WO2007055527A1

WO2007055527A1 - Cell search method in ofdm cellular system, frame transmission method thereof, and forward link frame structure thereof

Info

Publication number: WO2007055527A1
Application number: PCT/KR2006/004694
Authority: WO
Inventors: Il-Gyu Kim; Nam-Il Kim; Hyeong-Geun Park; Kap-Seok Chang; Young-Hoon Kim; Seung-Chan Bang
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2005-11-10
Filing date: 2006-11-10
Publication date: 2007-05-18

Abstract

Provided are a cell search method, a frame transmission method thereof, and a forward link frame structure thereof. The cell search method used by a terminal to search a target cell using reception signals received from a plurality of base stations, each base station transmitting a frame of its cell, in an Orthogonal Frequency-Division Multiplexing (OFDM) cellular system comprising a plurality cells to which a cell-specific scrambling code is assigned includes: detecting a hopping pattern of the target cell using reception sync channel symbols, which are signals corresponding to sync channel symbol positions of the reception signals, wherein the frame of each cell comprises M sync channel symbols code-hopped according to a hopping pattern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and respectively corresponding to each code group to which a scrambling code of each cell belongs, and an arbitrary hopping pattern used in the OFDM cellular system differs from a cyclically shifted result of the hopping pattern, other hopping patterns, or cyclically shifted results of the other hopping patterns; and detecting a code group of the target cell based on the detected hopping pattern. Accordingly, a cell search time and the complexity of the cell search can be reduced.

Description

CELL SEARCH METHOD IN OFDM CELLULAR SYSTEM, FRAME TRANSMISSION METHOD THEREOF, AND FORWARD LINK FRAME STRUCTURE THEREOF

Technical Field

The present invention relates to an Orthogonal Frequency-Divisio n Multiplexing (OFDM) cellular system, and more particularly, to a cell se arch method in an OFDM cellular system, a frame transmission method t hereof, and a forward link frame structure thereof.

Background Art

Wideband Code Division Multiple Access (WCDMA) systems of th e 3^rd Generation Partnership Project (3GPP) use a total of 512 long Pseu do-Noise (PN) scrambling codes in order to identify base stations of a for ward link. That is, adjacent base stations in a WCDMA system use a un ique long PN scrambling code as a scrambling code of forward link chan nels. When a mobile station is turned on, the mobile station must acqui re system timing of an initial cell and a long PN scrambling code identifier (ID) (it is also called a cell ID) of the initial cell. This process is called a mobile station's cell search process. The initial cell is determined acco rding to a location of the mobile station when the mobile station is turned on, and generally indicates a cell of a base station corresponding to the g reatest one of signal components of the base stations, which are include d in a forward link reception signal of the mobile station. The system ti ming indicates slot sync or a frame boundary.

In a WCDMA system, in order to easily perform the mobile station' s cell search process, the 512 long PN scrambling codes are grouped int o 64 code groups, and a Primary Synchronization Channel (PSC) and a Secondary Synchronization Channel (SSC) are included in a forward link channel. The PSC is used for a mobile station to acquire slot sync, an d the SSC is used for the mobile station to acquire a 10-msec frame bou ndary and a long PN scrambling code group ID.

The mobile station's cell search process in a WCDMA system is a ccomplished in 3 steps. In the first step, a mobile station acquires slot s ync using a PSC. In the WCDMA system, the 10-msec frame includes 15 slots. Each base station transmits a PSC in every 10 msec frame. The same PSC is used for the 15 slots, and all base stations use the sa me PSC. In the first step, the mobile station acquires slot sync using a matching filter suitable for the PSC.

In the second step, a long PN scrambling code group ID and a 10- msec frame boundary are acquired using the slot sync (i.e., slot timing inf ormation) acquired in the first step and a SSC.

In the third step, a long PN scrambling code ID corresponding to a long PN scrambling code used by the initial cell is acquired using a com mon pilot channel code correlator based on the 10-msec frame boundary and the long PN scrambling code group ID that were acquired in the sec ond step. That is, since 8 long PN scrambling codes are mapped to a si ngle long PN scrambling code group, in the third step, the mobile station calculates a correlation value of each of the 8 long PN scrambling codes and detects the long PN scrambling code ID used in the initial cell based on the calculated result. In WCDMA, a sync channel consists of a PSC and a SSC, and the PSC, the SSC, a common pilot channel, and other d ata channels are multiplexed in a Code Division Multiplexing (CDM) meth od based on a time domain direct sequence spread spectrum.

Recently, in the 3GPP, an OFDM-based wireless transmission tec hnology standardization is being established as a part of 3^rd Generation Long Term Evolution (3G-LTE) to compensate for disadvantages of WC DMA. The sync channel & common pilot channel structure and the mob ile station's cell search process used in WCDMA are suitable for Direct S equence Code Division Multiple Access (DS-CDMA) but cannot be applie d to an OFDM forward link. Thus, a forward link sync channel & commo n pilot channel structure and a mobile station's cell search method are re quired in an OFDM cellular system.

Brief Description of the Drawings

The above and other features and advantages of the present inve ntion will become more apparent by describing in detail exemplary embo diments thereof with reference to the attached drawings in which:

FIG. 1 a conceptual diagram for explaining how to group scrambli ng codes according to an embodiment of the present invention;

FIG. 2 is illustrates a structure of a forward link frame according to an embodiment of the present invention;

FIG. 3 illustrates a sub-frame containing a sync channel symbol a ccording to an embodiment of the present invention; FIG. 4 illustrates a hopping code according to an embodiment of t he present invention;

FIG. 5 is a table for describing the concept of cyclically shifted hop ping sequences (hopping patterns); FIG. 6 illustrates a structure of a sync channel symbol in the time domain according to an embodiment of the present invention;

FIG. 7 is a block diagram of a frame transmission apparatus accor ding to an embodiment of the present invention;

FIGS. 8 and 9 are a block diagram and a conceptual diagram, res pectively, of a diversity controller in a case where delay diversity is applie d to the frame transmission apparatus illustrated in FIG. 7, according to a n embodiment of the present invention;

FIG. 10 is a block diagram of a receiver of a mobile station accordi ng to an embodiment of the present invention; FIG. 11 is a block diagram of a first detector of the receiver illustra ted in FIG. 10, according to an embodiment of the present invention;

FIG. 12 is a graph illustrating differential correlation values calcula ted by a differential correlator illustrated in FIG. 11 , according to an embo diment of the present invention; FIG. 13 is a diagram for describing a signal used in a second dete ctor of the receiver illustrated in FIG. 10, according to an embodiment of t he present invention;

FIGS. 14 and 15 are block diagrams of the second detector of the receiver illustrated in FIG. 10, according to an embodiment of the present invention;

FIG. 16 is a block diagram of a hopping pattern detector illustrated in FIG. 14 or 15, according to an embodiment of the present invention;

FIG. 17 is a block diagram of a sequence correlation calculator HIu strated in FIG. 16, according to an embodiment of the present invention; FIG. 18 is a graph illustrating sequence correlation values calculat ed from sample values of a single reception sync channel symbol accordi ng to an embodiment of the present invention;

FIG. 19 illustrates Pχ (N-l) sequence correlation values stored i n a buffer illustrated in FIG. 16 when P = 5 and N = 41 , according to an embodiment of the present invention;

FIG. 20 is a conceptual diagram for explaining positions of frame boundaries and reception common pilot channel symbols according to an embodiment of the present invention; FIG. 21 is a block diagram of a third detector of the receiver illustr ated in FIG. 10, according to an embodiment of the present invention;

FIG. 22 is a conceptual diagram for explaining an operation of a pi lot correlator illustrated in FIG. 21 , according to an embodiment of the pr esent invention;

FIG. 23 is a block diagram of the first detector of the receiver illust rated in FIG. 10, according to another embodiment of the present inventi on;

FIG. 24 is a conceptual diagram for explaining an operation of a fr equency offset switching unit illustrated in FIG. 23, according to an embo diment of the present invention;

FIG. 25 is a flowchart illustrating a cell search method according t o an embodiment of the present invention;

FIG. 26 is a flowchart illustrating a cell search method according t o another embodiment of the present invention;

FIG. 27 is a flowchart illustrating a frame transmission method of a base station according to an embodiment of the present invention;

FIG. 28 is a block diagram of the second detector of the receiver il lustrated in FIG. 10, according to another embodiment of the present inv ention;

FIGS. 29 and 30 are diagrams for explaining an operation of a ho me cell component canceller illustrated in FIG. 28, according to an embo diment of the present invention;

FIG. 31 is a diagram for explaining a gating mode of a mobile stati on performing an adjacent cell search process in an idle mode according to an embodiment of the present invention; and

FIG. 32 is a flowchart illustrating an adjacent cell search method o f a mobile station according to an embodiment of the present invention.

Technical Problem

The present invention provides a cell search method in which an i nitial cell search and an adjacent cell search for handover are perform ed in an Orthogonal Frequency-Division Multiplexing (OFDM) cellular s ystem. The present invention also provides a frame transmission method for supporting the cell search method.

The present invention also provides a structure of a forward link fr ame used in the cell search method. Technical Solution

According to an aspect of the present invention, there is provided a cell search method used by a terminal to search a target cell using rec eption signals received from a plurality of base stations, each base statio n transmitting a frame of its cell, in an Orthogonal Frequency-Division Mu Itiplexing (OFDM) cellular system comprising a plurality cells to which a c ell-specific scrambling code is assigned, the cell search method comprisi ng: detecting a hopping pattern of the target cell using reception sync ch annel symbols, which are signals corresponding to sync channel symbol positions of the reception signals, wherein the frame of each cell compris es M sync channel symbols code-hopped according to a hopping pattern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and respec tively corresponding to each code group to which a scrambling code of e ach cell belongs, and an arbitrary hopping pattern used in the OFDM cell ular system differs from a cyclically shifted result of the hopping pattern, other hopping patterns, or cyclically shifted results of the other hopping p atterns; and detecting a code group of the target cell based on the detect ed hopping pattern.

According to another aspect of the present invention, there is prov ided a cell search method used by a terminal to search a target cell using reception signals received from a plurality of base stations, each base s tation transmitting a frame of its cell, in an Orthogonal Frequency-Divisio n Multiplexing (OFDM) cellular system comprising a plurality cells to whic h a cell-specific scrambling code is assigned, the cell search method co mprising: detecting a hopping pattern of the target cell using reception sy nc channel symbols, which are signals corresponding to sync channel sy mbol positions of the reception signals, wherein the frame of each cell co mprises M sync channel symbols code-hopped according to a hopping p attern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and r espectively corresponding to each code group to which a scrambling cod e of each cell belongs, and an arbitrary hopping pattern used in the OFD M cellular system differs from a cyclically shifted result of the hopping pat tern, other hopping patterns, or cyclically shifted results of the other hopp ing patterns; and detecting a frame boundary based on the detected hop ping pattern. According to another aspect of the present invention, there is prov ided a cell search method used by a terminal to search a target cell using reception signals received from a plurality of base stations, each base s tation transmitting a frame of its cell, in an Orthogonal Frequency-Divisio n Multiplexing (OFDM) cellular system comprising a plurality cells to whic h a cell-specific scrambling code is assigned, the cell search method co mprising: detecting a hopping pattern of the target cell using reception sy nc channel symbols, which are signals corresponding to sync channel sy mbol positions of the reception signals, wherein the frame of each cell co mprises M sync channel symbols code-hopped according to a hopping p attern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and r espectively corresponding to a scrambling code of each cell, and an arbit rary hopping pattern used in the OFDM cellular system differs from a cycl ically shifted result of the hopping pattern, other hopping patterns, or cycl ically shifted results of the other hopping patterns; and detecting a scram bling code of the target cell based on the detected hopping pattern.

According to another aspect of the present invention, there is prov ided a cell search method used by a terminal to search a target cell using reception signals received from a plurality of base stations, each base s tation transmitting a frame of its cell, in an Orthogonal Frequency-Divisio n Multiplexing (OFDM) cellular system comprising a plurality cells to whic h a cell-specific scrambling code is assigned, the cell search method co mprising: detecting a hopping pattern of the target cell using reception sy nc channel symbols, which are signals corresponding to sync channel sy mbol positions of the reception signals, wherein the frame of each cell co mprises M sync channel symbols code-hopped according to a hopping p attern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and r espectively corresponding to a scrambling code of each cell, and an arbit rary hopping pattern used in the OFDM cellular system differs from a cycl ically shifted result of the hopping pattern, other hopping patterns, or cycl ically shifted results of the other hopping patterns; and detecting a frame boundary based on the detected hopping pattern. According to another aspect of the present invention, there is prov ided a frame transmission method used by a base station belonging to a n arbitrary cell to transmit a frame in an Orthogonal Frequency-Division Multiplexing (OFDM) cellular system comprising a plurality cells to which a cell-specific scrambling code is assigned, the frame transmission meth od comprising: generating M sync channel code sequences forming a ho pping pattern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and respectively corresponding to a scrambling code of each cell or a c ode group to which the scrambling code belongs; and generating a frame comprising M sync channel symbols code-hopped on a frequency doma in using each of the generated M sync channel code sequences and tran smitting the generated frame, wherein an arbitrary hopping pattern used i n the OFDM cellular system differs from a cyclically shifted result of the h opping pattern, other hopping patterns, or cyclically shifted results of the other hopping patterns.

According to another aspect of the present invention, there is prov ided an adjacent cell search method used by a terminal to search a targe t cell using reception signals received from a plurality of base stations, ea ch base station transmitting a frame of its cell, in an Orthogonal Frequen cy-Division Multiplexing (OFDM) cellular system comprising a plurality eel Is to which a cell-specific scrambling code is assigned, the adjacent cell s earch method comprising: acquiring symbol sync and a frame boundary of an adjacent cell by considering symbol sync and a frame boundary of a home cell as the symbol sync and the frame boundary of the adjacent cell, wherein the frame of each cell comprises M sync channel symbols c ode-hopped according to a hopping pattern of the cell, where M is a natu ral number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and respectively corresponding to each c ode group to which a scrambling code of each cell belongs, and an arbitr ary hopping pattern used in the OFDM cellular system differs from a cycli cally shifted result of the hopping pattern, other hopping patterns, or cycli cally shifted results of the other hopping patterns; detecting a hopping pa ttern of the adjacent cell using reception sync channel symbols, which ar e signals corresponding to sync channel symbol positions of the receptio n signals; and detecting a code group of the adjacent cell based on the d etected hopping pattern.

According to another aspect of the present invention, there is prov ided an adjacent cell search method used by a terminal to search a targe t cell using reception signals received from a plurality of base stations, ea ch base station transmitting a frame of its cell, in an Orthogonal Frequen cy-Division Multiplexing (OFDM) cellular system comprising a plurality eel Is to which a cell-specific scrambling code is assigned, the adjacent cell s earch method comprising: acquiring symbol sync and a frame boundary of an adjacent cell by considering symbol sync and a frame boundary of a home cell as the symbol sync and the frame boundary of the adjacent cell, wherein the frame of each cell comprises M sync channel symbols c ode-hopped according to a hopping pattern of the cell, where M is a natu ral number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and respectively corresponding to a sera mbling code of each cell, and an arbitrary hopping pattern used in the OF DM cellular system differs from a cyclically shifted result of the hopping p attern, other hopping patterns, or cyclically shifted results of the other ho pping patterns; detecting a hopping pattern of the adjacent cell using rec eption sync channel symbols, which are signals corresponding to sync ch annel symbol positions of the reception signals; and detecting a scrambli ng code of the adjacent cell based on the detected hopping pattern.

According to another aspect of the present invention, there is prov ided a structure of a forward link frame transmitted by a base station belo nging to an arbitrary cell in an Orthogonal Frequency-Division Multiplexin g (OFDM) cellular system comprising a plurality cells to which a cell-spec ific scrambling code is assigned, the forward link frame comprising M syn c channel symbols sequence-hopped according to a hopping pattern of t he cell, where M is a natural number equal to or greater than 2, each hop ping pattern containing M sync channel code sequences and respectively corresponding to a scrambling code of each cell or a code group to whic h the scrambling code belongs, wherein an arbitrary hopping pattern use d in the OFDM cellular system differs from a cyclically shifted result of th e hopping pattern, other hopping patterns, or cyclically shifted results of t he other hopping patterns.

Advantageous Effects

According to the present invention, in an OFDM cellular system, a cell search time of a mobile station can be reduced, and a cell search uni t operating with low complexity can be implemented. In addition, according to a sync acquisition method, synchronizatio n can be acquired with low complexity. In addition, according to an adja cent cell search method, in an OFDM cellular system in which base statio ns are in a base station synchronous mode, an adjacent cell search proc ess can be efficiently performed, and thus handover can be smoothly per formed, and battery consumption of a mobile station can be reduced.

