Abstract:
A relay method is disclosed in a cellular communication system including an access node for providing an access service using resources of a licensed band to a particular terminal among a plurality of terminals with a partial licensed band of the full frequency spectrum, and a relay station for relaying communication between the terminal and an access node. The relay method includes performing base station-led resource allocation on a licensed band for a terminal and a relay station located in a service area of the base station, and performing relay station-led resource allocation on the licensed band and an unlicensed band for a terminal located in a service area of the relay station.

Description:
PRIORITY  
       [0001]     This application claims the benefit under 35 U.S.C. §119(a) of an application entitled “Relay System and Method for Cellular Communication” filed in the Korean Intellectual Property Office on Jun. 13, 2005 and assigned Serial No. 2005-50472, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to wireless communication, and in particular, to a relay system and method capable of extending a service area and increasing service capacity of a licensed band (LB) system using unlicensed band (UB) resources.  
         [0004]     2. Description of the Related Art  
         [0005]     The development and commercialization of various wireless communication technologies requires new frequency bands that do not overlap licensed bands for the existing wireless communication technology, due to the characteristics of wireless communication based on the limited frequency resources. However, almost every frequency band has now been used.  
         [0006]     Frequency spectra for wireless communication can be divided into licensed bands (LB) and unlicensed bands (UB). A licensed band wireless communication system (hereinafter LB system) includes an analog cellular system based on Advanced Mobile Phone Service (AMPS), a digital cellular system based on Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM), a Digital Cordless Phones (DCT) system, and a Personal Communication Service (PCS) system, while an unlicensed band wireless communication system (hereinafter UB system) includes Bluetooth®, Wireless Local Area Network (WLAN) based on an IEEE 802.11 standard, and Wireless Metropolitan Area Network (WMAN) based on an IEEE 802.16 standard.  
         [0007]     A plan for efficient frequency resource utilization for the next generation wireless communication is currently being discussed, and a standard for utilization of ultra-high frequency (UHF) and very high frequency (VHF) for television (TV) frequencies is now in preparation based on Cognitive Radio (CR) technology, the standard being led by IEEE 802.22 group of Institute of Electrical and Electronics Engineers (IEEE). The CR technology detects unused frequency bands that vary according to region or time, to efficiently utilize the unused frequency bands, and is aimed at efficient utilization of the frequency resources that are increasingly used.  
         [0008]     Up to the present, however, there has been proposed no specific resource management method using the CR technology. The use of the characteristics of the UB resources can contribute to the extension of a service area of the LB system that uses the limited resources, and to an increase in the system capacity through traffic load balancing.  
       SUMMARY OF THE INVENTION  
       [0009]     It is, therefore, an object of the present invention to provide a relay system and method for cellular communication, which can extend a service area and remove a shadow area of a system using a relay station.  
         [0010]     It is another object of the present invention to provide a relay system and method for cellular communication, which can prevent performance deterioration due to a traffic load of an LB system by arranging a relay station supporting UB resources in a cell boundary area or a shadow area.  
         [0011]     According to the present invention, there is provided a relay system in cellular communication wherein for a plurality of terminals requiring frequency resources for communication, an access node allocates resources of a licensed band allocated to a corresponding system in a frequency spectrum pool. The relay system includes at least one relay station, deployed in a cell boundary or a shadow area of the access node, for providing an access service for a base station with separate relay station frequency resources. The relay system includes a global spectrum coordinator for analyzing and managing usage of resources in the frequency spectrum pool, a first regional spectrum coordinator, installed in the base station, for analyzing and managing usage of resources of the licensed band, and a second regional spectrum coordinator, installed in the relay station, for analyzing and managing usage of resources of the unlicensed band. The first and second regional spectrum coordinators generate a licensed band available-resource list and an unlicensed band available-resource list, respectively, and transmit the available-resource lists to the global spectrum coordinator, and the global spectrum coordinator generates a global available-resource list based on the licensed band available-resource list and the unlicensed band available-resource list and transmits the global available-resource list to the base station and the relay station.  
