple access. The representative procedure 2200 may be implemented in a transceiver, including a receiver and a transmitter such as disclosed herein and/or illustrated in FIG. 14 and FIG. 15, respectively. The representative procedure 2200 may be carried out by other transceivers, as well.

[0223] Referring to FIG. 22, the transceiver may receive information indicating any of a CP duration and a fractional-sampling-rate-conversion configuration (2210). The transceiver may receive a signal during a configured symbol time (2212). The signal may include one or more FDM-OFDM symbols. The receiver may filter an OFDM symbol from the received signal using a sub-channel filter (not shown). The receiver, for example, may filter the one of the OFDM symbol from the FDM-OFDM symbols. The receiver may remove a CP from the OFDM symbol based the CP duration (2214) so as to form a CP-less OFDM symbol. The receiver may perform fractional sampling rate conversion on the resulting CP-less OFDM symbol based on the fractional-sampling-rate-conversion configuration (2216), and may further process the resulting signal into one or more modulation symbols (2218).

[0224] The representative procedure 2200 may be carried out in conjunction with the representative procedure 1700 (FIG. 17). For example, the signal received during the configured symbol time (2212) may correspond to one of the first and second OFDM symbols simultaneously transmitted on the respective sub-channels (1718). Additionally and/or alternatively, the information indicating any of a CP duration and a fractional-sampling-rate- conversion configuration (2210) may correspond to the CP configuration information signaled by the transmitter (not shown).

[0225] Prior to carrying out the representative procedure 2200, the transceiver may receive reference symbols, and may determine a CIR based on the reference symbols. The reference symbols may be transmitted from the transmitter/transceiver that transmits the signal (2212). As an alternative to receiving information indicating the CP duration, the transceiver may determine the CP duration based on the CIR and/or a set of rules. An advantage of this alternative is a reduction in signaling overhead.

[0226] Example Performance Evaluation

[0227] FIG. 23 is a graph illustrating an example performance evaluation of adaptive CP for DFT-spread-OFDM ("adaptive CP DFT-spread-OFDM"). The graph also includes performance of zero-tail DFT-spread-OFDM, for comparision. The extended pedestrian A (EPA) channel model of LTE is used. This model has a delay spread of 410 ns. The symbol duration is 2.083 μ , M = 1024 , T_c = l . l x 410ns, N + Q = 2048 and N = 1632 . A standard MMSE equalizer is used.

[0228] Two schemes have similar performance until about 15 dB when the adpative CP DFT- spread-OFDM scheme begins to outperform zero-tail DFT-spread-OFDM. The divergence in performance may be attributed to the adaptive CP DFT-spread-OFDM completely removing ISI whereas zero-tail DFT-spread-OFDM does not, and such difference becomes significant at high S R. The S R is shown only for the data portion of the signals. The evaluation shown is for QPSK. If higher order modulation scheme, e.g., 64-QAM, is used the divergence in performance is expected to occur at a lower SNR, and the performance benefit of the adaptive CP DFT-spread-OFDM may be realized for smaller values of SNR.

[0229] Example Embodiments

[0230] In an embodiment, a method may include making a length of a cyclic prefix (CP) proportional to a delay spread without adjusting symbol duration. In an embodiment, making the CP length proportional to a delay spread without adjusting symbol duration may include adjusting a clocking rate of digital-to-analog conversion (DAC) and/or a clocking rate of analog-to-digital conversion (ADC) according to the CP length. In an embodiment, making the CP length proportional to a delay spread without adjusting symbol duration may include performing fractional sampling rate conversion. Performing fractional sampling rate conversion may include any of using polyphase decomposition, and using a fractional delay approach with a Farrow structure. In an embodiment, making the CP length proportional to a delay spread without adjusting symbol duration may include directly computing an IDFT/DFT. In an embodiment, making the CP length proportional to a delay spread without adjusting symbol duration may include computing an IDFT/DFT with mixed radix.

