KR100985891B1 - Apparatus and method of searching cell for OFDMA based cellular mobile communication system - Google Patents

Abstract

Disclosed are a cell search apparatus and method for an orthogonal frequency division multiple access based cellular mobile communication system. According to an aspect of the present invention, there is provided a cell searching apparatus comprising: a preamble extracting unit configured to extract a preamble signal from a received frame; A reception preamble signal storage unit for storing the extracted preamble signal; A preamble sequence storage unit for storing a known preamble sequence corresponding to the index of each cell; A cell identification unit for estimating a cell index by using a correlation value between a preamble signal stored in the reception preamble signal storage unit and a preamble sequence stored in the preamble sequence storage unit; A channel estimator for estimating a channel from a base station corresponding to the estimated cell index; And a remover configured to remove a component of a preamble sequence corresponding to the estimated cell index from a preamble signal from the received preamble signal storage to generate a signal for identifying a neighbor cell of an already identified cell. After the negative cell index estimation and the channel estimation unit, the preamble signal stored in the reception preamble signal storage unit is updated with a signal for identifying a neighbor cell generated by the removal unit. According to the present invention, it is possible to estimate not only the cell where the cell search apparatus is currently located, but also the cell index of the neighboring cells and the corresponding channel.

Description

Apparatus and method of searching cell for OFDMA based cellular mobile communication system}

The present invention relates to an apparatus and method for cell searching for an Orthogonal Frequency Division Multiple Access (OFDMA) based cellular mobile communication system. The present invention relates to a cell searching apparatus and a method capable of searching even other cells of.

)와 세그먼트 인덱스(

)와의 관계는 다음 수학식과 같다.In the OFDMA mobile communication system, data transmission is usually performed in units of frames. 1 shows an example of a frame structure of a Wibro (Wireless Broadband) system based on the IEEE 802.16e OFDMA system. The WiBro system supports a time division duplex scheme, and one frame of the time division duplex scheme consists of a total of 42 OFDM symbols, and the configuration of downlink and uplink symbols is shown in FIG. Of these symbols, the preamble signal required for cell search is located at the first symbol of the frame and uses a BPSK signal amplified by 9 dB compared to the data symbol. Meanwhile, the preamble signal uses a different subcarrier set according to the segment.

) And segment index (

) Is shown in the following equation.

FIG. 2 is a diagram illustrating a preamble transmission structure for each segment of an OFDMA-based cellular mobile communication system. As shown, the subcarrier set for segment index 0, the subcarrier set for segment index 1, and the subcarrier set for segment index 2 are allocated subcarriers so as not to overlap each other.

Where 86 is the number due to the left 86 guard bands and no DC subcarriers are used.

In a cellular mobile communication system, in order to establish a connection for stable data transmission and reception between a terminal and a base station, it is required to find a cell in which a terminal is currently located, that is, a service providing cell in which a base station providing a current service is located. In the conventional cell search, only a cell index having the largest correlation value was found by calculating a correlation value between a received preamble signal and a preamble sequence stored in the terminal.

However, efficient network configuration, cell planning, and maintenance of communication network for eliminating the shadow area require identification of not only the cell where the cell search apparatus is currently located, but also surrounding cells, and estimation of channel and signal-to-noise ratio for each cell.

An object of the present invention is to provide a cell search method and apparatus capable of estimating a cell index and a corresponding channel of not only one cell in which the cell search device is currently located, but also other cells in the vicinity.

According to an aspect of the present invention, there is provided a cell search apparatus for an OFDMA-based cellular mobile communication system, including: a preamble extractor configured to extract a preamble signal from a received frame; A reception preamble signal storage unit for storing the extracted preamble signal; A preamble sequence storage unit for storing a known preamble sequence corresponding to the index of each cell; A cell identification unit for estimating a cell index by using a correlation value between a preamble signal stored in the reception preamble signal storage unit and a preamble sequence stored in the preamble sequence storage unit; A channel estimator for estimating a channel from a base station corresponding to the estimated cell index; And a remover configured to remove a component of a preamble sequence corresponding to the estimated cell index from a preamble signal from the received preamble signal storage to generate a signal for identifying a neighbor cell of an already identified cell. After the negative cell index estimation and the channel estimation unit, the preamble signal stored in the reception preamble signal storage unit is updated with a signal for identifying a neighbor cell generated by the removal unit.

The cell search apparatus may further include a time synchronizer for estimating time synchronization with respect to the received frame, and the preamble extractor may extract the preamble signal using the estimated time synchronization. The time synchronizer may include a first time synchronization metric calculated using an inter-symbol repetition characteristic in a time domain, a second time synchronization metric calculated using a CP interval, and a preamble signal. Time synchronization may be estimated using a third time synchronization metric calculated using a characteristic having two subsymbols as a relationship. In this case, the first time synchronization metric is a Schmidl time synchronization metric, the second time synchronization metric is a beek time synchronization metric, and the third time synchronization metric is a Park time synchronization metric. have. The time synchronizer may estimate the approximate time synchronization by comparing a first time synchronization metric with a first reference value, select a time window according to the estimated approximate time synchronization, and determine the second time synchronization metric and the third time synchronization. The current metric product multiplied by the time synchronization metric can be compared with the maximum value of the metric product calculated up to now, and the fine time synchronization can be estimated according to the comparison result.

