Abstract:
In a wireless communication system including a wireless transmit/receive unit (WTRU) which transfers data to a Node-B, data transmission parameters such as modulation and coding scheme (MCS) and transport block set (TBS) size are dynamically adjusted on a transmission time interval (TTI) basis, and hybrid-automatic repeat request (H-ARQ) processes used to control the transfer of data between the WTRU and the Node-B are initiated and released, as required. The WTRU transmits and retransmits data to the Node-B through an enhanced uplink (EU) dedicated channel (E-DCH) in accordance with data feedback information received from the Node-B. The WTRU queues data for transmission, and determines a transmission status of the data. The transmission status is set to one of “new transmission,” “successful transmission,” “retransmission” and “restarted transmission.” For each TTI, the WTRU initiates an EU transmission to the Node-B which identifies the assigned H-ARQ process, TBS size and MCS.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 11/140,034 filed May 27, 2005, which claims the benefit of U.S. Provisional Application No. 60/578,728 filed Jun. 10, 2004, which are incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The present invention is related to a wireless communication system including a wireless transmit/receive unit (WTRU) and a Node-B. More particularly, the present invention is related to a method and apparatus for dynamically adjusting data transmission parameters such as modulation and coding scheme (MCS) and transport block set (TBS) size, and assigning and releasing a hybrid-automatic repeat request (H-ARQ) process used to control the transfer of data between the WTRU and the Node-B. 
     BACKGROUND 
     In 3rd generation cellular systems, adaptive modulation and coding (AM&amp;C) and H-ARQ schemes are being investigated for incorporation into an enhanced uplink (EU) operation designed to offer low transmission latency, higher throughput, and more efficient use of physical resources. 
     The AM&amp;C scheme allows an MCS to be dynamically adjusted on a transmit time interval (TTI) basis whereby, for each TTI, the MCS is selected to make the most efficient use of radio resources and to provide the highest possible data rates. A less robust MCS uses less physical resources, but is more vulnerable to errors. A more robust MCS uses more physical resources, but offers greater protection against errors. 
     The H-ARQ scheme is used to generate transmissions and retransmissions with low latency. A primary aspect of the H-ARQ scheme is that data received in failed transmissions can be soft combined with successive retransmissions to increase the probability of successful reception. Either Chase Combining (CC) or incremental redundancy (IR) may be applied. When CC is applied, the same MCS is chosen for the retransmission. When IR is applied, a more robust MCS is used in each retransmission. 
     SUMMARY 
     The present invention is implemented in a wireless communication system including a WTRU which transfers data to a Node-B. Data transmission parameters such as TBS size are dynamically adjusted on a TTI basis. Optionally, MCS may also be adjusted. An H-ARQ process used to control the transfer of data between the WTRU and the Node-B is assigned and released, as required. The WTRU transmits and retransmits data to the Node-B through an enhanced uplink (EU) dedicated channel (E-DCH) in accordance with feedback information received from the Node-B. The WTRU queues data for transmission, and determines a transmission status of the data. The transmission status is set by a controller in the WTRU to one of “new transmission,” “successful transmission,” “retransmission” and “restarted transmission.” For each TTI, the WTRU initiates an EU transmission to the Node-B which identifies either explicitly or implicitly the retransmission number, new data indication, assigned H-ARQ process, TBS size and optionally MCS. 
     The transmission status of data is set by the controller in the WTRU to “new transmission” when the data is new data, to “successful transmission” when an acknowledge (ACK) message is received from the Node-B, to “retransmission” when a non-acknowledge (NACK) message or no response is received from the Node-B in response to the transmission of the new data, and optionally to “restarted transmission” when a retransmission count exceeds a predetermined maximum number of retransmissions. 
     If the transmission status is “new transmission”, an initial H-ARQ process is assigned. If the transmission status is “retransmission”, the same H-ARQ process is assigned while incrementing the retransmission counter. If the transmission status is “successful transmission”, the H-ARQ process is released. If the transmission status is “restarted transmission”, which is optional, an H-ARQ process is assigned while initializing the retransmission counter and incrementing a new data indicator (NDI). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding of the invention may be had from the following description of a preferred example, given by way of example and to be understood in conjunction with the accompanying drawing wherein: 
         FIG. 1  is a block diagram of a wireless communication system operating in accordance with the present invention; 
         FIG. 2  is a flow diagram of a process for initiating and releasing H-ARQ processes in accordance with the present invention; 
         FIG. 3  is a flow diagram of a process including method steps for implementing CC in accordance with the present invention; and 
         FIG. 4  is a flow diagram of a process including method steps for implementing IR in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereafter, the terminology “WTRU” includes but is not limited to a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, the terminology “Node-B” includes but is not limited to a base station, a site controller, an access point or any other type of interfacing device in a wireless environment. 
