KR101421988B1 - downlink synchronization method for LTE system - Google Patents

Abstract

), PSS2(

) 및 PSS3(

)라고 하고, 상기 2종류의 서로 다른 신규 신호를 PSS_C1 및 PSS_C2라고 할 때, PSS_C1 = PSS1+PSS2이고 PSS_C2 = PSS2+PSS3이거나 PSS_C1 = PSS1+PSS2이고 PSS_C2 = PSS1+PSS3이거나 PSS_C1 = PSS1+PSS3이고 PSS_C2 = PSS2+PSS3인 것을 특징으로 한다.The present invention relates to a downlink synchronization method in an LTE system in which correlation checking is performed using only two different signals generated by three different PSSs, thereby reducing the number of correlation tests in the synchronization process of the PSS.
A method for downlink synchronization in an LTE system includes: (a) combining two different PSSs (Primary Synchronization Signal) to generate two different new signals; (B) performing correlations between the new signals and the received signals to obtain positional information and correlation values of the received signals having the highest correlation; If it is determined in step (c) that the position information acquired in step (b) is the same, and if it is determined in step (c) that synchronization is performed by the PSS included in the new signal And (d) performing synchronization by a non-overlapped PSS among the new signals having a large correlation value when the signals are not identical.
In the above-described configuration, the three different PSSs are referred to as PSS1 (

), PSS2 (

) And PSS3 (

And PSS_C1 = PSS1 + PSS2 and PSS_C2 = PSS2 + PSS3 or PSS_C1 = PSS1 + PSS2 and PSS_C2 = PSS1 + PSS3 or PSS_C1 = PSS1 + PSS3, respectively, when the two different new signals are PSS_C1 and PSS_C2 PSS_C2 = PSS2 + PSS3.

Description

Description of the Related Art [0002] Downlink synchronization method for LTE system in LTE system [

The present invention relates to a downlink synchronization method in an LTE system, and more particularly, to a method and apparatus for reducing the number of correlation tests in a synchronization process of a PSS by performing correlation checking using only two different signals generated by three different PSSs To a downlink synchronization method in an LTE system.

In order for a mobile station to communicate with a specific base station in a mobile communication system, time synchronization with the base station must be achieved. To this end, the base station receives a synchronization signal (SS) containing a cell ID, which is unique information of its own, finds a base station that communicates with the base station by searching for cell ID information, (Downlink synchronization). In the LTE system, the base station transmits a synchronization signal SS at a 5 subframe period.

1 is a diagram for explaining a transmission / reception process of a downlink signal in an LTE system. As shown in FIG. 1, a base station transmits a synchronization signal SS at a 5-subframe period, and a terminal receives a base station signal at an arbitrary point in time. Meanwhile, in the LTE system, 504 cell IDs are defined, and different base stations are distinguished by different cell IDs. That is, the UE must find the location of the cell ID of the cell ID and the location of the cell ID of the found cell ID among the 504 different cell ID information, and synchronize with the base station signal.

Generally, in a base station synchronization process, the UE generates all possible candidate synchronization signals (SS), measures a correlation between the received base station signal and a candidate synchronization signal, finds a candidate synchronization signal having the highest correlation, Find the time position with the greatest correlation and find the synchronization position. Therefore, in the LTE system, the UE must perform 504 different correlation operations with the candidate synchronization signal and the received base station signal.

)는 아래의 수학식 1과 같이 표현된다.504 cell IDs of LTE system (

) Is expressed by the following equation (1).

)를 알기 위해서는

및

의 두 값을 알아야 한다.

및

는 서로 다른 종류의 동기신호(SS)인 프라이머리(primary) SS(PSS)와 세컨더리(secondary) SS(SSS)를 생성하는데 각각 사용된다.According to Equation (1) above, one cell ID

To know

And

You need to know the two values of.

And

Are used to generate a primary SS (PSS) and a secondary SS (SSS), which are different types of synchronization signals (SS), respectively.

