KR20080035992A - Cell search and bch demodulation method for ofdm system - Google Patents

Abstract

Cell search and BCH(Broadcasting Channel) demodulation methods for an OFDM(Orthogonal Frequency Division Multiplexing) system are provided to obtain the synchronization with low complexity and to offer a simple receiver structure without blind detection due to time ambiguity. A terminal obtains a sync block synchronization and the first sync channel sequence number by the first sync channel symbol included in the received frame(S1200). The boundary and scrambling code group is detected by the sync block synchronization and the second sync channel symbol included in the frame received by the terminal(S1210). A process for obtaining the scrambling code is performed by the first sync channel sequence number and the scrambling code group(S1220). A BCH included in the frame received by the terminal is modulated by the scrambling code so that the information of the wireless communication system is obtained. In the boundary and scrambling code group detection process, the number of BCH antennas or the length of CP(Cyclic Prefix) are obtained.

Description

PFDM cell search and BCH demodulation method

TECHNICAL FIELD The present invention relates to an OFDM cellular system, and more particularly, to a method for searching an initial cell and an adjacent cell in an OFDM cellular system and a method for demodulating a BC.

The present invention is derived from the research conducted as part of the IT new growth engine core technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. [Task Management Number: 2005-S-404-12, Title: 3G Evolution Wireless Transmission Technology Development] ].

In the 3GPP WCDMA scheme, a total of 512 long PN scrambling codes are used in the system to distinguish base stations of a forward link, and neighboring base stations use different long PN scrambling codes as scrambling codes of forward link channels. When power is applied to the mobile station, the mobile station should acquire the system timing of the base station to which the mobile station belongs (the base station with the largest received signal) and the long PN scrambling code ID used by the current base station. This is called a cell search process of the mobile station.

In WCDMA, 512 long scrambling codes are divided into 64 groups and have a primary sync channel and a secondary sync channel on the forward link to facilitate cell search. The primary synchronization channel causes the mobile station to acquire slot synchronization and the secondary synchronization channel causes the mobile station to acquire 10 msec frame boundary and long PN scrambling code group ID information.

The cell search method of the WCDMA method is largely composed of three steps. The first step is a step in which a mobile station acquires slot synchronization using a primary synchronization channel code (PSC). In WCDMA, the same PSC is transmitted in units of 15 slots every 10 msec, and the PSCs transmitted by all base stations are the same signal. In step 1, slot synchronization is obtained by using a matched filter for the PSC.

In the second step, the long PN scrambling code group information and the 10 msec frame boundary are obtained by using the slot timing information and the secondary scrambling code (SSC) obtained in the first step.

In step 3, a long PN scrambling code ID currently used by a base station is obtained using a common pilot channel code correlator by using the 10 msec frame boundary and the long PN scrambling code group information obtained in the previous step. That is, since eight scrambling codes are mapped to one code group, in step 3, the mobile station compares the eight PN scrambling code correlator outputs and detects the long PN scrambling code ID used by the current cell.

In the WCDMA scheme, a synchronization channel basically consists of a primary synchronization channel and a secondary synchronization channel, and the primary synchronization channel and the secondary synchronization channel, the common pilot channel, and other data channels are CDMA based on time-domain direct sequence spreading. Multiplexing is done in a manner.

Currently, in 3GPP, OFDM-based wireless transmission technology specification is in full swing as part of 3G Long Term Evolution (3G-LTE) to compensate for the shortcomings of WCDMA. The synchronization channel and common pilot channel structure used in the WCDMA and the cell search method of the mobile station are suitable for DS-CDMA and cannot be applied to the OFDM forward link. Accordingly, in a cellular system using OFDM, a synchronization channel and common pilot channel structure of a forward link, an initial cell search method of a mobile station, and a neighbor cell search method for handover are required.

An object of the present invention is to provide a cell search apparatus and method including neighbor cell search for initial cell search and handover in an OFDM cellular system.

Another object of the present invention is to provide an apparatus and method for transmitting a forward link frame for supporting the aforementioned cell search method.

Another object of the present invention is to provide an OFDM cellular system to which the aforementioned cell search method is applied.

Another object of the present invention is to provide a computer-readable recording medium containing a program for performing the cell search method described above.

Another object of the present invention is to provide a structure of a forward link frame used in the above-described cell search method.

In order to solve the above technical problem, the cell search method proposed by the present invention is a cell search method using a forward synchronization signal in a wireless communication system, the method comprising: (a) using a first synchronization channel symbol included in a frame received by a terminal; Obtaining a sync block sync and a primary sync channel sequence number; (b) detecting a boundary and a scrambling code group of the frame by using the sync block sync and a secondary sync channel symbol included in a frame received by the terminal; (C) acquiring a scrambling code using the primary sync channel sequence number and the scrambling code group, and (d) demodulating a BCH included in a frame received by the terminal using the scrambling code. And acquiring wireless communication system information.

In addition, the step (b) is characterized by detecting the number of BCH antennas or the CP length of the frame.

In addition, if a CRC error occurs as a result of demodulating the BCH included in the frame using the scrambling code, the process is performed again from the step (a), and the cell search is terminated when the CRC error does not occur. .

In addition, the CP length having the maximum value among the correlation values obtained by performing each correlation according to two possible second synchronization channel positions of a short CP and a long CP may be detected.

In addition, the step (c) is characterized in that the scrambling code belonging to the scrambling code group is characterized in that the scrambling code having the maximum value of the correlation value obtained by performing a correlation to the pilot channel of the frame, characterized in that.

In order to solve the above technical problem, the cell search method proposed by the present invention is a cell search method using a forward synchronization signal in a wireless communication system, the method comprising: (a) using a first synchronization channel symbol included in a frame received by a terminal; Obtaining sync block synchronization, (b) detecting a boundary of the frame, a BCH TTI boundary, and a scrambling code group by using the sync block synchronization and a secondary sync channel symbol included in a frame received by the terminal; (c) demodulating the BCH included in the frame through channel estimation of the secondary synchronization channel based on the frame boundary and the BCH TTI boundary to obtain a scrambling code and wireless communication system information. do.

In addition, the BCH included in the frame is characterized in that it comprises wireless communication system information including the scrambling code of the target cell with which the terminal communicates, timing information of the wireless communication system, bandwidth and the number of transmit antennas.

In order to solve the above technical problem, the frame transmission method proposed by the present invention is a method for transmitting a frame by a base station belonging to an arbitrary cell through a forward synchronization signal in a wireless communication system, including (a) sync block synchronization of a frame A primary sync channel sequence, a secondary sync channel sequence including a boundary of the frame and a group of scrambling codes of the cell, and a scrambling code and wireless communication system information of the cell and modulated by the secondary sync channel sequence Generating a broadcast channel (BCH), and (b) generating and transmitting a frame including the BCH and each sync channel symbol coded on a frequency using each of the generated sync channel sequences. It is characterized by.

