WO2015014407A1

WO2015014407A1 - Transmission mode arrangement for flexible time division duplexing (tdd)

Info

Publication number: WO2015014407A1
Application number: PCT/EP2013/066249
Authority: WO
Inventors: Timo Erkki Lunttila; Esa Tapani Tiirola; Frank Frederiksen
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2013-08-02
Filing date: 2013-08-02
Publication date: 2015-02-05

Abstract

Systems, methods, apparatuses, and computer program products for dynamically changing transmission mode is provided. One method includes, during transmission, the eNodeB transmitting only EPDCCH in flexible subframe(s). Depending on operation type(s), the eNodeB applying different DCI formats in the flexible subframe(s). The applying may include using at least one downlink control information (DCI) size to indicate that common reference signals (CRS) is not present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on demodulation reference signals (DMRS) only.

Description

DESCRIPTION

TITLE TRANSMISSION MODE ARRANGEMENT FOR FLEXIBLE TIME DIVISION DUPLEXING

(TDD)

BACKGROUND: Field: [0001] Embodiments of the invention generally relate to mobile communications networks, such as, but not limited to, the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E-UTRAN), and/or LTE- A. Description of the Related Art:

[0002] Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN) refers to a communications network including base stations, or Node Bs, and for example radio network controllers (RNC). UTRAN allows for connectivity between the user equipment (UE) and the core network. The RNC provides control functionalities for one or more Node Bs.

The RNC and its corresponding Node Bs are called the Radio Network Subsystem (RNS). In case of E-UTRAN (enhanced UTRAN), no RNC exists and most of the RNC functionalities are contained in the enhanced Node B (eNodeB or eNB). [0003] Long Term Evolution (LTE) or E-UTRAN refers to improvements of the

UMTS through improved efficiency and services, lower costs, and use of new spectrum opportunities. In particular, LTE is a 3GPP standard that provides for uplink peak rates of at least 50 megabits per second (Mbps) and downlink peak rates of at least 100 Mbps. LTE supports scalable carrier bandwidths from 20 MHz down to 1 .4 MHz and supports both Frequency Division Duplexing

(FDD) and Time Division Duplexing (TDD).

[0004] As mentioned above, LTE may also improve spectral efficiency in networks, allowing carriers to provide more data and voice services over a given bandwidth. Therefore, LTE is designed to fulfill the needs for high-speed data and media transport in addition to high-capacity voice support. Advantages of LTE include, for example, high throughput, low latency, FDD and TDD support in the same platform, an improved end-user experience, and a simple architecture resulting in low operating costs.

[0005] Further releases of 3GPP LTE (e.g., LTE Rel-10, LTE Rel-1 1 , LTE Rel-12) are targeted towards future international mobile telecommunications advanced (IMT-A) systems, referred to herein for convenience simply as LTE- Advanced (LTE-A).

[0006] LTE-A is directed toward extending and optimizing the 3GPP LTE radio access technologies. A goal of LTE-A is to provide significantly enhanced services by means of higher data rates and lower latency with reduced cost. LTE-A will be a more optimized radio system fulfilling the international telecommunication union-radio (ITU-R) requirements for IMT-Advanced while keeping the backward compatibility.

SUMMARY:

[0007] One embodiment is directed to a method including transmitting, by an eNodeB, enhanced physical downlink control channel (EPDCCH) in flexible subframe(s). The method may then include depending on operation type(s), applying different downlink control information (DCI) formats in the flexible subframe(s). The applying may include using at least one downlink control information (DCI) size to indicate that common reference signals (CRS) is not present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on demodulation reference signals (DMRS) only.

