Abstract:
A method and apparatus for dynamically configuring a memory for hybrid automatic repeat request (H-ARQ) processes in a receiving node to permit a more flexible H-ARQ memory configuration and improve the performance of H-ARQ processes. An H-ARQ memory in the receiving node is reserved for a plurality of H-ARQ processes. A transmitting node dynamically configures the H-ARQ memory in the receiving node for each H-ARQ transmission so that the memory requirement for a plurality of H-ARQ processes exceeds the H-ARQ memory capacity. If there is insufficient H-ARQ memory available to support H-ARQ transmissions, only a subset of the plurality of H-ARQ processes may be activated at a time. When there is insufficient H-ARQ memory for processing H-ARQ transmissions, a negative acknowledgement (NACK), an acknowledgement (ACK), nothing, and/or information indicating the reason for a failed transmission may be transmitted to a transmitting node.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. Provisional Patent Application No. 60/843,145 filed Sep. 8, 2006 and U.S. Provisional Patent Application. No. 60/764,842 filed Feb. 3, 2006, 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 transmitting node and a receiving node. More particularly, the present invention is related to a method for dynamically configuring a memory for hybrid automatic repeat request (H-ARQ) processes in a receiving node to permit a more flexible memory configuration and to improve the performance of H-ARQ processes. 
     BACKGROUND 
     Methods for improving data rates and the performance of wireless communication systems using H-ARQ processes are being investigated in the Third Generation Partnership Project (3GPP). 
     An H-ARQ scheme is used to generate transmissions and retransmissions with low latency. H-ARQ is a variation of an automatic repeat request (ARQ) error control method, which provides better performance than an ordinary ARQ method at the cost of increased implementation complexity. H-ARQ can be used in stop-and-wait retransmission or in selective repeat retransmission. Stop-and-wait retransmission is simpler to use. However, waiting for a receiver&#39;s acknowledgment of a signal reduces efficiency. Thus, multiple stop-and-wait H-ARQ processes are used in parallel to overcome the positive acknowledgement (ACK)/negative acknowledgement (NACK) round-trip delay due to this mechanism. Further, multiple H-ARQ processes allow high priority traffic to be sent immediately using a new H-ARQ process, rather than being stalled behind packets in transmission using an existing H-ARQ process. For example, when one H-ARQ process is waiting for an ACK, another H-ARQ process can be used to send more data. 
     In 3GPP, protocol messaging configures H-ARQ behavior, including H-ARQ memory availability. More specifically, the prior art permits protocol messages to configure an H-ARQ process with a buffer size and to exchange the buffer size with a communicating peer device, such as a WTRU or a Node-B. In the prior art, each H-ARQ process is configured with a particular H-ARQ memory limit. This configuration presents two limitations and inefficiencies. First, certain radio bearers may benefit from more H-ARQ processes, each with small memory requirements. Second, an application may benefit from fewer H-ARQ processes with larger buffer limits when the application has large memory requirements but can tolerate an increased number of H-ARQ retransmissions because the application does not have stringent delay requirements. 
     A challenge in implementing the H-ARQ mechanism is the receive memory requirement to buffer soft decoding decisions in the H-ARQ memory needed to implement incremental redundancy schemes. 
     Two of the desired improvements of long term evolution (LTE) of wideband code division multiple access (WCDMA) for universal mobile telecommunication systems (UMTS) are higher data rates as well as improved handling of different applications, particularly with different quality of service (QoS) requirements. LTE is also referred to as evolved universal terrestrial radio access (E-UTRA). To provide these desired improvements, LTE working groups are discussing flexible frame and transmission time interval (TTI) formats. Additionally, particular delay insensitive applications are able to tolerate a greater number of retransmissions. 
     As data rates increase, the amount of H-ARQ memory, (i.e. soft memory), needed for H-ARQ processes becomes a considerable cost factor for a baseband chipset. Therefore, H-ARQ memory optimizations are potentially a considerable design benefit. Unfortunately, the current H-ARQ memory allocation mechanism is too restrictive to handle these considerations. As a result, a new mechanism that permits for a more dynamic and flexible H-ARQ memory configuration is necessary. 
