Patent Publication Number: US-2015085721-A1

Title: Method and apparatus for enhancing ul harq process

Description:
RELATED APPLICATIONS 
     This application claims the priority benefit of U.S. Provisional Application Ser. No. 61/883,170 filed Sep. 26, 2013, which is herein incorporated by reference. 
    
    
     BACKGROUND 
     1. Field of Invention 
     The present disclosure relates to a method for determining an uplink hybrid automatic repeat request (UL HARQ) timeline. More particularly, the present disclosure relates to a method for determining the UL HARQ timeline of a time-division duplex (TDD) uplink-downlink (UL-DL) configuration according to a multicast-broadcast single frequency network (MBSFN) frame or to a special subframe. 
     2. Description of Related Art 
     Time division duplex (TDD) offers flexible deployments without requiring a pair of spectrum resources. Currently, Long Term Evolution (LTE) TDD allows for asymmetric downlink-uplink (DL-UL) allocations by providing seven different semi-statically configured DL-UL configurations. 
     The current mechanism for adapting DL-UL allocation is based on the system information change procedure. Additional mechanisms could include dynamic allocation of subframes to UL or to DL. Compared with the system information change procedure, the dynamic mechanisms allow a much shorter period for TDD DL-UL reconfiguration. Such an idea is termed “Further Enhancements to LTE TDD for DL-UL Interference Management and Traffic Adaptation” (eIMTA) in 3GPP. Allowing TDD DL-UL reconfiguration based on traffic adaptation brings the significant performance benefits in small cells. Furthermore, dynamic signaling mechanisms outperform that using the system information change procedure. 
     Although the TDD uplink-downlink configuration could be switched dynamically, the flexibility of current mechanisms is still not enough for adapting the traffic that varies dramatically. Therefore, there is a need to increase the flexibility in the TDD configurations. 
     SUMMARY 
     The disclosure provides a method for determining an uplink hybrid automatic repeat request (UL HARQ) timeline of a time-division duplex (TDD) uplink-downlink (UL-DL) configuration. The method for determining the UL HARQ timeline includes the following steps: allocating a subframe of the TDD UL-DL configuration for transmission of an UL HARQ ACK/NACK message or an UL grant message; and forming an equivalent uplink subframe from a downlink subframe by configuring the downlink subframe as a multicast-broadcast single frequency network (MBSFN) subframe or from a special subframe in the current TDD UL-DL configuration for transmission of data in response to the UL HARQ NACK message or to the UL grant message. 
     The disclosure provides an apparatus for wireless communication. The apparatus includes a processing module and a storage module. The storage module includes a time-division duplex (TDD) uplink-downlink (UL-DL) configuration for a uplink hybrid automatic repeat request (UL HARQ) process and one or more sequences of instructions to be executed by the processing module to perform: receiving an UL HARQ ACK/NACK message or an UL grant message in a subframe of the TDD UL-DL configuration; and in response to the UL HARQ NACK message or to the UL grant message, transmitting data in a downlink subframe configured as a multicast-broadcast single frequency network (MBSFN) subframe or in a special subframe of the TDD UL-DL configuration. 
     The disclosure provides an apparatus for wireless communication. The apparatus includes a processing module and a storage module. The storage module includes a time-division duplex (TDD) uplink-downlink (UL-DL) configuration for an uplink hybrid automatic repeat request (UL HARQ) process and one or more sequences of instructions to be executed by the processing module to perform: transmitting an UL HARQ ACK/NACK message or an UL grant message in a subframe of the TDD UL-DL configuration; and receiving data in response to the UL HARQ NACK message or to the UL grant message in a downlink subframe configured as a multicast-broadcast single frequency network (MBSFN) subframe or in a special subframe of the TDD UL-DL configuration. 
