KR20070099483A - Tdm based cell search method in ofdm cellular system, frame transmission method thereof and system thereof - Google Patents

Abstract

A cell searching method in an OFDM(Orthogonal Frequency Division Multiplexing) cellular system, a frame transmitting method, and a frame transmitter are provided to reduce a cell searching time in a mobile terminal by simplifying a cell searching device. A forward link frame has duration of 10ms and includes 20 sub-frames(110). Each of the sub-frames has a duration of 0.5ms and includes 7 OFDM symbols(120). A primary synchronous channel OFDM symbol(100-A) and a secondary synchronous channel OFDM symbol(101-A) are included in every ten sub-frames. Two first and second synchronous channel OFDM symbols are included in one frame. A repetition period(130) of the synchronous channel symbols is equal to a sum of lengths of ten sub-frames. When first and second synchronous channels are coupled with each other according to a TDM(Time Division Multiplexing) scheme, the first and second synchronous channels are arranged to be adjacent to each other, such that a channel estimation value of the first synchronous channel is used, while the second synchronous channel is coherently demodulated.

Description

TDM based cell search method in OFDM cellular system, frame transmission method, and apparatus for an ODF M cellular system having a primary synchronization channel and a secondary synchronization channel composed of TMDs }

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 a synchronization detector of FIG. 6 according to an exemplary embodiment of the present invention.

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

FIG. 9 is a diagram illustrating the structure of input signals S3 and S4 provided to the cell detector of FIG. 6 based on the sync block timing obtained by the sync detector of FIG. 6 according to an exemplary embodiment of the present invention.

10 is a block diagram illustrating a configuration of a cell detector of FIG. 7 according to an exemplary embodiment of the present invention.

FIG. 11 is a block diagram illustrating a configuration of a boundary and a cell identifier detector of FIG. 10 according to an exemplary embodiment of the present invention.

12 is a conceptual diagram of performing correlation with all possible cyclic shift sequences of a secondary sync channel to obtain a frame boundary and a cell identifier according to an embodiment of the present invention.

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

14 is a flowchart illustrating a neighbor cell search process when a home cell and a neighbor cell operate in synchronization with a base station according to an embodiment of the present invention.

15 is a flowchart illustrating a process of searching for neighbor cells by determining whether a home cell and a neighbor cell operate in synchronization with a base station according to an exemplary embodiment of the present invention.

The present invention relates to a cell search method and a frame transmission method therefor in an OFDM cellular system, and more particularly, to a method for searching an initial cell and a neighbor cell in an OFDM cellular system, and a mobile station, a base station, a system, and a frame structure using the same. It is about.

The 3rd Generation Partnership Project (3GPP) Wideband Code Division Multiple Access (WCDMA) scheme uses a total of 512 long PN scrambling codes in the system to distinguish the base stations of the forward link. The scrambling code is used as the scrambling code of the 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 the mobile station acquires slot synchronization by 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 structure of a forward link frame used in the above-described cell search method.

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.

In order to solve the above technical problem, a cell search method in an OFDM cellular system according to the present invention is performed by an eNB in an OFDM cellular system including a plurality of cells assigned with a cell-specific scrambling code. A method for a terminal searching for a target cell using a frame received from the base station, the method comprising: (a) a period of the first synchronization channel symbol using a first synchronization channel symbol included in a frame received by the terminal; Acquiring a sync and primary sync channel sequence number of a sync block corresponding to the second block; and (b) generating a sync included in a frame received by the terminal based on the obtained sync block sync and primary sync channel sequence number. Acquiring a boundary of the frame and a target cell of the terminal by using a secondary sync channel symbol; The.

In the step (a), the first synchronization channel symbol mapped to a subcarrier occupied for each sync block in the frequency domain may be used.

In addition, the step (a) calculates a differential correlation value using a repetition pattern on the time domain of the first synchronization channel symbol or all subcarriers in which the first synchronization channel symbol is allocated to the first synchronization channel in the frequency domain. In case of occupying, the synchronization value of the sync block is obtained by calculating a correlation value using a time domain signal corresponding to the first synchronization channel symbol.

In addition, the step (a) (a1) calculates a correlation value with the first synchronization channel symbol included in the frame received by the terminal for all samples of the first synchronization channel symbol used in the OFDM cellular system. And (a2) detecting the sync block timing of the sample corresponding to the maximum correlation value among the correlation values.

In addition, the step (a1) is a (a1-1) to the first sync channel symbol included in the frame received by the terminal for the time-domain waveform of all the first sync channel symbol samples used in the OFDM cellular system. Calculating a correlation value with a corresponding one or a few time domain signals, and (a1-2) each correlation value for the sample is separated from the position of each sample by each sync block length. Summing with the correlation value.

In addition, in step (a1), when the terminal is provided with a plurality of receiving antennas and receives a plurality of frames for each receiving antenna, samples of all primary sync channel symbols used in the OFDM cellular system are performed. Computing a correlation value of each first sync channel symbol included in a frame received by each reception antenna for each reception antenna with respect to (a1-2) and summing correlation values corresponding to the same sample for each reception antenna. It is characterized by including.