     SUMMARY 
     The present invention is related to a method for dynamically configuring a memory for hybrid automatic repeat request (H-ARQ) processes in a receiving node to permit a more flexible H-ARQ memory configuration and to improve the performance of H-ARQ processes. An H-ARQ memory in a receiving node is dynamically reserved for a plurality of H-ARQ processes. A transmitting node dynamically configures the H-ARQ memory in the receiving node for each new H-ARQ transmission. A receiving node signals a transmitting node during the establishment of an Radio Bearer utilizing H-ARQ transmission. The signaling informs a transmitting node of the capability to share an H-ARQ memory across a plurality of H-ARQ processes in a receiving node. The signaling informs a transmitting node of the capacity of an H-ARQ memory in a receiving node. An H-ARQ memory capacity is based on a maximum data rate and quality of service (QoS) requirement of a radio bearer. A transmitting node may dynamically configure the H-ARQ memory in a receiving node so that the memory requirement for a plurality of H-ARQ processes in aggregate exceeds the H-ARQ memory capacity of the receiving node. A transmitting node signals a receiving node instructing the receiving node to dynamically configure its H-ARQ memory accordingly. 
     If there is insufficient H-ARQ memory available at a receiving node to support H-ARQ transmission, only a subset of a plurality of H-ARQ processes may be activated at one time. When there is insufficient H-ARQ memory for processing a received H-ARQ transmission, a receiving node may signal a NACK, (with or without additional information indicating the insufficiency of the H-ARQ memory), an ACK, nothing, and/or information indicating the reason for the failed transmission may be transmitted to a transmitting node. 
    
    
     
       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 drawings wherein: 
         FIG. 1  is a block diagram of a wireless communication system configured in accordance with the present invention; 
         FIG. 2  is a flow diagram of a dynamically configured H-ARQ memory allocation process implemented by the system of  FIG. 1 ; and 
         FIG. 3  is a flow diagram of a dynamically configured H-ARQ memory configuration process implemented by the system of  FIG. 1  when the aggregated memory requirement for a set of H-ARQ processes exceeds H-ARQ memory capacity at a receiving node. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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, or any other type of user device capable of operating in a wireless environment. When referred to hereafter, the terminology “base station” includes but is not limited to a Node-B, a site controller, an access point (AP) or any other type of interfacing device capable of operating 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  configured in accordance with the present invention. The system  100  includes a receiving node  102  and a transmitting node  104  configured for H-ARQ transmissions. The receiving node  102  and the transmitting node  104  communicate via explicit signaling or implicit signaling using existing parameters. With respect to downlink H-ARQ transmissions, the receiving node  102  may be a WTRU and the transmitting node  104  may be a Node-B. With respect to uplink H-ARQ transmissions, the receiving node  102  may be a Node-B and the transmitting node may be a WTRU. 
     As shown in  FIG. 1 , the receiving node  102  includes a processor  110 , an H-ARQ memory  114 , a receiver  116 , and a transmitter  118 . The processor  110  is configured to dynamically configure the allocation of H-ARQ memory  114  in accordance with signals received from the transmitting node  104 . The processor  110  is configured to control a plurality of receiving H-ARQ processes  112 . 
     In an alternative embodiment, the processor  110  may be configured to dynamically configure the allocation of the H-ARQ memory  114  without receiving any signals from the transmitting node  104 . The processor  110  determines a configuration of the H-ARQ memory  114  by itself and signals the determined H-ARQ memory  114  configuration to the transmitting node  104  via the transmitter  118 . 
     The H-ARQ memory  114  is reserved for a plurality receiving H-ARQ processes  112 . The H-ARQ memory  114  may be referred to as soft memory. Preferably, the H-ARQ memory  114  is dynamically shared across a plurality of H-ARQ processes  112 . The H-ARQ memory  114  is dynamically allocated among H-ARQ processes  112 . When the aggregated soft memory requirement for the plurality of H-ARQ processes  112  exceeds the capacity of the H-ARQ memory  114 , only certain subsets of the plurality of H-ARQ processes  112  may be active at any given time. Further, the amount of configured H-ARQ  114  memory may depend on a maximum data rate and/or QoS requirements of the radio bearer or MAC flow. 
     The receiver  116  of the receiving node  102  is configured to receive signals from the transmitting node  104  that instruct the receiving node  102  to configure its H-ARQ memory  114  accordingly. The transmitter  118  of the receiving node  102  is configured to signal an H-ARQ memory sharing capability and/or the capacity of the H-ARQ memory  114  to the transmitting node  104 . The H-ARQ memory sharing capability indicates whether the receiving node  102  can share its H-ARQ memory  114  across the H-ARQ processes  112 . The signaling may be explicit or implicit in accordance with existing parameters. 
