Abstract:
A method for setting a header, having a header extension type field, of a protocol data unit in a radio link control layer of a wireless communications system includes configuring a “use of the special value of the header extension type field” mode, and setting the header extension type field to indicate that a last octet of the protocol data unit is a last octet of a service data unit when the last octet of the protocol data unit is the last octet of the service data unit and there is no concatenation of service data units inside the protocol data unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/938,705, filed on May 18, 2007 and entitled “Method and apparatus for POLL SUFI and special value of HE field clarifications in a wireless communication system”, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for setting packet headers in a wireless communications system, and more particularly, to a method and apparatus for reducing overhead, and preventing a receiver from wrongly reassembling Service Data Units. 
     2. Description of the Prior Art 
     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. 
     The access stratum of the 3G mobile telecommunications system comprises a radio resource control (RRC), radio link control (RLC), media access control (MAC), packet data convergence protocol (PDCP), broadcast/multicast control (BMC) and other sub-layers of different functions. The operations of the above-mentioned sub-layers are well known for those skilled in the art, and will not be further mentioned. A primary function of the RLC layer is providing different transmission quality processing, performing segmentation, reassembly, concatenation, padding, retransmission, sequence check, and duplication detection on transmitted data or control instructions based on different transmission quality requirements. The MAC layer can match packets received from different logic channels of the RLC layer to common, shared, or dedicated transport channels according to radio resource allocation commands of the RRC layer, for performing channel mapping, multiplexing, transport format selection, or random access control. 
     When the RLC layer operates in an acknowledged mode (AM), a header of an RLC PDU (Protocol Data Unit) comprises a two-bit HE (Header Extension Type) field utilized for indicating if the next octet is data or a Length Indicator (LI) and Extension (E) bit. The HE field has different values, and the corresponding description is as follows: 
     1. “00”: The succeeding octet contains data. 
     2. “01”: The succeeding octet contains LI and E bit. 
     3. “10” and “11”: Reserved. PDUs with this coding represents that a protocol error is occurred, and the PDUs will be discarded. 
     In order to decrease overhead, the prior art can configure a “use of the special value of the HE field” mode to set “10” of the HE field to indicate that the succeeding octet contains data and the last octet of the corresponding PDU is the last octet of an SDU (Service Data Unit). In other words, in the “use of the special value of the HE field” mode, if a PDU carries either a complete SDU or a segment of a SDU, and the complete SDU or the segment of the SDU ends at the end of the PDU, the HE field of the PDU will be set to “10.” As a result, an extra PDU carrying the corresponding LI is not needed, to decrease overhead. 
     Therefore, after the “use of the special value of the HE field” mode is configured, if a HE field of a PDU equals “10”, it implies that there is no SDU concatenation inside the PDU. However, the condition for setting the HE field to the special value is incorrect in the prior art as follows: if the last octet of a PDU is the last octet of an SDU, and the “use of the special value of the HE field” has been configured by higher layers, set the HE field to indicate that the last octet of the PDU is the last octet of an SDU. In such a situation, even if there are concatenated SDUs inside the PDU, the prior art still sets the HE field of the PDU to indicate that the last octet of the PDU is the last octet of an SDU. In other words, the receiver will consider the concatenated SDUs as the same SDU, and reassemble the SDUs incorrectly. 
     In short, the prior art does not precisely specify the condition for setting the HE field to the special value, leading the receiver to wrongly reassemble the SDUs, and causing system malfunction. 
     SUMMARY OF THE INVENTION 
     According to the claimed invention, a method for setting a header, having a header extension type field, of a protocol data unit in a radio link control layer of a wireless communications system comprises configuring a “use of the special value of the header extension type field” mode, and setting the header extension type field to indicate that a last octet of the protocol data unit is a last octet of a service data unit when the last octet of the protocol data unit is the last octet of the service data unit and there is no concatenation of service data units inside the protocol data unit. 
     According to the claimed invention, a communications device for accurately setting a header, having a header extension type field, of a radio link control protocol data unit in a wireless communications system comprises a control circuit for realizing functions of the communications device, a processor installed in the control circuit, for executing a program code to command the control circuit, and a memory installed in the control circuit and coupled to the processor for storing the program code. The program code comprises configuring a “use of the special value of the header extension type field” mode, and setting the header extension type field to indicate that a last octet of the radio link control protocol data unit is a last octet of a service data unit when the last octet of the radio link control protocol data unit is the last octet of the service data unit and there is no concatenation of service data units inside the radio link control protocol data unit. 
     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 
         FIG. 1  is a function block diagram of a wireless communications device. 
         FIG. 2  is a diagram of program code of  FIG. 1 . 
         FIG. 3  is a flowchart of a process according to an embodiment of the present invention. 
