Abstract:
A method for direct link in wireless communication system is provided, which is applied in a base station with functions for broadcast and time division duplex (TDD), the method comprising the following steps: receiving connection request signalings including position information from a plurality of subscriber stations (SSs) with global positioning systems (GPSs); determining the SSs which can carry out the direct link, according to the connection request signalings; allocating time slots to each SS which can carry out direct link in the scheduling; calculating a relative distance between the two SSs according to the position information; determining an initial transmit power for the transmitting SS, and adjusting it many times; finally, adding the adjusted transmit power value and the time slot information allocated to the SSs in the scheduling into the broadcast message.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 094138893 filed in Taiwan, R.O.C. on Nov. 4, 2005, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INNENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method for direct link in a wireless communication system, and more particularly, to a method for achieving a direct link applied in a central managed wireless communication system with broadcast function.  
         [0004]     2. Related Art  
         [0005]     Along with the continual progress of communication technology, the manner in which people access networks is gradually evolving from narrow band to broad band, and the manner for internet connection is evolving from wired connections to wireless connections. The IEEE 802.16 wireless transmission manner especially receives the attention of the masses, it can be used to transmit high-speed data, and can further resist multi-path effect, eliminate interference among symbols, resist selective frequency fading, and has a high channel availability, such that network disposition is more convenient and flexible, especially effective in solving the most troublesome last mile problem of network construction.  
         [0006]     Referring to  FIG. 1 , it is a schematic diagram of a conventional transmission manner in the IEEE 802.16 wireless network system. Taking two subscriber stations (SSs) as an example, connection request signalings  140  are first put forward to a base station (BS)  110  by SSs  120 ,  130 ; then the BS  110  determines whether or not to accept the connections of the first SS  120  and the second SS  130 , according to the present state of the wireless environment.  
         [0007]     Once the BS  110  accepts the connections of the first SS  120  and the second SS  130 , the decision is added into a broadcast message  160  to inform the two SSs  120 ,  130 , and unique connection IDs (CIDs) are assigned to the first SS  120  and the second SS 130  respectively as a reference to distinguish the two different SSs  120 ,  130 . In the IEEE 802.16 system, the BS  110  control all the wireless resource distributions, for distributing the wireless resource to each SS  120 ,  130  in a manner of time division duplex (TDD), and the BS  110  also may periodically send a broadcast message to the SSs  120 ,  130 , for informing the SSs  120 ,  130 , regarding data transmission  150 , of when data can be uploaded and when data must be received.  
         [0008]     As shown in  FIG. 2   a , it is a schematic diagram of a scheduling architecture of a frame  20 . According to the IEEE 802.16 system, one or more UpLink burst (UL Burst) time slots in the UpLink SubFrame (UL SubFrame)  210  are required by the SSs  120 ,  130  to upload data, and one or more DownLink Burst (DL Burst) time slots in the DownLink SubFrame (DL SubFrame)  220  are required by the SSs  120 ,  130  to receive data. Such a data distribution manner will cause the following situations when a same data is switched between the two SSs  120 ,  130 , as shown in  FIG. 2   b  and  2   c : in  FIG. 2   b , an SS A, and an SS C upload the “A→B data” and “C→D, E data” to the BS  110  in the nth frame respectively, while in  FIG. 2   c , an SS B, an SS D, and an SS E receive the “A→B data” and “C→D, E data” from the BS  110  in the (n+1)th frame respectively. And in such a manner, one or even multiple UL Burst time slots and one or more DL Burst time slots will be tied up more than normally, and data will appear in repeat in the UL SubFrame  210  and the DL SubFrame  220 , thus wasting wireless resources. And the BS  110  should receive and transmit data between the two SSs  120 ,  130 , and its loading is relatively heavy when the transmission is frequent.  
       SUMMARY OF THE INVENTION  
       [0009]     In view of the above problems, an object of the present invention is to provide a method for direct linking in a wireless communication system, by improving the scheduling mechanism of a BS, in which owing to that without changing SS specifications, the BS of the present invention may accept connection requests from more SSs, overall service efficiency of wireless resources can be raised, further reducing the distribution density of BSs, allowing for reduced operating costs.  
         [0010]     Therefore, to achieve the above object, a method for direct linking in a wireless communication system is disclosed by the present invention. It is applied in a time division duplex (TDD) BS with broadcast function, and a plurality of SSs is under the control of the BS, wherein each SS has a positioning device for obtaining position information of the SS. The method for achieving the direct link comprises the following steps:  
         [0011]     First, the BS may receive connection request signalings issued by a plurality of SSs respectively, wherein each connection request signaling includes position information of the SS.  
