Abstract:
A scheduling technique for wireless multihop relay communication systems is provided. With spatial separation caused by the shadowing effect of surrounding buildings, a base station and its relay stations in a single cell are divided into several groups by following the rule that stations with severe potential interference are separated into different groups. The base station arranges the scheduling of these groups and serves these groups sequentially in the time domain. To take advantage of shadow effect, the same radio resources can be scheduled for relay stations within the same group due to the isolation of interfering signals. In the present invention, base stations and relay stations are equipped with directional antennas or sector antennas to further exploit the advantage of spatial separations. Different relay groups can also reuse the radio resource through appropriate power control. The cell capacity can be enhanced substantially because of aggressive radio resource reuse.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 95137676, filed Oct. 13, 2006. All disclosure of the Taiwan application is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for grouping relay stations in a wireless multi-hop relay communication system and a system thereof. More particularly, the present invention relates to a scheduling method for a wireless multi-hop relay communication system for improving the transmission efficiency and capacity of the system. 
     2. Description of Related Art 
     Next generation mobile communication systems are envisioned to provide high-speed, high link quality, and high security transmissions, and are also expected to support various communication services. An effective resource schedule/allocation method has to be established to meet different quality of service (QoS) requirements from different users. Users located at cell boundary have worse link quality due to the long transmission distance to the base station, and users in the cell with severe shadowing effect also have worse link quality, thereby the foregoing users cannot perform high-speed data transmissions. To resolve the foregoing problem, the deployment density of base stations can be increased to shorten the propagation distances between the base stations and users so as to improve the link quality; or more base stations can be deployed at those areas with severe shadowing for improving the link quality of users in the areas. However, the cost of the base stations and the cost of the backhaul network connections will be substantially increased by the aforementioned method. On the other hand, the transmission power of the base station can be increased to improve the link quality and to reduce the cost of the base station. However, if the transmission power is increased, not only the transmission cost will be increased but also the interference level will be increased. 
     Multi-hop relay cell architecture is a good solution when considering all factors such as QoS, deployment cost, transmission power, and coverage area of the cell. Relay stations can be deployed within a cell to relay information from a base station to mobile stations with worse link quality, and vise versa. It has been shown that using relay stations may improve cell coverage, user throughput and system capacity. 
     Relay stations may be deployed at areas with severe shadowing or near the cell boundary, the users who can not be directly served by base station may be served by the relay stations, therefore the effective coverage area of the base station can be extended. 
     A single link with worse quality is divided into a plurality of links with better quality so that each of the links can provide higher transmission rate. However, since the same data will be duplicated and relayed over the air multiple times for multi-hop transmissions, it consumes the radio resources. 
     Besides, since there are a base station and several relay stations in a cell, to improve the spectrum efficiency, multiple serving stations may be active simultaneously if the potential interference is tolerant. 
     To obtain benefits for multi-hop relay communication systems, an efficient scheduling mechanism is required to arrange the transmissions of base stations and relay stations. 
     To improve the performance of a wireless communication system, a method of relay stations deployment in a Manhattan-like environment was provided in the Wireless World Initiative New Radio (WINNER) program. The Manhattan-like environment is a grid environment wherein the width of blocks is about 200 m and the width of streets is about 30 m. 
       FIG. 2  illustrates a first layout of relay stations in a Manhattan-like environment, wherein a base station  205  and four relay stations  201 ˜ 204  are disposed, and the base station and the relay stations all communicate with users through omni-directional antennas. However, since the relay stations are disposed outside of the coverage area  206  of the base station, each relay station requires an additional directional antenna pointing at the base station for communicating with the base station, and which increases the hardware cost of the relay stations. 
       FIG. 3  illustrates the transmission scheduling in such structure, wherein frame structures are transmitted within a single cell. The frame S 301  may be divided into two sub-frames S 302 ˜S 303 . The first sub-frame S 302  is further divided into 5 time slots S 304 ˜S 308 , wherein the base station  305  serves the 4 relay stations  301 ˜ 304  during the first 4 time slots S 304 ˜S 307  respectively and the base station  305  serves users within area  306  which is directly connected to the base station during the fifth time slot S 308 . The second sub frame S 303  is divided into two time slots S 309 ˜S 310 , and with the characteristics of spatial separation of the environment, the relay stations  301  and  302  serve users within the areas  307  and  308  connected thereto during the same time slot S 309 , and the relay stations  303  and  304  serve users within the areas  309  and  310  connected thereto during another time slot S 310 . 
