KR101208540B1 - Method And Apparatus For Initial Cell Search Using A Character Of Synchronization Code In CDMA Mobile Communications System - Google Patents

Abstract

The present invention relates to an initial cell search method and apparatus using synchronization code characteristics in a code division multiple access mobile communication system. According to the present invention, a predetermined number of candidate codes are selected by obtaining a correlation with a received signal using only a predetermined length portion of a sync code, and then an accurate sync code and timing sync are obtained by using the entire length of the selected candidate code. In the initial cell search, the amount of computation can be reduced while maintaining the accuracy of the synchronization estimation.

CDMA, TDD-LCR, initial cell search, sync code length, timing sync

Description

Method and Apparatus for Initial Cell Search Using A Character Of Synchronization Code In CDMA Mobile Communications System} in code division multiple access mobile communication system

1 is a flow chart illustrating the overall initial cell search process.

2 illustrates a subframe structure in TDD-LCR.

3 is a graph showing a correlation value using a SYNC_DL code having a length of 64 chips.

4 is a graph showing a correlation value using a SYNC_DL code having a length of 32 chips.

5 is a flowchart for explaining an initial cell search method according to an embodiment of the present invention.

6 is a view for explaining a method of selecting a candidate code of the initial cell search method according to an embodiment of the present invention.

7 is a view for explaining a method of estimating SYNC_DL code and timing synchronization used for a received signal in an initial cell search method according to an embodiment of the present invention.

8 is a diagram showing a feature configuration of an initial cell search apparatus according to an embodiment of the present invention.

The present invention relates to a code division multiple access (CDMA) mobile communication technology, and more particularly, to an initial cell search method and apparatus using a synchronization code characteristic.

In the TD-SCDMA system, a cell search process of a mobile station can be performed in four steps, through which a downlink sync code (SYNC_DL), a basic midamble code, a scrambling code, a frame sync, and a BCH information And chip timing information.

1 is a flowchart illustrating an overall initial cell search process.

First, step 1 is a step in which the terminal searches for a downlink pilot time slot (hereinafter referred to as "DwPTS"). The terminal finds the downlink sync code SYNC_DL used in the cell to search using 32 possible downlink sync codes SYNC_DL without knowing the cell information to be searched, and sends it to DwPTS. Synchronize timing

Thereafter, step 2 is a step of identifying a scrambling code and a midamble code, and the downlink synchronization code (SYNC_DL) of DwPTS found in step 1 corresponds to one code group having four basic midambles. The terminal may find the basic midamble used in the cell by a try and error method among the four basic midambles. In addition, since the basic midamble is associated with the scrambling code, the scrambling code can be found.

Step 3 is to perform multi-frame synchronization. That is, the terminal finds the MIB of the BCH multiple frame from the QPSK phase modulation of DwPTS for the P_CCPCH midamble.

Finally, step 4 is to read the information of the broadcast channel (BCH) through the information obtained through the above-described steps 1 to 3.

In operation 1 of the above-described process with reference to FIG. 1, the received signal is correlated with all 32 downlink sync codes (SYNC_DL) during the entire subframe, and the correlation value is obtained. It requires a lot of iterations and a lot of computation.

Specifically, in the initial cell search method of the 3GPP TDD LCR system, cell synchronization is estimated using a value having the largest correlation between the received signal and the downlink synchronization code (SYNC_DL). However, due to the influence of the multipath fading channel, the value of the correlation becomes unreliable. In order to attenuate this, the correlator or matched filter outputs are accumulated over several subframes and averaged to track the maximum value. However, this system requires a memory equal to the number 32 of the length (6400 chip), the oversample (n), and the downlink synchronization code of one subframe.

As a way to solve this problem, only the most correlated values are stored per subframe, the most frequent code and the synchronization point are tracked during several subframes, and one subframe is divided into several areas to correlate them. The method of applying the technique is proposed.