Mode for Invention The present invention will now be described more fully with refere nee to the accompanying drawings, in which exemplary embodiments of t he invention are shown.

The present invention relates to a method of searching a target ce Il using a hopping pattern. The target cell search process is divided into an initial cell search process and an adjacent cell search process to allo w handover to occur. In the present specification, it is assumed that the target cell is an initial cell, however, it will be understood by those of ordi nary skill in the art that the present invention can also be applied to the a djacent cell search process. In addition, in the present specification, an embodiment of a method of efficiently searching an adjacent cell when th e cell search method is applied to an Orthogonal Frequency-Division MuI tiplexing (OFDM) cellular system operating in a base station sync mode i s also suggested.

In general, each base station of an OFDM cellular system scrambl es OFDM symbols using a long PN scrambling code. However, since th e base station can use another scrambling code instead of the long PN s crambling code, any code used to scramble OFDM symbols is hereinafte r called a scrambling code for convenience of description.

Though it is assumed in the present specification for convenience of description that each of the base stations includes 2 transmission ante nnas to describe several transmission diversity schemes, it will be unders tood by those of ordinary skill in the art that the present invention can be applied to all base stations regardless of the number of transmission ant ennas and transmission diversity schemes to be used are not limited to t he several transmission diversity schemes.

Though it is assumed in the present specification for convenience of description that the mobile station includes 2 reception antennas to de scribe a reception diversity scheme using a simple summing method as a data combining method, it will be understood by those of ordinary skill i n the art that the present invention can be applied to all mobile stations r egardless of the number of reception antennas and a reception diversity scheme and a data combining method to be used are not limited to the d escribed reception diversity scheme and the simple summing method. In the present specification, an OFDM symbol related to a sync ch annel is called a sync channel symbol for convenience of description. A n example of the sync channel symbol is an OFDM symbol including eac h sync channel chip forming a sync channel code sequence. Each sync channel chip is used as a Fourier coefficient in a subcarrier frequency of a frequency band occupied by the sync channel. That is, the sync cha nnel code sequence indicates a sequence formed with sync channel chip s respectively mapped to subcarriers of the sync channel symbol. The sync channel may exist in a hierarchical structure including a Primary Sy nchronization Channel (PSC) and a Secondary Synchronization Channel (SSC) or in a non-hierarchical structure including a single sync channel. In the case of the hierarchical structure, a PSC code sequence indicat es a sequence formed with PSC chips respectively mapped to subcarrier s of a PSC symbol, and an SSC code sequence indicates a sequence for med with SSC chips respectively mapped to subcarriers of an SSC symb ol. In the hierarchical structure, an OFDM symbol including PSC chips and an OFDM symbol including SSC chips may separately exist by perfo rming Time Division Multiplexing (TDM) of the PSC and the SSC, and an OFDM symbol including both PSC chips and SSC chips may exist by per forming Frequency Division Multiplexing (FDM) of the PSC and the SSC. In the present specification, for convenience of description, for the former case, the OFDM symbol including PSC chips is called a PSC sy mbol, and the OFDM symbol including SSC chips is called an SSC symb ol, and for the latter case, the OFDM symbol including both PSC chips a nd SSC chips is called a sync channel symbol.

The present invention relates to a method of performing a cell sea rch including symbol sync acquisition, frame boundary detection, and scr ambling code detection, and is divided into an embodiment A in which th e cell search is performed using each hopping pattern respectively corres ponding to each code group to which a scrambling code belongs and an embodiment B in which the cell search is performed using each hopping pattern respectively corresponding to each a scrambling code.

According to the embodiment A of the present invention, symbol s ync is acquired in a first detection step, a code group and a frame bound ary are detected using a hopping pattern in a second detection step, and a scrambling code is detected using a pilot correlation in a third detection step. The embodiment B of the present invention is divided into an emb odiment B-1 , which comprises a first detection step in which symbol sync is acquired and a second detection step in which a code group and a fra me boundary are detected using a hopping pattern, and an embodiment B-2 comprising the first detection step, the second detection step, and a t hird detection step in which a detection result of the first detection step a nd a detection result of the second detection step are verified using a pil ot correlation. According to the embodiment A of the present invention, since a mobile station uses only scrambling codes belonging to the code group detected in the second detection step to detect a scrambling code, complexity in the scrambling code detection can be reduced. In additio n, according to the embodiment B-1 of the present invention, a quick cell search can be performed, and according to the embodiment B-2 of the pr esent invention, since verification is performed, a cell search more reliabl e than the embodiment B-1 of the present invention can be performed.

The embodiments A, B-1 , and B-2 of the present invention are co mmonly related to a sync channel design for the second detection step, a nd another embodiment of the present invention suggests a sync channe I in a non-hierarchical structure in which a sync channel to which a hoppi ng pattern used in the second detection step is applied can be used to a cquire symbol sync in the first detection step. That is, this embodiment suggests a method of performing both the first detection step and the se cond detection step using a single type of sync channel symbol.

However, the second detection step in the embodiments A, B-1 , a nd B-2 of the present invention can be applied to "a sync channel in a hie rarchical structure" since an SSC of the hierarchical structure and a sync channel of the non-hierarchical structure use a hopping pattern. That is, a difference between the two structures is that a PSC is used in the first detection step in the hierarchical structure whereas a sync channel use d in the second detection step is used in the first detection step in the no n-hierarchical structure.

The term 'symbol sync acquisition' will be used in the present spe cification as a comprehensive term for sync channel symbol timing detect ion, sync slot timing detection, and sync slot boundary detection. That is, since a sync slot is established based on a sync channel symbol (in the c ase of the non-hierarchical structure) or a PSC symbol (in the case of the hierarchical structure), sync channel symbol timing is equivalent to sync slot timing. In addition, since an SSC symbol (in the case of separatel y existing from the PSC symbol in the hierarchical structure) generally exi sts at a predetermined position in the sync slot, the sync slot timing detec tion indicates that a position of an OFDM symbol in which a PSC and an SSC exist in the sync slot has been detected. The term 'symbol sync in formation' will be used in the present specification as a comprehensive te rm for information on sync channel symbol timing, information on sync si ot timing, and information on a sync slot boundary.

The term 'frame boundary detection' will be used in the present sp ecification as a comprehensive term for frame boundary timing detection. The term 'frame boundary information' will be used in the present spec ification as a comprehensive term for information on frame boundary timi ng.

The term 'code group detection' will be used in the present specifi cation as a comprehensive term for code group identifier detection and c ode group detection, and the term 'code group information' will be used i n the present specification as a comprehensive term for a code group ide ntifier and a code group. The term 'scrambling code detection' will be u sed in the present specification as a comprehensive term for scrambling code identifier detection and scrambling code detection, and the term 'sc rambling code information' will be used in the present specification as a c omprehensive term for a scrambling code identifier and a scrambling cod e.

The term 'Fourier transform' will be used for convenience of descri ption in the present specification as a comprehensive term for discrete F ourier transform and fast Fourier transform.

FIG. 1 is a conceptual diagram for explaining how to group scram bling codes according to an embodiment of the present invention.

A scrambling code or scrambling code ID 100 used to scramble c ommon pilot channel symbols or data channel symbols is assigned to ea ch base station belonging to an OFDM cellular system. In particular, ac cording to the current embodiment, the number of scrambling codes use d in the OFDM cellular system is 512, wherein N_c =8 scrambling codes form a single code group. That is, according to the current embodiment , 64 code groups exist in the OFDM cellular system. Reference numeral 102 denotes a code group ID. The code group ID 102 corresponds to a cell group ID, and the scrambling code ID 100 corresponds to a cell ID. The above-described embodiment A is an embodiment in which th e number of scrambling codes included in a code group is more than 2, a nd the above-described embodiment B is an embodiment in which a grou ping process of scrambling codes is not performed, in other words, the n umber of scrambling codes included in a code group is 1.

FIG. 2 illustrates a structure of a forward link frame according to a n embodiment of the present invention.

Referring to FIG. 2, the forward link frame has a 10-msec duration and includes 20 sub-frames 110, each sub-frame having a 0.5-msec du ration. In FIG. 2, the horizontal axis represents time, and the vertical axi s represents frequency (OFDM subcarrier).

In the current embodiment, each sub-frame 110 includes 7 OFDM symbols 120. However, it will be understood by those of ordinary skill i n the art that the number of OFDM symbols per sub-frame can vary acco rding to a used system and a supporting service. For example, in a sub -frame structure providing a Multimedia Broadcast Multicast Service (MB MS), each sub-frame includes 6 OFDM symbols, and in this case, the len gth of a cyclic prefix is greater than that in the case where the number of OFDM symbols per sub-frame is 7. The number of types of OFDM sym bols illustrated in FIG. 2 is 3, i.e., a data channel symbol 120, a sync cha nnel symbol 122, and a common pilot channel symbol 124. The sync c hannel symbol 122 is the same as described above, and the common pil ot channel symbol 124 is an OFDM symbol including a pilot symbol and r elated to a common pilot channel, and the data channel symbol 120 is a n OFDM symbol not related to a sync channel or a common pilot channel . Referring to FIG. 2, each sub-frame 110 includes one common pilot c hannel symbol 124, wherein some sub-frames 110 include a single sync channel symbol 122 and the others include no sync channel symbol 122. The common pilot channel is used to estimate a channel for coher ent demodulation of a data channel of a forward link and also used for th e third detection step according to an embodiment of the present inventio n.

In the current embodiment, a single sync channel symbol 122 exis ts at every 4 sub-frames 110, and thus a total of 5 sync channel symbols 122 exist in the forward link frame (10 msec duration). In the present sp ecification, a group of 4 sub-frames 110, which corresponds to a time int erval 130 between sync channel symbols 122, is called a sync slot. Tha t is, according to the current embodiment, the number N_b of sync slots i n a single frame is 5, and each sync channel symbol 122 has the same r elative position in a corresponding sync slot. Reference numeral T140 i s related to sync slot timing detected in the first detection step, and refer ence numeral T150 is related to frame boundary timing detected in the s econd detection step.

Though the sync channel symbol 122 is located in the first OFDM symbol of a sub-frame 110 in the current embodiment, the position of the sync channel symbol 122 is not limited to this but can be located in any OFDM symbol of the sub-frame 110. However, for easiness of sync ac quisition and an increase of sync acquisition performance, it is preferable that the position of each sync channel symbol 122 in every sync slot is t he same. That is, it is preferable that an interval between adjacent sync channel symbols 122 is constant. In addition, as described above, in o rder to support both a service in which the number of OFDM symbols per sub-frame is 6 and a service in which the number of OFDM symbols per sub-frame is 7, it is preferable that the position of each sync channel sy mbol 122 is the far end of a corresponding sub-frame since a cell search can be performed regardless of the length of a cyclic prefix.

The OFDM symbols that remain due to the exclusion of the sync c hannel symbols 122, i.e., the data channel symbols 120 and the commo n pilot channel symbols 124, are scrambled with a cell-specific scramblin g code in order to identify each cell. That is, data symbols or pilot symb ols multiplied by a cell-specific scrambling code in a frequency domain ar e carried on subcarriers of the remaining OFDM symbols. In the present specification, each of a sync channel symbol, a co mmon pilot channel symbol, and a data channel symbol is called an OFD M symbol transmitted from each base station, a reception sync channel s ymbol a reception common pilot channel symbol, and a reception data ch annel symbol are respectively used as terms indicating a reception signal at a sync channel symbol position, a reception signal at a common pilot channel symbol position, and a reception signal at a data channel symbo I position among reception signals of a mobile station. The mobile statio n acquires information on the sync channel symbol position in the first de tection step and acquires information on the common pilot channel symb ol position and information on the data channel symbol position in the se cond detection step in which a frame boundary is detected. However, it will be understood by those of ordinary skill in the art that a forward link fr ame structure in which the information on the common pilot channel sym bol position and the information on the data channel symbol position can also be acquired in the first detection step can be designed.

A forward link frame transmitted from a base station belonging to an arbitrary cell according to an embodiment of the present invention incl udes M sync channel symbols code-hopped according to a hopping patte rn of the cell, where M is a natural number equal to or greater than 2.

According to the current embodiment, M = 5. In FIG. 2, ' h

^ = fy⁸\j{^s\ji!f\}{^g\hl^gη' indicates a hopping pattern, i.e., a hopping se quence, and g indicates a hopping pattern ID, i.e., a hopping sequence ID. In

5 sync channel code sequence indexes l^⁸\f^⁸\h^⁸\^⁸\h\⁸K That is, h^ indicates a sync channel code sequence index, which is an n-th ele ment of the hopping pattern h^{g) . A scheme using the characteristic tha t sync channel code sequences in a single frame are different from each other in every sync slot is called code hopping.

In FIG. 2, the sync channel symbol 122 at the position of referenc e numeral 160 includes a sync channel code sequence corresponding to the sync channel code sequence index h^ , and the sync channel symb ols 122 at the positions of reference numerals 162, 164, 166, and 168 re spectively include a sync channel cod nding to the s ync channel code sequence indexes

. The meanin g that a sync channel symbol includes a sync channel code sequence is that sync channel chips forming the sync channel code sequence are car ried on subcarriers of the sync channel symbol. An arbitrary hopping pattern used in the OFDM cellular system ac cording to the current embodiment may differ from a cyclically shifted res ult of the hopping pattern, other hopping patterns, and cyclically shifted r esults of the other hopping patterns. A set of hopping patterns having t his characteristic can be represented as "hopping pattern set unique to a cyclic shift operation". The cyclic shift will be described later in detail wit h reference to FIGS. 4 and 5.

Since each hopping pattern used in the embodiment A respectivel y corresponds to each code group and each hopping pattern used in the embodiment B respectively corresponds to each scrambling code, accor ding to the embodiment A, a hopping pattern of each cell specifies a fra me boundary and a code group of the cell, and according to the embodi ment B, a hopping pattern of each cell specifies a frame boundary and a scrambling code of the cell. A mobile station can perform the cell searc h process using a forward link frame containing sync channel symbols, w hich are generated by performing the above-described process, and com mon pilot channel symbols.

FIG. 3 illustrates a sub-frame containing a sync channel symbol a ccording to an embodiment of the present invention, e.g., a first sub-fram e 110 of a first sync slot as illustrated in FIG. 2.

In the sub-frame illustrated in FIG. 3, a first OFDM symbol 170 incl udes data symbols 184 and sync channel chips, i.e., sync symbols 186. A second OFDM symbol 180 is a common pilot channel symbol and incl udes pilot symbols 182 and data symbols 184 in an FDM format. The e ommon pilot channel symbol 180 or the pilot symbol 182 is used to estim ate a channel for coherent demodulating of a data channel of a forward Ii nk and also used for the third detection step according to an embodiment of the present invention. A sync channel can occupy all of a band 195, which remains, by e xcluding guard bands 193 and 194 or occupy a portion of the remaining band 195 as illustrated in FIG. 3. According to the current embodiment, a bandwidth indicated by reference numeral 190 is a sync channel occu pied bandwidth, and a portion of the remaining band 195 is occupied by data symbols 184 or used as a guard band.

The method in which only a portion of the remaining band 195 is o ccupied by a sync channel may be applied to a system which must supp ort a scalable bandwidth, such as a 3G-LTE system. That is, as illustrat ed in FIG. 3, by allowing the sync channel to occupy only a portion of a s ystem bandwidth 192, mobile stations using a 1.25-MHz bandwidth, mobi Ie stations using a 2.5-MHz bandwidth, and mobile stations using a 5-MH z bandwidth can acquire system timing of a target cell. For example, wh en the system bandwidth 192 is 20 MHz, only 1.25 MHz in the center, wh ich remains due to the exclusion of a DC subcarrier, is used. A cell search unit of a mobile station, which will be described later, can increase cell search performance by performing filtering so as to pa ss only a sync channel occupied band 190 illustrated in FIG. 3.