In addition, the step (b) is based on the sync block synchronization and the first synchronization channel sequence number obtained in the previous step, and corresponds to the cell identifier or the cell identifier group of each cell, the second synchronization channel sequence in the frequency domain By performing a cyclic shift on the second sync channel symbol mapped to the length of the total sub-carriers occupied by the second sync channel symbols included in the frame, the boundary of the frame and the target of the terminal Obtaining a cell.

The boundary of the frame and the target cell of the terminal are obtained using only one secondary synchronization channel symbol based on the difference between the respective secondary synchronization channel symbols within each cell and within the frame. do.

In addition, step (b) (b1) estimating a frequency offset using the first synchronization channel symbol existing in each sync block interval based on the sync block synchronization, (b2) the estimated frequency Correcting a frequency offset of the sync channel symbol based on an offset; and (b3) detecting a frame timing and a target cell identifier of the terminal by using the corrected sync channel symbol.

In addition, in step (b3), (b3-1) Fourier transforming the frequency offset corrected sync channel symbol into a signal in a frequency domain and then converting the frequency offset corrected sync channel symbol into a signal in a frequency domain. Calculating a correlation value with respect to the click-shifted second synchronization channel symbol, (b3-2) an index value corresponding to a maximum correlation value among the correlation values of the entire cyclically shifted second synchronization channel symbol ( λ) and (b3-3) detecting the frame timing and the cell identifier corresponding to the index value [lambda].

In addition, the step (b3-1) is to perform a Fourier transform on the time-domain signal corresponding to each sync channel symbol to obtain a value converted into the frequency domain for each signal, to the obtained frequency domain. Obtaining a value corresponding to the first synchronization channel symbol and a value corresponding to the second synchronization channel symbol among all converted values, and a value corresponding to the second synchronization channel symbol and all possible cyclic shifts And calculating a correlation value with respect to a value corresponding to the second secondary synchronization channel symbol.

The method may further include estimating a position of a sync channel from a value corresponding to the first sync channel symbol, and corresponding to a second sync channel symbol corresponding to the estimated position of the sync channel when calculating the correlation value. Computing a correlation value for the value is characterized in that.

In the step (b3-3), the target cell identifier of the terminal is detected by performing a module operation on all the number of synchronization channel symbols L used in the OFDM system at the index value [lambda]. .

In addition, the step (b3-3) is to detect the frame boundary identifier that is the maximum value of the natural number less than or equal to the index value [lambda] divided by the number of all synchronization channel symbols (L) used in the OFDM system. It features.

In addition, the step (b) is (b1) when the terminal is provided with a plurality of receiving antennas to receive a plurality of frames for each receiving antenna, the receiving antenna over each sync block length section based on the sync block synchronization Estimating each frequency offset by using a first synchronization channel symbol included in each received frame; (b2) a round channel symbol included in a received frame for each receiving antenna based on the estimated frequency offset; (B3) using the corrected synchronization channel symbol, frame timing and combining the correlation values for the second synchronization channel symbols included in the received frame for each receiving antenna. Detecting a target cell identifier of the terminal.

In addition, it is characterized in that the use of the filtered frame passing only the synchronous channel occupied band of the signal band of the OFDM cellular system.

In addition, the frame is a forward link frame, characterized in that it has a time duration of 10 msec and includes 20 subframes.

In addition, the subframe has a time length of 0.5 msec and includes seven OFDM symbols.

In addition, two primary sync channel symbols and a second sync channel symbol are present in the frame.

In addition, when the first synchronization channel sequence used in the OFDM cellular system is one, the first synchronization channel sequence of the first synchronization channel symbol may be the same sequence for each cell, or may be a first synchronization channel sequence used in the OFDM cellular system. When there is more than one difference sync channel sequence, the first sync channel sequence of the first sync channel symbol may have a different sequence for each adjacent cell.

In addition, the primary sync channel symbol may occupy only 1/2 of the allocated subcarriers or occupy all subcarriers.

In addition, the two secondary sync channel symbols use the same sequence every frame, but use different sequences for each sync block in the frame, and use different sequences for each of the two secondary sync channel symbols for each base station. It is characterized by.

The second sync channel symbol may include information mapped to a cell identifier or a cell identifier group of a cell transmitting a frame including the second sync channel symbol.

In addition, the repetition period of the first synchronization channel symbol is a sync block unit in one frame, and the repetition period of the second synchronization channel symbol is one frame unit.

In addition, each sync channel symbol in the frame occupies only a portion of the band used by the OFDM system with respect to the center of the frequency domain.

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

In order to solve the above technical problem, the present invention provides a frame transmission method in an OFDM cellular system in which an eNB belonging to an arbitrary cell transmits a frame in an OFDM cellular system including a plurality of cells assigned with a cell-specific scrambling code. A method, comprising: (a) a first synchronization channel sequence including synchronization of sync blocks of the frame and a second synchronization, including a boundary of the frame and a cell identifier of the cell or a cell identifier group to which the cell identifier belongs; Generating a channel sequence and (b) generating and transmitting a frame including respective sync channel symbols code-hopped on a frequency using each of the generated sync channel sequences.

In addition, as a forward link frame, a frame having a time duration of 10 msec and having 20 subframes is generated and transmitted.

In addition, the subframe has a time length of 0.5 msec and includes seven OFDM symbols.

