WO2014049169A1

WO2014049169A1 - Timing indication for dynamic time division duplex (tdd) uplink/downlink (ul/dl) reconfiguration

Info

Publication number: WO2014049169A1
Application number: PCT/EP2013/070326
Authority: WO
Inventors: Chun Hai Yao; Jie Zhen Lin; Hai Peng LEI; Kodo Shu
Original assignee: Nokia Siemens Networks Oy
Priority date: 2012-09-28
Filing date: 2013-09-30
Publication date: 2014-04-03

Abstract

Systems, methods, apparatuses, and computer program products for dynamic time division duplex (TDD) uplink/downlink (UL/DL) reconfiguration are provided. One method may include selecting a TDD UL/DL configuration, and transmitting a DCI to a UE. The DCI may include an indication for UL/DL HARQ-ACK feedback or UL/DL transmission.

Description

DESCRIPTION TITLE

TIMING INDICATION FOR DYNAMIC TIME DIVISION DUPLEX (TDD)

UPLINK/DOWNLINK (UL/DL) RECONFIGURATION

CROSS-REFERENCE TO RELATED APPLICATIONS:

[0001] This application claims priority to United States Provisional Application No. 61/707,315, filed on September 28, 2012. The entire contents of this earlier filed application is hereby incorporated by reference in its entirety.

BACKGROUND:

Field:

[0002] Embodiments of the invention generally relate to wireless communication systems, 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-Advanced (LTE-A). Some embodiments relate to LTE time division duplex (TDD) enhancements for traffic adaptation and uplink (UL) - downlink (DL) interference management.

Description of the Related Art:

[0003] 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 eNodeB (evolved Node B).

[0004] 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 3rd generation partnership project (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). Advantages of LTE are, 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-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). 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.

[0006] Currently, LTE TDD allows for asymmetric UL-DL allocations by providing seven different semi-statically configured TDD UL-DL configurations, as illustrated in Fig. 1. These allocations can provide between 40% and 90% DL subframes. The current mechanism for indicating UL-DL configuration is based on the system information change procedure with a 640ms period. The concrete TDD UL/DL configuration is semi-statically informed by system information block, type 1 (SIB-1 ) signaling.

[0007] As illustrated in Fig. 1 , the various UL-DL allocations can have either 5 ms or 10 ms switching point periodicity. Moreover, the allocations can include allocations for downlink, D, uplink U, and special S. The special subframes can be, for example, a guard period. TDD UL/DL configuration indication in LTE is currently based on the system information change procedure with a 640 ms period. The concrete TDD UL/DL configuration is semi-statically informed by SIB-1 signaling. SUMMARY:

[0008] One embodiment is directed to a method including selecting, by a network node, a time division duplex (TDD) uplink (UL)/downlink (DL) configuration. The method may also include transmitting a downlink control information (DCI) to a user equipment (UE). The downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a UL or DL acknowledgement/non-acknowledgement feedback or UL/DL transmission. The indication for the sub-frame is consistent with the selected DL/UL configuration. [0009] 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 select a time division duplex (TDD) uplink (UL)/downlink (DL) configuration, and transmit a downlink control information (DCI) to a user equipment (UE). The downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a UL or DL acknowledgement/non-acknowledgement feedback or UL/DL transmission. The indication for the sub-frame is consistent with the selected DL/UL configuration. [00010] Another embodiment is directed to a computer program embodied on a computer readable medium. The computer program is configured to control a processor to perform a process including selecting, by a network node, a time division duplex (TDD) uplink (UL)/downlink (DL) configuration, and transmitting a downlink control information (DCI) to a user equipment (UE). The downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a UL or DL acknowledgement/non-acknowledgement feedback or UL/DL transmission. The indication for the sub-frame is consistent with the selected DL/UL configuration.

[00011] Another embodiment is directed to a method including receiving, by a user equipment (UE), a downlink control information (DCI) from a network node. The downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a uplink (UL)/downlink (DL) acknowledgement/non-acknowledgement feedback or UL/DL transmission.

[00012] 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 receive a downlink control information (DCI) from a network node. The downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a uplink (UL)/downlink (DL) acknowledgement/non-acknowledgement feedback or UL/DL transmission. [00013] Another embodiment is directed to a computer program embodied on a computer readable medium. The computer program is configured to control a processor to perform a process including receiving, by a user equipment (UE), a downlink control information (DCI) from a network node. The downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a uplink (UL)/downlink (DL) acknowledgement/non- acknowledgement feedback or UL/DL transmission.