[0008] Another embodiment is directed to an apparatus including at least one processor and at least one memory comprising computer program code. The at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus at least to transmit enhanced physical downlink control channel (EPDCCH) in flexible subframe(s), and depending on operation type(s), to apply different downlink control information (DCI) formats in the flexible subframe(s). The at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to use at least one downlink control information (DCI) size to indicate that common reference signals (CRS) is not present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on demodulation reference signals (DMRS) only.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0009] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[00010] Fig. 1 illustrates UL/DL configurations for TD-LTE;

[00011] Fig. 2 illustrates an example radio frame showing Downlink (D), Uplink (U) and Special (S) subframes according to exemplary SI B-1 configuration #0, as well as an exemplary configuration of flexible (F) subframes, according to an embodiment;

[00012] Fig. 3 illustrates an example of the different subframe types from legacy UEs' and Rel-12 UEs' point of view, according to an embodiment; [00013] Fig. 4 illustrates an example of the association between control channels, search spaces and DCI formats, according to one embodiment;

[00014] Fig. 5a illustrates an apparatus according to one embodiment;

[00015] Fig. 5b illustrates an apparatus according to another embodiment; and

[00016] Fig. 6 illustrates a flow diagram of a method according to an embodiment.

DETAILED DESCRI PTION: [00017] It will be readily understood that the components of the invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of systems, methods, apparatuses, and computer program products for transmission modes for enhanced interference management and traffic adaptation (elMTA), as represented in the attached figures, is not intended to limit the scope of the invention, but is merely representative of selected embodiments of the invention.

[00018] The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, the usage of the phrases "certain embodiments," "some embodiments," or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. Thus, appearances of the phrases "in certain embodiments," "in some embodiments," "in other embodiments," or other similar language, throughout this specification do not necessarily all refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Additionally, if desired, the different functions discussed below may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the described functions may be optional or may be combined. As such, the following description should be considered as merely illustrative of the principles, teachings and embodiments of this invention, and not in limitation thereof.

[00019] Embodiments of the invention relate to Rel-12 Work Item elMTA - "Further Enhancements to LTE TDD for DL-UL Interference Management and Traffic Adaptation". More specifically, certain embodiments introduce concepts for transmission modes for elMTA, including the definition of DL control channel (PDCCH/EPDCCH) association.

[00020] As will be discussed in detail below, certain embodiments provide a scheme where the eNB can dynamically change the transmission mode without relying on radio resource control (RRC) signaling. In particular, during transmission, the eNB may transmit only enhanced physical downlink control channel (ePDCCH) in flexible subframe (i.e., no PDCCH transmission). Depending on operation types, the eNB may apply different downlink control information (DCI) formats in flexible subframe than in the fixed DL subframes. For example, the eNB may apply a larger DCI format size (such as DCI format 2A/B/C/D) for demodulation reference signals (DMRS) demodulation, and apply a smaller DCI format size (such as DCI format 0/1 A) for fallback operation.

[00021] The goal of elMTA work item is to enable more flexible time division duplexing (TDD) uplink-downlink (UL-DL) reconfiguration for traffic adaptation in, for example, small cells. The starting point following the Rel-12 assumptions is that the eNB may vary UL-DL configuration relatively often (for those UEs configured to flexible UL/DL mode) compared to the existing situation where UL- DL configuration is in practice very stationary.

[00022] Even though the 3GPP work item is still in the initial phases, some basic assumptions can be made including:

· There is a predefined cell-specific UL-DL configuration broadcasted in the cell using system information block #1 (SIB-1 ). The legacy UEs (e.g., Rel-8 to Rel-1 1 ) in the cell follow this configuration all the time.

• No new TDD UL-DL configurations are introduced: Flexible TDD reconfiguration can happen among existing (seven) configurations. The existing UL-DL configurations for TD-LTE are illustrated in Fig. 1.

• TDD reconfiguration can occur with (at most) radio frame (=10 ms) periodicity for those UEs configured to Flex configuration.

• In each UL-DL configuration there are fixed subframes where the link direction is always predetermined. These fixed subframes are denoted as D (Downlink), S (Special) and U (Uplink).

• Additionally, there are as well flexible subframes (denoted as F). Flexible (F) subframes can be used as D or U.

• The number of Flexible subframes may depend on the scenario (e.g., by SIB-1 configuration).

