WO2008016246A1

WO2008016246A1 - Ue data transmitting method and apparatus using cell search signal in synchronized cellular system

Info

Publication number: WO2008016246A1
Application number: PCT/KR2007/003652
Authority: WO
Inventors: Hyoseok Lee; Il-Gyu Kim; Hyeong-Geun Park; Young-Jo Ko; Kapseok Chang; Young-Hoon Kim; Seung-Chan Bang
Original assignee: Electronics And Telecommunications Research Institute; Samsung Electronics Co., Ltd
Priority date: 2006-07-31
Filing date: 2007-07-30
Publication date: 2008-02-07

Abstract

Provided are a method and apparatus for transmitting data using cell search signals in a mobile station. In a cellular system in which base stations are synchronized with each other, a mobile station determines its own location, using cell search signals that are received from base stations of a home cell and a neighboring cell, and estimates uplink delay time information. Thus, a RACH burst needs not to be transmitted, uplink delay time errors can be reduced, and accordingly, a guide period (GP) of an asynchronous RACH burst which is used to measure an uplink delay time can be shortened. Also, the mobile station can more accurately acquire its own location by receiving cell search signals from three or more base stations.

Description

UE DATA TRANSMITTING METHOD AND APPARATUS USING CELL SEARCH SIGNAL IN SYNCHRONIZED CELLULAR SYSTEM

TECHNICAL FIELD

The present invention relates to location determination and uplink timing informat ion acquisition of a mobile station, and more particularly, to a data transmission method and apparatus for estimating uplink delay time of a mobile station and allowing the mo bile station to determine its own location, using cell search signals that are received fro m a base station in a home cell and a base station in a neighboring cell, in a cellular sys tern in which base stations are synchronized with each other.

The present invention was supported by the Information Technology (IT) Resear ch & Development (R&D) program of the Ministry of Information and Communication (M IC) [Project management number: 2005-S-404-12, Project title: Research & Developme nt of Radio Transmission Technology for 3G evolution].

BACKGROUND ART

Recently, in a 3^rd Generation Partnership Project (3GPP), as a candidate radio tr ansmission technology for Long Term Evolution (LTE), it is considered that a Orthogon al Frequency Division Multiple Access (OFDMA) method is used as a downlink transmis sion method, and a Discrete Fourier Transform Spread OFDMA (hereinafter, referred to as "DFT Spread OFDMA" or "DFT-S-OFDMA") method is used as an uplink transmissi on method.

Also, in services such as a Multimedia Broadcast and Multicast Service (MBMS) service where all cells transmit data in common, a cellular system is generally configure d in which base stations of cells are synchronized with each other using a satellite in or der to obtain frequency diversity according to delay spread.

In an Orthogonal Frequency-Division Multiplexing (OFDM) system, when signals transmitted from a variety of mobile stations belonging to a base station reach the base station, signal orthogonality is maintained and the signals are easily demodulated in the base station only when the signals reach within a Cyclic Prefix (CP) of the base station . Thus, each mobile station receives uplink delay time or uplink delay time information (that is, round trip delay or timing advance information) according to a distance from the base station to the mobile station, from the base station, and refers to the received inf ormation upon uplink transmission.

Meanwhile, generally, a Random Access Channel (RACH) which is used by a m obile station when no uplink delay time information is received, among RACHs that are used to require resources to a base station, is called an asynchronous RACH. An asy nchronous RACH is particularly used to acquire uplink delay time information when a m obile station is initially powered on or when a mobile station is handed over to a neighbo ring cell.

Also, generally, since uplink delay time information changes when a mobile statio n is moved, a base station needs to inform the mobile station of uplink delay time infor mation per a predetermined time period. In order to inform the mobile station of uplink delay time information, recently, a method of allowing a mobile station to transmit an a synchronous RACH to a base station, among a variety of methods, is efficiently used.

The asynchronous RACH uses a wide bandwidth of 1.25Mhz in order to inform t he base station of uplink delay time information of the mobile station. Also, since the a synchronous RACH generates a maximum of uplink delay time of 6 μs per 1 km, a Ion g time of about 100 ms is needed as a guide period (GP) to support a cell having a rang e of 15 km, which consumes a large amount of resources.

Meanwhile, in a cellular system, a base station transmits a cell search signal peri odically so that mobile stations can recognize a cell to which the mobile stations present Iy belong. The cell search signal includes a cell ID for identifying a cell, and has excell ent auto correlation performance to catch a downlink timing.