Methods in which a sync channel uses subcarriers include a meth od of mapping sync channel chips to all subcarriers in the sync channel o ccupied band 190 and a method of mapping sync channel chips to subca rriers periodically positioning in the frequency domain in the sync channel occupied band 190 and mapping predetermined symbols to the remaini ng subcarriers. In particular, the embodiment illustrated in FIG. 3 corres ponds to the latter method, in which a sync channel chip is mapped to on e of two adjacent subcariers and a predetermined symbol is mapped to t he other one. The predetermined symbol may be a null symbol. In par ticular, if the latter method is used, a time domain signal of a sync chann el symbol excluding a cyclic prefix has a pattern repeated in a time doma in, which will be described later with reference to FIG. 4. In FIG. 3, C^w =

indicates a sync channel sequence used for co de hopping of a sync channel symbol denoted by reference numeral 170 in the forward link frame described above. That is, C^w

indicates a sync channel code sequence in whi ch a sync channel code index is k, and N denotes the length of the syn c channel code sequence. In addition, c[^k) is an n-th element of the sy nc channel code sequence in which a sync channel code index is k and c orresponds to a sync channel chip having a value of a complex number. That is c_n ^(k) is transmitted by being mapped to a subcarrier belonging to the sync channel occupied band 190 illustrated in FIG. 3.

An arbitrary sequence can be used as the sync channel code seq uence. However, according to an embodiment of the present invention, a Generalized Chirp Like (GCL) sequence defined using Equation 1 is us ed as the sync channel code sequence. .,JV - l, k = l,2,...,N-l (1 )

In Equation 1 , k , c^ and, N are the same as described above . In particular, in the GCL sequence, N is a prime number, and a total of N-1 GCL sequences exist. FIG. 4 illustrates a hopping code according to an embodiment of t he present invention. In detail, FIG. 4 illustrates a table showing hoppin g patterns respectively corresponding to code groups in the case where t he number of code groups is 64 as illustrated in FIG. 1 and the number M of sync channel symbols in a frame is 5 as illustrated in FIG. 2. The c urrent embodiment shows 64 hopping patterns (i.e., hopping codewords) of which a codeword length is 5 and a code alphabet size is 40. Each of the 64 hopping patterns is made up of a first sync channel code seque nee index, a second sync channel code sequence index, a third sync cha nnel code sequence index, a fourth sync channel code sequence index, and a fifth sync channel code sequence index. Referring to FIG. 4, a se cond sync channel code sequence index of a hopping pattern correspon ding to a code group ID of 3 is 21. A hopping pattern is assigned to each cell, and hopping pattern as signing methods include the embodiment A in which each hopping patter n respectively corresponding to each code group to which a scrambling c ode belongs is assigned and the embodiment B in which each hopping p attern respectively corresponding to each scrambling code is assigned. According to the embodiment A, different hopping patterns are assigned to cells having different code groups. For example, referring to FIGS. 1 and 4, a hopping pattern (5, 6, 7, 8, 9) corresponding to a code group ID of 0 is assigned to a cell having a scrambling code of which a scrambling code ID is 256, and a hopping pattern (10, 11 , 12, 13, 14) correspondin g to a code group ID of 1 is assigned to a cell having a scrambling code of which a scrambling code ID is 193.

A case where a base station of a cell having a scrambling code ID of 192 generates a forward link frame with reference to FIGS. 1 , 2, and 4 will now be described in order to describe a hopping pattern. A scram bling code having the scrambling code ID of 192 belongs to a code group having a code group ID of 0. A hopping pattern uniquely correspondin g to the code group ID of 0 is h^{s) = (ffi = 5, A^ = 6,/*J^s) = l,^^g) = 8, h[^g) = ή with reference to FIG. 4. That is, the code group ID of 0 uniquely corre sponds to the hopping pattern ID of g . Thus, the base station of the ce

Il inserts a GCL sequence obtained by substituting k = 5 into Equation 1 into the sync channel symbol at the position of reference numeral 160 ill ustrated in FIG. 2, inserts a GCL sequence obtained by substituting k - 6 in Equation 1 into the sync channel symbol at the position of refere nee numeral 162 illustrated in FIG. 2, and transmits the generated forwar d link frame to mobile stations. The sync channel symbols at the positio n of reference numerals 164, 166, and 168 illustrated in FIG. 2 can be de scribed as well.

A base station belonging to each cell generates a forward link fra me containing M sync channel symbols code-hopped according to an as signed hopping pattern and transmits the generated forward link frame to mobile stations. A mobile station detects a hopping pattern of a target base station from reception signals. The target base station is a base st ation corresponding to a cell for which the mobile station initially searche S.

FIG. 5 is a table for describing the concept of cyclically shifted hop ping sequences (hopping patterns). In detail, FIG. 5 shows hopping pat terns obtained by cyclically shifting the hopping pattern (5, 6, 7, 8, 9) corr esponding to the code group ID of 0 illustrated in FIG. 4 using cyclic shift counts 0, 1 , 2, 3, 4. Each cyclic shift index indicates a cyclically shifted count.

It can be known that the set of hopping patterns illustrated in FIG. 4 is a hopping pattern set unique to a cyclic shift operation. That is, the number of hopping patterns that can be obtained by cyclically shifting the 64 hopping patterns illustrated in FIG. 4 is 320 (=5x64), and the 320 ho pping patterns are different from each other. This characteristic allows a mobile station to detect both a code group ID and a frame boundary in the second detection step according to the embodiment A and detect bot h a scrambling code ID and a frame boundary in the second detection st ep according to the embodiment B.

A set of hopping patterns according to an embodiment of the pres ent invention requires only uniqueness to a cyclic shift operation, and in t he principle, the number of hits between any two of hopping patterns is n ot limited. The number of hits indicates the number of cases where the same sync channel code sequence index exists in the same position of t wo arbitrary hopping patterns, and is related to a Hamming distance. If the number of hits between two arbitrary hopping patterns is 0, a Hammi ng distance between the two arbitrary hopping patterns is equal to the ho pping codeword length M. Thus, the number of hits between two arbitra ry hopping patterns is equal to a value obtained by subtracting a Hammin g distance from a hopping codeword length. For example, the number of hits between the hopping pattern (5, 6, 7, 8, 9) and a hopping pattern ( 9, 11 , 13, 15, 17) is 0, and the number of hits between the hopping patter n (5, 6, 7, 8, 9) and a hopping pattern (11 , 13, 15, 17, 9) cyclically shifted from the hopping pattern (9, 11 , 13, 15, 17) by an amount of 4 is 1 (i.e., the fifth sync channel code sequence index 9 is hit). The minimum Ham ming distance between any two of the 320 hopping patterns that can be obtained considering a cyclic shift operation from the hopping code illustr ated in FIG. 4 is 4. In other words, the maximum number of hits betwee n any two of the 320 hopping patterns that can be obtained considering a cyclic shift operation from the hopping code illustrated in FIG. 4 is equal to or less than 1. However, another embodiment of the present invention uses a set of hopping patterns, i.e., a hopping code, which has uniqueness to a cy die shift operation and has a limited number of hits. This embodiment c an have an advantage in a situation where a dual mode mobile station fo r simultaneously supporting a Global System for Mobile Communication ( GSM) system and a 3G-LTE OFDM system should perform handover fro m the GSM system to the 3G-LTE OFDM system. That is, a time allow ed for the dual mode mobile station, which is demodulating a GSM forwa rd link signal, to end reception of the GSM forward link signal for a while and receive and search a 3G-LTE OFDM forward link signal having a diff erent frequency is around 4.6 msec. The minimum number of receivabl e sync channel symbols of the 3G-LTE OFDM forward link signal during 4.6 msec is 2 in the frame structure illustrated in FIG. 2. That is, the du al mode mobile station should perform the second detection step only wit h two sync channel symbols. If the number of hits between any two of t he 320 hopping patterns that can be obtained considering the cyclic shift operation is equal to or greater than 2, the dual mode mobile station may not perform the second detection step. Thus, in this system, the numb er of hits between any two of the 320 hopping patterns is preferably equa

I to or less than 1. That is, only if the minimum Hamming distance betw een any two of the 320 hopping patterns that can be obtained considerin g the cyclic shift operation is 4, the dual mode mobile station can perform a cell search according to the 3G-LTE OFDM system while the dual mo de mobile station is communicating in the GSM system, and perform har d handover.

Likewise, if the number of hits between any two of the 320 hoppin g patterns that can be obtained considering the cyclic shift operation is 0, the second detection step may be performed with only a single sync ch annel symbol. That is, in this case, any two of the 64 hopping patterns must not include any common sync channel code sequence index regard less of positions, and to do this, minimum 320 (64χ5) sync channel code sequences must exist in an OFDM cellular system according to an embo diment of the present invention. For example, a hopping code of which the number of hits is 0 can be applied to a case where the number of syn c channel symbols per frame is 4. That is, unlike the embodiment illustr ated in FIG. 2 in which the number of sync channel symbols per frame is

5, in the case where the number of sync channel symbols per frame is 4, the hopping code of which the number of hits is 0 can have an advantag e when the number of sync channel symbols acquired by a mobile statio n during 4.6 msec is 1 under the worst condition. In this case, the mobil e station can perform the second detection step including a process of d etθcting a hopping pattern of a target cell and a process of detecting a fr ame boundary only with a single sync channel symbol.

Thus, if it is assumed that the minimum number of sync channel s ymbols of a 3G-LTE OFDM system, which can be received during a 4.6- msec transmission gap duration of a GSM system, is Q, the maximum nu mber of hits between any two of hoping codewords that can be obtained considering the cyclic shift operation must be equal to or less than Q-1. In other words, if it is assumed that a hoping codeword length is L, the minimum Hamming distance of a hopping code considering the cyclic shi ft operation must be equal to or greater than L-Q+1.

As described above, both the embodiment using a set of hopping patterns having uniqueness to a cyclic shift operation and the embodime nt using a set of hopping patterns having uniqueness to a cyclic shift ope ration and a limited number of hits are within the scope and sprit of the pr esent invention.

FIG. 6 illustrates a structure of a sync channel symbol in the time domain according to an embodiment of the present invention.

Referring to FIG. 6, N_τ denotes the number of samples of the en tire sync channel symbol duration 200, N_cp denotes the number of sam pies of a cyclic prefix (CP) duration 210, and N₅. denotes the number of samples of a symbol duration 220 excluding the CP duration 210.

In particular, as illustrated in FIG.3, if sync channel chips are map ped to only odd-th or even-th subcarriers in a sync channel occupied ban d and null symbols are mapped to the remaining subcarriers, a first durati on 222 and a second duration 224 forming the duration denoted by refer ence numeral 220 have a specific pattern. If the sync channel symbol u ses DC component subcarriers, the first duration 222 and the second dur ation 224 have the same waveform in a time domain signal of a transmitt er end, and if the sync channel symbol does not use the DC component subcarriers, the second duration 224 has a waveform 180° phase revers ed from a waveform of the first duration 222. If a mobile station uses thi s time domain repetition pattern of the sync channel symbol, the mobile s tation can perform the first detection step with a simple structure using a differential correlation operation, which will be described later in detail. The first duration 222 and the second duration 224 may also be symmetr ical to each other. In this case, reverse differential correlation can be us ed. The differential correlation and the reverse differential correlation u sed in the first detection step, i.e., a symbol sync acquisition process, are within the spirit and scope of the present invention.

FIG. 7 is a block diagram of a frame transmission apparatus accor ding to an embodiment of the present invention. Referring to FIG. 7, th e frame transmission apparatus includes a sync channel generator 300, a common pilot channel generator 301 , a data channel generator 302, a diversity controller 303, OFDM symbol mappers 304-A and 304-B, scram biers 305-A and 305-B, inverse Fourier transformers 306-A and 306-B, C P insertion units 307-A and 307-B, intermediate frequency/radio frequenc y (IF/RF) units 308-A and 308-B, and transmission antennas 309-A and 309-B. In general, the frame transmission apparatus is included in a ba se station.

The data channel generator 302 generates data symbols such as reference numeral 184 of FIG. 3, and the common pilot channel generat or 301 generates pilot symbols such as reference numeral 182 of FIG. 3. The sync channel generator 300 generates sync channel chips, i.e., sy nc symbols, such as reference numeral 186 of FIG. 3, corresponding to a hopping pattern assigned to a cell to which the frame transmission appa ratus belongs. That is, if the hopping pattern assigned to the cell is (5, 6 , 7, 8, 9), the sync channel generator 300 generates N sync channel chip s obtained by substituting k - 5 into Equation 1 for a sync channel symb ol included in a first sync slot. If the number of subcarriers which can be used for mapping of a sync channel symbol is less than N, e.g., if N=41 and the number of subcarriers which can be of the syn c channel symbol is 38, the last 3 elements

of the syn c channel sequence defined using Equation 1 are not used.

Each of the OFDM symbol mappers 304-A and 304-B maps symb ols of the data channel, the pilot channel, and the sync channel to positio ns in the frequency domain as illustrated in FIG. 3. Each of the scrambl ers 305-A and 305-B multiplies an output of each of the OFDM symbol m appers 304-A and 304-B, i.e., a mapping result corresponding to OFDM symbols excluding a sync channel symbol from the mapping result, by a unique scrambling code of the cell in the frequency domain.

Each of the inverse Fourier transformers 306-A and 306-B perfor ms an inverse Fourier transform on the output of each of the scramblers 305-A and 305-B, and Each of the CP insertion units 307-A and 307-B in serts a CP into the output of each of the inverse Fourier transformers 30 6-A and 306-B. Each of the IF/RF units 308-A and 308-B up-converts an output si gnal of each of the CP insertion units 307-A and 307-B, which is a baseb and signal, to a band pass signal and amplifies the up-converted signal. Each of the transmission antennas 309-A and 309-B transmits the ampl ified signal.

The frame transmission apparatus illustrated in FIG. 7 transmits s ync channel symbols while achieving transmission diversity using the 2 tr ansmission antennas 309-A and 309-B. The transmission diversity usin g the diversity controller 303 illustrated in FIG. 7 will now be described, Sync channel symbols belonging to adjacent sync slots are transmitted t hrough different transmission antennas in order to achieve spatial diversi ty. For example, a sync channel symbol belonging to a first sync slot is transmitted through the first transmission antenna 309-A, a sync channel symbol belonging to a second sync slot is transmitted through the seco nd transmission antenna 309-B, and a sync channel symbol belonging to a third sync slot is transmitted through the first transmission antenna 30 9-A. This switching so as to achieve the spatial diversity is performed b y the diversity controller 303. That is, the transmission diversity scheme according to the current embodiment is a method of applying Time Swit ching Transmit Diversity (TSTD) to the sync channel, and the diversity co ntroller 303 provides an output of the sync channel generator 300 to the OFDM symbol mapper 304-A or 304-B by switching the output of the syn c channel generator 300.

Besides the TSTD diversity, delay diversity can be used as the tra nsmission diversity.

FiGS. 8 and 9 are a block diagram and a conceptual diagram, res pectively, of the diversity controller 303 in a case where the delay diversit y is applied to the frame transmission apparatus illustrated in FIG. 7, ace ording to an embodiment of the present invention. Referring to FIG. 8, the diversity controller 303 includes a delay w eight multiplier 310. N sync channel chips forming a single sync channe I code sequence are separated into two data paths. According to the up per data path, the sync channel chips are directly provided to the OFDM symbol mapper 304-A. According to the lower data path, the sync chan nel chips are input to the delay weight multiplier 310, and the output of th e delay weight multiplier 310 is input to the OFDM symbol mapper 304-B. FIG. 9 is a conceptual diagram for explaining an operation of the d elay weight multiplier 310. Referring to FIG. 9, the delay weight multiplier 310 delays the N g enerated sync channel chips and includes N multipliers.

Each of the N multipliers multiplies each of the N generated sync channel chips by a weight. A weight w(n) multiplied by a sync channel chip assigned to an n^th subcarrier used by the sync channel symbol, i.e., an n^th sync channel chip, is calculated using Equation 2. w(n) = exp{-j2πn - 2D_m /N_s), n = 0,\,2,...,N-\ (2)

In Equation 2, D_1n denotes a delay of an FFT sample unit in the ti me domain for an m^th transmission antenna, and N_s denotes the numb er of FFT samples. Since it is assumed, as illustrated in FIG. 3, that syn c symbols are carried on every other subcarrier, 2D_1n is used instead of

D_1n . If the number of transmission antennas 309-A and 309-B is 2 as ill ustrated in FIG. 7, a delay to the first transmission antenna 309-A is D₀ - O , and a delay to the second transmission antenna 309-B is D_x . Though the frame transmission apparatus having the two transmis sion antennas 309-A and 309-B has been described with reference to Fl GS. 7, 8, and 9, it will be understood by those of ordinary skill in the art t hat the transmission diversity scheme can be applied to a frame transmis sion apparatus having three or more transmission antennas using the sa me principle, and if a frame transmission apparatus has only one transmi ssion antenna 309-A, the transmission antenna 309-B, the OFDM symbo I mapper 304-B, the scrambler 305-B, the inverse Fourier transformer 30 6-B, the CP insertion unit 307-B, the IF/RF unit 308-B, and the diversity c ontroller 303 can be omitted. FIG. 10 is a block diagram of a receiver of a mobile station accordi ng to an embodiment of the present invention. The mobile station has a t least one reception antenna, and the mobile station according to the cur rent embodiment^'has 2 reception antennas. Referring to FIG. 10, the re ceiver of the mobile station includes reception antennas 400-A and 400- B, down-converters 410-A and 410-B, a cell search unit 500, a data chan nel demodulator 420, a controller 430, and a clock generator 440.