[00023] Fig. 2 illustrates an example radio frame showing Downlink (D),

Uplink (U) and Special (S) subframes according to exemplary SIB-1 configuration #0, as well as flexible (F) subframes available for Rel-12 UEs configured to flexible UL/DL mode. The example of Fig. 2 depicts TDD SIB-1 configured UL-DL configuration 0 as an example, but the same principle applies to other configurations as well. In addition to the SIB-1 configured UL-DL configuration, which defines whether a given subframe in the radio frame is downlink, special, or uplink subframe, in the case of flexible TDD UL-DL configurations, for example, some of the uplink subframes can be changed into downlink subframes.

[00024] One of the remaining aspects of elMTA work is the definition of transmission modes to be applied on flexible subframes when used as downlink subframes. As a result, certain embodiments provide concepts for transmission modes for elMTA, including the definition of DL control channel (PDCCH/EPDCCH) association.

[00025] One interesting alternative considered for elMTA is to omit the transmission of cell-specific reference signals (CRS) in the flexible DL subframes. This results in a mode of operation similar to New Carrier Type (NCT), but without losing the backward compatibility. Transmitting no CRS in flexible DL subframes facilitates so called NCT subframes. NCT subframes are seen as UL subframes from legacy UEs' point of view. UL usage of NCT subframes can be completely prevented by a specific eNB scheduler implementation and/or proper selection of NCT subframes. Meanwhile, NCT subframes are seen as NCT DL (or UL) subframes from Rel-12 UEs' point of view. On DL side, NCT subframes do not suffer from restrictions given by legacy

UEs. This will enable specific optimization of NCT subframes for DL usage compared to legacy downlink (D) subframes. Fig. 3 illustrates the different subframe types from legacy UEs' and Rel-12 UEs' point of view.

[00026] In LTE, DL transmission modes defined in TS 36.213 determine the key properties of the system operation. These include:

• Possible transmission schemes (e.g., closed loop MIMO, beamforming, Transmit Diversity, etc.).

• The possible CSI reporting modes.

• The reference symbols assumed for CSI measurement (both channel and the interference parts).

• DCI formats to be monitored.

• Search space in which different DCI formats are transmitted.

[00027] None of the existing transmission modes suit the elMTA NCT operation depicted above. Furthermore, combining the preferred control channel (EPDCCH/PDCCH) usage with elMTA/NCT transmission modes has not been considered earlier. This indicates that there is yet much opportunity to improve elMTA/NCT DL flexibility and performance compared to legacy downlink operation.

[00028] One embodiment provides the following arrangement for flexible elMTA/NCT subframes. In this embodiment, there is only EPDCCH configured for flexible elMTA/NCT subframes. It is noted that subframe #6 is a special case since it cannot be used as UL subframe (since it is a special subframe containing CRS). Hence, in this embodiment, subframe #6 is not considered as a flexible/NCT subframe (even though it may be used as either D or S). Within these flexible elMTA/NCT subframes, EPDCCH blind decoding may support at least two DCI size options. At least one DCI size option may be used to indicate that CRS is not present at all in the current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on DMRS only (this may be referred to as transmission mode or method #1 ). At least one other DCI size option may be used to indicate that CRS is present and PDSCH demodulation of the current subframe is based on CRS only (this may be referred to as transmission mode or method #2). In this case, from the perspective of the given UE, DMRS may be present only on physical resource block (PRB) pairs allocated to EPDCCH, while the CRS may be present only on PRB pairs allocated to the PDSCH, but potentially also be configured to be present over all non-EPDCCH PRB pairs.

[00029] A benefit of this embodiment is that the eNB may dynamically vary the RS strategy and related transmission scheme during flexible subframes based on various conditions, such as depending on the quality of the CSI that is available. This enables a considerable increase in the flexibility compared to statically configured transmission mode, where the transmission mode is configured through higher layer signaling (e.g., RRC signaling) and the CRS are always present. Improved flexibility can be achieved without any increase in the UE control channel blind decoding burden compared to current Rel-1 1 decoding burden, and without any additional ambiguity issues involved in UEs' blind decoding operation.

[00030] In some embodiments, there may also be some other functional differences between subframes triggered using two DCI size options. These differences include: (1 ) different CSI measurement and/or reporting procedure (depending on the presence of CRS); and (2) different multi-antenna strategy (e.g., beamforming, CRS-based closed-loop MIMO vs open-loop MIMO / transmit diversity).