         [0012]     According to the present invention, there is provided a relay method in a cellular communication system including an access node for providing an access service using resources of a licensed band to a particular terminal among a plurality of terminals with a partial licensed band of the full frequency spectrum, and a relay station for relaying communication between the terminal and an access node. The relay method includes performing base station-led resource allocation on a licensed band for a terminal and a relay station located in a service area of the base station, and performing relay station-led resource allocation on the licensed band and an unlicensed band for a terminal located in a service area of the relay station. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:  
         [0014]      FIG. 1  is a diagram illustrating architecture of a relay system according to the present invention;  
         [0015]      FIG. 2  is a diagram illustrating a frequency spectrum pool used in a relay system according to the present invention;  
         [0016]      FIG. 3  is a diagram for a description of an operation performed in an environment in which a relay system according to the present invention and a WLAN system coexist;  
         [0017]      FIG. 4  is a flowchart illustrating a relay method according to the present invention;  
         [0018]      FIG. 5  is a detailed flowchart illustrating the LB resource allocation process of  FIG. 4 ; and  
         [0019]      FIG. 6  is a detailed flowchart illustrating the UB resource allocation process of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0020]     With reference to the accompanying drawings, a description will now be made of a relay system and method for cellular communication according to the present invention. Descriptions of well-known functions and constructions are omitted for the sake of clarity and conciseness.  
         [0021]      FIG. 1  is a diagram illustrating architecture of a relay system according to the present invention. In  FIG. 1 , a service area of a base station  110  that performs communication based on a licensed band (LB) is divided into a first LB service area  101  for low-rate mobility and high-rate data transmission service and a second LB service area  102  for high-rate mobility and low-rate data transmission service. The first LB service area  101  and the second LB service area  102  form their own concentric circles, centering about the base station  110 , and the first LB service area  101  has a smaller radius than that of the second LB service area  102 .  
         [0022]     At least one relay station  130  is arranged in a boundary area or a shadow area of the base station  110 , forming an unlicensed (UB) service area  103 . The UB service area  103  is defined by transmission power of the farthest terminal desiring to communicate with the relay station  130 . In addition, the relay station  130  employs an interference avoidance area having a greater radius than that of the UB service area  103  to avoid interference to its neighbor relay stations, and coverage of the interference avoidance area is defined by broadcasting a beacon frame with transmission power which is a selected amount higher than the transmission power for the UB service area  103 .  
         [0023]     If there is a plurality of neighbor relay stations, the relay station  130  scans UB spectrum channels for the neighbor relay stations to detect the usage of the UB spectrum, and can allocate channels not overlapping with the channels of the neighbor relay stations to its mobile stations.  
         [0024]     Herein, the term “mobile station” refers to a variable-band transceiver communicable in various frequency bands, or a multi-mode multi-band terminal having various system interfaces.  
         [0025]      FIG. 2  is a diagram illustrating a frequency spectrum pool used in a relay system according to the present invention. A spectrum pool  20 , which is an available system frequency band, includes LBs and UBs. The LBs are divided into dedicated LBs  21  allocated to mobile stations  11  located in the first LB service area  101  and shared LBs  22  occupied by the mobile stations located in the second LB service area  102  through contention. The UBs  23  are allocated to the mobile stations located in the UB service area  103  by the relay station  130 .  
         [0026]     For example, the mobile station  11  located in the first LB service area  101  is allocated resources of the dedicated LBs  21 , the mobile station  15  located in the second LB service area  102  is allocated resources of the shared LBs  22 , and the mobile stations  12 ,  13  and  14  located in the UB service area  103  are allocated resources of the UBs  23 . The mobile stations  12  and  13  located in the UB service area  103  may be allocated the resources of the shared LBs  22  according to channel environment, because they are located even in the second LB service area  102 .  
         [0027]     In the present invention, the spectrum pool is divided into two LBs and one UB, and then allocated to mobile stations according to services. The number of LBs and UBs is subject to change according to the type and the number of systems deployed in a corresponding area, and to a resource management policy.  
         [0028]     The relay system according to the present invention further includes global spectrum coordinators (not shown), which are upper network elements, and regional spectrum coordinators (not shown) which are installed in the base station  110  and the relay station  130 . The global spectrum coordinator can be installed in a radio network controller (RNC) or an access point router (APR), or can be arranged as a separate network element.  
         [0029]     The regional spectrum coordinator periodically detects (senses) channel environments of a frequency band used in a corresponding base station or relay station to update a regional available-resource list indicating information on the channels currently available in the corresponding station, and transmits the updated regional available-resource list to the global spectrum coordinator. The global spectrum coordinator analyzes the regional available-resource lists collected from the base station and the relay station to generate a global available-resource list, and broadcasts the generated global available-resource list to the base station and the relay station.  
