Abstract:
A resource allocation method in a wireless communication system for providing a communication service in a given system frequency band to access terminals (ATs) within a broad-band service area around an access point (AP) and to ATs within a narrow-band service area having a radius larger than the radius of the broad-band service area. In the resource allocation method, the system frequency band is divided into a Time Division Duplexing (TDD) interval and a Frequency Division Duplexing (FDD) interval in time, and the TDD interval and the FDD interval are defined as TDD resources and FDD resources, respectively. The TDD resources are allocated to an AT within the broad-band service area, and the FDD resources are allocated to an AT within the narrow-band service area.

Description:
PRIORITY 
     This application claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on Dec. 28, 2005 and assigned Serial No. 2005-131768, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a wireless communication system, and in particular, to a multi-mode duplexing method for efficient resource management in a wireless communication system. 
     2. Description of the Related Art 
     Typically, there are two duplexing techniques: Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). In TDD, the same frequency band is divided into time slots and transmission and reception are alternately switched in time, for bi-directional communication. FDD provides bi-directional communication by dividing a given frequency band into a transmission band and a reception band. 
     A TDD communication system allocates time slots (or parts thereof) available to an Access Point (AP), to a user. This variable time slot allocation method enables asymmetrical communications. However, as a cell radius increases, a Round Trip Delay (RTD) increases the guard band between transmission time slots and reception time slots. As a result, transmission efficiency decreases. Accordingly, TDD is not feasible for a communication environment using a large cell radius like a macro cell. Moreover, since each cell does not use the same asymmetry rate in a multi-cell environment, serious frequency interference occurs between terminals at the boundary between neighboring cells. 
     An FDD communication system does not suffer a time delay in transmission or reception because a frequency band is divided for transmission and reception. Due to the absence of a time delay-caused RTD, FDD is suitable for the large cell radius environment like a macro cell. However, because of its fixed transmission and reception frequency bands, FDD is not feasible for asymmetrical transmission. 
     The 3 rd  Generation (3G) and future-generation mobile communication systems aim at providing concurrent provisioning of multimedia services with different traffic characteristics such as broadcasting and real-time video conferencing, in addition to traditional voice service. To efficiently provide these various services, duplexing techniques which consider the asymmetry and continuity of uplink and downlink transmission according Quality of Service (QoS), have been proposed. 
       FIG. 1  illustrates a conventional dual-band duplexing technique. In the conventional dual-band duplexing technique, an AP switches between a transmission mode and a reception mode on two frequency band channels, i.e., a broadband channel and a narrow band channel every predetermined same period. Access Terminals (ATs) connected to the AP operate in the opposite mode to that of the AP and are allocated resources for reception and transmission on the two frequency band channels such that they do not overlap. 
     In other words, AT # 1  and AT # 2  occupy two equal halves of a broadband channel  101   a  that the AP uses in transmission mode, during reception mode intervals  101   a - 1  and  101   a - 2 , respectively. AT # 3  and AT # 4  partially occupy a narrow band channel  103   a  that the AP uses for transmission, during reception mode intervals  103   a - 2  and  103   a - 1 , respectively. AT # 1  and AT # 4  occupy part of a broadband channel  101   b  that the AP uses in reception mode, during transmission mode intervals  101   b - 1  and  101   b - 2 , respectively. AT # 2  and AT # 3  partially occupy a narrow band channel  103   b  that the AP uses for reception, during transmission mode intervals  103   b - 2  and  103   b - 1 , respectively. 
     This dual-band duplexing technique suffers loss of the symmetry between uplink and downlink channels due to switching between bands. Also, it is difficult to control uplink and downlink resource rates according to traffic condition, and a multi-mode MODEM is required to support a plurality of bands, thereby increasing a terminal&#39;s manufacturing cost. 
       FIG. 2  illustrates a band switching duplexing technique. The uplink and downlink are switched in one band every predetermined period T (sec). Alongside TDD channel switching, different bands are used for the uplink and downlink, simultaneously. 
     However, the use of the same-band channels decreases flexibility of resource allocation (i.e. control of uplink and downlink resource rates) and channels are periodically switched. Therefore, asymmetric transmission is difficult to implement. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, the present invention provides a hybrid duplexing method for enabling efficient resource management by flexibly controlling uplink and downlink resource allocation according to a communication environment. 
     The present invention provides a hybrid duplexing method for maximizing system throughput by appropriate selective use of TDD and FDD according to uplink and downlink traffic characteristics in each cell. 
     The present invention provides a hybrid duplexing method for achieving the advantages of both TDD and FDD, i.e., broadband transmission and continuity by allocating resources to ATs near to an AP in TDD and to ATs at a cell boundary in FDD. 