However, these methods do not show satisfactory performance in terms of detection performance, required memory capacity, and computation amount. Thus, in order to obtain the synchronization code and timing information used for the received signal during the initial cell search, There is a need for a technique for reducing the memory capacity and the amount of computation required while having high detection performance.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide a method for acquiring a synchronization code and a timing synchronization used for a received signal with high detection performance with a small amount of calculation using the characteristics of the synchronization code.

The initial cell search method according to an embodiment of the present invention for achieving the above object is at least one candidate according to the size of the correlation value between the predetermined length portion, which is part of each sync code of the sync code set and the received signal Selecting a code; And acquiring a synchronization code and a timing synchronization used for the received signal according to a correlation value between the received signal and the selected full length portion of the at least one candidate code.

In this case, the predetermined length may be set such that the difference between the case where the correlation value between the predetermined length portions of each sync code is autocorrelation and the case where the correlation value is correlated is greater than or equal to a preset threshold value. Summing during the H subframes the correlation values computed using the predetermined length portion of the sync code during one subframe; And selecting N candidate code indices in order of the larger values among the summed correlation values.

The candidate code selecting step may further include: storing, during H subframes, a maximum value of the correlation values calculated using the predetermined length portion of the synchronization code during one subframe; And selecting N candidate code indices in the order of high frequency among the stored maximum values. The candidate code selecting step includes dividing one subframe into a plurality of regions and in each of the regions. Storing a maximum value of the correlation values calculated using the predetermined length portion of a synchronization code for H subframes; And selecting N candidate code indices in order of high frequency among the stored maximum values.

The synchronization code used for the received signal may further include: summing, for G subframes, the correlation values computed using the total length of each candidate code during one subframe; And selecting a candidate code representing the maximum value among the summed correlation values as a synchronization code used for the received signal, and calculating the total length of each candidate code during one subframe. Storing a maximum value of the correlation values for G subframes; And selecting a candidate code stored at the highest frequency among the stored correlation values as a synchronization code used for the received signal. Alternatively, one subframe is divided into a plurality of regions, and each of the Storing, during G subframes, a maximum value of the correlation values calculated using the sync code total length in regions; And selecting a candidate code stored at the highest frequency among the stored correlation values as a synchronization code used for the received signal.

The timing synchronization may further include: storing a timing index indicating a maximum value of correlation values calculated using the candidate code total length for each candidate code for each subframe; And selecting a timing index having the highest storage frequency among the timing indexes stored for the candidate code selected as the synchronization code used for the received signal as timing synchronization of the received signal. In the synchronization acquiring step, when a difference between the maximum value and the second largest value among the correlation values added during the G subframes is equal to or greater than a preset threshold, a synchronization code indicating the maximum value is used for the received signal. Select as a sync code or otherwise sum up during the G subframes even if the difference between the maximum value and the second largest value among the summed values during the G subframes is not greater than or equal to a preset threshold; A sync code representing the maximum value among correlation values is added to the received signal. It can also be selected as a used sync code.

In addition, each of the sync codes has a length of 64 chips, the predetermined length is 32 chips, and a predetermined length portion of the sync code may be a 32-chip portion of the first half of the sync code. The number may be four.

A synchronization code acquisition method used for a received signal according to another embodiment of the present invention includes selecting a candidate code according to a predetermined length portion of each sync code of the sync code set and the correlation values of the received signal. step; And acquiring a synchronization code used for the received signal according to the magnitude of a correlation value of the received signal with a full length portion of the selected candidate code.

In addition, a timing synchronization acquisition method according to another embodiment of the present invention includes selecting a candidate code according to a magnitude of correlation values between a predetermined length portion of each synchronization code of a synchronization code set and a received signal; And acquiring, as timing synchronization, a position at which the maximum value among the correlation values with the entire length portion of the candidate code selected appears.

