WO2012148896A2

WO2012148896A2 - Data aggregate point (dap) as a multiple-input multiple-output (mimo) coordination point

Info

Publication number: WO2012148896A2
Application number: PCT/US2012/034767
Authority: WO
Inventors: Ronald G. Murias; Lei Wang; Yingxue K. Li
Original assignee: Interdigital Patent Holdings, Inc.
Priority date: 2011-04-25
Filing date: 2012-04-24
Publication date: 2012-11-01
Also published as: TW201251359A; WO2012148896A3

Abstract

A method for multiple-input multiple-output (MIMO) communications between wireless transmit and receive units (WRTUs) includes receiving, at a aggregate point (DAP), data from a plurality of wireless transmit/receive units (WTRUs), aggregating, at the DAP, the data received from the plurality of WTRUs to provide an aggregate signal, transmitting the aggregate signal to at least two of the plurality of WTRUs for re-transmission, and determining a coding scheme for re-transmission of the data by the at least two of the plurality of WTRUs.

Description

DATA AGGREGATE POINT (DAP) AS A MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) COORDINATION POINT

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of 61/478,622 filed April 25, 2011, the contents of which are hereby incorporated by reference herein.

FIELD OF INVENTION

[0002] This application is related to wireless communications.

BACKGROUND

[0003] Machine type communication (MTC) is a form of data communication that includes one or more entities that do not necessarily need human interaction. A service optimized for MTC may differ from a service optimized for Human to Human communications and may differ from current mobile network communication services in that it may involve different market scenarios, data communications, lower costs and effort, a potentially very large number of communicating terminals with, to a large extent, little traffic per terminal. Examples of MTC devices include metering devices and tracking devices.

[0004] Categories of features that have been defined for MTC, each of them bringing different design challenges, may include time controlled access, time tolerant, packet switched (PS) only, online small data transmissions, offline small data transmissions, mobile originated only, infrequent mobile terminated, MTC monitoring, offline indication, jamming indication, priority alarm message (PAM), extra low power consumption, secure connection, location specific trigger, and group based MTC features including group based policing and group based addressing. SUMMARY

[0005] A method for multiple -input multiple -output (MIMO) communications between wireless transmit and receive units (WRTUs) includes receiving, at a aggregate point (DAP), data from a plurality of wireless transmit/receive units (WTRUs), aggregating, at the DAP, the data received from the plurality of WTRUs to provide an aggregate signal, transmitting the aggregate signal to at least two of the plurality of WTRUs for re-transmission, and determining a coding scheme for re-transmission of the data by the at least two of the plurality of WTRUs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein:

[0007] FIG. 1A is a system diagram of an example communications system in which one or more disclosed embodiments may be implemented;

[0008] 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. 1A;

[0009] FIG. 1C is a system diagram of an example radio access network and an example core network that may be used within the communications system illustrated in FIG. 1A;

[0010] FIG. 2 is a signal diagram illustrating example communications for a method of uplink (UL) multiple -input multiple -output (MIMO);

[0011] FIG. 3 is a block diagram illustrating a step in the method of UL

MIMO illustrated in FIG. 2;

[0012] FIG. 4 is a block diagram illustrating another step in the method of

UL MIMO illustrated in FIG. 2;

[0013] FIG. 5 is a block diagram illustrating another step in the method of

UL MIMO illustrated in FIG. 2; [0014] FIG. 6 is a block diagram illustrating a method of downlink (DL)

MIMO;

[0015] FIG. 7 is a block diagram illustrating a step in the method of DL

MIMO illustrated in FIG. 6;

[0016] FIG. 8 is a block diagram illustrating another step in the method of

DL MIMO illustrated in FIG. 6;

[0017] FIG. 9 is a block diagram illustrating another step in the method of

DL MIMO illustrated in FIG. 6; and

[0018] FIG. 10 is a signal diagram illustrating example communications for a method of MIMO that may be applied to multiple layers of aggregation.

