WO2008054122A1

WO2008054122A1 - Method and apparatus for allocating time-slot in time division duplex system

Info

Publication number: WO2008054122A1
Application number: PCT/KR2007/005404
Authority: WO
Inventors: Ra-Mi Lee; Seong-Soo Park; Dong-Hahk Lee; Jae-Hwang Yu; Jong-Tae Ihm; Se-Hyun Oh; Duk-Kyung Kim; Tae-Hyung Lee
Original assignee: Sk Telecom Co., Ltd.
Priority date: 2006-10-30
Filing date: 2007-10-30
Publication date: 2008-05-08
Also published as: CN101523770A; CN101523770B; KR100816256B1

Abstract

Disclosed is a method and an apparatus for allocating a time slot in a time-division duplex system. The method includes the steps of: detecting a first Mobile Station (MS) located in an adjacent area between a first cell and a second cell adjacent to the first cell among MSs located in the first cell formed by a first Base Station (BS); detecting a second MS located in an adjacent area neighboring to the first cell among MSs located in the second cell; finding an MS located in the farthest position from a second BS forming the second cell among the MSs located in the first cell; and allocating a first time slot corresponding to a second time slot allocated to the second MS to the MS located in the farthest position from the second BS.

Description

METHOD AND APPARATUS FOR ALLOCATING TIME-SLOT IN TIME DIVISION DUPLEX SYSTEM

Technical Field

[1] The present invention relates to a method for allocating a time slot in a mobile communication system, and more particularly to a method and an apparatus for allocating a time slot in a time-division duplex system for reducing interference occurring among time slots respectively belonging to different cells in an adjacent area between cells where uplink time slots are synchronized with downlink time slots. Background Art

[2] A Wideband Code Division Multiple Access (W-CDMA) scheme includes, as a duplex scheme, a Frequency-Division Duplex (FDD) scheme in which an uplink line and a downlink line are divided by the frequency, and a Time-Division Duplex (TDD) scheme in which an uplink line and a downlink line are divided by the time.

[3] The TDD scheme of the two duplex schemes has the merit that the allocation of uplink and downlink radio channels according to uplink/downlink traffic asymmetry can be effectively achieved. However, in the above TDD scheme, all wireless base stations within a system have the same transmit/receive (Tx/Rx) timing, and thus the effect of interference in an adjacent area among cells cannot be excluded.

[4] Hereinafter, with reference to FIGs. 1 and 2, interference effect occurring in an adjacent area among cells will be described.

[5] FIG. 1 schematically illustrates a TDD system to which a general method for allocating a time slot is applied, and FIG. 2 depicts Tx/Rx timing of data necessary to illustrate interference among adjacent cells, caused by the prior time slot allocation.

[6] In FIG. 1, a first cell 10 and a second cell 20 are depicted, and it is assumed that a radius of the second cell 20 is larger than a radius of the first cell 10.

[7] Both a first Base Station (BS) 12 of the first cell 10 and a second BS 22 of the second cell 20 are synchronized with each other at reference timing, and a backward synchronization is set in such a manner as to receive data from Mobile Stations (MSs) in the first and second cells 10 and 20 in accordance with the reference timing.

[8] A first propagation delay time (or radio wave propagation delay time) is caused when data is transferred from the first BS 12 to a first MS 14, and due to the first propagation delay time , while transferring data to the first BS 12, the first MS 14 makes the transfer of data to the first BS 12 earlier by a time interval equivalent to the first propagation delay time (refer to FIG. 2). Also, when the second BS 22 located in the second cell 20 whose radius is larger than a radius of the first cell 10 transfers data to a second MS 24, a second propagation delay time is caused. On this account, only if the second MS 24 must make the transfer of data to the second BS 22 earlier by a time interval equivalent to the second propagation delay time as well when the second MS 24 transfers data to the second BS 22, the data is delivered to the second BS 22 in accordance with a reference time of the second BS 22. At this time, since propagation delay time is relative to the distance between a BS and an MS, with reference to FIG. 2, the first propagation delay time is larger than the second propagation delay time .