Accordingly, a mobile station receives generally two or more cell search signals, selects a signal having the greatest strength from among the cell search signals, deter mines as a home cell a cell to which a base station transmitting the signal having the gr eatest strength belongs, and begins to communicate with the base station.

According to the present invention, in the cellular system using the OFDMA meth od, in which base stations are synchronized with each other, it is proposed a method in which a mobile station analyzes synchronized cell search signals received from a home cell and a neighboring cell, calculates a relative distance between the mobile station a nd a neighboring base station using cell configuration information, such as cell sizes, et c, which is included in the mobile station or already acknowledged to the mobile station through Broadcast channel (BCH) information, to acquire the mobile station's location i nformation, and thus reduces a GP of an asynchronous RACH by using the relative dist ance. DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL PROBLEM

The present invention provides a method in which a mobile station receives cell s earch signals from base stations of a home cell and neighboring cells, performs auto-co rrelation to obtain information regarding relative distances from the mobile station to the home cell and neighboring cells, and thus accurately estimates the mobile station's loc ation and uplink delay time information in correspondence to the number of the cell sea rch signals, and a method for reducing a Guide Period (GP) of a Random Access Chan nel (RACH) burst by accurately estimating a mobile station's location and uplink delay ti me information, in a cellular system using an Orthogonal Frequency Division Multiple A ccess (OFDMA) method, in which base stations are synchronized with each other.

The present invention also provides a method in which a mobile station acquires uplink delay time information using arrival-time differences between cell search signals r eceived from a home cell and neighboring cells, and can transmit uplink data without tra nsmitting an asynchronous RACH burst, in a cellular system in which base stations are synchronized with each other.

TECHNICAL SOLUTION According to the present invention, in a cellular system using a synchronized Ort hogonal Frequency Division Multiple Access (OFDMA) method, a mobile station has the capability of self-acquisition of uplink delay time, using arrival-time differences betwee n cell search signals received from base stations of a home cell and a neighboring cell, thereby reducing a Guide Period (GP) of an asynchronous Random Access Channel (R ACH) which is used to estimate the uplink delay time, and accurately estimating the mo bile station's location.

ADVANTAGEOUS EFFECTS

According to the present invention, in a cellular system using a synchronized Ort hogonal Frequency Division Multiple Access (OFDMA) method, a mobile station has the capability of self-acquisition of uplink delay time of a neighboring cell, using arrival-tim e differences between cell search signals received from base stations of a home cell an d the neighboring cell. Accordingly, the mobile station can transmit uplink data to the n eighboring cell without transmitting a Random Access Channel (RACH) burst to the nei ghboring cell.

Also, according to the present invention, a mobile station has the capability of sel f-acquisition of distances from the mobile station to base stations, using arrival-time diff erences of cell search signals, and estimates location errors according to the acquired distances from the mobile station to the base stations. Accordingly, it is possible to sig nificantly reduce errors of uplink delay time without a dedicated feedback of a base stati on with respect to a mobile station, and thus reduce a GP of an asynchronous RACH w hich is used to estimate the uplink delay time.

Also, according to the present invention, if a mobile station receives cell search s ignals from three or more base stations, the mobile station can more accurately estimat e its own location using the cell configuration information, for example, using the locatio n information of the base stations, etc.

DESCRIPTION OF THE DRAWINGS The above and other features and advantages of the present invention will beco me more apparent by describing in detail exemplary embodiments thereof with referenc e to the attached drawings in which:

FIG. 1 A is a conceptual view for explaining a method in which a mobile station ca n estimate its own location using cell search signals that are received from base station s of a home cell and a neighboring cell, according to an embodiment of the present inve ntion;

FIG. 1 B illustrates cell search signals that are received by the mobile station of Fl G. 1A from the base stations of the home cell and the neighboring cell;

FIG. 2 is a conceptual view for explaining a method of estimating a maximum est imation error of a distance from a mobile station to a base station, according to an emb odiment of the present invention;

FIG. 3 illustrates the structure of a 3G Long Term Evolution (LTE) uplink frame a ccording to an embodiment of the present invention;

FIG. 4A is a conceptual diagram for explaining a method of estimating a mobile s tation's location using cell search signals that are received by the mobile station from b ase stations of a home cell and two neighboring cells, according to another embodimen t of the present invention;

FIG. 4B illustrates cell search signals that are received by the mobile station of Fl G. 4A from the base stations of the home cell and the neighboring cells; FIG. 5 is a block diagram of a data transmission apparatus of a mobile station, a ccording to an embodiment of the present invention;

FIG. 6 is a block diagram of a data transmission apparatus of a mobile station, a ccording to another embodiment of the present invention; FIG. 7 is a flowchart of a data transmission method which is performed by a mob ile station, according to an embodiment of the present invention; and

FIG. 8 is a flowchart of a data transmission method which is performed by a mob ile station, according to another embodiment of the present invention.