BRIEF DESCRIPTION OF THE DRAWINGS:

[00014] For proper understanding of the invention, reference should be made to the accompanying drawings, wherein:

[00015] Fig. 1 illustrates seven kinds of TDD UL/DL configurations;

[00016] Fig. 2 illustrates an example of a subframe index on UL subframe 2 and flexible subframes, according to an embodiment;

[00017] Fig. 3 illustrates an example of HARQ timing, according to an embodiment;

[00018] Fig. 4a illustrates a block diagram of an apparatus according to one embodiment; [00019] Fig. 4b illustrates a block diagram of an apparatus according to another embodiment;

[00020] Fig. 5a illustrates a flow diagram of a method according to an embodiment; and

[00021] Fig. 5b illustrates a flow diagram of a method according to another embodiment.

DETAILED DESCRIPTION:

[00022] 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 providing LTE time division duplex (TDD) enhancements for traffic adaptation and uplink (UL) - downlink (DL) interference management, 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.

[00023] 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.

[00024] Evaluation results for dynamic TDD UL/DL configuration in an isolated pico cell scenario, multiple outdoor pico cell scenario, and macro-outdoor pico with activated co-channel interference scenario, demonstrate high performance gain in terms of cell average packet throughput when TDD reconfiguration period is set to 10ms compared to fixed TDD UL/DL configuration. Additionally, faster TDD UL/DL reconfiguration shows better performance especially in case of low or medium cell traffic load. In particular, dynamic TDD UL/DL configuration with 10ms switching scale outperforms than that with 200ms or 640ms. [00025] The current semi-static mechanism for TDD UL/DL configuration indication with 640ms period cannot adapt to the fast TDD UL/DL reconfiguration no matter what kind of TDD reconfiguration switching scale is adopted, e.g., 10ms, 30ms, 200ms or other scales less than 640ms. Therefore, current TDD configuration indication needs to be enhanced for fast TDD UL/DL reconfiguration. For instance, possible solutions for fast TDD UL/DL configuration indication include radio resource control (RRC) signaling, medium access control (MAC) signaling, and physical layer signaling.

[00026] For the RRC signaling solution, a typical time scale is on the order of 200ms. Ambiguity exists between the eNB and UE on the TDD UL/DL configuration, if the eNB does not know the exact time at which the UE applies the updated TDD UL/DL configuration during reconfiguration. Furthermore, the RRC signaling method is not applicable for the legacy UEs due to different hybrid automatic repeat request (HARQ) timings between practically RRC signaled and SIB-1 signaled and may impact legacy UE's radio resource management (RRM) and radio link monitoring (RLM) measurement.

[00027] Similar to the RRC signaling solution, the MAC signaling solution is also not applicable to legacy UEs. Ambiguity, between the eNB and UE on the TDD UL/DL configuration, as explained above, may still happen during reconfiguration. Additionally, considering MAC CE signaling does not have its own error recovery process and the HARQ-ACK corresponding to the physical downlink shared channel (PDSCH) containing the MAC CE signaling may be received incorrectly.

[00028] The physical layer signalling solution can support the fast TDD UL/DL reconfiguration with 10ms switching scale. The TDD UL/DL configuration can be explicitly indicated by a downlink physical signal or implicitly derived by the UE. This solution may have an impact on CSI measurement and is not applicable to legacy UEs. Considering the resulting UL/DL interference due to individual reconfiguration in each cell, the traffic adaptation capability on the time scale of 10ms may not be fully exploited in combination with interference mitigation schemes requiring coordination among cells. [00029] All of the three solutions outlined above would impact the PDSCH/PUSCH HARQ timing and UL grant timing during reconfiguration. Possible enhancements on HARQ timing and UL grant timing should be specified to handle HARQ processes and PUSCH transmission properly for TDD UL/DL reconfiguration. Additionally, the problem of reconfiguration ambiguity also needs to be addressed.

[00030] Rather than indicating the TDD UL/DL configuration with the signaling at different layers, certain embodiments of the invention provide a method in which the eNB does not need to inform the UE of the detailed TDD UL/DL configuration. In one embodiment, the DL/UL timing (e.g, DL/UL HARQ, PUSCH) may be explicitly or implicitly indicated by the specific downlink control information (DCI).

[00031] In general, the sub-frames that can be used in the direction of interest (UL/DL) may be indexed to save signalling bits compared to indexing all sub- frames. In the embodiment of the UL/DL configurations of Fig. 1 , sub-frame 1 need not indexed as it is a special subframe and cannot be used for UL data or control signalling transmission. In the embodiment, for example, sub-frame 0 need not indexed in the UL, as it can't be used in the UL in any configuration. If the indications are not restricted to a subset of configurations, such as in Fig. 1 , all sub-frames will need to be indexed. The below description assumes the subset of Fig. 1 is being used.

