Abstract:
A method and wireless transmit/receive unit (WTRU) for supporting enhanced uplink (EU) transmissions are disclosed. A WTRU is configured to provide hybrid automatic repeat request (H-ARQ) processes for supporting transmission over an enhanced uplink (EU) channel, to receive configuration information, wherein the configuration information indicates which H-ARQ processes are associated with a particular MAC-d flow, to allocate an H-ARQ process for transmission of data from the MAC-d flow, wherein the allocated H-ARQ process is from one of the associated H-ARQ processes, and to transmit data from the MAC-d flow over the EU channel using the allocated H-ARQ process.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 12/772,543 filed May 3, 2010, which is a continuation of U.S. patent application Ser. No. 11/139,880 filed May 27, 2005, which issued as U.S. Pat. No. 7,710,911 on May 4, 2010, which claims the benefit of U.S. Provisional Application Ser. No. 60/578,712 filed Jun. 10, 2004, the contents of which are incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The present invention is related to a hybrid-automatic repeat request (H-ARQ) operation in a wireless communication system including at least one wireless transmit/receive unit (WTRU), at least one Node-B and a radio network controller (RNC). More particularly, the present invention is a method and system for dynamically allocating H-ARQ processes in the WTRU for supporting enhanced uplink (EU) transmissions. 
     BACKGROUND 
     An EU operation reduces uplink (UL) latency, improves throughput, and provides more efficient use of physical radio resources. During EU operation, an H-ARQ process is used to support EU transmissions between a WTRU and a Node-B including the facilitation of a feedback process for reporting successful or unsuccessful EU data transmissions. 
     A number of EU H-ARQ processes are defined for each WTRU, and each WTRU supports multiple instances of H-ARQ processes simultaneously. Since a feedback cycle for each EU data transmission is relatively long when compared to UL transmission time, and a different number of transmissions may be required to achieve a successful transmission for each EU transmission, a WTRU is required to operate several H-ARQ processes simultaneously to provide increased data rates and reduced latency. 
     For any WTRU connection, multiple logical channels exist. These logical channels have different throughput, latency, error rates, and quality of service (QoS) requirements. To satisfy these requirements, the RNC sets a priority for each logical channel known as a medium access control (MAC) logical channel priority (MLP). The MLP is mapped to a dedicated channel MAC (MAC-d) flow which is connected to the EU MAC (MAC-e), which manages the EU H-ARQ processes. 
     A similar design exists for high speed downlink packet access (HSDPA) in a downlink (DL) channel. When higher priority data is required to be transmitted and all H-ARQ processes are already assigned for transmission of lower priority data, it is allowed to preempt the existing H-ARQ transmissions of lower priority with a higher priority transmission. When the preemption occurs, the lower priority data is rescheduled for an H-ARQ transmission at a later time. 
     A problem with H-ARQ process preemption is a loss of the benefit of combining. One important advantage of an EU H-ARQ operation is the ability to store received data from previous transmissions and to combine the previous transmissions with subsequent transmissions to increase the probability of a successful data transmission. However, when the H-ARQ processes are preempted, the stored data of the previous transmissions, and thus, the combining advantage of the H-ARQ processes is lost. 
     A reason for implementing H-ARQ process preemption is that the number of H-ARQ processes that can be configured in the WTRU is limited. While each H-ARQ process requires considerable memory for reception processing, the amount of memory in the WTRU is limited. 
     Because it is common to have a large amount of lower priority data and a small amount of higher priority data, when processing lower priority transmissions, it is necessary to avoid blocking of higher priority transmissions in order to maintain QoS requirements of the higher priority data. If lower priority data monopolizes the H-ARQ processes, it may degrade overall system performance. Moreover, since lower priority data allows greater latency, it can result in greater H-ARQ process holding time. 
     H-ARQ process preemption may solve the transmission prioritization problem, but at the expense of the loss of the combining benefit and, correspondingly, the less efficient use of radio resources. It is expected that the best overall performance is achieved in H-ARQ systems when a large percentage of the first and possibly second transmissions fail because a less robust modulation and coding scheme (MCS) requiring far less physical resources can be applied. In this case, when H-ARQ process preemption is employed, these initial transmissions and retransmissions will frequently have to be repeated to achieve successful transmission, which wastes radio resources utilized for the initial preempted transmissions. 