The cell search apparatus may further include a segment classification unit classifying the extracted preamble signals according to segments, and transferring the preamble signals corresponding to the classified segments to the reception preamble signal storage unit.

The cell search apparatus may further include an SNR estimator for estimating a signal-to-noise ratio from a base station corresponding to the estimated cell index.

The cell identification unit compares a correlation value between the differential vector of the stored preamble signal and the differential vector of the stored preamble sequence with a predetermined threshold value and extracts a cell index having the largest correlation value among cell indexes greater than the predetermined threshold value. can do. In this case, the cell identification unit may obtain a correlation value between the real part of the differential vector of the stored preamble signal and the differential vector of the stored preamble sequence as the correlation value.

When the remover removes components of the preamble sequence corresponding to the estimated cell index, the preamble sequence corresponding to the estimated cell index and the channel estimated by the channel estimator are included in the preamble signal from the preamble signal storage unit. The signal multiplied can be subtracted.

In addition, the cell search apparatus may receive a plurality of frames, estimate a cell index for each frame, and then consider a cell corresponding to each of the cell indices estimated in each frame as the identified cell.

According to an aspect of the present invention, there is provided a cell search method for an OFDMA-based cellular mobile communication system, comprising: extracting a preamble signal from a received frame; Estimating a cell index using a correlation value between the extracted preamble signal and a known preamble sequence; Estimating a channel from a base station corresponding to the estimated cell index; Generating a signal for identifying a neighboring cell of a cell already identified by removing a component of a preamble sequence corresponding to the estimated cell index from the extracted preamble signal; And estimating a cell index by using a correlation value between the generated signal and the previously known preamble sequence.

The cell searching method may further include estimating time synchronization with respect to the received frame, and extracting the preamble signal may extract the preamble signal by using the estimated time synchronization. In this case, estimating the time synchronization may include estimating the approximate time synchronization by comparing the first time synchronization metric calculated using the inter-symbol repetition characteristic in the time domain with the first reference value; And calculating the current metric product multiplied by the second time synchronization metric calculated using the size of the CP interval and the third time synchronization metric calculated using the property that the preamble signal has two subsymbols in the time domain. Comparing the maximum value of the calculated metric product and estimating fine time synchronization according to the comparison result.

The cell searching method may further include estimating a signal-to-noise ratio from the base station corresponding to the estimated cell index.

The estimating of the cell index may include comparing a correlation value of the extracted differential vector of the preamble signal and the differential vector of the preamble sequence with a predetermined threshold and having a largest correlation value among cell indexes greater than the predetermined threshold. Can be extracted. In the estimating of the cell index, the correlation value of the real part of the differential vector of the extracted preamble signal and the differential vector of the previously known preamble sequence may be obtained as the correlation value.

The generating of the signal for identification of the neighboring cell may include: subtracting a signal obtained by multiplying a preamble sequence corresponding to the estimated cell index by a channel multiplied by the channel estimator from the extracted preamble signal; A signal for identification can be generated.

In addition, the cell search method may receive a plurality of frames, estimate a cell index for each frame, and then consider a cell corresponding to each of the cell indices estimated in each frame as the identified cell.

In order to solve the above technical problem, according to the present invention, a computer-readable recording medium recording a program for executing a cell search method for an OFDMA-based cellular mobile communication system, the method for performing a cell search method described above A computer readable recording medium having a program recorded thereon is provided.

According to the present invention described above, the cell search apparatus can estimate not only one cell currently located, but also cell indexes and corresponding channels of other neighboring cells.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and the accompanying drawings, substantially the same components are denoted by the same reference numerals, and redundant description will be omitted. In addition, in the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

3 is a block diagram of a cell search apparatus for an OFDMA-based cellular mobile communication system according to an embodiment of the present invention. Referring to FIG. 3, the cell search apparatus according to the present embodiment includes a time synchronizer 100, a preamble extractor 200, a frequency synchronizer 300, a CP remover 400, and a serial / parallel converter 500. , The FFT processor 600, the segment classifier 700, and the cell searcher 800.

를 IFFT 변환하여 시간 영역에서의 신호

로 변환한다. 그리고 각 OFDM 심볼의 마지막

샘플들이 해당 OFDM 심볼에 순환전치(cyclic prefix : CP)로서 삽입된다. 시간 영역에서 i 번째 셀 신호의 d 번째 샘플은 다음 수학식과 같이 정의된다.Prior to describing the cell search apparatus according to the present embodiment, a preamble signal received from a base station of each cell will be described. The transmitter of the base station of the i th cell is a symbol corresponding to the k th subcarrier in the frequency domain.