[00032] One embodiment is directed to absolute referencing of the sub- frames. According to this embodiment, for DL HARQ timing indication, in each radio frame, subframe 2, 3, 4, 7, 8 and 9 are indexed from 0 to 5, i.e., 000 to 101 indicated in DCI. Three bits are proposed to be included in DCI format 1/1 A/1 B/1 D/2/2A/2B/2C/2D to indicate the aforementioned subframe index for A/N feedback corresponding to the DL subframe. It is noted that the indicated subframe is the nearest subframe after the timing, at which the UE received DCI format 1/1A/1 B/1 D/2/2A/2B/2C/2D, plus 4ms. Due to the nature of TDD UL/DL asymmetry subframe configuration, ACK/NACK (A/N) response to several PDSCHs as well as PDCCH indicating DL SPS release may be indicated by the proposed subframe index to transmit on the same uplink subframe. Those PDSCHs, as well as PDCCH indicating DL SPS release, compose the bundle window and use DAI in DCI format 1/1A/1 B/1 D/2/2A/2B/2C/2D to denote the accumulative number of PDCCH(s) with assigned PDSCH transmission(s) and PDCCH indicating downlink SPS release up to the present subframe, and such DAI can be updated from subframe to subframe. Upon detection of one or several PDSCH transmissions as well as PDCCH indicating DL SPS release whose A N response are indicated in the same subframe, the UE may transmit the A N bits generated by A/N bundling or A/N multiplexing in the indicated subframe.

[00033] For UL grant timing indication, in each radio frame, subframe 2, 3, 4, 7, 8 and 9 are indexed from 0 to 5. Three bits are proposed to be included in DCI format 0/4 to indicate the aforementioned subframe index for PUSCH transmission or retransmission. It is noted that the indicated subframe is the nearest subframe (corresponding to the index) after the timing, at which the UE received DCI format 0/4, plus 4ms.

[00034] For UL HARQ timing indication, in each radio frame, subframe 0, 1 , 3, 4, 5, 6, 7 and 9 are indexed from 0 to 7 since subframe 2 is always for UL transmission and subframe 8 is never used for physical HARQ indication channel (PHICH) transmission. Three bits are proposed to be included in DCI format 0/4 to indicate the aforementioned subframe index for DL PHICH transmission corresponding to the UL subframe to be scheduled. It is noted that the indicated subframe is the nearest subframe (corresponding to the index) after the timing, at which the UE transmits PUSCH, plus 4ms. Alternatively, PHICH timing can follow TDD UL/DL configuration 0. So A/N corresponding to PUSCH can be mapped to DL subframe 0, 1 , 5 or 6 since subframe 0, 1 , 5 and 6 are always used for DL transmission and guarantee the requirement of robustness due to not suffer the UL-DL interference from neighboring cells.

[00035] Another embodiment is directed to relative referencing of the sub- frames (relative to the DCI in which the offset is received). According to this embodiment, for DL HARQ timing indication, four bits are proposed to be included in DCI format 1/1A/1 B/1 D/2/2A/2B/2C/2D to indicate the subframe offset for A/N feedback corresponding to the DL subframe. These four bits are indexed from 0 to 15. The corresponding A/N feedback can be transmitted in the subframe after the 5 timing, at which the UE received DCI format 1/1A/1 B/1 D/2/2A/2B/2C/2D, plus the indicated subframe offset.

[00036] For UL grant timing indication, in this embodiment, three bits are proposed to be included in DCI format 0/4 to indicate the subframe offset for PUSCH transmission or retransmission. These three bits are indexed from 0 to 7. i o It is noted that the indicated subframe is the nearest subframe after the timing, at which the UE received DCI format 0/4, plus the indicated subframe offset. Alternatively, two bits are proposed to be included in DCI format 0/4 to indicate the subframe offset for PUSCH transmission or retransmission. These two bits are indexed from 0 to 3. It is noted that the indicated subframe is the nearest

15 subframe after the timing, at which the UE received DCI format 0/4, plus the indicated subframe offset + 4.

[00037] For UL HARQ timing indication, in this embodiment, three bits are proposed to be included in DCI format 0/4 to indicate the subframe offset for DL PHICH transmission corresponding to the UL subframe to be scheduled. These

20 three bits are indexed from 0 to 7. It is noted that the indicated subframe is the nearest subframe after the timing, at which the UE transmits PUSCH, plus the indicated subframe offset. Alternatively, two bits are proposed to be included in DCI format 0/4 to indicate the subframe offset for DL PHICH transmission corresponding to the UL subframe to be scheduled. These two bits are indexed

25 from 0 to 3. It is noted that the indicated subframe is the nearest subframe after the timing, at which the UE transmits PUSCH, plus the indicated subframe offset + 4.