         FIG. 4  is a schematic diagram of a wireless communications system. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 4 , which illustrates a schematic diagram of a wireless communications system  1000 . The wireless communications system  1000  can be a 3G mobile telecommunications system, an LTE (long-term evolution) system or other mobile communications systems, and is briefly composed of a network and a plurality of UEs. In  FIG. 4 , the network and the UEs are simply utilized for illustrating the structure of the wireless communications system  1000 . Practically, the network may comprise a plurality of base stations (Node Bs), radio network controllers and so on according to actual demands, and the UEs can be devices such as mobile phones, computer systems, etc. 
     Please refer to  FIG. 1 , which is a functional block diagram of a wireless communications device  100 . The communications device  100  is utilized for realizing the network or the UEs in  FIG. 4 . 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 wireless communications device  100 . In the wireless 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 wireless communications device  100 . The wireless 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, transmitting 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 first portion of a first layer, and the control circuit  106  can be utilized to realize functions of a second layer and a third layer. 
     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  comprises an application layer  200 , a Layer 3 interface  202 , and a Layer 2 interface  206 , and is coupled to a Layer 1 interface  218 . When a signal is transmitted, the Layer 2 interface  206  forms a plurality of SDUs  208  according to data outputted by the Layer 3 interface  202 , and stores the plurality of SDUs  208  in a buffer  212 . Then, based on the SDUs  208  stored in the buffer  212 , the Layer 2 interface  206  generates a plurality of PDUs  214 , and sends the plurality of PDUs  214  to a destination terminal through the Layer 1 interface  218 . In contrast, when a wireless signal is received, the signal is received through the Layer 1 interface  218 , then outputted as PDUs  214  to the Layer 2 interface  206 . The Layer 2 interface  206  restores the PDUs  214  to SDUs  208  and stores the SDUs  208  in the buffer  212 . Last, the Layer 2 interface  206  transmits the SDUs  208  stored in the buffer  212  to the Layer 3 interface  202 . 
     When the communications device  100  operates in AM, a header of a PDU  214  comprises a two-bit HE field utilized for indicating if the next octet is data or an LI and E bit. When the “use of the special value of the HE field” mode is configured, a reserved value of the HE field represents that the succeeding octet contains data and the last octet of the corresponding PDU is the last octet of an SDU. In such a situation, the embodiment of the present invention provides a header setting program code  220 , for accurately setting the value of the HE field. 
     Please refer to  FIG. 3 , which illustrates a schematic diagram of a process  30  in accordance with an embodiment of the present invention. The process  30  is utilized for setting a header of a PDU in an RLC layer of the wireless communications system  1000 . The header comprises an HE field. The process  30  can be compiled into the header setting program code  220 , and comprises the following steps: 
     Step  300 : Start. 
     Step  302 : Configure a “use of the special value of the HE field” mode. 
     Step  304 : Set the HE field to indicate that a last octet of the PDU is a last octet of an SDU when the last octet of the PDU is the last octet of the SDU and there is no concatenation of SDUs inside the PDU. 
     Step  306 : End. 
     According to the process  30 , after the “use of the special value of the HE field” mode is configured, if the last octet of a PDU is the last octet of an SDU, and there is no SDU concatenation inside the PDU, the embodiment of the present invention sets the HE field of the PDU to indicate that the last octet of the PDU is the last octet of the SDU, e.g., setting the value of the HE field to [1 0]. In other words, after the “use of the special value of the HE field” mode is configured, if there is no SDU concatenation inside a PDU, and an SDU ends at the end of the PDU, the embodiment of the present invention will sets the HE field of the PDU to indicate that the last octet of the PDU is the last octet of the SDU. As a result, an extra PDU carrying the corresponding LI is not needed, so as to decrease overhead. 
     Therefore, via the process  30 , after the “use of the special value of the HE field” mode is configured, if the last octet of a PDU is the last octet of an SDU, and there is no SDU concatenation inside the PDU, the embodiment of the present invention sets the HE field of the PDU to indicate that the last octet of the PDU is the last octet of the SDU. Oppositely, if the last octet of a PDU is the last octet of an SDU while there are concatenated SDUs inside the PDU, the embodiment of the present invention will not set the HE field of the PDU to indicate that the last octet of the PDU is the last octet of the SDU. As a result, the receiver will not wrongly reassemble the SDUs. 
     In summary, after the “use of the special value of the HE field” mode is triggered, if the last octet of a PDU is the last octet of an SDU, and there is no SDU concatenation inside the PDU, the embodiment of the present invention can set the HE field of the PDU to indicate that the last octet of the PDU is the last octet of the SDU. As a result, the embodiment of the present invention can reduce overhead, and prevent the receiver from wrongly reassembling SDUs. 
     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.