[00031] One embodiment may include a three-fold operation of the transmission mode/method and/or reference symbol configuration. For instance, in this embodiment, the eNB may apply different DCI sizes in flexible subframe depending on the operation type. For example, the large size DCI format (e.g., format 2A/B/C) may indicate the presence of DMRS for the scheduled PDSCH

(and that CRS are absent), and the compact size DCI format (e.g., format 0/1 A) may indicate CRS based fall-back operation for the PDSCH reception. In an embodiment, this smaller DCI format may be used for PDSCH scheduling only (PUSCH / UL scheduling is precluded). The UL/DL bit of the format 0/1A in one state can be used to indicate the CRS being transmitted over the full frequency band (possibly excluding the EPDCCH resources). The UL/DL bit of the format 0/1A in the other state can be used to indicate the CRS bandwidth being limited to the PDSCH resources being scheduled using the DCI format.

[00032] It is noted that the latter option of restricting the CRS transmission for fall-back operation allows for multiplexing UEs in fall-back mode and non-fallback modes within the same elMTA subframe.

[00033] According to another embodiment, the three-fold operation of the transmission mode and/or reference symbol configuration may have another setup. In this embodiment, the large size DCI format (e.g., format 2A/B/C/D) may indicate the presence of DMRS for the scheduled PDSCH, and the compact size DCI format (e.g., format 0/1A) may indicate fall-back operation for the PDSCH reception. In one example, the UL/DL bit of the format 0/1 A in one state may be used to indicate that the PDSCH transmission / demodulation is relying on common reference symbols (CRS). These CRS can either be based on full frequency distribution or only within the scheduled resources, for example. The

UL/DL bit of the format 0/1A in the other state may be used to indicate that the compact PDSCH allocation is based on DMRS being used for demodulation.

[00034] In some embodiments, there can also be some functional differences triggered via PDCCH (fixed DL subframes) and EPDCCH (NCT/elMTA subframes). This may include different starting OFDM symbol position for the PDSCH, scheduling of UL transmissions may be precluded in the flexible DL subframes (e.g., to reduce the size of DCI and/or reduce the impact of false positive problem) and to maintain consistency to the overall scheduling algorithm

(such that all UL subframes (including potential flexible DL subframe) are scheduled through non-flexible DL subframes (including the special subframe), and different functionality with respect to common/dedicated search space. For example, common search space may not be supported at all with EPDCCH. [00035] Therefore, according to an embodiment, for the subframes where

PDCCH exists (e.g., fixed D & S), EPDCCH is typically not configured and legacy transmission modes are applied as normal. In case EPDCCH is configured, it operates as normal Rel-1 1 EPDCCH such that it is used to schedule both UL and DL traffic. [00036] In the flexible DL subframes, EPDCCH is used for triggering PDSCH within the same subframe and at least one new transmission mode (TM) based on DMRS is added. In an embodiment, there is no PDCCH at all in any flexible subframes. In this case, the PDSCH may start from the first OFDMA symbol of the subframe. Correspondingly, the EPDCCH may start at the first OFDM symbol of the subframe. Scheduling of UL transmissions may be precluded in the flexible DL subframes.

[00037] The new carrier type transmission mode or method (NCT TM) to be used in flexible subframes containing no CRS can be characterized as discussed in the following. For DCI formats, as discussed above, the TM includes a possibility for transmission of at least two DCI Formats: large DCI, and compact

DCI. In addition, according to certain embodiments, it may be possible to transmit a very compact DCI (i.e., DCI 1 C).

[00038] The large DCI may include "regular" DMRS based operation, for example, using DCI 2D. When a UE decodes a large DCI, it may assume that DMRS are used as a demodulation reference for the PDSCH and that no CRS shall be present on the PDSCH PRBs.