[00038] Hence, the corresponding A/N feedback can be timely transmitted after detected PDSCH or PDCCH indicating DL SPS release and avoid the 30 introduction of larger round trip time (RTT) delay. Importantly, since there is no need to indicate TDD UL/DL configuration to the UE, the eNB can avoid frequently indicating the change of TDD UL/DL configuration and avoid the false alarm and ambiguity during the reconfiguration period. In that sense, the benefit of dynamic TDD reconfiguration can be achieved.

35 [00039] It is noted that the method to indicate A/N feedback or UL grant timing or DL PHICH timing is not restricted to PDCCH or PHICH. Enhanced PDCCH or enhanced PHICH are also included.

[00040] Currently, the common understanding is to dynamically change TDD UL/DL configuration within all kinds of 7 configurations to well match the traffic variation in uplink and downlink. As a result, subframe 0, 1 , 5 and 6 are always used for DL transmission and subframe 2 is always used for UL transmission. Other subframes, such as subframe 3, 4, 7, 8 and 9, may be used for uplink or downlink depending on the practical TDD UL/DL configuration.

[00041] However, embodiments do not exclude the possibility that only TDD UL/DL configuration 0, 1 , 2 and 6 with 5ms switching point periodicity are used for dynamic TDD UL/DL reconfiguration. Although it may not better match the traffic fluctuation, it has less complexity due to same switching point. In that sense, subframe 0, 1 , 5, 6 are used for downlink transmission, as well as subframe 2 and 7 being used for uplink transmission. The other subframes, subframe 3, 4, 8 and 9 are flexible subframes which can be used for downlink or uplink. The concrete transmission direction is dependent on the TDD UL/DL configuration selected by eNB.

[00042] The proposed HARQ timing according to certain embodiments of the invention can be implemented as discussed below. Fig. 2 illustrates the subframe index on UL subframe 2 and the flexible subframes. In Fig. 2, subframe 2, 3, 4, 7, 8 and 9 are indexed from 0 to 5 as an example. Meanwhile, in DCI format 1/1A/1 B/1 D/2/2A/2B/2C/2D, three bits are included to indicate the subframe index to carry A/N feedback. If the UE receives the PDSCH with assigned PDCCH or PDCCH indicating DL SPS release, it should know which subframe A/N shall be transmitted on. [00043] Fig. 3 illustrates an example of the HARQ timing, according to an embodiment. In the example of Fig. 3, if the current TDD UL/DL configuration is configuration 2 and the eNB schedules DL subframe 0, 1 and 3 to the UE, according to the timing rules of TDD UL/DL configuration 2, the eNB shall indicate the UE to transmit A/N feedback in subframe 7 by means of the same subframe index (01 1 ) in each DL grant. Upon detection of these three PDSCH 5 transmissions whose A/N response are indicated in the same subframe, the UE knows those PDSCHs are in the same bundle window and generate the A/N bits by A/N bundling or A/N multiplexing configured by higher layer signaling and then transmits the A/N bits in the subframe 7. According to the timing rules of TDD UL/DL configuration 2, if the eNB schedules DL subframe 4, 5, 6 and 8 to the UE, i o the eNB shall indicate the UE to transmit A/N feedback in subframe 2 by means of same subframe index (000) in each DL grant. Then, the UE will perform the similar operations as mentioned above. Regarding DL subframe 9, its corresponding A/N is transmitted in UL subframe 7 according to the timing rules of TDD UL/DL configuration 2 if the current TDD UL/DL configuration 2 is not

15 changed; otherwise, the eNB shall indicate the HARQ timing of DL subframe 9 to the UL subframe according to the timing rules of the newly changed TDD UL/DL configuration. Thus, the corresponding A/N feedback can be transmitted more timely and reliably.

[00044] Additionally, more dynamically, the eNB can completely change the 20 transmission direction in the flexible subframes (subframe 3, 4, 7, 8 and 9 as shown in Fig. 2) according to the traffic fluctuation in downlink and uplink while guaranteeing the transmission direction in the fixed subframes (subframe 0, 1 , 5 and 6 for downlink and 2 for uplink). That is, the eNB can change the TDD UL/DL configuration outside of the scope of currently specified seven kinds of TDD 25 UL/DL configurations. However, it is noted that the eNB should avoid the case that downlink is immediately followed by the uplink subframe.

[00045] In the HARQ timing scheme provided according to certain embodiments, it may be important for the eNB to change the TDD UL/DL configuration to match the instantaneous traffic variation in UL and DL for traffic

30 adaptation and avoid frequent indication of the change of TDD UL/DL configuration to the UE. Moreover, the UE can avoid decoding the indication of change of TDD UL/DL configuration and, therefore, avoid problems due to false alarm and ambiguity during the reconfiguration period. In that respect, from the UE's implementation point of view, UE complexity can be reduced. Therefore, the

35 benefit of dynamic TDD UL/DL reconfiguration can be achieved.

