Abstract:
A wireless communication system in an overlay network where systems using different frequency bands coexist. The wireless communication system includes at least one first duplexing system utilizing a first duplexing technique through a first frequency band, and at least one second duplexing system utilizing a second frequency band and a part of the first frequency band. The second duplexing system overlaps with the first duplexing system in coverage.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. § 119 to an application entitled “Enhanced Hybrid Duplexing Technology-Based Wireless Communication System” filed in the Korean Intellectual Property Office on Dec. 10, 2004 and assigned Serial No. 2004-104127, 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 a wireless communication system, and in particular, to a communication system and method capable of improving resource allocation flexibility and maximizing system performance through enhanced hybrid duplexing technology (EHDT) that selectively uses various duplex modes.  
         [0004]     2. Description of the Related Art  
         [0005]     Next generation wireless communication systems, including the 3 rd  generation (3G) mobile communication system, attempt to support a voice service and multimedia services having various traffic characteristics, e.g., broadcasting and real-time video conference services. In order to efficiently provide the multi-characteristic services, there is a need for a duplexing technique that takes into account the asymmetry and continuity of uplink and downlink transmission according to the service characteristics.  
         [0006]     Generally, the duplexing technique is classified into Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). TDD divides the same frequency band into time periods and alternately switches transmission bands and reception bands, thereby implementing bidirectional communication. FDD divides a given frequency band into transmission bands and reception bands, thereby realizing bidirectional communication.  
         [0007]     In a TDD-based communication system, a base station can allocate all or some of available time slots to a mobile station, and enables asymmetric communication through variable allocation of the time slots. However, in TDD, an increase in cell radius increases a guard interval between transmission and reception time slots due to a round trip delay, thereby reducing transmission efficiency. Therefore, in a communication environment of a cell with a large radius such as a macro cell, it is not preferable to use TDD. In addition, in a multicell environment, because cells are not equal to each other in the asymmetry ratio, TDD causes serious frequency interference between mobile stations located in a boundary between neighbor cells.  
         [0008]     In an FDD-based communication system, because transmission frequency bands are separated from reception frequency bands, there is no time delay for transmission or reception. As a result, there is no need for a round trip delay caused by a time delay, so that FDD is appropriate for a communication environment of a cell with a large radius such as a macro cell. However, FDD is not appropriate as duplexing technology for asymmetric transmission, because transmission frequency bands and reception frequency bands are fixed.  
         [0009]     Accordingly, there is a need to develop hybrid duplexing techniques that use both of the two duplexing schemes in consideration of the various communication environments and traffic characteristics of the next generation wireless communication system.  
         [0010]     However, the conventional hybrid duplexing technique has been proposed for an infrastructure hierarchical network, and does not take into account an overlay system network in which the conventional network overlaps another network.  
         [0011]     More specifically, even though most of a 3G standardization is complete, no detailed method for applying a hybrid duplexing technique has been proposed that takes into account the overlay network in which the next generation systems, which are roughly classified into the 3G system and an ad hoc network, overlap each other, and there is a limitation in applying the conventional hybrid duplexing technique to the overlay network.  
       SUMMARY OF THE INVENTION  
       [0012]     To address the above and other problems, the present invention provides an Enhanced Hybrid Duplexing Technology (EHDT) wireless communication system and method for efficient resource allocation in an overlay network in which different type systems coexist.  
         [0013]     To achieve the above and other objects, a wireless communication system is provided in an overlay network where systems using different frequency bands coexist. The system includes at least one first duplexing system operating based on a first duplexing technique through a first frequency band; and at least one second duplexing system operating using a second frequency band and a part of the first frequency band, the second duplexing system overlapping with the first duplexing system in coverage.  