BEST MODE

According to an aspect of the present invention, there is provided a method in whic h a mobile station transmits data using cell search signals. The method comprising, re ceiving cell search signals from a base station of a home cell and a base station of at Ie ast one neighboring cell, wherein the base station of the home cell is synchronized with the base station of the at least one neighboring cell; calculating an arrival-time differenc e of the cell search signals that are transmitted from the base station of the home cell a nd the base station of the at least one neighboring cell; and calculating uplink delay tim e of the at least one neighboring cell on the basis of the arrival-time difference.

According to another aspect of the present invention, there is provided a method in which a mobile station transmits data using cell search signals. The method comprisi ng, receiving cell search signals from a base station of a home cell and a base station o f at least one neighboring cell, wherein the base station of the home cell is synchronize d with the base station of the at least one neighboring cell; calculating an arrival-time dif ference of the cell search signals that are transmitted from the base station of the home cell and the base station of the at least one neighboring cell; and estimating distances from the mobile station to the base stations of the home cell and the at least one neighb oring cell on the basis of the arrival-time difference.

According to another aspect of the present invention, there is provided an apparatu s of transmitting data in a mobile station. The apparatus comprising, a receiver receivi ng cell search signals from a base station of a home cell and a base station of at least o ne neighboring cell, wherein the base station of the home cell is synchronized with the b ase station of the at least one neighboring cell; a time difference calculator calculating a n arrival-time difference of cell search signals that are transmitted from the base station of the home cell and the base station of the at least one neighboring cell; and an uplink delay time calculator calculating uplink delay time of the at least one neighboring cell on the basis of the arrival-time difference.

According to another aspect of the present invention, there is provided an apparatu s of transmitting data using location estimation in a mobile station. The apparatus com prising, a receiver receiving cell search signals from a base station of a home cell and a base station of at least one neighboring cell, wherein the base station of the home cell is synchronized with the base station of the at least one neighboring cell; a calculator ca lculating an arrival-time difference of the cell search signals that are transmitted from th e base station of the home cell and the base station of the at least one neighboring cell; and a location estimating unit estimating distances from the mobile station to the base stations of the home cell and the at least one neighboring cell on the basis of the arrival -time difference.

According to another aspect of the present invention, there is provided a comput er-readable recording medium having embodied thereon a program for executing the d ata transmission method which is performed by the mobile station using the cell search signals.

MODE OF THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the appended drawings. Like reference numerals in the drawings denot e like elements. In this specification, if it is determined that detailed descriptions relate d to functions or constructions well-known in the art make the concept of the present inv ention obscure unnecessarily, the detailed descriptions will be omitted.

Also, in the specification, the expression that a certain portion "includes" a certai n element means that the certain portion can further include other element as well as th e element, without meaning exclusion of any other elements.

In the present invention, a base station is located in each cell of a cellular system and wireless-communicates with mobile stations, and base stations of cells are synchr onized with each other. FIG. 1A is a conceptual view for explaining a method in which a mobile station ca n estimate its own location, using cell search signals that are received from a base stati on of a home cell and a base station of a neighboring cell, according to an embodiment of the present invention. FIG. 1 B illustrates cell search signals that are received by the mobile station of FIG. 1A from the base station of the home cell and the base station of the neighboring cell. FIG. 2 is a conceptual view for explaining a method of estimating maximum estimation errors of distances from mobile stations to a base station, accordi ng to an embodiment of the present invention.

Referring to FIGS. 1A and 1 B, the mobile station X estimates its own location by receiving cell search signals 140 and 150 from the base station 100 of the home cell A and the base station 110 of the neighboring cell B. Here, it is assumed that signals ar e linearly transmitted from the base stations 100 and 110 to the mobile station X. Sine e the base station 100 of the home cell A is synchronized with the base station 110 of t he neighboring cell B through a satellite, etc., the cell search signals are transmitted at t he same time. The mobile station X receives the cell search signals from the two base stations 100 and 110, and performs auto-correlation to catch a downlink timing. Duri ng cell searching, the mobile station X acquires cell IDs and downlink timings of the two base stations 100 and 110.