[00046] In addition, some embodiments can be extended to UL grant timing. Similarly, subframe 2, 3, 4, 7, 8 and 9 are indexed from 0 to 5 as an example. Meanwhile, in DCI format 0/4, three bits are included to indicate the subframe index for PUSCH transmission or retransmission.

[00047] For UL HARQ timing, according to currently specified PHICH timing, subframe 8 is never used for PHICH transmission. Therefore, in each radio frame, subframe 0, 1 , 3, 4, 5, 6, 7 and 9 are indexed from 0 to 7 by three bits. According to an embodiment, these three bits are proposed to be included in DCI format 0/4 to indicate the subframe index for DL PHICH transmission corresponding to the UL subframe to be scheduled. It is noted that the indicated subframe is the nearest subframe after the timing, at which the UE transmits PUSCH, plus 4ms.

[00048] Alternatively, PHICH timing can follow TDD UL/DL configuration 0. So A/N corresponding to PUSCH can be mapped to DL subframe 0, 1 , 5 or 6 since subframe 0, 1 , 5 and 6 are always used for DL transmission and guarantee the requirement of robustness do not suffer the UL/DL interference from neighboring cells. As a result, the PHICH timing problem can be solved when the UE works in dynamic TDD UL/DL reconfiguration mode.

[00049] Regarding the relative referencing of the sub-frames discussed above, an example is illustrated in Fig. 3 discussed above. More specifically, if the current TDD UL/DL configuration is configuration 2 and the eNB schedules DL subframe 0, 1 and 3 to the UE, according to the timing rules of TDD UL/DL configuration 2, the eNB may indicate the UE to transmit A/N feedback in subframe 7 by means of the corresponding subframe offset in each DL grant. For example, the subframe offsets in DL grant in DL subframe 0, 1 and 3 can be indicated as 7 (1 1 1 ), 6 (1 10) and 4 (100), respectively. Upon detection of these three PDSCH transmissions whose A/N response are transmitted in the same subframe, the UE knows those PDSCHs are in the same bundle window, generates the A/N bits by A/N bundling or A/N multiplexing configured by higher layer signaling, and then transmits the A/N bits in the subframe 7.

[00050] In the case of TDD UL/DL configuration 5, A/N corresponding to DL subframe 9 may be feedback in UL subframe 2. The HARQ timing offset is 13. This is the reason why 4 bits are used in DL grant to indicate the subframe offset for DL HARQ feedback.

[00051] The operations of UL HARQ timing and PUSCH timing may be similar to DL HARQ timing. Since the timing offset for UL HARQ and PUSCH timing is not larger than 7, two bits can be used to indicate the subframe offset. Then, the subframe for PHICH or PUSCH transmission can be indicated by the subframe offset + 4.

[00052] On the other hand, embodiments do not exclude the possibility that only TDD UL/DL configuration 0, 1 , 2 and 6 with 5ms switching point are used for dynamic TDD configuration. Although it may not better match the traffic fluctuation, it has less complexity due to same switching point. In that sense, subframes 0, 1 , 5, 6 are used for downlink transmission as well as subframes 2 and 7 for uplink transmission. The other subframes, 3, 4, 8 and 9 can be used for downlink or uplink. The concrete transmission direction is dependent on the TDD UL/DL configuration selected by the eNB. [00053] In one embodiment, a base station receives a UL/DL configuration from at least one neighbor base station and determines based on the at least one received UL/DL configuration and the UL/DL configuration of the base station which sub-frames will be non-conflicting or least interfered conflicting. Sub-frames are considered non-conflicting if they have the same direction in the UL/DL configuration of each of the at least one neighbor base stations (i.e., usually, special subframes are here considered to have DL transmission direction). In combination with a metric of interference strength suffered from individual neighbor base stations, it may be determined which of the conflicting sub-frames will have the least interference by considering the interference strength of only the neighbor base stations having a transmission direction opposite to that of the base station in an individual sub-frame.