[00039] The compact DCI, which in Rel-1 1 is used for UL allocations - and compact format DL allocations, may be used for fallback purposes when accurate CSI (especially PMI) is not available. In one embodiment, the compact DCI may be DCI 1A based, but could also be some other predefined mode. According to an embodiment, in case scheduling of PUSCH is not allowed in flexible DL subframes, there may be no need for DCI format 1A/0 flag to distinguish between an UL grant and a DL assignment (the flag can, for example, be always set to "1 " or removed or used for other purposes). However, this can be optional, for example when used in combination with NCT (no uncertainty between UL and DL), the existing functionality with respect to DCI 1A/0 may be kept. In an embodiment, when a UE decodes a compact DCI, the UE may assume that CRS are transmitted in the data region, and can be used as PDSCH demodulation reference. In addition, the UE may assume that DMRS are not transmitted in the PDSCH region. According to an embodiment, open loop transmit diversity transmission scheme is applied.

[00040] It should be noted that, from a DL control channel blind decoding perspective, this approach may not enforce more blind decoding attempts compared to the standard Rel-1 1 solution for EPDCCH operation, as the normal UL allocations scheduled through DCI format 0/1A are traded for DL allocations related to the fall-back mode for CRS based scheduling.

[00041] Fig. 4 illustrates an example of the association between control channels, search spaces and DCI formats, according to one embodiment. In an embodiment, the eNB selects for each flexible subframe between DMRS and CRS based modes (e.g., based on CSI). This can be done in fully dynamic manner and without any increase in UE complexity. It should be noted that the number of UE control channel (PDCCH/EPDCCH) blind decodings is essentially the same in both fixed and flexible subframes.

[00042] In view of the above, embodiments described herein for operating the flexible subframe scheduling provide effective means for having instant fallback to CRC-based operation whenever the CSI information may be incomplete, old, or seen as not trustworthy in general. This switch to and from fall-back mode can happen on an as needed basis and there is no need for using higher layer signaling to enable this switch in mode of operation.

[00043] Fig. 5a illustrates an example of an apparatus 10 according to an embodiment. In one embodiment, apparatus 10 may be a base station in a communications system, such as an eNodeB in LTE. It should be noted that one of ordinary skill in the art would understand that apparatus 10 may include components or features not shown in Fig. 5a. Only those components or features necessary for illustration of the invention are depicted in Fig. 5a.

[00044] As illustrated in Fig. 5a, apparatus 10 includes a processor 22 for processing information and executing instructions or operations. Processor 22 may be any type of general or specific purpose processor. While a single processor 22 is shown in Fig. 5a, multiple processors may be utilized according to other embodiments. In fact, processor 22 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application- specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples.

[00045] Apparatus 10 further includes a memory 14, which may be coupled to processor 22, for storing information and instructions that may be executed by processor 22. Memory 14 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor- based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. For example, memory 14 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, or any other type of non-transitory machine or computer readable media. The instructions stored in memory 14 may include program instructions or computer program code that, when executed by processor 22, enable the apparatus 10 to perform tasks as described herein.

[00046] Apparatus 10 may also include one or more antennas 25 for transmitting and receiving signals and/or data to and from apparatus 10. Apparatus 10 may further include a transceiver 28 configured to transmit and receive information. For instance, transceiver 28 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 25 and demodulate information received via the antenna(s) 25 for further processing by other elements of apparatus 10. In other embodiments, transceiver 28 may be capable of transmitting and receiving signals or data directly.

[00047] Processor 22 may perform functions associated with the operation of apparatus 10 including, without limitation, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 10, including processes related to management of communication resources.

[00048] In an embodiment, memory 14 stores software modules that provide functionality when executed by processor 22. The modules may include, for example, an operating system that provides operating system functionality for apparatus 10. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 10. The components of apparatus 10 may be implemented in hardware, or as any suitable combination of hardware and software.

[00049] In one embodiment, apparatus 10 may be a base station such as an eNodeB. In this embodiment, apparatus 10 may be controlled by memory 14 and processor 22 to transmit enhanced physical downlink control channel (EPDCCH) in flexible subframe(s). Depending on operation type(s), apparatus 10 may be further controlled by memory 14 and processor 22 to apply different downlink control information (DCI) formats in the flexible subframe(s).