DETAILED DESCRIPTION

[0019] With the deployment of MTC systems, a wide variety of devices with diverse capabilities may be envisioned to be operating under different conditions. One category of devices that may play a significant role in MTC deployments is "Low Mobility" devices. These devices may move infrequently, move within a restricted area (limited mobility) or not move at all. Another category of devices that may play a significant role is the "concentrator" or Data Aggregate Point (DAP). The DAP may provide an uplink (UL) and downlink (DL) service for local MTC devices, saving power and reducing overhead associated with network entry and packet overhead.

[0020] For MTC devices, power consumption and range may be issues.

Also of concern may be the potential for a large number of devices active in a given area, which may result in a heavy load on ranging and network access resources, while each MTC device may only have a small amount of data to transmit.

[0021] MTC devices may be small and limited in power (e.g., due to size and available power supplies). A DAP may be used to aggregate the UL and/or DL data for multiple MTC devices. An example use case for a DAP may be to have the local MTC devices connect (e.g., by radio or by wire) to the DAP and upload data. The DAP may then transmit aggregated data to the network base station. However, this scenario does not exploit the spatial diversity of the MTC devices local to a DAP.

[0022] Another feature common to current OFDM systems is multi-user

MIMO, where two or more independent radio terminals may transmit precoded data simultaneously to enhance and/or direct the transmitted signal. Multi-user MIMO may enhance range while reducing interference.

[0023] In embodiments described herein, multiple MTC devices may transmit precoded MIMO streams to a base station. By way of example, rather than aggregating and transmitting data from local MTC devices, the DAP may aggregate and apply precoding to the data and pass precoded MIMO streams back to several MTC devices capable of coordinated transmission to the base station. By way of another example, the DAP may pass precoder information to MTC devices along with unprecoded data. Upon receiving precoder information and unprecoded data, MTC devices may generate the precoded data stream on its own.

[0024] FIG. 1A is a diagram of an example communications system 100 in which one or more disclosed embodiments may be implemented. 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.

[0025] 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.

[0026] 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.

[0027] 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. [0028] 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).

[0029] 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).

[0030] 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).

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] FIG. IB is a system diagram of an example WTRU 102. 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 subcombination of the foregoing elements while remaining consistent with an embodiment.

[0037] The processor 118 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. [0038] 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.

[0039] 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 MIMO 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.

[0040] 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.

[0041] 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 (SIM) 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).

[0042] 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.

[0043] 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.

[0044] 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. [0045] 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, 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.

[0046] 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 RNCl42b. 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] FIG. 2 is a signal diagram illustrating example communications for a method of uplink multiple -input multiple -output (MIMO), and FIGs. 3, 4 and 5 are block diagrams illustrating steps in the method. In the examples illustrated in FIGs. 2 and 3, MTC devices (e.g., MTC devices 1, 2 and 3 in FIG. 2 and MTC devices 1, 2, 3, 4, 5 and 6 in FIG. 3) using a single radio capable of transmitting directly to the base station transmit a low power signal to the DAP. The DAP may aggregate data and determine an appropriate scheme for a subsequent cooperative transmission. Depending on various factors, such as channel conditions, the DAP may choose, for example, closed loop spatial multiplexing, open loop spatial multiplexing, or open loop diversity (e.g., space-time/frequency coding) scheme. In the examples illustrated in FIGs. 2 and 4, based on the selected cooperative scheme, the DAP transmits (with low power) aggregated data along with other control information to selected MTC devices (e.g., MTC devices 1 and 2 in FIG. 2 and MTC devices 1 and 6 in FIG. 4). In the examples illustrated in FIGs. 2 and 5, the selected MTC devices process and transmit MIMO signals to the base station at a time or times specified by the DAP.

[0052] While all devices may be capable of transmitting to the BS, there may be cases where some devices are unable to reach the AP but are able to reach the DAP. Figure 2, Device 3, for example, may not participate in the Aggregate UL, and that may be because it is unable to reach the BS. [0053] If closed loop spatial multiplexing is selected as a cooperative transmission scheme, the DAP may transmit precoded data to the MTC devices, or the DAP may transmit non-precoded data along with the precoder information. With the precoder information, the MTC devices may perform precoding operations locally. With the latter method, it may be possible to take advantage of the fact that certain portions of the aggregated data may be known to certain MTC devices. In decoding data at an MTC device, known data may be inserted into a systematic bit sequence and improve decoder performance. Therefore, DAP-to-MTC transmission efficiency may be improved.