IFFT transforms the signal in the time domain

Convert to And the last of each OFDM symbol

Samples are inserted as cyclic prefix (CP) in the corresponding OFDM symbol. The d th sample of the i th cell signal in the time domain is defined as in the following equation.

Here, N represents the total number of subcarriers.

The impulse response of the channel in the time domain is given by the following equation.

은 l 번째 멀티패스의 채널 계수를,

은 l 번째 멀티패스의 시간 지연을, L은 멀티패스 페이딩 채널 탭의 개수를 나타낸다. 그러면 시간 영역에서 d 번째 샘플의 수신되는 프리앰블 신호는 다음 수학식과 같이 얻어진다.here,

Is the channel coefficient of the lth multipath,

Denotes the time delay of the l-th multipath, and L denotes the number of multipath fading channel taps. Then, the received preamble signal of the d th sample in the time domain is obtained as in the following equation.

는 s 번째 세그먼트의 셀들의 집합,

는 i 번째 셀로부터 전송되는 프리앰블 신호의 전력을, n(d)는 평균 0와 분산

을 가지는 i.i.d(independent identically distributed) 복소 백색 가우시안 잡음 성분을 나타낸다. here,

Is the set of cells of the s-th segment,

Is the power of the preamble signal transmitted from the i-th cell, and n (d) is the mean 0 and variance

Represents an independent identically distributed (iid) complex white Gaussian noise component with.

Referring back to FIG. 3, the time synchronizer 100 estimates time synchronization with respect to the signal frame received through the antenna, and the preamble extractor 200 uses the time synchronization estimated by the time synchronizer 100. To extract the preamble signal from the received frame.

라고 하고 FFT 사이즈는

그리고 CP의 크기를

라고 한다.4 is a flowchart illustrating a process of estimating time synchronization in the time synchronizer 100 according to an embodiment of the present invention. The received signal of the d th sample in the time domain

And the FFT size

And the size of the CP

It is called.

은 한 프레임의 총 샘플 수를 의미한다. 현재 샘플 인덱스가 총 샘플의 수 보다 작다는 것은 아직 시간 동기가 끝나지 않았다는 것을 의미하며, 이하 S401단계가 수행된다.In step S400, the time synchronizer 100 checks whether the time synchronization is finished by comparing the current sample index with the total number of samples in one frame. here

Is the total number of samples in one frame. If the current sample index is smaller than the total number of samples, it means that time synchronization has not been completed yet.

In step S401, the time synchronizer 100 calculates a first time synchronization metric using the inter-symbol repetition characteristic in the time domain. As shown in FIG. 2, when information is loaded and transmitted every three subcarriers in the frequency domain, the symbols have a similarly repeated characteristic in the time domain. In this embodiment, a time synchronization metric is calculated using this characteristic. In particular, the time synchronizer 100 estimates the approximate time synchronization using a method according to Equation 3 proposed by Schmidl. In the WiBro system, the FFT size is not a multiple of three, so it does not divide by three, resulting in three similar subsymbols that are not exactly the same.

는 다음 수학식과 같다.Where the denominator is normalized to the power value of the received signal,

Is as shown in the following equation.

는 다음 수학식과 같다.Approximate time synchronization estimated according to the above equation

Is as shown in the following equation.

을 비교한다. 이 때 메트릭 값이 특정 문턱 값 보다 큰 경우에는, 그 인근에서 프레임 시작 위치가 존재한다고 가정하고 S403단계 이후의 단계가 수행된다.In step S402, the time synchronizer 100 calculates the Schmidle time synchronization metric calculated in step S401 and a predetermined reference value.

Compare At this time, if the metric value is larger than the specific threshold value, the step after step S403 is performed assuming that the frame start position exists in the vicinity thereof.

만큼 천 이 후 다시 S400단계가 수행된다.In step S403, the time synchronizer 100 sets a time window of a predetermined size as shown in the following equation. If the metric value is smaller than the above reference value, step S404 is performed. In order to reduce the computational complexity, a certain interval in the current sample is used.

After the transition, the step S400 is performed again.

는 윈도우

의 사이즈를 의미한다.here

Windows

Means the size.

When the Schmidl time synchronization metric value is larger than a specific threshold value, the time synchronizer 100 calculates the second time synchronization metric according to the following equation proposed by Beck, using the CP interval.

은 다음 수학식과 같다.Where the denominator is normalized to the power value of the received signal and the numerator

Is the following equation.