       FIG. 4  illustrates the layout of relay stations in a multi-cell structure, wherein the coverage area  406  of a single cell A and the coverage area  416  of a single cell B are arranged in a staggered way. The base stations  405  and  415  in  FIG. 4  respectively represent the positions of the base stations in cell A and cell B. The relay stations  401 ,  402 ,  403 , and  404  belong to cell A, and the relay stations  411 ,  412 ,  413 , and  414  belong to cell B. The arrangement of transmission frames thereof is shown in  FIG. 5 , wherein the arrangement of transmission frames between adjacent cells is to permute the operation orders of the sub-frames S 502 ˜S 503  in a frame S 501  so that interference between cells can be prevented. The main purpose of the relay stations is to extend the coverage area of the base station, however, the link quality of users at the boundary of the service range of the base station cannot be improved. Besides, all the base station are idled for some time durations in the frame structure, since base stations are the only serving stations connected to the backhaul networks and carrying the effective data, the transmission efficiency of the base station in this design is not ideal. 
       FIG. 6  illustrates the second layout of a base station  605  and four relay stations  601 ˜ 604  in a Manhattan-like environment, wherein the base station and the relay stations all communicate with users by using omni-directional antennas. Since the relay stations  601 ˜ 604  are disposed within the coverage area  606  of the base station, no additional directional antenna is required by each relay station for communicating with the base station and in the design, the link quality of users in the cell boundary can be improved. 
     In this layout with all serving stations equipped with omni-directional antennas, the feasible transmission scheduling is shown as  FIG. 7 .  FIG. 7  illustrates the transmission frame structure in a single cell, wherein the base station  705  respectively serves the four relay stations  701 ˜ 704  sequentially during the first four time slots S 701 ˜S 704 , and at the same time, the base station  705  serves users directly connected to the base station  705 . The relay stations  701  and  703  serve users connected thereto during the time slot S 705 . After that, the relay stations  702  and  704  serve users during the next time slot S 706 . The main purpose of such a layout is to improve the link quality of users at cell boundary; however, a complete transmission within a single cell requires at least 6 phases to be completed. When considering the multi-cell structure, because of the use of omni-directional antennas, the reuse factor of at least 2 is required to avoid the severe inter-cell interference, and thus decreases the overall system capacity. 
     Regardless of the first layout or the second layout that all serving stations are equipped with omni-directional antennas, all the base station and the relay stations are idled for some time in the frame structure, thus, the transmission efficiency thereof is not ideal. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a transmission scheduling method for a wireless multi-hop relay communication system, wherein relay stations are disposed within the coverage area of a base station for serving users with poor link quality to the base station. In the present invention, base stations and relay stations are equipped with directional antennas or sector antennas to further exploit the advantage of spatial separations inherited in the environment, and through the mechanism of grouping and permutation of transmission scheduling, interference inside a single cell and between adjacent cells is reduced, accordingly, the capacity of the system is improved. 
     The present invention provides a transmission scheduling method for a wireless multi-hop relay communication system. The wireless communication system includes at least one base station and at least one relay station. The transmission scheduling method includes following steps. Each of the relay stations measures the intensity of potential interference level from other relay stations and reports the measurement result to the base station. The base station separates the relay stations into N groups according to the potential interference levels, wherein N is an integer greater than 0 and the smaller the value of N is, the better. The relay stations are separated based on such a rule that those relay stations having potential interference level within a tolerable intensity range are put into the same group, and the relay stations in the same group can transmit data by reusing the same radio resources. If the relay stations are separated into N groups, N phases are considered a service period in the transmission scheduling mechanism. The base station determines the service order of the groups. The base station serves the relay stations in the j th  group during the i th  phase of a service period, wherein 1≦i, j≦N. Relay stations not in the j th  group serve users within the coverage areas with appropriate power control thereof during the i th  phase of the service period. 
     The transmission scheduling mechanism in the present invention is described as follows with time division duplex access as example. When a base station serves the relay stations of a particular group with directional antennas or sector antennas, the relay stations of other groups which are not served by the base station during this period serve users within their coverage areas by appropriate power control. According to the transmission scheduling mechanism, users of different groups can have time division multiple accesses with divisions in the time domain, while the relay stations within the same group can reuse the radio resources at the same time and on the same frequency through the characteristic of spatial separation, so that the transmission efficiency and the capacity of the system can be improved. 
     In a multi-cell structure, transmission scheduling between adjacent cells can be achieved by permuting group service order of the transmission scheduling of single cells. As to any two adjacent cells A and B, when the base station in cell A serves a particular group j in cell A during the i th  phase, the base station in the adjacent cell B serves another group k in cell B which has less interference to group j in cell A during the i th  phase, thus, high spectrum efficiency and high transmission efficiency of the system can be achieved. 
     In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, a preferred embodiment accompanied with figures is described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a flowchart of an actual implementation of the present invention. 
