KR100755820B1 - Apparatus for generating down link signal, and method and apparatus for cell search in cellular syste - Google Patents

Abstract

A method of generating a downlink signal in an OFDM-based cellular system and searching for a cell from the downlink signal is provided. To this end, the downlink signal includes a plurality of sync blocks generated by a plurality of subframes, and each sync block includes a combination of a cell group identification code for identifying a cell group and a frame sync identification code indicating information of a frame start point. The pattern is generated. Each sync block is assigned a different frame sync identification code.

Subframe, cell, cell group, sync, downlink

Description

TECHNICAL APPARATUS FOR GENERATING DOWN LINK SIGNAL, AND METHOD AND APPARATUS FOR CELL SEARCH IN CELLULAR SYSTE}

1 is a schematic block diagram of an apparatus for generating downlink signals in a cellular system according to an embodiment of the present invention.

2 illustrates a downlink frame structure of a cellular system according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating the downlink frame structure of FIG. 2 in detail.

4 is a diagram illustrating a signal waveform obtained by converting the downlink frame of FIG. 3 into a time domain.

5 is a diagram illustrating bandwidth scalability of a downlink frame according to an embodiment of the present invention.

6 illustrates bandwidth scalability of a downlink frame according to another embodiment of the present invention.

7 is a schematic block diagram of a cell search apparatus according to an embodiment of the present invention.

8 is a flowchart illustrating a cell searching method according to an embodiment of the present invention.

9 is a schematic block diagram of a synchronization estimator according to an embodiment of the present invention.

10 is a diagram illustrating a method of allocating a cell group separator and a frame sync ID according to an embodiment of the present invention.

11 is a diagram illustrating a method for allocating a cell group separator and a frame sync ID according to another embodiment of the present invention.

12 is a schematic block diagram of a cell group estimator according to an embodiment of the present invention.

The present invention relates to a method and apparatus for generating a downlink signal of a cellular system and a method and apparatus for searching for a cell, and more particularly, to a method for searching for a downlink cell in an orthogonal frequency division multiplexing (OFDM) based cellular system. It is about.

In a cellular system, for the initial synchronization, the terminal should be able to synchronize the time synchronization with the frequency synchronization based on the signal of the base station and perform cell search. After the terminal synchronizes initially, it should be able to track time and frequency, and it should be able to perform time and frequency synchronization and cell search of neighbor cells for handover.

In a synchronous cellular system, all base stations can synchronize frames using common time information from an external system. However, the cellular system currently being developed in the 3rd generation partnership project (3GPP) is an asynchronous system with independent frame time of all base stations. Unlike a synchronous cellular system, such an asynchronous cellular system requires a cell search process.

For this purpose, a method of acquiring synchronization using a separate preamble and searching for a cell has been proposed, but this method is not applicable to a system in which a preamble does not exist. In addition, a method of performing synchronization acquisition and cell search using pilot symbols located at the beginning and the end of a subframe has been proposed, but in this case, there is a problem in that a large number of pilots are used.

An object of the present invention is to provide a cell search method and apparatus capable of efficient synchronization acquisition and cell search by forming a plurality of synchronization channels in one frame in an OFDM-based cellular system.

In order to solve this problem, according to an embodiment of the present invention, an apparatus for generating a downlink signal of an orthogonal freqency division multiplexing (OFDM) based cellular system is provided. The downlink signal generating apparatus includes a pattern generator and a time-frequency mapper. The pattern generator generates a sync pattern for each of a plurality of sync blocks forming a frame of the downlink signal—a set of a plurality of contiguous subframes within a frame. In this case, the sync pattern includes a cell group number and start point information of the frame. The time-frequency mapper generates the downlink signal by mapping a synchronization pattern into a time-frequency domain.