Lastly, an initial cell search apparatus according to another embodiment of the present invention includes: a candidate code selecting module configured to select a candidate code according to a correlation between a predetermined length portion of each sync code of a sync code set and a received signal; And a synchronization code and a timing synchronization acquisition module for acquiring a synchronization code and a timing synchronization used for the received signal according to a correlation value of the received signal with a full length portion of the candidate code selected by the candidate code selection module. Characterized in that.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form, centering on the core functions of each structure and device, in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

The present invention relates to an initial cell search method and apparatus, and more particularly, to a method of estimating a DwPTS search, that is, a downlink sync code (SYNC_DL), and thus obtaining a timing sync as in step 1 of FIG. 1. As described above, the present invention obtains the correlation between the subframe and 32 intact downlink synchronization codes (SYNC_DL) in step 1 of FIG. Suggest ways to remove it. In one embodiment of the present invention, candidate groups are selected from 32 downlink sync codes (SYNC_DL) through operations with codes of some lengths rather than the entire lengths of sync codes, and then all of the selected downlink sync codes (SYNC_DL) only. We propose a method to reduce the amount of computation by performing code and timing estimation using length. To this end, the initial cell search method according to the present invention will be described in detail through features and advantages and disadvantages of various methods used for general synchronization code estimation and timing synchronization acquisition.

First, a method of using the maximum value of the correlation value in one general subframe will be described.

This method finds the maximum value by obtaining all correlations between the signal received in one subframe and the downlink sync code (SYNC_DL) available in the cell. At this time, reception synchronization is achieved. The method of finding the maximum value by obtaining correlation in one subframe received in this way is easy to implement. However, in a low SNR and multipath fading channel environment, the reliability of the correlation may be low because the level of the received signal is changed rapidly. Furthermore, when the sampling of the received signal is reduced, the timing error may be greater.

Next, a method of using the average by accumulating correlation values over several subframes will be described.

According to this method, a correlation between a received signal and all downlink sync codes (SYNC_DL) available in a cell is obtained, accumulated over several subframes, and averaged. When the largest value is found among the average values, reception synchronization is achieved at this time. According to this method, a timing correlation with high reliability can be obtained by reducing the level variation of the received signal due to fading effects.

However, since all correlations must be stored for 32 codes in each subframe received over several subframes, the memory increases. Furthermore, when a comparator that sequentially finds the maximum correlation when over-sampling a received signal is implemented, the burden of having to repeat comparison and storage by "6400 占 32 oversampling ratio" is imposed. In addition, if the number of subframes cannot be infinitely limited, the number of subframes may be limited, thereby causing the error value of a severely incorrect correlation to be accumulated and averaged by noise, which may cause performance degradation.

Next, a description will be given of a method of tracking the most frequent code and sync point for several subframes.

When the probability determined over several subframes is examined, the frequency of the maximum correlation value of the same code used for the received signal increases. This frequency of occurrence is used to remove the error correlations and average them with the remaining probable timing candidates. In this case, satisfactory timing synchronization is obtained.

According to this method, if only the index and correlation value of the code having the largest correlation value are stored during one subframe, the required memory size per subframe is significantly reduced.

However, in order to track high frequency codes and sync points during several subframes, many subframes need to be observed, and when a small number of subframes are observed, accuracy decreases. In addition, when the channel environment is not good, the correct downlink synchronization code cannot be found, and thus more subframes must be observed, otherwise the accuracy is significantly reduced.

Finally, a method of using a maximum value of correlation by dividing a subframe into several areas will be described.

One subframe is divided into several regions, correlations in each region are obtained to obtain a maximum value, and a maximum value for each region is added by selecting a code and region having the largest value during multiple subframes. The point with the highest frequency in the last selected area is selected as the point of synchronization.

According to this method, since the maximum correlation value for each region is summed over several subframes, only the number of correlation values need to be stored in the subframe to prevent the increase of memory. Can be. In addition, the initial synchronization with high reliability is obtained with only a few frames, rather than having only one maximum correlation value during one subframe.