를 이용해서 매번 동일한 PSS를 생성하고,

및

를 모두 이용해 서로 다른 두 종류의 SSS1, SSS2를 번갈아 가며 생성한다. LTE 시스템의 10 서브프레임 주기 안에서 앞의 5 서브프레임 주기에는 SSS1을 전송하고 뒤의 5 서브프레임 주기에는 SSS2를 전송한다.2 is a diagram illustrating a transmission period of a downlink synchronization signal in an LTE system. As shown in FIG. 2, the base station transmits a signal at every five subframe periods

The same PSS is generated every time,

And

To generate two different types of SSS1 and SSS2 alternately. In the LTE system, within the 10 subframe periods, SSS1 is transmitted in the previous 5 subframe periods and SSS2 is transmitted in the following 5 subframe periods.

값과 5 서브프레임 주기의 동기 위치를 찾는다. PSS를 이용한 동기화 과정에서 찾은

정보와 후보

값들을 이용하여 후보 SSS1와 후보 SSS2를 생성한 후에 동기화 과정을 통해 전체 10 서브프레임 안에서 앞의 5 서브프레임 주기의 동기인지 뒤의 5 서브프레임 주기의 동기인지 찾아낸다.FIG. 3 is a flowchart illustrating a downlink synchronization procedure of a UE in an LTE system, and FIG. 4 illustrates a downlink synchronization procedure using a PSS in FIG. As shown in FIG. 3 and FIG. 4, the UE performs a synchronization process using the PSS with respect to the received base station signal

Value and the synchronization position of the 5 subframe periods. I found in the synchronization process using PSS

Information and candidates

Values are used to generate the candidate SSS1 and the candidate SSS2, and then, in the synchronization process, it is determined whether the synchronization of the previous five subframe periods or the synchronization of the following five subframe periods in all 10 subframes.

The above synchronization process will be described in more detail as follows.

1. In the absence of the position information of the synchronous signal (SS), all signals within the 5 subframe periods are searched using the PSS to find the position of the synchronous signal (correlation calculation of PSS).

2. When the position of the synchronization signal SS is found by the PSS, 10 subframe periods are found using the SSS. If the received signal has a high correlation with the SSS1 among SSS1 and SSS2, which are two types of SSS, If the correlation with SSS2 is high, it is determined to be the following five subframe periods.

The synchronization process of the PSS to find the position of the synchronization signal SS requires a lot of computation and time delay because it carries out the correlation operation on a wide range of signals. On the other hand, since the position of the synchronization signal SS is already known by the PSS in the synchronization process of the SSS, only the correlation operation for determining the 10 subframe period information can be performed without searching for the position information.

However, in the downlink synchronization process using the conventional PSS, it is necessary to check the correlation with the received signals in the form of a large amount of time signals in order to find the position of the synchronization signal SS. This process requires a lot of computation and time delay. In addition, there are three kinds of PSS to be considered, so there is a burden to carry out the same process three times in total.

SUMMARY OF THE INVENTION The present invention has been conceived to solve the above-mentioned problems, and it is an object of the present invention to reduce the number of correlation tests in the synchronization process of the PSS by performing correlation checking using only two different signals generated by three different PSSs And to provide a downlink synchronization method in an LTE system.

A method for downlink synchronization in an LTE system includes: (a) combining two different PSSs (Primary Synchronization Signal) to generate two different new signals; (B) performing correlations between the new signals and the received signals to obtain positional information and correlation values of the received signals having the highest correlation; If it is determined in step (c) that the position information acquired in step (b) is the same, and if it is determined in step (c) that synchronization is performed by the PSS included in the new signal And (d) performing synchronization by a non-overlapped PSS among the new signals having a large correlation value when the signals are not identical.