[0054] Similarly, in an open loop diversity scheme, the DAP may transmit space-time (frequency) coded data to selected MTC devices, or the DAP may choose to transmit original aggregated data to MTC devices to take advantage of known data bits at MTC devices as described above. MTC devices may then perform space-time (frequency) coding locally. The DAP may also decide to use cyclic delay diversity (CDD) in a coordinated transmission, where each MTC device may transmit data at a different time offset specified by the DAP.

[0055] In the aforementioned cooperative schemes, it may be required that all aggregated data be available at the selected MTC devices. It may be preferred that all aggregated data bits be coded jointly by a channel encoder (e.g., a Turbo encoder, a convolutional encoder or LPDC encoder). The DAP may also send control information to MTC devices so that MTC devices may locate the bits that were originated from themselves and count them as known bits during a decoding process.

[0056] If open loop spatial multiplexing is selected as the cooperative transmission scheme, each MTC may only need to receive a portion of the aggregated data. The DAP may encode data separately. In a DAP to MTC transmission, orthogonal transmission may be used (e.g., FDMA, TDMA or CDMA). To improve spectral efficiency, the DAP may transmit simultaneously to multiple MTC devices on the same radio resources (MU-MIMO).

[0057] FIG. 6 is a signal diagram illustrating example communications for a method of downlink multiple-input multiple-output (MIMO), and FIGs. 7, 8 and 9 are block diagrams illustrating steps in the method. In a first phase (examples of which are illustrated in FIGs. 6 and 7), a base station may transmit aggregated data that may be heard by selected MTC devices (e.g., MTC devices 1, 2 and 3 in FIG. 6 and MTC devices 1 and 6 in FIG. 7). The modulation and coding scheme (MCS) selected in the first phase transmission may be aggressive so that the MTC devices may not be able to decode the aggregate data successfully. However, each MTC device may relay the received signal to the DAP in a second phase transmission (examples of which are illustrated in FIGs. 6 and 8). Upon receiving and combining signals from MTC devices, the overall signal quality may be improved. Therefore, the DAP may be able to decode the aggregated data. By way of example, two different relays may be considered. If all MTC devices relay simultaneously, the relayed signals may be combined in the air when arriving the DAP, resulting in better signal SNR. If relayed signal from M2M devices are not overlapped in either time or frequency, the DAP baseband may observe individual signals relayed by each of the selected MTC devices. Essentially, each MTC device may behave like a distributed antenna of the DAP. More advanced MIMO receivers may then be used to improve downlink reception at the DAP. In a third phase (examples of which are illustrated in FIGs. 6 and 9), the DAP may de-aggregate data into smaller packages and transmit the smaller packages to individual receivers (e.g., MTC devices 1, 2 and 3 in FIG. 6 and MTC devices 1, 2, 3, 4, 5 and 6 in FIG. 9). In the third phase, the DAP may simultaneously transmit to multiple MTC devices on a given radio resource block. To cancel inter-user interference, proper precoder information may be derived according to certain criteria. For example, zero-forcing precoder information may be used.

[0058] The DAP may use a separate frequency or radio technology for communication with MTC devices, as described below. Each MTC device may be equipped with two radios (e.g., Bluetooth/WiFi and WiMAX) and may transmit UL data to the DAP over the short range (e.g., Bluetooth/WiFi) radio. The DAP may aggregate the data and transmit (e.g., via Bluetooth) the aggregated (precoded or unprecoded) data to select MTC devices. The select MTC devices may then process and transmit the MIMO signals to the base station according to a cooperative MIMO scheme specified by the DAP.