Since it is difficult to accurately estimate the time synchronization using only the beak method using only the CP interval, in the present embodiment, a third time synchronization metric calculated by using a characteristic in which a preamble signal has two subsymbols in the time domain is conjugated. Use more. In operation S406, the time synchronizer 100 uses the signal of the real axis in the frequency domain, that is, a signal modulated by BPSK, and thus has a third time synchronization metric using a characteristic that the preamble symbol has two subsymbols that are paired with each other in the time domain. Calculate The third time synchronization metric may be calculated by using the following equation suggested by Park.

은 다음과 같다.Where the denominator is normalized to the power value of the received signal and the numerator

Is as follows.

을 비교한다. 이 때 두 메트릭의 곱

이 기존의 최고 메트릭

보다 크다면, S409단계에서 기존의 최고 메트릭

값을

로 대체하고, 기존의 미세 추정된 시간 동기도

에서 현재 샘플

로 대체한다. 만약 두 메트릭의 곱이 기존의 최고 메트릭 보다 더 작다면 바로 S410단계로 넘어가서 시간 윈도우가 끝났는지를 확인하게 된다. 만약 끝났다면 S404단계로 넘어가게 되고 그렇지 않다면 411단계로 넘어가 현재 샘플에서 한 샘플만큼 천이되게 된다.In step S407, the time synchronizer 100 multiplies the metric values calculated in each of steps S405 and S406, and becomes the highest value among the previously calculated metric values in step S408.

Compare Product of two metrics

This traditional best metric

If greater, the existing highest metric at step S409

Value

, And the existing fine estimated time synchronization

Current sample from

Replace with If the product of the two metrics is smaller than the existing highest metric, the process proceeds directly to step S410 to check whether the time window is over. If it is finished, the process proceeds to step S404. Otherwise, the process proceeds to step 411, where it is shifted by one sample from the current sample.

Finally, the estimated time synchronization is shown in Equation 11 below.

When the preamble signal is extracted by the preamble extractor 200, the frequency synchronizer 300 estimates and compensates for the frequency offset of the extracted preamble signal.

The frequency synchronizer 200 may calculate the phase of the correlation value using the CP of the preamble symbol and estimate the frequency offset. For example, the frequency synchronizer 200 may use the following equation suggested by Beck.

The CP remover 400 removes a cyclic prefix (CP) from the preamble symbol. The serial-to-parallel converter 500 converts the preamble signal into a parallel signal, and the FFT processor 660 converts the preamble signal into a signal in the frequency domain through fast Fourier transform. The preamble signal Y _k of the k-th subcarrier in the frequency domain is obtained by the following equation.

Here, N _k represents a noise component in the frequency domain, and Hi _{, k} represents a complex channel coefficient in the frequency domain.

The segment classifier 700 classifies the preamble signal from the FFT processor 600 according to the segment, and transmits the preamble signal corresponding to each classified segment to the cell search unit 800. For example, if a total of 1024 subcarriers use 86 left and right guard bands and do not use DC subcarriers, and the total number of subcarriers is 851, these subcarriers are 1 in every 3 subcarriers without overlapping each segment. The preamble signals are classified according to segment indices 0, 1, and 2 by using the feature of assigning them individually.

The cell search unit 800 receives a preamble signal of each segment from the segment classifier 700 and identifies each cell by using a preamble sequence of the received preamble signal and a preamble sequence corresponding to an index of each known cell. And estimate the channel and signal-to-noise ratio from the base station of each identified cell. The cell search unit 800 performs this cell search for each segment.

In detail, the cell search unit 800 includes a reception preamble signal storage unit 810, a cell identification unit 820, a preamble sequence storage unit 830, a channel estimator 840, and an SNR estimate as illustrated in FIG. 3. It comprises a government 850, the removal unit 860.

The reception preamble signal storage unit 810 receives a preamble signal of a segment classified by the segment classification unit 700, and stores the received preamble signal as an initial value. However, after one cell search is performed by the cell identifier 820, the channel estimator 840, and the SNR estimator 850, the preamble output from the remover 860 to search for the next cell. It receives a signal and updates its original values. The preamble sequence storage unit 830 stores a known preamble sequence corresponding to the index of each cell.

The cell identification unit 820 calculates a correlation value between the preamble signal from the reception preamble signal storage unit 810 and the preamble sequence corresponding to the index of each cell stored in the preamble sequence storage unit 830 and has the largest correlation. Extract the cell index.

를 입력받고, 프리앰블 시퀀스 저장부(830)로부터 j 번째 프리앰블 시퀀스

를 입력받는다. 수신된 프리앰블 신호

는 페이딩 채널을 통과한 것으로서 이를 그대로 이용하여 셀 식별을 수행하게 되면 성능의 열화를 가져올 수 있다. 따라서 이러한 성능의 열화를 줄이고자, 도시된 바와 같이 채널 보상부(821)를 마련한다. 채널 보상부(821)는 다음 수학식과 같 이 프리앰블 신호

의 차동 벡터(differential vector)를 계산한다. 서로 인접한 부반송파들은 비슷한 채널을 겪을 것이라는 가정을 하면, 비슷한 채널은 겪은 두 부반송파 신호를 곱하여 줌으로써 성능 열화를 막을 수 있다. 5 shows a detailed configuration of the cell identification unit 820 according to an embodiment of the present invention. The channel compensator 821 receives a preamble signal of the k-th subcarrier of the s-th segment from the received preamble signal storage 810.