     The features of the present invention may be incorporated into an integrated circuit (IC) or be configured in a circuit comprising a multitude of interconnecting components. 
       FIG. 1  is a block diagram of a wireless communication system  100  operating in accordance with the present invention. The system  100  comprises a WTRU  102 , a Node-B  104 , and a radio network controller (RNC)  106 . The WTRU  102  transmits data through an E-DCH  108  with a transmitter  120  and receives feedback with a receiver  122  from the Node-B  104  through a downlink (DL) signaling channel  110  based on an initiated H-ARQ process. When the Node-B  104  fails to decode the data sent by the WTRU  102 , the Node-B  104  transmits a NACK message to the WTRU  102  via the DL signaling channel  110  or does not transmit feedback which is interpreted as a NACK by the WTRU  102 . When the Node-B  104  succeeds to decode the data sent by the WTRU  102 , the Node-B  104  transmits an ACK message to the WTRU  102  which releases the H-ARQ process for other transmissions. The H-ARQ processes may either be designed to implement CC or IR. The RNC  106  controls overall operation of data transfers that occur between the Node-B  104  and the WTRU  102 , including radio resources allocation. The WTRU  102  includes a data buffer  112  for storing E-DCH data, an optional data lifespan timer  114  used to determine whether it is necessary to discard expired data, and a retransmission counter  116  used to determine whether data transmitted by the WTRU  102  but not received by the Node-B  104  should be retransmitted or whether H-ARQ transmission should be terminated or optionally restarted. The buffer  112 , the lifespan timer  114  and the retransmission counter  116  are controlled by a controller  118 . The controller  118  sets, (i.e., keeps track of), the status of each transmission associated with an H-ARQ process. 
       FIG. 2  is a flow diagram of a process  200  including method steps for controlling an H-ARQ process in accordance with the present invention. The H-ARQ process may be either synchronous or asynchronous. In a synchronous H-ARQ operation, the WTRU  102  keeps track of when responses to data transmissions between the WTRU  102  and the Node-B  104  are expected, and the periodicity of H-ARQ retransmissions is predetermined. In an asynchronous H-ARQ operation, the WTRU  102  transmits data and waits for the feedback for a predetermined period of time. 
     After the WTRU  102  initiates the H-ARQ process and the retransmission counter  116 , the WTRU  102  transmits data to the Node-B  104  via the E-DCH  108  during a current TTI (step  202 ). In step  204 , the WTRU  102  waits for feedback from the Node-B  104 . If the WTRU  102  receives an ACK message from the Node-B  104 , the WTRU  102  then sets the transmission status to “successful transmission”, releases the H-ARQ process and reinitiates the retransmission counter  116  (step  208 ) for subsequent data transmissions. 
     If, at step  206 , the WTRU  102  receives a NACK message or did not receive any response, the WTRU  102  determines whether the retransmission count indicated by the retransmission counter  116  is less than or equal to the maximum number of allowed retransmissions (step  212 ). 
     If the retransmission count as determined at step  212  is less than the maximum number of allowed retransmissions, the WTRU  102  sets, or maintains, the transmission status to “retransmission” and increments the retransmission counter  116  (step  214 ). The retransmission counter  116  is incremented each time the same data is retransmitted by the WTRU  102 . 
     If the retransmission count as determined at step  212  is equal to or greater than the maximum number of allowed retransmissions, the H-ARQ process transmission is terminated and reset for supporting subsequent data transmissions (step  213 ). Optionally the WTRU  102  may set the transmission status to “restarted transmission” and reinitiates the retransmission counter (step  216 ). After setting the transmission status to “restarted transmission”, the WTRU  102  reinitiates the H-ARQ transmission process as a “new transmission” or the WTRU  102  may optionally release the H-ARQ process (step  218 ). 
       FIG. 3  is a flow diagram of a process  300  including method steps for implementing CC in accordance with the present invention. The process  300  is performed on a TTI basis (step  302 ). In step  304 , the WTRU  102  determines whether EU physical resources have been assigned by the Node-B  104  and whether an H-ARQ process is available for the WTRU  102  to transmit data to the Node-B  104  via the E-DCH  108 . If EU physical resources have not been assigned, the WTRU  102  waits for the allocation of EU physical resources and the transmission of data is delayed until the next TTI (step  302 ). If EU physical resources have been allocated and an H-ARQ process is available, the WTRU  102  determines whether the data is new data (step  306 ). If the data is determined to be new data in step  306 , the WTRU  102  selects the highest priority data to transmit (step  308 ). Additionally, the WTRU  102  selects the MCS and TBS size that maximizes transmission of the highest priority data within an allowed limit (step  310 ). TBS size is chosen based on the Node-B  104  signaled maximum MCS and TBS size, transmit power available for the E-DCH  108 , MCS, and the data available in the buffer  112  for transmission. 