However, since the maximum correlation value of all 32 SYNC_DL codes has to be obtained, it still requires a large amount of computation.

Accordingly, the present invention proposes a method of reducing the amount of computation in initial cell search by obtaining a correlation using only a specific length of a part of the sync code by using the characteristics of the sync codes (SYNC_DL codes) located in DwPTS among subframes. do. As a concrete example, the subframe structure of the TDD-LCR and the characteristics of the synchronization code included in the double DwPTS will be described below.

2 is a diagram illustrating a subframe structure in a TDD-LCR.

In the 3GPP TDD LCR system, the downlink sync code SYNC_DL is located in the DwPTS following the first time slot as shown in FIG. 2. The DwPTS is 96 chips long and consists of a 32 chip guard region and 64 chips of SYNC_DL code. There are 32 types of SYNC_DL codes, and one SYNC_DL code is allocated to each base station.

In general, when searching for an initial cell, the code is estimated by correlating with 32 SYNC_DL codes during one subframe period, and initial synchronization is performed. However, since all the codes are correlated, the amount of computation increases.

FIG. 3 is a graph showing a correlation value using a SYNC_DL code having a length of 64 chips, and FIG. 4 is a graph showing a correlation value using a SYNC_DL code having a length of 32 chips.

When the correlation with the received signal is performed using the SYNC_DL code having a length of 64 chips, the auto-correlation value is compared with the maximum value among the cross-correlation values among other SYNC_DL codes as shown in FIG. 3. That is, the SYNC_DL code information and the timing information can be obtained using a property of having a high correlation value with the same code as the code used for the received signal. However, even when the correlation with the received signal is obtained using the SYNC_DL code of 32 chips in length, it can be seen that the autocorrelation value is two times higher than the cross-correlation values between other SYNC_DL codes as shown in FIG. 4.

Accordingly, in one embodiment of the present invention, a predetermined high likelihood that the autocorrelation value between the sync codes is used for the received signal using only a sync code of a length such that the autocorrelation value is greater than or equal to a predetermined threshold for discrimination from other cross-correlation values. After selecting the number of candidate codes, a method of obtaining timing synchronization with the final SYNC_DL code used for the received signal is again obtained by correlating the received codes with the candidate codes having the total length of 64 chips.

According to a specific embodiment of the present invention, a sync code used for a received signal using only 32 chips of half of the candidate code selection step among SYNC_DL codes having a total of 64 chips in length and then using four selected candidate codes in full length A method of obtaining timing synchronization is disclosed. In the above-described embodiment, even when the correlation with the received signal is performed using only 32 chip lengths, as shown in FIG. 4, the correlation between the autocorrelation value and the maximum value of the cross-correlation value is two times or more. The predetermined value for distinguishing between the correlation value and the cross-correlation value may be regarded as 16.

As described above, instead of performing the correlation operation using the total lengths of the 32 SYNC_DL codes, the candidate amount can be significantly reduced by selecting the candidate codes using only some of these lengths. However, when estimating the type and timing information of the sync code finally used for the received signal using only the above-described partial length, for example, 32 chip length, the accuracy may be deteriorated. Therefore, in the above-described embodiment of the present invention, Candidate codes are selected using some lengths, and the selected candidate codes are used for their entire lengths to enable accurate synchronization code estimation and timing information acquisition.

In order to describe the initial cell search method for acquiring the synchronization code and the timing information according to the present invention in more detail at each step, the general synchronization code and the timing synchronization acquisition process will be described below.

In the initial cell search, the UE finds the DwPTS in the subframe without information and timing information on the cell to be searched. As shown in FIG. 2, the DwPTS includes a 32 chip guard region and a 64 chip SYNC_DL code, and one of 32 SYNC_DL codes is selected and used.

A typical initial cell search method uses a correlation of the received signal with 32 SYNC_DL codes of 64 chips in length. In addition, in order to prepare for the effect on the channel, a correlation may be calculated and accumulated for several subframes to estimate synchronization. The process is as follows.