     It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the disclosed as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1A  is a schematic diagram illustrating uplink hybrid automatic repeat request (UL HARQ) timelines of seven time-division duplex (TDD) uplink-downlink (UL-DL) configurations in a Long Term Evolution (LTE) TDD communication system; 
         FIG. 1B  is a table illustrating the relationship between the UL HARQ ACK/NACK message and the corresponding uplink retransmission; 
         FIG. 2A  is a schematic diagram illustrating a modified TDD UL-DL configuration 1 according to one embodiment of this disclosure; 
         FIG. 2B  is a table illustrating the relationship between the UL HARQ ACK/NACK message and the corresponding uplink retransmission according to one embodiment of this disclosure; 
         FIG. 3A  is a schematic diagram illustrating a modified TDD UL-DL configuration 1 according to one embodiment of this disclosure; 
         FIG. 3B  is a table illustrating the relationship between the UL HARQ ACK/NACK message and the corresponding uplink retransmission according to one embodiment of this disclosure; 
         FIG. 4  is a flow diagram illustrating the method for determining an UL HARQ timeline of a TDD UL-DL configuration according to one embodiment of this disclosure; and 
         FIGS. 5  is a schematic diagram illustrating a wireless communication system according to one embodiment of this disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Referring to  FIG. 1A , a schematic diagram which illustrates uplink hybrid automatic repeat request (UL HARQ) timelines of seven time-division duplex (TDD) uplink-downlink (UL-DL) configurations in a Long Term Evolution (LTE) TDD communication system is presented. Each of the seven TDD UL-DL configurations shown in  FIG. 1A  takes three radio frames  101 - 103  as an example, but it is not limited thereto. Each of the radio frames  101 - 103  includes 10 subframes, e.g., special subframes, uplink subframes and downlink subframes. The number in the subframe corresponds to the index for an UL HARQ process. For example, in configuration 5, the uplink data transmission takes place in subframe 2 (index for UL HARQ process: 1) of the radio frame  101 , in which the subframe 2 corresponds to the subframe with a subframe index 2. When the uplink data is not successfully received by a serving base station, the serving base station transmits an UL HARQ NACK message back in subframe 8 (index for UL HARQ process: 1). Subsequently, the uplink data retransmission takes place in subframe 2 (index for UL HARQ process: 1) of the radio frame  102 , and so forth. 
     In a TDD system for LTE, UL HARQ would be implemented in a different manner from a FDD system where an HARQ ACK/NACK message in response to a transmission on a subframe would occur at a relatively fixed interval. However, for a TDD system, the UL HARQ ACK/NACK message in response to a transmission on a subframe would not occur at a fixed interval because of the variable numbers of uplink subframes and downlink subframes for different TDD configurations. In general, when a downlink subframe has been used to receive downlink data, a next uplink subframe which is at least four subframes away would be used to transmit the HARQ ACK/NACK message, and vice versa. The four subframes delay is due to the processing delay of the receiving end. 
     For example, in the configuration 1 shown in  FIG. 1A , when a first uplink data is transmitted by an user equipment (UE) in the subframe 2 of radio frame N, e.g., N=1, the corresponding UL HARQ ACK/NACK message would be received by the same UE in the subframe 6, which is 4 subframes away from the subframe 2, of radio frame N. Similarly when a second uplink data is transmitted in the subframe 3 of radio frame N, the corresponding UL HARQ ACK/NACK message would be received in the subframe 9, which is 6 subframes away from the subframe 3, of radio frame N. When the UL HARQ ACK/NACK message is received by the UE in the subframe 6, the corresponding retransmission would be transmitted by the UE in the subframe 2 of radio frame N+1, and so forth. When the UL HARQ ACK/NACK message is received by the UE at subframe 9, the corresponding retransmission would be transmitted by the UE at subframe 3 of radio frame N+1, and so forth. Therefore, the next uplink subframe is at least four subframes away from the subframe corresponding to the UL HARQ ACK/NACK message. 
