Abstract:
A method and apparatus are disclosed for efficient hybrid automatic repeat request (HARQ) process utilization for semi-persistent and dynamic data transmissions, wherein a reserved HARQ process identification (ID) can be reused. A subset of a plurality of HARQ process IDs is reserved to use for a semi-persistent allocation, and data is transmitted based on the semi-persistent allocation. A dynamic allocation is received via a physical downlink control channel (PDCCH). At least one of the reserved HARQ process IDs is selectively used for transmitting data based on the dynamic allocation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/035,273 filed Mar. 10, 2008, which is incorporated by reference as if fully set forth. 
     
    
     FIELD OF INVENTION 
       [0002]    This application is related to wireless communications. 
       BACKGROUND 
       [0003]    The basis for uplink. (UL) and downlink (DL) scheduling is dynamic scheduling. In a long term evolution (LTE) wireless communication system, scheduling information is transmitted during transmission timing intervals (TTIs) to a wireless transmit/receive unit (WTRU) via a physical downlink control channel (PDCCH). It has been agreed by radio access network (RAN) working groups (i.e., RAN2) to support semi-persistent scheduling for the DL and the UL in long term evolution (LTE). For semi-persistently scheduled wireless transmit/receive units (WTRUs) in a transmission time interval (TTI), a DL/UL grant does not need to be sent for initial data transmission. The only exception is when an evolved Node-B (eNB) wants to override the persistent resource assignment, which by definition should be infrequent. Otherwise, the sole purpose of a DL/UL persistent resource assignment is lost. As an optimization for voice over Internet protocol (VoIP), persistent scheduling is used for both DL and UL, where the resource for the initial transmissions is persistently allocated and the resources for the hybrid automatic repeat request (HARQ) retransmissions is dynamically allocated. 
         [0004]    For the DL, the HARQ Process identification (ID) of a re-transmission must be specified because the same cannot be inferred from the TTI in which the re-transmission occurs, (due to the asynchronous nature of DL re-transmissions). For dynamic scheduling, this is achieved via DL grant signaling. For semi-persistently scheduled WTRUs in a TTI, a DL grant is not sent for initial transmissions, and any subsequent adaptive re-transmissions require a DL grant which explicitly indicates the HARQ Process ID for the re-transmissions. 
         [0005]    A solution includes both the WTRU and the eNB to assume that the next available HARQ process-ID is used for a persistently scheduled DL transmission. However, this procedure would not be robust enough in the presence of errors. 
         [0006]    When HARQ processes are reserved for persistent transmissions, the HARQ processes left for dynamic transmission are limited. As such, it is not efficient to reserve several HARQ processes only for persistent transmissions if they finish the transmission successfully and cannot be used by other services for a long time. 
         [0007]    Therefore, there exists a need for a method to alleviate the above inefficiencies and concerns. 
       SUMMARY 
       [0008]    A method and apparatus are disclosed for efficient HARQ process utilization for semi-persistent and dynamic data transmissions, wherein a reserved HARQ process ID can be reused. A subset of a plurality of HARQ process IDs is reserved to use for a semi-persistent allocation, and data is transmitted based on the semi-persistent allocation. A dynamic allocation is received via a PDCCH. At least one of the reserved HARQ process IDs is selectively used for transmitting data based on the dynamic allocation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]    A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
           [0010]      FIG. 1  shows a wireless communication system that is configured to efficiently utilize HARQ processes; 
           [0011]      FIG. 2  shows an example of a relation between system frame numbers (SFNs) and reserved HARQ process IDs in the downlink; 
           [0012]      FIG. 3  shows an example of signaling for persistent retransmission and dynamic allocation; and 
           [0013]      FIG. 4  is a flow diagram of a procedure for efficiently utilizing HARQ processes for semi-persistent and dynamic data transmissions. 
       
    
    
     DETAILED DESCRIPTION  
       [0014]    When referred to hereafter, the terminology “wireless transmit/receive unit (WTRU)” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user device capable of operating in a wireless environment. 
         [0015]    When referred to hereafter, the terminology “evolved Node-B (eNB)” includes but is not limited to a base station, a site controller, an access point (AP), or any other type of interfacing device capable of operating in a wireless environment. 
