KR20070100012A - Method of cell searching in mobile communication system - Google Patents

Abstract

A cell searching method in a mobile communication system is provided to obtain rapidly a cell on an initial stage by reducing the complexity of a receipt side and shortening a cell searching time. A cell searching method in a mobile communication system comprises the following several steps. At least one tone is boosted regarding a code sequence for searching for a cell. The code sequence in which the tone is boosted is transmitted to a receipt side. The tone boosting step includes the following steps. An amplitude of a code element in correspondence with the tone in the code sequence is increased, and then the code sequence is modulated via plural sub-carriers. When the amplitude of the code element is increased, the tone is boosted while overall power allocated to the code sequence is regularly maintained.

Description

Cell search method in mobile communication system {Method of cell searching in mobile communication system}

1 is a view for explaining a cell search process according to the prior art.

2 is a view for explaining a frame structure applied to a communication system in the prior art.

3 is a block diagram of a preferred embodiment of the present invention.

=10,

=3,

=59의 톤(tone)에 부스팅을 한 경우의 예를 나타낸 도면이다.FIG. 4 is a diagram for each symbol when using a CAZAC sequence having M = 1 over three symbols in a preferred embodiment of the present invention.

= 10,

= 3,

Fig. 3 shows an example of boosting at a tone of = 59.

5A and 5B show amplitude values in a frequency domain and a time domain, respectively, for all 520 kinds of sequence types that can be generated in SA-CAZAC in the case of Ng = 521 and λ = 3 to which the present invention is applied. to be.

6A and 6B illustrate a cyclic correlation for all possible 520 sequences according to a change in λ value for Ng = 521 in SA-CAZAC according to an embodiment of the present invention (1, 2, 3, 4, 15). A diagram of a CDF of circular cross-correlation.

7A and 7B illustrate a cyclic cross correlation between a sequence in which a zeroth tone is boosted in a CAZAC sequence having M = 10 in a frequency domain and a time domain, respectively, and 520 sequences having a remaining boost index, according to an embodiment of the present invention. Figure is shown.

8 is a view for explaining another preferred embodiment of the present invention.

FIG. 9 is a diagram illustrating an embodiment of a method in which a transmitting side transmits a CAZAC sequence boosted by a specific tone in a first step and the receiving side receives the CAZAC sequence to detect a cell group ID.

FIG. 10 is a diagram illustrating an embodiment of a method in which a transmitting side transmits a SA-CAZAC sequence boosted by a specific tone in a second step and the receiving side receives the CAZAC sequence to detect a cell ID.

11A and 11B show signal magnitudes in the frequency domain of a code sequence transmitted and magnitudes in the time domain after performing IFFT, respectively, according to a preferred embodiment of the present invention.

12A and 12B illustrate a correlation result of a received signal R and all sequences C ^M according to an exemplary embodiment of the present invention.

13A and 13B illustrate cyclic cross-correlation of a '99 -10 'SA-CAZAC sequence and a' 199-10 'SA-CAZAC sequence with respect to a frequency domain and a time domain, respectively.

The present invention relates to a mobile communication system. More specifically, the present invention relates to a method in which a mobile station can efficiently perform cell search in a cell-based mobile communication system.

In a mobile communication system, a mobile station uses a preamble transmitted by a broadcasting method in order to search for a cell to which it belongs. Various codes may be used to effectively search for neighboring cells using the preamble, and may be implemented by limiting a frequency or spreading code used.

These methods determine cell search performance by the sequence itself, which is a constant modulus of CAZAC as an example of a sequence with good autocorrelation characteristics and Peak to Average Power Ratio (PAPR). and zero autocorrelation) sequences. The mobile station can effectively search for cells using the CAZAC sequence. However, in an environment in which other cells are detected at the same time, such as a cell boundary region, the mobile station cannot search the neighboring cells with a simple algorithm, and calculates a correlation for a sequence corresponding to all cells to perform a full search. You have no choice but to perform this.

1 is a diagram illustrating a cell searching process according to the prior art. As shown in FIG. 1, the cell transmits a preamble 11 to allow mobile stations to distinguish the cell before transmitting data or control information. When the mobile station intends to communicate with the cell, it receives the preamble 11 transmitted from the cell and performs channel estimation using the same.

In order to distinguish the cells by receiving the preamble, the mobile station has a code set 12 composed of codes corresponding to each cell, and uses the correlation value and the signal transmitted from the correlator 13. Perform a cell search. In the cell search method described above, the cell search algorithm should be simple in order to perform the cell search efficiently.

라 하고, j 번째 셀에 할당되어 있는 프리앰블 코드를

라 하면, 셀은 제어나 데이터 정보를 방송하기 전에, 상기 프리앰블 코드를 전송하고, 그 후에 채널 추정을 정밀하게 하거나 동기를 정밀하게 맞출 수 있는 정보를 추가로 전송한다. 2 is a structural diagram of an embodiment of a frame applied to a communication system. First, the preamble code set that the cell can transmit

The preamble code assigned to the j th cell

In this case, the cell transmits the preamble code before broadcasting control or data information, and then additionally transmits information for precise channel estimation or precise synchronization.

The receiver acquires a signal of the received preamble portion and checks a preamble code set and correlation value thereof. Equation 1 shows a correlation value checking method.