Is received, the j-th preamble sequence from the preamble sequence storage unit 830

Get input. Received Preamble Signal

Is passed through a fading channel, and if the cell identification is performed using the fading channel, performance may be degraded. Therefore, to reduce such degradation in performance, a channel compensator 821 is provided as shown. The channel compensator 821 is a preamble signal as shown in the following equation.

Compute the differential vector of. Assuming that subcarriers adjacent to each other will experience similar channels, performance degradation can be prevented by multiplying the two subcarrier signals through similar channels.

에 대하여도 다음 수학식과 같이 차동 벡터(differential vector)를 계산한다. The channel compensator 821 is a preamble sequence from the preamble sequence storage unit 830 similarly to the received preamble signal.

The differential vector is also calculated for.

개 있다면 상기된 연산은

번 만큼 수행되어야 할 것이다. Here, j is a cell index that is a candidate for extracting the cell index, and the preamble sequence is totaled.

If you have

It will have to be done as many times.

와

의 상관 값을 구한다. 이 때 목표 오류 발생 확률(false alarm probability)을 일정하게 유지 시키면서 반복적으로 셀 탐색을 수행하기 위하여, 본 실시예에서는 송신기가 주파수 영역에서 프리앰블 심볼의 실수축에만 신호를 실어서 보낸다는 특성을 이용한 다. 따라서 채널 보상된 수신 프리앰블 신호

로부터 실수부 처리기(822)을 통해 실수부만 획득하고, 이 신호를 이용하여 다음 수학식과 같이 상관 값을 구한다. The cell identifier 820 uses the real part processor 822, the multiplier 823, the power detector 824, the moving averagers 825 and 826, and the divider 827 as shown.

Wow

Find the correlation value of. In this embodiment, in order to repeatedly perform a cell search while keeping a target false alarm probability constant, in this embodiment, a transmitter uses a characteristic of transmitting a signal only on a real axis of a preamble symbol in a frequency domain. . Thus channel compensated receive preamble signal

From the real part processor 822, only the real part is obtained, and the correlation value is obtained using the signal as shown in the following equation.

Where K is the total length of the preamble sequence, and the denominator is normalized to the power values of the channel compensated received preamble signals.

번 째 후보 셀 인덱스를 갖는 프리앰블 시퀀스와의 상관 값

가 얻어지게 되며, 오류 발생 확률(false alarm probability)을 일정하게 유지시키기 위해 특정 문턱값

와 비교한다. 그리고 다음 수학식과 같이, 상관 값이 특정 문턱값보다 큰 후보들 중에서 가장 큰 상관 값을 가지는 셀 인덱스

를 추출한다. By the correlation operation

Correlation value with preamble sequence having first candidate cell index

Is obtained, and a specific threshold is set to keep the false alarm probability constant.

Compare with And, as shown in the following equation, the cell index having the largest correlation value among candidates whose correlation value is larger than a specific threshold value

Extract

과의 비교 결과 그보다 더 큰 값을 가지는 셀 인덱스가 존재하지 않는다면 셀 탐색부(800)는 현재 수행 중인 세그먼트에 대한 셀 탐색을 종료하고, 아직 셀 탐색이 수행되지 않은 다른 세그먼트에 대하여 셀 탐색을 수행한다.If a certain threshold

If there is no cell index with a larger value as a result of the comparison with, the cell search unit 800 terminates the cell search for the currently performing segment, and performs the cell search for another segment for which the cell search has not yet been performed. do.

The channel estimator 840 receives the cell index extracted from the cell identifier 820 and estimates a channel from the base station corresponding to the received cell index.

는 프리앰블 시퀀스 저장부(830)로 입력되고 프리앰블 시퀀스 저장부(830)는 그 셀 인덱스에 해당하는 추정된 프리앰블 시퀀스 (

)를 채널 추정부(840)로 전달한다. 6 shows a detailed configuration of the channel estimator 840 according to an embodiment of the present invention. Referring to FIG. 6, the cell index extracted by the cell identification unit 820

Is input to the preamble sequence storage unit 830 and the preamble sequence storage unit 830 stores an estimated preamble sequence corresponding to the cell index.

) Is transmitted to the channel estimator 840.