         FIG. 2  illustrates the first setup of a base station and a plurality of relay stations of a single cell in a Manhattan-like environment according to a conventional technique. 
         FIG. 3  illustrates the transmission frame structure within a single cell of the first setup in a Manhattan-like environment according to a conventional technique. 
         FIG. 4  illustrates the setup of base stations and relay stations of multiple cells of the first setup in a Manhattan-like environment according to a conventional technique. 
         FIG. 5  illustrates the transmission frame structure between multiple cells of the first setup in a Manhattan-like environment according to a conventional technique. 
         FIG. 6  illustrates the second setup of a base station and a plurality of relay stations with omni-directional antennas in a Manhattan-like environment according to a conventional technique. 
         FIG. 7  illustrates the transmission frame structure within a single cell of the second setup with all serving stations equipped with omni-directional antennas in a Manhattan-like environment. 
         FIG. 8  illustrates the setup of a base station and a plurality of relay stations with directional antennas or sector antennas according to an exemplary embodiment of the present invention. 
         FIG. 9  illustrates the first phase of transmission scheduling for uplink transmission and downlink transmission within a single cell according to an exemplary embodiment of the present invention. 
         FIG. 10  illustrates the second phase transmission scheduling for uplink transmission and downlink transmission within a single cell according to an exemplary embodiment of the present invention. 
         FIG. 11  illustrates the first phase transmission scheduling for uplink transmission and downlink transmission between adjacent cells according to an exemplary embodiment of the present invention. 
         FIG. 12  illustrates the second phase transmission scheduling for uplink transmission and downlink transmission between adjacent cells according to an exemplary embodiment of the present invention. 
         FIG. 13  illustrates the operations of single cell transmission scheduling during various phases according to an exemplary embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following embodiments will be described with a Manhattan-like environment as an example, and those having ordinary knowledge in the art should be able to implement the present invention in any other environment according to the spirit of the present invention and the descriptions of the following embodiments. In following embodiments, interference level is weakened by spatial separation produced by the shadowing effect of surrounding buildings in a Manhattan-like environment. 
       FIG. 8  illustrates the layout of relay stations in a Manhattan-like environment according to an embodiment of the present invention. Referring to  FIG. 8 , a microcell covers 690*690 square meters, and the base station  805  is disposed at a crossroad and four relay stations  801 ,  802 ,  803 , and  804  are disposed at intersections of the two crossed streets with other streets in four directions, which is, the relay stations  801 ˜ 804  are disposed at the intersections of the line of sight (LOS) and the non line of sight (NLOS) of the base station  805 . 
     The base station  805  uses four directional antennas or a four-sector antenna for transmitting data to users in the streets in four directions and the relay stations  801 ˜ 804 , and the relay stations  801 ˜ 804  use two directional antennas or two-sector antennas for data transmission with users within the NLOS of the base station  805 . In other words, the base station  805  and four relay stations  801 ˜ 804  serve all users within the coverage area  811  of a cell. Wherein users within the LOS of the base station can have single-hop links to the base station, while users outside of the LOS of the base station can establish multi-hop links to the base station through the relay stations. 
       FIG. 1  illustrates the detailed implementation flow of the present invention. First, after the base station  805  and the relay stations  801 ˜ 804  are started up in step S 101 , the relay stations  801 ˜ 804  respectively measure the intensities of interference level from other relay stations and the base stations in step S 102 , wherein the potential interference level may be measured by measuring the data signal or the reference signal transmitted by the relay stations and base stations respectively. In step S 103 , the relay stations  801 ˜ 804  report the measurement results thereof back to the base station  805 . Next, the base station  805  separates the relay stations  801 ˜ 804  into groups according to the measurement results reported by the relay stations  801 ˜ 804 . The base station  805  separates those relay stations which may potentially go beyond a tolerable interference threshold into different groups. For example, relay station  801  and relay station  803  are put into group A, while relay station  802  and relay station  804  are put into group B. Or, if the transmission target of one of the relay stations  801 ˜ 804  is another relay station and the target relay station cannot receive and send data at the same time, the two relay stations are put into different groups. The smaller the number of groups is the better. 
     In step S 104 , the base station  805  arranges transmission scheduling of the relay stations  801 ˜ 804  after the relay stations  801 ˜ 804  are grouped. Wherein the number of groups is considered as the number of phases in a service period for transmission scheduling. Finally, in step S 105 , the base station  805 , the relay stations  801 ˜ 804 , and the users start to communicate with each other. 
     In the present embodiment, if the number of groups is N, then a service period of a complete transmission scheduling can be divided into N phases, and downlink transmission and uplink transmission are contained in each phase. The foregoing one service period may be the length of a frame and the frame is divided into N phases, while the foregoing one service period may also be the length of a plurality of frames and the frames are divided into N phases all together. The downlink and uplink transmissions during various phases in a frame are arranged according to the definition of the frame, for example, the downlink and uplink transmissions during various phases may be arranged alternatively, or the downlink transmission of various phases are arranged first and then the uplink transmissions thereof are arranged. While the arrangement of downlink and uplink transmission is not limited by the present invention. In the present embodiment, the relay stations  801 ˜ 804  are separated into 2 groups, accordingly, a service period is divided into 2 phases. 