는 코드셋에 존재하는 임의의 코드, N 은 코드의 길이,

는 자기상관의 지연성분을 나타낸다. 여기서,

에 대한 비용

는 수학식 2와 같이 나타낼 수 있다.In Equation 1,

Is any code in the codeset, N is the length of the code,

Represents the delay component of autocorrelation. here,

Cost for

May be represented as in Equation 2.

If the cost is calculated for all codes constituting the code set, and a code having the maximum value is selected from the calculated costs, a cell corresponding to the selected code can be searched. A cell search method using the cell cost is shown in Equation 3.

According to the prior art as described above, all the codes constituting the code set must be searched for cell searching. That is, since a search must be performed for all possible code combinations in the mobile station, there is a problem in that a cell cannot be efficiently searched due to a complicated calculation amount.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art as described above, and an object of the present invention is to provide a method for enabling a mobile station to efficiently search for a cell in a mobile communication system.

It is another object of the present invention to provide a method that can reduce the complexity of the receiving side for cell search and shorten the cell search time to enable fast initial acquisition.

Another object of the present invention is to provide a method capable of reducing cell search errors.

It is still another object of the present invention to provide a method for extending the types of code sequences available in a mobile communication system.

In one aspect of the present invention for achieving the above object, the method for transmitting a code sequence for cell search according to the present invention, in the method for transmitting a code sequence for cell search in a cell-based mobile communication system, code sequence for cell search Boosting at least one or more tones and transmitting the code sequence boosted by the at least one or more tones to a receiving side.

As a detailed feature of the invention, the at least one tone boosting step includes increasing an amplitude of a code element corresponding to the at least one or more tones in the code sequence, and performing the code sequence on a plurality of sub-carriers. It can be made including the step of modulating).

As another detailed feature of the invention, it is desirable to increase the amplitude of the code element such that the at least one tone is boosted while keeping the overall power assigned to the code sequence constant.

As another detailed feature of the present invention, it is preferable that a specific tone of the at least one or more tones forms a predetermined correspondence with an index for identifying the code sequence in a set of code sequences including the code sequence. It features.

In another aspect of the present invention, the signal processing method for cell search according to the present invention is a signal processing method for efficient cell search in a cell-based mobile communication system, the amplitude of a specific code element in a cell search code sequence Increasing and modulating the code sequence through a plurality of sub-carriers. It is desirable to adjust the amplitude of the code elements to keep the overall power allocated to the code sequence constant.

In another aspect of the present invention, a method of transmitting a code sequence for cell discovery according to the present invention is a method of transmitting a code sequence for cell discovery in a cell-based mobile communication system, the method comprising: identifying a cell group including at least one cell; Transmitting to the receiving side a first code sequence for transmitting a second code sequence for identifying a specific cell included in the cell group identified by the first code sequence. A specific tone of at least one code sequence of the first code sequence and the second code sequence is boosted and transmitted.

In another aspect of the present invention, the cell search method in the mobile communication system according to the present invention, in the cell search method in a cell-based mobile communication system, receives a code sequence signal transmitted by boosting a specific tone from the transmitting side And obtaining a code index identifying the code sequence from an element index identifying a code element corresponding to the boosted particular tone, and identifying a cell using the code index. It features.

In still another aspect of the present invention, there is provided a cell search method in a cell-based mobile communication system, the method comprising: receiving a code sequence signal in which a specific tone is boosted and transmitted from a transmitter, and a code element corresponding to the boosted specific tone; Obtaining a cell group identifier for identifying a cell group including at least one cell from an element index for identifying a; and identifying a particular cell included in the cell group using the code sequence. It features.

In another aspect of the present invention, a cell search method in a mobile communication system according to the present invention, in the cell search method in a cell-based mobile communication system, at least one or more using a first code sequence transmitted from a transmitting side Obtaining a cell group identifier identifying a cell group containing a cell, and identifying a specific cell included in the cell group identified by the cell group identifier using a second code sequence transmitted from the transmitting side And obtaining a cell identifier, wherein a specific tone of at least one code sequence of the first code sequence and the second code sequence is boosted and transmitted.

In still another aspect of the present invention, a transmitting apparatus according to the present invention is a transmitting apparatus of a cell-based mobile communication system, comprising: means for adjusting an amplitude of a code element to boost a specific tone in a cell search code sequence; And means for converting a code sequence into a signal in a time domain.

The construction, operation and other features of the present invention will be readily understood by the preferred embodiments of the present invention described below. The embodiments described below are examples in which the technical idea according to the present invention is applied to an Orthogonal Frequendy Division Multiplexing (OFDM) system.

For the purpose of illustrating the basic concepts of the present invention, DC and guard carriers, CP, channel and noise environments are not considered. In addition, for ease of explanation, it is assumed that one resource is one OFDM symbol in an OFDM system, and that a sequence is inserted in a frequency domain. The sequence to be used is described as an example of the Zadoff-Chu CAZAC sequence, but it is also possible to use other kinds of sequences having good correlation characteristics.