Received signals r = {r ₀ , r ₁ , ...} are generally oversampled and received rather than chip rates. On the other hand, the l-th SYNC_DL code may be represented by S ^l = (s ₀ ^l , s ₁ ^l , ..., s ₆₃ ^l ). s _i ¹ is a QPSK symbol, 0 ≦ ^l ≦ 32 is the index for the SYNC_DL codes, and i is the chip index. The equation for the correlation between the received signal and the l-th SYNC_DL code may be defined as follows.

와 그 위치 정보

는 다음과 같은 최대 유사 관계 추적 (Maximum Likelihood Detection)방법에 의해 구할 수 있다. Thus, downlink sync code having a correlation maximum

And its location information

Can be obtained by the following Maximum Likelihood Detection method.

)로 추정하고, 그 값이 발생한 곳을 최종 동기지점(

)으로 추정한다.Where OSR represents the oversampling rate. Through this process, the code having the maximum correlation value is converted into a downlink sync code (

), And where the value occurred is the final sync point (

Estimate).

However, tracking SYNC_DL code and timing information with only one subframe information increases the probability of tracking incorrect information. Therefore, this error probability can be reduced by accumulating the maximum value of correlation for several subframes. Of course, instead of accumulating all of the correlation values of the 32 synchronization codes in a plurality of subframes in the above description, only the correlation values of the synchronization codes representing the maximum values in one subframe are stored, and then the synchronization codes having a high frequency. And a method for acquiring timing synchronization, or a method for acquiring a timing synchronization with a high frequency by accumulating one subframe into a predetermined region and accumulating a synchronization code having a maximum value in each region. . However, the following description will focus on a method of acquiring a synchronization code and a timing synchronization using a maximum value by storing all correlation values with all 32 synchronization codes during a predetermined frame.

In the above-described example, when the correlation value is accumulated during the H subframes by the number of subframes that accumulate the correlation value, the previous equation may be expressed as follows.

As such, a code indicating the maximum value by accumulating correlation values during H frames is estimated as a sync code, and thus, accuracy can be improved by acquiring timing information. However, a large amount of computation is required when all correlations are obtained for 32 SYNC_DL codes having 64 chips in length during H frames.

Therefore, in one embodiment of the present invention, after selecting the candidate code through the correlation between the 32 received SYNC_DL codes and the received signal, only the first 32 chips of the 64 chips are selected, and then the correct sync code A method of obtaining timing information is proposed. In the preferred embodiment of the present invention, the above-described candidate code selection step is not selected through the correlation value in one frame, but the correlation value using 32 chips of the synchronization code is accumulated for H frames, We propose a method of selecting four codes as candidate codes in large order among the values, and then transferring them to the step of obtaining the correct sync code and timing sync. This method will be described in detail with reference to the drawings.

5 is a flowchart illustrating an initial cell search method according to an embodiment of the present invention.

First, the candidate code selection step of the initial cell search method according to the embodiment shown in the left side of FIG. 5 will be described.

In a preferred embodiment of the present invention, only the first 32 chips of the 64 chip length sync code are used in step S501 during the candidate code selection step. Due to the nature of the sync code, it is easy to distinguish between the autocorrelation value and the value representing the maximum value among the cross-correlation values as shown in FIG. 4 only by the length of 32 chips. However, the present invention is not necessarily limited thereto as long as it includes the features of the present invention.

으로 표현될 수 있으며, 여기서

은 QPSK 심볼이고, l은 SYNC_DL 코드들에 대한 인덱스이며, 0≤l≤31을 만족한다. The l-th SYNC_DL code with only the first 32 chips selected

Can be expressed as

Is the QPSK symbol, l is the index for the SYNC_DL codes, and satisfies 0 ≦ l ≦ 31.

Meanwhile, in step S502, a correlation between the received signal and the 32 SYNC_DL codes obtained in step S501 is obtained. The equation for the correlation between the received signal and the 1 st SYNC_DL code may be expressed as follows.