[00054] Based at least in part on the sub-frames determined to be non- conflicting or least interfered, the base station may determine UL/DL A/N feedback timing in the corresponding DL/UL grant. In one embodiment, if the base station provides indications in all non-conflicting sub-frame, it will provide all UL/DL A/N feedback in non-conflicting sub-frames by indicating the subframe index of non- conflicting subframes in DL/UL grant. If there are insufficient resources in the non- conflicting sub-frames, indications for A/N may be provided for the least interfered subframes. In this manner, the base station provides additional protection to A/N transmissions. [00055] For example, if a base station adopts, in reference to Fig. 1 , UL/DL configuration 0 for a subsequent frame and receives signaling that neighbor base stations intend to adopt UL/DL configuration 1 and 6 for the subsequent frame, UL A/N may be indicated in sub-frames 2, 3, 7 or 8. It is naturally preferable to first fill all non-conflicting subframes before filling conflicting subframes. If the neighbor base station adopting UL/DL configuration 6 provides stronger interference to the base station than the neighbor base station adopting UL/DL configuration 1 , the base station can determine that subframe 9 will be substantially more interfered than sub-frame 4 and indicate the least interfered sub-frame 4 for any A/N feedback that does not fit in the non-conflicting sub-frames. [00056] In general, the base station may use the UL/DL configuration information and the type of signaling (grants, A/N feedback resources, or resources for other types of signaling) to determine in which sub-frames to indicate the specific signaling corresponding to a relative level of protection sought for the signaling desired to be transferred in the frame. [00057] Fig. 4a illustrates an example of an apparatus 10 according to an embodiment. In one embodiment, apparatus 10 may be a base station, such as an eNB, supporting the dynamic TDD UL/DL reconfiguration procedures described herein. 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. 4a. Only those components or feature necessary for illustration of the invention are depicted in Fig. 4a.

[00058] As illustrated in Fig. 4a, 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. 4a, 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. [00059] 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.

[00060] 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 demodulates 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.

[00061] 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. [00062] 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.

[00063] As mentioned above, according to one embodiment, apparatus 10 may be an eNB. In this embodiment, apparatus 10 may be controlled by memory 14 and processor 22 to select a TDD UL/DL configuration, and to transmit a DCI to the UE. The DCI may include an indication of the DL/UL configuration. Example formats of the DCI indication are discussed in detail above according to several embodiments.

[00064] Fig. 4b illustrates an example of an apparatus 20 according to another embodiment. In an embodiment, apparatus 20 may be a UE supporting the dynamic TDD UL/DL reconfiguration procedures described herein. 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. 4b. Only those components or feature necessary for illustration of the invention are depicted in Fig. 4b.

[00065] As illustrated in Fig. 4b, 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. 4b, 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.

[00066] 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 5 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 i o 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.

15 [00067] 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

20 demodulates 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.

[00068] Processor 32 may perform functions associated with the operation of apparatus 20 including, without limitation, precoding of antenna gain/phase 25 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.

[00069] In an embodiment, memory 34 stores software modules that provide functionality when executed by processor 32. The modules may include, for 30 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.

35 [00070] As mentioned above, according to one embodiment, apparatus 20 5 may be a UE. In this embodiment, apparatus 20 may be controlled by memory 34 and processor 32 to receive a DCI from an eNB. The received DCI may include an indication of the DL/UL configuration. Apparatus 20 may then be further controlled by memory 34 and processor 32 to transmit A/N bits according to the DL/UL configuration received in the DCI. i o [00071] Fig. 5a illustrates a flow diagram of a method according to one embodiment. In an embodiment, the method of Fig. 5 may be performed by a eNB. According to one embodiment, the method includes, at 500, selecting a TDD UL/DL configuration. The method may then include, at 510, transmitting a DCI to a UE. The DCI may contain an indication of a sub-frame allocated to the UE for a

15 UL or DL ACK/NACK feedback or UL/DL transmission wherein the indication for the sub-frame is consistent with the selected DL/UL configuration. The indication of the sub-frame may comprise an index of the sub-frame according to an indexing where only the sub-frames that can potentially be used in the direction of the grant according to a plurality of DL/UL configurations are indexed sequentially.

20 The indication of the sub-frame may alternatively comprise an index of the sub- frame according to an indexing where all sub-frames of the frame are indexed sequentially. The indication may be an absolute index or an offset to the sub- frame indicated for the grant.

[00072] The method may further include, at 520, determining whether A/N bits 25 corresponding to the UL or DL transmission can and should be placed in the frame obeying a minimum time offset to sub-frame indicated for the UL or DL ACK/NACK feedback or UL/DL transmission in accordance with the selected DL/UL configuration. For example, where in relation to Fig. 1 , DL/UL configuration 0 is selected and a PUSCH is scheduled in sub-frame 3, it may be determined 30 that A/N bits for this PUSCH cannot be placed in the frame according to the selected DL/UL configuration when obeying a 4 ms offset, whereas if DL/UL configuration 3 is selected and a PUSCH is scheduled in sub-frame 3, it may be determined that A/N bits for this grant can be placed in the frame in sub-frame 9 according to the selected DL/UL configuration.

35 [00073] The method may further include, at 530, indicating in the downlink control information A/N bit resources corresponding to the DL/UL transmission obeying to the minimum time offset according to the TDD UL/DL configuration. In accordance with the prior example where configuration 3 is used, 3 bits may be placed in the downlink control information to indicate that resources for the A/N feedback in UL.