RF signal type frames transmitted from base stations are received through the reception antennas 400-A and 400-B and converted to bas eband signals S1 and S2 by the down-converters 410-A and 410-B. The cell search unit 500 searches for a target cell using a sync ch annel symbol and a common pilot channel symbol included in the down-c onverted signals S1 and S2. As a result of the cell search, symbol sync hronization information, frame boundary information, code group informa tion, and scrambling code information can be detected as described abo ve.

The controller 430 controls the cell search unit 500 and the data c hannel demodulator 420. That is, the controller 430 controls timing and descrambling of the data channel demodulator 420 based on a cell searc h result acquired by controlling the cell search unit 500. The data chann el demodulator 420 demodulates a reception data channel symbol includ ed in the down-converted signals S1 and S2 under control of the contrail er 430. All the hardware in the mobile station operates by being synchr onized with a clock generated by the clock generator 440.

The cell search unit 500 includes sync channel band filters 510-A and 510-B, a first detector 520, a second detector 540, and a third detect or 580.

The sync channel band filters 510-A and 510-B perform band pas s filtering for passing only the sync channel occupied band 190 from a mong the entire system bandwidth 192 illustrated in FIG. 3 with respect t o the down-converted signals S1 and S2.

The first detector 520 acquires symbol sync information S5 using a sync channel symbol included in the filtered signals S3 and S4. The s econd detector 540 acquires code group information S7 and frame boun dary information S6 using the acquired symbol sync information S5 and t he 64 hopping patterns illustrated in FIG. 4 pre-stored in a memory (not s hown) of the mobile station according to the embodiment A. The secon d detector 540 acquires scrambling code information S7 and frame boun dary information S6 using the acquired symbol sync information S5 and t he 64 hopping patterns illustrated in FIG. 4 pre-stored in the memory of t he mobile station according to the embodiment B.

The second detector 540 can increase detection performance by performing frequency offset estimation and compensation before detecti ng the code group information or scrambling code information S7 and th e frame boundary information S6. In this case, estimated frequency off set information S8 can be provided to the third detector 580 to perform th e third detection step.

The third detector 580 detects a scrambling code of the target cell by means of a pilot correlation of the down-converted signals S1 and S2 based on the detected code group information S7 and frame boundary in formation S6 according to the embodiment A. In detail, the third detecto r 580 extracts a signal corresponding to a position of the common pilot c hannel symbol from among the down-converted signals S1 and S2, i.e., t he reception common pilot channel symbol, based on the detected frame boundary information S6, calculates correlation values between the rec eption common pilot channel symbol and scrambling codes belonging to a code group corresponding to the detected code group information S7, and detects the scrambling code of the target cell based on the calculate d correlation values.

Since the second detector 540 has detected the scrambling code, the cell search unit 500 according to the embodiment B-1 does not includ e the third detector 580, considering calculation complexity and detection speed. However, the cell search unit 500 according to the embodimen t B-2 includes the third detector 580 to perform verification of the detectio n result of the first detector 520 and the detection result of the second de tector 540. That is, the third detector 580 according to the embodiment B-2 p erforms the verification of the detection result of the first detector 520 an d the detection result of the second detector 540 by means of a pilot corr elation of the down-converted signals S1 and S2 based on the detected scrambling code information S7 and frame boundary information S6. T he signal processing corresponding to the pilot correlation of the third det ector 580 according to the embodiment B-2 is the same as the signal pro cessing corresponding to the pilot correlation of the third detector 580 ac cording to the embodiment A. However, a scrambling code used in the pilot correlation according to the embodiment B-2 can vary according to what verification algorithm is used. According to a verification algorithm according to an embodiment of the present invention, the third detector 5 80 according to the embodiment B-2 performs a pilot correlation using on Iy a scrambling code corresponding to the detection result of the second detector 540, i.e., the scrambling code information S7, compares the cal culated pilot correlation value to a predetermined threshold, and determi nes based on the comparison result whether the detection result of the fir st detector 520 and the detection result of the second detector 540 are re liable. However, it will be understood by those of ordinary skill in the art that besides the verification algorithm according to this embodiment, vari ous verification algorithms can exist such as an algorithm of analyzing all pilot correlation values calculated using all scrambling codes for the pilo t correlation and determining based on the analysis result whether the de tection result of the first detector 520 and the detection result of the seco nd detector 540 are reliable.

Though the third detector 580 uses the down-converted signals S 1 and S2 in FIG. 10, if the reception common pilot channel symbol is not affected by the sync channel band filters 510-A and 510-B, the outputs S 3 and S4 of the sync channel band filters 510-A and 510-B can be used f or the pilot correlation instead of the down-converted signals S1 and S2. FIG. 11 is a block diagram of the first detector 520 of the receiver i llustrated in FIG. 10, according to an embodiment of the present inventio n. Referring to FIG. 11 , the first detector 520 includes differential correl ators 521 -A and 521 -B, an accumulator 523, and a timing determiner 52 4. In detail, the current embodiment is an embodiment for symbol sync acquisition in a case where a sync channel symbol (a PSC symbol in the hierarchical structure) has a time domain repetition pattern. However, it will be understood by those of ordinary skill in the art that besides the cur rent embodiment, by using various other embodiments, such as a matchi ng filter method based on a reference signal corresponding to the sync c hannel symbol (an OFDM symbol related to the PSC symbol in the hierar chical structure), the symbol sync acquisition can be performed even if th e sync channel symbol (the OFDM symbol related to the PSC symbol in t he hierarchical structure) does not have the time domain repetition patter n.

Each of the differential correlators 521-A and 521-B multiplies a s ample value of each of the output signals S3 and S4 of the sync channel band filters 510-A and 510-B by a sample value received previously to th e current sample value by a time corresponding to an N_s /2 sample usi ng the time domain signal repetition characteristic of sync channel symb ols illustrated in FIGS. 3 and 6 and accumulates the multiplication result. Here, N_s is the same as described in FIG. 6, and N₅ /2 corresponds to the number of samples of the first duration 222 or the second duratio n 224.

Equations 3 and 4 represent outputs of the differential correlators 521-A and 521-B at an arbitrary sample point n according to an embodi ment of the present invention.

In Equations 3 and 4, ( )^* denotes a complex conjugate value, a denotes a reception antenna index having 0 or 1 , r_o( ) corresponds t

0 reference character S3, and r_x( ) corresponds to reference character S4.

A square of an absolute value and the absolute value are obtaine d in Equations 3 and 4 in order to maintain performance of the first detec tor 520 regardless of an initial frequency offset. Unlike Equation 3 or 4, if the absolute value is not obtained, the symbol sync acquisition perform ance may be decreased in a state where the initial frequency offset is lar ge.

It can be known with reference to FIGS. 2 and 6 that the number o f samples corresponding to a sync slot length is 4χ 7 χ N_r , and a single s ync channel symbol is included in continuous 4x 7 x N₇. samples starting from an arbitrary sample position. Thus, each of the differential correla tors 521 -A and 521 -B calculates a differential correlation value of each of the continuous 4 x 7 x N₇. samples starting from an arbitrary sample po sition and provides the calculated differential correlation values to the tim ing determiner 524, and the timing determiner 524 determines a position of a sample, which corresponds to the maximum differential correlation v alue among the 4χ 7χ N₇. differential correlation values, as sync channe

1 symbol timing. However, the first detector 520 illustrated in FIG. 11 ma y include the accumulator 523 in order to increase symbol sync acquisitio n performance. The accumulator 523 combines the outputs of the differential corr elators 521 -A and 521 -B, which correspond to the same sample position, calculates combining values at Ax I x N₇. sample positions, and accum ulates each combining value for samples separated by every sync slot Ie ngth from each sample position. That is, an output γ(n) of the accumu lator 523 can be represented by Equation 5. γ{n)= ∑z(n + bL) (5)

Here, z(n) denotes the combining result corresponding to a sam pie index position n , and if a simple summing method as the combining method is used, z{n)= z_Q{n)+z_x{n). L denotes the number of samples corresponding to a sync slot (e.g. Λχ l χ N_τ with reference to FIGS. 2an d 6). B denotes the number of accumulations. If the first detector 52

0 includes the accumulator 523, the timing determiner 524 determines a position of a sample corresponding to the maximum value from among γ(6) , γ{\) , ..., χ(4χ 7χN_τ -l) stored in the accumulator 523 as sync ch annel symbol timing and outputs the symbol sync information S5, which i s information on the sync channel symbol timing, to the second detector 540. That is, N₁. symbols starting from the sample position correspon ding to the maximum value are samples of a reception sync channel sym bol. FIG. 12 is a graph illustrating differential correlation values calcula ted by the differential correlator 521 -A or 521 -B illustrated in FIG. 11 , ace ording to an embodiment of the present invention. For convenience of description, it is assumed that the differential correlation values are obtai ned in an ideal channel environment in which fading or noise does not ex ist in a forward link channel.

In FIG. 12, the horizontal axis represents time or a sample positio n index, and the vertical axis represents a differential correlation value. Reference numeral 627 denotes a position of a first sample for which the differential correlator 521 -A or 521 -B performs the differential correlatio n. The differential correlator 521 -A or 521 -B calculates a differential cor relation value of each of L samples 628A starting from the first sample position 627A and provides the calculated L differential correlation valu es to the accumulator 523. Thereafter, the differential correlator 521 -A or 521 -B calculates a differential correlation value of each of L samples 628B starting from a position 627B of a sample next to a sample for whi ch the differential correlator 521 -A or 521 -B performed the last differentia

1 correlation and provides the calculated L differential correlation values to the accumulator 523. The differential correlator 521 -A or 521 -B rep eats this process B times. L denotes the number of samples per sync slot, and reference numeral 629 corresponds to the accumulator 523. A mong all the differential correlation values corresponding to the positions of the continuous L samples, sample positions 630A, 630B, and 630C at which a peak occurs exist as illustrated in FIG. 12.

FIG. 13 is a diagram for describing a signal used in the second de tector 540 of the receiver illustrated in FIG. 10, according to an embodim ent of the present invention.

Reference numerals 641 -A, 641 -B, 641 -C, 641 -D, and 641 -E den ote sync channel symbol timings, and in particular, the first sync channel symbol timing 641 -A is called initial reference timing in the present specif ication. These sync channel symbol timings are detected by the first det ector 520 as described above, and information on the sync channel sym bol timings is provided to the second detector 540. According to the for ward link frame illustrated in FIG. 2, one of reference numerals 641 -A, 64 1-B, 641 -C, 641 -D, and 641 -E is a frame boundary.

In FIG. 13, reference numerals 642-A, 642-B, 642-C, 642-D, and 642-E correspond to samples of a reception sync channel symbol used i n the second detector 540, and it can be known with reference to FIGS, 6, 10, and 13 that the signal is obtained by removing N_CP samples of ea ch CP from the signal S3 or S4. The CP can be removed based on the initial reference timing 641 -A, and regardless of whether this CP removin g process is performed by the first detector 520, the second detector 540 , or another component (not shown), the CP removing process is within t he scope and sprit of the present invention.

The second detector 540 detects a hopping pattern of a target cell using the samples 642-A, 642-B, 642-C, 642-D, and 642-E from which CPs are removed. That is, the second detector 540 uses N₃ sample v alues in every sync slot. FIGS. 14 and 15 are block diagrams of the second detector 540 of the receiver illustrated in FIG. 10, according to an embodiment of the pr esent invention. FIG. 14 is a block diagram of the second detector 540 A according to the embodiment A, and FIG. 15 is a block diagram of the second detector 540B according to the embodiment B. The second detector 540A includes a frequency offset compensat or 542, a hopping pattern detector 544, a code group detector 546, and a frame boundary detector 548.

The frequency offset compensator 542 stores P x N₃ samples (64

2-A through 642-E) provided from each of the sync channel band filters 5 10-A and 510-B over several sync slot length durations based on the syn c channel symbol timing 641 -A and estimates a frequency offset S8 usin g the Px N₃ stored samples (642-A through 642-E). Thereafter, the fr equency offset compensator 542 compensates for frequency offsets of th e P^χ N_s samples (642-A through 642-E) based on the estimated freque ncy offset S8 and provides the compensated Px N₃ signal samples S9 and S10 to the hopping pattern detector 544. Here, P denotes the nu mber of sync channel symbols used for the hopping pattern detection an d can be determined according to a condition of uniqueness to a cyclic s hift operation and a limitation condition of the number of hits. For conve nience of description, it is assumed that P is the number of sync chann el symbols per frame (5 in FIG. 2).

Equations 6 and 7 illustrate frequency offset compensation metho ds of the frequency offset compensator 542. Equations 6 and 7 use the time domain repetition pattern of the sync channel symbols illustrated in

FIG. 6. In particular, Equation 6 illustrates a frequency offset compens ation method in a case where a transmitter end transmits a signal without

Here, R_s denotes an OFDM sampling frequency, A denotes the number of reception antennas, P denotes the number of sync channel symbols used for the frequency offset compensation, a denotes a rec eption antenna index, and r_{a p}(n) denotes an n^th sample value of a p^th re ception sync channel symbol from the initial reference timing 641 -A provi ded from the first detector 520 with respect to an a^th reception antenna. Referring to FIG. 13, r_{O 2}(«) denotes an n^th sample among N_s sample s corresponding to reference numeral 642-B. Equation 8 illustrates a frequency offset compensation method of t he frequency offset compensator 542. n = 0,1,2,.. Jf₅ -I (8)

r\ _p (n) is a result sample obtained by performing the frequency o ffset compensation of r_{a p}(n) . That is, the frequency offset compensato r 542 compensates for frequency offsets of P*N_S received samples as illustrated in FIG. 13 based on the frequency offset S8 estimated using th e frequency offset compensation method illustrated in Equation 8. The f requency offset compensator 542 provides the frequency offset compens ated P x N_s samples S9 and S10 ( r\ _p ) to the hopping pattern detector 544.

The hopping pattern detector 544 detects a hopping pattern of a t arget cell using the Pχ N_s received samples S9 and S10 and provides hopping pattern information S11 corresponding to the detected hopping pattern to the code group detector 546 and the frame boundary detector 548. The code group detector 546 detects a code group of the target c ell based on the hopping pattern information S11 , and the frame boundar y detector 548 detects a frame boundary based on the hopping pattern in formation S11.

The second detector 540B includes a frequency offset compensat or 552, a hopping pattern detector 554, a scrambling code detector 556, and a frame boundary detector 558.

The embodiment illustrated in FIG. 15 is different from the embodi ment illustrated in FIG. 14 in that the scrambling code detector 556 repla ces the code group detector 546. That is, the scrambling code detector

556 detects a scrambling code of the target cell based on the hopping pa ttern information S11

FIG. 16 is a block diagram of the hopping pattern detector 544 or 554 illustrated in FIG. 14 or 15, according to an embodiment of the prese nt invention. The hopping pattern detector 544 or 554 includes sequenc e correlation calculators 665-A and 665-B, a combiner 656, a buffer 657, a hopping pattern storage unit 659, and a hopping pattern information ge nerator 658. The sequence correlation calculator 665-A calculates correlation v alues of N_s samples S9 of a reception sync channel symbol and all syn c channel code sequences used by the OFDM cellular system. Likewis e the sequence correlation calculator 665-B calculates correlation values of N_s samples S10 of a reception sync channel symbol and all sync ch annel code sequences used by the OFDM cellular system. In the prese nt specification, the correlation value of N_s samples and each sync cha nnel code sequence is called a sequence correlation value for convenien ce of description. That is, sequence correlation values corresponding to the number of sync channel code sequence used by the OFDM cellular system are calculated with respect to a single sync channel symbol.

Though the sequence correlation calculators 665-A and 665-B de al with different signals S9 and S10 due to respective reception antennas , the other signal processing process is the same for the sequence correl ation calculators 665-A and 665-B. Thus, a detailed signal processing p rocess will be described based on the sequence correlation calculator 66 5-A.