         [0016]      FIG. 1  shows a wireless communication system  100  including a WTRU  105  and an eNB  110 , which communicate over a PDCCH  115  and a physical uplink control channel (PUCCH)  120 . The WTRU  105  includes a transmitter  125 , a receiver  130 , a processor  135  and a buffer  140 . The eNB  110  includes a transmitter  145 , a receiver  150  and a processor  155 . 
         [0017]    A method is described below for efficiently utilizing DL and UL HARQ resources. In the DL, if a subset of HARQ process IDs are reserved for semi-persistent transmission, the reserved HARQ processes may also be used for dynamic allocation when data associated with a certain reserved HARQ process ID has been successfully transmitted, (i.e., receive an acknowledgement (ACK) from the WTRU  105 ) and before the reserved HARQ process ID will be used at a next associated system frame number (SFN) moment. For example if one HARQ process m is reserved to associate with an odd SFN, as shown in  FIG. 2 , and then if a HARQ process in starts transmission at SFN1 and finishes before SFN2, the HARQ process m may be used by dynamic scheduling. In this way, the HARQ process m can be fully utilized without wasting the resource. Also, the dynamic allocation can override the existing HARQ process m such that this process does not finish its transmission. 
         [0018]    Alternatively, the dynamic allocation uses the reserved HARQ process when all unreserved HARQ processes are used up, (or are unavailable), and the reserved HARQ process has successfully transmitted the packet or reached the maximum number of retransmissions, or the time is long enough for dynamic allocation and transmission before using this HARQ process ID at the associated SFN for persistent transmission. 
         [0019]    Whether to use the reserved HARQ process ID for dynamic scheduling between two associated SFNs using the same reserved HARQ process ID can be signaled in a radio resource control (RRC) message during a persistent allocation setup. For example, it can be put together with reserved HARQ IDs. The configuration may also be signaled in a PDCCH when activating the DL persistent scheduling. 
         [0020]      FIG. 2  shows an example whereby HARQ processes are reserved with associated SFNs for DL persistent scheduling. In  FIG. 2 , SFN1 refers to an odd SFN and SFN2 refers to an even SFN. SFN1 and SFN2 are used here as example to show initial packets to transmit at the odd and even SFN moments. The shaded rectangles represent retransmitted packets. As an example, HARQ processes m and n are reserved for the DL persistent scheduling. The SFN, when the initial transmission is sent, is coupled with the HARQ process ID. As such, when an initial transmission is sent in an odd SFN, the retransmission is sent through the HARQ process m. In accordance with this example shown in  FIG. 2 , HARQ process n is used when the initial transmission is sent in an even SFN, and the HARQ process m is used for retransmission 3 times. The NACKs in  FIG. 2  represent a failed transmission using HARQ process m in the DL failed, whereby the WTRU  105  sends the NACK to the eNB  110 , so that eNB  110  will retransmit using HARQ process m. 
         [0021]    Still, referring to  FIG. 2 , once one reserved DL HARQ process m has successfully finished DL persistent transmission, for example between two odd SFNs, before the next consecutive odd SFN to use HARQ process in for a new DL persistent transmission, the HARQ process x can be used by the eNB  110  for dynamic scheduling if all unreserved HARQ processes are used up (or are unavailable). Thus, the WTRU  105  may differentiate whether the data from the same HARQ process is for persistent retransmissions or for new dynamic allocation using explicit signaling. The PDCCH signaling can be used for explicitly signaling dynamic scheduling when sharing the reserved HARQ process, for example the HARQ process ID m. 
         [0022]    A new data indicator (NDI) in the PDCCH may indicate to the WTRU  105  that this is for new dynamic scheduling if the DL allocation using a reserved HARQ process ID occurs after the WTRU  105  successfully receives the DL persistent data and sends an acknowledgement (ACK) to the eNB  110 , or the maximum number of retransmissions has been reached. The WTRU  105  may also determine whether it is a retransmission from a retransmission sequence number (RSN). Also, the DL scheduling grant carried on the PDCCH can use one bit to indicate whether the DL scheduling is for dynamic or persistent allocation. 
         [0023]    If the DL dynamic transmission using the reserved HARQ process cannot be successfully received before the next SFN, when this reserved HARQ process has to be used for DL persistent transmission, then any DL dynamic transmission should be suspended and the WTRU  105  should empty the buffer  140  which stores the DL dynamic transmission data using the reserved HARQ process. 