     Since the legacy UEs and the eIMTA UEs might have a different understanding of the current TDD DL-UL configuration, it would be noted that if a downlink subframe is dynamically changed to an uplink subframe for the eIMTA UE, the legacy UEs obtain incorrect downlink channel quality measurement. The reason is that when the eIMTA UE transmits uplink data to the serving base station, the uplink data may be introduced to the other legacy UEs as interference since the legacy UEs are configured to receive data. However, if an uplink subframe is dynamically changed to a downlink subframe, no interference is introduced. The reason is that a serving base station of the UEs would have control over when the UEs suppose to transmit uplink data to the serving base station. In other words, no interference is introduced to the other UEs since the serving base station could control the UEs not to transmit uplink data in the UL subframes. Therefore, no uplink data interferes with the downlink data transmitted in the downlink subframe which is changed from the uplink subframe. 
     Referring also to  FIG. 1B , a table  130  illustrating the relationship between the UL HARQ ACK/NACK message and the uplink retransmission from another perspective is presented. Table  130  is a lookup table for deciding a subframe for the UL retransmission when an UL HARQ ACK/NACK message is received. That is to say, when an UL HARQ NACK message is received in subframe n, the UL transmission in response to the UL HARQ NACK message is in subframe n+k, in which k is the number in table  130 . Take TDD UL/DL configuration 1 as an example, when an UL HARQ NACK message is received by the UE in subframe 1, the corresponding uplink retransmission is in subframe 7, in which the number “7” is obtained by n+k, i.e., 1+6. For another example, when an UL grant message is received in subframe 4, the corresponding UL transmission is in subframe 8, in which the number “8” is also obtained by n+k, i.e., 4+4. 
     In some embodiments, the UL HARQ ACK/NACK message and the uplink retransmission could be an uplink grant message and an uplink transmission respectively. 
     In order to preserve backward compatibility and allow legacy user equipments (UEs) to perform downlink signal quality measurement, downlink subframes configured as multicast-broadcast single frequency network (MBSFN) subframes can be utilized such that the legacy UEs only monitor PDCCH of the MBSFN subframes. The remaining symbols in the downlink subframe corresponding to the MBSFN can then be utilized to perform UL transmission for eIMTA UEs. The LTE TDD radio frame structure and the DL-UL configuration are defined in  FIG. 2A . 
     Referring to  FIG. 2A , a schematic diagram illustrating a modified TDD UL-DL configuration 1 according to one embodiment of this disclosure is presented. Each of radio frames  201 - 203  in the modified TDD UL/DL configuration 1 has 10 subframes, in which the subframes includes a plurality of special subframes, uplink subframes and downlink subframes. Each subframe includes 14 symbols. The subframe 4 and the subframe 9 of the radio frames  201 - 203  are originally DL subframes. In the present embodiment, the downlink subframes 4 and 9 are configured as MBSFN subframes. 
     Take the downlink subframe 4 of the radio frame  201  as an example, the downlink subframe 4 is configured as the MBSFN subframe  210  in the present embodiment. The MBSFN subframe  210  includes symbols  211 - 224 , in which the symbol  211  is for PDCCH signaling, and the symbols  212 - 224  are for broadcasting signals. It should be noted that the MBSFN subframe  210  could be configured such that the legacy UEs only monitors the symbol  211  for the PDCCH signals. The remaining symbols  212 - 224  can be used by the eIMTA UEs for uplink transmission of data. Therefore, the subframe 4 can be utilized as an equivalent uplink subframe. Similar to those mentioned above, the subframe 9 can also be utilized as another equivalent uplink subframe if the subframe 9 is configured as a MBSFN subframe. 