[9] When downlink data is transmitted from the first BS 12 to the first MS 14

(reception or Rx), if the second MS 24 located at the edge of a larger cell area transmits uplink data to the second BS 22, uplink/downlink interference may occur even though the downlink/uplink transmissions are performed in different time slots. Further, because the uplink signal of the second MS 24 is stronger than the downlink signal of the first MS 12, much larger uplink/downlink interference occurs. Moreover, the larger the difference between the radius of the first cell 10 and the radius of the second cell 20 is, the more seriously the uplink/downlink interference occurs. Disclosure of Invention Technical Problem

[10] Accordingly, the present invention has been proposed so as to take the above-stated circumstances into consideration, and it is an object of the present invention to provide a method and an apparatus for allocating a time slot in a Time-Division Duplex (TDD) system for reducing interference occurring among time slots respectively belonging to different cells in an adjacent area among cells where uplink time slots are synchronized with downlink time slots in a mobile communication system employing a TDD scheme. Technical Solution

[11] In accordance with a first aspect of the present invention for attaining the above object, there is provided a method for allocating a time slot in a TDD system, including the steps of: detecting a first Mobile Station (MS) located in an adjacent area between a first cell and a second cell adjacent to the first cell among MSs located in the first cell formed by a first Base Station (BS); detecting a second MS located in an adjacent area neighboring to the first cell among MSs located in the second cell; finding an MS located in the farthest position from a second BS forming the second cell among the MSs located in the first cell; and allocating a first time slot corresponding to a second time slot allocated to the second MS to the MS located in the farthest position from the second BS.

[12] In accordance with a second aspect of the present invention for attaining the above object, there is provided a method for allocating a time slot in a TDD system, including the steps of: detecting a first Mobile Station (MS) and a second MS located in a handoff area of a first cell and a second cell; finding an MS located in the farthest position from a second BS forming a second cell among MSs located in a first cell, by a first Base Station (BS) forming the first cell if a radius of the second cell is larger than a radius of the first cell; and allocating a first time slot corresponding to a second time slot allocated to the second MS to the MS located in the farthest position from the second BS.

[13] In accordance with a third aspect of the present invention for attaining the above object, there is provided an apparatus for allocating a time slot in a TDD system, including: a Mobile Station (MS) location management unit for detecting location information and status information of an MS located in a handoff area of a first cell and a cell adjacent to the first cell and then detecting an MS located in the farthest position from a Base Station (BS) forming the adjacent cell among MSs located in the first cell; a BS information management unit for managing BS information including cell radius information dominated by a BS adjacent to the first cell; a time slot scheduling unit for scheduling time slots of MSs managed by the MS location management unit; and a time slot allocation unit for allocating a time slot of the first MS under the control of the time slot scheduling unit.

[14] In accordance with a fourth aspect of the present invention for attaining the above object, there is provided a recording medium, having a program stored therein, and being readable by a computer, wherein the program includes the steps of: detecting a first Mobile Station (MS) and a second MS located in an adjacent area between a first cell formed by a first Base Station (BS) and a second cell having a radius larger than a radius of the first cell; finding an MS located in the farthest position from a second BS forming the second cell among the MSs located in the first cell; allocating a first time slot corresponding to a second time slot allocated to the second MS to the MS located in the farthest position from the second BS; and performing allocation of a time slot required for a downlink signal of the first MS after the transmission of an uplink signal by the second MS has been completed.