         [0024]    At least one transmission time interval (TTI) needs to occur before the reserved HARQ process m for the next immediate associated SFN for a new DL persistent transmission. The buffer  140  stores data for the on-going dynamic transmission associated with the reserved HARQ process m. The buffer  140  should be flushed and parameters for HARQ process m should be reset to the configurations for initial DL persistent transmission. 
         [0025]    Alternatively, in addition to reserving a subset of HARQ process IDs for DL persistent transmissions, a subset (preferably more than one) of HARQ process IDs for UL persistent transmissions may also be reserved. The reserved HARQ process IDs for UL persistent transmissions may also be used for UL dynamic transmissions when the reserved HARQ process has finished UL persistent transmission successfully, or has reached the maximum number of retransmissions and there is still time before using the same HARQ process in the next associated SFN for UL persistent transmission. The unreserved HARQ processes for UL dynamic scheduling may be used, and then the reserved HARQ processes are used once the unreserved HARQ processes are all used. 
         [0026]    If a subset of HARQ process IDs is to be reserved for UL persistent transmissions, it may be signaled in the RRC during the UL persistent scheduling setup process. As described above for the DL, the configuration of whether to use the reserved HARQ process ID for UL dynamic scheduling between two associated SFNs that use the same reserved HARQ process ID can be signaled in an RRC message during persistent allocation setup. For example, the signaling may be put together with the reserved HARQ IDs. Alternatively, the configuration may be signaled in the PDCCH when activating the UL persistent allocation. 
         [0027]    If the WTRU  105  receives an UL grant with a reserved HARQ ID and NDI indicating a new packet before the next associated SFN for UL persistent transmission, then the WTRU  105  realizes that this UL grant is for dynamic scheduling by reusing (or sharing) the reserved HARQ process and the WTRU  105  can start to use that HARQ process and allocated parameter for UL dynamic transmission. 
         [0028]    If WTRU  105  detects an ACK, but received an UL grant with the same HARQ process ID indicating a retransmission, then the WTRU  105  knows that a negative acknowledgement (NACK) is detected as an ACK in error and the UL allocation is still for retransmission of the on going UL persistent transmission. 
         [0029]    If the WTRU  105  detects a NACK, but the UL grant with a reserved HARQ process ID and NDI indicates a new data packet, then the WTRU  105  knows that the ACK may be detected as a MACK and the new UL grant is for dynamic scheduling before the next SFN and therefore, to use the reserved HARQ process. 
         [0030]    If the WTRU  105  does not detect either an ACK or a NACK at the expected time, the WTRU  105  knows the ACK/NACK is lost. If the WTRU  105  later detects an UL grant using the reserved HAN process with NDI indicating a new data packet, then the WTRU  105  knows the DL ACK is lost and that the reserved HARQ process is used for dynamic scheduling. Otherwise, if the WTRU  105  detects UL grant using a reserved. HARQ process ID, but the RSN indicates a retransmission, then the WTRU  105  knows the DL NACK is lost and the allocation is for persistent retransmissions. 
         [0031]    If WTRU  105  reserves the HARQ process for UL dynamic transmission, X number of Ms, for example one (1), before the start of the next SFN to use the same reserved HARQ process t for UL persistent transmission, the WTRU  105  flushes the buffer  140  with the unfinished UL dynamic transmission associated with HARQ process t to prepare for the next UL persistent transmission. 
         [0032]    A method for PDCCH signaling for allocation of persistent retransmission and dynamic transmission is disclosed. In accordance with this method, there are multiple ways to signal to the WTRU  105  whether the allocation for retransmissions is for the same initial transmission to avoid the ambiguity at the WTRU  105 . If the HARQ process ID along with the RSN is included in the DL allocation for retransmission of persistent scheduling, it is possible to avoid ambiguity at WTRU  105  without reserving a subset of HARQ processes for persistent scheduling. 