를 추정된 프리앰블 시퀀스

로 나눠준다. 그러면 프리앰블 심볼 생성기(841)는 추정된 셀 인덱스에 해당하는 세그먼트에 상응하는 부반송파 집합에 부반송파를 할당하여 주파수 영역에서 OFDM 심볼을 생성한다. 이렇게 생성된 프리앰블 심볼은 IFFT 처리부(842)를 통해 IFFT 변환되고, 비교기와 제로 삽입기(843)는 IFFT 변환된 신호를 특정 문턱값

과 비교하여

이상인 값과 CP 구간 내에 있는 신호들을 제외한 신호들을 0으로 대체시킨다. 그리고 FFT 처리부(844)를 통해 FFT 변환되면 원하는 추정된 채널

가 얻어진다. The divider 845 receives the preamble signal from the receive preamble sequence storage 810.

Estimated preamble sequence

Divide by. The preamble symbol generator 841 then generates an OFDM symbol in the frequency domain by allocating subcarriers to a subcarrier set corresponding to a segment corresponding to the estimated cell index. The preamble symbol generated in this way is IFFT-converted through the IFFT processor 842, and the comparator and the zero inserter 843 specify a threshold value of the IFFT-converted signal.

In comparison with

Signals other than the above values and signals within the CP interval are replaced with zeros. And if the FFT is transformed through the FFT processor 844, the desired estimated channel

Is obtained.

The SNR estimator 850 receives the cell index extracted from the cell identifier 820 and estimates a signal-to-noise ratio from the base station corresponding to the received cell index.

First, the noise power can be easily obtained from the left and right guard bands. The following equation represents the estimated noise power.

Here, G represents the number of subcarriers of the left and right guard bands.

The signal power can be estimated by the following equation.

Where e _p represents the estimation error of the signal power. The signal-to-noise ratio of the received signal can be obtained by using the above-described signal power and noise power as shown in the following equation.

The remover 860 generates a signal for identifying a neighboring cell of a cell that has already been identified by removing a component of a preamble sequence corresponding to the cell index estimated from the preamble signal from the reception preamble signal storage 810.

는 프리앰블 시퀀스 저장부(830)로 입력되고 프리앰블 시퀀스 저장부(830)는 그 셀 인덱스에 해당하는 추정된 프리앰블 시퀀스 (

)를 제거부(860)로 전달한다. 7 shows a specific configuration of the removal unit 860 according to an embodiment of the present invention. Referring to FIG. 7, the cell index extracted by the cell identification unit 820

Is input to the preamble sequence storage unit 830 and the preamble sequence storage unit 830 stores an estimated preamble sequence corresponding to the cell index.

) Is delivered to the removal unit 860.

The remover 860 multiplies the estimated channel with the estimated preamble sequence by using the multiplier 861, subtracts it from the preamble signal from the reception preamble signal storage 810, and then corresponds to the preamble corresponding to the previously estimated cell index. Remove the signal. The signal from which the preamble signal corresponding to the previously estimated cell index generated by the remover 860 is removed is transferred to the receiving preamble sequence storage unit 810 to search for the next cell. As described above, the reception preamble sequence storage unit 810 updates the original signal values with the signal values received from the removal unit 860. Using the updated signal as a reception preamble signal, the operations of the cell identification unit 820, the channel estimator 840, and the SNR estimator 850 are repeated. Therefore, each time the operation of the cell identification unit 820, the channel estimator 840, and the SNR estimator 850 is repeated, a new cell index is estimated, and channel estimation and SNR estimation of the corresponding cell are performed.

8 is a flowchart of a cell search method for an OFDMA-based cellular mobile communication system according to an embodiment of the present invention. The cell search method according to the present embodiment includes the steps processed in the cell search apparatus described above. Therefore, even if omitted below, the above description of the cell search apparatus is also applied to the cell search method according to the present embodiment.

When the signal frame is received through the antenna, the time synchronization is estimated for the received frame (step S810), the preamble signal is extracted using the estimated time synchronization (step S820), and the frequency offset is estimated and compensated for (step S820). Step S830). The cyclic prefix (CP) is removed from the preamble symbol, converted into a parallel signal, and then converted into a signal in the frequency domain through fast Fourier transform (step S840). Next, when the preamble signal in the frequency domain is classified according to the segment (step S850), a cell search consisting of steps S860 to S890 to be described later is performed on each preamble signal corresponding to each segment.

First, a cell index to which a current cell search apparatus belongs is estimated by calculating a correlation value between a preamble signal extracted from a received frame and a known preamble sequence and extracting a cell index having the largest correlation (step S860). If the cell index is estimated, the channel from the base station corresponding to the estimated cell index is estimated (step S870), and the signal-to-noise ratio from the base station corresponding to the estimated cell index is estimated (step S880).

The preamble signal extracted from the received frame removes a component of a preamble sequence corresponding to the cell index estimated in step S860 to generate a signal for identifying a cell already identified, that is, a neighbor cell of the cell found in step S860. (Step S890). The removal of the component of the preamble sequence corresponding to the estimated cell index is performed by subtracting a signal obtained by multiplying the preamble sequence corresponding to the cell index estimated in step S860 by the channel estimated by step S870 in the preamble signal.