[00074] The method may further include, at 540, selecting a second TDD UL/DL configuration for a subsequent frame. This configuration may be the same or different than the configuration for the frame. This second selecting may be used when, at 520, it is concluded that the A/N bits cannot be placed in the frame.

[00075] The method may further include, at 550, indicating in the downlink control information A/N bit resources corresponding to the UL or DL transmission obeying to the minimum time offset according to the second TDD UL/DL configuration. eNB firstly checks whether the subframe used for UL/DL A/N feedback or UL/DL transmission goes in the same frame. If yes, eNB indicates the subframe index according to the timing of current TDD UL/DL configuration; if not, then it checks the second TDD UL/DL configuration to be used in subsequent frame and indicate the subframe index in the next frame based on the second configuration.

[00076] In any of the steps according to Fig. 5, the TDD UL/DL configuration is not signaled to the UE, regardless of whether it is changed.

[00077] Fig. 5b illustrates a flow diagram of a method according to one embodiment. In an embodiment, the method of Fig. 5b may be performed by a UE. According to one embodiment, the method includes, at 560, receiving a downlink control information from an eNB, wherein the downlink control information comprises an indication of a sub-frame allocated to the UE for a UL/DL A/N feedback or UL/DL transmission. The indication of each sub-frame may comprise an index of the sub-frame according to an indexing where only the sub-frames that can potentially be used in the direction of the grant according to a plurality of DL/UL configurations are indexed sequentially. The indication of each sub-frame may alternatively comprise an index of the sub-frame according to an indexing where all sub-frames of the frame are indexed sequentially. The indication may be an absolute index or an offset to the sub-frame indicated for the 5 grant.

[00078] The method may further include, at 570, determining a sub-frame for the grant in accordance with the indexing of the grant and determining a sub- frame for the A/N feedback in accordance with the indexing of the A/N resources.

[00079] The method may further include, at 580, transmitting and/or receiving i o the grant and A N feedback in at least one frame in accordance with the TDD UL/DL configurations in the at least one frame without having determined the TDD UL/DL configurations.

[00080] In some embodiments, the functionality of any of the methods described herein, such as those of Figs. 5a and 5b, may be implemented by

15 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

20 hardware and software.

[00081] Certain embodiments of the invention provide several advantages. For example, some embodiments benefit from dynamic TDD UL/DL reconfiguration used in LTE-LAN. In addition, other advantages include explicit HARQ timing indication for UE A/N feedback in uplink, flexible HARQ timing and

25 reduced RTT, no ambiguity problems during TDD UL/DL reconfiguration, reuse of the current HARQ timing and A/N generation and feedback mechanism as much as possible. Also, embodiments avoid the frequent TDD UL/DL reconfiguration indication for the eNB, and avoid the frequent decoding of TDD UL/DL reconfiguration indication for the UE and simplify UE implementation. Some

30 embodiments also guarantee the reliability of dynamic TDD UL/DL reconfiguration, and avoid false alarms due to dynamic TDD UL/DL reconfiguration.

[00082] 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, 35 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.

Claims

We Claim:

1. A method, comprising:

selecting, by a network node, a time division duplex (TDD) uplink (UL)/downlink (DL) configuration; and

transmitting a downlink control information (DCI) to a user equipment (UE), wherein the downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a UL or DL acknowledgement/non-acknowledgement feedback or UL/DL transmission,

wherein the indication for the sub-frame is consistent with the selected DL/UL configuration.

2. The method according to claim 1 , wherein the indication of the sub-frame comprises an index of the sub-frame according to an indexing where only sub- frames that can potentially be used in a direction of the grant according to a plurality of DL/UL configurations are indexed sequentially.

3. The method according to claim 1 , wherein the indication of the sub-frame comprises an index of the sub-frame according to an indexing where all sub- frames of the frame are indexed sequentially.

4. The method according to any one of claims 1 -3, wherein the indication is an absolute index or an offset to the sub-frame indicated for the grant.

5. The method according to any one of claims 1 -4, further comprising determining whether acknowledgement/non-acknowledgement bits corresponding to the

UL/DL transmission should be placed in the frame obeying a minimum time offset to the UL/DL grant according to the TDD UL/DL configuration.

6. The method according to any one of claims 1-5, further comprising indicating, in the downlink control information (DCI), acknowledgement/non-acknowledgement bit resources corresponding to the UL/DL transmission obeying the minimum time offset according to the TDD UL/DL configuration.

7. The method according to any one of claims 1 -6, further comprising selecting a second TDD UL/DL configuration for a subsequent frame.

8. The method according to claim 7, further comprising indicating, in the downlink control information (DCI), acknowledgement/non-acknowledgement bit resources corresponding to the UL/DL transmission obeying the minimum time offset according to the second TDD UL/DL configuration.