         [0033]    The SFNs may be used for persistent allocation for transmission and retransmissions (DL/UL), and HARQ IDs may be used for dynamic allocation for initial transmissions and retransmissions. When making resource allocation for retransmissions, only the HARQ process ID is included in the PDCCH for dynamic allocation. As such, there is no HARQ process ID in the PDCCH for persistent transmission. When the eNB  110  makes a DL or UL resource allocation, the eNB  110  cannot use the same HARQ process for any unfinished dynamic and persistent transmissions. In that way, the WTRU  105  is able to know if the DL or UL allocation is for dynamic and persistent transmissions. 
         [0034]    Using SFNs for persistent allocation can differentiate between different persistent transmission periods.  FIG. 3  illustrates an example operation using the SFN and a HARQ ID for persistent and dynamic allocation. For example, when retransmission for initial persistent transmission occurs after SFN2, if SFN1 is used in persistent allocation for retransmission of SFN1 packet based on the RSN value in signaling, then the WTRU  105  will have no ambiguity to differentiate whether to combine the allocation with the SFN1 or SFN2 packets. 
         [0035]    When reserved the HARQ ID is received by the WTRU  105  for resource allocation, the WTRU  105  knows that the reserved HARQ process has already finished its persistent transmission and can be used for dynamic allocation. For example, in  FIG. 3 , once HARQ ID 2, (assuming that it is mapped to SFN2), has successfully finished the persistent transmissions, then HARQ ID 2 may be used for dynamic allocation and, if the WTRU  105  decodes HARQ ID2 in the resource allocation, then the WTRU  105  knows this HARQ process is used for dynamic allocation. Although the PDCCH  115  is used in this example, the same principle holds true also for the PUCCH  120 . 
         [0036]    It is preferable that the activation time for persistent transmission is long enough to allow the eNB  110  to realize whether activation signaling included in the PDCCH has been successfully decoded by the WTRU  105  or not. To make sure the PDCCH for DL/UL persistent scheduling activation is successfully received by the WTRU  105 , an ACK/NACK may be sent by the WTRU  105  for persistent activation signaling to the eNB  110 , so that eNB  110  can retransmit persistent activation signaling for a synchronized DL or UL persistent transmission. The allocation of UL ACK/NACK resources should be predetermined if this mechanism is going to be used. 
         [0037]    Referring again to  FIG. 1 , the WTRU  105  controls the allocation of HARQ resources. The processor  135  is configured to reserve a subset of a plurality of HARQ process IDs to use for a semi-persistent allocation. The receiver is configured to receive a dynamic allocation via the DL PDCCH. The transmitter  125  is configured to transmit data based on the semi-persistent allocation, and selectively use at least one of the reserved HARQ process IDs for transmitting data based on the dynamic allocation. 
         [0038]    A HARQ process associated with at least one of the reserved HARQ process IDs may be used over a time period between two different SFN moments to transmit data. When data associated with the at least one reserved HARQ process ID was previously transmitted, the reserved HARQ process ID may not be used until a next associated SFN moment. The reserved HARQ process IDs may be used after all unreserved HARQ process IDs have been used. The reserved HARQ process IDs may be used by higher priority services. The reserved HARQ process IDs may be included in an RRC message. 
         [0039]      FIG. 4  is a flow diagram of a procedure  400  for efficiently utilizing HARQ processes for semi-persistent and dynamic data transmissions. In step  405 , a subset of a plurality of HARQ resources is reserved to use for a semi-persistent allocation. In step  410 , data is transmitted based on the semi-persistent allocation. In step  415 , a dynamic allocation is received via a DL PDCCH. In step  420 , at least one of the reserved HAN process IDs is selectively used for transmitting data based on the dynamic allocation. 
         [0040]    Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements. The methods or flow charts provided herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable storage medium for execution by a general purpose computer or a processor. Examples of computer-readable storage mediums include a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). 
         [0041]    Suitable processors include, by way of example, a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) circuits, any other type of integrated circuit (IC), and/or a state machine. 
         [0042]    A processor in association with software may be used to implement a radio frequency transceiver for use in a wireless transmit receive unit (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC), or any host computer. The WTRU may be used in conjunction with modules, implemented in hardware and/or software, such as a camera, a video camera module, a videophone, a speakerphone, a vibration device, a speaker, a microphone, a television transceiver, a hands free headset, a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit, a liquid crystal display (LCD) display unit, an organic light-emitting diode (OLED) display unit, a digital music player, a media player, a video game player module, an Internet browser, and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB) module.