In addition, a frame in which two primary sync channel symbols and a second sync channel symbol exist is generated and transmitted.

In addition, when the first synchronization channel sequence used in the OFDM cellular system is one, the first synchronization channel sequence of the first synchronization channel symbol may be the same sequence for each cell, or may be a first synchronization channel sequence used in the OFDM cellular system. When there is more than one difference sync channel sequence, the first sync channel sequence of the first sync channel symbol may have a different sequence for each adjacent cell.

In addition, the primary sync channel symbol may occupy only 1/2 of the allocated subcarriers or occupy all subcarriers.

In addition, the two secondary sync channel symbols use the same sequence every frame, but use different sequences for each sync block in the frame, and use different sequences for each of the two secondary sync channel symbols for each base station. It is characterized by.

The second sync channel symbol may include information mapped to a cell identifier or a cell identifier group of a cell transmitting a frame including the second sync channel symbol.

In addition, the repetition period of the first synchronization channel symbol is a sync block unit in one frame, and the repetition period of the second synchronization channel symbol is one frame unit.

In addition, each sync channel symbol in the frame is characterized by generating and transmitting a frame to occupy only a portion of the band used by the OFDM system based on the center of the frequency domain.

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 synchronization channel symbols may be transmitted using spatial diversity, time switching transmission diversity, or precoding vector switching transmission diversity.

In order to solve the above technical problem, the neighbor cell search method in the OFDM cellular system proposed by qkfuad includes a frame of a cell belonging to an eNB in an OFDM cellular system including a plurality of cells assigned with a cell-specific scrambling code. In a method for a UE searching for an adjacent cell using a frame received from the base station, when the home cell and the neighbor cell operate in a base station synchronization mode, based on the sync block synchronization acquired from the frame received from the home cell In this case, the UE acquires the neighbor cell by using the second synchronization channel symbol included in the frame received from the neighbor cell.

And detecting a cell identifier of the neighboring cell by calculating a correlation value for the zero shifted secondary synchronization channel symbol among all possible cyclically shifted secondary synchronization channel symbols used in the OFDM cellular system. And detecting a frame timing and an OFDM symbol timing of a frame received from the neighboring cell by using a time domain signal corresponding to a second sync channel symbol of the neighboring cell.

The method may further include determining whether the home cell and the neighbor cell operate in the base station synchronization mode by receiving the control channel of the home cell.

In addition, when the cell search method searches for neighbor cells for handover of the terminal, step (b3) is performed without performing steps (b1) and (b2).

In order to solve the above technical problem, a cell search apparatus in an OFDM cellular system according to the present invention is configured to transmit a frame of a cell to which a base station belongs in an OFDM cellular system including a plurality of cells assigned with a cell-specific scrambling code. An apparatus for searching for a target cell by a terminal using a frame received from the base station, wherein the terminal corresponds to a period of the first synchronization channel symbol by using a first synchronization channel symbol included in a frame received by the terminal. Acquiring a boundary of the frame and a target cell of the terminal by using a synchronization detector for acquiring synchronization of a sync block and a second synchronization channel symbol included in a frame received by the terminal based on the acquired sync block synchronization And a cell detector.

In order to solve the above technical problem, an apparatus for transmitting a frame in an OFDM cellular system according to the present invention transmits a frame by a base station belonging to an arbitrary cell in an OFDM cellular system including a plurality of cells assigned with a cell-specific scrambling code. An apparatus, comprising: generating a first synchronization channel sequence including synchronization of a sync block of the frame and a second synchronization channel sequence including a boundary of the frame and a cell identifier of the cell or a code group to which the cell identifier belongs And a frame transmitter configured to generate and transmit a frame including each sync channel symbol coded on a frequency by using each of the sync channel generator and the generated sync channel sequence.

The frame transmitter may include an OFDM symbol mapping unit that maps data values of each channel included in the frame to respective positions on a frequency and time domain.

The frame transmitter may include a scrambling unit that multiplies the cell-specific scrambling code on a frequency domain with respect to the remaining OFDM symbols except for the synchronization channel symbols included in the frame among the mapped results.

The frame transmitting unit may include a CP inserting unit inserting a cyclic prefix that enables demodulation of an OFDM signal in the terminal even in a multipath delay of a channel including the frame.

In order to solve the above technical problem, the neighboring cell search apparatus in the OFDM cellular system according to the present invention transmits a frame of a cell to which a base station belongs in an OFDM cellular system including a plurality of cells assigned a cell-specific scrambling code. An apparatus for searching for an adjacent cell by a terminal using a frame received from the base station, wherein, when a home cell and an adjacent cell operate in a base station synchronization mode, based on a sync block synchronization acquired from a frame received from the home cell In this case, the UE acquires the neighbor cell by using the second synchronization channel symbol included in the frame received from the neighbor cell.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

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 or a time switching diversity (TSTD), a precoding vector switching transmission diversity, a frequency switching transmission diversity (FSTD), and the like. 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.

“Sink block detection” is a term used to mean sync block boundary detection and will be used in this specification. The sense of detecting a sync block also means OFDM symbol synchronization, a position of a primary sync channel in a sync block, and a position of a secondary sync channel. I mean.

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. .