         [0030]     The regional available-resource list of the relay station can be transmitted to the global spectrum coordinator via the base station, or can be directly transmitted to the global spectrum coordinator over a separate channel. The global available-resource list can be transmitted to the relay station via the base station, or can be directly transmitted to the relay station over a separate channel. Also, the global spectrum coordinator can be installed in the base station. Alternatively, without the global spectrum coordinator, the relay station and the base station can directly exchange the regional available-resource lists with each other to manage the resources.  
         [0031]      FIG. 3  is a diagram for a description of an operation performed in an environment in which a relay system according to the present invention and a WLAN system coexist. The architecture of  FIG. 3  includes a relay system centering about LB-based base stations  310  and  320  whose service areas and frequency spectra are extended by relay stations  317  and  327  supporting UB resources, and a WLAN system centering about UB-based access nodes  330  and  340 .  
         [0032]     In the cellular system, the base stations  310  and  320  have first LB service areas  301  and  303 , and second LB service areas  302  and  304 , respectively, and relay stations  315  and  325  have UB service areas  317  and  327 , respectively. Mobile stations  30  and  34  located in the first LB service areas  301  and  303  are allocated dedicated LB resources  21  under the control of the base stations  310  and  320 , and mobile stations  31 ,  32 ,  36  and  37  located in the overlapping areas between the second LB service areas  302  and  304  and the UB service areas  317  and  327  are selectively allocated shared LB resources  22  or UB resources  23  under the control of the relay stations  315  and  325  according to channel environments. Mobile stations  33  and  35  located in the non-overlapping areas between the second LB service areas  302  and  304  and the UB service areas  317  and  327  are allocated the UB resources  23  by the relay stations  315  and  325 .  
         [0033]     The WLAN access nodes  330  and  340  arranged in the overlapping areas between their service areas and the service areas of the base stations  310  and  320  allocate the UB resources  23  to the terminals  331 ,  332 ,  333 ,  341 ,  342  and  343  in the WLAN service areas  337  and  347  according to a WLAN standard. The access nodes  330  and  340  have Request-to-Send/Clear-to-Send (RTS/CTS) areas  339  and  349  for an RTS/CTS function, and the RTS/CTS areas  339  and  349  are determined by transmission power of an RTS frame from the farthest terminal  313  that can communicate with the access nodes  330  and  340 . When broadcasting a CTS frame in response to the RTS frame, it is preferable for the access nodes  330  and  340  to broadcast the CTS frame with transmission power which is a selected amount higher than the reception power of the CTS frame.  
         [0034]     When the relay stations of the relay system share the UB resources with the WLAN system, there is a need for a scheme for avoiding interference during communication between the relay stations and the mobile stations, and communication between the access nodes and the terminals.  
         [0035]     To this end, the relay station of the relay system and the access node of the WLAN system sense the interference avoidance area of their neighbor relay stations and the RTS/CTS area of the access nodes (in other words, detect beacon frames broadcast from the relay stations and CTS frames broadcast from the access nodes), and allocate the channels which do not interfere with each other, or adjust transmission power for the same channel, thereby avoiding the interference.  
         [0036]     Although the WLAN system is used as a counterpart network of the relay system in the present invention, any UB-based system can be applied to the present invention.  
         [0037]      FIG. 4  is a flowchart illustrating a relay method according to the present invention.  
         [0038]     Referring to  FIG. 4 , upon receiving a resource request from a mobile station located in a UB service area controlled by a relay station  130  in step S 410 , the relay station  130  determines in step S 420  whether the corresponding mobile station is located outside a service area of a base station  110 . If the mobile station is located outside the service area of the base station  110 , the relay station  130  enters a UB resource allocation mode in step S 430 . However, if the mobile station is located inside the service area of the base station  110 , the relay station  130  determines in step S 440  whether there is any available LB resource, based on a global available-resource list received from a global spectrum coordinator or an available LB resource list received from a base station. If it is determined that there is any available LB resource, the relay station  130  enters an LB resource allocation mode in step S 450 . Otherwise, the relay station  130  enters the UB resource allocation mode in step S 430 .  