According to another embodiment of the present invention, a cell search apparatus of a terminal of an orthogonal frequency division multiplexing (OFDM) based cellular system is provided, which includes a receiver, first estimators to third estimators. The receiver receives a signal in which one frame consists of a plurality of sync blocks. Here, each sync block—a set of adjacent subframes—are a combination of a cell group identification code for distinguishing a cell group from a plurality of OFDM symbols and a frame sync identification code for indicating a start point of the frame. A synchronous pattern is formed. The first estimator estimates the start point of the sync block from the sync pattern, the second estimator estimates the cell group number of the cell group corresponding to the frame start point and the cell to which the terminal belongs, using the start point of the sync block, and the third estimator Estimates the number of a cell to which the UE belongs by using a cell classification scrambling code included in a pilot symbol of the frame.

According to another embodiment of the present invention, a method for searching for a cell in a terminal of an orthogonal frequency division multiplex (OFDM) based cellular system is provided. First, a downlink frame including a plurality of sync blocks having a sync pattern formed of a combination of a cell group identification code for identifying a cell group to which the UE belongs and a frame sync identification code for indicating a start point of a frame, a code combination, is provided. Receive and estimate the starting point of the sync block in the received downlink frame. The cell group number and frame synchronization are obtained from the estimated start point of the sync block and the sync pattern, and the cell number is obtained from the cell classification scrambling code included in the downlink frame.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, except to exclude other components unless otherwise stated.

A method and apparatus for generating a downlink signal and a cell search method and apparatus for a cellular system according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

1 is a schematic block diagram of an apparatus for generating a downlink signal of a cellular system according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating a downlink frame structure of a cellular system according to an embodiment of the present invention.

As shown in FIG. 1, the apparatus 100 for generating a downlink signal according to an embodiment of the present invention may include a pattern generator 110, a code generator 120, a time-frequency mapper 130, an OFDM transmitter 141, and the like. And a transmit antenna 142, which is formed at a base station (not shown) of the cellular system. As shown in FIG. 2, the downlink signal generated by the downlink signal generating apparatus 100 according to the embodiment of the present invention includes a plurality of sync blocks 210, and each sync block 210 includes a plurality of sub-blocks. It is formed as a set of frames 220. In this case, information for cell group identification and information for estimating frame synchronization are allocated to initial symbol periods 230a and 230b of each sync block 210. Each sync block 210 is assigned a different frame sync identification code.

The pattern generator 110 generates a sync pattern and a pilot pattern of a downlink signal using a set of orthogonal codes representing cell number information, cell group information, and information for identifying frame sync. The pattern generator 110 assigns a series of orthogonal codes to cell group numbers for recognizing a cell group, and uses a series of orthogonal codes to recognize a starting point of a frame. Hereinafter, orthogonal codes assigned to cell group numbers are referred to as " cell group identification codes " for convenience of explanation, and orthogonal codes used to recognize the starting point of a frame are referred to as " frame synchronization identification codes. &Quot; The pattern generator 120 generates a code set by matching the cell group identification code and the frame synchronization identification code, respectively, and allocates the code set over the frequency domain of the synchronization channel symbol section of the downlink signal to generate a synchronization pattern of the downlink signal. . The pattern generator 110 generates a pilot pattern of the downlink signal by allocating a unique scrambling code allocated to each cell in the cellular system to encode common pilot symbols and data symbols in the pilot channel symbol period.

The code generator 120 generates a set of orthogonal codes used as a cell group identification code and a frame sync identification code, respectively, and transmits them to the pattern generator 110. The pattern generator 110 uses these orthogonal code sets to generate a synchronization pattern and Create a pilot pattern.

The time-frequency mapper 130 maps the data to the time and frequency domain by using the synchronization pattern information and the pilot pattern information generated by the pattern generator 110, the frame structure information and the transmission traffic data transmitted from the outside. Thus, a frame of the downlink signal (200 in FIG. 2) is formed.

OFDM transmitter 141 then receives the downlink signal from time-frequency mapper 130 and transmits this signal via transmit antenna 142.