[0231] In an embodiment, a transmitter and a receiver may coordinate to facilitate adapting a CP to the delay spread. In an embodiment, the transmitter and the receiver may coordinate in adapting a CP to the delay spread by agreeing on a CP length. In an embodiment, the transmitter may send a reference signal for the receiver to directly measure or infer the delay spread. The receiver may report or otherwise communicate the delay spread to the transmitter. The transmitter may determine the CP length based on the communicated delay spread, e.g., according to a preset rule. The transmitter may notify the receiver of the determined CP length.

[0232] In an embodiment, the transmitter may send a reference signal for the receiver to directly measure or infer the delay spread. The receiver may determine the CP length based on the measured or inferred delay spread, e.g., according to a preset rule. The receiver may notify the transmitter of the determined CP length.

[0233] In an embodiment, the transmitter may send a reference signal for the receiver to directly measure or infer the delay spread. The receiver may report or otherwise communicate the delay spread to the transmitter. The transmitter and receiver may independently determine the CP length based on the delay spread, e.g., according to a preset rule. The transmitter and receiver may indicate to the other the CP length it independent determined.

[0234] In an embodiment in which making the CP length proportional to a delay spread without adjusting symbol duration includes adjusting a clocking rate of digital-to-analog conversion (DAC) and/or a clocking rate of analog-to-digital conversion (ADC) according to the CP length, the transmitter may determine the CP length, IDFT/DFT size, total bandwidth to be used, subcarriers to be used, and the clocking rate for DAC in the transmitter and the clocking rate for the ADC in the receiver, and may sends such information to the receiver. The sent information may be in the form of quantized values or indices mapped to the quantized values, for example. In an embodiment, the receiver may configure the symbol format according to the received information about the CP length, the DFT size, and the clocking rate for the ADC. The receiver may extract data from the subcarriers scheduled by the transmitter, and may perform other receiver functions.

[0235] In an embodiment in which making the CP length proportional to a delay spread without adjusting symbol duration includes performing fractional sampling rate conversion, the transmitter may determine the CP length, IDFT/DFT size, total bandwidth to be used, subcarriers to be used, and respective sampling rate conversion fractions for the transmitter and the receiver, and may send the information to the receiver. The sent information may be in the form of quantized values or indices mapped to the quantized values. In an embodiment, the receiver may configure the symbol format according to the received information about the CP length, the DFT size, and the sampling rate conversion fraction. The receiver may extracts data from the subcarriers scheduled by the transmitter, and may performs other receiver functions. [0236] In an embodiment, a method to support scheduling to efficiently support multiple users is provided. The method may include quantizing a delay spread by partitioning a range of the delay spread into subintervals. The method may also include setting a CP length according to the quantized delay spread. The method may further include scheduling users of equal quantized delay spread for simultaneous transmissions and receiving. The method may further include scheduling users in the same beam with a maximum CP of such users. This scheduling may be carried out, for example when schedule of users of equal quantized delay spread is not possible and/or less efficient.

[0237] In embodiment, a method may include using per-channel filtered transmissions for multiple user support where the CP length adaptation is performed on a per user basis or a per user group basis. The method may include performing the CP length adaptation. Performing the CP length adaptation may include adapting the CP length without adjusting OFDM or DFT- spread-OFDM symbol duration (i.e., constant symbol duration). Alternatively, the method may include adapting the CP length while changing the OFDM or DFT-spread-OFDM duration by the same amount

[0238] Conclusion

[0239] Although features and elements are provided above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations may be made without departing from its spirit and scope, as will be apparent to those skilled in the art. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly provided as such. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods or systems.