In addition, the first sync channel symbol and the second sync channel symbol are configured on a TDM basis, and generate and transmit a frame to be immediately adjacent to each other.

The sync channel symbol and the BCH are present in the same subframe within the frame, and the BCH is coherent demodulated by channel estimation using the secondary sync channel symbol.

The BCH included in the frame includes timing information, bandwidth, and number of transmit antennas of the wireless communication system, and is demodulated using the frame boundary, the number of transmit antennas, and the scrambling code.

As described above, the present invention can reduce a cell search time of a mobile station in an OFDM cellular system, and can implement a cell search method that operates with low complexity.

In addition, synchronization acquisition is possible with low complexity by the synchronization signal transmission method of the present invention.

In addition, since the TTI boundary of the BCH can be obtained by using the synchronization channel before demodulating the BCH, there is no need to perform blind detection by time ambiguity during BCH decoding, thereby simplifying the receiver structure.

Hereinafter, a method and an apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

Each base station of an OFDM cellular system generally scrambles an OFDM symbol using a long pseudo noise scrambling code, but may use a different kind of scrambling code in addition to the long pseudo noise scrambling code. In the following description, it is called a scrambling code.

A base station according to an embodiment of the present invention includes a method including a plurality of transmission antennas, a time switching diversity (TSTD), a precoding vector switching transmission diversity, or a frequency switching transmission diversity (FSTD). The transmission diversity may be performed by a method, and in the drawings of the present specification, a base station having two transmission antennas is described for convenience.

In addition, the mobile station according to an embodiment of the present invention may perform reception diversity by a method including a plurality of reception antennas, and in the drawings of the present specification, a mobile station having two reception antennas is described for convenience. . In the case of a mobile station having such a structure, data of each data path according to reception diversity should be combined. In the present specification, a simple summation is used in the present specification, but the present invention is not limited thereto. It is obvious to those who do it.

The present invention relates to a method for cell searching including synchronization acquisition, frame boundary detection, and cell identifier detection (also called scrambling code detection) in an OFDM cellular system.

The term “sink block detection” is used herein to mean the detection of the sync block boundary 141, and the meaning of the detection of the sync block is the OFDM symbol synchronization, the position of the primary sync channel in the sync block, and the second sync channel. This means that the location is also detected.

Also, “frame boundary detection” will be used herein to refer to detecting timing 140 of a frame boundary, and “frame boundary information” will be used herein as a term encompassing information about the timing of the frame boundary. .

In addition, " BCH ( Broadcasting CHannel ) TTI () Boundary Detection "is a term used to mean boundary detection of a channel coding block of a BCH, and the TTI length of a BCH may be an integer multiple of the frame length, and typically two 10 msec frames (that is, 20 msec) or four frames (ie 40 msec).

"Scrambling code detection" will be used herein as a term encompassing scrambling code identifier detection and scrambling code detection, and "scrambling code information" will be used herein as a term encompassing scrambling code identifiers and scrambling code.

In an OFDM-based LTE system, one base station (Node-B) is composed of several sector cells, and the base station is divided into different random sequences, and the sector division in the base station is divided into different orthogonal codes. Thus, each cell of the system is divided by a composite code sequence generated by multiplying the random sequence by an orthogonal code. In the present invention, the synthesized code is referred to as a cell-specific "scrambling code".

The "scrambling code group" refers to the group of scrambling codes used in the system. For example, if there are 513 scrambling codes used in the system, they are divided into 171 groups so that three scrambling codes belong to each group.

In the present invention, "secondary sync channel sequence" means a set of secondary sync channel "chips" mapped to a subcarrier occupied by a second sync channel symbol in a frequency domain.

In the present invention, the "primary sync channel sequence" means a set of primary sync channel "chips" mapped to a subcarrier occupied by a primary sync channel symbol in a frequency domain.

In this specification, for convenience, the term Fourier Transform is used as a term encompassing a Discrete Fourier Transform and a Fast Fourier Transform. In the present invention, "secondary sync channel sequence" means a set of secondary sync channel "chips" mapped to a subcarrier occupied by a second sync channel symbol in a frequency domain.

In the present invention, the "primary sync channel sequence" means a set of primary sync channel "chips" mapped to a subcarrier occupied by a primary sync channel symbol in a frequency domain.

In this specification, for convenience, the term Fourier Transform is used as a term encompassing a Discrete Fourier Transform and a Fast Fourier Transform.

1 is a view showing the structure of a forward link frame according to an embodiment of the present invention. Referring to FIG. 1, each of the forward link frames has a duration of 10 msec and consists of 20 subframes 110.

In Figure 1, the horizontal axis is the time axis and the vertical axis is the frequency (OFDM subcarrier) axis.

Each subframe is 0.5 msec long and includes seven OFDM symbols 120. In the example of FIG. 1, one primary sync channel OFDM symbol 100-A and a second sync channel OFDM symbol 101-A exist in every 10 subframes, so that there are a total of two primary syncs in one frame (10 msec). There are channel symbols and two secondary sync channel symbols.

In this case, the repetition period 130 of the synchronization channel symbol is equal to the length of 10 subframes, and the number of repetition periods of the total synchronization channel symbols in one frame is two. For convenience, the repetition period of the synchronization channel symbol is called a sync block.

That is, FIG. 1 illustrates that the number of sync blocks 130 in one frame (10 msec) is two. In this case, the length of the sync block is 5 msec. As shown in the example of FIG. 1, when the primary sync channel and the secondary sync channel are combined by the TDM scheme, the adjacent channel is directly adjacent to use the channel estimate value of the primary sync channel when coherent demodulation of the secondary sync channel occurs. It must be placed in the area.

For the remaining OFDM symbols except for the sync channel symbol portion, a cell-specific scrambling code is multiplied in the frequency domain to distinguish each cell.

2 is a diagram illustrating a subframe including a sync channel symbol according to an embodiment of the present invention. An example is subframe 0 of the first sync block of FIG. 1.

In addition, in the example of FIG. 2, an example in which the BCH exists in the same subframe as the synchronization channel is given. As mentioned above, the TTI length of the BCH may be an integer multiple of the frame, that is, 20 msec or 40 msec.