         [0014]     Additionally, there is provided a wireless communication method in an overlay network where different types of cellular systems for providing a communication service to mobile stations in their coverage area using different frequency bands coexist. The method includes the steps of: receiving, by a current system associated with a mobile station, a request for resource of a different type system from the mobile station; determining if there is available resource of the different type system; determining if the current system is located in a boundary of the different type system, if there is available resource of the different type system; and allocating resources of the different type system to the mobile station, if the current system is not located in a boundary of the different type system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     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:  
         [0016]      FIG. 1  is a schematic diagram illustrating an overlay network to which an EHDT duplexing method according to the present invention is applicable;  
         [0017]      FIG. 2A  is a conceptual diagram illustrating an EHDT duplexing method according to an embodiment of the present invention;  
         [0018]      FIG. 2B  is a system configuration diagram illustrating the EHDT system according to an embodiment of the present invention;  
         [0019]      FIG. 2C  is a conceptual diagram illustrating resource allocation in the EHDT system according to an embodiment of the present invention;  
         [0020]      FIG. 3  is a schematic diagram illustrating a resource sharing technique for an EHDT system according to an embodiment of the present invention;  
         [0021]      FIG. 4  is a flowchart illustrating an EHDT duplexing method according to an embodiment of the present invention;  
         [0022]      FIG. 5  is a conceptual diagram illustrating an EHDT duplexing method according to an embodiment of the present invention;  
         [0023]      FIG. 6  is a resource graph illustrating an FDD mode of an HDT system in an EHDT duplexing method according to an embodiment of the present invention;  
         [0024]      FIG. 7  is a flowchart illustrating an EHDT duplexing method according to an embodiment of the present invention; and  
         [0025]      FIG. 8  is a conceptual diagram illustrating an EHDT duplexing method according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]     Several preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness.  
         [0027]      FIG. 1  is a schematic diagram illustrating an overlay network to which an EHDT duplexing method according to the present invention is applicable. As illustrated in  FIG. 1 , the present invention is applied to a cellular environment in which a cluster of micro cells (or pico cells)  120  are formed within a macro cell  110  with wider coverage on an overlapping basis. Each of the micro cells  120  is divided into an inner region  122  and an outer region  124 .  
         [0028]      FIG. 2A  is a conceptual diagram illustrating an EHDT duplexing method according to an embodiment of the present invention. More specifically,  FIG. 2A  illustrates a hybrid duplexing method using an FDD uplink band  210 , an FDD downlink band  220 , and a newly proposed additional band  230 .  
         [0029]     Referring to  FIG. 2A , the macro cell  110  is implemented with an FDD system that uses the existing FDD uplink resource  210  and downlink resource  220 , and the micro cell  120  is implemented with a hybrid duplexing system that uses the additional TDD resource  230  and the existing FDD uplink resource  210 . That is, the micro cell  120  allocates TDD downlink resource  230   d  and TDD uplink resource  230   u  in the additional band  230  to a mobile station located in the inner region  122 , and allocates the TDD downlink resource  230   d  and the FDD uplink resource  210  to a mobile station located in the outer region  124 .  
         [0030]     In the EHDT system, the FDD uplink resource  210  can be designed such that it separately includes a sharing band shared by the FDD system and a hybrid duplexing system, or borrows FDD uplink resource unused by the FDD system at the request of the HDT system.  
         [0031]      FIG. 2B  is a system configuration diagram illustrating the EHDT system according to an embodiment of the present invention, and  FIG. 2C  is a conceptual diagram illustrating resource allocation in the EHDT system according to an embodiment of the present invention. Referring to  FIGS. 2B and 2C , in an overlay system in which FDD macro cells and HDT micro cells overlap each other, if a mobile station (MS) # 1   251  and a mobile station # 2   252  are located in an inner region  122  of a micro cell  120 , the mobile station # 2   252  is located nearer to an outer region  124  compared with the mobile station # 1   251 , and a mobile station # 3   253  is located in the outer region  124 , the micro cell  120  allocates a slot # 3   233  of TDD downlink resource  230   d  and a slot # 4   234  of TDD uplink resource  230   u  to the mobile station # 1   251 , allocates a slot # 2   232  of the TDD downlink resource  230   d  and a slot # 5   235  of the TDD uplink resource  230   u  to the mobile station # 2   252 , and allocates a slot # 1   231  of the TDD downlink resource  230   d  and FDD uplink resource  240  to the mobile station # 3   253 . The FDD uplink resource  240 , i.e., a part of the FDD uplink resource  210  for a macro cell  110 , is shared by the micro cell  120  and the macro cell  110  or borrowed by the micro cell  120  when necessary.  
         [0032]     In order for the HDT system for the micro cell  120  to share the resources with the FDD system for the macro cell  110  or borrow unused resources of the FDD system, the two systems are connected to a radio network controller (RNC) or a mobile switching center (MSC). Accordingly, the HDT system shares uplink resource information with FDD systems connected to the RNC.  
         [0033]     When an HDT system (micro cell) is located in an FDD system (macro cell), it is possible for the HDT system to share/borrow uplink resources of the same FDD cell. As long as there is no interference, the HDT system can borrow uplink resources for neighbor FDD systems.  
         [0034]     When an HDT system is located in a boundary between two FDD systems, the HDT system determines one FDD system that it desires to use, according to conditions of available uplink resources of neighbor FDD systems, such as positions of mobile stations located in the outer region  124  and signal-to-interference plus noise ratio (SINR) levels, or reception signal levels, for the neighbor FDD systems.  