3 is a block diagram of a preferred embodiment of the present invention. Referring to FIG. 3, the SA-CAZAC sequence generation module 41 generates a SA-CAZAC sequence by performing data processing according to the present invention on a specific CAZAC sequence. Sequence mapping module 42 is mapped to subcarriers (sub-carrier), the SA-CAZAC sequence output from the SA-CAZAC sequence generation module 41 in the frequency domain. The IFFT module 43 converts the frequency domain signal into a time domain signal through an IFFT operation. The CP insertion module 45 inserts a protection section (CP). Code sequences transmitted to a receiver through a channel are received at the receiver by mixing noise in the transmission process. The signal received at the receiving side is removed by the CP removal module 47, the guard interval is removed, converted by the FFT module from the time domain signal to the frequency domain signal, the sequence demapping module 49 in the frequency domain Sequence demapping is done. The boost tone search module 50 searches for boosted tones in the sequence sequence in which sequence demapping has been performed, and the cell ID search module 51 searches for cell IDs using the found boosting tones. Hereinafter, the SA-CAZAC sequence generation method by the SA-CAZAC sequence generation module 41 and the cell search method by the boost tone search module 49 and the cell ID search module 50 will be described in detail.

The k-th element of the Zadoff-Chu CAZAC sequence for the code type index M of length N is expressed as Equation 4 and Equation 5 for the case where N is even and odd. Here, in the method of generating different kinds of sequences, there are various other methods such as a method of cyclic shifting the CAZAC sequence in consideration of the maximum delay spread of the channel, but for convenience of description Consider only the case where different sequences are generated by different M values.

의 경우, 수학식 6을 이용하여 코드 인덱스 M을 부스트 인덱스

로 변환한다.Boosted index according to code type M

In the case of Equation 6, the code index M is the boost index.

Convert to

은 M 값들에 대해 일대일 매핑 관계에 있다. 상기 인덱스 변환 함수의 예로는 선형 함수, 랜덤 함수 등 어떠한 형태든 상관없으며, 일대일 대응을 만족하면 된다.In Equation 6, index () represents an index conversion function,

Has a one-to-one mapping to M values. An example of the index conversion function may be any form such as a linear function or a random function, and one-to-one correspondence may be satisfied.

번째 톤(tone)을 부스팅(boosting)시키는 것을 특징으로 한다. 여기서,

번째 톤을 부스팅시킨다고 하는 것은 상기 코드 시퀀스의

번째 엘리먼트에 할당되는 전력(power)을 다른 엘리먼트에 비해 더 크게 한다는 의미이다. The present invention relates to a code sequence

Boosting the second tone. here,

Boosting the first tone means that the code sequence

This means that the power allocated to the first element is larger than other elements.

번째 톤(tone)을 부스팅(boosting)시킬 수 있는 구체적인 방법의 일 예를 설명하기 위한 것이다. 본 문서에서 특정 톤이 부스팅된 CAZAC 시퀀스를 SA(Single-tone Added)-CAZAC 시퀀스라 정의하기로 한다.Equation 7 is

It is intended to describe an example of a specific method of boosting the second tone. In this document, a CAZAC sequence in which a particular tone is boosted will be defined as a single-tone added (SA) -CAZAC sequence.

은 수학식 4 및 수학식 5에 의해 생성된 일반적 의미의 CAZAC 시퀀스이고,

, M은 N과 서로 소인 자연수 들(예를 들어, N이 소수인 경우, M=1, 2,... N-1)이다. 또한,

는 양의 실수인 부스팅 인자(boosting factor)이며,

는 다음의 수학식 8과 같다.In equation (7)

Is a CAZAC sequence of general meanings generated by equations (4) and (5),

, M are natural numbers that are prime with N (for example, when N is a prime number, M = 1, 2, ... N-1). Also,

Is a positive real boosting factor,

Equation 8 is as follows.

은

번째 톤이 부스팅된 SA-CAZAC 시퀀스를 의미하는 것으로서, 상기

번째 톤이 부스팅되기 전의 원래의 CAZAC 시퀀스의

번째 엘리먼트의 진폭에

를 곱해줌으로써 그에 할당되는 전력을

배만큼 부스팅시켰음을 의미한다. 수학식 8의

는 상기 CAZAC 시퀀스 전체에 할당되는 전력을 동일한 수준에서 유지하기 위한 것이다. 즉, 상기 CAZAC 시퀀스 전체에 할당되는 전력을 동일하게 유지하면서 상기

번째 톤을 부스팅시키기 위하여 다른 톤들에 할당되는 전력이 일정 정도 줄이는 것을 의미한다.In equation (7)

silver

Means the boosted SA-CAZAC sequence,

Of the original CAZAC sequence before the first tone was boosted.

The amplitude of the first element

Multiply by the power

It means you have boosted twice. Of Equation 8

Is for maintaining the power allocated to the entire CAZAC sequence at the same level. That is, the power allocated to the entire CAZAC sequence is kept the same.

This means that the power allocated to other tones to boost the first tone is reduced to some extent.

번째 톤을 부스팅시키기 위한 작업을 수행하는 것이다. 다른 방법으로서, 상기 CAZAC 시퀀스에 대해 IFFT를 통해 서브 캐리어에 의한 변조 과정을 거친 후에 상기

번째 톤을 부스팅시키는 것도 가능하다.Equations 7 and 8 illustrate that before the CAZAC sequence symbol is converted into a time domain signal, i.e., before performing IFFT conversion,

To boost the second tone. Alternatively, the CAZAC sequence is subjected to a subcarrier modulation process through an IFFT for the CAZAC sequence.