According to the subframe shown in FIG. 2, the traffic data subcarrier 170, the primary sync channel subcarrier 180, and the null carrier 190 are included in the OFDM symbol period 100 -A in which the primary sync channel symbol is transmitted. The OFDM symbol interval 101 -A through which the secondary synchronization channel symbol is transmitted includes a traffic data subcarrier 170 and a secondary synchronization channel subcarrier 181.

The other OFDM symbol 115 includes a traffic data subcarrier 170, a pilot subcarrier 191, and the like.

As described above, the last two OFDM symbols in a subframe are secondary sync channel and primary sync channel symbols, respectively. In addition, the BCH 192 may be inserted and transmitted in a subframe including a synchronization channel.

The BCH is a channel for transmitting system information necessary for the mobile station, such as system timing information, bandwidth used by the system, and information on the number of base station transmit antennas, to the mobile station in the cell.

As a method of allocating a sync channel occupying band, the sync channel may occupy the remaining bands except the guard band, but only a part of the remaining bands may occupy the sync channel.

An example of a system to which the latter method can be applied is a system that must support scalable bandwidth, such as a 3G-LTE system.

That is, in order for all mobile stations using only 1.25 MHz, mobile stations using 2.5 MHz, and all mobile stations using 5 MHz, 10 MHz, 15 MHz, 20 MHz, etc. to acquire synchronization of the base station system, as shown in FIG. Each channel symbol occupies only a portion of the total system bandwidth 160. For example, when the system bandwidth is 10 MHz, only 1.25 MHz in the center of the circuit except for the DC subcarrier is used.

Meanwhile, as will be described later, the cell searcher of the mobile station can improve cell search performance by performing filtering to pass only the sync channel occupation band 150.

Referring to FIG. 2, the primary sync channel and the secondary sync channel occupy only a part of the band 150 of the entire band 160 as described above. As illustrated in FIG. 2, the primary synchronization channel may use only one of two adjacent subcarriers and not use the other one.

In addition, one method may use all subcarriers in the sync channel occupation band except the guard band. As an example of subcarrier allocation of a primary sync channel symbol, the present invention describes a method of using only one of two adjacent carriers and not using one as an example. In this case, a predetermined number of values are assigned to the unused subcarriers. An example of the number is '0'. This is called a null symbol.

In particular, when using the latter method, a time domain signal of a synchronous channel symbol except for a cyclic prefix (hereinafter, referred to as a "synchronous channel symbol signal") is repeated in the time domain as shown in FIG. 3. Has

3 is a conceptual diagram of a first synchronization channel symbol signal in a time domain according to an embodiment of the present invention.

4 is a diagram illustrating a symbol-mapped form of a sync channel sequence according to an embodiment of the present invention.

Referring to FIG. 3, N _T represents the number of samples of the entire OFDM symbol interval, N _CP represents the number of samples of the cyclic prefix interval 200, and N _S represents the number of samples of the symbol interval 210 excluding the cyclic prefix interval. .

3, the differential correlator may be used in the first cell search.

For 3G-LTE, two kinds of cyclic prefix (CP) lengths are defined. That is, Long CP and Short CP.

Long CP is mainly used for MBMS (Multicase and Broadcast Multi-meadia Service) and Short CP is mainly used for unicast service. In case of using Long CP, the number of OFDM symbols per subframe is 6 and in case of Short CP, the number of OFDM symbols per subframe is 7

In this case, the symbol period 210 of the secondary synchronization channel in the subframe is different when using the Long CP and when using the Short CP. As a result, Hypothesis test should be performed on two possible positions in the cell search step 2.

In addition, since the symbol interval of the BCH may be different for the above two cases, it is necessary to estimate the exact location of the BCH using CP length information obtained in the cell search step and use it for BCH demodulation.

On the other hand, in the secondary sync channel, all subcarriers except the DC carrier can be used in the sync channel occupied band except the guard band. For example, in 3G-LTE, the sync channel occupied band is defined as 1.25 MHz, and the total number of subcarriers in the band is 128, and 72 subcarriers except the dual guard band and the DC subcarrier are subcarriers allocated to the secondary sync channel. Can be used.

Meanwhile, in the forward link frame according to an embodiment of the present invention, the primary sync channel sequence and the secondary sync channel sequence allocated to the base station are respectively represented by the primary sync channel sync channel symbol and the secondary sync channel symbol. To a subcarrier of. A component mapped to each of the synchronization channel subcarriers is defined as a "chip."

The length of the sequence of the primary synchronization channel is the same as the number of subcarriers allocated to one primary synchronization channel symbol (36 in the example of FIG. 4), and is repeated every primary synchronization channel symbol interval. The length of the sync channel sequence is equal to the total number of frequency domain subcarriers allocated to the secondary sync channel symbols allocated within the TTI length of the BCH (288 if the TTI of the BCH is 20 msec, as in the example of FIG. 4). It is characterized by. As a result, the period of the primary sync channel sequence becomes the sync block 130 and the period of the secondary sync channel sequence becomes the BCH TTI length.

That is, the primary sync channel sequence transmitted by any cell for every primary sync channel symbol can be expressed by Equation 1 below.

In Equation 1, each element of the primary sync channel sequence is defined as a "chip" of the primary sync channel sequence. In the above equation, N ₁ is the number of subcarriers (36 in the example of FIG. 4) assigned to the primary sync channel symbol in one primary sync channel symbol.

In the primary sync channel, the same primary sync channel sequence is transmitted in every symbol.

The reason for this is that the first sync channel sequence uses the same sequence for every primary sync channel symbol, so that when a receiver uses a correlator using the time domain waveform of the first sync channel sequence in the first step of cell search, a correlator is used. This is to allow sync block boundary to be obtained.

In addition, all cells used in the system are based on using one same sync channel sequence as the primary sync channel sequence, but in some cases, a small number (eg, 8 or less) may be used.

In the present invention, a case where the number of primary sync channel sequences used in the system is one will be described as an example.

Any code sequence having good correlation characteristics may be used as the primary sync channel sequence, but a generalized chirp like (GCL) sequence may be used as an example.

Meanwhile, the secondary synchronization channel sequence corresponds one-to-one with the scrambling code group.

The secondary sync channel sequence has a one-to-one correspondence with the scrambling code group and also provides the mobile station with information about the frame boundary and BCH TTI boundary information. That is, the mobile station that acquires the sync block boundary 141 using the primary synchronization channel detects the cell identifier using the secondary synchronization channel and simultaneously detects the frame boundary 140 and the TTI boundary of the BCH. (The CP length can also be detected at this time.) To do this, the length of the secondary sync channel sequence is equal to the total number of subcarriers (288 in FIG. 4) allocated to secondary sync channel symbols in the BCH TTI.