     During the first phase, as shown in  FIG. 9 , the base station  905  serves the relay stations  901  and  903  in the first group (referred to as group A thereinafter) and users within the LOS  906 ˜ 907  of the base station  905  in the direction of group A. The operations of the base station serving the group A include downlink transmission and/or uplink transmission. 
     The downlink transmission refers to that the base station  905  transmits data to the relay stations  901  and  903  in group A and to users within the LOS  906 ˜ 907  of the base station  905  in the direction of group A. During the same phase, the relay station  902  in the second group (referred to as group B thereinafter) relays the data received from the base station  905  during the previous phase to users within the NLOS of the base station and within the LOS  908 ˜ 909  of group B, and the relay station  904  in group B relays the data received from the base station  905  during the previous phase to users within the NLOS of the base station and within the LOS  910 ˜ 911  of group B. Moreover, according to the actual requirement, those having ordinary knowledge in the art would also be able to make the base station  905  to serve users within the service areas  912 ˜ 913  around the base station  905  and in the direction of group B with appropriate power control by lower transmission power during the first phase. Wherein, the lower transmission power allows the interference generated by the base station to the relay stations to be lower than a tolerable threshold. 
     The uplink transmission refers to the relay stations  901  and  903  in group A and users within the LOS  906 ˜ 907  of the base station  905  in the direction of group A transmit data to the base station  905 . During the same phase, the relay station  902  in group B receives the uplink data from users within the areas  908  and  909 , and the relay station  904  in group B receives the uplink data from users within the areas  910  and  911 . Moreover, according to the actual requirement, those having ordinary knowledge in the art would be able to make users within the service areas  912  and  913  around the base station  905  and in the direction of group B to transmit uplink data to the base station  905  during the first phase. 
     During the second phase, as shown in  FIG. 10 , the base station  905  serves the group B and users within the LOS  1006  and  1007  of the base station  905  in the direction of group B. The operation of the base station  905  serving the group B includes downlink transmission and/or uplink transmission. 
     The downlink transmission during the second phase refers to the base station  905  transmitting data to the relay stations  902  and  904  in group B and users within the LOS  1006  and  1007  of the base station  905  in the direction of group B. During the same phase, the relay stations  901  and  903  in group A respectively relay the data received from the base station  905  during the previous phase to users within the NLOS of the base station and within the LOS  1008 ˜ 1009  and  1010 ˜ 1011  of group A. Moreover, according to the actual requirement, those having ordinary knowledge in the art would be able to make the base station  905  to serve users in the service areas  1012  and  1013  around the base station  905  and in the direction of group A with appropriate power control by lower transmission power during the second phase. 
     The uplink transmission during the second phase refers to the relay stations  902  and  904  in group B and users within LOS  1006  and  1007  of the base station  905  in the direction of group B transmit data to the base station  905 . During the same phase, the relay station  901  in group A receives the uplink data from users in areas  1008  and  1009 , and the relay station  903  in group A receives the uplink data from users within areas  1010  and  1011 . Moreover, according to the actual requirement, those having ordinary knowledge in the art would be able to make users within the areas  1012  and  1013  to transmit uplink data to the base station  905  during the second phase. 
     In a multi-cell structure, the service orders of transmission scheduling of two adjacent cells are permuted with interferences between cells and the signal quality of users at cell boundary in consideration, as shown in  FIG. 11 . Wherein the cells adjacent to cell A (coverage area  1106 ) in four directions are cell B (coverage area  1116 ), cell C (coverage area  1126 ), cell D (coverage area  1136 ), and cell E (coverage area  1146 ). A base station  1115  and relay stations  1111 ˜ 1114  are disposed in the coverage area  1116  of cell B; a base station  1125  and relay stations  1121 ˜ 1124  are disposed in the coverage area  1126  of cell C; a base station  1135  and relay stations  1131 ˜ 1134  are disposed in the coverage area  1136  of cell D; and a base station  1145  and relay stations  1141 ˜ 1144  are disposed in the coverage area  1146  of cell E. In the present embodiment, the service orders of cells B˜E are assumed to be the same. Accordingly, only cell B will be described below as an example. 
     Within the coverage area  1106  of cell A, when the base station  1105  serves the relay stations  1101  and  1103  in group A and users within the LOS of the base station  1105  in the direction of group A (i.e. the group A which performs single cell transmission scheduling), the adjacent base stations in four directions, for example, the base station  1115  in the coverage area  1116  of cell B, serves the relay stations  1112  and  1114  in group B and users in the LOS of the base station  1115  in the direction of group B (i.e. the group B which performs single cell transmission scheduling). Meanwhile, the relay stations  1102  and  1104  in group B within the coverage area  1106  of cell A and the relay stations  1111  and  1113  in group A within the coverage area  1116  of cell B perform data transmission (serving users). In the present embodiment, the base stations  1105  and  1115  respectively transmit data to users within areas  1107 ˜ 1108  and  1117 ˜ 1118  with lower transmission power. 