     Referring also to  FIG. 2B , a table  230  illustrating the relationship between the UL HARQ ACK/NACK message and the uplink retransmission is presented. Compared to TDD UL/DL configuration 1 of table  130  in  FIG. 1B , the TDD UL/DL configuration 1 in the table  230  has two more numbers corresponding to the subframe 0 and subframe 5. In other words, the TDD UL/DL configuration 1 in the table  230  have more subframes to perform the UL HARQ process, which makes the UL HARQ process more flexible. In more details, when HARQ ACK/NACK message or an uplink grant message is received in subframe 0 or in subframe 5, the TDD UL/DL configuration 1 provides an equivalent uplink frame for uplink retransmission of data in response to the UL HARQ NACK message or for uplink transmission of data in response to the UL grant message, in which the equivalent uplink subframe is the MBSFN subframe. For example, when an UL HARQ NACK message is received in subframe 0, i.e., a downlink subframe, data in response to the UL HARQ NACK message is transmitted in the subframe 4, i.e., 0+4, in which subframe 4 is the MBSFN subframe. 
     Alternatively, the special subframes can also be utilized for eIMTA UEs to perform uplink transmission. Referring to  FIG. 3A , a schematic diagram illustrating a modified TDD UL/DL configuration 1 according to one embodiment of this disclosure is presented. Each of the radio frames  301 - 303  includes 10 subframes, and each subframe includes 14 symbols. In the present embodiment, the special subframes, i.e., the subframe 1 and the subframe 6 of each radio frame  301 - 303  are utilized to perform an equivalent uplink transmission. 
     In more details, take subframe 6, i.e., the special subframe, of the radio frame  301  as an example, the special subframe includes 14 symbols  311 - 324 , in which the symbols  311 - 312  are utilized for downlink pilot time slot (DwPTS), the symbols  313 - 322  are utilized for guard period (GP), and symbols  323 - 324  are utilized for uplink pilot time slot (UpPTS) in the present embodiment. However, numbers of symbols corresponding to the DwPTS, the GP and the UpPTS respectively can be configured by the base station; therefore, the numbers of symbols corresponding to the DwPTS, the GP and the UpPTS respectively are not limited thereto. Since no data is transmitted in the GP in the original configuration, the uplink transmission of the data can be allocated in the GP in the present embodiment. Therefore, the subframe 6, i.e., the special subframe, can be utilized as an equivalent uplink subframe. Similar to those mentioned above, the subframe 1, i.e., the special subframe, can also be utilized as an equivalent uplink subframe. 
     In some embodiments, one symbol (e.g. symbol  313 ) of the GP is not utilized for the uplink transmission since the symbol (e.g. symbol  313 ) of the GP is utilized to avoid the interference caused by the downlink transmission in the DwPTS. In other words, no data is transmitted in one symbol (e.g. symbol  313 ) of the GP. 
     In some embodiments, multiple symbols (e.g. the symbols  313 - 315 ) are not utilized for the uplink transmission so as to avoid the interference caused by the downlink transmission in the DwPTS. In other words, no data is transmitted in multiple symbol (e.g. symbols  313 - 315 ) of the GP. 
     In some embodiments, the uplink transmission of the data in response to the UL HARQ NACK message or to the UL grant message takes place in both the GP and the UpPTS. 
     In some embodiments, the last symbol  324  of the UpPTS may be configured for a transmission of a sounding reference signal (SRS), in which the SRS is for channel estimation of uplink channels. However, the transmission of the SRS is configured by the base station. In other words, the base station may signal to the legacy UEs such that the legacy UEs would not transmit the SRS. Therefore, all symbols of the UpPTS can be utilized to perform an equivalent uplink transmission by the eIMTA UEs. 
     Referring also to  FIG. 3B , a table  330  illustrating the relationship between the UL HARQ ACK/NACK message and the uplink retransmission is presented. Compared to TDD UL/DL configuration 1 of table  130  in  FIG. 1B , the TDD UL/DL configuration 1 in the table  330  has two more numbers corresponding to the subframe 0 and subframe 5. In other words, the TDD UL/DL configuration 1 in the table  330  have more subframes to perform the UL HARQ process, which makes the UL HARQ process more flexible. In more details, when an UL HARQ ACK/NACK message or an UL grant message is received in subframe 0 or in subframe 5, the TDD UL/DL configuration 1 provides an equivalent uplink frame for uplink retransmission of data in response to the UL HARQ NACK message or for uplink transmission of data in response to the UL grant message, in which the equivalent uplink subframe is the special subframe. 