It is also possible to boost the second tone.

은 코드 종류 인덱스 M과 일대일 매핑 관계지만, 매 상황에 따라 같은 값일 필요는 없다. 예를 들면, M=1,2,..., N-1 일 때, 각 코드에 대해 부스팅되는 인덱스는 l=1,2,..., N-1 이어도 되고, l=35,2,11,50,... 이 되어도 된다. 또한, 여러 심볼 구간에 걸쳐 랜덤화(randomization) 혹은 평균화(averaging) 등의 목적으로 같은 코드 종류 인덱스 M의 시퀀스를 심볼에 따라 다른 부스트 인덱스를 사용하여 호핑(hopping)하는 것도 가능하다. 예를 들면, M=10인 코드 종류에 대해, 첫 번째 심볼은

을 사용하고, 두 번째 심볼은

, 세 번째 심볼은

등으로 사용하는 것이 가능하다. At this time, the boosting index

Is a one-to-one mapping with code type index M, but it does not have to be the same in every situation. For example, when M = 1,2, ..., N-1, the index boosted for each code may be l = 1,2, ..., N-1, and l = 35,2, 11,50, ... It is also possible to hop a sequence of the same code type index M using different boost indices according to symbols for the purpose of randomization or averaging over several symbol intervals. For example, for a code type with M = 10, the first symbol is

And the second symbol is

, The third symbol is

It is possible to use such as.

=10,

=3,

=59의 톤(tone)에 부스팅을 한 경우의 예를 나타낸 도면이다. 상기한 바와 같은 호핑 방법을 통해, 부스팅된 톤(tone)이 심한 페이딩(deep fading)을 겪음으로 인해 발생할 수 있는 셀 검출 에러 확률을 감소시키는 효과를 얻을 수 있다.4 is a symbol for each symbol when using the CAZAC sequence of M = 1 over three symbols

= 10,

= 3,

Fig. 3 shows an example of boosting at a tone of = 59. Through the hopping method as described above, it is possible to obtain an effect of reducing the probability of cell detection error that may occur due to the boosted tone undergoing deep fading.

가 수신측에서 수신되었을 때 다음의 수학식 9와 같이 표현될 수 있다.Sequence processed data according to equation (7)

When is received at the receiving side can be expressed as shown in equation (9).

는 시퀀스 M 이 k 번째 부반송파에서 겪는 채널의 페이딩 값이며,

은 AWGN (Additive White Gaussian Noise) 값이다.here,

Is the fading value of the channel that the sequence M experiences on the kth subcarrier,

Is AWGN (Additive White Gaussian Noise) value.

의

번째 톤이 부스팅되어 전송되었기 때문에 상기 수신측은 종래기술과 같이 상관관계를 계산하기 위한 복잡한 연산을 수행할 필요 없이 단순 FFT 복조 과정만을 수행하여 부스팅 인덱스를 검색함으로써 주파수 영역에서 셀 ID를 검출할 수 있다.

of

Since the second tone is boosted and transmitted, the receiver can detect the cell ID in the frequency domain by performing a simple FFT demodulation process and searching the boosting index without performing a complicated operation for calculating correlation as in the prior art. .

을 찾아낸 후, 다음의 수학식 11을 이용하여 부스트 인덱스

을 코드 인덱스 M'으로 변환함으로써 셀 ID를 검색하는 것이다.An example of a method of detecting a code index (cell ID) by receiving a code sequence signal of Equation 9 at the receiving side is a boost index using Equation 10 below.

After finding, boost index using Equation 11 below

To retrieve the cell ID by converting to the code index M '.

는 인덱스 역변환 함수를 나타내며, 수학식 6과 역함수의 관계에 있다. In Equation 11,

Denotes an index inverse transform function and is in inverse relation to equation (6).

=3의 경우의 SA-CAZAC에서 생성 가능한 모든 시퀀스 종류 520 가지에 대해 각각 주파수 영역과 시간 영역에서의 크기(amplitude) 값을 도시한 도면이다. 여기서, 각 시퀀스 종류에 대한 부스트 인 덱스

은 코드 인덱스 M과 같은 경우이다. (즉,

=M) 이 경우 생성 가능한 총 시퀀스의 개수는 520 개이다. 기존의(original) CAZAC 시퀀스를 사용하여 셀 탐색을 하는 경우 상관 값 비교를 위해 520×(Ng-1) 번의 복소 곱셈 연산을 수행하여 그 중 가장 큰 값을 갖는 코드 인덱스 M을 검출해야 하지만(총 521×520=270920 번의 복소 곱셈 수행), 본 발명의 일 실시예에 따른 SA-CAZAC 시퀀스를 사용하여 셀 탐색을 하는 경우에는 수신된 신호의 521 개 (Ng)의 톤(tone)의 전력 혹은 크기에 대해 단순히 최대값을 찾는 동작만을 필요로 한다.5A and 5B show Ng = 521 to which the present invention is applied;

FIG. 3 shows amplitude values in a frequency domain and a time domain, respectively, for all 520 kinds of sequences that can be generated in SA-CAZAC. Where the boost index for each sequence type

Is the same as the code index M. (In other words,

= M) In this case, the total number of sequences that can be generated is 520. When searching for cells using the original CAZAC sequence, we need to perform 520 × (Ng-1) complex multiplication operations to compare the correlation values, but detect the code index M with the largest value among them (total 521 x 520 = 270920 complex multiplications), when performing a cell search using the SA-CAZAC sequence according to an embodiment of the present invention, the power or magnitude of 521 (Ng) tones of the received signal We simply need to find the maximum value for.