     According to one aspect of the present invention, in a resource allocation method in a wireless communication system for providing a communication service in a given system frequency band to access terminals within a broad-band service area around an access point and to access terminals within a narrow-band service area having a radius larger than the radius of the broad-band service area, the system frequency band is divided into a TDD interval and an FDD interval in time, and the TDD interval and the FDD interval are defined as TDD resources and FDD resources, respectively. The TDD resources are allocated to an access terminal within the broadband service area, and the FDD resources are allocated to an access terminal within the narrow-band service area. 
     It is preferred that in the TDD and FDD resources defining step, odd-numbered TDD resources are set as downlink TDD resources and even-numbered TDD resources are set as uplink TDD resources. 
     It is preferred that in the TDD and FDD resources defining step, the FDD resources are divided in frequency into a plurality of downlink channels and a plurality of uplink channels. 
     It is preferred that in the FDD resource allocating step, at least one downlink channel, at least one uplink channel, or at least one uplink and downlink channels are allocated, the at least one uplink and downlink channels not being in use for a neighbor cell. 
     According to another aspect of the present invention, in the TDD and FDD resources defining step, the TDD resources are divided in frequency into downlink TDD resources and uplink TDD resources, the FDD resources are divided in frequency into downlink FDD resources and uplink FDD resources, the downlink FDD resources are divided in frequency into a plurality of downlink channels, and the uplink FDD resources are divided in frequency into a plurality of uplink channels. 
     According a further aspect of the present invention, in the TDD and FDD resources defining step, the TDD resources are divided in time into downlink TDD resources and uplink TDD resources, the FDD resources are divided in frequency into downlink FDD resources and uplink FDD resources, the downlink FDD resources are divided in frequency into a plurality of downlink channels, and the uplink FDD resources are divided in frequency into a plurality of uplink channels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  illustrates graphs showing a conventional dual-band duplexing technique; 
         FIG. 2  illustrates graphs showing a conventional band-switching duplexing technique; 
         FIG. 3  is a graph illustrating a resource dividing method in a hybrid duplexing method according to the present invention; 
         FIG. 4  is a graph illustrating a hybrid duplexing method according to a first embodiment of the present invention; 
         FIG. 5A  is a graph illustrating a hybrid duplexing method according to a second embodiment of the present invention; 
         FIG. 5B  is a diagram illustrating the cell configuration of a communication system to which the hybrid duplexing method illustrated in  FIG. 5A  is applied; and 
         FIG. 6  is a graph illustrating a hybrid duplexing method according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
       FIG. 3  is a graph conceptually illustrating a resource dividing method in a hybrid duplexing method according to the present invention. 
     Referring to  FIG. 3 , a given system frequency band is divided into a plurality of sub-bands, each sub-band being divided in time into a broad-band service interval and a narrow-band service interval. The broad-band service interval is allocated to nearby ATs to provide a broad-band service, and the narrow-band service interval is in turn branched into a plurality of channels in frequency, for allocation to remote ATs to provide a narrow-band service. For notational simplicity, a block defined by the bandwidth of each sub-band and its broad-band service interval is called broad-band resources  10  and a block defined by the bandwidth of each sub-band and its narrow-band service interval is called narrow-band resources  20 . 
       FIG. 4  is a graph illustrating a hybrid duplexing method according to a first embodiment of the present invention. The broad-band resources  10  of  FIG. 3  are divided into downlink (DL) broad-band resources  10   d  and uplink (UL) broad-band resources  10   u , which alternate with each other in time, and generates differently in a frequency domain from those of a neighboring sub-band. The narrow-band resources  20  of  FIG. 3  are divided into a plurality of downlink narrow-band channels  20   d  and uplink narrow-band channels  20   u  in the same time interval. Since the downlink and uplink broad-band resources  10   d  and  10   u  alternate with each other, the broad-band service has constant reciprocity. Compared to the narrow-band resources, the broad-band resources do not need a guard band to distinguish channels. Hence, resources are saved. 
       FIG. 5A  is a graph illustrating a hybrid duplexing method according to a second embodiment of the present invention. A given system frequency band can be divided in frequency into a downlink band  510  and an uplink band  520 . Each sub-band is divided in time into a broad-band interval  501  and a narrow-band interval  502 . 
     According to of the present invention, a block defined by the downlink band  510  and the broad-band interval  501  is called downlink broad-band resources  510   w , and a block defined by the downlink band  510  and the narrow-band interval  502  is called downlink narrow-band resources  510   n . A block defined by the uplink band  520  and the broad-band interval  501  is called uplink broad-band resources  520   w , and a block defined by the uplink band  520  and the narrow-band interval  502  is called uplink narrow-band resources  520   n.    