The correlation as shown in Equation 4 is repeated for one subframe to obtain a maximum value for each code in step S503. In order to repeat this process during the H subframe, step S504 determines whether correlation accumulation has been performed during the H frame, and if it is not the H frame, proceeds to step S505 to increase the subframe index and repeat the above-described process, If accumulation is completed during the H frame, the flow proceeds to step S506. In this case, the maximum value of the accumulated correlation may be expressed as follows.

Thereafter, in step S506, four of the 32 largest K values are selected, and in step S507, corresponding code indices, for example, a, b, c, and d, are shown in the second step shown on the right side of FIG. Pass it to.

The second step according to an embodiment of the present invention is to obtain accurate sync code and timing sync using the total length of the candidate code of 64 chips selected through the first step. Specifically, referring to the example related to FIG. 5, in step S508, correlations with the received signal are obtained for each candidate SYNC_DL code in step S509, using 64 chips, which are the total lengths of the four candidate codes received in step S507.

In a preferred embodiment of the present invention, the correlation calculation is not performed only in one subframe, but the correlation value is accumulated over a predetermined frame, and then the maximum value thereof is used to enable more accurate sync code estimation.

That is, the correlation value as described above in step S510 is repeated for several subframes, and the maximum value of the correlation is accumulated for each code. The accumulation of such correlation values may be repeated only for a predetermined G frame, or may be repeated until a difference between the largest value and the next largest value among the accumulated correlation values is greater than or equal to a preset threshold. Step S511 obtains the largest and second largest values of the accumulated correlation values accordingly, and in step S512 repeats only the number of preset G subframes regardless of whether the difference is greater than or equal to the threshold. If set to, it is determined whether the correlation value has accumulated by the number of subframes. Accordingly, if the difference between the first largest value and the second largest value is greater than or equal to a predetermined threshold value, or if correlation values are accumulated by a predetermined G subframe, the process proceeds to step S514; otherwise, the process proceeds to step S513. After increasing the index of the frame, the above-described process may be repeated.

Thereafter, in step S514, the code having the largest value among the accumulated correlation values is estimated as the SYNC_DL code used for the received signal.

On the other hand, when the maximum cumulative value of the correlation value obtained in step S510 is stored for each SYNC_DL code index, the index generated the maximum correlation value. Through this, an index having the highest frequency in which the maximum value occurs in the SYNC_DL code selected as the synchronization code used for the received signal in step S514 may be obtained as timing synchronization in step S516.

A synchronization code acquisition method, a timing synchronization acquisition method, and an initial cell search method including the same according to an embodiment of the present invention described above with reference to FIG. 5 include a first step of selecting a candidate code and a final synchronization code and timing synchronization. In the second step, the maximum value for each code among the correlation values calculated during one subframe is repeatedly accumulated for a predetermined frame for more accurate initial cell search, and then the synchronization code and the maximum value among the accumulated values are accumulated. And / or acquiring timing, but storing only the index of the synchronization code representing the maximum correlation value among the 32 synchronization codes during one subframe as described above according to the required accuracy, arithmetic amount and storage capacity, etc. It can be used together with the method of dividing the subframe into predetermined areas and storing the maximum value of each area. Yes, it is obvious to those skilled in the art.

In the case of using the method of storing only the index of the code having the largest correlation value for each subframe in the candidate code selection step, the final synchronization code, and the timing acquisition step, the burden of the storage capacity of the memory is higher than the aforementioned method. It can be reduced further, but it is necessary to set H and G to a larger number in order to increase the reliability. Therefore, an appropriate combination can be implemented in consideration of the accuracy of the required synchronization estimation, memory capacity, and computation amount.

Hereinafter, the candidate code selection step, the final synchronization code estimation, and the timing synchronization acquisition step according to an embodiment of the present invention will be described in detail with reference to FIGS. 6 and 7.