     SUMMARY 
     The present invention is a method and apparatus for dynamically allocating H-ARQ processes in the WTRU for supporting EU transmissions. The H-ARQ processes in the WTRU are reserved for specific transport channels (TrCHs), dedicated channel medium access control (MAC-d) flows or logical channels associated with different data transmission priority classes. The WTRU allocates H-ARQ processes from those reserved H-ARQ processes that are available. Optionally, a higher priority channel may be allowed to allocate an H-ARQ process reserved for lower priority channels. Lower priority H-ARQ processes may be preempted. The preemption may be restricted by urgency of data transmission, (for example, close to expiration of lifespan timer), or by RNC configuration of H-ARQ processes. Alternatively, a common pool of H-ARQ processes may be configured and an H-ARQ process may be allocated from the common pool in accordance with a priority of each channel, and lower priority H-ARQ may be preempted. 
     In accordance with the present invention, lower priority data may achieve maximum data rates, and higher priority transmissions may be initiated at any time without requiring the need for H-ARQ process preemption. By reserving H-ARQ processes for specific channels and allowing the WTRU to dynamically allocate these H-ARQ processes, the EU data rate and transmission latency for these channels can be better guaranteed to meet their QoS requirements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding of the invention may be had from the following description of a preferred embodiment, 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 in accordance with the present invention; 
         FIG. 2  is a flow diagram of a process for allocating H-ARQ processes of the system of  FIG. 1  in accordance with a first embodiment of the present invention; 
         FIG. 3  is a flow diagram of a process for allocating H-ARQ processes of the system of  FIG. 1  in accordance with a second embodiment of the present invention; and 
         FIG. 4  is a flow diagram of a process for allocating H-ARQ processes of the system of  FIG. 1  in accordance with a third embodiment of 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  includes at least one WTRU  102 , at least one Node-B  104  and an RNC  106 . The RNC  106  controls overall EU operation via an Iub/Iur  112  by configuring EU parameters for the Node-B  104  and the WTRU  102 , such as configuration of H-ARQ processes  124  in the WTRU  102 , initial transmit power level, maximum allowed EU transmit power or available physical resources. An UL EU channel  108  is established between the WTRU  102  and the Node-B  104  for facilitating EU transmissions. The UL EU channel  108  includes an enhanced dedicated channel (E-DCH) for transmission of E-DCH data and may also include a separate UL EU signaling channel. The UL EU signaling may also be transmitted via the E-DCH. 
     The WTRU  102  includes a controller  122 , a plurality of H-ARQ processes  124 , a memory  126  and a transmitter/receiver  128 . The controller  122  controls overall procedures of H-ARQ assignment and E-DCH transmissions. Furthermore, the controller  122  keeps track of the status of each transmission associated with an H-ARQ process. The memory  126  stores E-DCH data for transmission. The H-ARQ processes  124  and the memory  126  may be partitioned to support a plurality of priority classes which will be explained in further detail hereinafter. 
     For E-DCH transmissions, the WTRU  102  sends a channel allocation request to the Node-B  104  via the UL EU channel  108 . In response, the Node-B  104  sends channel allocation information to the WTRU  102  via a DL EU signaling channel  110 . After EU physical resources are allocated for the WTRU  102 , the WTRU  102  transmits E-DCH data via the UL EU channel  108 . In response to the E-DCH transmissions, the Node-B sends an acknowledge (ACK) or non-acknowledge (NACK) message for H-ARQ operation via the DL EU signaling channel  110 . 
     The memory requirement for H-ARQ operation is primarily a problem for the receiver. For HSDPA, the number of H-ARQ processes and the memory reserved for each H-ARQ process is minimized. For EU, the memory requirement in the WTRU is not as restricted as is the case for HSDPA. It is a maximum data rate that limits the minimization of the H-ARQ processes and the memory requirements. For each “stop and wait” H-ARQ process transmission, there is a cycle of generating the transmission and waiting for and processing feedback for that transmission. In order to have the ability for continuous transmission, several H-ARQ processes are required to operate in sequence. 
     Since the memory requirement of the WTRU  102  is not as much of a concern in EU, the number of H-ARQ processes  124  and the memory  126  reserved for each priority class may exceed the number of H-ARQ processes required to achieve particular data rates for each priority class. The WTRU  102  can be configured for more H-ARQ processes than that can be used at one time. In accordance with one embodiment, the H-ARQ processes are reserved for specific TrCHs, MAC-d flows or logical channels which can be dynamically allocated by the WTRU  102  at any time so that preemption of an already assigned H-ARQ process and the corresponding loss of the combining benefit can be avoided. 