     The downlink narrow-band resources  510   n  and the uplink narrow-band resources  520   n  are in turn respectively divided into N downlink narrow-band channels  510 - 1  to  510 -N, and N uplink narrow-band channels  520 - 1  to  520 -N, in frequency. 
     The downlink and uplink broad-band resources  510   w  and  520   w  are allocated to ATs in close proximity with (i.e., near to) an AP during the broad-band interval  501 , and the downlink and uplink narrow-band resources  510   n  and  520   n  are allocated to ATs far from the AP during the narrow-band interval  501 . 
       FIG. 5B  is a diagram illustrating the cell configuration of a communication system using the hybrid duplexing method illustrated in  FIG. 5A . 
     Referring to  FIG. 5B , seven cells  51  to  57  form one cluster. Each cell is divided into a broad-band service area  58  and a narrow-band service area  59  situated about a BS BS 1 - 7  located in each of the seven cells  51 - 57 . The radius of the broad-band service area  58  is smaller than that of the narrow-band service area  59 . 
     MSs located within the broad-band service area  58  are allocated the downlink and uplink broad-band resources  510   w  and  520   w  of  FIG. 5A . Since the broad-band service areas of adjacent cells are located at a sufficient distance from each other, they do not interfere with each another despite the use of the same broad-band resources  510   w  and  520   w  during the same broad-band interval. 
     Meanwhile, ATs within the narrow-band service area  59  are allocated available narrow-band channels among the downlink narrow-band channels  510 - 1  to  510 -N of the downlink narrow-band resources  510   n  of  FIG. 5  and the uplink narrow-band channels  520 - 1  to  520 -N of the uplink narrow-band resources  520   n  of  FIG. 5 . 
     Each BS that manages its cell shares channel use information with its neighbor BSs, so that it can allocate uplink and downlink narrow-band channels not in use for the neighbor cells. Therefore, inter-cell interference is avoided in the narrow-band service area  59 . 
     For example, in case where a cell  51  at the center of the cluster allocates resources to an AT within its narrow-band service area  58 , if the neighbor cells  52  to  57  use the downlink narrow-band channels  510 - 2  to  510 - 7  and the uplink narrow-band channels  520 - 1  to  520 - 7  during the narrow-band-interval  502 , the cell  51  allocates uplink and downlink narrow-band channels among the remaining channels to the MS. 
       FIG. 6  is a graph illustrating a hybrid duplexing method according to a third embodiment of the present invention. System resources can be divided in time into a TDD interval and an FDD interval and the TDD interval is in turn divided in time into a downlink TDD interval and an uplink TDD interval. The FDD interval is divided in frequency into a downlink FDD band and an uplink FDD band. The downlink and uplink FDD bands are further divided into downlink FDD narrow-band channels  610   d - 1  to  610   d -N and uplink FDD narrow-band channels  610   u - 1  to  610   u -N. 
     Downlink broad-band resources  610   d  defined by the system frequency band and the downlink TDD interval and uplink broad-band resources  610   u  defined by the system frequency band and the uplink TDD interval are allocated to ATs within the broad-band service area  58  of each cell illustrated in  FIG. 5B  to provide the broad-band service. The downlink narrow-band resources  610   d  defined by the downlink FDD band and the downlink FDD interval and the uplink narrow-band resources  610   u  defined by the uplink FDD band and the uplink FDD interval are allocated to ATs within the narrow-band service area  59  of each cell illustrated in  FIG. 5B  to provide the narrow-band service. Needless to say, the downlink and uplink narrow-band resources  610   d  and  610   u  are allocated on a downlink and uplink narrow-band channel basis in such a manner that the downlink and uplink narrow-band channels do not overlap with those of a neighbor cell. 
     While the TDD interval and the FDD interval are symmetrical in the embodiments of the present invention, they can be set asymmetrically according to a system environment or a traffic environment and it is also possible to control the number of TDD or FDD intervals in a unit time. Furthermore, broad-band resources allocated in TDD can be further time-divided or frequency-divided when needed. Regarding narrow-band resources allocated in FDD, the number of channels to be allocated can be controlled according to channel quality and a required number. 
     As described above, the hybrid duplexing method of the present invention allocates resources in TDD and FDD in combination, taking into account a communication environment. Therefore, QoS is guaranteed and resources are efficiently managed, as well. 
     In addition, the radius of a TDD-based broad-band service area is restricted and channel information is shared with a neighbor cell. Hence, channels of an FDD-based narrow-band service area are allocated, not overlapping with those of neighbor cells. Consequently, inter-cell interference is prevented. 
     While the 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 invention as defined by the appended claims.