[0059] Initially, capability signaling may be required. When an MTC device registers with a DAP, the following capabilities (in addition to existing capability negotiations) may be negotiated: M2M device power source (e.g., whether it is battery powered); whether the MTC device is capable of directly communicating with a base station in addition to a DAP; whether the MTC device is capable of transmitting cooperative MIMO; and MTC device transmitter details (e.g., maximum power, antenna gain, etc.).

[0060] In addition, MTC devices may periodically measure radio link quality between the MTC device and the base station and report it to the DAP. MTC devices with good link quality to the base station may be more likely to be selected by the DAP to participate in a subsequent coordinated transmission.

[0061] Data transmissions to the DAP may follow whatever normal procedures currently exist. For DAP uplink transmissions to the base station, the MTC devices selected for coordinated transmission may receive data from the DAP and transmit at the appropriate time.

[0062] Upon aggregating data received from MTC devices, the DAP may send a request to the base station asking for a grant for uplink transmission. After receiving the uplink transmission grant, which may specify the timing of the transmission and other attributes such as a power control command, the DAP may derive the timing information for the coordinated transmission and send it to the selected MTC devices. The DAP may also send a power control command to MTC devices so that they may adjust transmission power accordingly. In general, all transmissions from selected MTC devices should arrive at the base station simultaneously within the (sub)frames specified by the uplink grant. In certain scenarios, the DAP may direct MTC devices so that their transmitted signals arrive at the base station at slightly different times (e.g., in CDD mode).

[0063] Alternatively, the DAP may coordinate with the selected MTC devices to request an uplink transmission grant. In this approach, the selected MTC devices may send UL transmission requests at a time specified by the DAP. The joint transmission between the DAP and the selected MTC devices may improve a signal-to-noise ratio (SNR) observed by the base station, even though the base station may not be aware of the involvement of the MTC devices. After sending the UL transmission request, each of the selected MTC devices may monitor the downlink control channel transmitted from the base station for a certain period of time, in order to receive the UL transmission grant. The selected MTC devices may also monitor the downlink control channel from the DAP in order to receive the UL grant forwarded by the DAP.

[0064] The UL allocations for the DAP coordinated UL MIMO may be addressed to a cooperative set as a group (e.g., the recipient of a UL allocation may be the group identified by a pre-assigned group identification (ID)). As long as the stations in the cooperative set are listening to the DL, they may be informed of radio link resources allocated for their UL MIMO transmissions, without any station to relay such UL allocation information.

[0065] Alternatively, the UL allocations for the DAP coordinated UL MIMO transmissions may be addressed to the DAP or a specific station in the cooperative set, and the recipient of such UL allocations may need to relay the allocation information to other stations in the cooperative set. In this case, the offset between the UL allocation Information Element (IE) transmission and the allocated UL resource may be required to be set to be sufficient to accommodate the processing and transmission time for all the stations in the cooperative set to obtain the UL allocation information in time for the cooperative UL MIMO transmissions. Such a requirement may not be able to be met by some existing air interface designs, e.g., 802.16e and 802.16m. Therefore, changes may be needed in the UL allocation mechanisms to provide sufficient offset for the proposed DAP coordinated UL MIMO transmissions.

[0066] For a DAP coordinated DL MIMO scheme, the stations in a cooperative set should be in a proper receiving mode and have the right information to receive and decode the corresponding DL MIMO transmissions. For example, in 802.16m systems, the stations in the cooperative set need to receive the DL allocation Information Element (IEs) to gain the knowledge regarding the DL transmission in order to correctly receive and decode it. Therefore, the DL allocation IEs should be provided to the stations in the cooperative set in time for the stations to receive the DL MIMO transmissions properly. Similar to the UL, one way is to set the recipient of the DL allocation IEs to the group of the cooperative set. As long as the stations are listening to the DL when the DL allocation IEs are transmitted, they will receive the DL allocation IEs correctly, without needing any stations to relay the DL allocation IEs.

[0067] For closed loop multiplexing to work in a coordinated transmission mode, it may also be required that MTC devices measure channel state information (CSI) periodically and forward the measured CSI to the DAP so that the DAP may derive appropriate precoder information.