[0240] It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used herein, the term "video" may mean any of a snapshot, single image and/or multiple images displayed over a time basis. As another example, when referred to herein, the terms "user equipment" and its abbreviation "UE" may mean (i) a wireless transmit and/or receive unit (WTRU), such as described supra; (ii) any of a number of embodiments of a WTRU, such as described supra; (iii) a wireless-capable and/or wired-capable (e.g., tetherable) device configured with, inter alia, some or all structures and functionality of a WTRU, such as described supra; (iii) a wireless-capable and/or wired-capable device configured with less than all structures and functionality of a WTRU, such as described supra; or (iv) the like. Details of an example WTRU, which may be representative of any WTRU recited herein, are provided herein with respect to FIGs. 1A-1E.

[0241] In addition, the methods provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer- readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

[0242] Variations of the method, apparatus and system provided above are possible without departing from the scope of the invention. In view of the wide variety of embodiments that can be applied, it should be understood that the illustrated embodiments are examples only, and should not be taken as limiting the scope of the following claims. For instance, the embodiments provided herein include handheld devices, which may include or be utilized with any appropriate voltage source, such as a battery and the like, providing any appropriate voltage.

[0243] Moreover, in the embodiments provided above, processing platforms, computing systems, controllers, and other devices containing processors are noted. These devices may contain at least one Central Processing Unit (CPU") and memory. In accordance with the practices of persons skilled in the art of computer programming, reference to acts and symbolic representations of operations or instructions may be performed by the various CPUs and memories. Such acts and operations or instructions may be referred to as being "executed," "computer executed" or "CPU executed."

[0244] One of ordinary skill in the art will appreciate that the acts and symbolically represented operations or instructions include the manipulation of electrical signals by the CPU. An electrical system represents data bits that can cause a resulting transformation or reduction of the electrical signals and the maintenance of data bits at memory locations in a memory system to thereby reconfigure or otherwise alter the CPU's operation, as well as other processing of signals. The memory locations where data bits are maintained are physical locations that have particular electrical, magnetic, optical, or organic properties corresponding to or representative of the data bits. It should be understood that the embodiments are not limited to the above-mentioned platforms or CPUs and that other platforms and CPUs may support the provided methods.

[0245] The data bits may also be maintained on a computer readable medium including magnetic disks, optical disks, and any other volatile (e.g., Random Access Memory (RAM")) or non-volatile (e.g., Read-Only Memory (ROM")) mass storage system readable by the CPU. The computer readable medium may include cooperating or interconnected computer readable medium, which exist exclusively on the processing system or are distributed among multiple interconnected processing systems that may be local or remote to the processing system. It should be understood that the embodiments are not limited to the above-mentioned memories and that other platforms and memories may support the provided methods.

[0246] In an illustrative embodiment, any of the operations, processes, etc. described herein may be implemented as computer-readable instructions stored on a computer-readable medium. The computer-readable instructions may be executed by a processor of a mobile unit, a network element, and/or any other computing device.

[0247] There is little distinction left between hardware and software implementations of aspects of systems. The use of hardware or software is generally (but not always, in that in certain contexts the choice between hardware and software may become significant) a design choice representing cost vs. efficiency tradeoffs. There may be various vehicles by which processes and/or systems and/or other technologies described herein may be effected (e.g., hardware, software, and/or firmware), and the preferred vehicle may vary with the context in which the processes and/or systems and/or other technologies are deployed. For example, if an implementer determines that speed and accuracy are paramount, the implementer may opt for a mainly hardware and/or firmware vehicle. If flexibility is paramount, the implementer may opt for a mainly software implementation. Alternatively, the implementer may opt for some combination of hardware, software, and/or firmware.

[0248] The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, flowcharts, and/or examples. Insofar as such block diagrams, flowcharts, and/or examples contain one or more functions and/or operations, it will be understood by those within the art that each function and/or operation within such block diagrams, flowcharts, or examples may be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In an embodiment, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), and/or other integrated formats. However, those skilled in the art will recognize that some aspects of the embodiments disclosed herein, in whole or in part, may be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein may be distributed as a program product in a variety of forms, and that an illustrative embodiment of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include, but are not limited to, the following: a recordable type medium such as a floppy disk, a hard disk drive, a CD, a DVD, a digital tape, a computer memory, etc., and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.).