[00050] According to an embodiment, the flexible subframe(s) comprise enhanced interference management and traffic adaptation (elMTA)/new carrier type (NCT) subframe(s). In an embodiment, apparatus 10 may be further controlled by memory 14 and processor 22 to use at least one downlink control information (DCI) size to indicate that common reference signals (CRS) are not present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on demodulation reference signals (DMRS) only. In some embodiments, apparatus 10 may be further controlled to use at least one other downlink control information (DCI) size to indicate that common reference signals (CRS) are present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on the common reference signals (CRS) only.

[00051] In one embodiment, the at least one downlink control information (DCI) size comprises a larger size downlink control information (DCI) format (e.g., larger than the one indicating CRS based transmission) configured to indicate a presence of the demodulation reference signals (DMRS) for the scheduled physical downlink shared channel (PDSCH). Meanwhile, in an embodiment, the at least one other downlink control information (DCI) size comprises a compact size downlink control information (DCI) format configured to indicate the common reference signals (CRS) based fallback operation for the physical downlink shared channel (PDSCH) reception.

[00052] According to an embodiment, the compact size downlink control information (DCI) format, e.g., format 0/1A, is used for physical downlink shared channel (PDSCH) scheduling only. In one example, an uplink/downlink (UL/DL) bit of the format 0/1A in one state is used to indicate the common reference signals (CRS) being transmitted over a full frequency band. In this example, the uplink/downlink (UL/DL) bit of the format 0/1 A in another state is used to indicate the common reference signals (CRS) bandwidth being limited to the physical downlink shared channel (PDSCH) resources being scheduled using the compact size downlink control information (DCI).

[00053] In another example, an uplink/downlink (UL/DL) bit of the format 0/1 A in one state is used to indicate that the physical downlink shared channel (PDSCH) transmission is relying on the common reference signals (CRS). In this example, the uplink/downlink (UL/DL) bit of the format 0/1A in another state is used to indicate that compact physical downlink shared channel (PDSCH) allocation is based on demodulation reference signals (DMRS).

[00054] Fig. 5b illustrates an example of an apparatus 20 according to another embodiment. In an embodiment, apparatus 20 may be a UE. It should be noted that one of ordinary skill in the art would understand that apparatus 20 may include components or features not shown in Fig. 5b. Only those components or features necessary for illustration of the invention are depicted in Fig. 5b.

[00055] As illustrated in Fig. 5b, apparatus 20 includes a processor 32 for processing information and executing instructions or operations. Processor 32 may be any type of general or specific purpose processor. While a single processor 32 is shown in Fig. 5b, multiple processors may be utilized according to other embodiments. In fact, processor 32 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application- specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples.

[00056] Apparatus 20 further includes a memory 34, which may be coupled to processor 32, for storing information and instructions that may be executed by processor 32. Memory 34 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor- based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. For example, memory 34 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, or any other type of non-transitory machine or computer readable media. The instructions stored in memory 34 may include program instructions or computer program code that, when executed by processor 32, enable the apparatus 20 to perform tasks as described herein.

[00057] Apparatus 20 may also include one or more antennas 35 for transmitting and receiving signals and/or data to and from apparatus 20. Apparatus 20 may further include a transceiver 38 configured to transmit and receive information. For instance, transceiver 38 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 35 and demodulate information received via the antenna(s) 35 for further processing by other elements of apparatus 20. In other embodiments, transceiver 38 may be capable of transmitting and receiving signals or data directly.

[00058] Processor 32 may perform functions associated with the operation of apparatus 20 including, without limitation, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 20, including processes related to management of communication resources.

[00059] In an embodiment, memory 34 stores software modules that provide functionality when executed by processor 32. The modules may include, for example, an operating system that provides operating system functionality for apparatus 20. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 20. The components of apparatus 20 may be implemented in hardware, or as any suitable combination of hardware and software.

[00060] As mentioned above, according to one embodiment, apparatus 20 may be a UE. In this embodiment, apparatus 20 may be controlled by memory 34 and processor 32 to receive, from an eNodeB, only enhanced physical downlink control channel (EPDCCH) in flexible subframe(s). As mentioned above, different downlink control information (DCI) formats may be applied in the flexible subframe(s). One format may be a large size DCI format, and the other format may be a compact size DCI format. The large size DCI format may be used to indicate that common reference signals (CRS) are not present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on demodulation reference signals (DMRS) only. The compact size downlink control information (DCI) format may be used to indicate that common reference signals (CRS) are present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on the common reference signals (CRS) only.