6 is a view for explaining a method of selecting a candidate code of the initial cell search method according to an embodiment of the present invention.

FIG. 6 illustrates accumulating correlation values between 32 SYNC_DL codes having a half length of a total of 64 chips and a received signal during H subframes in the candidate code selection method according to an embodiment of the present invention.

32 SYNC_DL codes may be represented as SYNC_DL 0 to SYNC_DL 31 as shown in FIG. 6, and each SYNC_DL code is a part having a first 32 chip length of the total 64 chip lengths as shown in the lower side of FIG. 6. It is preferable. Then, the result of accumulating such a correlation value for H frame is shown in the lower right of FIG. That is, the accumulated correlation values of SYNC-DL code indices 0 to 31 are different from each other, and four indices representing the largest values are selected as a, b, c, and d. The indexes of the four candidate codes thus selected are then transferred to the final sync code estimation and timing synchronization acquisition stages, which are the second stage in one embodiment of the present invention.

FIG. 7 is a diagram for describing a method of estimating SYNC_DL code and timing synchronization used for a received signal in an initial cell search method according to an embodiment of the present invention.

As described above with reference to FIG. 6, the indexes a, b, c, and d of four selected candidate codes are received, and the respective rear codes SYNC-DL a and SYNC-DL as shown in the lower left of FIG. 7. The total length (64 chips) of b, SYNC-DL c, and SYNC-DL d) is used to obtain correlation with the received signal. This correlation value is preferably repeated for a predetermined frame for more accurate sync code estimation, and FIG. 7 illustrates accumulating correlation values during the G subframe. The number of subframes accumulating such correlation values may be a number determined in advance, or may be repeated until a difference between the largest value and the second largest value among the accumulated correlation values is greater than or equal to a predetermined threshold. .

As such, the accumulated value of the correlation between the four candidate codes a, b, c, and d candidate codes and the received signal during the G subframe may be shown as shown in the lower right of FIG. 7. In this case, for example, the difference between the SYNC-DL code (SYNC-DL c) representing the largest value and the SYNC-DL code (SYNC-DL d) representing the second largest value is greater than or equal to a predetermined threshold, or in advance the G sub. By deciding to accumulate as many frames as possible, the SYNC_DL code (SYNC-DL c) representing the maximum value can be estimated as the sync code used for the received signal. In addition, the timing synchronization can be obtained through the frequency of the timing point representing the maximum value in each subframe for the SYNC-DL c thus selected.

Meanwhile, an initial cell search apparatus according to another embodiment of the present invention will be described.

8 is a diagram illustrating a feature configuration of an initial cell search apparatus according to an embodiment of the present invention.

An initial cell search apparatus according to an embodiment of the present invention largely includes a candidate code selection module 801 and a synchronization and timing synchronization acquisition module 802. Specifically, the candidate code selection module 801 is calculated by the correlation operator 803 and the correlation operator that perform a correlation operation using only 32 chip portions of the SYNC_DL code instead of using the entire length of the 32 SYNC_DL codes. A storage means 804 capable of accumulating correlation values for a predetermined subframe, and a candidate code index selector for selecting a predetermined number of correlation values accumulated in the storage means 804, for example, four candidate code indexes. 805 may be included.

The indices of the candidate codes selected by the candidate code selection module 801, for example, a, b, c, and d, are then input to the synchronization code and timing synchronization acquisition module 802 to obtain accurate synchronization codes and timing synchronization. It is used for the process.

On the other hand, the synchronization code and timing synchronization acquisition module 802 is specifically a correlation calculation unit 806 for obtaining a correlation with the received signal using the candidate code # 64 chip full length selected by the candidate code selection module 801, Storage means 807 for storing the correlation values calculated by the correlation calculation unit 806 and the timing index when these correlation values indicate a maximum value, and correlation values for each candidate code stored in the storage means. And a synchronization code and a timing synchronization estimator 808 for selecting a synchronization code indicating a maximum value, and estimating timing synchronization through a frequency of a timing index in which a maximum value of correlation for the synchronization code is shown. .

