Abstract:
A method for improving transmission of a downlink shared transport channel in a wireless communications system is provided in the present invention to avoid redundant signaling. The method includes steps of mapping a broadcast control channel to a downlink shared transport channel for transmitting a system information broadcast message through the downlink shared transport channel, and forming a packet without any headers according to the system information broadcast message.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60940975, filed on May 31, 2007 and entitled “Method and Apparatus for Improving MAC-ehs header of BCCH and PCCH mapped to HS-DSCH in a Wireless Communication System”, 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 improving transmission of a downlink shared transport channel in a wireless communications system, and more particularly, to a method and apparatus for improving a packet header of a packet transmitted when a broadcast control channel is mapped to a downlink shared transport channel. 
         [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 the third generation mobile telecommunication technology, the 3rd Generation Partnership Project (3GPP) provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate. 
         [0006]    On the basis of HSDPA, the 3GPP further introduces HS-DSCH (High Speed Downlink Shared Channel) reception in a CELL_FACH, a CELL_PCH and a URA_PCH state, allowing the UE in these states to monitor an HS-DSCH accompanied with a Shared Control Channel for HS-DSCH (HS-SCCH) for downlink data reception, so as to improve a peak data rate, a signaling delay, a state transition delay, download times and flexible cell capacity. 
         [0007]    In the HS-DSCH reception, a Media Access Control (MAC) layer utilizes a MAC-ehs entity for mapping logical channels to an HS-DSCH. Associated logical channels are dedicated-type logical channels including a Dedicated Control Channel (DCCH) and a Dedicated Traffic Channel (DTCH) or common-type logical channels including a Paging Control Channel (PCCH) and a Broadcast Control Channel (BCCH). Detailed operations of the MAC-ehs entity can be found in the MAC protocol specification formulated by the 3GPP, and are not narrated herein. 
         [0008]    On the other hand, please refer to  FIG. 1 , which illustrates a schematic diagram of a MAC-ehs Protocol Data Unit (PDU). The MAC-ehs PDU is a transmission packet of the MAC-ehs entity, and consists of a plurality of reordering PDUs and a corresponding MAC-ehs header. Each reordering PDU consists of at least one consecutive MAC-ehs Serving Data Unit (SDUs) or segments of MAC-ehs SDUs belonging to the same priority queue, or reordering queue. A MAC-ehs SDU, i.e. an upper layer PDU, is either a MAC-c PDU or a MAC-d PDU. For the MAC-ehs header, five header fields are defined in the MAC protocol as follows: Logical channel identifier (LCH-ID), Length (L), Transmission Sequence Number (TSN), Segmentation Indication (SI) and Flag (f). The LCH-ID field provides identification of a logical channel corresponding to each MAC-ehs SDU or segment of MAC-ehs SDU in the MAC-ehs packet. The L field provides data length of each MAC-ehs SDU or segment of MAC-ehs SDU. The TSN field provides an identifier for a TSN of each reordering PDU for reordering purpose. The SI field indicates whether MAC-ehs SDUs included in each reordering PDU are segmented and segmentation type of the reordering PDU for reassembly. The F field then indicates if more header fields are present in the MAC-ehs header or not. 
         [0009]    However, when the BCCH is mapped to the HS-DSCH, the MAC-ehs header generated according to the prior art is redundant, which means a user equipment (UE) is able to receive messages transmitted on the BCCH through the HS-DSCH successfully without using the MAC-ehs header. Analysis on each filed of the MAC-ehs header is given in the following. 
         [0010]    First, when the HS-DSCH reception is performed, BCCH mapped to HS-DSCH is utilized for transmitting a SYSTEM INFORMATION CHANGE INDICATION message to UEs operated in the CELL_FACH or the CELL_PCH state. For BCCH reception, a BCCH specific H-RNTI (Radio Network Temporary Identifier) indicated in system information is utilized by the UEs for listening to the HS-SCCH to receive packet data of the BCCH through the HS-DSCH. In this case, MAC packets received by the UE can be identified belonging to the BCCH by the BCCH specific H-RNTI, so there is no need to include the LCH-ID field in the MAC-ehs header. 