The term "scrambling code detection" will be used herein in terms of scrambling code identifier detection and scrambling code detection, and the term "scrambling code information" will be used herein in terms of scrambling code identifiers and scrambling code.

In the present invention, a "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 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 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. 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 9 of the first sync block of FIG. 1.

According to the subframe disclosed in FIG. 2, the traffic data subcarrier 230, the primary sync channel subcarrier 240, and the null carrier 260 in the OFDM symbol interval 100 -A in which the primary sync channel symbol is transmitted. It includes.

The OFDM symbol interval 101 -A through which the secondary synchronization channel symbol is transmitted includes a traffic data subcarrier 230, a secondary synchronization channel subcarrier 250, and a null carrier 2600.

The other OFDM symbol 200 includes a traffic data subcarrier 230 or a pilot subcarrier.

As such, the last two OFDM symbols in the subframe are primary sync channel symbols and secondary sync channel symbols, respectively.

The example of FIG. 2 is merely an example, and the symbol position of the sync channel may be located at another symbol in the sync block 130.

Importantly, the sync channel positions are the same in all sync blocks in which sync channels exist.

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 220.

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 210.

In FIG. 2, the primary sync channel and the secondary sync channel occupy only a part of the band 210 of the entire band 220 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 uses all subcarriers in the sync channel occupied 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 a pattern 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 300, and N _S represents the number of samples of the symbol interval 310 excluding the cyclic prefix interval. .

3, the differential correlator may be used in the first cell search. On the other hand, as mentioned above, if the primary sync channel uses all subcarriers in the sync channel occupied band except the guard band, the differential correlator cannot be used and correlation is performed by generating the waveform in the time domain of the primary sync channel in advance at the receiving end. Use a correlator to

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 total number of subcarriers in a band is defined as 1.25 MHz, and the total number of subcarriers in the band is 128, and 75 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 the 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 map to a subcarrier. A component mapped to each of the synchronization channel subcarriers is defined as a “chip”.

The length of the sequence of the primary sync channel is the same as the number of subcarriers (37 in the example of FIG. 4) allocated to one primary sync channel symbol, and is repeated every primary sync channel symbol interval. The length of the sync channel sequence is equal to the total number of frequency domain subcarriers (150 in the example of FIG. 4) allocated to the plurality of secondary sync channel symbols in the frame.

As a result, the period of the first synchronization channel sequence is the sync block 130, and the period of the second synchronization channel sequence is one frame.

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 Equation 1, N ₁ is the number of subcarriers (37 in the example of FIG. 4) allocated 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 enable the acquisition of sync lock boundaries.

In addition, all cells used in the system are based on using one same sync channel sequence as a primary sync channel sequence, but in some cases, a plurality of cells (eg, 8 or less) may be used. In this case, the adjacent cells may use different ones of the plurality of primary sync channel sequences. In this case, when using a correlator based on a time domain signal, a plurality of time domain signal correlators are required in the first cell search.

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 sync channel sequence may correspond one-to-one with a cell identifier or a cell identifier group. In the present invention, a case in which the secondary sync channel sequence and the cell identifier correspond one-to-one will be described.

The secondary sync channel sequence has a one-to-one correspondence with a cell identifier and also provides information on a frame boundary to the mobile station. 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.

To do this, the length of the secondary sync channel sequence is equal to the total number of subcarriers (150 in FIG. 4) allocated to the secondary sync channel in the frame.

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

는 시퀀스 번호가 k(또는 셀 식별자 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 cell identifier number k).

In Equation 1, P is the number of secondary synchronization channel symbols in a frame (2 in the example of FIGS. 1 and 4) and N ₂ is a DC subcarrier and guard in secondary synchronization channel symbols 101 -A and 101 -B. The number of subcarriers allocated to the secondary synchronization channel, excluding subcarriers for the band, is 75 in the example of FIG. 4. As a result, the length of the secondary synchronization channel sequence becomes PxN ₂ .

As the secondary sync channel sequence, an arbitrary sequence having good cross-correlation property may be used. For example, an extended GCL sequence that extends the GCL sequence may be used to increase the number of sequences.

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

로 표현되고, 두 번째 동기채널 심볼에 대한 부분 시퀀스는

로 표현되는데, 이들 부분 시퀀스는 모두 다름을 특징으로 한다. 따라서 이동국에서 프레임내 P개의 2차 동기채널 중 1개의 2차 동기채널 심볼만 이용하더라도 셀탐색 2단계에서 프레임 경계 및 셀 식별자 혹은 스크램블링 코드 식별자 검출이 가능해진다.Sub-sequences for each secondary sync channel symbol of the secondary sync channel sequence, that is, the partial sequence for the first secondary sync channel symbol in the frame in FIG.

The subsequence for the second sync channel symbol is

These subsequences are all characterized by differentiation. Therefore, even if the mobile station uses only one secondary sync channel symbol among P secondary sync channels in the frame, the frame boundary and the cell identifier or the scrambling code identifier 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 modulated to a value corresponding to a sync slot number.

라고 했을 때, 상기 앞 부분에 해당하는 시퀀스

는

가 되고 뒷 부분에 해당하는 시퀀스

는

가 된다.That is,

, The sequence corresponding to the preceding part

Is

And the sequence that comes after

Is

Becomes

Here, a corresponds to a modulation symbol value corresponding to the first sync block (for example, 1) and b corresponds to a modulation symbol value corresponding to the second sync block (for example, -1).