Advantageous Effects

[15] In a method and an apparatus for allocating a time slot in a TDD system of the present invention, Tx/Rx timing of an uplink line and Tx/Rx timing of a downlink line are different from each other, and it is also possible to reduce, to the minimum, interference among adjacent cells caused by the strength of an uplink signal or a downlink signal, which is relative to a location of each MS within a cell, i.e. the distance between a BS and each MS, thereby enlarging the Rx performance of an MS. Brief Description of the Drawings [16] The above and other exemplary features, aspects, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[17] FIG. 1 schematically illustrates a TDD system to which a general method for allocating a time slot is applied;

[18] FIG. 2 depicts Tx/Rx timing of data necessary to illustrate interference among adjacent cells, caused by the prior time slot allocation;

[19] FIG. 3 schematically illustrates a TDD system to which a method for allocating a time slot according to an embodiment of the present invention is applied;

[20] FIG. 4 is a block diagram schematically illustrating an apparatus for allocating a time slot according to an embodiment of the present invention; and

[21] FIG. 5 depicts Tx/Rx timing of data necessary to describe a method for allocating a time slot according to an embodiment of the present invention. Best Mode for Carrying Out the Invention

[22] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

[23] FIG. 3 schematically illustrates a Time-Division Duplex (TDD) system to which a method for allocating a time slot according to an embodiment of the present invention is applied, and FIG. 4 is a block diagram schematically illustrating an apparatus for allocating a time slot according to an embodiment of the present invention.

[24] With reference to FIG. 3, the TDD system to which the method for allocating a time slot is applied is configured to include a first BS 120, a first cell 100 formed by the first BS 120, and MS_A 140 and MS_B 160 located in adjacent cells and handoff areas 400 and 500 among multiple MSs included in the first cell 100. As adjacent cells to the first cell 100, a second cell 200 formed by a second BS 220, a third cell 300 formed by a third BS 320, and the like can be cited. In addition, a handoff area between the first cell 100 and the second cell 200 is designated by reference numeral 400, and a handoff area between the first cell 100 and the third cell 300 is designated by reference numeral 500.

[25] The first to third BSs 120, 220, and 320 are under the control of respective BS controllers (not illustrated), and in one embodiment, each of the first to third BSs 120, 220, and 320 communicates with MSs existing in an area of the relevant BS at timing determined by the relevant BS controller. Additionally, the BS controller can determine a configuration of a time slot used by a BS to transfer a signal, and also carries out roles, such as controlling line access of a mobile network, controlling handover among adjacent cells, and the like. At this time, BSs of all cells have the same reference time.

[26] The first BS 120 includes such units as illustrated in FIG. 4, and schedules time slots of MSs located in areas neighboring to cells (e.g., the second cell 200 and the third cell 300) adjacent to the first cell 100 formed by the first BS 120.

[27] Namely, the first BS 120 is configured to include a MS location management unit

122, a BS information management unit 124, a time slot scheduling unit 126, and a time slot allocation unit 128, and a description will be omitted of a basic configuration required to form a BS except for the above units.

[28] The MS location management unit 122 receives, from a Mobile Switching

Controller (MSC) or a Home Location Register (HLR), location information of MSs located in adjacent areas (e.g., handoff areas 400 and 500) to adjacent cells among multiple MSs located in the first cell 100, and then detects status information of the relevant MS.

[29] The MS location management unit 122 detects location information of MSs by inter-working with a Location-Based Service (LBS) server. To cite one example, the MS location management unit 122 which has received information on a cell having a radius larger than a radius of the first cell from the following BS information management unit 124 gains access to the LBS server and then requests location information of the MS located in the first cell, so as to find an MS within the first cell, located in the farthest position from a BS that forms the cell having a larger radius. Thereafter, the MS location management unit 122 refers to location information of the MS received from the LBS server, and then extracts the MS located in the farthest position from the BS that forms the cell having a radius larger the radius of the first cell.

[30] The BS information management unit 124 manages BS information of at least one cell adjacent to the first cell 100 and radio waves transmission area information, i.e. information on a radius of a cell, of the relevant BS. Information on BSs is stored in a BS controller to which the relevant BS belongs, or in an MSC, and every time BS information belonging to an adjacent cell is changed, the changed BS information is updated in the BS controller or the MSC, and then the updated BS information is transferred to the BS information management unit 124 of the first BS.