         [0011]    In addition, based on a Radio Resource Control (RRC) specification formulated by the 3GPP, the SYSTEM INFORMATION CHANGE INDICATION message is transmitted in Transparent Mode (TM), and the RRC layer shall add padding when the encoded SYSTEM INFORMATION CHANGE INDICATION message does not fill a transport block. In this case, a whole transport block received by the HS-DSCH only contains one MAC SDU, and includes no padding bits added by the MAC layer. So the L field is not needed in the MAC-ehs header. 
         [0012]    On the other hand, according to a change request R2-072305 disclosed by the 3GPP, no MAC-ehs reordering queue is configured for BCCH reception as specified in an information element (IE) “RB information parameters for BCCH mapped to HS-DSCH.” Thus, when a transport block corresponding to the BCCH is received, the MAC layer just passes the received transport block to the RRC layer without reordering. So the TSN field is not needed in the MAC-ehs header. 
         [0013]    Moreover, according to a change request R2-072258 disclosed by the 3GPP, the network would not perform segmentation for MAC-ehs SDUs from the BCCH as specified in a subclause 6.2“Relation between MAC Functions and Transport Channels.” So, the SI field is not needed in the MAC-ehs header. If all of the above four fields are not present, the F filed is not needed either. 
         [0014]    In short, when the BCCH is mapped to the HS-DSCH, the MAC-ehs header included in the MAC-ehs PDU is redundant, which causes extra signaling overhead and waste of system resources. 
       SUMMARY OF THE INVENTION 
       [0015]    It is therefore an objective of the present invention to provide a method and apparatus for improving transmission of a downlink shared transport channel in a wireless communications system, so as to avoid extra signaling overhead and to enhance system efficiency. 
         [0016]    According to the present invention, a method for improving transmission of a downlink shared transport channel in a wireless communications system is disclosed. The method includes steps of mapping a broadcast control channel to a downlink shared transport channel by a media access control, named MAC hereinafter, protocol entity for transmission of a system information broadcast message through the downlink shared transport channel; and forming a MAC protocol data unit, named PDU hereinafter, according to the system information broadcast message, wherein the MAC PDU comprises no header fields. 
         [0017]    According to the present invention, a communications device used in a wireless communications system for improving transmission of a downlink shared transport channel is further disclosed. The communications device includes 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 includes steps of mapping a broadcast control channel to a downlink shared transport channel by a media access control, named MAC hereinafter, protocol entity for transmission of a system information broadcast message through the downlink shared transport channel; and forming a MAC protocol data unit, named PDU hereinafter, according to the system information broadcast message, wherein the MAC PDU comprises no header fields. 
         [0018]    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 
         [0019]      FIG. 1  illustrates a schematic diagram of a MAC-ehs PDU. 
           [0020]      FIG. 2  is a schematic diagram of a wireless communications system. 
           [0021]      FIG. 3  is a functional block diagram of a communications device. 
           [0022]      FIG. 4  is a diagram of the program code shown in  FIG. 3 . 
           [0023]      FIG. 5  illustrates a schematic diagram of a process according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Please refer to  FIG. 2 , which is a schematic diagram of a wireless communications system  400 . The wireless communications system  400  is preferred to be a High Speed Package Access (HSPA) system or a Long Term Evolution (LTE) system of a third generation (3G) mobile communications system, and is briefly formed with a network terminal and a plurality of user equipments. In  FIG. 2 , the network terminal and the user equipments are simply utilized for illustrating the structure of the wireless communications system  400 . Practically, the network terminal may include a plurality of base stations, radio network controllers, and so on according to actual demands, and the user equipments (UEs) can be apparatuses such as mobile phones, computer systems, etc. 