A short sequence having a sequence length N ₂ of the number of subcarriers allocated to the secondary synchronization channel symbol as described above is mapped to a modulation symbol value corresponding to the sync block number as described above in every secondary synchronization channel symbol region, thereby increasing the total length. The method of making and using a secondary synchronization channel sequence that becomes P * N ₂ also does not depart from the scope of the present invention.

1 and 4, the cell searcher of the present invention synchronizes using a correlator using a differential correlator or a time domain waveform of a primary sync channel sequence in a first step. Acquiring a block boundary 141 -A or any one of 141-B and obtaining a sync channel sequence number, that is, a cell identifier using a secondary sync channel sequence correlator in the cell search step 2, while simultaneously obtaining a 10 msec frame boundary ( 140-A, 140-B) are also acquired at the same time.

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 number corresponds to a scrambling code group number. 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.

Meanwhile, as another embodiment of the present invention, the number of scrambling codes (number of cell identifiers) may be allocated to be a product of the number of primary sync channel sequences and the number of secondary sync channel hopping codes (cell identifier groups). For example, if there are eight primary sync channel sequences and the total number of scrambling codes (ie, cell identifiers) is 512, the secondary sync channel hopping codes may be allocated to 64 (ie, 512 = 8 × 64). In this case, all scrambling codes (ie, cell identifiers) are classified into 64 groups, and each group is composed of eight scrambling codes, and the scrambling codes in each group are specified (or one-to-one) by different primary sync channel sequences. To be mapped).

In this case, the third step of cell searching is not necessary. In this case, in the first cell search, time domain correlation is performed on a plurality of primary synchronization channel sequences to acquire primary synchronization channel sequence information together with sync block synchronization. Thus, one of eight scrambling codes included in each group is obtained. To be specified.

Next, when the frame boundary and the secondary synchronization channel hopping code number (that is, the cell identifier group number) are acquired in step 2, one group of the 64 groups can be specified. Thereby, one scrambling code (ie, cell identifier) can be identified and detected. As a result, the cell identifier information may be obtained by using a combination of the obtained primary sync channel sequence number and secondary sync channel hop code number.

In the present invention, an example in which the cell search procedure is composed of only one cell search step and two cell search steps is given.

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 and pilot channel generator 512 generates traffic data or pilot data to be transmitted, as shown by reference numeral 230 of FIG. 2, and the sync channel generator 500 generates reference numerals 240 and 250 of FIG. 2 or 4. A primary sync channel sequence and a secondary sync channel sequence defined as in Equations 1 and 2 are generated.

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 performs scrambling inherent to the 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 your code.

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.

In addition to the TSTD and precoding vector switching, frequency switching transmit diversity (FSTD) may be applied.

In this case, a sequence element mapped to an even subcarrier among subcarriers allocated to a primary sync channel symbol is transmitted as a first antenna and a sequence element mapped to an odd subcarrier is transmitted to a second antenna. A sequence element mapped to an even subcarrier among carriers is a first antenna and a sequence element mapped to an odd subcarrier is transmitted to a second antenna.

In this case, the diversity control unit 513 also plays a role.

6 is a block diagram showing the 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 controller 640 may include a synchronization mode determination unit that receives a control channel of the home cell and determines whether the home cell and the neighbor cell operate in the base station synchronization mode.

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.

The cell searcher 620 is divided into sync channel band filter units 621 -A and 621 -B, a sync detector 622, and a cell detector 623.

For the down-converted signals S1 and S2, the sync channel band filter units 621 -A and 621 -B only use the sync channel occupied band 210 among the entire OFDM signal band 220 as described with reference to FIG. 2. Band pass filtering is performed.

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

The cell detector 623 detects a cell identifier and 10 msec frame timing information from the received signal by using the acquired sync block timing information S5.

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

7 is a block diagram illustrating a configuration of a synchronization detector of FIG. 6 according to an exemplary embodiment of the present invention. Referring to FIG. 7, the synchronization detector 622 according to an embodiment of the present invention may include a correlation value calculator 701 -A, 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-numbered or odd-numbered carriers among the carriers belonging to the sync channel occupancy band, the differential correlator using the repetition pattern of FIG. 3 in the time domain is illustrated. 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.

Outputs of the correlation value calculators 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 correlation value calculators 701 -A and 701-B are generated per sync block length, and the timing detector 710 outputs peak values among these correlation values. A position of a sample that generates a peak value is detected, and the detected sample position is determined as a synchronization channel symbol timing.

However, the synchronization detector 622 according to an embodiment of the present invention may further include an accumulator 703 as shown in FIG. 7 to increase symbol synchronization 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 synchronization detector 622 includes the accumulator 703, the timing detector 710 detects a maximum value among 9600 values stored in the accumulator 703 to detect the sample position of the detected maximum value by using the detected timing information ( It outputs as S5).

8 is a graph illustrating correlation values calculated for each sample position by the correlation value calculator 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 denotes the position of the first sample for which the first correlation value calculator performs correlation.