         [0012]     Then, the BS may determine whether, in each connection request signaling, there is at least one set of a plurality of SSs which can carry out the direct link, i.e. one transmitting SS requesting transmission of a data, and at least one receiving SS requesting reception of such a data.  
         [0013]     If the determination is yes, the BS may allocate a plurality of time slots to each set of SSs which can carry out the direct link in the scheduling, to carry out data transmission of the UL Burst and the DL Burst.  
         [0014]     Then, the BS may calculate a relative distance between the two according to the position information corresponding to each SS in the set.  
         [0015]     Next, after calculation, the BS may determine an initial transmit power of the transmitting SS according to such a relative distance.  
         [0016]     And the BS may perform the try and error with the SS many times to confirm. whether data are received normally, and then adjust according to the receiving state, and finally, add an adjusted transmit power for direct link of the transmitting SS and a plurality of time slots for direct link distributed in such a scheduling into a next broadcast message.  
         [0017]     The features and practices of the present invention are illustrated by a most preferred embodiment with reference to accompanying drawings as follows.  
         [0018]     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein:  
         [0020]      FIG. 1  is a schematic diagram of a conventional transmission manner in the IEEE 802.16;  
         [0021]      FIG. 2   a  is a schematic diagram of a scheduling architecture of a conventional frame;  
         [0022]      FIG. 2   b  is a schematic diagram of a scheduling architecture of the conventional frame according to a first embodiment;  
         [0023]      FIG. 2   c  is a schematic diagram of a scheduling architecture of the conventional frame according to a second embodiment;  
         [0024]      FIG. 3  is a schematic diagram of a transmission manner according to the present invention;  
         [0025]      FIG. 4   a  is a flow chart of the method according to the present invention;  
         [0026]      FIG. 4   b  is a flow chart for terminating the direct link according to the present invention;  
         [0027]      FIG. 5   a  is a schematic diagram of a scheduling architecture of a frame disclosed in the present invention; and  
         [0028]      FIG. 5   b  is a schematic diagram of a scheduling architecture of a frame disclosed in an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     A method for direct link in a wireless communication system will be disclosed in the present invention. In the following detailed illustration of the present invention, many particular details will be described to provide an integral description of the present invention. However, those skilled in the art may implement the present invention without using the particular details, or by using alternative elements or methods. In other cases, the known methods, procedures, parts, and circuits are not illustrated in detail to avoid unnecessary confusion regarding the emphases of the present invention.  
         [0030]     The present invention is to improve the situation of wasting of wireless resources and over loading of the BS  110  caused by the conventional technology. Referring to  FIG. 3 , it is a schematic diagram of a transmission manner disclosed in the present invention, wherein compared with the  FIG. 1  of the conventional manner, the SSs  120 ,  130  of the present invention have a global positioning systems (GPSs) whose GPS antennas may receive position information  310 ,  320  from many satellites  180  in space or other positioning devices, for example devices for positioning in a trilateration manner by using the BS signal, positioning according to identifiers on a diagram, or positioning by cellular technology, etc., to obtain the current position of each SS.  
         [0031]     Supposing the position information  310  of the first SS  120  is (Xa, Ya), and the position information  320  of the second SS  130  is (Xb, Yb). Referring to  FIG. 4   a , it is a flow chart of the method disclosed by the present invention. When the SSs  120 ,  130  put forward a connection request signaling  340  to the BS 1   10 , its individual position information  310 ,  320  may be added into the connection request signaling  340  (Step  410 ). The BS  110  may know which SSs  120 ,  130  need to carry out the UL Burst time slot and the DL Burst time slot from the connection ID (CID) after receiving these connection request signalings  340 , wherein the connection request signaling  340  put forward by the SS of the UL Burst, supposed to be the first SS  120 , comprises the CID regarding to which SS to transmit data. For example, in  FIG. 2   b  of the conventional art, “A→B data” is the UL Burst  230  put forward by the SS A, while “A→B data” in  FIG. 2   c  is a DL Burst  235  put forward by the SS B, and similarly, “C→D, E data” in  FIG. 2   b  is a UL Burst  240  put forward by the SS C, while “C→D, E data” in  FIG. 2   c  is a DL Burst  245  put forward by the SS D and the SS E.  
         [0032]     According to these information of transmitting data, the BS  110  may determine that the SS A and the SS Blare of a set of SSs  120 ,  130  which can carry out the direct link  170  (Step  420 ), while the SS C and the SSs D, E together are also a set. However, on the scheduling mechanism of the TDD, two frames  20  must be used, wherein in the first frame  20 , the BS  110  is used to receive the data uploaded by the SS of the UL Burst, and the uploaded data are not transmitted to the SS of the DL Burst until the second frame  20  has been reached, such is the heart of the conventional problem.  