As a result, the secondary sync channel sequence is represented by Equation 2 below.

는 시퀀스 번호가 k(또는 해당 셀의 스크램블링 코드 그룹 번호가 k)인 2차 동기채널 시퀀스의 n 번째 칩이다.In other words,

Is the nth chip of the secondary sync channel sequence whose sequence number is k (or the scrambling code group number of the cell).

In Equation 1, P is the number of secondary synchronization channel symbols in the BCH TTI (4 in the example of FIG. 4), and N ₂ is the DC subcarrier and guard band in the secondary synchronization channel symbols 101 -A and 101 -B. The number of subcarriers allocated to the secondary synchronization channel except for the subcarriers for FIG. 4 is 72 in the example of FIG. 4. As a result, the length of the secondary synchronization channel sequence becomes PxN ₂ .

The secondary sync channel sequence is characterized in that the same sequence is transmitted every frame for a signal transmitted by a base station apparatus of one cell, and different sync channel sequences are used for each cell.

That is, a cell of the present invention is assigned a secondary sync channel sequence mapped to a cell-specific cell identifier group, and each chip of the allocated sync channel sequence is loaded on each subcarrier belonging to a sync channel occupation band. .

로 표현되고, 두 번째 2차 동기채널 심볼(101-B)에 대한 부분 시퀀스는

로 표현되며 세 번째 2차 동기채널 심볼(101-C)에 대한 부분 시퀀스는

되고 네 번째 2차 동기채널 심볼(101-D)은

이들 부분 시퀀스는 서로 다름을 특징으로 한다.For each secondary sync channel symbol subsequence of the secondary sync channel sequence, that is, for example, in FIG. 4, the partial sequence for the first secondary sync channel symbol 101 -A in the BCH TTI length 280 is

And the partial sequence for the second secondary sync channel symbol 101-B is

And the partial sequence for the third secondary sync channel symbol 101-C is

And the fourth secondary sync channel symbol 101-D

These partial sequences are characterized by differences.

Therefore, even if the mobile station uses only one secondary sync channel symbol among P secondary sync channels in a frame, the scrambling code group identifier, frame border, and BCH TTI boundary can be detected in the cell search step 2.

There may be a number of methods for creating a partial sequence of the secondary sync channel sequence. For example, a sequence having a length of N ₂ may be multiplied by a modulation symbol value corresponding to P sync slot numbers in a BCH TTI.

라고 했을 때, 도 4와 같에 P가 4일 때 총 4개의 싱크 블록 중 첫 번째 싱크 블록에 있는 2차 동기채널에 대응되는 부분 시퀀스

는

가 되고 두 번째 싱크 블록에 대응되 는 부분 시퀀스

는

가 되며 세 번째 싱크 블록에 대응되는 부분 시퀀스

는

가 되며 네번째 싱크 블록에 대응되는 부분 시퀀스

는

가 된다.For a forward link in a cell with a scrambling code group number of k, this sequence

In FIG. 4, when P is 4, the partial sequence corresponding to the secondary synchronization channel in the first sync block of the 4 sync blocks is shown.

Is

The subsequence corresponding to the second sync block

Is

Subsequence corresponding to the third sync block

Is

Subsequence corresponding to the fourth sync block

Is

Becomes

Where a is a modulation symbol value corresponding to the first sync block per four sync blocks in the BCH TTI, b is a second sync block, c is a third sync block, and d is a modulation symbol value corresponding to a fourth sync block. For example, assuming that QPSK modulation, a phase is 1 + j, b is 1-j, c is -1-j, and d is -1-j.

In this case, the mobile station receiver can obtain the BCH TTI boundary by coherently correlating the secondary synchronization channel through the channel estimation value using the primary synchronization channel and demodulating the modulation symbol value. You will know.

A short sequence having the sequence length N ₂ of the number of subcarriers allocated to the secondary synchronization channel symbol as described above is used as a modulation symbol value corresponding to the sync block number in the secondary synchronization channel symbol region of the BCH TTI as described above. The method of making and using a secondary sync channel sequence having a total length of P * N ₂ by mapping does not depart from the scope of the present invention.

When this case is if the 171 days the number (N _G) of the scrambling code group used by the system at the cell search stage 2 only performs correlation of the 171 secondary synchronization channel sequence. In this case, each correlation length is equal to the number N ₂ of subcarriers allocated to one secondary synchronization channel symbol. For convenience, this method is referred to as secondary synchronization channel sequence allocation method 1.

The second method of creating a partial sequence of the secondary sync channel sequence is the number of scrambling code groups N used in the system, the sequence length being the number of subcarriers N ₂ assigned to the secondary sync channel symbol as described above. The first N _G sequences are made twice as much as _G so that the first secondary sync channel symbol (101-A, 101-C) of each frame is followed by the second N _G sequence of second frame of each frame. Mapping to (101-B, 101-D), but in the BCH TTI (280), even-numbered and odd-numbered frames are distinguished by BPSK modulation of the secondary synchronization channel.

는

가 되고 뒷 부분에 해당하는 시퀀스

는

가 된다.In this case, in Equation 2, the secondary sync channel partial sequence corresponding to the first sync block of the even-numbered frame in the BCH TTI.

Is

And the sequence that comes after

Is

Becomes

는

가 되고 뒷 부분에 해당하는 시퀀스

는

가 된다.On the other hand, the second sync channel subsequence corresponding to the first sync block of the odd frame

Is

And the sequence that comes after

Is

Becomes

는 상기 N_G × 2개의 시퀀스 중 앞의 N_G 개의 시퀀스 중 스크램블링 코드 그룹 k 번에 해당하는 2차 동기채널 시퀀스이고

는 N_G × 2개의 시퀀스 중 뒤의 N_G 개의 시퀀스 중 스크램블링 코드 그룹 k 번에 해당하는 시퀀스이다.here

Is a secondary synchronization channel sequence corresponding to the scrambling code group k of the preceding N _G sequences among the N _G × 2 sequences

Is a sequence corresponding to the scrambling code group k of the next N _G sequences among the N _G × 2 sequences.

In this case, the number of correlators is doubled in the second cell search compared to the first method. For convenience, this method is called secondary sync channel sequence allocation method 2.

On the other hand, when the TTI of the BCH is 40 msec, the secondary synchronization channel sequence allocation method 2 may be slightly modified. That is, sync block 0 of each of the four frames in the BCH TTI uses the front of 2N _G sequences, and sync block 1 uses the latter of 2N _G sequences, and the BCH TTI boundary is QPSK. Can be detected using.