       FIG. 12  illustrates the operations during the next phase. Within the coverage area  1106  of cell A, when the base station  1105  serves the relay stations  1102  and  1104  in group B and users within the LOS of the base station  1105  in the direction of group B, the adjacent base stations in four directions, for example, the base station  1115  in the coverage area  1116  of cell B, serves the relay stations  1111  and  1113  in group A and users within the LOS of the base station  1115  in the direction of group A. Meanwhile, the relay stations  1101  and  1103  in group A within the coverage area  1106  of cell A and the relay stations  1112  and  1114  in group B within the coverage area  1116  of cell B perform data transmission (serving users). In the present embodiment, the base stations  1105  and  1115  respectively transmit data to users within areas  1207 ˜ 1208  and  1217 ˜ 1218  with lower transmission power. 
       FIG. 13  illustrates the operations of transmission scheduling during various phases of a single cell. Referring to  FIGS. 9 ,  10 , and  13 , the operations S 1311  and S 1312  during the first phase S 1310  of single cell transmission scheduling include the base station  905  serving the relay stations  901  and  903  in group A and users within area  906 ˜ 907 . During the same phase, the operations S 1313  and S 1314  of a single cell transmission scheduling S 1310  include the relay stations  902  and  904  in group B respectively serving users within areas  908 ˜ 909  and areas  910 ˜ 911 . Moreover, according to the actual requirement, those having ordinary knowledge in the art may also make the operations S 1315  and S 1316  during the first phase S 1310  of a single cell transmission scheduling to be the base station serving users within areas  912 ˜ 913 . 
     The operations S 1323  and S 1324  during the second phase S 1320  of a single cell transmission scheduling include the base station  905  serving the relay stations  902  and  904  in group B and users within areas  1006 ˜ 1007 . During the same phase, the operations S 1321  and S 1322  of the single cell transmission scheduling are that the relay stations  901  and  903  in group A respectively serve users within areas  1008 ˜ 1009  and areas  1010 ˜ 1011 . Moreover, according to the actual requirement, those having ordinary knowledge in the art may also make the operations S 1325  and S 1326  during the second phase S 1320  of a single cell transmission scheduling to be the base station serving users within areas  1012 ˜ 1013 . 
     In a multi-cell structure, the service orders of the transmission scheduling in the frame structures of two adjacent cells are permuted with interferences between cells and the signal quality of users at cell boundary in consideration. 
     Table 1 shows related comparisons between the present invention and the conventional technique. Wherein the “frequency reuse factor” shows the proportion of usable frequency of a single cell to the usable frequency of the system; since a base station is the only serving station connected to the backhaul network in a cell, the “effective frame” shows the number of frames a base station receives and sends during a service period; and the “capacity gain” is the gain obtained with the “frequency reuse factor” and the “effective frame” in consideration. The present invention is compared to the second setup in the WINNER&#39;s design with all serving stations equipped with omni-directional antennas of the same coverage areas. “Design 1 of the present invention” is the design wherein the base station does not serve users around the base station with lower transmission power, and “design 2 of the present invention” is the design wherein the base station serves users around the base station with appropriate power control by lower transmission power. 
     In the second setup in the WINNER&#39;s design with all serving stations equipped with omni-directional antennas, data has to be transmitted between adjacent cells on different frequencies to prevent interference between two adjacent cells, thus, the “frequency reuse factor” thereof is ½. In this design, 6 phases are needed to complete downlink transmission and/or uplink transmission, the actual number of frames transmitted by the base station is 4, thus, the “effective frame” is ⅔. 
     According to the present embodiment, in the first design of the present invention, data is transmitted on the same frequency between adjacent cells, thus, the “frequency reuse factor” thereof is 1. And during the two phases of a complete downlink transmission, the base station actually transmits 4 frames, thus, the “effective frame” thereof is 2, and uplink transmission is similar to downlink transmission. Besides, if it is assumed that the “capacity gain” of the second setup in the WINNER&#39;s design with all serving stations equipped with omni-directional antennas is 1, then the first design of the present invention excels 2 times in the usage of frequency spectrum and the “effective frame” of the first design of the present invention is 3 times of those of the second setup in the WINNER&#39;s design with all serving stations equipped with omni-directional antennas, thus, the “capacity gain” is 6. 
     In the second design of the present invention, since data is transmitted on the same frequency between adjacent cells, thus, the “frequency reuse factor” thereof is 1. During the 2 phases of a complete downlink transmission, the base station actually transmits 8 frames, thus, the “effective frame” is 4, and uplink transmission is similar to downlink transmission. Besides, if the “capacity gain” of the second setup in the WINNER&#39;s design with all serving stations equipped with omni-directional antennas is assumed to be 1, then the first design of the present invention excels 2 times in the usage of frequency spectrum and the “effective frames” of the first design of the present invention is 6 times of those of the second setup in the WINNER&#39;s design with all serving stations equipped with omni-directional antennas, thus, the “capacity gain” is 12. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Comparisons between the present invention and conventional technique 
               