), PSS2(

) 및 PSS3(

)라고 하고, 상기 2종류의 서로 다른 신규 신호를 PSS_C1 및 PSS_C2라고 할 때, PSS_C1 = PSS1+PSS2이고 PSS_C2 = PSS2+PSS3이거나 PSS_C1 = PSS1+PSS2이고 PSS_C2 = PSS1+PSS3이거나 PSS_C1 = PSS1+PSS3이고 PSS_C2 = PSS2+PSS3인 것을 특징으로 한다.In the above-described configuration, the three different PSSs are referred to as PSS1 (

), PSS2 (

) And PSS3 (

And PSS_C1 = PSS1 + PSS2 and PSS_C2 = PSS2 + PSS3 or PSS_C1 = PSS1 + PSS2 and PSS_C2 = PSS1 + PSS3 or PSS_C1 = PSS1 + PSS3, respectively, when the two different new signals are PSS_C1 and PSS_C2 PSS_C2 = PSS2 + PSS3.

According to the downlink synchronization method in the LTE system, since the synchronization position (SS) position checking process using the existing three different PSS synchronization can be performed by two synchronization processes, the calculation amount and the time delay Can be reduced by 1/3.

1 is a diagram for explaining a transmission / reception process of a downlink signal in an LTE system;
2 is a diagram for explaining a transmission period of an LTE system synchronous downlink synchronization signal;
3 is a flowchart illustrating downlink synchronization of a UE in an LTE system.
FIG. 4 is a diagram for explaining a downlink synchronization process using the PSS in FIG. 3; FIG.
5 is a flowchart illustrating a downlink synchronization method in the LTE system according to the present invention.
6 is a computer simulation of the correlation between (PSS_C1 = PSS1 + PSS2) and (PSS_C2 = PSS2 + PSS3) of the received signal including PSS1.
7 is a computer simulation of the correlation between the received signal including PSS2 and (PSS_C1 = PSS1 + PSS2) and (PSS_C2 = PSS2 + PSS3).
8 is a computer simulation of the correlation between (PSS_C1 = PSS1 + PSS2) and (PSS_C2 = PSS2 + PSS3) of a received signal including PSS3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of a downlink synchronization method in an LTE system will be described in detail with reference to the accompanying drawings.

에 의해 총 3가지이고 아래의 수학식 2와 같이 정의된다.PSS available in LTE standard

And is defined by the following equation (2).

에 의해 서로 다른 루트 인덱스(root index)

를 이용한 길이 62의 Zadoff-Chu(ZC) 시퀀스(sequence)로 PSS를 정의한다. 한편 LTE 시스템은 OFDM 변조방식을 사용하므로 전송단에서 주파수축에서 모든 디지털 신호 처리를 진행한 후 IFFF(Inverse FFT)하여 시간 신호로 변형하여 신호를 전송한다.As shown in Equation 2 above,

(Root index)

PSS is defined as a Zadoff-Chu (ZC) sequence having a length of 62, On the other hand, since the LTE system uses the OFDM modulation scheme, all the digital signals are processed on the frequency axis at the transmission end, and then the signals are transformed into time signals by IFFF (Inverse FFT).

Therefore, when the UE proceeds downlink synchronization for the first time, it must find a synchronization signal SS in a received signal in the form of a time signal. Since the ZC sequence of the frequency signal type defined above has a characteristic of being excellent in correlation even if it is transformed into a time signal form, the synchronization process can be performed even in a time signal form.

에 대해 총 3가지의 PSS를 생성한 후 이들을 IFFT하여 시간 신호 형태로 변형하여 시간 신호 형태의 수신신호와의 상관성 검사를 진행하여 동기신호(SS) 위치를 찾아야 한다. 본 발명에서는 기존의 3회의 서로 다른 PSS 동기화를 이용한 동기신호(SS) 위치 검사 과정이 2회의 동기화 과정으로 가능하다. Therefore,

The PSS is transformed into a time signal by IFFT to search for the position of the synchronization signal SS by performing a correlation check with the received signal of the time signal type. In the present invention, it is possible to perform a synchronous signal (SS) position checking process using three different PSS synchronizations in the past by two synchronization processes.

5 is a flowchart illustrating a downlink synchronization method in the LTE system of the present invention.

