Abstract:
A method for handling retransmissions used in a transmitter of a wireless communications system includes initiating a Hybrid Automatic Repeat Request process, transmitting a packet with a first sequence number, and transmitting the packet with a second sequence number and marking the packet as a new packet when a transmission number of the packet with the first sequence number reaches a configured maximum number of transmissions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/743,727, filed on Mar. 24, 2006 and entitled “Method and Apparatus for Handling Maximum Number of Transmissions in HARQ”, the contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method and apparatus for handling retransmissions in a wireless communications system, and more particularly to a method and related apparatus for increasing transmission efficiency and throughput of a Hybrid Automatic Repeat Request process. 
         [0004]    2. Description of the Prior Art 
         [0005]    The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting third generation mobile telecommunication technology, the prior art provides High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), which are used to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate. 
         [0006]    In the prior art, HSDPA and HSUPA adopt Hybrid Automatic Repeat Request (HARQ) technology to enhance retransmission rate and reduce transmission delay. HARQ is a technology combining Feed-forward Error Correction (FEC) and ARQ methods, triggers retransmission according to positive/negative acknowledgement signals (ACK/NACK) transmitted from a receiving end, and stores useful information of the last failure transmission for later use. In order to minimize the number of retransmission requests, HARQ uses one of two Soft-Combining methods to ensure that messages can be successfully decoded, which are Chase Combining (CC) and Incremental Redundancy (IR). CC transmits a packet the same as the erroneous packet, and the decoder combines all the received packets before performing decoding. IR increases redundancy to help recovering transmission errors, which sequentially transmits packets having parts of the erroneous packet, and the decoder combines the packets. 
         [0007]    Using HARQ, a transmitter can rapidly retransmit erroneous data packet according to acknowledgement signals provided by a receiver. Therefore, when the number of retransmissions is great enough, the receiver can successfully receive packets transmitted from the transmitter unless the receiver is out of a transmission range of the transmitter. However, in order to avoid radio resource waste caused by too many retransmissions, the prior art can set a maximum number of retransmissions. For example, according to Medium Access Control (MAC) protocol specification, “3GPP TS 25.321 V6.7.0” defined by the 3rd Generation Partnership Project (3GPP), an HARQ profile comprises a maximum number of transmissions. After the maximum number of transmissions of a packet, if the packet is not successfully received, the transmitter discards the packet and flushes the buffer. The retransmission of the abandoned packet relies on upper layer or outer ARQ, so that extra delay is induced and transmission efficiency is decreased. 
       SUMMARY OF THE INVENTION 
       [0008]    According to the present invention, a method for handling retransmissions used in a transmitter of a wireless communications system comprises initiating a Hybrid Automatic Repeat Request process, transmitting a packet with a first sequence number, and transmitting the packet with a second sequence number and marking the packet as a new packet when a transmission number of the packet with the first sequence number reaches a configured maximum number of transmissions. 
         [0009]    According to the present invention, a communications device of a wireless communications system utilized for reducing transmission delay when handling retransmissions comprises a control circuit for realizing functions of the communications device, a processor installed in the control circuit for executing a program code to operate the control circuit, and a memory coupled to the processor for storing the program code. The program code comprises initiating a Hybrid Automatic Repeat Request process, transmitting a packet with a first sequence number, and transmitting the packet with a second sequence number and marking the packet as a new packet when a transmission number of the packet with the first sequence number reaches a configured maximum number of transmissions. 
         [0010]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a function block diagram of a wireless communications device. 
           [0012]      FIG. 2  is a diagram of program code of  FIG. 1 . 