             
          
           
               
                   
                 Frequency reuse 
                 Effective 
                 Capacity 
               
               
                   
                 factor 
                 frames 
                 gain 
               
               
                   
                   
               
             
          
           
               
                 The second setup in the 
                 ½ 
                 ⅔ 
                 1 
               
               
                 WINNER&#39;s design with 
               
               
                 all serving stations 
               
               
                 equipped with 
               
               
                 omni-directional antennas 
               
               
                 Design 1 of the present 
                 1 
                 2 
                 6 
               
               
                 invention 
               
               
                 Design 2 of the present 
                 1 
                 4 
                 12 
               
               
                 invention 
               
               
                   
               
             
          
         
       
     
     In summary, according to the present invention, in a wireless multi-hop relay communication system, the service areas of the base station and relay stations are divided into a plurality of regions by using the shadowing effect of the surroundings. The intensities of interference level are measured by the relay stations and sent to the base station, and the base station separates the relay stations into different groups according to the intensities of potential interference level reported by the relay stations, so that the base station serves the groups sequentially in the time domain. With good isolations of interfering signal due to shadow effect, the same radio resources can be reused and scheduled for different relay stations to substantially improve the system capacity with insignificant interference increment. In a multi-cell structure, universal frequency reuse is achieved by permuting the group service orders of transmission scheduling of adjacent cells. Through the mechanism of grouping and permutation of transmission scheduling, interference inside a single cell and between adjacent cells is prevented and high spectrum efficiency is achieved through aggressive radio frequency reuse. Furthermore, in the transmission scheduling structure provided by the present invention, the base station can transmit data during various phases; thus, the effective cell/system capacity can be improved considerably. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.