[00061] In an embodiment, when apparatus 20 decodes the large size DCI, it may assume that DMRS are used as a demodulation reference for the PDSCH and that no CRS is present on the PDSCH PRBs. According to an embodiment, when apparatus 20 decodes the compact size DCI, it may assume that CRS are transmitted in the data region and can be used as PDSCH demodulation reference. In addition, for the compact size DCI, apparatus 20 may assume that DMRS are not transmitted in the data region.

[00062] Fig. 6 illustrates an example of a flow diagram of a method, according to an embodiment. The method includes, at 600, transmitting, by an eNodeB, enhanced physical downlink control channel (EPDCCH) in flexible subframe(s). The method may further include, at 610, depending on operation type(s), applying different downlink control information (DCI) formats in the flexible subframe(s).

[00063] The applying may include using a larger size downlink control information (DCI) to indicate that common reference signals (CRS) is not present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on demodulation reference signals (DMRS) only. The applying may also include using a compact size downlink control information (DCI) to indicate that common reference signals (CRS) is present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on the common reference signals (CRS) only.

[00064] In some embodiments, the functionality of any of the methods described herein, such as those illustrated in Fig. 6 discussed above, may be implemented by software and/or computer program code stored in memory or other computer readable or tangible media, and executed by a processor. In other embodiments, the functionality may be performed by hardware, for example through the use of an application specific integrated circuit (ASIC), a programmable gate array (PGA), a field programmable gate array (FPGA), or any other combination of hardware and software.

[00065] One having ordinary skill in the art will readily understand that the invention as discussed above may be practiced with steps in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although the invention has been described based upon these preferred embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of the invention. In order to determine the metes and bounds of the invention, therefore, reference should be made to the appended claims.

Claims

WE CLAIM:

1. A method, comprising: transmitting, by an eNodeB, enhanced physical downlink control channel (EPDCCH) in flexible subframe(s); depending on operation type(s), applying different downlink control information (DCI) formats in the flexible subframe(s), wherein the applying comprises using at least one downlink control information (DCI) size to indicate that common reference signals (CRS) is not present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on demodulation reference signals (DMRS) only.

2. The method according to claim 1 , wherein the flexible subframe(s) comprise time division duplexing (TDD) enhanced interference management and traffic adaptation (elMTA)/new carrier type (NCT) subframe(s).

3. The method according to claims 1 or 2, wherein the applying comprises using at least one other downlink control information (DCI) size to indicate that common reference signals (CRS) is present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on the common reference signals (CRS) only.

4. The method according to any of claims 1 , 2, or 3, wherein the at least one downlink control information (DCI) size comprises a larger size downlink control information (DCI) format indicating a presence of the demodulation reference signals (DMRS) for the scheduled physical downlink shared channel (PDSCH).

5. The method according to claim 3, wherein the at least one other downlink control information (DCI) size comprises a compact size downlink control information (DCI) format indicating the common reference signals (CRS) based fallback operation for the physical downlink shared channel (PDSCH) reception.

6. The method according to claim 5, wherein the compact size downlink control information (DCI) format is used for physical downlink shared channel (PDSCH) scheduling only.

7. The method according to claim 6, wherein an uplink/downlink (UL/DL) bit of the compact format 0/1A in one state is used to indicate the common reference signals (CRS) being transmitted over a full frequency band.

8. The method according to claim 6, wherein an uplink/downlink (UL/DL) bit of the compact format 0/1 A in another state is used to indicate the common reference signals (CRS) bandwidth being limited to the physical downlink shared channel (PDSCH) resources being scheduled using the compact size downlink control information (DCI).

9. The method according to claim 6, wherein an uplink/downlink (UL/DL) bit of the compact format 0/1 A in one state is used to indicate that the physical downlink shared channel (PDSCH) transmission is relying on the common reference signals (CRS).