     The H-ARQ operation may be either synchronous or asynchronous between the WTRU  102  and the Node-B  104 . In an asynchronous H-ARQ operation, the mechanism for selecting H-ARQ processes at the WTRU  102  are not known to the Node-B  104 , therefore, the H-ARQ process should be identified in each transmission. In a synchronous H-ARQ operation, the mechanism for selecting H-ARQ processes at the WTRU  102  are predetermined and known to the Node-B  104 . The Node-B  104  may identify the H-ARQ process used at the WTRU  102  based on the predetermined transmission schedule. Each E-DCH transmission includes a new data indicator (NDI) indicating that the transmission is either a “new transmission” or a “retransmission.” The initial value of the NDI indicates that the transmission is a “new transmission.” A retransmission sequence number of each H-ARQ transmission provides similar information. In a synchronous H-ARQ operation, the Node-B  104  can determine which H-ARQ process was used at the WTRU  102  and what transmissions should be combined with what previous transmissions based on when the transmission is sent. 
       FIG. 2  is a flow diagram of a process  200  for allocating H-ARQ processes  124  in the WTRU  102  in accordance with a first embodiment of the present invention. The RNC  106  configures the WTRU  102 , such as the number of H-ARQ processes  124  and/or memory partitioning associated with each logical channel, MAC-d flow, transport channel (TrCH) or data priority class are configured (step  202 ). This is preferably performed through layer-3 radio resource control (RRC) signaling procedures. 
     For each transmit time interval (TTI), at step  204 , the WTRU  102  may dynamically allocate an H-ARQ process associated with the TrCH, MAC-d flow or logical channel being serviced. The WTRU  102  determines whether physical resources have been allocated by the Node-B  104  (step  206 ). If physical resources have not been allocated, the process  200  returns to step  204  to wait for the next TTI. If physical resources have been allocated, the WTRU  102  selects data in the highest priority class to transmit in the current TTI (step  208 ). The WTRU  102  determines what data to transmit using a selected H-ARQ process  124 , preferably based on absolute priority. In such case, the data in the highest priority takes precedence over data in a lower priority class each time a new H-ARQ process is assigned. 
     If there is no data waiting for transmission, the process  200  returns to step  204  to wait for the next TTI. If there is data to be transmitted and data in the highest priority class is selected in step  208 , the WTRU  102  determines whether an H-ARQ process  124  has already been assigned to other data having an “unsuccessful transmission” status (step  210 ). If an H-ARQ process  124  has been allocated to other data that has not been successfully transmitted, (i.e., feedback information including a NACK message has been received), and is not waiting for data feedback information, the earliest assigned H-ARQ process associated with this priority class is selected at step  212  and the H-ARQ process is transmitted in the current TTI (step  214 ). The earliest assigned H-ARQ process may be determined by either the lowest transmission sequence number (TSN) or the highest number of retransmissions compared to other H-ARQ processes assigned in the same priority data. 
     If there is currently no H-ARQ process assigned to other data having an “unsuccessful transmission” status, the WTRU  102  determines whether there is an H-ARQ process associated with the TrCH, MAC-d flow or logical channel, available for supporting the transmission of data in this priority class (step  216 ). If there is an available H-ARQ process, the WTRU  102  allocates one of the reserved H-ARQ processes  124  associated with the priority class of the selected data (step  218 ). The priority class may be mapped to configured H-ARQ processes associated with at least one of a logical channel, a MAC-d flow and a TrCH. If there is no available H-ARQ process for the TrCH, MAC-d flow or logical channel of the selected data, the priority class is marked as being blocked for the current TTI (step  220 ). The process  200  then returns to step  208  to select the next highest priority data. The H-ARQ processes associated with the TrCHs, MAC-d flows or logical channels supporting lower priority classes wait for a TTI where physical resources are allocated and all outstanding ready-to-transmit higher priority H-ARQ processes have been serviced. 
     It is required to limit the number of H-ARQ processes required to achieve maximum data rates for each logical channel, MAC-d flow or TrCH. The RNC  106  can limit the maximum number of H-ARQ processes reserved for at least one of a logical channel, a MAC-d flow and a TrCH. This effectively limits the maximum data rate of each logical channel, MAC-d flow or TrCH, when lower priority H-ARQ processes are already assigned. High priority data may have a limited number of H-ARQ processes that limits the maximum data rate, but still provides for low transmission latency. For example, signaling radio bearers (SRBs) require low latency, but not high data rates of traffic channels. The SRB TrCH, MAC-d flow, or logical channel may then be configured by the RNC with RRC procedures for a higher priority and one or more H-ARQ processes dedicated for this channel. 
       FIG. 3  is a flow diagram of a process  300  for allocating H-ARQ processes in the WTRU  102  in accordance with a second embodiment of the present invention. The RNC  106  configures the WTRU  102 . For example, the number of H-ARQ processes and/or memory partitioning associated with each logical channel, MAC-d flow, TrCH or data priority class is configured (step  302 ). This is preferably performed through RRC procedures. 