The structure of the initial cell search apparatus according to the embodiment of the present invention as described above with reference to FIG. 8 is merely an exemplary structure and need not be limited thereto. For example, the correlation calculation unit 803 and the storage means 804 of the candidate code selection module 801 may include the correlation calculation unit 806 and the storage means 807 of the synchronization code and timing synchronization acquisition module 802, and the respective operational capacities, It will be apparent to those skilled in the art that the storage capacity may be implemented by the same physical means.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

According to the multiplexing method according to an embodiment of the present invention as described above, after selecting a candidate code using only a synchronization code of a predetermined length and not the entire length of the synchronization code, the candidate code is correlated with the received signal using the entire length only for the selected candidate code. By obtaining the relationship and obtaining the synchronization code and the timing synchronization, it is possible to effectively reduce the amount of computation required for initial cell search while maintaining the accuracy of the estimated synchronization code and the timing synchronization.

Claims (16)

Selecting at least one candidate code according to a magnitude of correlation values between a predetermined length portion, which is a part of each sync code of the sync code set, and a received signal; And Acquiring a synchronization code and a timing synchronization used for the received signal according to a correlation value between the received signal and a selected full length portion of the at least one candidate code, And the predetermined length is set such that a difference between the case where the correlation value between the predetermined length portions of each sync code is autocorrelation and the case of cross correlation is greater than or equal to a preset threshold. delete The method of claim 1, The candidate code selection step, Summing during the H subframes the correlation values computed using the predetermined length portion of the sync code during one subframe; And And selecting N candidate code indices in order of the largest value among the summed correlation values. The method of claim 1, The candidate code selection step, Storing, during H subframes, a maximum value of the correlation values calculated using the predetermined length portion of the sync code during one subframe; And Selecting N candidate code indices in order of high frequency among the stored maximum values. The method of claim 1, The candidate code selection step, Dividing one subframe into a plurality of regions and storing, during H subframes, a maximum value of the correlation values calculated using the predetermined length portion of the synchronization code in each of the regions; And Selecting N candidate code indices in order of high frequency among the stored maximum values. delete delete delete The method of claim 1, The timing synchronization is, Storing a timing index indicating a maximum value of correlation values calculated using the candidate code total length for each of the candidate codes every subframe; And Selecting a timing index having the highest frequency of occurrence of the maximum value of the calculated correlation values among the timing indexes stored for the candidate code selected as the synchronization code used for the received signal, as the timing synchronization of the received signal; Initial cell search method, characterized in that. The method of claim 1, In the synchronizing code and timing synchronization acquiring step, when the difference between the maximum value and the second largest value among the correlation values added during the G subframes is greater than or equal to a preset threshold, the synchronization code indicating the maximum value is received. Selecting as a sync code used for the initial cell search method. The method of claim 1, In the synchronizing code and timing synchronization acquiring step, the sum summed during the G subframes even if the difference between the maximum value and the second largest value among the summed values during the G subframes is not greater than or equal to a preset threshold. And selecting a sync code representing the maximum value among correlation values as a sync code used for the received signal. The method of claim 1, Each said sync code is 64 chips long, The predetermined length is 32 chips, and the predetermined length portion of the sync code is the first 32 chip portion of the sync code. 13. The method of claim 12, The selected number of candidate codes is four initial cell search method. delete delete A candidate code selecting module selecting a candidate code according to a magnitude of correlation values between a predetermined length portion, which is a part of each sync code of the sync code set, and a received signal; And A synchronization code and a timing synchronization acquisition module for acquiring a synchronization code and a timing synchronization used for the received signal according to a correlation value of the received signal with a full length portion of the candidate code selected by the candidate code selection module; , And the predetermined length is set such that a difference between the case where the correlation value between the predetermined length portions of each sync code is autocorrelation and the case of cross correlation is greater than or equal to a preset threshold.

Images