2, one frame 200 of a downlink signal of a cellular system according to an embodiment of the present invention consists of N _sync blocks 210, and each sync block 210 has N _sub subframes ( 220). One OFDM symbol 230a of the downlink signal uses N _t subcarriers having a frequency width of Δf. Pilot symbol periods 240a to 240e in which pilot data are located are formed in the first portion of each subframe 220 constituting one sync block 210. In the first subframe of one sync block 210, sync symbol intervals 230a and 230b in which data including a cell group identification code and a frame sync identification code are located are formed. In this case, the sync symbol intervals 230a and 230b may be located in the first OFDM symbol interval of the first subframe or in the last OFDM symbol interval of the first subframe. The sync symbol intervals 230a and 230b are divided into two frequency bands 250 and 260 over the frequency domain, and cell group identification codes and sync identification codes are inserted into the bands 250 and 260, respectively. As shown in FIG. 2, the pattern generator 110 is not formed over the entire frequency domain of the sync symbol intervals 230a and 230b, and assigns codes only to some frequency bands in the center excluding the DC subcarrier to generate a sync pattern. Create In the 3GPP system, the downlink frame 200 is composed of 20 subframes 220, one subframe 220 corresponds to a time of 0.5msec, 7 for Unicast transmission, 6 for Multicast transmission It is configured to have OFDM symbol intervals. In the downlink frame of the 3GPP system, for example, the sync block 210 may include five subframes 220. In this case, the repetition period of the sync channel symbol interval in one frame is 4 (pcs). )

Next, a method of generating a sync pattern and a pilot pattern in the pattern generator 110 of FIG. 1 will be described in detail with reference to FIGS. 3 and 4.

FIG. 3 is a diagram illustrating OFDM symbols of a sync channel symbol section in which a sync pattern is generated, and FIG. 4 is a diagram illustrating a signal waveform obtained by converting the sync channel symbol section of FIG. 3 to a time domain.

As shown in FIG. 3, the pattern generator 110 includes a frequency band 250 and a frame for insertion of a cell group identification code with only a predetermined bandwidth centered on a central subcarrier in the entire frequency band of the synchronization channel symbol period 230a. By dividing the frequency band 260 for the insertion of the synchronization identification code, each orthogonal code is sequentially inserted to generate a synchronization pattern.

의 직교 부호 집합을 할당하고, 프레임 동기 식별을 위한 주파수 밴드(260)에는

의 직교 부호 집합을 할당하여 동기 패턴을 형성한다. 여기서, k는 셀 그룹 번호, u는 프레임 동기 식별 부호의 번호, N_G는 셀 그룹 식별 부호의 길이, N_F는 프레임 동기 식별 부호의 길이를 의미한다. 본 발명의 실시예에 따른 패턴 생성기(110)는 셀 그룹 식별 부호와 프레임 동기 식별 부호로 GCL(generalized chirp like) 코드를 이용할 수 있으며, 이들 부호는 수학식 1 및 수학식 2와 같이 나타낼 수 있다.The pattern generator 110 assigns orthogonal codes in two independent sets of orthogonal codes transmitted from the code generator 120 to the frequency bands 250 and 260. Referring to FIG. 3, the pattern generator 110 may include a frequency band 250 for cell group identification.

Assigns an orthogonal code set of to the frequency band 260 for frame synchronization identification.

A synchronization pattern is formed by assigning a set of orthogonal codes. Here k denotes a cell group number, u denotes a number of frame synchronization identification codes, N _G denotes a length of a cell group identification code, and N _F denotes a length of a frame synchronization identification code. The pattern generator 110 according to an embodiment of the present invention may use a generalized chirp like (GCL) code as a cell group identification code and a frame synchronization identification code, and these codes may be represented by Equation 1 and Equation 2. .

Orthogonal codes as shown in Equations 1 and 2 are assigned to positions as shown in FIG. 3 to generate a synchronization pattern. That is, the pattern generator 110 assigns orthogonal codes obtained from Equations 1 and 2 to every even or every odd subcarrier in the frequency bands 250 and 260 without sequentially assigning the orthogonal codes to the adjacent subcarriers. Subcarriers between subcarriers allocated with orthogonal codes are operated as nulling subcarriers with no sequence assigned thereto. Therefore, the subcarriers in the sync channel symbol section in which the sync pattern is formed occupy approximately 2 * [(N _G + N _F ) + N _B ] (hereinafter referred to as N _S ) subcarrier bands including the null subcarriers. Here, N _B means the number of subcarriers of the guard band.