Table 1 shows all possible in the time domain when the boosting factor λ varies from 1 to 15 in SA-CAZAC (just as in the above example) in the case of Ng = 521. The average PAPR and maximum PAPR are summarized for the sequence case.

λ Average PAPR [dB] Max PAPR [dB] λ Average PAPR [dB] Max PAPR [dB] One 0 0 9 0.663324 0.663377 2 0.14787 0.147882 10 0.711712 0.711768 3 0.257537 0.257558 11 0.757009 0.757068 4 0.347471 0.3475 12 0.799635 0.799697 5 0.424824 0.424858 13 0.839923 0.839988 6 0.493257 0.493297 14 0.878143 0.878211 7 0.554946 0.554991 15 0.914516 0.914587 8 0.611308 0.611356

Here, when λ = 1, the same sequence as the original CAZAC sequence before boosting. Although λ should be selected in consideration of the trade-off of PAPR and λ, as shown in Table 1, PAPR values that do not degrade significantly in the original CAZAC sequence within the range of Ng = 521 and λ ≦ 15 are selected. The PAPR value is within the operating range, so there is no problem. Of course, the case where λ> 15 is not excluded.

6A and 6B illustrate cyclic cross-correlation of all possible 520 sequences according to a change in λ value for Ng = 521 in SA-CAZAC according to an embodiment of the present invention (0 to 15). ) Is a drawing of a CDF. SA-CAZAC sequence according to an embodiment of the present invention can be confirmed that there is almost no deterioration of the cross-correlation characteristics compared to the conventional CAZAC sequence. For a very large value of lambda, the lambda value can be set in consideration of a trade-off relationship with the correlation characteristic deterioration. Accordingly, it can be seen that the proposed SA-CAZAC sequence can be used for other purposes such as correlation-based synchronization sequences in addition to cell searching.

As another preferred embodiment of the present invention, a method of boosting a specific tone of a code sequence may consider a two-step cell search method using one resource (for example, one OFDM symbol). Specifically, in a communication system, a plurality of cells are divided into cell groups including at least one or more cells, and information for identifying a specific cell group and a specific cell group are identified by a method of boosting a specific tone of the code sequence. It represents information that identifies a specific cell to which it belongs. For example, one code sequence consisting of a total of N code elements may be viewed as different N code sequences according to the index of the code element being boosted. That is, the code sequence in which the first code element is boosted and the code element in which the second code element is boosted can be clearly distinguished from the receiver side, and thus can be viewed as different code sequences.

For example, two-step detection is possible by using an index of a boosted code element, that is, a boosted index, for identifying cell group IDs, and using an original sequence before boosting for final cell ID detection. In this case, when the receiver receives a code sequence signal boosted by a specific tone, a boost index is searched to obtain a cell group ID using the found boost index, and the cell group is obtained by using the original sequence before being boosted. The cell search process may be performed by obtaining a specific cell ID belonging to. In this case, the cell group ID matched to each boost index and the specific cell ID according to each code sequence are information that the receiving side needs to know in advance or stored by signaling from the cell.

In another embodiment, a specific CAZAC sequence may be selected, and different tones may be boosted for the selected CAZAC sequence to be used as a cell search code sequence. For example, when only M = 10 is used in a CAZAC sequence with Ng = 521, the number of cell IDs that can be generated for the sequence is a total of 521 boost indices = 0 to 520. Here, the boosting factor lambda value was set to 5. For example, for the same CAZAC sequence with M = 10 as a synchronization channel used by all cells, it is possible to boost different tones for each cell. In this case, since the correlation value between the SA-CAZAC sequences boosted by different tones is very large and is regarded as almost the same sequence, it is possible to obtain initial synchronization by the same process as using the existing CAZAC sequence. In addition, a simple FFT demodulation converts a corresponding signal into a frequency domain so that cells can be distinguished only by simple size comparison.

7A and 7B show cyclic cross-correlation between a boosted zeroth tone in a CAZAC sequence with M = 10 in the frequency domain and a time domain, respectively, and 520 sequences with the remaining boost indices. Drawing. As shown in FIGS. 7A and 7B, when only boosted tones for the same M are changed, the correlation between sequences shows that the sequences can be regarded as almost identical sequences. Can be. If this method is applied to a common Synchronization Channel (SCH) channel in which all cells use the same sequence, fast synchronization can be performed, and cell discovery can be performed with the SCH.

8 is a view for explaining another preferred embodiment of the present invention, in which the embodiment described by FIG. 8 includes two or more resources (eg, two or more OFDM symbols) by a method of boosting a specific tone of a code sequence. According to an exemplary embodiment of the present invention, a cell search is performed using a two-step process.