[0068] To support downlink MU-MIMO (from the DAP to MTC devices), the

DAP may transmit reference symbols so that MTC devices may estimate the channel between the DAP and MTC devices and feed it back to the DAP. In a TDD system, an alternative may be for MTC devices to transmit sounding reference symbols so that the DAP may measure the channel. After the DAP obtains channel information, either through feedback from MTC devices or through sounding, proper precoder information may be derived to support MU- MIMO.

[0069] In the first and second phase transmission (MTC device to and from the DAP), the transmitter may receive ACK/NACK messages from the intended receiver and retransmits them if needed. In the third phase transmission (e.g., coordinated transmission), the base station may send an ACK/NACK message to the DAP. If all or a subset of data is not received correctly at the base station (indicated by a NACK message), the DAP may determine a data portion to be retransmitted and send a command to the MTC devices which may then retransmit the data portion that was not received correctly.

[0070] If the UL allocations and the HARQ acknowledgements are provided to the cooperative set as a group, then the synchronous UL HARQ procedure may work as it is, as long as all the stations in the cooperative set may receive the DL from the BS correctly, where the synchronous UL HARQ refers to the UL HARQ schemes with synchronous retransmission allocations (e.g., the UL HARQ as specified in 802.16m and long term evolution (LTE)).

[0071] However, if the UL allocations and HARQ acknowledgements are provided to the station (a device or the DAP) that requested the UL allocations, and such allocations and corresponding HARQ acknowledgements need to be signaled to the cooperative set, then the synchronous UL HARQ schemes may need to have a longer interval between the synchronous UL retransmission allocations than a currently commonly used interval (e.g., four subframes in 802.16m synchronous UL HARQ). This may be due to the additional processing and transmission time required for the UL allocation information and HARQ acknowledgement to be propagated to all the stations.

[0072] The asynchronous UL HARQ may work with the proposed DAP coordinated UL MIMO scheme, as long as the UL allocations for the transmissions and retransmissions may be timely and properly provided to the stations in the cooperative set.

[0073] With a DAP coordinated DL MIMO scheme, for the DL data from the BS to the stations in the cooperative set, the HARQ acknowledgements may be transmitted by the DAP and/or designated station(s) after the DL diversity combining/decoding is completed. If a retransmission is needed, the information about the retransmission may be provided to all the stations in the cooperative set so that the stations may receive the retransmission properly.

[0074] The concepts covered in this disclosure describe networks containing a "single layer" of aggregation between MTC devices and the base station. However, they may also be applied to two or more layers of aggregation (e.g., as illustrated in FIG. 10). For example, a local DAP may collect data from several MTC devices and send an aggregate package to a wide-area DAP. The wide-area DAP may use the same MIMO techniques described above, where the local DAPs act as smart antennas.

[0075] The same variation may be applied to the DL, where a wide-area

DAP may collect and process signals received by other DAPs (and/or MTC devices), apply MIMO processing to the signals, and distribute de-aggregated feeds to local DAPs (which, in tern, may de-aggregate and distribute the de- aggregated feeds to MTC devices). This extension may apply to multiple layers of aggregation and MIMO processing.

[0076] EMBODIMENTS

[0077] 1. A method for multiple -input multiple -output (MIMO) communications between wireless transmit and receive units (WRTUs) comprising:

[0078] receiving, at a aggregate point (DAP), data from a plurality of wireless transmit/receive units (WTRUs);

[0079] aggregating, at the DAP, the data received from the plurality of

WTRUs to provide an aggregate signal;

[0080] transmitting the aggregate signal to at least two of the plurality of

WTRUs for re-transmission; and

[0081] determining a coding scheme for re-transmission of the data by the at least two of the plurality of WTRUs.

[0082] 2. The method of embodiment 1, further comprising receiving, by the WTRU, data and re-transmission information indicating a time to retransmit the data.

[0083] 3. The method of embodiments 1-2, further comprising retransmitting the data at the time indicated by the re-transmission information.

[0084] 4. The method of embodiments 1-3, wherein the received and retransmitted data is aggregate data from a plurality of WTRUs.