         [0035]      FIG. 3  is a schematic diagram illustrating a resource sharing technique for an EHDT system according to an embodiment of the present invention. In  FIG. 3 , two FDD systems  310  and  320  and two HDT systems  330  and  340  are deployed, and base stations  311 ,  321 ,  331 , and  341  of the systems are connected to an RNC  390  with a wire network. More specifically, the HDT system  330  is located in a boundary of the FDD system # 1   310  and the FDD system # 2   320 . A mobile station # 1   351 , a mobile station # 2   361 , and a mobile station # 3   371  are located in an outer region of the HDT system  330 , and connected to the HDT base station  331 .  
         [0036]     In this situation, the HDT system # 1   330  shares uplink resources of the FDD system # 1   310 . Therefore, the mobile stations,  351 ,  361 , and  371  transmit signals through the uplink resources of the FDD system # 1   310  with the power requested by the HDT base station  331 . In this case, the uplink signals transmitted by the mobile stations  351 ,  361 , and  371  may interfere with the FDD system # 2   320 .  
         [0037]     In  FIG. 3 , if the mobile station # 1   351 , the mobile station # 2   361 , and the mobile station # 3   371  have the same SINR level, interference of the mobile station # 3   371  to the FDD system # 2   320  is greater than interference of the mobile station # 1   351  and the mobile station # 2   361  to the FDD system # 2   320 . Therefore, the HDT system # 1   330  determines which FDD system&#39;s uplink resources it will use according to SINR levels for neighbor FDD systems of the mobile stations. The mobile stations transmit uplink signals to the HDT base station with power lower than the uplink power used for direct transmission to the FDD base station.  
         [0038]     The EHDT system according to the present invention can reuse uplink resources of another neighbor FDD system as uplink resources for a mobile station located in an outer region of an HDT system. In this case, there is no need for control by the RNC, contributing to a reduction in the amount of control channel information.  
         [0039]     If the FDD system is a Code Division Multiple Access (CDMA) system (interference limited system), an HDT cell can reuse uplink codes used in another FDD system or independently allocate uplink codes. If the FDD system is a Frequency Division Multiple Access (FDMA) or Orthogonal Frequency Division Multiple Access (OFDMA) system (resource limited system), the HDT cell can orthogonally allocate frequency resources (or frequency patterns) allocated to an uplink for the same FDD cell, or can apply frequency reuse division or frequency reuse allocation with a cell.  
         [0040]      FIG. 4  is a flowchart illustrating an EHDT duplexing method according to an embodiment of the present invention. Referring to  FIG. 4 , if an HDT system receives an FDD uplink resource request message from an HDT mobile station in step S 401 , after making call setup at the request of the HDT mobile station located in its coverage, the HDT system transmits a request for FDD uplink resource information of neighbor FDD base stations and receives corresponding information provided from an RNC (or MSC) in step S 402 . Alternatively, the HDT system can periodically receive the FDD uplink resource information of the neighbor FDD systems from the RNC, without the request of the HDT base station.  
         [0041]     In step S 403 , the HDT system determines if there is an overlapping FDD base station whose coverage overlaps with its own coverage, based on the information provided from the RNC. If there is an overlapping FDD system, in step S 404 , the HDT system determines if there are available unused FDD uplink resources in the overlapping FDD system. If there are unused FDD uplink resources, the HDT system determines if it is located in a boundary of the overlapping FDD system in step S 405 . If the HDT system is not located in a boundary of the overlapping FDD system, the HDT system allocates uplink resource of the overlapping FDD system to the HDT mobile station in step S 410 .  
         [0042]     However, if the HDT system is located in the boundary of the overlapping FDD system, the HDT system receives, from the RNC, information on the amount of interference to the HDT system, caused by neighbor FDD systems, in step S 406 , and receives channel information from the HDT mobile station in step S 407 . Preferably, the channel information can include path gain, SINR level, and reception power level of the corresponding channel.  
         [0043]     Subsequently, the HDT system determines if there are available FDD uplink resources in the neighbor FDD systems in step S 408 . If there is no available resource in any neighbor FDD system, the HDT system determines if a co-channel uplink interference level of the nearest FDD system is lower than a threshold in step S 409 .  
         [0044]     If the interference level of the nearest FDD system is lower than the threshold, the HDT system allocates uplink resource of the overlapping FDD system to the HDT mobile station in step S 410 .  