     For example, when an UL HARQ NACK message is received in the subframe 0, i.e., a downlink subframe, the data in response to the UL HARQ NACK message is transmitted in the subframe 6, i.e., 0+6, in which the subframe 6 is the special subframe. 
     Referring to  FIG. 4 , a flow diagram illustrating the method  400  for determining an UL HARQ timeline of a TDD UL-DL configuration is presented. The method  400  is configured to add more equivalent uplink subframes in the TDD UL-DL configuration. 
     In step S 402 , a subframe of the TDD UL-DL configuration is allocated for transmission of an UL HARQ ACK/NACK message or of an UL grant message. 
     In some embodiments, the subframe of the TDD UL-DL configuration in the step S 402  may be a downlink subframe or a special subframe. 
     In step S 404 , an equivalent uplink subframe is formed from a downlink subframe by configuring the downlink subframe as a MBSFN frame or a special subframe in the TDD UL-DL configuration, in which the equivalent uplink subframe is utilized for uplink transmission in response to the UL HARQ NACK message or to the UL grant message. 
     Referring to  FIG. 5 , a schematic diagram illustrating a wireless communication system  500  according to one embodiment of this disclosure is presented. In the present embodiment, the wireless communication system  500  is an LTE TDD system, but it is not limited thereto. The wireless communication system  500  includes a base station  510 , i.e., an eNodeB, and a plurality of UEs  520 , in which the base station  510  serves the UEs  520 . 
     In some embodiments, the UEs can be mobile phones, tablets, computer systems, etc. 
     The base station  510  includes a processing module  511  and a storage module  512 . The storage module  512  stores at least one TDD UL-DL configuration, e.g., TDD UL-DL configuration 1, for the UL HARQ process and one or more sequences of instructions to be executed by the processing module  512  to perform the following steps. 
     First, the base station  510  transmits an UL HARQ ACK/NACK message or an UL grant message in a subframe of the TDD UL-DL configuration. Subsequently, the base station  510  receives data in response to the UL HARQ NACK message or to the UL grant message in a downlink subframe configures as a MBSFN frame or in a special subframe of the TDD UL-DL configuration. 
     Each of the UEs  520  includes a processing module  521  and a storage module  522 . The storage module  522  stores the TDD UL-DL configuration for the UL HARQ process and one or more sequences of instructions to be executed by the processing module  521  to perform the following steps. 
     First, the UE  520  receives an UL HARQ ACK/NACK message or an UL grant message in a subframe of the TDD UL-DL configuration. Subsequently, the UE  520  transmits data in response to the UL HARQ NACK message or to the UL grant message in a downlink subframe configured as a MBSFN frame or a special subframe of the TDD UL-DL configuration. 
     In some embodiments, the processing module  511  and the processing module  512  may be a central processing unit or a processor respectively. 
     In some embodiments, the storage module  512  and the storage  522  may respectively be non-volatile memory such as read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), and electrically erasable programmable read only memory (EEPROM) devices, volatile memory such as static random access memory (SRAM), dynamic random access memory (DRAM), and double data rate random access memory (DDR-RAM); optical storage devices such as compact disc read only memories (CD-ROMs) and digital versatile disc read only memories (DVD-ROMs), and magnetic storage devices such as hard disk drives (HDD) and floppy disk drives. 
     Based on the aforesaid embodiments, the method for determining an UL HARQ timeline of a TDD UL-DL configuration increases the number of uplink subframes, i.e., the uplink frames and the equivalent uplink frames, for data retransmission or data transmission. Moreover, the UL HARQ timeline proposed in the present disclosure also avoids the interference caused by the dynamic configurations of eIMTA UEs to the legacy UEs. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.