     For each TTI at step  304 , the WTRU  102  dynamically allocates H-ARQ processes. The WTRU  102  determines whether physical resources have been allocated by the Node-B  104  (step  306 ). If physical resources have not been allocated, the process  300  returns to step  304  to wait for the next TTI. If physical resources have been allocated, the WTRU  102  determines the highest priority data to transmit in the current TTI (step  308 ) each time a new H-ARQ process is assigned. 
     If there is no data waiting for transmission, the process  300  returns to step  304  for the next TTI. If there is data to be transmitted, the WTRU  102  determines whether an H-ARQ process has already been assigned to other highest priority data having an “unsuccessful transmission” status (step  310 ). If an H-ARQ process has been allocated to other highest priority active data that has not been successfully transmitted, (i.e., status of NACK feedback received) and is not waiting for data feedback information, the earliest assigned H-ARQ process associated with the priority class is selected at step  312  and the H-ARQ process is transmitted in the current TTI (step  314 ). 
     If there are no currently assigned H-ARQ processes for the highest priority data, the WTRU  102  determines whether there is an H-ARQ process available associated with a TrCH, MAC-d flow or logical channel for this priority class (step  316 ). If there is an available H-ARQ process for the priority class of the selected data, the WTRU  102  allocates one of the reserved H-ARQ processes for this priority class (step  318 ), and the H-ARQ process is transmitted at step  314 . 
     If there are no available H-ARQ processes for the priority class of the selected data, the WTRU  102  determines whether there are available H-ARQ processes for lower priority class (step  320 ). If there are available H-ARQ processes associated with a lower priority class, the process  300  branches to step  318  to allocate the H-ARQ process associated with the lower priority class, and the allocated H-ARQ process is transmitted (step  314 ). If, at step  320 , it is determined that there are no available H-ARQ processes associated with a lower priority class, this priority class is blocked for the current TTI (step  322 ), and the process  300  returns to step  308  to select the next highest priority data. 
     Optionally, the H-ARQ processes allocated for lower priority classes may be preempted if there is no available H-ARQ process associated with a lower priority class. The RNC  106  configures the number of H-ARQ processes reserved for each priority class. If a large number of H-ARQ processes are reserved for higher priority data, there would be less preemption. If fewer H-ARQ processes are reserved for higher priority data, then there would be more preemption. 
       FIG. 4  is a flow diagram of a process  400  for allocating H-ARQ processes of the WTRU  102  in accordance with a third embodiment of the present invention. The RNC  106  configures a common pool of H-ARQ processes, the number of which exceeds the maximum number of H-ARQ processes that can be used at any time by the WTRU  102  (step  402 ). 
     For each TTI at step  404 , the WTRU  102  dynamically allocates H-ARQ processes. The WTRU  102  determines whether physical resources have been allocated by the Node-B  104  (step  406 ). If physical resources have not been allocated, the process  400  returns to step  404  to wait for the next TTI. If physical resources have been allocated, the WTRU  102  selects data in the highest priority class to transmit in the current TTI (step  408 ). 
     If there is no data waiting for transmission, the process  400  returns to step  404  to wait for the next TTI. If there is data to be transmitted and the highest priority data is selected, the WTRU  102  determines whether an H-ARQ process has already been assigned to other highest priority data having an “unsuccessful transmission” status (step  410 ). If an H-ARQ process has been allocated to other highest priority active data that has not been successfully transmitted, (i.e., status of NACK feedback received), and is not waiting for data feedback information, the earliest assigned H-ARQ process associated with the priority class is selected at step  412  and the H-ARQ process is transmitted in the current TTI (step  414 ). 
     If there are no currently assigned H-ARQ processes for other highest priority data, the WTRU  102  determines whether there is an available H-ARQ process (step  416 ). If there is an available H-ARQ process, the WTRU  102  allocates the available H-ARQ process (step  418 ), and the allocated H-ARQ process is transmitted at step  414 . 
     If, at step  416 , it is determined that there is no available H-ARQ process, the WTRU  102  determines whether there is an H-ARQ process already allocated for a lower priority class data (step  420 ). If there is an H-ARQ process already allocated for a lower priority class data, the H-ARQ process allocated for the lowest priority class data is preempted (step  422 ). The preempted H-ARQ process is allocated for the selected data and the allocated H-ARQ process is transmitted (steps  418 ,  414 ). If there is no H-ARQ process already allocated for a lower priority class data, this priority class is blocked for the current TTI (step  424 ), and the process  400  returns to step  408  to select the next highest priority data. 
     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.