         [0039]      FIG. 5  is a detailed flowchart illustrating the LB resource allocation process S 450  of  FIG. 4 .  
         [0040]     Referring to  FIG. 5 , the relay station  130  determines in step S 451  whether there is any dedicated LB resource, based on the global available-resource list or the available LB resource list. If there is any dedicated LB resource, the relay station  130  requests the base station  110  to allocate the dedicated LB resource to the corresponding mobile station in step S 452 . However, if there is no available dedicated LB resource, the relay station  130  allocates shared LB resources to the corresponding mobile station in step S 453 . After allocating the dedicated or shared LB resource, the relay station  130  updates a regional spectrum list (regional available-resource list) in step S 454 , and transmits the updated regional spectrum list to the global spectrum coordinator or a regional spectrum coordinator of the base station  110  in step S 455 . In other words, when both of the dedicated LB resource and the shared LB resource are available, the relay station  130  preferentially allocates the dedicated LB resource to the mobile station. When only one of the dedicated LB resource and the shared LB resource is available, the relay station  130  allocates the available resource to the mobile station.  
         [0041]      FIG. 6  is a detailed flowchart illustrating the UB resource allocation process S 430  of  FIG. 4 .  
         [0042]     Referring to  FIG. 6 , upon entry into the UB resource allocation mode, the relay station  130  senses a UB resource channel in step S 431 , and determines in step S 432  whether the channel is in an idle state. If the UB resource is available, the relay station  130  calculates the maximum data transmission power P_data based on reception power from the mobile station in step S 433 , and determines the maximum beacon frame transmission power P_max using the maximum data transmission power P_data in step S 434 . If a UB service area  103  is determined by the maximum data transmission power P_data, an interference avoidance area  105  is determined by the maximum beacon frame transmission power P_max. After determining the maximum beacon frame transmission power P_max, the relay station  130  broadcasts a beacon frame with the maximum beacon frame transmission power P_max in response to the resource request signal received from the mobile station in step S 435 , and allocates the corresponding UB resource to the mobile station in step S 436 . Because the beacon frame includes a unique identifier (ID) of the relay station  130 , the relay station  130  adjusts a size of the UB service area  103  according to whether there is any detected beacon frame from another relay station, and to the transmission power of the beacon frame, if any. In other words, upon receiving a beacon frame broadcast from another relay station, the relay station  130  avoids interference between the relay stations by reducing its own beacon frame transmission power P_max and data transmission power P_data to their minimum allowable levels. In addition, the relay station  130  can transmit information on a flag bit indicating priority in the beacon frame broadcast from another relay station to adjust levels of the beacon frame transmission power and the data transmission power, thereby avoiding the interference between the relay stations.  
         [0043]     Although it is assumed in the present invention that several mobile stations occupy the same UB resource on a contention basis, if there is a plurality of relay stations deployed in one base station, it is also possible to reduce interference between relay stations by allowing the relay stations to employ different channels of the same UB resource.  
         [0044]     In addition, when UB service areas of relay stations overlap each other, a mobile station can perform handoff between relay stations or between a relay station and a base station based on such parameters as required Quality-of-Service (QoS) and priority, and a received signal-to-interference-and-noise ratio (SrNR).  
         [0045]     Further, in an environment where wireless networks using UB resources such as the relay system and the WLAN system are deployed in an overlapping manner, a relay station can share UB resources with the corresponding wireless network.  
         [0046]     Moreover, in the present invention, the UB service areas and the interference avoidance areas can be defined by RTS/CTS using a WLAN contention avoidance mechanism, and the interference avoidance areas are determined by CTS transmission power broadcast by the relay station.  
         [0047]     As described above, the relay system according to the present invention deploys relay stations employing UB resources in cell boundaries or shadow areas of an LB-based base station, thereby extending the total service area and removing the shadow areas.  
         [0048]     Further, the relay system according to the present invention decentralizes control for resource allocation by deploying relay stations in the cell boundaries of the LB-based base station, thus contributing to a reduction in control complexity of the base station and to the guarantee of traffic load balancing.  
         [0049]     In addition, the relay system according to the present invention classifies LB resources into dedicated LB resources and shared LB resources, introduces UB resources, and defines allocation priorities of the resources, to allocate the optimal resources according to traffic environments, thereby contributing to efficient resource management and an increase in the system capacity.  
         [0050]     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.