         [0045]     If it is determined in step S 408  that there are available FDD uplink resources in the neighbor FDD systems, the HDT system selects, among the neighbor FDD systems, an FDD system that has the minimum co-channel interference caused by the HDT mobile station or can obtain the highest SINR level in step S 420 , and allocates FDD uplink resource of the selected FDD system to the HDT mobile station in step S 421 .  
         [0046]      FIG. 5  is a conceptual diagram illustrating an EHDT duplexing method according to and embodiment of the present invention. More specifically,  FIG. 5  illustrates a hybrid duplexing method using the existing narrowband TDD uplink resource  520   u  and downlink resource  520   d , and TDD resources of the newly proposed additional band  530 .  
         [0047]     Referring to  FIG. 5 , a macro cell  110  is implemented with a narrowband TDD system that uses the existing narrowband TDD uplink resource  520   u  and downlink resource  520   d , and a micro cell  120  is implemented with a hybrid duplexing (HDT) system that uses the broadband TDD resources of the additional band  530  and the existing narrowband TDD uplink resource  520   u . The micro cell  120  allocates uplink resource  530   u  and downlink resource  530   d  of the additional TDD band  530  to a mobile station located in an inner region  122  thereof, and allocates the TDD downlink resource  530   d  of the additional broadband  530  and the narrowband TDD uplink resource  520   u  to a mobile station located in an outer region  124  thereof.  
         [0048]     The narrowband TDD uplink resource  520   u  is shared by a TDD system  110  implemented with a macro cell and an HDT system  120  implemented with a micro cell, or a part thereof is previously allocated for the HDT system  120 . The HDT system checks availability of the narrowband TDD uplink resource  520   u  at the request of a mobile station, and dynamically shares (or borrows) the narrowband TDD uplink resource  520   u  according to the check result.  
         [0049]     In a technique of previously allocating the narrowband TDD uplink resource  520   u  for the HDT system  120 , the HDT system  120  analyzes the amount of resources required by mobile stations at every frame or every session, and allocates a predetermined amount of the TDD uplink resource  520   u  for a predetermined period.  
         [0050]     Because the narrowband TDD system  110  shares uplink resources with the HDT system  120 , uplink and downlink time slot switching points of the two systems are set on an alternating basis, such that an uplink (or downlink) for the broadband TDD should not be equal to an uplink (or downlink) for the narrowband TDD at the same time. Through the setting, the two TDDs can simultaneously operate independently when necessary. In addition, if needed, the HDT system can operate in an FDD mode using the narrowband TDD uplink resource  520   u  and the broadband TDD uplink resource  530   u.    
         [0051]      FIG. 6  is a resource graph illustrating an FDD mode of an HDT system in an EHDT duplexing method according to an embodiment of the present invention. As illustrated in  FIG. 6 , by alternately setting uplink and downlink time slot switching points of the narrowband TDD resource and the broadband TDD resource, the HDT system  120  can obtain continuity, which is a characteristic of the FDD mode, using the narrowband TDD uplink resource  520   u  and the broadband TDD uplink resource  530   u.    
         [0052]      FIG. 7  is a flowchart illustrating an EHDT duplexing method according to an embodiment of the present invention. More specifically, the EHDT duplexing method illustrated in  FIG. 7  is the same as the EHDT duplexing method illustrated in  FIG. 4 , except that the FDD uplink resource of  FIG. 4  is replaced with the TDD uplink resource and the FDD system is replaced with the TDD system. Therefore, a detailed description thereof will be omitted herein for simplicity.  
         [0053]      FIG. 8  is a conceptual diagram illustrating an EHDT duplexing method according to another embodiment of the present invention. In  FIG. 8 , a macro cell  110  is implemented with an FDD system that uses the existing FDD uplink resource  810  and downlink resource  820 , and a micro cell  120  is implemented with an HDT system that uses TDD resource  830  of an additional band and FDD uplink resource  850   u .  FIG. 8  is similar in application to  FIG. 2A  except that the HDT system uses the FDD uplink resource  850   u  of the additional band as uplink resource, instead of the existing FDD uplink resource  810 . Therefore, a detailed description thereof will be omitted herein for simplicity.  
         [0054]     As described above, the EHDT system according to the present invention enables efficient resource management through resource sharing and reusing between hybrid duplexing technique-based systems in an overlay network where different type systems coexist.  
         [0055]     In addition, the novel EHDT system can minimize intersystem interference by sharing or borrowing resources taking into account the resource utilization situations of the neighbor systems, and can maximize the entire system capacity through a traffic load balancing effect.  
         [0056]     While the present invention has been shown and described with reference to certain preferred embodiments 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 present invention as defined by the appended claims.