[31] Also, the BS information management unit 124 finds an area where the strength of a signal propagated from a BS (referring to FIG. 3, the reference numeral 220) that forms a cell having a radius larger than the radius of the first cell 100 is the weakest, and then transfers, to the MS location management unit 122, location information on the area where the strength of the signal is the weakest. In this case, the MS location management unit 122, requesting the LBS server to transfer location information of MSs located in the area where the strength of the signal is the weakest, receives the location information of MSs, and then can detect an MS located in the farthest position from a BS that forms the adjacent cell.

[32] In another applied embodiment, if a BS of each cell adjacent to the first cell 100 is informed of handoffs by MSs located in the first cell 100, the BS information management unit 124 receives information on the MS, and then transfers the received information on the MS to the MS location management unit 122. At this time, the MS location management unit 122 extracts an MS located in the farthest position from the BS 220 forming a second cell 200 having a radius larger than the radius of the first cell 100 among MSs, each of which has reported the handoff to the BSs of the adjacent cells.

[33] As the time slot scheduling unit 126 extracts radius information of adjacent cells by using information provided by the BS information management unit 124, it compares each of the extracted radius information of the adjacent cells with its own cell radius, and then specially manages information on cells (referring to FIG. 3, the second cell 200), each of which has a radius larger than its own cell radius. Also, the time slot scheduling unit 126 detects an MS_C 240 located in the handoff area 400 between the first cell 100 and the cell having a larger radius among MSs located in a cell having a radius larger than the radius of the first cell 100. As the MS_C 240 transmits/receives data to/from the second BS 220, the time slot scheduling unit 126 schedules a time slot (i.e., a channel) of the MS_A 140 which is located in the first cell 100 and located in a position adjacent to the MS_C 240. Additionally, when the MS_C 240 located in the second cell 200 having a radius larger than the radius of the first cell 100 transfers data to the second BS 220, the time slot scheduling unit 126 does not allocates a downlink time slot to the MS_A 140, but allocates the downlink time slot to the MS_B 160 located in a position relatively far from the MS_C 240.

[34] The reason is that since a second distance between the second BS 220 and the

MS_C 240 is larger than a first distance between the first BS 120 and the MS_A 140, the MS_C 240 must transfer data to the second BS 220 by using a strong uplink signal, and accordingly, serious interference occurs when data is downloaded from the first BS 120 to the MS_A 140.

[35] The time slot allocation unit 128 allocates a time slot scheduled by the time slot scheduling unit 126 to an MS located in the first cell 100. At this time, the time slot allocation unit 128 performs allocation of an uplink time slot and a downlink time slot in the same direction in all cells.

[36] A description will be made of an operating state of the present invention configured as described above. [37] FIG. 5 depicts Tx/Rx timing of data necessary to describe a method for allocating a time slot according to an embodiment of the present invention.

[38] Even if all BSs (the first to third BSs according to an embodiment of the present invention) are synchronized with one another and the same time slot is allocated in the same direction, in a TDD system in which a backward synchronization is performed, uplink interference and downlink interference can occur among adjacent time slots of adjacent cells. At this time, in an embodiment of the present invention, with respect to two time slots which are neighboring in a spot where an upward switching and a downward switching occur, the time slots are allocated by using channel conditions around an MS, thereby reducing interference among adjacent cells.

[39] In an embodiment of the present invention, it is assumed that the first to third BSs

120, 220, and 320 have the same reference time, an uplink time slot and a downlink tine slot are allocated in the same direction in all cells, and the control of backward timing is perfectly achieved.

[40] Hereinafter, a description will be made in more detail with reference to FIG. 5 depicting Tx/Rx timing of data.

[41] First, the first BS 120, the second BS 220, and the third BS 320 are synchronized with one another at a reference time.

[42] The reference numeral 400 designates an adjacent area between the first cell 100 and the second cell 200, the reference numeral 500 designates an adjacent area between the first cell 100 and the third cell 300, and as an example of an adjacent area, a handoff area and the like can be cited.