에 대한 PSS의 3가지 신호를 편의상 PSS1(

), PSS2(

) 및 PSS3(

)이라고 표현한다. 이 경우에 2종류의 서로 다른 신규 신호를 PSS_C1 및 PSS_C2라 하면, 예를 들어 PSS_C1 = PSS1+PSS2이고 PSS_C2 = PSS2+PSS3이 될 수 있다.As shown in FIG. 5, according to the downlink synchronization method in the LTE system of the present invention, in step S100, two different new signals are generated by combining three different PSSs.

The three signals of PSS for PSS1 (for convenience)

), PSS2 (

) And PSS3 (

). In this case, for example, PSS_C1 = PSS1 + PSS2 and PSS_C2 = PSS2 + PSS3 can be obtained when two different new signals are PSS_C1 and PSS_C2.

Next, in step S110, the correlation processing is performed on the received signals using the two types of new signals PSS_C1 and PSS_C2. In step S120, the received signals having the highest correlation with the two new signals PSS_C1 and PSS_C2 And acquires the correlation value at that time.

) 인 것으로 판단하고 단계 S140으로 진행하여 이 위치 정보를 동기 위치로 결정한다.Next, in step S130, the corresponding PSS is determined based on the two pieces of position information acquired in step S120. If the two pieces of position information are identical in step S130, the corresponding PSS is determined as PSS2

), And proceeds to step S140 to determine the position information as the synchronous position.

)을 해당하는 PSS로 판단하고 그 위치 정보를 동기 위치로 결정하는 반면에 PSS_C2와의 상관 값이 크다면 PSS3(

)를 해당하는 PSS로 판단하고 그 위치 정보를 동기 위치로 결정한다.On the other hand, if it is determined in step S130 that the two pieces of position information are different, the process proceeds to step S150, where the non-overlapped PSS is determined as the corresponding PSS among the signals having a large correlation value, and the position information thereof is determined as the synchronous position. That is, if the correlation value with PSS_C1 is large, among PSS_C1, PSS_C2 and PSS1

) Is determined as the corresponding PSS and the position information is determined as the synchronous position. On the other hand, if the correlation value with PSS_C2 is large, PSS3

) Is determined to be the corresponding PSS, and the position information is determined as the synchronization position.

값에 의해 서로 다른 ZC sequence 신호가 된다. 동일한 ZC 시퀀스 신호 간의 상관 값은 매우 큰 반면에 서로 다른 ZC 시퀀스 신호 간의 상관 값은 작게 되므로 임의의 두 신호 A와 B의 상관 값을 XCOR(A,B)라고 할 때 아래와 같은 관계를 얻을 수 있다.Meanwhile, in the LTE system of the present invention, the downlink synchronization method utilizes the correlation property of the ZC sequence. PSS is different

The ZC sequence signal is different depending on the value. Since the correlation value between the same ZC sequence signals is very large while the correlation value between different ZC sequence signals is small, the following relationship can be obtained when the correlation value between arbitrary two signals A and B is XCOR (A, B) .

XCOR (PSSW, PSSW) >> XCOR (PSSW, PSSV), V? W

XCOR (PSS1 + PSSX, PSS1) = XCOR (PSS1, PSS1) + XCOR (PSSX, PSS1)

XCOR (PSS2 + PSSY, PSS2) = XCOR (PSS2, PSS2) + XCOR (PSSY, PSS2)

XCOR (PSS3 + PSSY, PSS3) = XCOR (PSS3, PSS3) + XCOR (PSSZ, PSS3), Z?

For example, if the received signal includes PSS1, the correlation between the received signal and A = PSS1 + PSS2 is highly correlated by the PSS1 included in A. Also, high correlation is shown between the received signal and B = PSS1 + PSS3. However, if PSS2 is included in the received signal, the correlation between the received signal and A is high, but the correlation between the received signal and B is low.