  By converting the sync pattern generated in this way into the time domain, a signal waveform as shown in Fig. 4 can be obtained. FIG. 4 shows signal waveforms of a portion excluding a cyclic prefix of an OFDM symbol, and it can be seen that two repetitive patterns are generated in the time domain due to two types of orthogonal codes.

As shown in FIG. 3, the apparatus 100 for generating a downlink signal according to an embodiment of the present invention is provided between a subcarrier to which each sequence is allocated over a frequency domain of a sync channel symbol interval to which a cell group separator and a sync identification code are assigned. A signal is generated by forming a synchronization pattern such that one null subcarrier exists in the channel. Therefore, the received signal generated and transmitted in this manner has a repetition pattern as shown in FIG. 4, and the terminal receiving the downlink frame obtains initial symbol synchronization using the signal pattern of FIG. 4 and estimates a frequency offset. do.

Here, the length (N _F) of the length (N _G) and a frame synchronization identification code of the cell group identification code inserted in each sync channel symbol interval of the downlink frame may be set different from each other, and the length information of these identification codes The synchronization pattern information is shared between the terminal and the base station.

The terminal receiving the downlink frame 200 having the synchronization pattern as shown in FIG. 3 sequentially demodulates two frequency bands 250 and 260 for each sync block, thereby obtaining information on the cell group number and the frame start point. This makes it possible to quickly and efficiently search for cells. In addition, by dividing the frequency domain of the sync channel symbol interval into two frequency bands, and assigning the same or different types of sequences, it is possible to prevent the degradation of correlation performance due to frequency selective fading.

In the embodiment of the present invention, although the cell group identification code has been described as being inserted before the frame synchronization identification code on the frequency axis of the synchronization channel symbol interval, the synchronization pattern can be generated by changing the positions of these codes. In the embodiment of the present invention, although the same type of orthogonal code is used as the cell group identification code and the frame synchronization identification code, different types of orthogonal codes may be used, and the identification code may be Hadamard code, It can be selected from common orthogonal codes, including KAZAC code, Gold code, Golay code, pseudo-noise (PN) code.

5 is a diagram illustrating bandwidth scalability of a downlink frame according to an embodiment of the present invention, and FIG. 6 is a diagram illustrating bandwidth scalability of a downlink frame according to another embodiment of the present invention. .

5 and 6 are diagrams showing the bandwidth of the synchronization channel symbol interval shown in FIG. 3 compared with the total bandwidth supported by the cellular system. The downlink signal generating apparatus 100 according to the embodiment of the present invention generates a synchronization pattern by inserting orthogonal codes into the center portion of the frequency band as shown in FIGS. 2 and 3. In the cellular system, since the UE supports different bandwidths according to the class of each UE, the MS can support the bandwidth scalability of the UE through such a frame configuration. 5 shows a case in which a sync pattern is allocated to a 1.25 MHz band among frequency bands. Traffic data may be allocated and transmitted to an OFDM symbol having no synchronization pattern generated in the synchronization channel symbol period. 6 illustrates a case in which a sync pattern is allocated to a 1.25 MHz band or a 5 MHz band among frequency bands, all of the transmitted sync patterns may be accommodated in a terminal supporting a bandwidth of 5 MHz or more, but a 1.25 MHz bandwidth and a 2.5 MHz bandwidth In the terminal supporting the only synchronization pattern of a part of the center portion can be accommodated. The downlink frame according to the embodiment of the present invention can extract the cell group number and the starting point information of the frame synchronization only by the partial synchronization pattern that is accommodated, thereby supporting bandwidth scalability.

Next, a method of searching for a cell by the terminal using the downlink signal generated as described above will be described in detail with reference to FIGS. 7 to 8.