     Still referring to  FIG. 1 , the transmitting node  104  includes a processor  120 , an H-ARQ memory  124 , a receiver  126 , and a transmitter  128 . The processor  120  is configured to dynamically configure the H-ARQ memory  114  in the receiving node  102 . This memory configuration includes partitioning the H-ARQ memory across the plurality of H-ARQ processes  112 . 
     The processor  120  in the transmitting node  104  is configured to manage and configure the H-ARQ memory  114  in the receiving node  102 . During a transport format (TF) selection process, the processor  120  is configured to measure the H-ARQ memory  114  used by radio bearers, or MAC flows, being serviced in a current transmission time interval (TTI) when determining a transport block (TB) size and a modulation and coding scheme (MCS). The TF selection process may also consider the total data available to transmit, beyond the current TTI, and to reserve capacity in the H-ARQ memory  114  for subsequent TTIs to permit continuous, or almost continuous, transmission during the TTI for the currently selected TF transmission. The result is that the TB is sized to match the dynamically configurable H-ARQ memory  114  resources. Consequently, the dynamic configuration of the H-ARQ memory  114  in the receiving node  102  improves the performance of the H-ARQ processes  112  and the radio bearers and MAC flows mapped to the HARQ processes. The processor  120  is also configured to process a plurality of transmitting H-ARQ processes  122 . 
     The transmitter  128  of the transmitting node  104  is configured to signal an H-ARQ memory configuration command or recommendation to the receiving node  102 . As an example, with respect to downlink transmissions, the transmitter sends a command that the receiving node  102  must follow. As another example, with respect to uplink transmissions, the transmitter sends a recommendation that the receiving node  102  may follow. The transmitter  128  signals the receiving node  102  via explicit or implicit signaling using existing parameters. A transport format combination indicator (TFCI), a transport format resource indicator (TFRI), or other transmission associated signaling may be used to implicitly signal the H-ARQ memory requirement for each H-ARQ process to the receiving node  102 . Further, knowledge of an H-ARQ process identity (ID) may be used to implicitly identify the H-ARQ memory requirement for an H-ARQ process  112 . This information can be used to implicitly signal the H-ARQ memory  114  configuration to the receiving node  102 . Alternatively, the transmitter  128  may explicitly signal the amount of H-ARQ memory  124  in the transmitting node  104  that has been allocated to the receiving node  102  With these mechanisms HARQ process memory partitioning may be coordinated between the transmitter and receiver each TTI a new HARQ process transmission is initiated. 
     Another method of implicit identification of the HARQ memory requirement is when the scheduler identifies a specific TF or subset of allowed TF&#39;s that may be utilized by the transmitter. Then, the receiver HARQ memory  114  is partitioned based on the scheduling information. 
       FIG. 2  is a flow diagram of a dynamically configured H-ARQ memory allocation process  200  implemented by the system  100  of  FIG. 1 . In step  202 , the receiving node  102  reserves an H-ARQ memory  114  for a plurality of H-ARQ processes  112 . In step  204 , the receiving node  102  signals an H-ARQ memory sharing capability and/or the capacity of the H-ARQ memory  114  to the transmitting node  104 . Note that step  204  may only be needed when the receiver is a WTRU. The signaling indicates to the transmitting node  104  whether the receiving node  102  is capable of sharing the H-ARQ memory  114  across the plurality of H-ARQ processes  112 . The signaling may also indicate the capacity of the H-ARQ memory  114  in the receiving node  102 . The signaling may be explicit or implicit in accordance with existing parameters. 
     In step  206 , the transmitting node  104  dynamically configures (partitions) the H-ARQ memory  114  in the receiving node  102  for H-ARQ processes  112  to improve the performance of H-ARQ processes  112 . In step  208 , the transmitting node  104  signals an H-ARQ memory configuration command or recommendation potentially in each new HARQ transmission to the receiving node  102 . The signaling for partitioning of HARQ memory may be explicit or implicit. Preferably, the transmitting node uses fast physical layer signaling to configure and reconfigure the soft memory partitions between the H-ARQ processes  112  in the H-ARQ memory  114 . The transmitting node  104  may also use Layer 2 MAC or Layer 3 radio resource control (RRC) signaling to configure and reconfigure the soft memory partitions between the H-ARQ processes  112  in the H-ARQ memory  114 . As an optional embodiment, the association of H-ARQ processes  112  with specific radio bearers may be reconfigured through MAC or RRC signaling. The signaling is invoked upon establishment, release, or reconfiguration of the radio bearers. Consequently, the H-ARQ memory  114  in the receiving node  102  is dynamically configured to permit the improved performance of H-ARQ processes  112  at any potential time a new HARQ process transmission is initiated. It should be noted that after steps  202  and  204 , steps  206  and  208  may repeat each TTI a new HARQ process transmission is initiated. 