[43] When the second BS 220 of the second cell 200 transmits data to the MS_C 240 located in an adjacent area neighboring to the first cell 100, propagation delay time, whose length equals to tl, is caused. Accordingly, so that data transmitted from the MS_C 240 to the second BS 220 may be delivered in accordance with the reference time, the MS_C 240 transfers data to the second BS 220 beforehand by a time interval equivalent to the propagation delay time. At this time, if data is transferred downward (i.e., Rx) from the first BS 120 to the MS_A 140, since interference in the MS _C 240 is caused by a strong uplink signal whose transfer has been made earlier, the first BS 120 does not allocate a time slot to the MS _A, but instead, allocates a time slot required for downlink transfer (i.e., Rx) to the MS_B 160 located in a position relatively far from the second BS 220.

[44] Simultaneously, the first BS 120 allocates a time slot to the MS_A 140 at a time point uplink transmission (Tx) is completed by the MS_C 240, and accordingly enables the MS _A 140 to be less affected by interference caused by uplink Tx from the MS_C 240.

[45] If it is assumed that the second cell 200, the first cell 100, and the third cell 300 come in order that the size of cell radius of each BS becomes smaller, a process for allocating time slots in the first cell, the second cell, and the third cell is as follows. Namely, from the viewpoint of the first BS 120, because the influence of interference occurring in the third cell 300 is smaller than the influence of interference occurring in the second cell 200, in a case where a channel of an MS located in the handoff area 500 corresponding to the adjacent area between the first cell and the third cell is scheduled, there is no need to consider the strength of a signal generated when an MS located in the third cell 300 performs uplink Tx to the third BS 320.

[46] However, from the viewpoint of the third BS 320, since a radius of the first cell 100 is larger than a radius of the third cell 300 itself, it is possible for the above-described process to adjust a time slot of an MS located in the third cell 300 in response to signal strength generated during uplink Tx performed by the MS_B 160 located in the handoff area 500 corresponding to an adjacent area.

[47] Hereinafter, on the assumption that among cell radiuses of BSs, a radius of the second cell 200 is the largest, a radius of the first cell 100 is large in the second rank, and a radius of the third cell 300 is smaller than the radius of the first cell 100, a detailed description will be made of embodiments of the present invention.

[48]

[49] 1st EMBODIMENT

[50] A first BS 120 forming the first cell 100 detects an MS located in an adjacent area between the first cell 100 and the second cell 200 having a second radius larger than a first radius of the first cell 100. Since the MS, as described above, is subject to interference, depending on Tx/Rx signals of MSs located in other adjacent cells, there is a need for allocating a time slot in such a manner as to reduce the interference.

[51] Also, the first BS 120 detects an MS (hereinafter, referred to as an "MS_C 240") located in the adjacent area neighboring to the first cell among MSs located in the second cell.

[52] Thereafter, the first BS 120 finds an MS (referring to FIG. 3, an MS_B 160) located in the farthest position from a second BS 220 forming the second cell 200 among MSs located in the first cell 100. Based on the result of finding an MS, a time slot corresponding to a time slot allocated to the MS_C is allocated to an MS_B 160 located in the farthest position. In addition, after the MS_C 240 located in the second cell 200 the first BS 120 has completed the transmission of an uplink signal, the first BS 120 allocates a time slot required for a downlink signal to an MS_A 140 located in a position adjacent to the MS_C 240.

[53] At this time, in a method for finding an MS located in the farthest position from the second BS 220 by the first BS 120, after the first BS 120 gains access to an LBS server and then requests location information of all MSs located in the first cell 100, the first BS 120 can extract, from the location information, an MS (in FIG. 3, the MS_B 160) located in the farthest position from the second BS 220.