9. An apparatus, comprising:

at least one processor; and

at least one memory comprising computer program code,

wherein 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

select a time division duplex (TDD) uplink (UL)/downlink (DL) configuration; and

transmit a downlink control information (DCI) to a user equipment (UE), wherein the downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a UL or DL acknowledgement/non-acknowledgement feedback or UL/DL transmission,

10. The apparatus according to claim 9, wherein the indication of the sub-frame comprises an index of the sub-frame according to an indexing where only sub- frames that can potentially be used in a direction of the grant according to a plurality of DL/UL configurations are indexed sequentially.

1 1. The apparatus according to claim 9, wherein the indication of the sub-frame comprises an index of the sub-frame according to an indexing where all sub- frames of the frame are indexed sequentially.

12. The apparatus according to any one of claims 9-1 1 , wherein the indication is an absolute index or an offset to the sub-frame indicated for the grant.

13. The apparatus according to any one of claims 9-12, 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 determine whether acknowledgement/non-acknowledgement bits corresponding to the UL/DL transmission should be placed in the frame obeying a minimum time offset to the UL/DL grant according to the TDD UL/DL configuration.

14. The apparatus according to any one of claims 9-13, 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 indicate, in the downlink control information (DCI), acknowledgement/non-acknowledgement bit resources corresponding to the UL/DL transmission obeying the minimum time offset according to the TDD UL/DL configuration.

15. The apparatus according to any one of claims 9-14, 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 select a second TDD UL/DL configuration for a subsequent frame.

16. The apparatus according to claim 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 indicate, in the downlink control information (DCI), acknowledgement/non-acknowledgement bit resources corresponding to the UL/DL transmission obeying the minimum time offset according to the second TDD UL/DL configuration.

17. The apparatus according to any one of claims 9-16, wherein the apparatus comprises an evolved node B (eNB).

18. 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 1-8.

5 19. A method, comprising:

receiving, by a user equipment (UE), a downlink control information (DCI) from a network node,

wherein the downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a uplink (UL)/downlink (DL) i o acknowledgement/non-acknowledgement feedback or UL/DL transmission.

20. The method according to claim 19, wherein the indication of the sub-frame comprises an index of the sub-frame according to an indexing where only sub- frames that can potentially be used in a direction of the grant according to a

15 plurality of DL/UL configurations are indexed sequentially.

21. The method according to claim 19, wherein the indication of the sub-frame comprises an index of the sub-frame according to an indexing where all sub- frames of the frame are indexed sequentially.

20

22. The method according to any one of claims 19-21 , wherein the indication is an absolute index or an offset to the sub-frame indicated for the grant.

23. The method according to any one of claims 19-22, further comprising 25 determining a sub-frame for the grant in accordance with the indexing of the grant and determining a sub-frame for the acknowledgement/non-acknowledgement feedback in accordance with the indexing of the acknowledgement/non- acknowledgement resources.

30 24. The method according to any one of claims 19-23, further comprising transmitting and/or receiving the grant and acknowledgement/non- acknowledgement feedback in at least one frame in accordance with time division duplex (TDD) uplink (UL)/downlink (DL) configurations in at least one frame without having determined the TDD UL/DL configurations.

35

25. An apparatus, comprising:

at least one processor; and

at least one memory comprising computer program code, 5 wherein 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

receive a downlink control information (DCI) from a network node, wherein the downlink control information (DCI) comprises an indication of a sub-frame allocated to the user equipment (UE) for a uplink (UL)/downlink (DL) i o acknowledgement/non-acknowledgement feedback or UL/DL transmission.

26. The apparatus according to claim 25, wherein the indication of the sub-frame comprises an index of the sub-frame according to an indexing where only sub- frames that can potentially be used in a direction of the grant according to a

15 plurality of DL/UL configurations are indexed sequentially.

27. The apparatus according to claim 25, wherein the indication of the sub-frame comprises an index of the sub-frame according to an indexing where all sub- frames of the frame are indexed sequentially.

20

28. The apparatus according to any one of claims 25-27, wherein the indication is an absolute index or an offset to the sub-frame indicated for the grant.

29. The apparatus according to any one of claims 25-28, wherein the at least one 25 memory and the computer program code are further configured, with the at least one processor, to cause the apparatus at least to determine a sub-frame for the grant in accordance with the indexing of the grant and determine a sub-frame for the acknowledgement/non-acknowledgement feedback in accordance with the indexing of the acknowledgement/non-acknowledgement resources.

30

30. The apparatus according to any one of claims 25-29, 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 transmit and/or receive the grant and acknowledgement/non-acknowledgement feedback in at least one frame in

35 accordance with time division duplex (TDD) uplink (UL)/downlink (DL) configurations in at least one frame without having determined the TDD UL/DL configurations.

31. 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 19-24.