The sequence correlation calculator 665-A will now be described with reference to FIG. 13 and Equation 1. The sequence correlation cal culator 665-A calculates N-1 sequence correlation values with respect to N_y samples corresponding to reference numeral 642-A. Since the nu mber of GCL sequences used in Equation 1 is Ν-1 , N-1 sequence correl ation values are calculated with respect to every N₅ samples of a single reception sync channel symbol. When the number P of reception sync channel symbols used to detect a hopping pattern is 5, Ν-1 sequence c orrelation values are calculated with respect to samples of each of refere nee numerals 642-B, 642-C, 642-D, and 642-E.

The combiner 656 combines Ν-1 sequence correlation values out put from the sequence correlation calculator 665-A and Ν-1 sequence co rrelation values output from the sequence correlation calculator 665-B ba sed on each sync channel code sequence. In the current embodiment, a simple summing method is used as a data combining method. That is , the combiner 656 provides Ν-1 combined sequence correlation values t o the buffer 657 for every reception sync channel symbol. Since FIG. 1 6 is based on a case where the mobile station achieves reception diversit y using two reception antennas, another embodiment of the present inve ntion in which the reception diversity is not used does not include the co mbiner 656 and the sequence correlation calculator 665-B. The buffer 657 buffers Ν-1 combined sequence correlation values of each of P reception sync channel symbols. That is, Px (N-Y) com bined sequence correlation values are stored in the buffer 657.

The hopping pattern storage unit 659 stores information regardin g all hopping patterns used by the OFDM cellular system as illustrated in FIG. 4.

The hopping pattern information generator 658 detects a hopping pattern of a target cell by calculating a correlation value of each of the ho pping patterns stored in the hopping pattern storage unit 659 ('658'iir '65

9'≤. Φ3) ) and cyclically shifted results of the stored hopping patterns ba sed on the Px (N -I) combined sequence correlation values and provid es the hopping pattern information S11 , which is information on the hopp ing pattern of the target cell, to a next stage. In the present specificatio n, in order to distinguish correlation values of hopping patterns from sequ ence correlation values, the correlation values of hopping patterns are ca lied hopping pattern correlation values for convenience of description. If the OFDM cellular system uses the hopping patterns illustrated in FIG.

4, the hopping pattern information generator 658 calculates 320 hopping pattern correlation values. According to an embodiment of the present i nvention, a hopping pattern correlation value corresponding to each hop ping pattern is calculated by summing 5 sequence correlation values corr esponding to 5 sync channel code sequence indexes included in the hop ping pattern. FIG. 17 is a block diagram of the sequence correlation calculator

665-A illustrated in FIG. 16, according to an embodiment of the present i nvention. The sequence correlation calculator 665-A includes a recepti on sync symbol extractor 670, a differential coder 653, and a sequence c orrelation generator 680. In particular, the current embodiment illustrate s a configuration to calculate a correlation value in a case where a sync c hannel code sequence is achieved based on a GCL sequence.

The reception sync symbol extractor 670 extracts reception sync s ymbols from each reception sync channel symbol, each reception sync s ymbol being carried on a subcarrier on which a sync channel chip is carri ed from among subcarriers of each reception sync channel symbol. Th e reception sync symbol extractor 670 includes a Fourier transformer 65 1 and a demapper 652. The Fourier transformer 651 acquire N_s data values by Fourier transforming the N_s samples S9, and the demapper 6

52 extracts N reception symbols, i.e., N reception sync symbols, corresp onding to subcarriers to which the sync channel chips are mapped from among the acquired N_s data values.

The differential coder 653 performs differential encoding by multipl ying a complex conjugate value of an odd-th reception sync symbol by a reception sync symbol adjacent to the odd-th reception sync symbol for e very odd-th reception sync symbols of each reception sync channel symb ol as defined by Equation 9.

Here, y(n) denotes an output of the demapper 652, and u(n) de notes an output of the differential coder 653. The differential encoding i s performed so as to obtain only a linear phase transition corresponding t o a GCL sequence index k from N frequency domain signal component s. That is, if an environment in which channel distortion or noise does n ot exist is assumed, u(n) is represented by Equation 10.

In Equation 10, A: denotes a GCL sequence index, which can ha ve a value from 1 to N-1 as illustrated in Equation 1. The sequence correlation generator 680 performs inverse Fourier transformation on multiplication results of each reception sync channel s ymbol and determines each sequence correlation value with each magnit ude value of the inverse Fourier transformation result. The sequence c orrelation generator 680 includes an inverse Fourier transformer 654 and a magnitude calculator 655.

The inverse Fourier transformer 654 generates N complex sample s per reception sync channel symbol by performing inverse Fourier transf ormation on the outputs, i.e., u(θ),u(l),...,u(N -i) of the differential coder 653. The magnitude calculator 655 calculates a magnitude value of a complex sample by summing a square of a real number component and a square of an imaginary number component for each of the generated N complex samples. In particular, according to an embodiment of the pr esent invention, a first value of the calculated N magnitude values is disc arded, and only the remaining N-1 magnitude values are provided to the combiner 656. That is, second through N-th magnitude values are sequ ence correlation values corresponding to GCL sequence indexes k = 1 t hrough N-1 in Equation 1.

FIG. 18 is a graph illustrating sequence correlation values calculat ed from sample values of a single reception sync channel symbol accordi ng to an embodiment of the present invention. That is, FIG. 18 is a gra ph illustrating outputs of the sequence correlation calculators 665-A and 665-B.

The horizontal axis represents GCL sequence indexes, and the ve rtical axis represents a sequence correlation value of a GCL sequence c orresponding to each GCL sequence index. In particular, FIG. 18 illustr ates an output of the sequence correlation calculator 665-A or 665-B wh en a target cell GCL sequence index k contained in the samples of the reception sync channel symbol is 2. Referring to FIG. 18, a sequence c orrelation value is largest when k is 2. In particular, if channel distortio n or noise does not exist, sequence correlation values excluding a case where A: is 2 are 0 which is different from the illustration of FIG. 18.

FIG. 19 illustrates Px(N-I) sequence correlation values stored i n the buffer 657 illustrated in FIG. 16 when P = 5 and N = 41 , accordin g to an embodiment of the present invention. That is, FIG. 19 shows gr aphs illustrating sequence correlation values calculated from samples of each of reception sync channel symbols corresponding to p=0, 1 , 2, 3, a nd 4 from the top. In each graph, the horizontal axis represents GCL sequence index es, and the vertical axis represents sequence correlation values.

The graphs illustrated in FIG. 19 will now be described with refere nee to FIG. 13. Reference numeral 662-A indicates N-1 sequence corre lation values calculated using N_s samples corresponding to reference n umeral 642-A₁ i.e., an output of the combiner 656, and reference numera I 662-B indicates N-1 sequence correlation values calculated using N_s s amples corresponding to reference numeral 642-B. Reference numeral s 662-C, 662-D, and 662-E are described as well. The hopping pattern information generator 658 calculates N_G χ P hopping pattern correlation values using the P x (N-I) sequence corre lation values and provides a hopping pattern correlation index correspon ding to the maximum hopping pattern correlation value to next stages as the hopping pattern information S11. The next stages are the code gro up detector 546 and the frame boundary detector 548 according to the e mbodiment A or the scrambling code detector 556 and the frame bounda ry detector 558 according to the embodiment B. N_G χ P denotes the nu mber of hopping patterns which can be obtained considering a cyclic shif t operation, and the hopping pattern correlation index has a value of one of 0 through N_G χP-\ . Here, N_G denotes the number of hopping patt erns used in the system, and P denotes the number of sync channel co de sequences included in a single hopping pattern. According to FIG. 4 , N_G =64, and P =5.

A hopping pattern correlation value q(i) corresponding to a hoppi ng pattern correlation index according to an embodiment of the present i nvention is represented by Equation 11.

Here, mod denotes a modular operator, |_*J denotes the maxim urn value out of integers equal to or less than x , and h_x(y) denotes a y* ^h sync channel code sequence index of a hopping pattern whose hoppin g pattern ID is x . For example, when /^(2) is 7 with reference to FIG.

4. v_p(k) is a sequence correlation value corresponding to a sequence i ndex k from among Ν-1 sequence correlation values calculated using a p^th reception sync channel symbol. FIG. 19 illustrates Px (N-I) seq uence correlation values such as v_o(δ)=12 , v₂(lθ)=1.5 , etc. Referring to FIG. 4, a hopping pattern correlation value correspon ding to a hopping pattern (5, 6, 7, 8, 9) whose hopping pattern ID is 0 is q(θ), and a hopping pattern correlation value corresponding to a hopping pattern (9, 5, 6, 7, 8), which is "1" cyclically shifted from the hopping patt em (5, 6, 7, 8, 9), is g(l). That is, a hopping pattern correlation index i corresponding to a result, which is "p " cyclically shifted from a hopping pattern whose hopping pattern ID is m , \s mχP+p .

A process of calculating q(i) by referring to FIGS. 19 and 4 will n ow be described in detail. q(θ) is a hopping pattern correlation value of a hopping pattern (5, 6, 7, 8, 9) whose hopping pattern ID m is 0 and c yclic shift index p is 0, i.e., ?(θ)=O.9+1.9+1.6+1.7+1.7=7.8. Likewise, g(2) is a hopping pattern correlation value of a hopping pattern (8, 9, 5, 6, 7) whose hopping pattern ID m is 0 and cyclic shift index p is 2, i. e., g(2)=10.2+8.3+9.4+9.1 +8.9=45.9. Through this process, q(θ), q(l) , through to ^(FxJV₀ -I) are calculated, and if #(2) has the maximum v alue, the hopping pattern information generator 658 provides hopping pat tern information " Z_1113x = 2 " to a next stage. Here, Z_1118x = max q (i) . Accordi ng to the embodiment A, using the characteristic that each hopping patte rn respectively correspond to each code group, the code group detector 546 detects a code group of a target cell based on a result of an operatio n L*_maχ ÷ P\ ■ Likewise, according to the embodiment B, using the chara cteristic that each hopping pattern respectively correspond to each sera mbling code, the scrambling code detector 556 detects a scrambling cod e of the target cell based on the result of the operation [z_max ÷ p\ . This i s because the result of the operation Lz_max ÷p\ is a hopping pattern ID of the target cell.

The frame boundary detector 548 or 558 can determine one of 5 f rame boundary candidates 641-A, 641-B, 641-C, 641-D, and 641-E illustr ated in FIG. 13 as a frame boundary based on a cyclic shift index which i s a result of a modular operation (z_max)_mod/, . If the cyclic shift index is 2, t he frame boundary detector 548 or 558 determines a position of referenc e numeral 642-C as a frame boundary. That is, a cyclic shift index is inf ormation indicating how far a frame boundary separates from the initial r eference timing 641-A in sync slot length units. FIG. 20 is a conceptual diagram for explaining positions of a fram e boundary and reception common pilot channel symbols according to a n embodiment of the present invention. Referring to FIG. 20, each rece ption common pilot channel symbol includes N_τ samples as other OFD M symbols, including a CP duration having N_CP samples and a remaind er duration 679 having N_s samples.

Reference numeral 675 denotes a frame boundary detected by th e second detector 540. Since a forward link frame according to an emb odiment of the present invention has common pilot channel symbols ace ording to a predetermined rule based on the frame boundary, the third de tector 580 can extract reception common pilot channel symbols from rec eived signals S1 and S2 based on frame boundary information S6 receiv ed from the second detector 540 and the predetermined rule. That is, t he third detector 580 extracts reception common pilot channel symbols r eferred to as reference numeral 678 based on the frame boundary referr ed to as reference numeral 675 corresponding to the frame boundary inf ormation S6. Thereafter, the third detector 580 performs scrambling co de detection according to the embodiment A or a verification process ace ording to the embodiment B by applying a pilot correlation to each of the extracted reception common pilot channel symbols.

In detail, according to the embodiment B-2, the third detector 580 calculates a pilot correlation value of each of the reception common pilot channel symbols and a scrambling code corresponding to scrambling co de information S7, compares the calculated pilot correlation value to a pr edetermined threshold, and determines whether a detection result of the first detector 520 and a detection result of the second detector 540.

In detail, according to the embodiment A, the third detector 580 ca lculates pilot correlation values of each of the reception common pilot ch annel symbols and scrambling codes belonging to a code group corresp onding to code group information S7 and determines a scrambling code corresponding to the maximum pilot correlation value from among the cal culated pilot correlation values as a scrambling code of a target cell. Th e embodiment A induces an effect that complexity of the receiver can be reduced, by searching for only scrambling codes belonging to a detected code group. That is, the third detector 580 can determine the scrambli ng code of the target cell by searching for only N_c=8 scrambling codes fr om among a total of 512 scrambling codes with reference to FIG. 1. He re, N_c denotes the number of scrambling codes per code group. FIG. 21 is a block diagram of the third detector 580 of the receiver illustrated in FIG. 10, according to an embodiment of the present inventi on. Referring to FIG. 21 , the third detector 580 includes frequency offse t compensators 681-A and 681-B, Fourier transformers 682-A and 682-B , pilot symbol extractors 683-A and 683-B, pilot correlators 684-A and 68 4-B, accumulators 686-A and 686-B, a combiner 687, and a peak detect or 688.

Since each of the frequency offset compensators 681 -A and 681- B can detect the common pilot channel symbol duration 678 of each sub- frame based on the frame boundary information S6 received from the se cond detector 540, each of the frequency offset compensators 681 -A an d 681 -B extracts a reception common pilot channel symbol from the dow n-converted signals S1 or S2 and frequency offset compensates the N_s samples 679 excluding the CP of samples of the common pilot channel symbols using Equation 8. Here, the frequency offset estimation value S8 received from the second detector 540 can be used for the frequency offset compensation according to the current embodiment.

Each of the Fourier transformers 682-A and 682-B performs Fouri er transformation on the N_s frequency offset compensated samples.

Each of the pilot symbol extractors 683-A and 683-B extracts N_p recept ion pilot symbols from the Fourier transformed signal. Here, referring to

FIG. 3, the reception pilot symbols indicate reception symbols correspo nding to subcarriers to which the pilot symbols 182 are mapped from am ong the N_s reception symbols included in the Fourier transformed signa

I.

Each of the pilot correlators 684-A and 684-B calculates pilot corr elation values of the extracted N_p reception pilot symbols and each of t he N_c scrambling codes corresponding to the code group information S 7. Here, a pilot correlation method (a method of calculating the pilot cor relation values) can be represented by Equations 12 through 15 which wi

Il be described later. Each of the pilot correlators 684-A and 684-B inclu des N_c pilot correlators per code calculating N_c pilot correlation values in a parallel method. In FIG. 21 , g_o,g_x,-,g_Nc^ indicate scrambling co de IDs of N_c scrambling codes corresponding to the code group inform ation S7.

An output of each of the N_c pilot correlators per code is accumul ated in each accumulator-per-code included in the accumulators 686-A a nd 686-B for every sub-frame. Referring to FIG. 2, since one reception common pilot channel symbol per sub-frame exists, each accumulator-p er-code accumulates pilot correlation values corresponding to each sera mble code, which correspond to a pre-set number of sub-frames. The combiner 687 including N_c combiner-per-codes generates N_c decision variables in a parallel method by combining outputs of the a ccumulator-per-codes in two data paths corresponding the same scrambl ing code. Here, the two data paths are paths occurring according to the reception diversity as described above. It will be understood by those of ordinary skill in the art that the combiner 687 and the blocks in the low er part can be omitted if reception diversity is not used. The peak detec tor 688 detects a scrambling code S11 of a target cell by detecting a sera mbling code corresponding to a decision variable having the maximum v alue out of the N_c decision variables provided by the combiner 687. T hrough this process, the mobile station can detect a scrambling code of a base station having the shortest radio distance or a base station providi ng the highest reception signal intensity to the mobile station.

Though a detailed configuration of the third detector 570 accordin g to the embodiment A has been described in FIG 21 , It will be understoo d by those of ordinary skill in the art that a detailed configuration of the th ird detector 570 according to the embodiment B-2 can be derived from th e above description.

FIG. 22 is a conceptual diagram for explaining an operation of the pilot correlator 684-A or 684-B illustrated in FIG. 21 , according to an emb odiment of the present invention.