[0249] Those skilled in the art will recognize that it is common within the art to describe devices and/or processes in the fashion set forth herein, and thereafter use engineering practices to integrate such described devices and/or processes into data processing systems. That is, at least a portion of the devices and/or processes described herein may be integrated into a data processing system via a reasonable amount of experimentation. Those having skill in the art will recognize that a typical data processing system may generally include one or more of a system unit housing, a video display device, a memory such as volatile and non-volatile memory, processors such as microprocessors and digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices, such as a touch pad or screen, and/or control systems including feedback loops and control motors (e.g., feedback for sensing position and/or velocity, control motors for moving and/or adjusting components and/or quantities). A typical data processing system may be implemented utilizing any suitable commercially available components, such as those typically found in data computing/communication and/or network computing/communication systems.

[0250] The herein described subject matter sometimes illustrates different components contained within, or connected with, different other components. It is to be understood that such depicted architectures are merely examples, and that in fact many other architectures may be implemented which achieve the same functionality. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively "associated" such that the desired functionality may be achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as "associated with" each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated may also be viewed as being "operably connected", or "operably coupled", to each other to achieve the desired functionality, and any two components capable of being so associated may also be viewed as being "operably couplable" to each other to achieve the desired functionality. Specific examples of operably couplable include but are not limited to physically mateable and/or physically interacting components and/or wirelessly interactable and/or wirelessly interacting components and/or logically interacting and/or logically interactable components.

[0251] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

[0252] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, where only one item is intended, the term "single" or similar language may be used. As an aid to understanding, the following appended claims and/or the descriptions herein may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and/or "an" should be interpreted to mean "at least one" or "one or more"). The same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to "at least one of A, B, or C, etc." is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., "a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B." Further, the terms "any of followed by a listing of a plurality of items and/or a plurality of categories of items, as used herein, are intended to include "any of," "any combination of," "any multiple of," and/or "any combination of multiples of the items and/or the categories of items, individually or in conjunction with other items and/or other categories of items. Moreover, as used herein, the term "set" is intended to include any number of items, including zero. Additionally, as used herein, the term "number" is intended to include any number, including zero.

[0253] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0254] As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein may be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as "up to," "at least," "greater than," "less than," and the like includes the number recited and refers to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.

[0255] Moreover, the claims should not be read as limited to the provided order or elements unless stated to that effect. In addition, use of the terms "means for" in any claim is intended to invoke 35 U.S.C. §112, ]f 6 or means-plus-function claim format, and any claim without the terms "means for" is not so intended.

Claims

CLAIMS What is claimed is:

1. A method implemented in a transmitter, the method comprising:

generating a first orthogonal frequency division multiplexing (OFDM) symbol mapped to a first sub-channel of a channel and having a symbol duration and a first cyclic prefix (CP) duration based on a first channel impulse response (CIR);

applying a first sub-channel filter to the first OFDM symbol;

generating a second OFDM symbol mapped to a second sub-channel of the channel and having the same symbol duration and a second CP duration based on a second CIR; applying a second sub-channel filter to the second OFDM symbol; and

simultaneously transmitting the first and second filtered OFDM symbols on the first and second sub-channels, respectively.

2. The method of claim 1, wherein simultaneously transmitting the first and second OFDM symbols comprises:

transmitting the first and second OFDM symbols during a common symbol time period.

3. The method of any of the claims 1-2, wherein the first and second sub-channels are adjacent sub-channels.

4. The method of any of the claims 1-3, wherein generating a first OFDM symbol comprises: generating a first symbol having a first duration based on the symbol duration and the first CP duration;

generating a first CP based on the first symbol and the first CP duration; and

inserting the first CP into the first symbol.