[54] In another applied embodiment, so as to find an MS located in the farthest position from the second BS 220, first, the first BS 120 finds, within an area of the first cell 100, an area where the strength of a signal propagated from the second BS 220 is the weakest. Then, if the first BS 120 requests the LBS server to provide location information of an MS located in an area where the strength of radio waves is the weakest, the first BS 120 can extract an MS (in FIG. 3, the MS_B 160) located in the farthest position from the second BS 220.

[55] According to another applied embodiment, in another method for finding an MS located in the farthest position from the second BS 220 the first BS 120, the first BS 120 inquires if a BS forming each cell adjacent to the first cell 100 has been informed of handoffs by MSs located in the first cell 100, and then requests a list about the MSs, each of which has reported the handoff. The first BS 120 receives the list about the MSs, each of which has reported the handoff to the BSs of the adjacent cells, and then extracts an MS located in the farthest position from the second BS 220 among listed MSs.

[56]

[57] 2nd EMBODIMENT

[58] To describe another method for allocating a time slot in a TDD system, a first BS

120 of a first cell 100 detects MSs located in a handoff area between the first cell 100 and a second cell 200. Then, if a radius of the second cell 200 is larger than a radius of the first cell 100, the first BS 120 forming the first cell 100 finds an MS located in the farthest position from a second BS 220 forming the second cell 200 among the MSs located in the first cell 100.

[59] At this time, a method for finding the MS located in the farthest position from the second BS 220 employs various methods described in the first embodiment.

[60] The first BS 120 allocates, to the MS located in the farthest position from the second BS 220, a time slot corresponding to a time slot allocated to an MS (an MS_C 240) within the second cell 200, located in a handoff area 400.

[61] Until the MS_C 240 generating a strong uplink Tx signal completes the transfer of a signal, the first BS 120 does not allocate a time slot required for downlink transfer (i.e., Rx) to an MS_A 140 located in a position adjacent to the MS_C 240, but instead, allocates a time slot to the MS_A 140 if the uplink transfer of the MS_C 240 is completed, thereby reducing interference.

[62] It is also possible to realize the present invention as codes readable by a computer in a recording medium readable by a computer. The recording medium readable by the computer includes all kinds of recording devices in which data readable by a computer system is stored. As examples of recording mediums, Read only Memory (ROM), Random Access Memory (RAM), Compact Disc-Read Only Memory (CD-ROM), a magnetic tape, a floppy disc, an optical data storage device, and others can be cited, and a storage device implemented in the form of carrier wave (e.g., transfer through the internet) is included as well. Also, the recording mediums readable by the computer are distributed to computer systems connected over a network, and accordingly, codes readable by a computer are not only stored in the recording mediums but are also performed in a distributed scheme.

[63] The merits and effects of exemplary embodiments, as disclosed in the present invention, and as so configured to operate above, will be described as follows.

[64] As described above, in a method and an apparatus for allocating a time slot in a

TDD system of the present invention, Tx/Rx timing of an uplink line and Tx/Rx timing of a downlink line are different from each other, and it is also possible to reduce, to the minimum, interference among adjacent cells caused by the strength of an uplink signal or a downlink signal, which is relative to a location of each MS within a cell, i.e. the distance between a BS and each MS, thereby enlarging the Rx performance of an MS.

[65] While the invention has been shown and described with reference to a certain exemplary 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. Therefore, the spirit and scope of the present invention must be defined not by described embodiments thereof but by the appended claims and equivalents of the appended claims.

Claims

[1] A method for allocating a time slot in a Time-Division Duplex (TDD) system, the method comprising the steps of:

(a) detecting a first Mobile Station (MS) located in an adjacent area between a first cell and a second cell adjacent to the first cell among MSs located in the first cell formed by a first Base Station (BS);

(b) detecting a second MS located in an adjacent area neighboring to the first cell among MSs located in the second cell;

(c) finding an MS located in the farthest position from a second BS forming the second cell among the MSs located in the first cell; and

(d) allocating a first time slot corresponding to a second time slot allocated to the second MS to the MS located in the farthest position from the second BS.