Referring to FIG. 22, reference numerals 695 and 696 respectivel y denote an input and an output of the pilot symbol extractors 683-A or 6 83-B. That is, the signal corresponding to reference numeral 695 includ es reception pilot symbols and reception data symbols in a frequency do main. In this case, referring to FIG. 3, the reception pilot symbols indica te reception symbols corresponding to subcarriers on which pilot symbols 182 are carried from among the reception symbols referred to as refere nee numeral 695. The pilot symbol extractor 683-A or 683-B extracts Np reception pilot symbols from the signal referred to as reference num eral 695. In FIG. 22, X{n) denotes an n^th reception pilot symbol in the frequency domain, and N_P =12.

Equations 12 through 15 represent a pilot correlation method.

U4iicj4i))lx(4i ₊ 2lcj4i ₊ 2-jf}} (15)

Here, c_gt (u) denotes a u^th element of a scrambling code whose s crambling code ID is g_k . In Equations 12 through 15, X(i) = a,c(i). H ere, σ, denotes a channel frequency response of an i^th subcarrier, and c(i) denotes an element of a scrambling code mapped to a subcarrier in a transmitter end.

A fading channel has a characteristic in that channel frequency re sponse values are almost the same for adjacent subcarriers but different from each other for subcarriers far from each other. Equation 12 becom

JV-I es ]Tα, , and thus, a wireless fading effect is coherently added for symb

(=0 ols x{ ) far from each other in the frequency domain. Thus, the detec tion performance of the conventional pilot correlation method defined by Equation 12 is decreased in the fading channel, and significantly decreas ed if a correlation length N is large.

However, Equations 13 through 15 represent the differential correl

ation. For example, Equation 13 becomes , and thu

s a better performance can be achieved than the conventional pilot correl ation method defined by Equation 12. Unlike Equation 13 using differential multiplication between adjace nt reception pilot symbols, Equation 14 uses differential multiplication bet ween every other reception pilot symbols as referred to as reference nu meral 697 of FIG. 22. The pilot correlation method defined by Equation 14 may be advantageous in an initial cell search mode in which the mobil e station cannot know whether the number of transmission antennas of a base station is 1 or 2.

If the number of transmission antennas of a target base station is 2, the target base station transmits even-th pilot symbols through a first tr ansmission antenna and odd-th pilot symbols through a second transmis sion antenna, and thus pilot symbols that are adjacent in the frequency d omain undergo fully independent fading. In FIG. 22, X(θ),x(2),... are r eception pilot symbols corresponding to the even-th pilot symbols, and x(l),x(3),... are reception pilot symbols corresponding to the odd-th pilot symbols. Thus, if the number of transmission antennas is 2, when the mobile station performs differential multiplication between adjacent recep tion pilot symbols as in Equation 13, detection performance may be deer eased. However, if Equation 14 is used, as illustrated by reference num eral 697 of FIG. 22, differential multiplication 697-A between even-th rec eption pilot symbols and differential multiplication 697-B between odd-th reception pilot symbols are performed, and thus scrambling code detecti on performance can be increased regardless of whether the number of tr ansmission antennas of the target base station is 1 or 2. In order to red uce calculation complexity, Equation 14 can be replaced by Equation 15 by using only the even-th reception pilot symbols and ignoring the odd-th reception pilot symbols.

When the mobile station is turned on, an error of the clock generat or 440 may be 3 pulses per million (PPM) or more. If this error is conver ted to a value used in a 2 GHz band, the error is 6 KHz or more, lf a fre quency offset is large in the initial cell search process, the search perfor mance in the first detection step may be significantly decreased. There is no performance problem in the second and third detection steps since frequency offset compensation is performed. FIG. 23 is a block diagram of the first detector 520 of the receiver i llustrated in FIG. 10, according to another embodiment of the present inv ention. Referring to FIG. 23, the first detector 520 includes frequency of fset switching units 530-A and 530-B, differential correlators 531 -A and 5 31 -B, an accumulator 532, and a timing determiner 533. Since function s and operations of the differential correlators 531 -A and 531 -B, the accu mulator 532, and the timing determiner 533 are the same as those illustr ated in FIG. 11 , a detailed description thereof is omitted, and only the fre quency offset switching units 530-A and 530-B will be described.

If a correlation operation handling absolute values is performed as in Equation 3 or 4, no decrease of detection performance according to a frequency offset can be considered. However, if a general correlation operation different from Equation 3 or 4 is performed, the frequency offse t switching units 530-A and 530-B according to an embodiment of the pre sent invention may be further included. The frequency offset switching unit 530-A or 530-B multiplies an in put signal r{n) by an arbitrary frequency offset component as in Equatio n 16, wherein a different offset value is used in every unit duration during the first detection step (hereinafter, a first detection unit duration). r'(n) denotes an output signal of the frequency offset switching unit 530- A or 530-B and is an object of the differential correlation operation.

FIG. 24 is a conceptual diagram for explaining an operation of the frequency offset switching unit 530-A or 530-B illustrated in FIG. 23, acco rding to an embodiment of the present invention.

FIG. 24 illustrates frequency offsets values used by the frequency offset switching unit 530-A or 530-B, and the frequency offset values are 0 KHz₁ -6 KHz, and 6 KHz. In FIG. 24, five 10-msec cell search unit dur ations are shown. The first detector 520 can safely operate even with a n initial frequency offset of more than 18 KHz by using the frequency offs et switching method illustrated in FIG. 24.

FIG. 25 is a flowchart illustrating a cell search method according t o an embodiment of the present invention, which corresponds to the emb odiment A in which each hopping pattern respectively corresponds to ea ch code group.

The cell search method of a mobile station according to the curren t embodiment includes operations sequentially processed by the cell sea rch unit 500 illustrated in FIG. 10 according to the embodiment A. Thus, although not fully described, the contents relating to the cell search unit 500 illustrated in FIG. 10 also apply to the cell search method according t o the current embodiment.

Referring to FIG. 25, symbol synchronization is acquired from a re ception signal in operation S800. Here, the reception signal is a signal r eceived by the mobile station when each base station transmits a frame of its cell. As described above, a frame of each cell includes M sync ch annel symbols code-hopped according to a hopping pattern of the cell an d includes at least one common pilot channel symbol scrambled with a s crambling code of the cell. An arbitrary hopping pattern used in the OF DM cellular system according to the present embodiment differs from a c yclically shifted result of the hopping pattern, other hopping patterns, or c yclically shifted results of the other hopping patterns.

A signal processing method used in operation S800 varies accordi ng to a forward link frame structure and a sync channel structure. For e xample, the time domain repetition pattern detection method and the mat ching filter method described above can be used for the signal processin g method. In operation S820, hopping pattern correlation values are calculat ed using reception sync channel symbols extracted from the reception si gnal based on the acquired symbol synchronization information, and a h opping pattern of a target cell is detected based on the calculated hoppin g pattern correlation values. A signal processing method used in operat ion S820 is the same as described for the second detector 540.

In operation S840, a code group and a frame boundary of the targ et cell are detected based on the detected hopping pattern. As describ ed above, the code group of the target cell is a code group respectively c orresponding to the detected hopping pattern, and the frame boundary is determined based on a cyclic shift index of the detected hopping patter n. A signal processing method used in operation S840 is the same as d escribed above.

In operation S860, pilot correlation values of the common pilot cha nnel symbol and each scrambling code belonging to the detected code g roup are calculated, and a scrambling code of the target cell is detected based on the calculated pilot correlation values.

In operation S880, a verification process is performed to determin e whether the detection result of operations S800 through S860 is reliabl e, and if the verification result is negative, the process proceeds to opera tion S800 and performs a cell search using a subsequent observing dura tion. If the verification result is positive, the cell search process accordi ng to an embodiment of the present invention ends. For example, the v erification result is negative if a pilot correlation value corresponding to th e scrambling code of the target cell is less than a predetermined threshol d. Though not shown in FIG. 25, it will be understood by those of ordina ry skill in the art that a fine tuning operation for fine tuning frequency and timing can be further included after operation S860, and the verification p rocess of operation S880 can be omitted for a quick cell search. FIG. 26 is a flowchart illustrating a cell search method according t o another embodiment of the present invention, which corresponds to th e embodiment B in which each hopping pattern respectively corresponds to each scrambling code.

The cell search method of a mobile station according to the curren t embodiment includes operations sequentially processed by the cell sea rch unit 500 illustrated in FIG. 10 according to the embodiment B. Thus, although not fully described, the contents relating to the cell search unit 500 illustrated in FIG. 10 also apply to the cell search method according t o the current embodiment.

In the current embodiment, a frame of each cell includes M sync c hannel symbols code-hopped according to a hopping pattern of the cell a nd includes at least one common pilot channel symbol scrambled with a scrambling code of the cell. An arbitrary hopping pattern used in the OF DM cellular system according to the present embodiment differs from a c yclically shifted result of the hopping pattern, other hopping patterns, or c yclically shifted results of the other hopping patterns. Since operation S900 to acquire symbol synchronization and oper ation S920 to detect a hopping pattern are the same as operations S800 and S820, a detailed description is omitted.

In operation S940, a scrambling code and a frame boundary of th e target cell are detected based on the detected hopping pattern. As de scribed above, the scrambling code of the target cell is a scrambling cod e respectively corresponding to the detected hopping pattern, and the fra me boundary is determined based on a cyclic shift index of the detected hopping pattern. A signal processing method used in operation S940 is the same as described above. In operation S960, a verification process is performed to determin e whether the detection result of operations S900 through S940 is reliabl e, and if the verification result is negative, the process proceeds to opera tion S900 and performs a cell search. If the verification result is positive , the cell search process according to an embodiment of the present inve ntion ends. For example, a corresponding to the scrambling code of the target cell is calculated, and if the calculated pilot correlation value is les s than a predetermined threshold, the verification result is negative.

In particular, FIG. 26 is a flowchart corresponding to the embodim ent B-2, and as described above, the embodiment B-1 in which operation S960 to perform the verification process is omitted for a quick cell searc h also exists. Though not shown in FIG. 26, it will be understood by tho se of ordinary skill in the art that a fine tuning operation for fine tuning fre quency and timing can be further included after operation S940.

FIG. 27 is a flowchart illustrating a frame transmission method of a base station according to an embodiment of the present invention. Ref erring to FIG. 27, the base station's frame transmission method accordin g to the current embodiment includes operations sequentially processed by the blocks of the frame transmission apparatus illustrated in FIG. 7. Thus, although not fully described, the contents described relating to the frame transmission apparatus illustrated in FIG. 7 also apply to the frame transmission method according to the current embodiment. In operation S1000, the sync channel generator 400 generates sy nc channel chips corresponding to a hopping pattern of the base station, i.e., sync symbols. Simultaneously, the data channel generator 402 and the common pilot channel generator 401 generate data symbols and pil ot symbols, respectively. The OFDM symbol mappers 404-A and 404-B map the generated sync symbols, data symbols, and pilot symbols to e ach subcarrier. Through this process, sync channel symbols are code-h opped according to sync channel sequences included in the hopping patt ern.

Here, according to the embodiment A, the hopping pattern corresp onds to a code group to which a scrambling code belongs, and according to the embodiment B, the hopping pattern corresponds to the scramblin g code. In addition, an arbitrary hopping pattern used in the OFDM cell ular system differs from a cyclically shifted result of the hopping pattern, other hopping patterns, or cyclically shifted results of the other hopping p atterns.

In operation S1010, symbols that remain due to the exclusion of th e sync channel symbols are scrambled in the frequency domain by the s cramblers 405-A and 405-B.

In operation S1020, a forward link frame is generated by performi ng inverse Fourier transformation on each of the sync channel symbols a nd the scrambled remaining symbols in the inverse Fourier transformers 406-A and 406-B and inserting CPs into the forward link frame in the CP insertion units 407-A and 407-B.

In operation S1030, the generated forward link frame is transmitte d through an RF channel by the IF/RF units 408-A and 408-B and the tra nsmission antennas 409-A and 409-B.

The embodiments A and B of the present invention have been de scribed. It will be understood by those of ordinary skill in the art that the embodiments A and B can be used for an initial cell search performed b y a mobile station and also used for an adjacent cell search using the pri nciple of the present invention. However, an efficient adjacent cell sear ch method using the principle will now be suggested by assuming that an OFDM cellular system operating in the base station synchronous mode i s used. Here, the OFDM cellular system operating in the base station s ynchronous mode indicates a synchronous OFDM cellular system.

A cellular system is divided into an asynchronous cellular system i n which frame timings of all base stations are independent to each other and a synchronous cellular system in which frame timings of all base stat ions are synchronized and mapped to each other. An example of the as ynchronous cellular system is a WCDMA system, and examples of the sy nchronous cellular system are an Interim Standard (IS)-95 system and a CDMA2000 system in which all base stations operate by being synchroni zed with Global Positioning System (GPS).

A 3G-LTE system basically uses an OFDM transmission method a s a forward link transmission method. In this case, a timing difference b etween OFDM symbols of signals received from cells adjacent to a cell b oundary must be less than a CP duration. Only if this condition is satisfi ed, orthogonality between subcarriers of the signals received from the ad jacent cells is maintained. One of systems satisfying the condition is a s ynchronous OFDM cellular system. Since all base stations in the synch ronous OFDM cellular system operate in the base station synchronous m ode, frame boundaries (frame timings) of frames transmitted from each b ase station are matched to each other.

The cell search process performed in a cellular system includes th e initial cell search process performed when a mobile station is turned on as described above and the adjacent cell search process for detecting fr ame timing and a scrambling code of an adjacent cell so as to perform h andover in an idle or call mode after completing the initial cell search pro cess.

In the idle or call mode, an error of the clock generator 440 illustra ted in FIG. 10 is close to 0 since a frequency offset can be continuously estimated using a signal received from a home cell. Thus, in the adjace nt cell search process, the frequency offset switching units 530-A and 53 0-B of FIG. 23 do not have to operate in the first detection step described above. In addition, frequency offset compensation in the frequency off set compensators 542, 552, 681 -A, and 681 -B illustrated in FIGS. 14, 15, and 21 does not have to be performed in the second and third detection steps, and an input signal bypasses to a next stage.

As described above, when an OFDM cellular system operates in a base station synchronous mode, the first detection step in an adjacent c ell search process can be omitted. That is, since a frame boundary of a signal received from an adjacent cell is within an error range of a CP fro m a frame boundary of a home cell, the first detector 520 illustrated in Fl

G. 10 does not have to operate. That is, if an operation of the first dete ctor 520 is described, the first detector 520 considers symbol synchroniz ation of the home cell as symbol synchronization of the adjacent cell.

In order to support seamless handover, a mobile station must be a ble to perform the adjacent cell search process even when the intensity o f reception signals from adjacent cells is equal to or less than the intensit y of a reception signal from a home cell. That is, the mobile station mus t continuously measure the intensity of a reception signal of an adjacent cell (i.e., a reception signal received from the adjacent cell) in the idle or call mode and report the measurement result to a base station. In this c ase, if the base station operates in the base station synchronous mode, since a sync channel symbol transmitted from the base station of the ho me cell and a sync channel symbol transmitted from the base station of t he adjacent cell overlap in the time domain, if the mobile station uses the second detection step, the cell search performance may be decreased. To address this problem, in an adjacent cell search method of a m obile station according to an embodiment of the present invention, a horn e cell component cancellation block is further included next to the combin er 656 illustrated in FIG. 16 in the second detection step.

FIG. 28 is a block diagram of the second detector 540 illustrated i n FIG. 10, according to another embodiment of the present invention. R eferring to FIG. 28, the second detector 540 further includes a home cell component canceller 1070 in addition to the configuration illustrated in Fl G. 16.

Since functions and operations of sequence correlation calculator s 1065-A and 1065-B, a combiner 1056, a buffer 1057, and a hopping pa ttern storage unit 1059 are the same as those of the sequence correlatio n calculators 665-A and 665-B, the combiner 656, the buffer 657, and th e hopping pattern storage unit 659, a detailed description is omitted for c onvenience.

The home cell component canceller 1070 cancels a home cell co mponent from the output of the combiner 1056. That is, the home cell c omponent canceller 1070 replaces a sequence correlation value corresp onding to a sync channel code sequence of a home cell among N-1 com bined sequence correlation values by a predetermined number, e.g., 0. Since the mobile station has determined a hopping pattern of the home c ell, the home cell component can be cancelled.

FIGS. 29 and 30 are diagrams for explaining an operation of the h ome ceil component canceller 1070 illustrated in FIG. 28 according to an embodiment of the present invention.

FIG. 29 corresponds to an input of the home cell component cane eller 1070. That is, FIG. 29 illustrates correlation results of all sync cha nnel code sequences used in the system with respect to each of 5 recept ion sync channel symbols. FIG. 29 shows a case where a hopping patt ern of the home cell is (5, 6, 7, 8, 9). In this case, the home cell compo nent canceller 1070 replaces sequence correlation values corresponding to (5, 6, 7, 8, 9) by 0.