In other words, 1 + j is multiplied by the second frame of the first frame, 4-1 is multiplied by 1-j in the second frame, -1-j in the third frame, and -1 + j in the fourth frame. In this case, even if only one secondary synchronization channel symbol is detected in the second cell search, the mobile station can acquire not only the cell scrambling code group information and the 10 msec frame boundary but also the TTI boundary of the BCH.

Meanwhile, after cell searching, the mobile station needs to demodulate a BCH (Broadcasing Channel) to obtain system information. However, when transmit diversity is applied to the BCH to reduce the frame error rate, the MS may need to know the number of diversity antennas applied. In this case, frame boundary information and information on the number of antennas applied to the BCH may be simultaneously inserted into the secondary synchronization channel.

1 and 4, the cell searcher of the present invention syncs using a correlator using a differential correlator or a time domain waveform of a primary sync channel sequence in a first step. 10 msec frame boundary while acquiring block boundary (any one of 141-A and 141-B) and acquiring a sync channel sequence number, i. (140-A, 140-B) and BCH TTI boundaries are also acquired at the same time.

In addition, when the secondary synchronization channel includes transmit diversity antenna information applied to the BCH, the antenna information is simultaneously acquired in the cell search step 2. Coherent correlation using channel estimates using the primary synchronization channel may be performed to improve performance when performing secondary synchronization channel correlation. Details will be described later.

The number of secondary sync channel sequences used in the system is less than or equal to the number of scrambling codes used in the system. If the number of secondary synchronization channel sequences used in the system is equal to the number of scrambling codes used in the system, the secondary synchronization channel sequence number corresponds one-to-one with the scrambling code number (or cell identifier).

If the number of secondary synchronization channel sequences is smaller than the number of scrambling codes, the secondary synchronization channel sequence numbers correspond to the scrambling code group numbers. In this case, three more cell searches are required. That is, in step 2 of cell searching, only frame boundary and scrambling code group information are acquired, and in step 3, one of possible scrambling code numbers in the group must be found. Step 3 is performed using a parallel domain correlator in the frequency domain for the common pilot signal of the forward link.

5 is a block diagram showing the configuration of a base station according to an embodiment of the present invention. Referring to FIG. 5, the synchronization channel generator 500, the traffic channel and pilot generator 512, the diversity controller 513, the OFDM symbol mapping units 514-A and 514-B, and the scrambling unit 515- A, 515-B), inverse Fourier transform units 516-A, 516-B, CP inserters 517-A, 517-B, IF / RF units 518-A, 518-B, and transmit Antennas 519-A and 519-B.

The traffic channel, BCH, and pilot channel generator 512 generates traffic data 230, BCH 280, or pilot data 270 to be transmitted, as shown by reference numeral 230 of FIG. 500 generates a primary sync channel sequence and a secondary sync channel sequence as shown by reference numerals 240 and 250 of FIG. 2 or 4 or defined by Equations 1 and 2 above.

The OFDM symbol mapping units 514-A and 514-B map data values of respective channels to respective positions on the frequency / time domain as in the example of FIG. 2.

The scrambling unit 515-A or 515-B generates a unique scrambling code for each base station on the frequency domain for OFDM symbols other than sync channel symbols in the output of the OFDM symbol mapping unit 514-A or 514-B, that is, the mapping result. Multiply by

The inverse Fourier transform units 516 -A and 516 -B inverse Fourier transform the outputs of the scrambling units 515-A and 515-B to generate a time domain signal.

CP inserters 517-A and 517-B insert a cyclic prefix to the output of the inverse Fourier transforms 516-A and 516-B to enable demodulation of the OFDM signal even with a multipath delay of the channel. do.

The IF / RF units 518-A and 518-B up-convert the output signals of the CP insertion units 517-A and 517-B, which are baseband signals, to a band pass signal. Amplify the signal.

Transmission antennas 519-A and 519-B transmit the amplified signals.

In the example of FIG. 5, it can be seen that there are two transmission antennas 519 -A and 519 -B. That is, if the base station according to an embodiment of the present invention has only one transmission antenna 519-A without the transmission antenna 519-B, the OFDM symbol mapping unit 514-B and the scrambling unit 515-B ), The inverse Fourier transform unit 516-B, the CP insertion unit 517-B, the IF / RF unit 518-B, and the diversity control unit 513 may be omitted.

In FIG. 5, a synchronization channel symbol is transmitted with transmission diversity using two transmission antennas to a transmitting end of a base station system.

Transmitting diversity through the diversity control unit 513 illustrated in FIG. 5 will be described below. In order to obtain spatial diversity, sync channel symbols belonging to adjacent sync blocks are transmitted to different antennas.

For example, the two primary sync channel symbols and the second sync channel symbol in the first sync block are the first transmit antenna 519-A, the primary sync channel symbol and the second sync channel symbol in the second sync block. Transmits to the second transmit antenna 519-B.

The diversity control unit 513 performs switching for performing the above-mentioned diversity. That is, as a method of applying Time Switching Transmit Diversity (TSTD) to a synchronization channel, the diversity controller 513 switches the output of the synchronization channel generator 500 so that the OFDM symbol mapping unit 514-. A) or to the OFDM symbol mapping unit 514-B.

In addition to the above-described spatial diversity or TSTD diversity, the present invention may be applied as a precoding vector switching transmission diversity.

Precoding vector switching is a precoding vector for two transmit antennas, for example, as shown in Equation 3 below. The first sync channel symbol and the second sync channel symbol in the second sync block are transmitted using the coding vector and are transmitted in the second precoding vector.

In the above equation, the first element of the precoding vector is the weight for the first antenna and the second element is the weight for the second antenna.

When the precoding vector switching diversity is applied, the diversity controller 513 switches the precoding vector to the OFDM symbol mapping unit 514-A or the OFDM symbol mapping unit 514-B. To provide.

The precoding vector switching may be performed in units of frames. That is, the method of multiplying the same precoding vector in one frame and multiplying other precoding vectors in an adjacent frame does not depart from the scope of the present invention.

Equation (3) describes only an example of two transmitting antennas and two precoding vectors, and two transmitting antennas and two or more precoding vectors, and four transmitting antennas and two or more precoding vectors. In this case, it can also be modified.

In addition to the TSTD and precoding vector switching, frequency switching transmit diversity (FSTD) may be applied. In this case, the sequence element mapped to the even subcarrier among the subcarriers assigned to the primary sync channel symbol is transmitted as the first antenna and the sequence element mapped to the odd subcarrier is transmitted to the second antenna and similarly assigned to the secondary sync channel symbol. A sequence element mapped to an even subcarrier among subcarriers is a first antenna, and a sequence element mapped to an odd subcarrier is transmitted to a second antenna. In this case, the diversity controller also plays a role.