[2] The method as claimed in claim 1, wherein a radius of the second cell is larger than a radius of the first cell.

[3] The method as claimed in claim 1 or 2, wherein step (c) is performed if a signal is intended to be transmitted from the second MS to the second BS and simultaneously the signal is intended to be transmitted from the first BS to the first MS.

[4] The method as claimed in claim 3, wherein the first BS and the second BS have the same reference time.

[5] The method as claimed in claim 1 or 2, which further comprises a step of performing allocation of a time slot required for a downlink signal of the first MS after the transmission of an uplink signal by the second MS has been completed.

[6] The method as claimed in claim 5, wherein an uplink time slot for the uplink signal and a downlink time slot for the downlink signal are allocated in the same direction in all cells.

[7] The method as claimed in claim 6, wherein the second BS receives a signal during a preset time slot by transferring the signal to the second BS beforehand by a time interval equivalent to a time delay caused when the second MS receives the signal from the second BS.

[8] The method as claimed in claim 7, wherein, in step (c), the step of finding an MS located in the farthest position from a second BS comprises the substeps of: (c-1) gaining access to a location-based service server and then requesting location information of a MS located in the first cell, by the first BS; and (c-2) finding the location information of the MS, and then extracting the MS located in the farthest position from the second BS among MSs located in the first cell.

[9] The method as claimed in claim 8, wherein step (c-1) comprises the steps of: finding, by the first BS, an area where a strength of a signal propagated from the second BS is the weakest in the first cell; and gaining access to the location-based service server, and then requesting location information of an MS located within the area where the strength of the signal propagated from the second BS is the weakest in the first cell, by the first BS.

[10] The method as claimed in claim 7, wherein, in step (c), the step of finding an MS located in the farthest position from a second BS comprises the substeps of:

(c-i) requesting, by the first BS, an MS located in the first cell to transfer location information of the MS;

(c-ii) finding, by the first BS, an MS located in an area where a strength of a signal propagated from the second BS is the weakest in the first cell after the first

BS receives the location information of the MS; and

(c-iii) extracting the MS located in the farthest position from the second BS among MSs found in substep (c-ii).

[11] The method as claimed in claim 7, wherein, in step (c), the step of finding an MS located in the farthest position from a second BS among the MSs located in the first cell comprises the substeps of: requesting, by the first BS, a BS of each cell adjacent to the first cell to provide information on MSs located in the first cell, each of which has reported handoff to the BSs of the cells adjacent to the first cell; and finding the MS located in the farthest position from the second BS among the multiple pieces of information on the MSs received from the BSs of the cells adjacent to the first cell.

[12] A method for allocating a time slot in a Time-Division Duplex (TDD) system, the method comprising the steps of:

(A) detecting a first Mobile Station (MS) and a second MS located in a handoff area of a first cell and a second cell;

(B) finding an MS located in the farthest position from a second BS forming a second cell among MSs located in a first cell, by a first Base Station (BS) forming the first cell if a radius of the second cell is larger than a radius of the first cell; and

(C) allocating a first time slot corresponding to a second time slot allocated to the second MS to the MS located in the farthest position from the second BS.

[13] The method as claimed in claim 12, wherein, in step (B), the step of finding an

MS located in the farthest position from a second BS among MSs located in a first cell comprises the substeps of: requesting, by the first BS, a BS of each cell adjacent to the first cell to provide information on MSs located in the first cell, each of which has reported handoff to the BSs of the cells adjacent to the first cell; and finding the MS located in the farthest position from the second BS among the multiple pieces of information on the MSs received from the BSs of the cells adjacent to the first cell.

[14] The method as claimed in claim 12, wherein step (B) comprises the steps of: finding, by the first BS, an area where a strength of a signal propagated from the second BS is the weakest in the first cell; and gaining access to the location-based service server, and then requesting location information of an MS located within the area where the strength of the signal propagated from the second BS is the weakest in the first cell, by the first BS.