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

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 is a diagram illustrating the structure of input signals S3 and S4 provided to the cell detector of FIG. 6 based on the sync block timing obtained by the sync detector of FIG. 6 according to an exemplary embodiment of the present invention.

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

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.

10 is a block diagram illustrating a configuration of a cell detector of FIG. 7 according to an exemplary embodiment of the present invention. Referring to FIG. 10, a frequency offset corrector 1000 and a boundary and cell identifier detector 1010 are included.

The frequency offset corrector 1000 sets the sync channel symbol timing 900 based on the output S5 of the sync detector 622, and sets the sync channel symbol timing 900 in each sync block length section based on the sync channel symbol timing 900. Over the received signal samples 910-A and 910-B of the 2xN _S primary sync channel estimation positions provided from the respective sync channel band filters 621 -A and 621 -B, and then using the same. First, estimate the frequency offset, and correct the frequency offset for the 4xN _S received signal samples (910-A, 920-A, 910-B, 920-B) based on the estimated frequency offset. The corrected 4xN _S received signal samples S9 and S10 are provided to the boundary and cell identifier detector 1010.

The boundary and cell identifier detection unit 1010 detects the scrambling code identifier and the 10 msec frame timing by using the frequency offset corrected samples S9 and S10 and then passes them to the control block.

The boundary and cell identifier detector 1010 performs Fourier transform of Ns received sample values for each of the synchronization channel symbol positions 910 -A, 920-A, 910-B, and 920-B, and then converts the received sample values into signals in the frequency domain. Correlate all possible cyclic shifts of the possible secondary sync channel sequences, select the correlation component with the highest value among them, and take the identifier and cyclic shift index value of the corresponding secondary sync channel sequence to obtain the cell expression of the target cell. Acquire frame timing as well as asterisks simultaneously.

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 configuration of a boundary and a cell identifier detector of FIG. 10 according to an exemplary embodiment of the present invention. Referring to FIG. 11, second correlation value calculators 1100 -A and 1100 -B, a combiner 1110, a shift sequence detector 1120, a frame boundary detector 1132, and a cell identifier detector 1131. It is composed of an index search unit 1130 consisting of.

The mobile station does not know what the secondary sync channel sequence identifier and cyclic shift index mapped to the received secondary sync channel symbols 920-A and 920-B are. 920-B) Fourier transforms for each N _S samples are converted into a signal in the frequency domain, and then correlation is required for all possible secondary sync channel sequences and possible cyclic shifts of secondary sync channel sequences.

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 second correlation value calculator 1100 -A or 1100 -B performs a Fourier transform on each of the synchronization channel symbols S9 and S10 that have been frequency offset corrected by the frequency offset correction unit 1000, and then converts them into signals in the frequency domain. Correlation is calculated for both possible secondary sync channel sequences and possible cyclic shifts of the secondary sync channel sequence.

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 second correlation value calculators 1100 -A and 1100 -B to provide the PxL combined correlation values to the shift sequence detector 1120.

Where L is the number of secondary sync channel sequences (or the number of cell identifiers) and P is the number of shifts (or the number of sync blocks per frame) of the possible secondary sync channel sequences and is 2 in the example of FIGS. 1 and 4. .

After all, the shift sequence detector 1120 selects a maximum value among the correlation values of all the PxL shifted sequences, and then transfers the index value λ of the maximum value to the scrambling code (cell) identifier detector 1131 and the frame boundary detector 1132. to provide.

The scrambling code (cell) identifier detector 1131 detects the scrambling code identifier (or section identifier) of the target base station by performing an L module operation on the output received from the shift sequence detector 1120. That is, it is expressed as Equation 4 below.

Scrambling Code Identifier = λ _{mod L}

In Equation 4, [lambda] is an output of the shift sequence detector 1120. L is the total number of sync channel sequences used in the system.

The frame boundary detector 1132 obtains frame boundary information by performing an operation defined by Equation 5 below to the output received from the shift sequence detector 1120.

Frame boundary identifier = [λ ÷ L]

In Equation 5, [x] means a natural number having a maximum value among natural numbers less than or equal to x.

The frame boundary identifier is a secondary synchronization channel symbol interval (920−2) of P (where P = 2 in the example of FIG. 9 corresponding to FIGS. 1 and 4) where a 10 msec frame boundary is used in the code & boundary detector 650. The distance from the first position 930-A of A through 920-B) in units of sync block length is shown.

That is, when the frame boundary identifier is 0, the 10 msec frame boundary becomes the first secondary sync channel position 930-A, and when the frame boundary identifier is 1, the second secondary sync channel position 930-B. .

The second correlation value calculators 1100 -A and 1100 -B may include Fourier transform units 1101-A and 1101 -B, demapped units 1102-A and 1102-B, and channel estimators 1103-A. , 1103-B) and second-order synchronization channel correlation value calculators 1204-A and 1104-B.

The Fourier transform units 1101-A and 1101-B perform Fourier transform on time domain samples 910-A, 920-A, 910-B, and 920-B corresponding to the respective sync channel symbol regions. Obtain N _S frequency-domain transformed values for the symbol.

Demapping unit (1102-A, 1102-B ) is the acquired PxN ₁ values corresponding to sub-carriers of the total frequency primary synchronization channel from the converted value sequence (see Fig. 4) and a secondary synchronization sub-carriers of the channel sequence The value of ₂ PxN (refer FIG. 4) is acquired.