If the BCH and sync channel are always in the same subframe and apply the same diversity to the BCH and sync channel that are in the same subframe, for example, in subframe 0 (sink block 0) in FIG. When the first precoding vector of Equation 3 is simultaneously applied to the BCH and the synchronization channel, and the second precoding vector is simultaneously applied to the BCH and the synchronization channel in subframe 10 (sink block 1), the second synchronization channel is used. After making an estimate, it can be used for coherent demodulation of the BCH.

In this case, the mobile station can coherently demodulate the BCH without knowing the number of transmit diversity antennas applied to the BCH. In this case, it is not necessary to include antenna number information applied to the BCH in the secondary synchronization channel.

6 is a block diagram illustrating a configuration of a receiver of a mobile station according to an embodiment of the present invention. The mobile station has at least one receiving antenna, and FIG. 6 is an exemplary diagram of the case of two receiving antennas.

6, a receiver of a mobile station according to an embodiment of the present invention includes a receiving antenna 600-A, 600-B, a down converter 610-A, 610-B, and a cell searching unit. 620, a data channel demodulator 630, a controller 640, and a clock generator 650.

Frames in the form of RF signals transmitted from each base station are received through the receiving antennas 600-A and 600-B, and then the baseband signals S1 and S2 through the down-converters 610-A and 610-B. Is converted to).

The cell search unit 620 searches for a target cell by using the synchronization channel symbols included in the down-converted signals S1 and S2. Examples of cell search results include detecting sync channel symbol timing, frame boundaries, and cell identifiers of a target cell. Examples of searching for a target cell include a case where a mobile station initially searches for an initial cell, or a handover. For example, searching adjacent cells.

The controller 640 controls the cell search unit 620 and the data channel demodulator 630.

That is, the controller 640 controls the timing, inverse scrambling, and the like of the data channel demodulator 630 based on the cell search result obtained by controlling the cell searcher 620.

The data channel demodulator 630 demodulates the traffic channel data as shown by reference numeral 230 of FIG. 2 included in the down-converted signal under the control of the controller 640. Meanwhile, all hardware of the mobile station is operated in synchronization with the clock generated by the clock generator 650.

Referring to FIG. 6, the cell searcher 620 is divided into sync channel band filters 621 -A and 621 -B, a sync block sync detector 622, and a group / boundary detector 623.

The sync channel band filters 621 -A and 621 -B pass only the sync channel occupied band 210 of the entire OFDM signal band 220 as described with reference to FIG. 2 with respect to the down-converted signals S1 and S2. Band pass filtering is performed.

The sync block sync detector 622 obtains the sync block timing S5 using the primary sync channel symbols included in the filtered signals S3 and S4.

The group / boundary detection unit 623 uses the obtained sync block timing information S5, and the scrambling code group S6 and 10 msec frame timing information S7, BCH TTI boundary information S8, and CP from the received signal. Length information and, if necessary, information on the number of diversity transmit antennas applied to the BCH is detected.

 Meanwhile, the group / boundary detector 623 may increase the detection performance by performing frequency offset estimation and compensation before detecting the cell identifier and the frame timing.

The code detector 624 uses the scrambling codes belonging to the scrambling code group S6 for the received signal by using the scrambling code group S6, the frame boundary S7, and the CP length information acquired by the group / boundary detector. The correlation is performed on the pilot channel 270 to detect the scrambling code number (ie, cell identifier) by taking the maximum value.

The BCH demodulator 625 demodulates the BCH using at least the BCH TTI boundary S8 to obtain system information and passes it to the controller 640. In this case, channel estimation for coherent demodulation of the BCH may use a pilot symbol 270 or a second synchronization channel.

On the other hand, when the same diversity is applied to the BCH and the synchronization channel, coherent demodulation of the BCH is possible using the secondary synchronization channel, so that the code detector may be omitted and the BCH may be directly demodulated. Since the BCH information includes cell identifier information (ie, scrambling code information used by the cell), the code detector 624 may be omitted.

7 is a block diagram illustrating a configuration of the sync block synchronization detector of FIG. 6 according to an exemplary embodiment of the present invention. Referring to FIG. 7, the sync block synchronization detector 622 includes correlators 621 -A and 621 -B, 701 -A and 701-B, a signal combiner 702, an accumulator 703, and a timing detector. 710.

In the example of FIG. 7, assuming that the sync channel symbols use even or odd carriers among the carriers belonging to the sync channel occupancy band, the differential correlator uses the repeating pattern of FIG. 3 in the time domain. The mobile station receiver may store the time domain waveform of the first synchronization channel sequence represented by Equation 1 in advance and perform a correlation in the time domain.

The outputs of the correlators 701 -A and 701-B are accumulated in the accumulator 703 via the signal combiner 702.

Referring to the example of the frame structure of FIG. 1, 9600 outputs of the correlators 701 -A and 701-B are generated per sync block length, and the timing determiner 710 determines a peak value among these correlation values. The position of the sample generating the peak value) is detected, and the detected sample position is determined as the first synchronization channel symbol timing.

However, the sync block sync detector 622 according to an embodiment of the present invention may further include an accumulator 703 as shown in FIG. 7 to increase symbol sync detection performance.

The accumulator 703 adds each correlation value for each of 9600 sample positions and adds each correlation value for samples spaced apart by each sync block length from each sample position.

When the sync block sync detector 622 includes an accumulator 703, the timing determiner 710 detects a maximum value of 9600 values stored in the accumulator 703 to detect a sample position of the detected maximum value. It outputs as timing information S5.

8 is a graph showing correlation values calculated for each sample position by the correlator of FIG. 7 according to an exemplary embodiment of the present invention.

It shows a case where the channel between the base station transmitter and the mobile station receiver assumes a channel environment as long as there is no fading and noise.

The horizontal axis represents the time axis or the sample index, and the vertical axis represents the correlation value at each position of the horizontal axis.

Reference numeral 800 indicates the position of the first sample for which the correlator performs correlation.

The correlators 701-A and 701-B obtain a correlation value from the position of the first sample, calculate the final 9600 correlation values, and provide them to the accumulator 703. The process of calculating 9600 correlation values again and providing them to the accumulation unit 703 from the next position of the sample from which the correlation was last calculated before is repeated.

Among each M samples, as a result of the repetition pattern of the sync channel symbol, there is a point where a peak occurs as shown in FIG. 8.

FIG. 9 illustrates a structure of an input signal provided to the group / boundary / antenna number detector of FIG. 6 based on the sync block timing obtained by the sync block synchronization detector of FIG. 6 according to an exemplary embodiment of the present invention. .