FIG. 30 corresponds to an output of the home cell component can celler 1070. In FIG. 30, the sequence correlation values corresponding to (5, 6, 7, 8, 9), which are home cell components, are replaced by 0. T hus, the hopping pattern information generator 1058 detects one or more of hopping patterns that remain due to the exclusion of the hopping patt ern of the home cell.

In the adjacent cell search process of a cellular system in which b ase stations operate in the base station synchronous mode, the hopping pattern information generator 1058 according to an embodiment of the pr esent invention does not have to detect a cyclic shift index of an adjacent cell. As described above, since all base stations are matched to the fr ame sync, a frame timing of the adjacent cell is the same as a frame timi ng of the home cell. Thus, the hopping pattern information generator 10

58 in the adjacent cell search process according to an embodiment of th e present invention does not have to calculate all of PχN_G hopping patt ern correlation values in the cellular system in which base stations operat e in the base station synchronous mode but calculates N_G hopping patt ern correlation values. Each hopping pattern correlation value is repres ented by Equation 17. rih∑VuM")), i-0,l,...,N_G -l (17)

H=O

When Equation 17 is compared to Equation 10, the number of ho pping pattern correlation values is reduced by an amount 1/P. This is b ecause a cyclic shift index does not have to be considered in the adjacen t cell search process in the base station synchronous mode. The hoppi ng pattern information generator 1058 calculates the N₀ hopping patter n correlation values obtained by Equation 17 and provides a hopping patt ern correlation index corresponding to the maximum hopping pattern corr elation value to a next stage as the hopping pattern information S11.

The third detection step in the base station synchronous mode is performed the same as the operation of the third detector 580 illustrated i n FIG. 10 excluding non-compensation of a frequency offset.

In a cellular system operating in the base station synchronous mo de, when an adjacent cell is searched in the idle mode of a mobile statio n according to another embodiment of the present invention, in order to minimize power consumption of the mobile station, the mobile station us es a gating mode in which operations of the remainder blocks 410-A, 410 -B, 500, 420, and 430 excluding the clock generator 440, which supports a frame clock synchronized with a frame boundary of a home cell, are tur ned on/off as illustrated in FIG. 31.

FIG. 31 is a diagram for explaining the gating mode of a mobile st ation performing the adjacent ceil search process in the idle mode accor ding to an embodiment of the present invention. Referring to FIG. 31 , t he mobile station's receiver searches an adjacent cell only during ON dur ations 1100 in which a reception sync channel symbol and a reception co mmon pilot channel symbol exist and does not perform a reception opera tion of a receiver end, such as adjacent cell search or down conversion, during OFF durations 1101. That is, the mobile station can reduce batte ry consumption by performing a cell search only using signals received d uring the ON durations 1100.

FIG. 32 is a flowchart illustrating an adjacent cell search method o f a mobile station according to an embodiment of the present invention. Referring to FIG. 32, the mobile station's adjacent cell search method a ccording to the current embodiment includes operations sequentially pro cessed by the cell search unit 500 in the base station synchronous mode . Thus, although not fully described, the contents described relating to t he cell search unit 500 illustrated in FIG. 10 and the second detector 540 illustrated in FIG. 28 also apply to the adjacent cell search method acco rding to the current embodiment.

In operation S1100, the first detector 520 considers synchronizatio n and a frame boundary of a home cell as synchronization and a frame b oundary of an adjacent cell, and the second detector 540 detects a hoppi ng pattern of the adjacent cell from reception sync channel symbols base d on the synchronization and frame boundary of the adjacent cell. In operation S1110, the second detector 540 detects a code grou p of the adjacent cell based on the detected hopping pattern.

In operation S1120, the third detector 580 detects a scrambling co de of the adjacent cell based on the detected code group and a receptio n common pilot channel symbol.

The embodiment illustrated in FIG. 32 corresponds to a case wher e each hopping pattern respectively corresponds to each code group. If each hopping pattern respectively corresponds to each scrambling code , in operation S1110, the second detector 540 detects a scrambling code of the adjacent cell based on the detected hopping pattern, and operati on S1120 does not have to be performed.

The invention can also be embodied as computer readable codes on a computer readable recording medium. The computer readable rec ording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer re adable recording medium include read-only memory (ROM), random-acc ess memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical dat a storage devices, and carrier waves (such as data transmission through the Internet). The computer readable recording medium can also be dis tributed over network coupled computer systems so that the computer re adable code is stored and executed in a distributed fashion. Also, functi onal programs, codes, and code segments for accomplishing the present invention can be easily construed by programmers skilled in the art to w hich the present invention pertains.

While the present invention has been particularly shown and desc ribed with reference to exemplary embodiments thereof, it will be underst ood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

What is claimed is:

1. A cell search method used by a terminal to search a target cell using reception signals received from a plurality of base stations, eac h base station transmitting a frame of its cell, in an Orthogonal Frequenc y-Division Multiplexing (OFDM) cellular system comprising a plurality cell s to which a cell-specific scrambling code is assigned, the cell search me thod comprising: detecting a hopping pattern of the target cell using reception sync channel symbols, which are signals corresponding to sync channel symb ol positions of the reception signals, wherein the frame of each cell comp rises M sync channel symbols code-hopped according to a hopping patte rn of the cell, where M is a natural number equal to or greater than 2, eac h hopping pattern containing M sync channel code sequences and respe ctively corresponding to each code group to which a scrambling code of each cell belongs, and an arbitrary hopping pattern used in the OFDM ce llular system differs from a cyclically shifted result of the hopping pattern, other hopping patterns, or cyclically shifted results of the other hopping patterns; and detecting a code group of the target cell based on the detected ho pping pattern.

2. The cell search method of claim 1 , further comprising detec ting a frame boundary based on the detected hopping pattern.

3. The cell search method of claim 1 or 2, wherein the frame o f each cell is made up of M sync slots having the same time duration, an d each sync channel symbol is located at the same position in each sync slot.

4. The cell search method of claim 2, wherein the frame of ea ch cell comprises at least one common pilot channel symbol scrambled with a scrambling code of the cell, wherein the cell search method further comprises calculating pilot correlation values indicating correlation values of a reception common pil ot channel symbol, which is a signal corresponding to a common pilot ch annel symbol position from among the reception signal, and scrambling c odes belonging to the detected code group and detecting a scrambling of the target cell based on the calculated pilot correlation values.

5. The cell search method of claim 1 or 2, wherein the detecti ng of the hopping pattern comprises: calculating hopping pattern correlation values indicating correlatio n values of each of each hopping pattern used in the OFDM cellular syst em and cyclically shifted results of the hopping pattern and the reception sync channel symbols; and determining a hopping pattern corresponding to the maximum hop ping pattern correlation value as a hopping pattern of the target cell.

6. The cell search method of claim 5, wherein the calculating of the hopping pattern correlation values comprises: calculating sequence correlation values indicating correlation valu es of each sync channel code sequence used in the OFDM cellular syste m and the reception sync channel symbols; and calculating each hopping pattern correlation value by summing se quence correlation values corresponding to each hopping pattern correla tion.

7. The cell search method of claim 1 or 2, wherein the sync ch annel code sequence is made up of sync channel chips generated based on a Generalized Chirp Like (GCL) sequence.

8. The cell search method of claim 6, wherein the sync chann el code sequence is made up of sync channel chips generated based on a GCL sequence, wherein the calculating of the sequence correlation values compri ses: extracting reception sync symbols from each reception sync chan nel symbol, each reception sync symbol being carried on a subcarrier on which a sync channel chip is carried from among subcarriers of each rec eption sync channel symbol; and multiplying a complex conjugate value of an odd-th reception sync symbol by a reception sync symbol adjacent to the odd-th reception syn c symbol for every odd-th reception sync symbols of each reception sync channel symbol.

9. The cell search method of claim 6, wherein the calculating of the sequence correlation values comprises: if the terminal has a plurality of reception antennas and acquires a reception signal through each of the plurality of reception antennas, calc ulating sequence correlation values per antenna indicating correlation val ues of each sync channel code sequence and the reception sync channe

I symbols contained in the reception signal per antenna; calculating the sequence correlation values by combining the sequ ence correlation values corresponding to the same sync channel code se quence of the plurality of reception antennas.

10. The cell search method of claim 1 , 2, or 4, wherein a sync c hannel symbol included in the frame of each cell contains sync channel c hips mapped to subcarriers positioning at every predetermined period in a sync channel occupied band and predetermined symbols mapped to th e remainder subcarriers of the sync channel occupied band, wherein the cell search method further comprises acquiring symbo I synchronization using a time domain repetition pattern of each sync cha nnel symbol contained in the reception signal.

11. The cell search method of claim 10, wherein the sync chan nel symbol included in the frame of each cell contains sync channel chip s mapped to odd-th or even-th subcarriers of a sync channel occupied ba nd and predetermined symbols mapped to the remainder subcarriers of t he sync channel occupied band, wherein the cell search method further comprises acquiring symbo I synchronization using a time domain repetition pattern of each sync cha nnel symbol contained in the reception signal.

12. The cell search method of claim 10, wherein the predetermi ned symbols are null symbols.

13. The cell search method of claim 11 , wherein the acquiring of the symbol synchronization comprises: calculating differential correlation values of sample positions of the reception signal; and acquiring the symbol synchronization by determining a sample po sition corresponding to the maximum differential correlation value as a sy nc channel symbol timing.

14. The cell search method of claim 13, wherein the calculating differential correlation values comprises: if the terminal has a plurality of reception antennas and acquires a reception signal through each of the plurality of reception antennas, calc ulating differential correlation values per antenna indicating differential co rrelation values of sample positions of the reception signal per antenna; and combining the differential sequence correlation values per antenn a corresponding to the same sample position, wherein the acquiring of the symbol synchronization by determinin g a sync channel symbol timing comprises determining a sync channel s ymbol timing based on the combining result.

15. The cell search method of claim 13, wherein the frame of e ach cell is made up of M sync slots having the same time duration, and e ach sync channel symbol is located at the same position in each sync slo t, wherein the calculating differential correlation values comprises: calculating differential correlation values per sync slot indicating di fferential correlation values of sample positions in sync slots; and combining the differential sequence correlation values per sync si ot corresponding to sample positions having the same relative sample po sition in each sync slot, wherein the acquiring of the symbol synchronization by determinin g a sync channel symbol timing comprises determining a sync channel s ymbol timing based on the combining result.

16. The cell search method of claim 11 , wherein the detecting of the hopping pattern comprises: estimating a frequency offset using at least one of the reception sy nc channel symbols; compensating for a frequency offset of each of the reception sync channel symbols based on the estimated frequency offset; and detecting the hopping pattern based on the compensated receptio n sync channel symbols.

17. The cell search method of claim 10, further comprising perf orming filtering to pass only the sync channel occupied band with respect to the reception signal, wherein the acquiring of the symbol synchronization and the detec ting of the hopping pattern respectively comprise acquiring the symbol sy nchronization and detecting the hopping pattern using the filtered recepti on signal.

18. The cell search method of claim 10, wherein the acquiring of the symbol synchronization is performed after frequency offset compe nsating for the reception signal by changing a frequency offset in each u nit symbol sync acquisition duration.

19. The cell search method of claim 4, wherein a sync channel symbol included in the frame of each cell contains sync channel chips m apped to subcarriers positioning at every predetermined period in a sync channel occupied band and predetermined symbols mapped to the rema inder subcarriers of the sync channel occupied band, wherein the cell search method further comprises: acquiring symbol synchronization using a time domain repetition p attern of each sync channel symbol contained in the reception signal; an d performing verification of an acquisition result of the acquiring of t he symbol synchronization, a detection result of the detecting of the code group, a detection result of the detecting of the frame boundary, and a d etection result of the detecting of the scrambling code, based on a result obtained by comparing a pilot correlation value corresponding to the dete cted scrambling code to a predetermined threshold.

20. The cell search method of claim 19, wherein if a verification result of the performing of the verification is negative, the acquiring of th e symbol synchronization, the detecting of the code group, the detecting of the frame boundary, and the detecting of the scrambling code are perf ormed again.

21. A cell search method used by a terminal to search a target cell using reception signals received from a plurality of base stations, eac h base station transmitting a frame of its cell, in an Orthogonal Frequenc y-Division Multiplexing (OFDM) cellular system comprising a plurality cell s to which a cell-specific scrambling code is assigned, the cell search me thod comprising: detecting a hopping pattern of the target cell using reception sync channel symbols, which are signals corresponding to sync channel symb ol positions of the reception signals, wherein the frame of each cell comp rises M sync channel symbols code-hopped according to a hopping patte rn of the cell, where M is a natural number equal to or greater than 2, eac h hopping pattern containing M sync channel code sequences and respe ctively corresponding to each code group to which a scrambling code of each cell belongs, and an arbitrary hopping pattern used in the OFDM ce llular system differs from a cyclically shifted result of the hopping pattern, other hopping patterns, or cyclically shifted results of the other hopping patterns; and detecting a frame boundary based on the detected hopping patter n.

22. The cell search method of claim 21 , wherein the frame of e ach cell is made up of M sync slots having the same time duration, and e ach sync channel symbol is located at the same position in each sync slo t.

23. The cell search method of claim 21 or 22, wherein a sync c hannel symbol included in the frame of each cell contains sync channel c hips mapped to subcarriers positioning at every predetermined period in a sync channel occupied band and predetermined symbols mapped to th e remainder subcarriers of the sync channel occupied band, wherein the cell search method further comprises acquiring symbo I synchronization using a time domain repetition pattern of each sync cha nnel symbol contained in the reception signal.

24. The cell search method of claim 23, wherein the sync chan nel symbol included in the frame of each cell contains sync channel chip s mapped to odd-th or even-th subcarriers of a sync channel occupied ba nd and predetermined symbols mapped to the remainder subcarriers of t he sync channel occupied band, wherein the cell search method further comprises acquiring symbo I synchronization using a time domain repetition pattern of each sync cha nnel symbol contained in the reception signal.

25. A cell search method used by a terminal to search a target cell using reception signals received from a plurality of base stations, eac h base station transmitting a frame of its cell, in an Orthogonal Frequenc y-Division Multiplexing (OFDM) cellular system comprising a plurality cell s to which a cell-specific scrambling code is assigned, the cell search me thod comprising: detecting a hopping pattern of the target cell using reception sync channel symbols, which are signals corresponding to sync channel symb ol positions of the reception signals, wherein the frame of each cell comp rises M sync channel symbols code-hopped according to a hopping patte m of the cell, where M is a natural number equal to or greater than 2, eac h hopping pattern containing M sync channel code sequences and respe ctively corresponding to a scrambling code of each cell, and an arbitrary hopping pattern used in the OFDM cellular system differs from a cyclicall y shifted result of the hopping pattern, other hopping patterns, or cyclicall y shifted results of the other hopping patterns; and detecting a scrambling code of the target cell based on the detect ed hopping pattern.

26. The cell search method of claim 25, further comprising dete cting a frame boundary based on the detected hopping pattern.

27. The cell search method of claim 25 or 26, wherein the fram e of each cell is made up of M sync slots having the same time duration, and each sync channel symbol is located at the same position in each sy nc slot.

28. The cell search method of claim 25 or 26, wherein the dete cting of the hopping pattern comprises: calculating hopping pattern correlation values indicating correlatio n values of each of each hopping pattern used in the OFDM cellular syst em and cyclically shifted results of the hopping pattern and the reception sync channel symbols; and determining a hopping pattern corresponding to the maximum hop ping pattern correlation value as a hopping pattern of the target cell.

29. The cell search method of claim 28, wherein the calculating of the hopping pattern correlation values comprises: calculating sequence correlation values indicating correlation valu es of each sync channel code sequence used in the OFDM cellular syste m and the reception sync channel symbols; and calculating each hopping pattern correlation value by summing se quence correlation values corresponding to each hopping pattern correla tion.

30. The cell search method of claim 25 or 26, wherein the sync channel code sequence is made up of sync channel chips generated ba sed on a Generalized Chirp Like (GCL) sequence.

31. The cell search method of claim 29, wherein the sync chan nel code sequence is made up of sync channel chips generated based o n a GCL sequence, wherein the calculating of the sequence correlation values compri ses: extracting reception sync symbols from each reception sync chan nel symbol, each reception sync symbol being carried on a subcarrier on which a sync channel chip is carried from among subcarriers of each rec eption sync channel symbol; and multiplying a complex conjugate value of an odd-th reception sync symbol by a reception sync symbol adjacent to the odd-th reception syn c symbol for every odd-th reception sync symbols of each reception sync channel symbol.