Channel estimation unit (1103-A, 1103-B ) are each subcarrier by using the primary synchronization channel sequence which is represented by the equation (1) stored in advance from the de-mapping section PxN _one of the primary synchronization channel frequency domain received sample value received from the Perform channel estimation for.

The secondary sync channel code correlator cross-correlates the PxN _two secondary sync channel frequency domain received sample values received from the de-mapping unit with possible PxL shifted secondary sync channel sequences.

At this time, in order to increase the detection probability, the channel estimation is corrected for each subcarrier using the channel estimation values passed from the channel estimators 1103-A and 1103-B to perform cross correlation.

PxN ₂ of the secondary synchronization channel frequency domain received samples and the possible value of the shift PxL secondary synchronization channel sequence and the cross-correlation will be described with reference to FIG.

12 is a conceptual diagram of performing correlation with all possible cyclic shift sequences of a secondary sync channel to obtain a frame boundary and a cell identifier according to an embodiment of the present invention.

Given that the demapper output 1200 for the first secondary sync channel symbol position and the demapper output 1210 for the second secondary sync channel symbol position are not known which part is a frame boundary, Cross correlation is performed for all possible sequences of Equations 6 (0 cyclic shift) and 7 (1 cyclic shift).

As a result, the total number of outputs of the second synchronization channel correlation calculator is 2xL (P = 2).

The PxL code correlator outputs are combined for each component in the combiner 1110 and passed to the shift sequence detector.

The shift sequence detector 1120 detects a maximum value of the P * L outputs of the combiner 110, and detects an index value λ corresponding to the maximum value by using a scrambling code (cell) identifier detector 1131 and a frame boundary detector 1132. Pass it to).

The scrambling code (cell) identifier detector 1131 detects the cell identifier of the target base station by performing an L module operation as shown in Equation 4 on the output λ received from the shift sequence detector 1120 to detect the cell identifier of the target base station. Pass it to).

The frame boundary detector 1132 performs the operation defined by Equation 5 on the output λ received from the shift sequence detector 1120, obtains frame boundary information, and passes it to the controller 640.

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

As mentioned above, step S1300 is a sync block synchronization acquisition step and step S1310 is a step of detecting a frame boundary and a scrambling code identifier including frequency offset correction.

The maximum value of the correlation value for the sync channel sequence detected in step 2 and its shifted sequence is compared with a preset threshold value, and when the value is larger than the threshold value (S1320), the cell search is completed. do.

14 is a flowchart illustrating a neighbor cell search process when a home cell and a neighbor cell operate in synchronization with a base station according to an embodiment of the present invention.

15 is a flowchart illustrating a process of searching for neighbor cells by determining whether a home cell and a neighbor cell operate in synchronization with a base station according to an exemplary embodiment of the present invention.

Only the initial cell search performed by the mobile station when the initial power is applied is mentioned. There may also be a handover cell search performed by the mobile station for handover in an idle state or a call state.

At the time of handover cell search, since the mobile station is already performing frequency correction from the home cell signal, the frequency offset correction block in FIG. 10 can be bypassed (S1520).

When the target base station to be searched by the home cell and the mobile station operates in the base station asynchronous mode, the sync block synchronization of the target base station is performed by using the primary synchronization channel received from the target base station in step 1 similarly to the initial synchronization acquisition process. First, in operation S1510, a cell identifier of the target cell is obtained through cyclic shift correlation of the secondary synchronization channel, and a frame boundary is acquired at operation S1400 and S1530.

The neighbor cell search process for handover at this time is the same as the process of FIG. 13 (S1410 and S1540).

If the target base station to which the home cell and the mobile station are to be searched operates in the base station synchronization mode, the cell search step 1 may not be necessary because the frame boundaries of the home cell and the adjacent cell coincide with each other (S1500).

In this case, only the second cell search step is required, and since the frame boundary is known in the second cell search step, correlation may be performed only for the zero shift sequence, that is, the secondary sync channel sequence corresponding to the Hypothesis 0 part of FIG. 12.

In this case, since the delay of the signal received from the home cell and the neighbor cell may be different, the accurate frame timing of the neighbor cell reception signal is detected by using the time domain signal of the secondary sync channel sequence of the neighbor cell after detecting the cell identifier of the target cell. And OFDM symbol timing.

The invention can also be embodied as computer readable code on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD_ROM, magnetic tape, floppy disks, and optical data storage, and may also include those implemented in the form of carrier waves (e.g., transmission over the Internet). . 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.

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.

As described above, in the OFDM cellular system, the cell search time of the mobile station can be reduced, and a cell searcher operating with low complexity can be implemented.

In addition, the synchronization acquisition method of the present invention enables synchronization acquisition with low complexity.