Based on the timing 900 obtained by the sync block synchronization detector 622, the cyclic prefix of the region corresponding to the primary sync channel symbol and the region corresponding to the secondary sync channel symbol is removed, and every sync block. Sample values corresponding to the estimated primary sync channel position and secondary sync channel are input to the group / boundary detector 623.

At this time, since the mobile station does not know the CP length in the initial synchronous acquisition mode, sample values for both possible cases, that is, the case of Long CP and the case of Short CP, must enter the group / boundary detector.

On the other hand, reference numerals 910-A and 910-B indicate the positions of the primary synchronization channel symbols obtained at the obtained timing 900 and 920-A and 920-B denote secondary synchronization channel symbols obtained at the obtained timing 900. Indicates the position of.

The sample values of the primary sync channel are used for coherent correlation of the secondary sync channel. This will be described later.

FIG. 10 is a block diagram illustrating a configuration of the group / boundary detection unit of FIG. 7 according to an exemplary embodiment of the present invention. Referring to FIG. 10, a frequency offset correction unit 1000 and a boundary / group / CP length detector 1010 are included.

The frequency offset corrector 1000 sets the sync channel symbol timing 900 based on the output S5 of the sync block sync detector 622, and based on the sync channel symbol timing 900, each sync block The received signal samples 910-A and 910-B of 2 × N _S primary sync channel estimation positions provided from the respective sync channel band filters 621 -A and 621 -B are stored over the length section. After that, the frequency offset is first estimated using the frequency offset, and the frequency of the 4 × N _S received signal samples 910 -A, 920-A, 910-B, and 920-B is based on the estimated frequency offset. After the offset is corrected, the corrected 4 × N _S received signal samples are provided to the boundary / group / CP length detector 1010.

The boundary / group / CP length detector 1010 detects a scrambling code group identifier, 10 msec frame timing, BCH TTI boundary and CP length information by using the frequency offset corrected samples S10 and S11, and then passes them to a control block. give.

Ns received sample values for each of the sync channel symbol positions 910-A, 920-A, 910-B, and 920-B are Fourier-transformed into signals in the frequency domain, and then correlated with all possible secondary sync channel sequences. And demodulate the modulation symbols included in the secondary synchronization channel to simultaneously acquire not only the scrambling code group of the target cell but also frame timing, BCH TTI boundary, CP length, and BCH antenna number information if necessary.

In this case, the primary sync channel components 910 -A and 910 -B are used as channel estimation for coherent correlation of the secondary sync channel sequence.

FIG. 11 is a block diagram illustrating a specific configuration of the boundary / group / CP length detection unit of FIG. 10 according to an exemplary embodiment of the present invention. Referring to FIG. 11, a code correlation diagram calculating unit 1100 -A and 1100 -B, a combiner 1110, a code group detector 1120, a boundary detector 1130, and a CP length detector 1140 It is made, including.

The code correlation diagram calculation units 1100 -A and 1100 -B perform Fourier transform on each of the synchronization channel symbols S10 and S11 that have been frequency offset corrected by the frequency offset correction unit 1000, and then convert them into signals in the frequency domain. for the secondary synchronization channel sequence (number of secondary synchronization channel sequence used in the system N _G or _G 2N) are all calculated correlation.

In this case, the primary sync channel components 910 -A and 910 -B are used as channel estimation for coherent correlation of the secondary sync channel sequence.

The combiner 1110 combines the outputs of the code correlation diagram calculators 1100 -A and 1100 -B and provides them to the code group detector 1120, the boundary detector 1130, and the CP length detector 1140.

The code group detector 1120 detects a code group corresponding to a second synchronization channel sequence having a maximum size in the code correlation output.

The boundary detector 1130 detects a frame boundary and the BCH TTI boundary by using a value corresponding to a correlation having a maximum size in the code correlation output. In more detail, that is, when the TTI length of the BCH is 20 msec and the secondary synchronization channel sequence allocation method 1 of the present invention is used at the transmitter, the TTI boundary of the BCH by demodulating the modulation symbols of the QPSK modulated secondary synchronization channel. At the same time, a 10 msec frame boundary can be obtained.

When the second synchronization channel sequence allocation method 2 of the present invention is used at the transmitting end, the boundary detection unit 1130 determines that the number of secondary synchronization channel sequences corresponding to the maximum value of the code correlation output is the first of 2N _G in total. If one of the N _G signals is obtained, the acquired sync channel symbol is considered to be located in the first sync block in the frame, and if one of the following N _G signals is obtained, the acquired sync channel symbol is located in the second sync block in the frame. After acquiring the frame boundary, demodulating the modulation symbols of the secondary synchronization channel, and obtaining the BCH TTI boundary.

The CP length detector 1140 detects the CP length by using a value corresponding to a correlation having a maximum value in the code correlation output according to two possible secondary sync channel positions of Short CP and Long CP. If the CP length of the subframe in which the synchronization channel is present is fixed in the system, the CP length detector may not be driven.

Referring to FIG. 11, the code correlation diagram calculating units 1100-A and 1100-B may include Fourier transform units 1101-A and 1101-B, demapping units 1102-A and 1102-B, and channel weights. And a code correlation unit 1104 -A and 1104 -B.

Fourier transformers 1101-A and 1101-B perform Fourier transform on time-domain samples 910-A, 920-A, 910-B, and 920-B corresponding to respective sync channel symbol regions. The N _S frequency-domain transformed values are obtained with respect to the symbol of N, and the demapping units 1102-A and 1102-B are N ₁ corresponding to the subcarriers of the primary sync channel sequence among the obtained total frequency transformed values. 4 values (see FIG. 4) and N ₂ values (see FIG. 4) for the subcarriers of the secondary synchronization channel sequence.

Channel estimation unit (1103-A, 1103-B ) is the de-mapping section (1102-A, 1102-B ) represented by the equation 1 N ₁ of the primary synchronization channel frequencies stored in advance from a domain received sample value received from the first Channel estimation is performed for each subcarrier using a differential sync channel sequence.

The secondary synchronization channel code correlation unit (1104-A, 1104-B ) is the de-mapping for N ₂ of the secondary synchronization received from the sub-channel frequency domain received sample value and the possible N _G dog or 2N _G of the secondary synchronization channel sequence and a Perform cross-correlation.

In this case, cross-correlation is performed by correcting channel distortion for each subcarrier by using channel estimation values passed from the channel estimators 1103-A and 1103-B.

12 is a flowchart illustrating a cell searching process of a mobile station according to an embodiment of the present invention.