5. The method of any of the claims 1-4, further comprising:

determining the first CP duration based on the first CIR.

6. The method of any of the claims 1-5, further comprising:

receiving the first CIR from a first receiver.

7. The method of any of the claims 1-6, wherein generating a second OFDM symbol comprises: generating a second symbol having a second duration based on the symbol duration and the second CP duration;

generating a second CP based on the second symbol and the second CP duration; and inserting the second CP into the second symbol.

8. The method of any of the claims 1-7, further comprising:

determining the second CP duration based on the second CIR.

9. The method of any of the claims 1-8, further comprising:

receiving the second CIR from a second receiver.

10. The method of any of the claims 1-9, wherein the first sub-channel comprises a first set of subcarriers, wherein the second sub-channel comprises a second set of subcarriers, and wherein the second set of subcarriers is orthogonal to the first set of subcarriers.

11. The method of any of the claims 1-10, further comprising:

sending, to a first receiver, information/signaling indicating the first CP duration; and sending, to a second receiver, information/signaling indicating the second CP duration.

12. The method of any of the claims 1-11, further comprising:

sending, to a first receiver, information/signaling indicating a first filter configuration corresponding to the first sub-channel filter; and

sending, to a second receiver, information/signaling indicating a first filter configuration corresponding to the first sub-channel filter.

13. The method of any of the claims 1-10, further comprising:

sending, to a first receiver, information/signaling indicating a first CP configuration, including the first CP duration and a first filter configuration corresponding to the first sub-channel filter; and

sending, to a second receiver, information/signaling indicating a second CP configuration, including the second CP duration and a second filter configuration corresponding to the second sub-channel filter

14. The method of any of the claims 1-13, wherein applying a first sub-channel filter to the first OFDM symbol comprises:

filtering one or more spectral components from the first OFDM symbol.

15. The method of any of the claims 1-14, wherein applying a second sub-channel filter to the second OFDM symbol comprises:

filtering one or more spectral components from the second OFDM symbol.

16. A transmitter comprising:

a first waveform generator configured to generate a first orthogonal frequency division multiplexing (OFDM) symbol mapped to a first sub-channel of a channel and having a symbol duration and a first cyclic prefix (CP) duration based on a first channel impulse response (CIR);

a first sub-channel filter configured to filter the first OFDM symbol;

a second waveform generator configured to generate a second OFDM symbol mapped to a second sub-channel of the channel and having the same symbol duration and a second

CP duration based on a second CIR;

a second sub-channel filter configured to filter the second OFDM symbol; and

a radio frequency chain configured to simultaneously transmit the first and second filtered

OFDM symbols on the first and second sub-channels, respectively.

17. The transmitter of claim 16, wherein:

the first waveform generator is configured to:

generate a first symbol having a first duration based on the symbol duration and the first CP duration;

generate a first CP based on the first symbol and the first CP duration; and

insert the first CP into the first symbol.

18. The transmitter of any of the claims 16-17, wherein the first waveform generator configured to determine the first CP duration based on the first CIR.

19. The transmitter of any of the claims 16-18, wherein:

the second waveform generator is configured to:

generate a second symbol having a second duration based on the symbol duration and the second CP duration;

generate a second CP based on the second symbol and the second CP duration; and insert the second CP into the second symbol.

20. The transmitter of any of the claims 16-19, wherein the second waveform generator configured to determine the second CP duration based on the second CIR.

21. A method implemented in a receiver, the method comprising:

receiving information indicating a cyclic prefix (CP) duration and a filter configuration; configuring a sub-channel filter based on the received filter configuration;

receiving a signal during a configured symbol time;

filtering an orthogonal frequency division multiplexing (OFDM) symbol from the received signal using the sub-channel filter; and

removing a CP from the OFDM symbol based the CP duration.