7 is a schematic block diagram of a cell search apparatus according to an embodiment of the present invention, and FIG. 8 is a flowchart illustrating a cell search method according to an embodiment of the present invention.

Referring to FIG. 7, the cell search apparatus 400 according to an embodiment of the present invention includes a receiver 410, a symbol synchronization estimator 420, a Fourier transformer 430, a cell group estimator 440, and a cell number estimator 450. The Fourier transform 430 may perform a Fast Fourier transform (FFT).

As shown in FIG. 8, the receiver 410 receives a signal transmitted from a base station, and the symbol synchronization estimator 420 filters the received signal by a bandwidth allocated to the synchronization channel, removes a guard interval, and then performs differential correlation. In step S110, symbol synchronization or subframe synchronization is obtained and the frequency offset is estimated. Next, the Fourier transformer 430 performs Fourier transform on the received signal based on the symbol synchronization estimated by the symbol synchronization estimator 420 (S120). The cell group estimator 440 obtains frame synchronization by estimating a frame start point from a sequence of sync channel symbol intervals included in a Fourier transformed received signal (S130). The cell number estimator 440 estimates the cell number using the scrambling code information included in the pilot symbol interval (S140).

Next, subframe synchronization acquisition and frequency offset estimation of the symbol synchronization estimator 420 will be described in detail with reference to FIG.

9 is a schematic block diagram of a symbol synchronization estimator 420 according to an embodiment of the present invention.

9, the symbol synchronization estimator 420 according to an embodiment of the present invention includes a filter unit 421, a delay unit 422, a correlation unit 423, a power detector 424, a comparison unit 425, and a frequency. The offset detection unit 426 is included.

The symbol synchronization estimator 420 estimates the subframe synchronization and the frequency offset from the received signal of the synchronization channel symbol section having the time domain signal waveform as shown in FIG. In this case, the symbol synchronization estimator 420 may estimate the last OFDM symbol interval point of the subframe in which the synchronization pattern is formed and the frequency offset at that time.

)만을 추출한다. 필터부(421)는 대역 통과 필터링(bandpass filtering)을 할 수 있다. 이때, 필터부(421)의 출력 신호

의 길이는 N_S에 해당한다.The filter unit 421 filters the time-domain received signal by the bandwidth allocated to the synchronization channel, removes the guard interval, and removes signals of the center N _S subcarrier bands in which a synchronization pattern is formed among all frequency bands corresponding to the synchronization channel symbol intervals.

Extract only). The filter unit 421 may perform bandpass filtering. At this time, the output signal of the filter unit 421

The length of N corresponds to N _S.

)를 유효 심볼 길이(N_S)의 1/2에 해당하는 시간만큼 지연시킨다. 상관부(423)는 현재 입력된 수신 신호(

)와 지연부(422)의 출력 신호(

)에 대하여 유효 심볼 길이의 1/2에 해당하는 샘플 구간 동안 차등 상관을 수행한다. 이때, 상관부(423)에서 이루어지는 차등 상관은 아래의 수학식 3과 같이 표현될 수 있다.The delay unit 422 is a filtered received signal (

) Is delayed by a time corresponding to 1/2 of the effective symbol length N _S. The correlator 423 receives the currently received signal (

) And the output signal of the delay unit 422 (

Differential correlation is performed during the sample interval corresponding to 1/2 of the effective symbol length. In this case, the differential correlation made by the correlation unit 423 may be expressed as in Equation 3 below.

)을 선택하여, 이를 초기 심볼 동기로 설정한다.The power detector 424 receiving the correlation result Y of Equation 3 calculates the magnitude of the differential correlation value of the received signal, that is, the power of the received signal. The comparator 425 is a time point at which the output value of the power detector 424 becomes maximum (

), And set it as the initial symbol synchronization.

)을 추정한다.And the frequency offset detector 426 is the initial frequency offset (

Estimate).