[0085] 5. The method of embodiments 1-4, wherein the received data is precoded.

[0086] 6. The method of embodiments 1-5, wherein the received data is non-precoded, and the WTRU further receives precoder information with the non- precoded data.

[0087] 7. The method of embodiment 6, further comprising the WTRU performing precoding operations on the non-precoded data prior to retransmitting the received data. [0088] 8. The method of embodiments 1-7, wherein the received data is space-time coded.

[0089] 9. The method of embodiments 1-8, wherein the received data is not space-time coded, the method further comprising performing space-time coding on the received data.

[0090] 10. The method of embodiments 2-9, wherein the re-transmission information indicates a time to re-transmit the data that is the same time for a plurality of WTRUs.

[0091] 11. The method of embodiments 2-10, wherein the retransmission information indicates a time to re-transmit the data that is a different time for each of a plurality of WTRUs based on cyclic delay diversity (CDD).

[0092] 12. The method of embodiments 1-11, wherein the WTRU is a machine-type communications (MTC) device.

[0093] 13. The method of embodiments 1-12, further comprising periodically measuring a radio link quality between the WTRU and a base station and reporting the measured radio link quality to a data aggregate point (DAP).

[0094] 14. The method of embodiments 2-13, wherein the determined scheme for re-transmission of the data is one of the closed loop spatial multiplexing scheme and the open loop spatial multiplexing scheme, and the aggregate signal includes precoded data.

[0095] 15. A wireless transmit/receive unit (WTRU) comprising:

[0096] a receiving unit configured to receive data and re-transmission information indicating a time to re-transmit the data; and

[0097] a transmitting unit configured to re-transmit the data at the time indicated by the re-transmission information.

[0098] Although features and elements are described 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. In addition, the methods described 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.

" " "

Claims

CLAIMS What is claimed:

1. A method for multiple -input multiple -output (MIMO) communications between wireless transmit and receive units (WRTUs) comprising:

receiving, at an aggregate point (DAP), data from a plurality of wireless transmit/receive units (WTRUs);

aggregating, at the DAP, the data received from the plurality of WTRUs to provide an aggregate signal;

transmitting the aggregate signal to at least two of the plurality of WTRUs for re-transmission; and

determining a coding scheme for re-transmission of the data by the at least two of the plurality of WTRUs.

2. The method of claim 1, further comprising receiving, by the WTRU, data and re-transmission information indicating a time to re-transmit the data.

3. The method of claim 1, further comprising re-transmitting the data at the time indicated by the re-transmission information.

4. The method of claim 3, wherein the received and re-transmitted data is aggregate data from a plurality of WTRUs.

5. The method of claim 1, wherein the received data is precoded.

6. The method of claim 1, wherein the received data is non-precoded, and the WTRU further receives precoder information with the non-precoded data.

7. The method of claim 6, further comprising the WTRU performing precoding operations on the non-precoded data prior to re-transmitting the received data.

8. The method of claim 1, wherein the received data is space-time coded.

9. The method of claim 1, wherein the received data is not space-time coded, the method further comprising performing space-time coding on the received data.

10. The method of claim 2, wherein the re-transmission information indicates a time to re-transmit the data that is the same time for a plurality of WTRUs.

11. The method of claim 2, wherein the re-transmission information indicates a time to re-transmit the data that is a different time for each of a plurality of WTRUs based on cyclic delay diversity (CDD).

12. The method of claim 1, wherein the WTRU is a machine-type communications (MTC) device.

13. The method of claim 1, further comprising periodically measuring a radio link quality between the WTRU and a base station and reporting the measured radio link quality to a data aggregate point (DAP).

14. The method of claim 2, wherein the determined scheme for retransmission of the data is one of the closed loop spatial multiplexing scheme and the open loop spatial multiplexing scheme, and the aggregate signal includes precoded data.

15. A wireless transmit/receive unit (WTRU) comprising:

a receiving unit configured to receive data and re-transmission information indicating a time to re-transmit the data; and

a transmitting unit configured to re-transmit the data at the time indicated by the re-transmission information.