Claims (23)

In an OFDM cellular system including a plurality of cells assigned a cell-specific scrambling code, as a base station transmits a frame of a cell to which the base station uses a frame received from the base station, the terminal searches for a target cell, (a) acquiring a sync block and a first sync channel sequence number of a sync block corresponding to a period of the first sync channel symbol by using a first sync channel symbol included in a frame received by the terminal; And (b) acquiring the boundary of the frame and the target cell of the terminal by using the second synchronization channel symbol included in the frame received by the terminal based on the acquired sync block synchronization and primary synchronization channel sequence number; Cell searching method in an OFDM cellular system comprising: a. The method of claim 1, wherein step (a) And a first order synchronization channel symbol mapped to a subcarrier occupied by each sync block in a frequency domain. The method of claim 1, wherein step (a) Computing the differential correlation value using a repeating pattern in the time domain of the first sync channel symbol or when the first sync channel symbol occupies all subcarriers allocated to the first sync channel in the frequency domain. And obtaining a synchronization of the sync block by calculating a correlation value using a time domain signal corresponding to a synchronization channel symbol. The method of claim 1, wherein step (b) Based on the sync block sync and primary sync channel sequence numbers obtained in the previous step, A second identifier corresponding to a cell identifier or a cell identifier group of each cell and mapped in the frequency domain such that the length of the secondary synchronization channel sequence is equal to the length of the total subcarriers occupied by the secondary synchronization channel symbols included in the frame; And performing a cyclic shift on a secondary sync channel symbol to obtain a boundary of the frame and a target cell of the terminal. The method of claim 4, wherein OFDM, characterized in that for obtaining the boundary of the frame and the target cell of the terminal using only one secondary synchronization channel symbol based on the difference between the secondary synchronization channel symbols for each cell and within the frame. Cell discovery method in cellular system. The method of claim 1, wherein step (b) (b1) estimating a frequency offset using the first sync channel symbol existing in each sync block section based on the sync block sync; (b2) correcting a frequency offset of the sync channel symbol based on the estimated frequency offset; And (b3) detecting a frame timing and a target cell identifier of the terminal by using the corrected sync channel symbol; cell searching method in an OFDM cellular system, comprising: The method of claim 1, Cell filtering method in an OFDM cellular system, characterized in that for using the filtered frame passing only the synchronous channel occupied band of the signal band of the OFDM cellular system. The method according to any one of claims 1 to 7, 2. The cell searching method of the OFDM cellular system according to claim 2, wherein two primary sync channel symbols and a second sync channel symbol are present in the frame. The method of claim 8, When there is only one primary sync channel sequence used in the OFDM cellular system, the first sync channel sequence of the first sync channel symbol may be the same sequence for each cell or may be used in the OFDM cellular system. The method of cell searching in an OFDM cellular system, characterized in that when there is more than one channel sequence, a different sequence is used for each adjacent cell of the first sync channel sequence of the first sync channel symbol. The method of claim 8, The second secondary sync channel symbol uses the same sequence every frame, but uses a different sequence for each sync block in a frame, and uses a different sequence for each of the second secondary sync channel symbols for each base station. A cell search method in an OFDM cellular system. The method of claim 10, And wherein the secondary sync channel symbol includes information mapped to a cell identifier or a cell identifier group of a cell transmitting a frame including the secondary sync channel symbol. The method of claim 8, The repetition period of the first synchronization channel symbol is a sync block unit in one frame, and the repetition period of the second synchronization channel symbol is a frame unit. The method according to any one of claims 1 to 7, Each sync channel symbol in the frame occupies only a portion of a band used by the OFDM system with respect to the center of the frequency domain. The method according to any one of claims 1 to 7, The primary sync channel symbol and the secondary sync channel symbol are configured on a TDM basis and disposed immediately adjacent to each other. A method for transmitting a frame by a base station belonging to an arbitrary cell in an OFDM cellular system including a plurality of cells assigned with a cell-specific scrambling code, (a) generating a first synchronization channel sequence including synchronization of sync blocks of the frame and a second synchronization channel sequence including a boundary of the frame and a cell identifier of the cell or a cell identifier group to which the cell identifier belongs; Doing; And and (b) generating and transmitting a frame including each sync channel symbol coded on a frequency by using each of the generated sync channel sequences. The method of claim 15, A frame transmission method in an OFDM cellular system, characterized by generating and transmitting a frame in which two primary synchronization channel symbols and a secondary synchronization channel symbol exist. The method of claim 16, When there is only one primary sync channel sequence used in the OFDM cellular system, the first sync channel sequence of the first sync channel symbol may be the same sequence for each cell or may be used in the OFDM cellular system. The method of transmitting a frame in an OFDM cellular system, wherein when there is more than one channel sequence, different sequences are used for adjacent cells in the first sync channel sequence of the first sync channel symbol. The method of claim 16, And the primary sync channel symbol occupies only 1/2 of an allocated subcarrier or occupies all subcarriers. The method of claim 16, The secondary sync channel symbol includes information mapped to a cell identifier or a cell identifier group of a cell transmitting a frame including the secondary sync channel symbol. The method of claim 16, The repetition period of the first synchronization channel symbol is a sync block unit in one frame, and the repetition period of the second synchronization channel symbol is one frame unit. The method of claim 15, Each sync channel symbol in the frame generates and transmits a frame to occupy only a portion of a band used by the OFDM system with respect to a center of a frequency domain. The method of claim 15, 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 arranged immediately adjacent to the frame transmission method in an OFDM cellular system. The method of claim 15, wherein step (b) And transmitting the synchronization channel symbols by using spatial diversity, time switching transmission diversity, or precoding vector switching transmission diversity.

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