If a signal for identification of the next cell is generated in step S890, the flow returns to step S860, this time steps S860 to S890 are repeated with the signal generated in step S890 instead of the preamble signal extracted from the frame. That is, the cell index of the neighboring cell of the already identified cell is estimated by calculating a correlation value between the signal generated in step S890 and a preamble sequence known in advance and extracting a cell index having the largest correlation (step S860). The channel from the base station corresponding to the estimated cell index is estimated (step S870), and the signal-to-noise ratio from the base station corresponding to the estimated cell index is estimated (step S880). As described above, steps S860 to S890 are repeated, and neighboring cells are sequentially searched starting from the cell to which the current cell search apparatus belongs.

와 특정 문턱값

와의 비교 결과 그보다 더 큰 값을 가지는 셀 인덱스가 존재하지 않게 되면 현재 수행 중인 세그먼트에 대한 셀 탐색을 종료하고, 아직 셀 탐색이 수행되지 않은 다른 세그먼트에 대하여 셀 탐색을, 즉 S860단계 내지 S890단계를 수행한다. Although not shown, the correlation value as described with respect to the cell identification unit 820 described above in step S860

And a certain threshold

If there is no cell index with a larger value as a result of the comparison, the cell search for the currently performing segment is terminated, and the cell search is performed for another segment that has not yet been performed. To perform.

Although the above-described embodiment has been described as performing a cell search in one received frame, the above-described operation may be performed from several frames, and the cell search results for each frame may be combined to obtain a cell search result. After receiving a plurality of predetermined frames and performing a cell search for each frame, the estimated cell index is stored in each frame, and when the cell search is completed in all frames, the stored total cell index is regarded as the found cell. For example, if cell indexes 0, 1, and 2 are estimated in the first frame, and cell indexes 1 and 3 are estimated in the second frame, the cells corresponding to cell indexes 0, 1, 2, and 3 are generally identified. can do. In this case, the signal-to-noise ratio can be estimated more accurately by estimating the signal-to-noise ratio corresponding to the cell index estimated in each frame for each cell index and then taking the average value of the signal-to-noise ratio.

When signals passing through the bad channel in the first frame pass through the good channel in the second frame or the third frame, the cell index corresponding to the channel may be extracted in the second frame or the third frame. Therefore, assuming that each frame is received through an independent channel, it is possible to benefit from diversity by integrating the cell search results obtained for the various frames. For example, signals that pass through a bad channel in the first frame may pass through a good channel in the second frame or the third frame, thereby increasing the probability of estimating the cell index. In the case of using a plurality of frames, when the threshold value used in estimating the cell index is set in consideration of the number of independent frames, the probability of error occurrence can be kept constant.

Meanwhile, the above-described embodiments of the present invention can be written as a program that can be executed in a computer, and can be implemented in a general-purpose digital computer that operates the program using a computer-readable recording medium. The computer-readable recording medium may include a magnetic storage medium (eg, ROM, floppy disk, hard disk, etc.), an optical reading medium (eg, CD-ROM, DVD, etc.) and a carrier wave (eg, internet). Storage medium).

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 shows an example of a frame structure of a Wibro (Wireless Broadband) system based on the IEEE 802.16e OFDMA system.

FIG. 2 is a diagram illustrating a preamble transmission structure for each segment of an OFDMA-based cellular mobile communication system.

3 is a block diagram of a cell search apparatus for an OFDMA-based cellular mobile communication system according to an embodiment of the present invention.

4 is a flowchart illustrating a process of estimating time synchronization in the time synchronizer 100 according to an embodiment of the present invention.

5 shows a detailed configuration of the cell identification unit 820 according to an embodiment of the present invention.

6 shows a detailed configuration of the channel estimator 840 according to an embodiment of the present invention.

7 shows a specific configuration of the removal unit 860 according to an embodiment of the present invention.

8 is a flowchart of a cell search method for an OFDMA-based cellular mobile communication system according to an embodiment of the present invention.

Claims (20)