In the exemplary embodiment of the present invention, the initial symbol synchronization and the frequency offset are detected by performing differential correlation in the domain only on the time domain signal corresponding to one synchronization channel symbol interval, but the other synchronization channel in one downlink frame is described. Differential correlation may be performed by accumulating time-domain signals in a symbol period. In addition, in order to improve the estimation performance, data obtained from a synchronization pattern of a plurality of frames may be accumulated and differentially correlated.

The Fourier transformer 430 performs Fourier transform on the received signal based on the subframe synchronization estimated by the symbol synchronization estimator 420.

Next, frame synchronization and cell group number estimation from the sync pattern of the Fourier transformed received signal, performed by the cell group estimator 440, will be described in detail with reference to FIGS. 10 to 12. First, a synchronization pattern generation of a downlink frame will be described with reference to FIGS. 10 and 11, and a method of estimating a cell group number and frame synchronization from the generated synchronization pattern will be described with reference to FIG. 12.

10 and 11 are diagrams showing a method of assigning a sync pattern shown in FIG. The downlink generating apparatus according to the embodiment of the present invention generates a synchronization pattern by combining the cell group identification code C ^(k) and the frame synchronization identification code C ^(u) . 10 and 11 illustrate a combination of these cell group identification codes and frame synchronization identification codes in the form of (k, u) (A in FIG. 10, A ′ in FIG. 11). ) Assumes four sync blocks 210.

FIG. 10 illustrates a case where a sync pattern is generated by combining orthogonal codes with only the same frame sync identifiers C ⁽¹⁾ , C ⁽²⁾ , C ⁽³⁾ , and C ⁽⁴⁾ in all cell groups in a cellular system. will be. 10 is a case in which cells 1 to 4 are classified to form cell group 1, cells 5 to 8 are cell group 2, and cells 9 to 12 form cell group 3. The code combination in the case of using C ^(k) (k is a cell group number, k = 1, 2, 3, ...) as the cell group identification code. As shown in Fig. 10, when the synchronization pattern is formed, the same frame synchronization identification code is transmitted in all cells, so that macro diversity gain can be obtained. That is, the terminal receiving the downlink frame performs correlation on the synchronization channel symbol interval to obtain frame synchronization, and detects the frame synchronization identification code. Since all cells use the same code, the correlation characteristics are improved. Synchronous acquisition performance can be improved. In this case, the number of classifiable cell groups may be set equal to the length of the code set for identification of the cell group, and the frame synchronization identification code may be set shorter than the length of the cell group discrimination code due to diversity gain. have.

FIG. 11 illustrates a case in which the frame 200 of the downlink signal is formed by using a code combination formed by assigning different frame synchronization identification codes to each cell group. In such a case, the number of frame synchronization identification codes available in the cellular system is equal to the length of the codes. When the synchronization pattern is formed as shown in FIG. 11, since various frame synchronization identification codes are used, the number of possible combinations between the cell group number and the frame synchronization identification codes increases, so that the case shown in FIG. In comparison, the number of identifiable cell groups can be increased.

The code combination information according to the embodiment of the present invention is shared between the base station and the terminal and used for cell searching of the terminal.

12 is a schematic block diagram of a cell group estimator 440 according to an embodiment of the present invention.

As shown in FIG. 12, a cell group estimator 440 according to an embodiment of the present invention includes a code storage unit 441, a correlator 442, an inverse Fourier transform 444, and a comparison unit 444. .

The code storage unit 441 stores cell group identification codes and orthogonal codes used as frame synchronization identification codes allocated to the synchronization channel symbol intervals, and stores information of code combinations forming a synchronization pattern. On the other hand, when the terminal knows in advance information (cell number and cell group information) about the cell to which it belongs and its surroundings (that is, when the terminal is in a call state or is waiting for a call), the candidate code combination is extracted and left. The cell search may be performed using this.

The correlator 442 conjugates each of the orthogonal codes included in the code combination stored in the code storage unit 441 on the basis of the estimated sync block start point based on the received Fourier-transformed sync channel symbol interval signal. Is multiplied by the Fourier transformed received signal.