         [0033]     Therefore, the present invention is to solve such a problem. Referring to  FIG. 5   a , it is a schematic diagram of a scheduling architecture of the frame  20  disclosed in the present invention. Similarly, compared with  FIG. 2   a  of the conventional manner, the scheduling mechanism of the present invention further comprises an intersected DirectLink SubFrame  250 , besides the previous sub-frame of the broadcast message  160 , a UL SubFrame  210  and a DL SubFrame  220 , wherein each sub-frame is cut equally into a plurality of time slots, and the cutting number depends on the number of SSs requesting data transmission, and each time slot in the DirectLink SubFrame  250  is allocated to each set of SSs  120 ,  130  which can carry out the direct link  170  (Step  430 ), wherein each set includes a transmitting SS and at least one receiving SS.  
         [0034]     Each SS will add individual position information  310 ,  320  to a connection request signaling  340  when putting forward it. Therefore, the BS  110  can calculate a relative distance between the two SSs  120 ,  130  which can carry out the direct link  170 , and calculates an initial transmit power required for transmitting data by a transmitting SS corresponding to such a relative distance. If more than one receiving SS receive the same data, the transmitting SS of the data may transmit by an initial transmit power corresponding to the one with the longest distance among the receiving SSs (Step  440 ).  
         [0035]     Finally, the BS  110  may add the time slot information allocated in the scheduling and an initial transmit power value required by the transmitting SS into the broadcast message  360  sent to each SS  120 ,  130  (Step  450 ); as shown in  FIG. 5   b , the SS A may obtain the initial transmit power value required for transmitting to the SS B after receiving the broadcast message  360  sent by the BS  110 , and transmit the “A→B data” to the SS B in the first time slot of the DirectLink SubFrame  250 , and the SS B also receives the “A→B data” in the first time slot of the DirectLink SubFrame  250  according to the scheduling information in the broadcast message  360 .  
         [0036]     Similarly, the SS C may obtain an initial transmit power value required for emitting over a longer distance when transmitting to the SSs D, E after receiving the broadcast message  360  sent by the BS  110 , and transmits the “C→D, E data” to the SSs D, E in the second time slot of the DirectLink SubFrame  250 , and the SSs D, E also receive the “C→D, E data” in the second time slot of the DirectLink SubFrame  250  respectively, according to the scheduling information in the broadcast message  360 .  
         [0037]     Referring to  FIG. 4   b , the receiving SS will transmit a response message of the data transmission result to the BS  110  (Step  510 ) after receiving a single data, for example, a receiver signal strength indicator (RSSI) value, a bit error rate (BER), a packet error rate (PER), and other types of response messages. When any one of the response messages received from the receiving SS is lower than a respective predetermined threshold, the BS  110  alters a modulation mode or a channel coding mode of the two SSs  120 ,  130 , and then carries out the try and error many times (Step  520 ) and determines whether to terminate the direct link  170  (Step  530 ).  
         [0038]     If it is determined that the transmission still fails after many adjustments, for example, the RSSI is always lower than the predetermined first threshold, the BER is always higher than the predetermined second threshold, the PER is always higher than the predetermined third threshold, or the adjusted transmit power of the transmitting SS has exceeded a maximum transmit power of the transmitting SS, the two SSs  120 ,  130  which were previously determined to be able to carry out the direct link  170  cannot transmit data in the manner of direct link  170 , and must still transmit or receive data in a conventional manner (Step  540 ).  
         [0039]     Comparing  FIG. 2   a  of the conventional manner with  FIG. 5   a  of the present invention, it can be discovered that although in a scheduling of the BS  110 , a frame  20  is averagely divided into  8  time slots including a broadcast message  160 , the BS  110  may perform data transmission service for  7  SSs simultaneously in the conventional manner, while for  FIG. 5   a  of the present invention, the BS  110  may serve  10  SSs simultaneously. For a further comparison, supposing a BS  110  may divide a frame  20  into n time slots in the conventional manner, it may perform data transmission service for n−1 SSs in n−1 time slots in a most preferred case, except a time slot used as the broadcast message  160 , while through the present invention, it may serve 2(n−1) SSs in n time slots in the most preferred case, which is two times that of the conventional manner, such that the service efficiency of the BS  110  is increased indeed.  
         [0040]     Through the scheduling mechanism of the BS disclosed in the present invention, without any need to change the specification of the SS, the BS of the present invention may accept connection requests from more SSs simultaneously, raising the overall service efficiency of wireless resources, shortening the transmission time of each SS, and further reducing distribution density of the BS, thereby cutting down the operating cost.  
         [0041]     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.