A cell search apparatus for an OFDMA-based cellular mobile communication system, A preamble extractor extracting a preamble signal from the received frame; A reception preamble signal storage unit for storing the extracted preamble signal; A preamble sequence storage unit for storing a known preamble sequence corresponding to the index of each cell; A cell identification unit for estimating a cell index by using a correlation value between a preamble signal stored in the reception preamble signal storage unit and a preamble sequence stored in the preamble sequence storage unit; A channel estimator for estimating a channel from a base station corresponding to the estimated cell index; And A remover configured to remove a component of a preamble sequence corresponding to the estimated cell index from a preamble signal from the received preamble signal storage to generate a signal for identifying a neighbor cell of an already identified cell; And a preamble signal stored in the reception preamble signal storage unit after cell index estimation of the cell identification unit and channel estimation unit of the channel estimator is updated with a signal for identification of a neighbor cell generated by the removal unit. The method of claim 1, A time synchronizer for estimating time synchronization with respect to the received frame; And the preamble extractor extracts the preamble signal using the estimated time synchronization. The method of claim 2, The time synchronizer may include a first time synchronization metric calculated using an intersymbol repetition characteristic in a time domain, a second time synchronization metric calculated using a size of a CP interval, and two preamble signals having a conjugate relationship in a time domain. And estimating time synchronization using a third time synchronization metric calculated using characteristics having two subsymbols. The method of claim 3, The first time synchronization metric is a Schmidl time synchronization metric, The second time synchronization metric is a beek time synchronization metric, And the third time synchronization metric is a Park time synchronization metric. The method of claim 3, The time synchronization unit estimates time synchronization by comparing a first time synchronization metric with a first reference value, selects a time window according to the estimated time synchronization, and selects the second time synchronization metric and a third time synchronization metric. Comparing the current multiplied metric product with the maximum value of the previously calculated metric product and estimating fine time synchronization according to the comparison result between the current metric product and the maximum value of the previously calculated metric product Navigation device. The method of claim 1, And classifying the extracted preamble signal according to a segment and transferring a preamble signal corresponding to each classified segment to the reception preamble signal storage. The method of claim 1, And an SNR estimator for estimating a signal-to-noise ratio from the base station corresponding to the estimated cell index. The method of claim 1, The cell identification unit may store the stored preamble signal.

Differential vector of

And the stored preamble sequence

Differential vector of

Comparing the correlation value with a predetermined threshold value and extracting a cell index having the largest correlation value among cell indexes having the correlation value larger than the predetermined threshold value. Where s is the s-th segment, k is the k-th subcarrier, j is the j-th preamble sequence, and superscript * represents the complex conjugate. The method of claim 8, The cell identification unit stores the stored preamble signal as the correlation value.

Differential vector of

Real part of the and the stored preamble sequence

Differential vector of

And obtaining a correlation value of. The method of claim 1, When the remover removes components of the preamble sequence corresponding to the estimated cell index, the preamble sequence corresponding to the estimated cell index and the channel estimated by the channel estimator are included in the preamble signal from the preamble signal storage unit. A cell search apparatus, which subtracts a multiplied signal. The method of claim 1, The cell search apparatus receives a plurality of frames, estimates a cell index for each frame, and then considers a cell corresponding to each of the cell indexes estimated in each frame as the identified cell. . A cell search method for an OFDMA-based cellular mobile communication system, Extracting a preamble signal from the received frame; Estimating a cell index by using a correlation value between the extracted preamble signal and a known preamble sequence Estimating a channel from a base station corresponding to the estimated cell index Generating a signal for identifying a neighboring cell of a cell already identified by removing a component of a preamble sequence corresponding to the estimated cell index from the extracted preamble signal; And Estimating a cell index using a correlation value between the generated signal and the previously known preamble sequence. The method of claim 12, Estimating time synchronization with respect to the received frame; The extracting of the preamble signal may include extracting the preamble signal using the estimated time synchronization. The method of claim 13, Estimating the time synchronization, Estimating time synchronization by comparing a first time synchronization metric calculated using an inter symbol repetition characteristic in a time domain with a first reference value; And The previously calculated metric product multiplied by the second time synchronization metric calculated using the size of the CP interval and the third time synchronization metric calculated using the characteristic that the preamble signal has two subsymbols in the time domain are conjugated. Comparing the maximum value of the metric product and estimating fine time synchronization according to a result of the comparison between the current metric product and the maximum value of the previously calculated metric product. The method of claim 12, Estimating a signal-to-noise ratio from the base station corresponding to the estimated cell index. The method of claim 12, Estimating the cell index, The extracted preamble signal

Differential vector of

And the known preamble sequence

Differential vector of

Comparing the correlation value with a predetermined threshold value and extracting a cell index having the largest correlation value among cell indexes having the correlation value larger than the predetermined threshold value. Where s is the s-th segment, k is the k-th subcarrier, j is the j-th preamble sequence, and superscript * represents the complex conjugate. The method of claim 16, Estimating the cell index, The extracted preamble signal as the correlation value

Differential vector of

Real part of the preamble sequence

Differential vector of

A cell search method comprising obtaining a correlation value of. The method of claim 12, The generating of the signal for identification of the neighboring cell may include subtracting a signal obtained by multiplying a preamble sequence corresponding to the estimated cell index by a channel estimated by the channel estimator from the extracted preamble signal. Navigation method. The method of claim 12, The cell searching method may include receiving a plurality of frames, estimating a cell index for each frame, and then considering a cell corresponding to each of the cell indices estimated in each frame as an identified cell. . A computer-readable recording medium having recorded thereon a program for executing a cell searching method for an OFDMA-based cellular mobile communication system. A computer-readable recording medium having recorded thereon a program for executing the cell searching method according to any one of claims 12 to 20.

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