[15] The method as claimed in claim 13 or 14, wherein the second BS receives a signal during a preset time slot by transferring the signal to the second BS beforehand by a time interval equivalent to a time delay caused when the second MS receives the signal from the second BS.

[16] The method as claimed in claim 15, wherein an uplink time slot for an uplink signal and a downlink time slot for a downlink signal are allocated in the same direction in all cells.

[17] The method as claimed in claim 16, wherein the first BS and the second BS have the same reference time.

[18] The method as claimed in claim 17, which further comprises a step of performing allocation of a time slot required for a downlink signal of the first MS after the transmission of an uplink signal by the second MS has been completed.

[19] An apparatus for allocating a time slot in a Time-Division Duplex (TDD) system, the apparatus comprising: a Mobile Station (MS) location management unit for detecting location information and status information of an MS located in a handoff area of a first cell and a cell adjacent to the first cell and then detecting an MS located in the farthest position from a Base Station (BS) forming the adjacent cell among MSs located in the first cell; a BS information management unit for managing BS information including cell radius information dominated by a BS adjacent to the first cell; a time slot scheduling unit for scheduling time slots of MSs managed by the MS location management unit; and a time slot allocation unit for allocating a time slot of the first MS under the control of the time slot scheduling unit.

[20] The apparatus as claimed in claim 19, wherein all BSs forming the first cell and cells adjacent to the first cell have the same reference time.

[21] The apparatus as claimed in claim 20, wherein the time slot allocation unit allocates an uplink time slot and a downlink time slot in the same direction in all cells.

[22] The apparatus as claimed in claim 21, wherein the MS location management unit receives information on cells having radiuses larger than a radius of the first cell from the BS information management unit, gains access to a location-based service server so as to find an MS located in the farthest position from a BS forming each cell, requests location information of MSs located in the first cell, and then extracts the MS located in the farthest position on the basis of the location information.

[23] The apparatus as claimed in claim 22, wherein the BS information management unit finds an area where a strength of a signal propagated from a BS forming a cell having a radius larger than the first cell is the weakest, and then transfers, to the MS location management unit, location information on the area where the strength of the signal is the weakest; and wherein the MS location management unit, requesting the location-based service server to transfer location information of an MS located within the area where the strength of the signal is the weakest, receives the location information of the MS, and then detects an MS located in the farthest position from the BS forming the adjacent cell.

[24] The apparatus as claimed in claim 22, wherein, if a BS of each cell adjacent to the first cell is informed of handoffs by the MSs located in the first cell, the BS information management unit receives information on the MSs, and then transfers the received information on the MSs to the MS location management unit; and wherein the MS location management unit extracts an MS located in the farthest position from a BS forming a cell having a radius larger than the radius of the first cell among the MSs on which the information has been provided.

[25] The apparatus as claimed in any of claims 22 to 24, wherein, so as to coincide backward synchronizations of MSs with one another, each of the MSs transfers a signal to a BS forming the first cell and cells adjacent to the first cell beforehand by a time interval equivalent to a time delay caused when each of the MSs located in the first cell and the cells adjacent to the first cell receive the signal.

[26] A recording medium, having a program stored therein, and being readable by a computer, wherein the program comprises the steps of: detecting a first Mobile Station (MS) and a second MS located in an adjacent area between a first cell formed by a first Base Station (BS) and a second cell having a radius larger than a radius of the first cell; finding an MS located in the farthest position from a second BS forming the second cell among the MSs located in the first cell; allocating a first time slot corresponding to a second time slot allocated to the second MS to the MS located in the farthest position from the second BS; and performing allocation of a time slot required for a downlink signal of the first MS after the transmission of an uplink signal by the second MS has been completed.

[27] The recording medium as claimed in claim 26, wherein the first BS and the second BS have the same reference time, and wherein the program further comprises a step of allocating an uplink time slot and a downlink time slot in the same direction in all cells.