As mentioned above, step 1 (S1200) is a sync block synchronization acquisition step, and step 2 (S1210) is a step of detecting a frame boundary and scrambling code group including frequency offset correction and the number of BCH antennas or pilot hopping, and step 3 ( S1220 is a step of detecting an intra-group scrambling code based on the information obtained in step 2 and uses a pilot symbol 191.

Step 4240 is a step of coherent demodulation of the BCH using the scrambling code obtained in step 3. Secondary synchronization channels may be used for channel estimation for coherent demodulation of BCH.

In the last step, if a CRC error occurs during BCH decoding, the process returns to step 1 and if the CRC error does not occur, the cell search is completed. In step 2 of FIG. 12, the CP length detection and the number of antennas applied to the BCH may be further included.

13 is a flowchart illustrating a cell searching process of a mobile station according to another exemplary embodiment of the present invention.

Step 1 (S1300) is a sync block synchronization acquisition step, and step 2 (S1310) is a step for detecting a frame boundary including a frequency offset correction, a BCH TTI boundary, and a scrambling code group, and step 3 is based on the information obtained in step 2 Coherent demodulation is performed on the basis of channel estimation of the secondary synchronization channel. In this case, since cell identifier information (or scrambling code information) is included in the BCH data, it is not necessary to perform pilot correlation.

In the final step, if a BCH CRC error occurs, the process returns to step 1, and if no CRC error occurs, the cell search is completed.

The invention can also be embodied as computer readable code on a computer readable recording medium. Computer-readable recording media include all kinds of recording devices that store data that can be read by a computer system. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disks, optical data storage devices, and the like, which are also implemented in the form of carrier waves (for example, transmission over the Internet). Include. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. In addition, functional programs, codes, and code segments for implementing the present invention can be easily inferred by programmers in the art to which the present invention belongs.

As described above, optimal embodiments have been disclosed in the drawings and the specification. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not intended to limit the scope of the present invention as defined in the claims or the claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a view showing the structure of a forward link frame according to an embodiment of the present invention.

2 is a diagram illustrating a subframe including a sync channel symbol according to an embodiment of the present invention.

3 is a conceptual diagram of a first synchronization channel symbol signal in a time domain according to an embodiment of the present invention.

4 is a diagram illustrating a symbol-mapped form of a sync channel sequence according to an embodiment of the present invention.

5 is a block diagram showing the configuration of a base station according to an embodiment of the present invention.

6 is a block diagram showing the configuration of a receiver of a mobile station according to an embodiment of the present invention.

7 is a block diagram illustrating a configuration of the sync block synchronization detector of FIG. 6 according to an exemplary embodiment of the present invention.

8 is a graph showing correlation values calculated for each sample position by the correlator of FIG. 7 according to an exemplary embodiment of the present invention.

FIG. 9 illustrates a structure of an input signal provided to the group / boundary detection unit of FIG. 6 based on the sync block timing obtained by the sync block synchronization detector of FIG. 6 according to an exemplary embodiment of the present invention.

FIG. 10 is a block diagram illustrating a configuration of the group / boundary detection unit of FIG. 7 according to an exemplary embodiment of the present invention.

FIG. 11 is a block diagram illustrating a configuration of a group / boundary detection unit of FIG. 10 according to an exemplary embodiment of the present invention.

12 is a flowchart illustrating a cell searching process of a mobile station according to an embodiment of the present invention.

13 is a flowchart illustrating a cell searching process of a mobile station according to another exemplary embodiment of the present invention.

Claims (11)

A cell search method using a forward synchronization signal in a wireless communication system, (a) acquiring sync block synchronization and primary synchronization channel sequence numbers using primary synchronization channel symbols included in a frame received by the terminal; (b) detecting a boundary and a scrambling code group of the frame by using the sync block synchronization and the secondary synchronization channel symbol included in the frame received by the terminal; (c) acquiring a scrambling code using the primary sync channel sequence number and the scrambling code group; And and (d) demodulating the BCH included in the frame received by the terminal using the scrambling code to obtain wireless communication system information. The method of claim 1, The step (b) is a cell search method for a wireless communication system, characterized in that for detecting the number of BCH antennas or the CP length of the frame. The method of claim 2, When a CRC error occurs as a result of demodulating the BCH included in the frame using the scrambling code, the process is performed again from the step (a), and the cell search is terminated when the CRC error does not occur. Cell discovery method in the system. The method of claim 2, A wireless communication system characterized by detecting a CP length having a maximum value among correlation values obtained by performing respective correlations according to two possible second synchronization channel positions of a short CP and a long CP. How to search for cells in. The method of claim 1, wherein step (c) And a scrambling code having a maximum value among correlation values obtained by performing correlation on a pilot channel of the frame with the scrambling codes belonging to the scrambling code group. A cell search method using a forward synchronization signal in a wireless communication system, (a) acquiring sync block synchronization using a primary sync channel symbol included in a frame received by the terminal; (b) detecting a boundary of the frame, a BCH TTI boundary, and a scrambling code group by using the sync block synchronization and a secondary synchronization channel symbol included in a frame received by the terminal; And (c) demodulating the BCH included in the frame through channel estimation of the secondary synchronization channel based on the frame boundary and the BCH TTI boundary to obtain a scrambling code and wireless communication system information; A cell search method in a wireless communication system. The method of claim 6, The BCH included in the frame includes a scrambling code of a target cell with which the terminal communicates, timing information of a wireless communication system, wireless communication system information including bandwidth and the number of transmit antennas. Navigation method. A method for transmitting a frame by a base station belonging to an arbitrary cell through a forward synchronization signal in a wireless communication system, (a) a primary synchronization channel sequence including sync block synchronization of a frame, a secondary synchronization channel sequence including a frame boundary and a scrambling code group of the cell; Generating a broadcasting channel (BCH) including a scrambling code of the cell and wireless communication system information and modulated by the secondary synchronization channel sequence; And (b) generating and transmitting a frame including each sync channel symbol code-bound on the frequency and the BCH using each of the generated sync channel sequences; and a frame in a wireless communication system, comprising: Transmission method. The method of claim 8, The primary sync channel symbol and the secondary sync channel symbol are configured on a TDM basis and generate and transmit a frame to be immediately adjacent to each other. The method of claim 8, The sync channel symbol and the BCH are present in the same subframe in the frame, and the BCH is coherent demodulated by channel estimation using the secondary sync channel symbol. . The method of claim 8, The BCH included in the frame includes timing information, a bandwidth, and a number of transmit antennas of a wireless communication system, and is demodulated using the frame boundary, the number of transmit antennas, and a scrambling code.

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