10. The method according to claim 6, wherein an uplink/downlink (UL/DL) bit of the compact format 0/1 A in another state is used to indicate that compact physical downlink shared channel (PDSCH) allocation is based on demodulation reference signals (DMRS).

1 1 . The method according to claims 4 or 5, wherein the larger size downlink control information (DCI) format and the compact size downlink control information (DCI) format are transmitted in the enhanced physical downlink control channel (EPDCCH) user equipment specific search space.

12. The method according to claims 4 or 5, wherein the larger size downlink control information (DCI) format and the compact size downlink control information (DCI) format are transmitted in the enhanced physical downlink control channel (EPDCCH) common search space.

13. The method according to claim 5, wherein the compact size downlink control information (DCI) format is transmitted in the enhanced physical downlink control channel (EPDCCH) common search space.

14. An apparatus, comprising: at least one processor; and at least one memory comprising computer program code, the at least one memory and the computer program code configured, with the at least one processor, to cause the apparatus at least to transmit enhanced physical downlink control channel (EPDCCH) in flexible subframe(s); depending on operation type(s), apply different downlink control information (DCI) formats in the flexible subframe(s), wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to use at least one downlink control information (DCI) size to indicate that common reference signals (CRS) is not present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on demodulation reference signals (DMRS) only.

15. The apparatus according to claim 14, wherein the flexible subframe(s) comprise time division duplexing (TDD) enhanced interference management and traffic adaptation (elMTA)/new carrier type (NCT) subframe(s).

16. The apparatus according to any one of claims 14 or 15, wherein the at least one memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to use at least one other downlink control information (DCI) size to indicate that common reference signals (CRS) is present in a current subframe and physical downlink shared channel (PDSCH) demodulation of the current subframe is based on the common reference signals (CRS) only.

17. The apparatus according to claim 14, wherein the at least one downlink control information (DCI) size comprises a larger size downlink control information (DCI) format configured to indicate a presence of the demodulation reference signals (DMRS) for the scheduled physical downlink shared channel (PDSCH).

18. The apparatus according to claim 16, wherein the at least one other downlink control information (DCI) size comprises a compact size downlink control information (DCI) format configured to indicate the common reference signals (CRS) based fallback operation for the physical downlink shared channel (PDSCH) reception.

19. The apparatus according to claim 18, wherein the compact size downlink control information (DCI) format is used for physical downlink shared channel (PDSCH) scheduling only.

20. The apparatus according to claim 19, wherein an uplink/downlink (UL/DL) bit of the compact format 0/1A in one state is used to indicate the common reference signals (CRS) being transmitted over a full frequency band.

21 . The apparatus according to claim 19, wherein an uplink/downlink (UL/DL) bit of the compact format 0/1 A in another state is used to indicate the common reference signals

(CRS) bandwidth being limited to the physical downlink shared channel (PDSCH) resources being scheduled using the compact size downlink control information (DCI).

22. The apparatus according to claim 19, wherein an uplink/downlink (UL/DL) bit of the compact format 0/1 A in one state is used to indicate that the physical downlink shared channel (PDSCH) transmission is relying on the common reference signals (CRS).

23. The apparatus according to claim 19, wherein an uplink/downlink (UL/DL) bit of the compact format 0/1 A in another state is used to indicate that compact physical downlink shared channel (PDSCH) allocation is based on demodulation reference signals (DMRS).

24. The apparatus according to claims 17 or 18, wherein the larger size downlink control information (DCI) format and the compact size downlink control information (DCI) format are transmitted in the enhanced physical downlink control channel (EPDCCH) user equipment specific search space.

25. The apparatus according to claims 17 or 18, wherein the larger size downlink control information (DCI) format and the compact size downlink control information (DCI) format are transmitted in the enhanced physical downlink control channel (EPDCCH) common search space.

26. The apparatus according to claim 18, wherein the compact size downlink control information (DCI) format is transmitted in the enhanced physical downlink control channel (EPDCCH) common search space.

27. The apparatus according to any one of claims 14-26, wherein the apparatus comprises an eNodeB.

28. A computer program, embodied on a computer readable medium, wherein the computer program is configured to control a processor to perform a method according to any one of claims 1-13.