That is, when the correlation unit 442 performs conjugation operations sequentially over the frequency domain on the sequences of the synchronization channel sections of the received downlink frame, operations for cell group recognition and operations for frame synchronization estimation are sequentially performed. Since it is performed, the time required for cell searching can be shortened.

The inverse Fourier transform 444 performs inverse Fourier transform on each of the cell group identification band and the frame synchronization identification band among the signals output from the correlator 442 to generate time domain signals, respectively. do. In this case, the inverse Fourier transform 444 may perform an inverse fast Fourier transform (IFFT). The comparison unit 444 selects a maximum value from the time domain signals output from the inverse Fourier transform unit 443, extracts code combination information to have a maximum value from the code storage unit 441, and selects a cell group number and The frame sync can be identified. For example, in the case shown in FIG. 10, if the code combination information extracted by the comparison unit 444 is (1, 2), the cell group to which the current terminal belongs is a cell group 1, and the terminal initiates estimation of frame synchronization. Since the viewpoint corresponds to the second sync block of the downlink frame, the starting point of the frame can be estimated.

Finally, the terminal estimates the cell number using the scrambling information included in the pilot symbol interval. At this time, since the UE knows the cell group information, the UE estimates the cell number based on the scrambling information of the cells belonging to the cell group. Here, the general cell number estimation method may be used for cell number estimation, such as a method using power sum of a subcarrier set of pilot symbols.

Although an embodiment of the present invention has been described as estimating a cell number from scrambling information of a pilot symbol interval, the cell number may be estimated using a symbol of a common channel interval including system information of a base station.

In the embodiment of the present invention, the cell group identification code is assigned to the sync pattern, but one of two bands of the sync symbol interval may be assigned a cell identification code instead of a cell group identification code to generate a downlink frame. In this case, cell number estimation using a scrambling code may be used as a process for verifying cell number information obtained from a synchronization pattern.

As described above, the components described in the embodiments of the present invention may include at least one digital signal process (DSP) processor, a controller, an application specific integrated circuit (ASIC), a programmable logic device such as a field programmable gate array (FPGA), and other electronic devices. Or it may be implemented in hardware consisting of a combination thereof. At least some of the functions or processing procedures described in the embodiments of the present invention may be implemented in software, and such software may be recorded in a recording medium. In addition, the components, functions, and processing procedures described in the embodiments of the present invention may also be implemented as a combination of hardware and software.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

As described above, according to the exemplary embodiment of the present invention, cell group search and frame synchronization may be estimated using a plurality of synchronization patterns formed in one frame. Subframe synchronization may also be estimated using the synchronization pattern.

Claims (21)