The mobile station X receives the cell search signals 140 and 150 from the base stations 100 and 110 of the home cell A and neighboring cell B, and calculates a time di fference T_b-T₃ between a time at which the cell search signal 140 is received and a time at which the cell search signal 150 is received. The mobile station X can estimate upl ink delay time information of the neighboring cell B and distances from the mobile statio n X to the base stations 100 and 110, using the time difference T_b-T_a. The smaller the time difference T_b-T₃ is, the more distant the mobile station X is I ocated from the base station 100 of the home cell A. Accordingly, an error of the esti mated distance between the base station 100 in the home cell A and the mobile station X is the maximum when the cell search signals 140 and 150 are concurrently received f rom the two base stations 100 and 110, that is, when the mobile station X is located at an edge between the home cell A and the neighboring cell B rather than in the home ce H A.

Referring to FIG. 2, when a mobile station concurrently receives cell search sign als from a base station 200 of a home cell A and a base station 210 of a neighboring ce Il B, the possible locations of the mobile station include a location 230 (represented by a mobile station X") nearest to the base station 200 and a location 250 (represented by a mobile station X') most distant from the base station 200. If the location of the bas e station 200, the nearest possible location 230, and the most distant possible location 250 are approximately modeled to a right triangle, a maximum estimation error can be c alculated to (2V3 -l)« 0.154 , according to distance ratios corresponding to the edge len gths of the right triangle.

Hereinafter, a method of estimating uplink delay time information and distances f rom a mobile station to base stations, according to an arrival-time difference between t wo signals, will be described in more detail. If times at which cell search signals are received from the base station 200 of the home cell A and the base station 210 of the neighboring cell B are respectively T_a and

T_b, the radiuses of the home cell A and the neighboring cell B are respectively RA and R

_B, distances between a mobile station and the base stations 200 and 210 of the home c ell A and the neighboring cell B are respectively DA and D_B, uplink delay time informatio n of the home cell A and the neighboring cell B are respectively TA and TB, a location er ror is E, and the speed of light is C, the variables have relationships expressed by Equa tions 1 , 2, 3, and 4.

T_A = D_A /C (1 ) T_B = D_B IC (2)

T_B - T_A = T_b -T_a (3)

R_A + R_B ≤ D_A + D_B ≤ \Λ5(R_A + R_B) (4)

Equations 1 and 2 represent the relationships between the uplink delay time infor mation TA and TB and the distances DA and DB. Equation 3 represents the relationship between the uplink delay time information TA and TB and the times T₃ and T_b at which t he cell search signals are received. The mobile station can estimate the difference T_b- T₃ between the times T₃ and T_b at which the cell search signals are received. Accordin gly, by using the difference T_b-T_a, the uplink delay time information TB of the neighborin g cell B can be estimated when handover is performed, that is, when the mobile station knows the uplink delay time information TA of the home cell A.

Accordingly, the mobile station can transmit data using the estimated uplink dela y time information of the neighboring cell B, without transmitting an asynchronous RAC H burst in order to acquire the uplink delay time information of the neighboring cell B. Equation 4 is induced from the case illustrated in FIG. 2, and a constant 1.15 in

Equation 4 is an approximate value of 2/V3 . When a mobile station initially accesses the base station 200 of the home cell A, and when a mobile station tries to know its ow n location information DA and DB, the location information D_A and D_B can be obtained fr om Equation 4. The process is as follows. Since T_b-T_a is known, D_B-D_A can be obtai ned using Equations 1 , 2, and 3.

If it is assumed that D_B-D_A is k, Equation 5 is obtained.

D_B - D_A = k,D_B = k + D_A (5)

If Equation 5 is substituted for Equation 4, Equation 4 is rewritten to Equation 6. Thus, DA can be obtained from Equation 6 and D_B can be obtained from Equation 5.

(R_A + R_B - k) _^ UW_t + R_t -k)

2 ^A 2 (6)

Therefore, if the mobile station knows only information for the sizes of the home cell A and neighboring cell B, the mobile station can know the distances from the mobil e station to the base stations of the home cell A and neighboring cell B. Information fo r the size of a cell corresponding to a cell ID can be stored in advance in the mobile stat ion through a well-known method, or can be informed to the mobile station through a br oadcast channel (BCH) from the corresponding base station.