Referring to FIG. 8, the transmitting side, that is, a specific cell, transmits the first and second code sequences to the receiving side, respectively, during two OFDM symbols. The two OFDM symbols may be located adjacent to each other or may be located apart from each other by a predetermined symbol. The first code sequence is for informing a receiver of a cell group ID for identifying a specific cell group including at least one cell, and the second code sequence is for the specific cell identified by the first code sequence. This is to inform a cell ID for identifying a specific cell included in the group. A specific tone of at least one code sequence of the first code sequence and the second code sequence is boosted and transmitted. The first and second code sequences may be transmitted in the form of reference signals such as a preamble, a midamble, and a pilot signal.

According to which code sequence of the first code sequence and the second code sequence to boost a particular tone can be classified into three transmission schemes. The first method is a method of boosting a specific tone of the first code sequence and the second code sequence does not apply boosting, and the second method is configured to boost the second code without applying boosting to the first code sequence. A method of boosting a specific tone of a sequence, and a third method, is a method of boosting a specific tone of the first and second code sequences.

In FIG. 8, a process of acquiring a cell group ID by the first code sequence is called a 'first step', and a process of acquiring a cell ID by the second code sequence is called a 'second step'. It will be called. Assuming that there are four cell groups, each cell group can be identified using four different code sequences as the first code sequence. Assuming that each cell group includes at most 130 cells, the second code group includes the second cell group. There must be at least 130 code sequences (actually, if you do not consider the two-step cell search process, you can use 520-4 = 516 sequences as the code sequence, but consider the two-step search process. Consider only the sequence.) Accordingly, the total number of cell IDs is 520 (= 4 * 130). In addition, in the example described below, it is assumed that a cell group ID including a cell transmitting the first and second code sequences is '2' and a cell ID is '128'.

If the transmitting side transmits the first and second code sequences during two symbols consecutive or separated from each other according to the first to third methods, the receiving side receives the first code sequence in the first step. The cell group ID must be retrieved, and the cell ID must be retrieved by receiving the second code sequence. According to the first to third methods, the receiving side receives a first code sequence in which the specific tone is boosted in the first step (first method, third method), or the first code in which the specific tone is not boosted. Receive the sequence (second method). In addition, the receiving side receives a second code sequence in which the specific tone is not boosted in the second step (first method) or receives a second code sequence in which the specific tone is boosted (second method, third method). . Hereinafter, a detailed operation process of the receiving side in the first and second steps will be described.

In the embodiments described below, the first and second code sequences do not overlap, and the inserted sequence length is Ng = 520 and the SA-CAZAC sequence in which a specific tone of a CAZAC sequence or any CAZAC sequence is boosted. Assume to use In generating a CAZAC sequence of Ng = 520, a method of generating a sequence of length 520 by generating a decimal length sequence of Ng '= 521 and discarding the last one may be considered. By the above method, the number of available CAZAC sequences can be increased.

First stage

(1) When the transmitting side transmits a CAZAC sequence in which a particular tone is not boosted (second method)

When the transmitting side transmits a CAZAC sequence in which a specific tone is not boosted, the receiving side correlates the received CAZAC sequence with a plurality of CAZAC sequences that may be used as a cell group ID known to the receiving side. Is used to detect the cell group ID.

For example, when four CAZAC sequences of cell group ID (Mg) = 1, 2, 3, and 4 are used as the first code sequence to identify four cell groups, the receiving side is represented by Equation 12 below. Accordingly, the cell group ID Mg 'can be detected.

은 수신 신호를 나타내는 열 벡터(column vector)이고,

은 m의 셀 그룹 인덱스를 갖는 CAZAC 시퀀스이다.here,

Is a column vector representing the received signal,

Is a CAZAC sequence with a cell group index of m.

For example, if the transmitting side transmits a CAZAC sequence with Mg = 2 in the first step and the receiving side detects a CAZAC sequence with Mg '= 2 in the received signal, a cell appearing in the first code sequence The group ID is '2'.

(2) When the transmitting side transmits a SA-CAZAC sequence in which a specific tone is boosted (first method and third method)

FIG. 9 is a diagram for describing an example of a method in which a transmitting side transmits a CAZAC sequence boosted by a specific tone in a first step and the receiving side receives the CAZAC sequence to detect a cell group ID.

Referring to FIG. 9, in the first step, the transmitter divides the entire tone by the number of corresponding cell group IDs (four here) and boosts and transmits the tone of the center of the corresponding group. FIG. 9 illustrates that a tone corresponding to a tone index 194 is boosted and transmitted when the cell group ID to which the transmitter belongs is '2'. At this time, the transmitting side and the receiving side should know information about each cell group ID region by prior appointment or signaling.

The receiving side receives the SA-CAZAC sequence transmitted from the transmitting side and performs a demodulation process to detect the boosted tone in a specific cell group search region, as shown in FIG. 9. The cell group ID corresponding to the detected specific cell group search region may be searched for. The receiving side receiving the SA-CAZAC sequence to detect the boosted specific tone can be performed by simple FFT demodulation, so the operation can be very simple. 9 is an example of the case where the number of cell group IDs is four, but when performing the final cell ID detection in step 2, it is possible to divide into more cell groups in order to perform a simpler process.

2nd step

In the above, it is assumed that there are four cell groups, and it is assumed that up to 130 cells are included in each cell group. Since the cell group ID is detected through the first step, in the second step, a specific cell ID may be detected among a maximum of 130 cells included in the specific cell group.