           [0013]      FIG. 3  is a flowchart of a process according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Please refer to  FIG. 1 , which is a functional block diagram of a communications device  100 . For the sake of brevity,  FIG. 1  only shows an input device  102 , an output device  104 , a control circuit  106 , a central processing unit (CPU)  108 , a memory  110 , a program code  112 , and a transceiver  114  of the communications device  100 . In the communications device  100 , the control circuit  106  executes the program code  112  in the memory  110  through the CPU  108 , thereby controlling an operation of the communications device  100 . The communications device  100  can receive signals input by a user through the input device  102 , such as a keyboard, and can output images and sounds through the output device  104 , such as a monitor or speakers. The transceiver  114  is used to receive and transmit wireless signals, delivering received signals to the control circuit  106 , and outputting signals generated by the control circuit  106  wirelessly. From a perspective of a communications protocol framework, the transceiver  114  can be seen as a portion of Layer  1 , and the control circuit  106  can be utilized to realize functions of Layer  2  and Layer  3 . Preferably, the communications device  100  is utilized in a third generation (3G) mobile communications system. 
         [0015]    Please continue to refer to  FIG. 2 .  FIG. 2  is a diagram of the program code  112  shown in  FIG. 1 . The program code  112  includes an application layer  200 , a Layer  3   202 , and a Layer  2   206 , and is coupled to a Layer  1   218 . The Layer  2   206  comprises two sub-layers: a radio link control (RLC) entity  224  and a media access control (MAC) entity  226 . A primary function of the RLC entity  224  is providing different transmission quality processing, performing segmentation, reassembly, concatenation, padding, retransmission, ciphering, sequence check, and duplication detection on transmitted data or control instructions based on different transmission quality requirements. The MAC entity  226  can match packets received from different logic channels of the RLC entity  224  to common, shared, or dedicated transport channels according to radio resource allocation commands of the Layer  3  (RRC layer)  202 , for performing channel mapping, multiplexing, transport format selection, or random access control. 
         [0016]    In some applications, such as when realizing high-speed uplink packet access (HSUPA) functions, the MAC entity  226  can execute an HARQ process, and retransmit packets based on acknowledgement signals outputted from a receiver. In this situation, the present invention provides a retransmission handling program code  220  utilized for timely triggering of packet retransmissions, in order to reduce transmission delay and avoid radio resource waste. Please refer to  FIG. 3 , which is a flowchart diagram of a process  30  according to the present invention. The process  30  is utilized in a transmitter of the wireless communication system for handling retransmissions, and comprises the following steps:
       Step  300 : Start.   Step  302 : Initiate an HARQ process.   Step  303 : Transmit a packet with a first sequence number.   Step  304 : Transmit the packet with a second sequence number and mark the packet as a new packet when a transmission number of the packet with the first sequence number reaches a configured maximum number of transmissions.   Step  306 : End.       
 
         [0022]    According to the process  30 , in an HARQ process, when a packet reaches the configured maximum number of transmissions and is not received successfully, the transmitter marks the packet as a new packet and retransmits it to the receiver, so as to flush soft buffer of the receiver. In other words, retransmissions in the present invention do not rely on upper layer or outer ARQ, so that transmission delay is reduced and transmission efficiency can be enhanced. Preferably, the transmitter can count the transmission number of the packet with a counter, and reset the counter when the packet is marked as a new packet. Besides, the (second) sequence number of the retransmitted packet can be equal to or different from the (first) sequence number of the original packet. 
         [0023]    Therefore, in the HARQ process, if the counter counting the transmission number of a packet reaches the maximum number of transmissions stored in HARQ Profile and the transmitter does not receive any acknowledgement signal corresponding to the packet, the transmitter will keep the sequence number of the packet or set another sequence number for the packet, mark the packet as a new packet, and retransmit the packet to the receiver. When the receiver receives the packet marked as the new packet, the receiver flushes buffer before soft combination, so as to avoid the potential problems that the buffer may contain data of a different packet erroneously. Therefore, the present invention can retransmit packets without upper layer retransmission or outer ARQ, so as to increase transmission efficiency and throughput of an HARQ process. 
         [0024]    In summary, in an HARQ process, when a packet reaches the configured maximum number of transmissions and is not received successfully, the present invention marks the packet as a new packet and retransmits it to the receiver, so that the receiver can flush buffer to avoid the potential problems of buffer corruption. Meanwhile, the present invention can retransmit packets without upper layer retransmission or outer ARQ, so as to increase transmission efficiency and throughput of the HARQ process. 
         [0025]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.