Referring to FIG. 1A, on the basis of the estimated distances from the mobile sta tion X to the base stations 100 and 110, it is determined that the mobile station X can b e located at a line 130. Mathematically, this means that the mobile station X is located on a hyperbolic curve whose focal points correspond to the base stations 100 and 110 of the two cells A and B on an orthogonal coordinate.

Meanwhile, as illustrated in FIG. 2, by measuring times at which cell search sign als are respectively received from the base station 200 of the home cell A and the base station 210 of the neighboring cell B, the mobile station can estimate the distance from t he mobile station to the base station 200 of the home cell A within an error range of abo ut 15%, and thus reduce by about 15% a GP of an asynchronous RACH used to acquir e uplink delay time information when random access for data transmission is tried.

Therefore, in the case of a cell having the size of 15 km, a GP of 15ms, instead of a GP of generally 100 ms, can be assigned to an asynchronous RACH burst, and ac cordingly, more messages can be transmitted through the asynchronous RACH.

According to the current embodiment, when an initial asynchronous RACH burst and a periodic asynchronous RACH burst are transmitted, GP resources can be saved, and a mobile station can know uplink delay time information on the basis of size inform ation of cells, and thus needs not to transmit an asynchronous RACH requiring uplink d elay time information to a base station, or can use a longer RACH transmission period c ompared to a conventional technique. FIG. 3 illustrates the structure of a 3G Long Term Evolution (LTE) uplink frame a ccording to an embodiment of the present invention.

In an Orthogonal Frequency-Division Multiplexing (OFDM) system, when uplink s ignals output from a plurality of mobile stations reach a base station, the base station c an prevent inter carrier interference from being generated when demodulating the uplin k signals if the uplink signals reach within a cyclic prefix (CP) of the base station. Sine e the respective mobile stations are located at different distances with respect to the ba se station, uplink delay time information of the uplink signals is changed for each mobile station and according to the movement of the mobile station. Thus, the base station needs to periodically inform the uplink delay time information of the mobile stations. In a 3^rd Generation Partnership Project Long Term Evolution (3GPP LTE), when a mobile station is initially powered on or handed over to a different cell, the mobile station trans mits an asynchronous RACH to a base station of the different cell, and the base station informs the mobile station of uplink delay time information through the result of auto-cor relation on the asynchronous RACH. A signal which is sent by the mobile station so th at the mobile station can know uplink delay time information per a predetermined period has a high possibility of using an asynchronous RACH.

Referring to FIG. 3, a single wireless frame 300 includes a RACH transmission p art for transmitting RACH bursts and a data transmission part for transmitting user pack et data. The data transmission part includes a plurality of data sub-frames 310, and th e RACH transmission part includes one or more RACH sub-frames 320. Each RACH sub-frame 320 is divided into a plurality of sub-bands. The mobile station uses only a sub-band in a RACH sub-frame when transmitting a RACH burst.

Each RACH burst 350 includes a preamble 351 and a GP 355. Since the RAC H burst is a signal which is transmitted from a mobile station to a base station while no uplink timing is caught, the RACH burst needs to have a GP which is proportional to the size of a cell to which the base station belongs in order to prevent inter carrier interfere nee and inter symbol interference from being generated.

FIG. 4A is a conceptual diagram for explaining a method of estimating the locatio n of a mobile station, using cell search signals that are received by the mobile station fr om base stations of a home cell and two neighboring cells, according to another embod iment of the present invention. FIG. 4B illustrates cell search signals that are received by the mobile station of FIG. 4A from the base stations of the home cell and the neighb oring cells. Referring to FIGS. 4A and 4B, the mobile station X receives the cell search signa

Is 440, 450, and 460 respectively from the base stations 400, 410, and 420. When the mobile station X can receive cell search signals transmitted from three or more base st ations, the mobile station X can acquire its exact location, as well as the distance from t he mobile station X to the base station 400 of the home cell A, using a general triangula tion principle.

A first distance from the mobile station X to the base station 400 is estimated fro m a time difference T_a-T_b between a time at which the cell search signal 440 transmitte d from the base station 400 of the home cell A is received by the mobile station X and a time at which the cell search signal 450 transmitted from the base station 410 of the n eighboring cell B is received by the mobile station X, so that a first location hyperbolic c urve 470 can be estimated. Also, a second distance from the mobile station X to the b ase station 400 is estimated from a time difference T_a-T_c between a time at which the c ell search signal 440 transmitted from the base station 400 of the home cell A is receive d by the mobile station X and a time at which the cell search signal 460 transmitted fro m the base station 420 of the neighboring cell C is received by the mobile station X₁ so t hat a second location hyperbolic curve 480 can be estimated. An intersection of the fir st and second hyperbolic curves 470 and 480 becomes the location of the mobile statio n X.