(1) When the transmitting side transmits a CAZAC sequence in which a specific tone is not boosted (first method)

If the transmitting side transmits the CAZAC sequence in which the specific tone is not boosted in step 2 so that the receiving side can retrieve the cell ID, the receiving side correlates the received CAZAC sequence with a plurality of known CAZAC sequences. The relationship is taken to detect the cell ID. Since the receiving side obtains the cell group ID through the first step, when the correlation between the CAZAC sequences for cell identification of the cells included in the cell group corresponding to the cell group ID and the received CAZAC sequence is obtained, a final cell is obtained. You can get the ID.

For example, assuming that 130 CAZAC sequences of Mg = 1, ..., 130 can be used, the receiving side can detect the cell ID by the following equation (13).

은 수신 신호를 나타내는 column vector 이고,

은 m의 인덱스를 갖는 CAZAC 시퀀스이다.here,

Is a column vector representing the received signal,

Is a CAZAC sequence with an index of m.

The detected cell ID is used to determine the final cell ID together with the cell group ID detected in the first step. For example, if the CAZAC sequence corresponding to Mg = 128 is transmitted in the second step, and Mg '= 130 is detected, the combination of the final cell ID is (cell group ID in the first step-in the second step). Cell ID) = (2-128).

(2) When the transmitting side transmits a CAZAC sequence boosted by a specific tone (second method, third method)

FIG. 10 is a diagram illustrating an embodiment of a method in which a transmitting side transmits a SA-CAZAC sequence boosted by a specific tone in a second step and the receiving side receives the CAZAC sequence to detect a cell ID.

Referring to FIG. 10, when a total tone is divided into 130 cell detection regions for a CAZAC sequence having a total length of 520, each cell detection region is detected by a specific cell group detected in the first step. Corresponds to each cell included in the. The cell to which the sender, i.e., the receiver, currently belongs, boosts a specific tone included in a cell search area corresponding to its cell ID and transmits it to the receiver. In the example of FIG. 10, the 509th tone included in the 128th cell search region is boosted and transmitted. When the receiver receives and demodulates the SA-CAZAC sequence as illustrated in FIG. 10, the boosted tone is detected. In this case, the cell search area number including the boosted tone may be detected as a cell ID.

As another preferred embodiment of the present invention, for a code sequence set consisting of a plurality of code sequences, a method of varying the position (boost index) of the boosted tone of each code sequence included in the code sequence set may be considered.

For example, there are a total of 520 possible code sequence types for the CAZAC sequence of Ng = 521, but since the number of boosted indexes can be set to 521 for each code sequence, a total of 521 x 520 = 270920 types It can be extended to the sequence type of. In other words, when the transmitting side and the receiving side share a CAZAC sequence set of Ng = 521, up to 520 cells can be distinguished by the CAZAC sequence set without boosting a specific tone. By varying the position of the boosted tones, up to 270920 cells can be distinguished. As a result, the number of code sequences available for cell searching is expanded.

According to this method, the receiver must perform cell search through two steps of boost index search and final code sequence search. That is, when the receiver receives a code sequence having a certain boost index from the transmitter, the receiver may search for the boost index and then detect a cell to which it belongs by searching for the final code sequence. In this case, one cell may be identified by a boost index and a code index, and thus a specific cell ID may be expressed in the form of 'A-M'. Where A is the boost index and M is the code index of the CAZAC sequence. In other words, 'A-M' means a code sequence in which the A-th tone of the M-th code sequence is boosted. In the CAZAC code sequence of Ng = 521, A has one of 0, 1, ..., 520, and M has one of 1, ..., 520.

Code transmitted when the 99th tone of the CAZAC code sequence corresponding to the code index '10' is boosted by a boosting factor λ = 5 ('99 -10 ') in a specific cell and transmitted to the receiver. The signal magnitude in the frequency domain of the sequence and the magnitude in the time domain after performing the IFFT are shown in FIGS. 11A and 11B, respectively.

For convenience of explanation, if the reception side receives the signal transmitted by the transmission side as it is, the signal received in the time domain is r (column vector) and the frequency domain signal after FFT is R (column vector), 10 can be used to detect the boost index. When the boost index is detected, the received code index and the 520 sequences C ^M (M = 1, 2, ..., 520) (column vector) which are known to the receiver by using the following equation (14) After calculating the correlation, find the code index that corresponds to the largest value.

12A is a diagram illustrating a correlation result between a signal R received in the frequency domain and all sequences C ^M under the above conditions. If the time domain value c ^M of the signal r and C ^M received in the time domain is known in advance, the correlation result is shown in FIG. 12B. That is, M 'may be detected in the frequency domain with respect to the received signal, or M' may be directly detected in the time domain without detecting the boost index.

When boosting a specific tone with different boost indices for the same CAZAC sequence, for example, the SA-CAZAC sequence with '99 -10 'and the SA-CAZAC sequence with' 199-10 'do not maintain low correlation. Do not. 13A and 13B illustrate cyclic cross-correlation of a '99 -10 'SA-CAZAC sequence and a' 199-10 'SA-CAZAC sequence with respect to a frequency domain and a time domain, respectively. In other words, when the position (boost index) of the boosted tone is different for a specific CAZAC sequence, separation using correlation is difficult. That is, in a code sequence that is regarded as the same signal and has an 'A-M' index, the value of A is difficult to detect through correlation.