     For each transport channel (TrCH), dedicated channel medium access control (MAC-d) flow or logical channel, a list of allowed TBS sizes, a retransmission limit and allowed transmission latency, (i.e., MAC data “lifespan”), are determined. The allowable MCS and TBS sizes are the maximum that the WTRU  102  is allowed to transmit for the current physical resources allocation period. The configuration is either signaled from the RNC  106  in accordance with radio resource control (RRC) procedures or uniquely specified by a standard. The chosen MCS and TBS size may be either explicitly signaled (preferably from the Node-B) or derived from an associated parameter such as a channel quality indicator (CQI) and/or transport format combination (TFC) index. The CQI may represent the maximum allowed WTRU interference or transmit power. The Node-B  104  may signal this information in the initial channel assignment. Alternatively, the Node-B  104  may send this information when the WTRU  102  requests additional EU channel allocations. 
     In step  312 , the WTRU  102  then generates at least one EU MAC (MAC-e) protocol data unit (PDU) based on the selected TBS size, and assigns an H-ARQ process for transmission of the MAC-e PDU. In step  314 , the WTRU  102  initializes the retransmission counter  116 , increments an NDI and optionally sets the lifespan timer  114  in the WTRU  102 . The NDI is used to indicate when new data is being transmitted and when the Node-B  104  needs to clear the soft buffer associated with the H-ARQ process that is being transmitted. The initial value of the retransmission counter  116  may be interpreted as a transmission of new data and, in such a case, the NDI parameter is not needed. The WTRU  102  then initiates an EU transmission to the Node-B  104  identifying the current H-ARQ process, TBS size, (if not assigned by the Node-B  104 ), and MCS. The H-ARQ process and MCS may be implicitly known by the Node-B  104  due to a specified H-ARQ process operation, and thus may not need to be signaled by the WTRU  102  to the Node-B  104 . 
     When CC is supported, the TBS size information is identified to the Node-B  104  for each transmission and retransmission, unless TBS is identified by the Node-B  104  in the physical channel allocation. Retransmissions have the same MCS and TBS as applied in the initial transmission in the case of CC. 
     Referring back to step  306 , if it is determined that the data is not new data, a determination is made as to whether the WTRU  102  utilizes the lifespan timer  114  (step  315 ). If the WTRU  102  utilizes the lifespan timer  114 , the process  300  proceeds to step  316  to determine whether the lifespan timer  114  has expired. If the lifespan timer  114  has expired, the WTRU  102  discards the data and releases, (i.e., frees), the H-ARQ process (step  318 ), and the process  300  returns to step  302 . Optionally, when the lifespan timer  114  is close to expiration, the WTRU  102  may use a more robust MCS to increase the probability of successful transmission. 
     The retransmission counter  116  in the WTRU  102  is incremented each time a data transmission is not successful and thus not acknowledged by the Node-B  104 . If the lifespan timer  114  has not yet expired, or if the WTRU  102  does not utilize the lifespan timer  114 , the process  300  proceeds to step  320  for retransmission of the data whereby the WTRU  102  determines whether the retransmission count is less than the maximum number of allowed retransmissions. If the retransmission count is less than the maximum number of allowed retransmissions, the status of transmission is set to or maintained as “retransmission,” the WTRU  102  increments the retransmission counter  116  (step  322 ) and uses the same H-ARQ process, TBS, MCS and NDI, (if not incorporated with the retransmission counter) (step  324 ). The WTRU  102  then initiates an EU transmission to the Node-B  104  identifying the H-ARQ process, (this may be implicitly known and may not need be signaled to the Node-B), TBS size (if not assigned by the Node-B), and MCS in the associated physical control channel (step  330 ). 
     If the retransmission count reaches or exceeds the maximum number of allowed retransmissions, the process  300  proceeds to step  318  to discard the data and release the H-ARQ process. Alternatively, if restarted transmissions are determined to be allowed in optional step  325 , the status of transmission is set to “restarted transmission,” and the WTRU  102  initializes the retransmission counter  116 , increments the NDI and assigns a new H-ARQ process (step  326 ). If the previously transmitted data stored in the soft combining buffer is disrupting successive retransmissions, it is better to clear the soft buffer and restart the H-ARQ transmission to increase the probability of successful transmission. Therefore, when the maximum number of retransmissions for a particular H-ARQ process is reached, the NDI, (or an initialized retransmission count), is sent to indicate that the H-ARQ transmissions have been restarted. When the Node-B  104  receives the incremented NDI, (or the transmission count set to the initial value), the Node-B  104  clears the soft combining buffer of the previously received data. 