When three base stations exist as in the above embodiment, if the location of a mobile station is estimated using arrival-time differences of signals transmitted from the three base stations, the location of the mobile station is represented by only two indepe ndent variables. Accordingly, the location of the mobile station can be estimated in a 2 -dimensional plane and height information of the mobile station is not acquired. Theref ore, in order to acquire the 3-dimensional location of the mobile station, which includes i ts height information, it is preferable that the mobile station receives signals from four or more base stations.

The above-described embodiment is similar to the case of GPS in that the locati on of a mobile station is acquired using only signals that are received by the mobile stati on, that is, by a receiver, without individual information from a base station, that is, from a transmitter. That the mobile station receives signals from four or more base station s corresponds that GPS requires signals including time information that are transmitted from four satellites in order to acquire location information including three coordinates in a 3-dimensional space. In the above-described embodiment, the mobile station can acquire its more ace urate location by measuring arrival-times between cell search signals that are transmitte d from thee or more base stations. The mobile station needs to be aware of the size a nd configuration (the base station's location) of a neighbor cell corresponding to the nei ghboring cell's ID. The size and configuration of the neighboring cell can be stored in advance in the mobile station by a well-known method so that the mobile station is awar e of the size and configuration of the neighboring cell, or can be acknowledged to the m obile station through a Broadcast Channel (BCH) from a base station.

FIG. 5 is a block diagram of a data transmission apparatus of a mobile station us ing cell search signals, according to an embodiment of the present invention. FIG. 7 is a flowchart of a data transmission method which is performed using cell search signals by a mobile station, according to an embodiment of the present invention. Hereinafte r, the operation of the data transmission apparatus of the mobile station illustrated in Fl G. 5 will be described with reference to FIG. 7.

Referring to FIGS. 5 and 7, the data transmission apparatus 500 of the mobile st ation includes a receiver 510, a time difference calculator 520, an uplink delay time calc ulator 530, and a transmitter 540. Calculating of a time difference and uplink delay tim e has been described above, and accordingly, a detailed description therefor will be omi tted.

The receiver 510 receives cell search signals from base stations of a home cell a nd a neighboring cell, wherein the base station of the home cell is synchronized with the base station of the neighboring cell (operation S710). The mobile station can receive one or more cell search signals from one or more neighboring cells. Each cell search signal includes a cell ID.

The time difference calculator 520 calculates an arrival-time difference between t he cell search signals that are received from the base stations of the home cell and the neighboring cell (operation S720). In detail, the time difference calculator 520 measur es times at which the cell search signals are received, and calculates a time difference between the times. A method of measuring the difference between the times includes a variety of methods including an auto-correlation method. If the time difference calcul ator 520 receives cell search signals respectively from base stations of two or more nei ghboring cells as well as the home cell, the time difference calculator 520 calculates tim e differences between a time at which a cell search signal is received from the base sta tion of the home cell and times at which cell search signals are received from the base stations of the neighboring cells, and thus obtains two or more time differences.

The uplink delay time calculator 530 calculates uplink delay times of the neighbo ring cells on the basis of the time differences (operation S730). Since the mobile stati on already knows the uplink delay time of the home cell when the mobile station is hand ed over to a different cell, the uplink delay time calculator 530 can calculate the uplink d elay times of the neighboring cells, using the time differences and the uplink delay time of the home cell. Accordingly, the mobile station needs not to try random access throu gh an asynchronous RACH burst in order to know the uplink delay times of the neighbor ing cells.

The transmitter 540 transmits uplink data to the base stations of the neighboring cells on the basis of the uplink delay times of the neighboring cells (operation S740).

FIG. 6 is a block diagram of a data transmission apparatus of a mobile station us ing cell search signals, according to another embodiment of the present invention. Fig . 8 is a flowchart of a data transmission method which is performed using cell search si gnals by a mobile station, according to another embodiment of the present invention. Hereinafter, the operation of a data transmission apparatus of the mobile station, as NIu strated in FIG. 6, will be described with reference to FIG. 8.