32. The cell search method of claim 29, wherein the calculating of the sequence correlation values comprises: if the terminal has a plurality of reception antennas and acquires a reception signal through each of the plurality of reception antennas, calc ulating sequence correlation values per antenna indicating correlation val ues of each sync channel code sequence and the reception sync channe I symbols contained in the reception signal per antenna; calculating the sequence correlation values by combining the sequ ence correlation values corresponding to the same sync channel code se quence of the plurality of reception antennas.

33. The cell search method of claim 25 or 26, wherein a sync c hannel symbol included in the frame of each cell contains sync channel c hips mapped to subcarriers positioning at every predetermined period in a sync channel occupied band and predetermined symbols mapped to th e remainder subcarriers of the sync channel occupied band, wherein the cell search method further comprises acquiring symbo I synchronization using a time domain repetition pattern of each sync cha nnel symbol contained in the reception signal.

34. The cell search method of claim 33, wherein the sync chan nel symbol included in the frame of each cell contains sync channel chip s mapped to odd-th or even-th subcarriers of a sync channel occupied ba nd and predetermined symbols mapped to the remainder subcarriers of t he sync channel occupied band, wherein the cell search method further comprises acquiring symbo I synchronization using a time domain repetition pattern of each sync cha nnel symbol contained in the reception signal.

35. The cell search method of claim 33, wherein the predetermi ned symbols are null symbols.

36. The cell search method of claim 34, wherein the acquiring of the symbol synchronization comprises: calculating differential correlation values of sample positions of the reception signal; and acquiring the symbol synchronization by determining a sample po sition corresponding to the maximum differential correlation value as a sy nc channel symbol timing.

37. The cell search method of claim 36, wherein the calculating differential correlation values comprises: if the terminal has a plurality of reception antennas and acquires a reception signal through each of the plurality of reception antennas, calc ulating differential correlation values per antenna indicating differential co rrelation values of sample positions of the reception signal per antenna; and combining the differential sequence correlation values per antenn a corresponding to the same sample position, wherein the acquiring of the symbol synchronization by determinin g a sync channel symbol timing comprises determining a sync channel s ymbol timing based on the combining result.

38. The cell search method of claim 36, wherein the frame of e ach cell is made up of M sync slots having the same time duration, and e ach sync channel symbol is located at the same position in each sync slo t, wherein the calculating differential correlation values comprises: calculating differential correlation values per sync slot indicating di fferential correlation values of sample positions in sync slots; and combining the differential sequence correlation values per sync si ot corresponding to sample positions having the same relative sample po sition in each sync slot, wherein the acquiring of the symbol synchronization by determinin g a sync channel symbol timing comprises determining a sync channel s ymbol timing based on the combining result.

39. The cell search method of claim 34, wherein the detecting of the hopping pattern comprises: estimating a frequency offset using at least one of the reception sy nc channel symbols; compensating for a frequency offset of each of the reception sync channel symbols based on the estimated frequency offset; and detecting the hopping pattern based on the compensated receptio n sync channel symbols.

40. The cell search method of claim 33, further comprising perf orming filtering to pass only the sync channel occupied band with respect to the reception signal, wherein the acquiring of the symbol synchronization and the detec ting of the hopping pattern respectively comprise acquiring the symbol sy nchronization and detecting the hopping pattern using the filtered recepti on signal.

41. The cell search method of claim 33, wherein the acquiring of the symbol synchronization is performed after frequency offset compe nsating for the reception signal by changing a frequency offset in each u nit symbol sync acquisition duration.

42. The cell search method of claim 33, wherein the frame of e ach cell contains at least one common pilot channel symbol scrambled w ith a scrambling code of the cell, wherein the cell search method further comprises calculating a pil ot correlation value indicating a correlation value of a reception common pilot channel symbol, which is a signal corresponding to a position of the common pilot channel symbol form among the reception signal, and the detected scrambling code and performing verification of an acquisition re suit of the acquiring of the symbol synchronization, a detection result of t he detecting of the scrambling code, and a detection result of the detecti ng of the frame boundary, based on the calculated pilot correlation value.

43. The cell search method of claim 42, wherein if a verification result of the performing of the verification is negative, the acquiring of th e symbol synchronization, the detecting of the frame boundary, and the d etecting of the scrambling code are performed again.

44. A cell search method used by a terminal to search a target cell using reception signals received from a plurality of base stations, eac h base station transmitting a frame of its cell, in an Orthogonal Frequenc y-Division Multiplexing (OFDM) cellular system comprising a plurality cell s to which a cell-specific scrambling code is assigned, the cell search me thod comprising: detecting a hopping pattern of the target cell using reception sync channel symbols, which are signals corresponding to sync channel symb ol positions of the reception signals, wherein the frame of each cell comp rises M sync channel symbols code-hopped according to a hopping patte rn of the cell, where M is a natural number equal to or greater than 2, eac h hopping pattern containing M sync channel code sequences and respe ctively corresponding to a scrambling code of each cell, and an arbitrary hopping pattern used in the OFDM cellular system differs from a cyclicall y shifted result of the hopping pattern, other hopping patterns, or cyclicall y shifted results of the other hopping patterns; and detecting a frame boundary based on the detected hopping patter n.

45. The cell search method of claim 44, wherein the frame of e ach cell is made up of M sync slots having the same time duration, and e ach sync channel symbol is located at the same position in each sync slo t.

46. The cell search method of claim 44 or 45, wherein a sync c hannel symbol included in the frame of each cell contains sync channel c hips mapped to subcarriers positioning at every predetermined period in a sync channel occupied band and predetermined symbols mapped to th e remainder subcarriers of the sync channel occupied band, wherein the cell search method further comprises acquiring symbo I synchronization using a time domain repetition pattern of each sync cha nnel symbol contained in the reception signal.

47. The cell search method of claim 46, wherein the sync chan nel symbol included in the frame of each cell contains sync channel chip s mapped to odd-th or even-th subcarriers of a sync channel occupied ba nd and predetermined symbols mapped to the remainder subcarriers of t he sync channel occupied band, wherein the cell search method further comprises acquiring symbo I synchronization using a time domain repetition pattern of each sync cha nnel symbol contained in the reception signal.

48. A frame transmission method used by a base station belon ging to an arbitrary cell to transmit a frame in an Orthogonal Frequency- Division Multiplexing (OFDM) cellular system comprising a plurality cells t o which a cell-specific scrambling code is assigned, the frame transmissi on method comprising: generating M sync channel code sequences forming a hopping pa ttern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and re spectively corresponding to a scrambling code of each cell or a code gro up to which the scrambling code belongs; and generating a frame comprising M sync channel symbols code-hop ped on a frequency domain using each of the generated M sync channel code sequences and transmitting the generated frame, wherein an arbitrary hopping pattern used in the OFDM cellular sy stem differs from a cyclically shifted result of the hopping pattern, other h opping patterns, or cyclically shifted results of the other hopping patterns.

49. The frame transmission method of claim 48, wherein the for ward link frame is made up of M sync slots having the same time duratio n, and each sync channel symbol is located at the same position in each sync slot.

50. The frame transmission method of claim 48, wherein the sy nc channel code sequence is made up of sync channel chips generated based on a Generalized Chirp Like (GCL) sequence.

51. The frame transmission method of claim 48, wherein each sync channel symbol contains sync channel chips mapped to subcarriers positioning at every predetermined period in a sync channel occupied b and and predetermined symbols mapped to the remainder subcarriers of the sync channel occupied band.

52. The frame transmission method of claim 51 , wherein each sync channel symbol contains sync channel chips mapped to odd-th or e ven-th subcarriers of a sync channel occupied band and predetermined s ymbols mapped to the remainder subcarriers of the sync channel occupi ed band.

53. The frame transmission method of claim 51 or 52, wherein t he predetermined symbols are null symbols.

54. The frame transmission method of claim 48, wherein the tra nsmitting of the generated frame comprises transmitting the sync channe I symbols using time switching transmission diversity or time delay trans mission diversity.

55. The frame transmission method of claim 48, wherein each sync channel code sequence occupies a partial bandwidth of a forward Ii nk band of the OFDM cellular system in the frequency domain.

56. The frame transmission method of claim 55, wherein each sync channel code sequence occupies the partial bandwidth around the center frequency of the forward link band.

57. A structure of a forward link frame transmitted by a base st ation belonging to an arbitrary cell in an Orthogonal Frequency-Division Multiplexing (OFDM) cellular system comprising a plurality cells to which a cell-specific scrambling code is assigned, the forward link frame compri sing M sync channel symbols sequence-hopped according to a hopping pattern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and respectively corresponding to a scrambling code of each cell or a code gr oup to which the scrambling code belongs, wherein an arbitrary hopping pattern used in the OFDM cellular sy stem differs from a cyclically shifted result of the hopping pattern, other h opping patterns, or cyclically shifted results of the other hopping patterns.

58. The forward link frame structure of claim 57, wherein the fo rward link frame is made up of M sync slots having the same time duratio n, and each sync channel symbol is located at the same position in each sync slot.

59. The forward link frame structure of claim 57, wherein the nu mber of sync channel code sequences continuously matched between th e arbitrary hopping pattern used in the OFDM cellular system, the cyclica Hy shifted result of the hopping pattern, the other hopping patterns, and t he cyclically shifted results of the other hopping patterns is less than N, where N is a natural number less than M-1.

60. The forward link frame structure of claim 57, wherein the nu mber of sync channel code sequences continuously matched between th e arbitrary hopping pattern used in the OFDM cellular system, the cyclica Hy shifted result of the hopping pattern, the other hopping patterns, and t he cyclically shifted results of the other hopping patterns is less than 1.

61. The forward link frame structure of claim 57, wherein no co mmon sync channel code sequence exists between the arbitrary hopping pattern used in the OFDM cellular system and other hopping patterns.

62. The forward link frame structure of any one of claims 57 to 61 , wherein the forward link frame has a 10-msec time duration, and M is 5.

63. The forward link frame structure of any one of claims 57 to 61 , wherein the forward link frame contains at least one common pilot ch annel symbol scrambled with a scrambling code of the cell.

64. The forward link frame structure of claim 57, wherein each sync channel code sequence is made up of sync channel data generated based on a Generalized Chirp Like (GCL) sequence.

65. The forward link frame structure of claim 57, wherein each sync channel symbol contains sync channel data according to the sync c hannel code sequence at positions of subcarriers positioning at every pre determined period in a sync channel occupied band and contains predet ermined symbols at positions of the remainder subcarriers of the sync ch annel occupied band.

66. The forward link frame structure of claim 57, wherein each sync channel symbol contains sync channel data according to the sync c hannel code sequence at positions of odd-th or even-th subcarriers of a s ync channel occupied band and contains predetermined symbols at posit ions of the remainder subcarriers of the sync channel occupied band.

67. The forward link frame structure of claim 65 or 66, wherein the predetermined symbols are null symbols.

68. The forward link frame structure of claim 57, wherein each sync channel code sequence occupies a partial bandwidth of a forward Ii nk band of the OFDM cellular system in the frequency domain.

69. The forward link frame structure of claim 68, wherein each sync channel code sequence occupies the partial bandwidth around the center frequency of the forward link band.

70. An adjacent cell search method used by a terminal to searc h a target cell using reception signals received from a plurality of base st ations, each base station transmitting a frame of its cell, in an Orthogonal

Frequency-Division Multiplexing (OFDM) cellular system comprising a pi urality cells to which a cell-specific scrambling code is assigned, the adja cent cell search method comprising: acquiring symbol sync and a frame boundary of an adjacent cell b y considering symbol sync and a frame boundary of a home cell as the s ymbol sync and the frame boundary of the adjacent cell, wherein the fra me of each cell comprises M sync channel symbols code-hopped accordi ng to a hopping pattern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and respectively corresponding to each code group to which a scrambling code of each cell belongs, and an arbitrary hopping pattern used in the OFDM cellular system differs from a cyclically shifted result o f the hopping pattern, other hopping patterns, or cyclically shifted results of the other hopping patterns; detecting a hopping pattern of the adjacent cell using reception sy nc channel symbols, which are signals corresponding to sync channel sy mbol positions of the reception signals; and detecting a code group of the adjacent cell based on the detected hopping pattern.

71. The adjacent cell search method of claim 70, wherein the fr ame of each cell comprises at least one common pilot channel symbol sc rambled with a scrambling code of the cell, wherein the adjacent cell search method further comprises calcula ting pilot correlation values indicating correlation values of a reception co mmon pilot channel symbol, which is a signal corresponding to a commo n pilot channel symbol position from among the reception signal, and scr ambling codes belonging to the detected code group and detecting a scr ambling of the adjacent cell based on the calculated pilot correlation valu es.

72. The adjacent cell search method of claim 70 or 71 , wherein the detecting of the hopping pattern comprises: calculating hopping pattern correlation values indicating correlatio n values of each hopping pattern used in the OFDM cellular system and t he reception sync channel symbols; and determining a hopping pattern corresponding to the maximum hop ping pattern correlation value from among hopping patterns remaining by excluding a hopping pattern of the home cell as a hopping pattern of the adjacent cell.

73. The adjacent cell search method of claim 70 or 71 , wherein the detecting of the hopping pattern comprises: calculating sequence correlation values indicating correlation valu es of each sync channel code sequence used in the OFDM cellular syste m and the reception sync channel symbols and replacing a sequence cor relation value corresponding to a sync channel code sequence of the ho me cell from among the calculated sequence correlation values with a pr edetermined number; calculating each hopping pattern correlation value by summing se quence correlation values corresponding to each hopping pattern used in the OFDM cellular system; and determining a hopping pattern corresponding to the maximum hop ping pattern correlation value as a hopping pattern of the adjacent cell.

74. The adjacent cell search method of claim 70 or 71 , wherein the detecting of the hopping pattern, the detecting of the code group, an d the detecting of the scrambling code are performed only a predetermin ed duration containing a sync channel symbol position and a common pil ot channel symbol position, which are detected based on the synchroniz ation and frame boundary of the home cell in a mobile station idle mode.

75. An adjacent cell search method used by a terminal to searc h a target cell using reception signals received from a plurality of base st ations, each base station transmitting a frame of its cell, in an Orthogonal Frequency-Division Multiplexing (OFDM) cellular system comprising a pi urality cells to which a cell-specific scrambling code is assigned, the adja cent cell search method comprising: acquiring symbol sync and a frame boundary of an adjacent cell b y considering symbol sync and a frame boundary of a home cell as the s ymbol sync and the frame boundary of the adjacent cell, wherein the fra me of each cell comprises M sync channel symbols code-hopped accordi ng to a hopping pattern of the cell, where M is a natural number equal to or greater than 2, each hopping pattern containing M sync channel code sequences and respectively corresponding to a scrambling code of each cell, and an arbitrary hopping pattern used in the OFDM cellular system d iffers from a cyclically shifted result of the hopping pattern, other hopping patterns, or cyclically shifted results of the other hopping patterns; detecting a hopping pattern of the adjacent cell using reception sy nc channel symbols, which are signals corresponding to sync channel sy mbol positions of the reception signals; and detecting a scrambling code of the adjacent cell based on the dete cted hopping pattern.

76. The adjacent cell search method of claim 75, wherein the d etecting of the hopping pattern comprises: calculating hopping pattern correlation values indicating correlatio n values of each hopping pattern used in the OFDM cellular system and t he reception sync channel symbols; and determining a hopping pattern corresponding to the maximum hop ping pattern correlation value from among hopping patterns remaining by excluding a hopping pattern of the home cell as a hopping pattern of the adjacent cell.

77. The adjacent cell search method of claim 75, wherein the d etecting of the hopping pattern comprises: calculating sequence correlation values indicating correlation valu es of each sync channel code sequence used in the OFDM cellular syste m and the reception sync channel symbols and replacing a sequence cor relation value corresponding to a sync channel code sequence of the ho me cell from among the calculated sequence correlation values with a pr edetermined number; calculating each hopping pattern correlation value by summing se quence correlation values corresponding to each hopping pattern used in the OFDM cellular system; and determining a hopping pattern corresponding to the maximum hop ping pattern correlation value as a hopping pattern of the adjacent cell.

78. The adjacent cell search method of claim 75, wherein the d etecting of the hopping pattern, the detecting of the code group, and the detecting of the scrambling code are performed only a predetermined dur ation containing a sync channel symbol position and a common pilot cha nnel symbol position, which are detected based on the synchronization a nd frame boundary of the home cell in a mobile station idle mode.