22. A receiver comprising a processor, a radio frequency chain, a sub-channel filter and a waveform generator, wherein:

the processor is configured to:

receive information indicating a cyclic prefix (CP) duration and a filter configuration; and

configure the sub-channel filter based on the received filter configuration;

the radio frequency chain is configured to receive a signal during a configured symbol time; the sub-channel filter is configured to filter an orthogonal frequency division multiplexing

(OFDM) symbol from the received signal; and

the waveform generator is configured to remove a CP from the OFDM symbol based the

CP duration.

23. A method implemented in a transmitter, the method comprising:

receiving information indicating a cyclic prefix (CP) duration and a filter configuration; configuring a sub-channel filter based on the received filter configuration;

generating an orthogonal frequency division multiplexing (OFDM) symbol mapped to an assigned sub-channel of a channel and having a symbol duration and the cyclic prefix

(CP) duration;

applying the sub-channel filter to the OFDM symbol; and

transmitting the filtered OFDM symbol on the assigned sub-channels.

24. The method of claim 23, further comprising: receiving a grant for the sub-channel.

25. A transmitter comprising a processor, a radio frequency chain, a sub-channel filter and a waveform generator, wherein:

the processor is configured to:

receive information indicating a cyclic prefix (CP) duration and a filter configuration; and

configure the sub-channel filter based on the received filter configuration;

the waveform generator is configured to generate an orthogonal frequency division multiplexing (OFDM) symbol mapped to an assigned sub-channel of a channel and having a symbol duration and the cyclic prefix (CP) duration;

the sub-channel filter is configured to filter the OFDM symbol; and

radio frequency chain is configured to transmit the filtered OFDM symbol on the assigned sub-channels.

26. The transmitter of claim 25, wherein the processor is configured to receive a grant for the sub-channel.

27. A method implemented in a transmitter, the method comprising:

determining a cyclic prefix (CP) duration based on a channel impulse response (CIR) and one or more quality of service parameters;

generating an orthogonal frequency division multiplexing (OFDM) symbol having the determined CP duration and a configured symbol duration; and

transmitting the OFDM symbol on a sub-channel of a channel.

28. The method of claim 27, wherein generating an OFDM symbol comprises:

adjusting a clocking rate of digital-to-analog conversion (DAC) according to the CP duration.

29. The method of claim 27, wherein generating an OFDM symbol comprises:

performing fractional sampling rate conversion to generate a symbol having a duration based on the symbol duration and the CP duration;

generating a CP based on the symbol and the CP duration; and

appending the CP to the symbol..

30. The method of claim 29, wherein performing fractional sampling rate conversion comprises: using polyphase decomposition.

31. The method of claim 29, wherein performing fractional sampling rate conversion comprises: using fractional delay with a Farrow structure.

32. A method implemented in a transmitter, the method comprising:

determining a cyclic prefix (CP) duration based on a channel impulse response (CIR); performing fractional sampling rate conversion using a farrow structure to generate a symbol having a duration based on an configured orthogonal frequency division multiplexing (OFDM) symbol duration and the determined CP duration;

generating a CP based on the symbol and the CP duration;

appending the CP to the first symbol;

converting the symbol to an OFDM symbol having the determined CP duration and a configured OFDM symbol duration; and

transmitting the OFDM symbol on a sub-channel of a channel.

33. A transmitter comprising a waveform generator, a farrow structure and a radio frequency chain, wherein: the waveform generator is configured to determine a cyclic prefix (CP) duration based on a channel impulse response (CIR);

the farrow structure is configured to perform fractional sampling rate conversion to generate a symbol having a duration based on an configured orthogonal frequency division multiplexing (OFDM) symbol duration and the determined CP duration;

the waveform generator is configured to:

generate a CP based on the symbol and the CP duration;

insert the CP into the symbol; and

convert the symbol to an OFDM symbol having the determined CP duration and a configured OFDM symbol duration; and

a radio frequency chain is configured to transmit the OFDM symbol on a sub-channel of a channel.