         [0025]    Please refer to  FIG. 3 , which is a functional block diagram of a communications device  100 . The communications device  100  can be utilized for realizing the network terminal or the user equipments in  FIG. 2 . For the sake of brevity,  FIG. 2  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  supports HS-DSCH (High Speed Downlink Shared Channel) reception in a CELL_FACH, a CELL_PCH and a URA_PCH state. 
         [0026]    Please continue to refer to  FIG. 4 .  FIG. 4  is a diagram of the program code  112  shown in  FIG. 3 . 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 3  202  includes a radio resource control (RRC) entity  222  for controlling the Layer 1  218  and the Layer 2  206  with RRC messages and information elements (IEs). Furthermore, the RRC entity  222  can change an RRC state of the communications device  100  among an Idle mode, a CELL_PCH, a URA_PCH, a CELL_FACH or a CELL_DCH state. The Layer 2  206  includes a radio link control (RLC) layer and a media access control (MAC) layer, which exchange packets via logical channels. In addition, the MAC layer exchanges MAC packets with the Layer 1  218  via transport channels. In the HS-DSCH reception, the MAC layer is utilized for mapping logical channels to an HS-DSCH. Associated logical channels are dedicated-type logical channels including a Dedicated Control Channel (DCCH) and a Dedicated Traffic Channel (DTCH) or common-type logical channels including a Paging Control Channel (PCCH) and a Broadcast Control Channel (BCCH). 
         [0027]    When the HS-DSCH reception is performed, BCCH mapped to HS-DSCH is utilized for transmission of a SYSTEM INFORMATION CHANGE INDICATION message. In this case, the embodiment of the present invention provides a header configuration improvement program code  220  in the program code  112  for improving a packet header of a packet transmitted when a broadcast control channel is mapped to a downlink shared transport channel. Please refer to  FIG. 5 , which illustrates a schematic diagram of a process  30  according to an embodiment of the present invention. The process  30  is utilized for improving transmission of a downlink shared transport channel in a wireless communications system, and can be compiled into the header configuration improvement program code  220 . The process  30  includes the following steps: 
         [0028]    Step  300 : Start. 
         [0029]    Step  302 : Map a broadcast control channel to a downlink shared transport channel by a MAC protocol entity for transmission of a system information broadcast message through the downlink shared transport channel. 
         [0030]    Step  304 : Form a MAC protocol data unit (PDU) according to the system information broadcast message, wherein the MAC PDU comprises no header fields 
         [0031]    Step  306 : End. 
         [0032]    According to the process  30 , a broadcast control channel is mapped to a downlink shared transport channel by the MAC protocol entity for transmitting a system information broadcast message through the downlink shared transport channel. Then, a MAC PDU is formed according to the system information broadcast message, wherein there is no header field included in the MAC PDU in the embodiment of the present invention. Preferably, a specific radio network temporary identifier is utilized for transmission of the system information broadcast message through the downlink shared transport channel. In addition, the system information broadcast message is transmitted in Transparent Mode (TM), and the RRC layer shall add padding when the system information broadcast message being transmitted does not fill a transport block. In this situation, the MAC PDU only includes one MAC SDU corresponding to the system information broadcast message, and includes no padding bits added by the MAC layer. 
         [0033]    Thus, when the broadcast control channel is mapped to the downlink shared transport channel, there is no MAC header included in the MAC PDU being transmitted, and packet data of the broadcast control channel can still be correctly transmitted through the downlink shared transport channel. Consequently, extra signaling overhead can be reduced in the embodiment of the present invention, as well as system resources and electric power consumed by handling the packet header. 
         [0034]    Note that, in the embodiment of the present invention, the downlink shared transport channel can be a High Speed Downlink Shared Channel (HS-DSCH) of the HSPA system or a Downlink Shared Channel (DL-SCH) of the LTE system, and not restricted herein. 
         [0035]    As mentioned above, when the broadcast control channel is mapped to the downlink shared transport channel, no MAC header is included in the MAC PDU of the present invention, so that extra signaling overhead can be reduced, as well as system resources and electric power consumed by handling the header. 
         [0036]    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.