The technical features of the present invention as described above are applicable to the 3GPP Long Term Evolution (LTE) system, which is currently under discussion. Cell search methods discussed in 3GPP LTE are classified into three categories.

1) In case of performing synchronization acquisition and cell identification with different SCH (Synchronization Channel) sequence for each cell

2) SCH is a case where all cells perform synchronization acquisition using the same sequence, and cell identification by reference signal (reference signal, pilot signal)

3) Cell group identification and synchronization acquisition using a sequence of different SCHs for each cell group, and final cell identification by reference signal

In all three cases, the specific cell search method according to the preferred embodiments of the present invention as described above may be applied. In particular, in the case of 2), if the technical feature according to the present invention is applied, the effect of using the same sequence for each cell in the SCH can be obtained without the need for a reference signal.

In addition, the CP (Cyclic Prefix) for the OFDM symbol of the current LTE downlink is to use one of two cases 'long CP' and 'short CP' in one subframe (subframe). The SA-CAZAC sequence according to the present invention has an advantage of finding a boosted tone index regardless of whether it is 'short' or 'long' even when the FFT is performed based on the 'short CP'.

In the above, the change of the code sequence according to the technical features of the present invention is limited to the purpose for cell searching, but other functions of the communication system performed by using the code sequence such as initial synchronization, time and frequency synchronization acquisition, channel estimation, etc. It is obvious that the technical features according to the present invention can be applied in performing the same.

It is apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit and essential features of the present invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

According to the present invention, the following effects can be obtained.

First, since the cell ID can be detected by a simple size comparison after FFT demodulation at the receiver, that is, the UE reduces complexity of the receiver for cell search.

Second, by shortening the cell search time, fast initial acquisition is possible.

Third, fast cell search for handover is possible.

Fourth, cell detection error probability is reduced during cell search.

Fifth, by using a common SCH, it can be used to obtain a fast initial synchronization, and by performing cell division with it, two purposes of resource saving and fast cell search can be achieved.

Sixth, the available sequence types can be extended for cell searching.

Seventh, in an OFDM symbol using two or more CP lengths, cell searching may be performed regardless of CP lengths.

Eighth, while exhibiting the effects described above, no deterioration occurs in the main characteristics (excellent correlation characteristics, low PAPR, etc.) of the conventional CAZAC sequence.

Claims (14)

A method of transmitting a code sequence for cell search in a cell-based mobile communication system, Boosting at least one or more tones for the cell search code sequence; And And transmitting the code sequence boosted by the at least one tone to a receiver. The method of claim 1, wherein the at least one tone boosting step comprises: Increasing the amplitude of code elements corresponding to the at least one or more tones in the code sequence; And modulating the code sequence through a plurality of sub-carriers. The method of claim 2, Increasing the amplitude of the code element such that the at least one tone is boosted while keeping the overall power allocated to the code sequence constant. The method of claim 1, A specific one of the at least one tone comprises a predetermined correspondence with an index for identifying the code sequence among a set of code sequences including the code sequence. Transmission method. The method of claim 4, wherein And if the index of the code sequence is L, the specific tone is an L th tone. The method of claim 1, The code sequence is a code sequence transmission method for cell search, characterized in that the CAZAC sequence. A signal processing method for efficient cell search in a cell based mobile communication system, Increasing the amplitude of a particular code element in the cell search code sequence; And And modulating the code sequence through a plurality of sub-carriers. The method of claim 7, wherein And adjusting the amplitude of the code elements other than the code element to maintain a constant total power allocated to the code sequence. A method of transmitting a code sequence for cell search in a cell-based mobile communication system, Transmitting a first code sequence for identifying a cell group including at least one cell to a receiving side; And Transmitting to the receiving side a second code sequence for identifying a specific cell included in the cell group identified by the first code sequence, And a specific tone of at least one code sequence of the first code sequence and the second code sequence is boosted and transmitted. In the cell search method in a cell-based mobile communication system, Receiving a code sequence signal from which a specific tone is boosted and transmitted from a transmitting side; Obtaining a code index identifying the code sequence from an element index identifying a code element corresponding to the boosted particular tone; And And identifying a cell by using the code index. The method of claim 10, And a predetermined correspondence relationship between the element index and the code index. In the cell search method in a cell-based mobile communication system, Receiving a code sequence signal from which a specific tone is boosted and transmitted from a transmitting side; Obtaining a cell group identifier identifying a cell group comprising at least one cell from an element index identifying a code element corresponding to the boosted particular tone; And And identifying a specific cell included in the cell group by using the code sequence. In the cell search method in a cell-based mobile communication system, Obtaining a cell group identifier for identifying a cell group including at least one cell using a first code sequence transmitted from a transmitting side; And Obtaining a cell identifier identifying a specific cell included in the cell group identified by the cell group identifier using a second code sequence transmitted from the transmitting side, And a specific tone of at least one code sequence of the first code sequence and the second code sequence is boosted and transmitted. In the transmitting device of a cell-based mobile communication system, Means for adjusting the amplitude of the code element to boost a particular tone in the cell search code sequence; And Means for converting the code sequence into a signal in a time domain.

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