Referring to FIGS. 6 and 8, the data transmission apparatus 600 includes a recei ver 610, a calculator 620, a location estimating unit 630, an uplink information estimatin g unit 640, and a transmitter 650. The receiver 610 receives cell search signals from base stations of a home cell a nd at least one neighboring cell, wherein the mobile station is synchronized with the bas e station of the home cell (operation S810). The mobile station can receive cell search signals from one or more neighboring cells. Each cell search signal includes a cell ID

The calculator 620 calculates an arrival-time difference of the cell search signals that are transmitted from the base stations of the home cell and neighboring cell (operat ion S820). That is, the calculator 620 measures times at which the cell search signals are received, and calculates a difference between the measured times. A method of measuring the times at which the cell search signals are received can include a variety of methods such as an auto-correlation method.

The location estimating method 630 estimates location errors and distances from the mobile station to the base stations of the home cell and neighboring cell, on the ba sis of the time difference (operation S830). A method of estimating the distances from the mobile station to the base stations of the home cell may be one of a variety of well- known methods for converting a time into a distance. In order to estimate the distance s and location errors, cell information is used together with the arrival-time difference of the cell search signals. The cell information includes information regarding the sizes o f the home cell and neighboring cell. The cell information is already stored in the mobil e station, or can be acquired through a BCH from a base station. Also, the location est imating unit 630 can receive cell search signals from two or more neighboring cells, esti mates distances from the mobile station and the base stations of the two or more neigh boring cells on the basis of arrival-time differences of the cell search signals, and accur ately estimates the location of the mobile station on the basis of the estimated distance s and the location information of the additional base stations. The location information of the base stations is already stored in the mobile station, or can be acquired through a BCH from the base stations.

The uplink information estimating unit 640 reverse-estimates the uplink delay tim e information, on the basis of the estimated values of the location errors of the mobile st ation and the cell information for the base stations (operation S840). The cell informati on includes the size information of the home cell and neighboring cells. The cell infor mation can be already stored in the mobile station, or can be acquired through a BCH fr om the base stations. The uplink delay time information includes one of a round trip d elay time and a timing advance. The transmitter 650 determines whether an asynchronous (RACH) burst needs t o be transmitted in order to request additional uplink delay time information to the base stations (operation S850). When an asynchronous RACH burst needs to be transmitte d, the transmitter 650 determines the size of a GP of the asynchronous RACH burst on the basis of the uplink delay time information (operation S860). If the transmitter 650 r eceives an acknowledge (ACK) signal including the uplink delay time information from t he base stations after the mobile station transmits the asynchronous RACH burst (oper ation S870), the transmitter 650 transmits uplink data on the basis of the uplink delay ti me information (operation S880). Since the uplink information estimating unit 640 esti mates uplink delay time information per a predetermined period, the transmitter 650 ca n reduce the number of RACH burst transmissions by setting the transmission period of the RACH burst to be longer than the transmission period of a RACH burst which is se t by a conventional mobile station. Also, when no RACH burst transmission is needed, the transmitter 650 can transmit uplink data to the base stations using the uplink delay time information which is acquired by the estimation, without transmitting any RACH bur st to the base stations (operation S890).

The present invention can also be embodied as computer readable codes on a c omputer readable recording medium. The computer readable recording medium is an y data storage device that can store data which can be thereafter read by a computer s ystem. Examples of the computer readable recording medium include read-only mem ory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, o ptical data storage devices, and carrier waves (such as data transmission through the I nternet). The computer readable recording medium can also be distributed over netwo rk coupled computer systems so that the computer readable code is stored and execute d in a distributed fashion. Also, functional programs, codes, and code segments for ac complishing the present invention can be easily construed by programmers skilled in th e art to which the present invention pertains.

While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that vario us changes in form and details may be made therein without departing from the spirit a nd scope of the invention as defined by the appended claims. The preferred embodim ents should be considered in descriptive sense only and not for purposes of limitation. T herefore, the scope of the invention is defined not by the detailed description of the inve ntion but by the appended claims, and all differences within the scope will be construed as being included in the present invention.

Claims

1. A method in which a mobile station transmits data using cell search signals, th e method comprising: receiving cell search signals from a base station of a home cell and a base station of at least one neighboring cell, wherein the base station of the home cell is synchronize d with the base station of the at least one neighboring cell; calculating an arrival-time difference of the cell search signals that are transmitted fr om the base station of the home cell and the base station of the at least one neighborin g cell; and calculating uplink delay time of the at least one neighboring cell on the basis of the a rrival-time difference.