       FIG. 3  is a flow diagram of a dynamically configured H-ARQ memory allocation process  300  implemented by the system  100  of  FIG. 1  when the aggregated H-ARQ memory requirement for a set of H-ARQ processes  112  exceeds the H-ARQ memory  114  at the receiving node  102 . 
     In step  302 , the receiving node  102  reserves an H-ARQ memory  114  for a plurality of H-ARQ processes  112 . The H-ARQ memory  114  capacity may be changed by the receiving node  102 . In step  304 , the receiving node  102  signals an H-ARQ memory sharing capability and/or the capacity of the H-ARQ memory  114  to the transmitting node  104 . The signaling indicates to the transmitting node  104  whether the receiving node  102  is capable of sharing the H-ARQ memory  114  across the plurality of H-ARQ processes  112 . The signaling may also indicate the capacity of the H-ARQ memory  114  in the receiving node  102 . The signaling may be explicit or implicit in accordance with existing parameters. 
     In step  306 , the transmitting node  104  dynamically configures the H-ARQ memory  114  in the receiving node  102  so that the aggregated memory requirement for the plurality of H-ARQ processes  112  exceeds the capacity of the H-ARQ memory  114 . In step  308 , the transmitting node  104  signals an H-ARQ memory configuration command or recommendation potentially in each new HARQ transmission to the receiving node  102 . 
     In step  310 , the receiving node  102  determines whether there is sufficient H-ARQ memory  114  available to support an H-ARQ transmission. If there is insufficient H-ARQ memory  114  to support an H-ARQ transmission and support soft combining, one of the following three options  312 ,  314 , and  316  may be implemented for an failed H-ARQ transmissions. 
     In step  312  (option  1 ), the receiving node  102  signals a NACK to the transmitting node  104 . The NACK informs the transmitting node  104  that the H-ARQ transmission has not been received correctly. 
     In step  314  (option  2 ), the receiving node  102  signals an ACK to the transmitting node  104 . The ACK falsely indicates that the receiving node  102  has received an H-ARQ transmission when the receive node  102  does not want the transmit node  104  to retransmit the H-ARQ transmission. This procedure exists to prevent H-ARQ retransmission when there is insufficient H-ARQ memory  114  available. This scenario assumes that it is not possible for the receiving node  102  to inform the transmit node  104  that no H-ARQ memory  114  is available. This is beneficial in H-ARQ schemes where H-ARQ retransmissions are not self-decodable. If a separate ARQ scheme exists to correct residual H-ARQ transmission errors, the ARQ scheme could recover the transmission. 
     In step  316  (option  3 ), the receiving node  102  waits for sufficient H-ARQ memory  114  to become available to support an H-ARQ transmission. The receiver node  102  signals nothing back to the transmitting node  104 . 
     In an alternative embodiment, the receiving node  102  may signal additional information indicating the reason for the failure to support the H-ARQ transmission. For example, the failure was due to a shortage of H-ARQ memory  114 . This additional information may be signaled along with the ACK/NACK signaling described above. Further, the additional information may be signaled in place of the ACK/NACK signaling. 
     As an informative example, suppose that an H-ARQ memory  114  in a receiving node  102  has a one (1) Mb capacity and supports four identically configured H-ARQ processes. This process  300  permits a fifth H-ARQ process to be instantiated so that the H-ARQ memory  114  is not guaranteed to be sufficient for the H-ARQ processes  112 . The H-ARQ memory  114  may contain soft memory partitions that are preconfigured to support multiple H-ARQ processes  112 . The dynamic configuration of H-ARQ processes  112  may ensure that the H-ARQ memory  114  capacity is not exceeded. 
     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. 
     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. The methods or flow charts provided in the present invention may be implemented in a computer program, software, or firmware tangibly embodied 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). 
     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 in 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. 
     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) module.