     In step  328 , a new H-ARQ transmission is initiated using the same TBS and, optionally, a more robust MCS may be selected for the “new transmission” to increase the probability of successful delivery (step  328 ). In order to allow this change in MCS, the TBS may be segmented into several independent transmissions. In the case a transmission is being reinitiated with more redundancy (either by change of MCS or just less puncturing) the previous TBS may no longer fit in the allocated physical resource. In this case the original transmission may be segmented into multiple separate transmissions that do not exceed the requirement. The WTRU  102  then initiates an EU transmission to the Node-B which identifies the current H-ARQ process, (may be implicitly known to the Node-B), TBS size and MCS, (if not assigned by the Node-B), in the associated physical control channel (step  330 ). 
       FIG. 4  is a flow diagram of a process  400  including method steps for implementing IR in accordance with the present invention. The process  400  is performed on a TTI basis (step  402 ). In step  404 , the WTRU  102  determines whether EU physical resources have been assigned by the Node-B  104  and whether an H-ARQ process is available for the WTRU  102  to transmit data to the Node-B  104  via the E-DCH  108  (step  404 ). If EU physical resources have not been assigned, the WTRU  102  waits for the allocation of EU physical resources and the transmission of data is delayed until the next TTI (step  402 ). If EU physical resources have been allocated and an H-ARQ process is available, the WTRU  102  determines whether the data is new data (step  406 ). If the data is determined to be new data in step  406 , the WTRU  102  selects the highest priority data to transmit (step  408 ). Additionally, the WTRU  102  selects the maximum TBS size and corresponding TFC maximizing transmission of the highest priority data using the most robust MCS allowed (step  410 ). 
     In step  412 , the WTRU  102  then generates at least one MAC-e PDU based on the selected TBS size, and assigns an H-ARQ process for transmission of the MAC-e PDU. In step  414 , the WTRU  102  initializes the retransmission counter  116 , increments an NDI and optionally sets the lifespan timer  114  in the WTRU  102  (step  414 ). The NDI is used to indicate when new data is being transmitted and when the Node-B  104  needs to clear the soft buffer associated with the H-ARQ process that is being transmitted. The initial value of the retransmission counter  116  may be interpreted as a transmission of new data and, in such a case, the NDI parameter is not needed. The WTRU  102  then initiates EU transmission to the Node-B  104  identifying the current H-ARQ process, TBS size and MCS in the associated physical control channel (step  430 ). The H-ARQ process and MCS may be implicitly known by the Node-B  104  due to a specified H-ARQ process operation, and thus may not need to be signaled by the WTRU  102  to the Node-B  104 . 
     Referring back to step  406 , if it is determined that the data is not new data, a determination is made as to whether the WTRU  102  utilizes the lifespan timer  114  (step  415 ). If the WTRU  102  utilizes the lifespan timer  114 , the process  400  proceeds to step  416  to determine whether the lifespan timer  114  has expired. If the lifespan timer  114  has expired, the WTRU  102  discards the data and releases, (i.e., frees), the H-ARQ process (step  418 ), and the process  400  returns to step  402 . Optionally, when the lifespan timer  114  is close to expiration, the WTRU  102  may use a more robust MCS to increase the probability of successful transmission. 
     The retransmission counter  116  in the WTRU  102  is incremented each time a data transmission is not successful and thus not acknowledged by the Node-B  104 . If the lifespan timer  114  has not yet expired, or if the WTRU  102  does not utilize the lifespan timer  114 , the process  400  proceeds to step  420  for retransmission of the data whereby the WTRU  102  determines whether the retransmission count is less than the maximum number of allowed retransmissions. If the retransmission count is less than the maximum number of allowed retransmissions, the status of transmission is set to or maintained as “retransmission,” and the WTRU  102  increments the retransmission counter  116  and selects a more robust MCS, if allowed (step  422 ). In step  424 , the WTRU  102  uses the same H-ARQ process, TBS/TFC and NDI. 
     For IR, determination of the MCS and TBS size takes into account support of the most robust MCS, what is required by the data which is ready to transmit in the WTRU  102 , and available WTRU transmit power. With each retransmission, a more robust MCS may be chosen for the same TBS. The initial transmissions with less robust MCS allow for a larger TBS size, but this size is restricted so that the same TBS can still be supported by the most robust MCS. Also, for determination of the TBS, the WTRU available transmit power for EU must be taken into account the most robust MCS allowed, even though the most robust MCS may not be required for successful transmission. 
     If the retransmission count reaches or exceeds the maximum, the process  400  proceeds to step  418  to discard the data and release the H-ARQ process. Alternatively, if restarted transmissions are determined to be allowed in step  425 , the status of transmission is set to “restarted transmission,” and the WTRU  102  initializes the retransmission counter  116 , increments the NDI and assigns a new H-ARQ process (step  426 ). In step  428 , the same TBS/TFC is used and an MCS is selected. 
     Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. 
     While the present invention has been described in terms of the preferred embodiment, other variations which are within the scope of the invention as outlined in the claims below will be apparent to those skilled in the art.