2. The method of claim 1 , wherein each cell search signal includes a cell ID.

3. The method of claim 1 , further comprising transmitting uplink data to the base station of the at least one neighboring cell, using the uplink delay time.

4. A method in which a mobile station transmits data using cell search signals, th e method comprising: receiving cell search signals from a base station of a home cell and a base station of at least one neighboring cell, wherein the base station of the home cell is synchronize d with the base station of the at least one neighboring cell; calculating an arrival-time difference of the cell search signals that are transmitted fr om the base station of the home cell and the base station of the at least one neighborin g cell; and estimating distances from the mobile station to the base stations of the home cell an d the at least one neighboring cell on the basis of the arrival-time difference.

5. The method of claim 4, further comprising: estimating a location error of the mobile station on the basis of the estimated dist ances; determining the size of a guide period (GP) of a random access channel burst th at is to be transmitted to the base stations of the home cell and the at least one neighbo ring cell, on the basis of the location error; and transmitting uplink data to the base stations of the home call and the at least one neighboring cell, on the basis of uplink delay time information which is acquired from r esponses of the base stations of the home cell and the at least one neighboring cell wit 5 h respect to the random access channel burst.

6. The method of claim 4, wherein each cell search signal includes a cell ID.

7. The method of claim 4, wherein the calculating of the arrival-time difference coo mprises performing auto-correlation on the cell search signals and calculating the arriva l-time difference.

8. The method of claim 4, further comprising estimating a location of the mobile st ation on the basis of the estimated distances and location information of the base statio5 ns of the home cell and the at least one neighboring cell.

9. The method of claim 4, further comprising: estimating a location error of the mobile station on the basis of the estimated distanc es; 0 estimating uplink delay times of the home cell and the at least one neighboring cell, on the basis of the location error; and transmitting uplink data to the base stations using the uplink delay times.

10. An apparatus of transmitting data in a mobile station, the apparatus comprisin? g: a receiver receiving cell search signals from a base station of a home cell and a bas e station of at least one neighboring cell, wherein the base station of the home cell is sy nchronized with the base station of the at least one neighboring cell; a time difference calculator calculating an arrival-time difference of cell search signal0 s that are transmitted from the base station of the home cell and the base station of the at least one neighboring cell; and an uplink delay time calculator calculating uplink delay time of the at least one neigh boring cell on the basis of the arrival-time difference.

11. The apparatus of claim 10, wherein each cell search signal includes a cell ID.

12. The apparatus of claim 10, further comprising a transmitter transmitting uplink data to the base station of the at least one neighboring cell, using the uplink delay time

13. An apparatus of transmitting data using location estimation in a mobile station , the apparatus comprising, a receiver receiving cell search signals from a base station of a home cell and a bas e station of at least one neighboring cell, wherein the base station of the home cell is sy nchronized with the base station of the at least one neighboring cell; a calculator calculating an arrival-time difference of the cell search signals that are tr ansmitted from the base station of the home cell and the base station of the at least on e neighboring cell; and a location estimating unit estimating distances from the mobile station to the base st ations of the home cell and the at least one neighboring cell on the basis of the arrival-ti me difference.

14. The apparatus of claim 13, wherein the location estimating unit estimates a Io cation error of the mobile station on the basis of the estimated distances, the apparatus further comprising: an uplink information estimating unit determining the size of a Guard Period (GP) of a random access channel burst, on the basis of the location error of the mobile station; and a transmitter transmitting uplink data to the base stations of the home cell and the at least one neighboring cell, on the basis of uplink delay time information which is acquir ed from responses of the base stations of the home cell and the at least one neighborin g cell with respect to the random access channel burst.

15. The apparatus of claim 13, wherein each cell search signal includes a cell ID.

16. The apparatus of claim 13, wherein the calculator calculates the arrival-time d ifference by performing auto-correlation on the cell search signals.

17. The apparatus of claim 13, wherein the location estimating unit estimates a Io cation of the mobile station, on the basis of the estimated distances and location inform ation of the base stations.

18. The apparatus of claim 14, wherein the location estimating unit estimates the location error of the mobile station on the basis of the estimated distances, the apparat us further comprising: an uplink information estimating unit estimating uplink delay times of the home c ell and the at least one neighboring cell, on the basis of the location error of the mobile station; and a transmitter transmitting uplink data to the base stations of the home cell and th e at least one neighboring cell, using the uplink delay times.

19. A computer-readable recording medium having embodied thereon a program for executing the method of one of claims 1 through 9.