An apparatus for generating downlink signals in a cellular system based on orthogonal freqency division multiplexing (OFDM), A sync pattern is generated for each of a plurality of sync blocks forming a frame of a downlink signal—a set of a plurality of contiguous subframes within a frame, the sync pattern including a cell group number and starting point information of the frame; Pattern generator; And A time-frequency mapper for generating the downlink signal by mapping the sync pattern to a time-frequency domain Downlink signal generation device comprising a. The method of claim 1, The pattern generator, Generating the synchronization pattern by a combination of a cell group identification code for distinguishing the cell group and a frame synchronization identification code for indicating a start point of the frame, And a plurality of downlink signal generating apparatuses for allocating the sync patterns generated by different code combinations. The method of claim 2, The pattern generator, And generating the code combination such that different frame synchronization identification codes are located in each of the plurality of sync blocks in the one downlink frame. The method of claim 3, The pattern generator, And generating the synchronization pattern by the code combination generated by the same frame synchronization identification code in the downlink frame transmitted to all cells belonging to the plurality of cell groups. The method according to any one of claims 2 to 4, And the cell group identification code and the frame synchronization identification code are sets of orthogonal codes, respectively. The method of claim 5, The pattern generator, And generating the sync pattern to be located in the same OFDM symbol period in the plurality of sync blocks. The method of claim 6, The pattern generator, And generating the sync pattern in an initial OFDM symbol period in the sync block. The method of claim 7, wherein The pattern generator, And a downlink signal generation device for generating a synchronization pattern in a preset bandwidth among subcarrier bands allocated to the OFDM symbol period. The method of claim 8, The pattern generator, Dividing the set bandwidth into two frequency bands, and inserting the cell group identification code and the frame synchronization identification code into each frequency band to generate a synchronization pattern. A cell search apparatus of a terminal of an orthogonal frequency division multiplexing (OFDM) based cellular system, A frame receives a signal consisting of a plurality of sync blocks-a set of adjacent subframes, each cell representing a cell group identification code for distinguishing a cell group from a plurality of OFDM symbols and a starting point of the frame A receiver in which a synchronization pattern is formed of a combination of frame synchronization identification codes to generate a code combination; A first estimator for estimating a starting point of the sync block from the sync pattern; A second estimator for estimating a cell group number of a cell group corresponding to a cell start point and a cell to which the terminal belongs by using a start point of the sync block; And A third estimator for estimating the number of a cell to which the terminal belongs by using a cell classification scrambling code included in a pilot symbol of the frame Cell navigation device comprising a. The method of claim 10, The receiver, And a sync pattern formed in the frame includes a plurality of orthogonal codes. The method according to claim 10 or 11, wherein The first estimator, A filter unit configured to extract a signal having the sync pattern of the received frame; A delay unit delaying the extracted signal by a time corresponding to 1/2 of the OFDM symbol interval and outputting the delayed signal; A correlation unit that performs correlation with the output signal of the filter unit and the output signal of the delay unit for a time corresponding to 1/2 of the OFDM symbol interval; And A comparator for estimating the timing at which the square of the absolute value of the output signals of the correlator is maximized as a start point of a sync block; Cell navigation device comprising a. The method according to claim 10 or 11, wherein The second estimator, A cell search apparatus for storing a plurality of code combinations forming the sync pattern, taking a conjugate for each code of the stored code combination, and estimating a starting point of the received frame through a multiplication operation with the sync pattern . The method of claim 13, The second estimator, And inverse Fourier transform a result value of the multiplication operation to select a maximum value, extract a code combination corresponding to the maximum value, and estimate a start point and a cell group number of the frame. The method of claim 13, When the terminal knows the information about the current cell and the neighboring cells in advance, And extracting a plurality of code combinations estimated to form the synchronization pattern in advance, and estimating a start point of the frame and a cell group number using the extracted code combinations. A method for searching for a cell in a terminal of an orthogonal frequency division multiplexing (OFDM) based cellular system, Receiving a downlink frame including a plurality of sync blocks having a sync pattern formed of a combination of a cell group identification code for identifying a cell group to which the terminal belongs and a frame sync identification code for indicating a start point of a frame Making; Estimating a starting point of the sync block in the received downlink frame; Obtaining a cell group number and frame synchronization from the start point of the estimated sync block and the sync pattern; And Acquiring a cell number from a cell classification scrambling code included in the downlink frame Cell navigation method comprising a. The method of claim 16, And the sync pattern is formed at a start position of a sync block of the downlink frame. The method of claim 16, Starting point estimation step of the sync block, Calculating a correlation value between a plurality of subcarrier signals on which the synchronization pattern is formed and a signal for delaying the plurality of subcarrier signals by a predetermined time; And Estimating a timing at which the square of the absolute value of the correlation is maximized as a start point of a sync block; Cell navigation method comprising a. The method of claim 18, The delay time of the subcarrier signal is a time corresponding to 1/2 of the OFDM symbol length of the downlink frame. The method according to any one of claims 16 to 19, And wherein the code combination comprises a plurality of orthogonal codes. The method of claim 16, The frame synchronization acquiring step, Taking a conjugate of each orthogonal code of the code combination and performing a multiplication operation with the subcarrier signal of the synchronization pattern; Extracting a maximum value after inverse Fourier transforming a result value of the multiplication operation; And Obtaining frame synchronization information and a cell group number from the code combination corresponding to the maximum value Cell navigation method comprising a.

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