)를 해당하는 PSS라고 판단한다.6 is a graph simulating a correlation between a received signal including PSS1 and (PSS_C1 = PSS1 + PSS2) and (PSS_C2 = PSS2 + PSS3). As shown in FIG. 6, the maximum correlation positions of PSS_C1 and PSS_C2 are different from each other. In this case, the magnitudes of the respective correlation values are compared, and PSS1 (

) Is determined to be the corresponding PSS.

)를 해당하는 PSS라고 판단한다.FIG. 7 is a computer simulation of the correlation between the received signal including PSS2 and (PSS_C1 = PSS1 + PSS2) and (PSS_C2 = PSS2 + PSS3). As shown in FIG. 7, the maximum correlation positions of PSS_C1 and PSS_C2 are the same. In this case, PSS2 (PSS_C1 and PSS_C2) included in both PSS_C1 and PSS_C2

) Is determined to be the corresponding PSS.

)를 해당하는 PSS로 판단한다.FIG. 8 is a graph simulating a correlation between a received signal including PSS3 and (PSS_C1 = PSS1 + PSS2) and (PSS_C2 = PSS2 + PSS3). As shown in FIG. 8, the maximum correlation positions of PSS_C1 and PSS_C2 are different from each other. In this case, the magnitude of each correlation value is compared and PSS3 (

) As the corresponding PSS.

On the other hand, unlike the above-described embodiment, PSS_C1 = PSS1 + PSS2 can be defined as two different types of new signals, and PSS_C2 = PSS1 + PSS3. In this case, if the two maximum correlation positions in PSS_C1 and PSS_C2 are the same, PSS1 is determined as the corresponding PSS. On the other hand, if the maximum correlation positions are different from each other, after comparing the magnitude of the correlation value, if the correlation value for PSS_C1 is large, PSS2 is determined as a corresponding PSS, whereas if the correlation value for PSS_C2 is large, PSS3 is determined as a corresponding PSS.

PSS_C1 = PSS1 + PSS3, and PSS_C2 = PSS2 + PSS3 may be defined as two different types of new signals. In this case, if the two maximum correlation positions in PSS_C1 and PSS_C2 are the same, PSS3 is determined as the corresponding PSS. On the other hand, if the maximum correlation positions are different from each other, after comparing the magnitude of the correlation value, if the correlation value for PSS_C1 is large, PSS1 is determined as a corresponding PSS, whereas if the correlation value for PSS_C2 is large, PSS2 is determined as a corresponding PSS.

The downlink synchronization method in the LTE system is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical idea of the present invention. The downlink synchronization method in the LTE system of the present invention can be applied to the advanced LTE-A system in the LTE system as it is, and the LTE system is used as the concept including the LTE-A system in the claims.

Claims (4)

(A) combining two different PSSs (Primary Synchronization Signal) to generate two different new signals;
(B) performing a correlation operation on at least one received signal of each of the new signals and the PSS to obtain positional information and a correlation value of the received signal having the highest correlation;
(C) determining whether the position information obtained in the step (b) is identical to the position information acquired in the step
As a result of the determination in step (c), synchronization is performed by the PSSs redundantly included in the new signal, but when they are not the same, synchronization among the new signals having a large correlation value by the non- And (d) performing the downlink synchronization in the LTE system. The method according to claim 1,
The three different types of PSSs are referred to as PSS1 (

), PSS2 (

) And PSS3 (

), And when the above two different new signals are PSS_C1 and PSS_C2,
PSS_C1 = PSS1 + PSS2 and PSS_C2 = PSS2 + PSS3. The method according to claim 1,
The three different types of PSSs are referred to as PSS1 (

), PSS2 (

) And PSS3 (

), And when the above two different new signals are PSS_C1 and PSS_C2,
PSS_C1 = PSS1 + PSS2 and PSS_C2 = PSS1 + PSS3. The method according to claim 1,
The three different types of PSSs are referred to as PSS1 (

), PSS2 (

) And PSS3 (

), And when the above two different new signals are PSS_C1 and PSS_C2,
PSS_C1 = PSS1 + PSS3 and PSS_C2 = PSS2 + PSS3.

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