KR20190086249A - Low-complexity Sphere Search-based Adaptive Spatial Modulation method and MIMO system using the same - Google Patents

Abstract

The present invention relates to a low complexity adaptive spatial modulation (ASM) method using sphere search (SS) as a spatial modulation technique of a multi-antenna system. In an SS-ASM method, when searching for an optimal modulation scheme for adaptive spatial modulation (ASM), only some vectors are searched using the SS, where a search space is reduced to error vectors in a sphere.

Description

[0001] The present invention relates to a low-complexity adaptive spatial modulation method using a sphere search and a multi-input /

The present invention belongs to the field of spatial modulation of a multi-antenna system.

Spatial modulation (SM) is an energy efficient signaling technology that handles the tradeoff between multiplexing and diversity gain in a Multiple-Input Multiple-Output (MIMO) system.

The SM scheme achieves a high spectral efficiency (SE) as a whole using the antenna index dimension of the MIMO system, and the activation at each instant of a unit transmit antenna requires only a single RF chain at the transmitter, . The SM scheme solves the internal channel interference and internal antenna synchronization problems.

In order to improve the performance of the SM-MIMO system, an Adaptive Space Modulation (ASM) technique has been proposed which improves SE or BER by combining SM and adaptive modulation. And to maximize the number of users.

Another ASM technique called modulation order selection (MOS) has been proposed to achieve a constant rate and improve BER performance.

Specifically, to maximize the free distance (FD) that leads to the minimum BER, the MOS algorithm performs an exhaustive search (ES) on the ASM set and all error vectors of each ASM.

A simplified ASM scheme, called candidate reduction (CR) and one-bit reallocation (OBRA), has been proposed to determine the local optimal solution with low complexity.

This limits the search space of the ASM mode to a smaller set based on the ASM mode and their variability. Numerical analysis shows that only a small degradation in BER performance occurs when compared with an optimized technique based on a small MIMO system.

As described above, the spatial modulation (SM) is a technique for transmitting a signal using only one of the transmit antennas of a multi-antenna system and transmitting information using the index of the antenna used for transmission together with the transmitted symbol, It is possible to improve the reception error rate performance by adaptively selecting the modulation scheme for each antenna according to the channel state (adaptive space modulation).

However, the conventional method has a problem that a high calculation amount is required for selecting an optimal modulation method.

Korean Patent No. 1771503 discloses a method comprising: arranging indexes of reception antennas in order of expected values of Euclidean distances calculated for signals received by respective reception antennas; Aligning the indexes of the transmit antennas in the order of the output of the maximum non-combining filter; Wherein the Euclidean distance value is a geometric distance between two points on an n-dimensional space, and wherein the Euclidean distance is a geometric distance between two points on the n-dimensional space, The symbol output, the received signal value, the transmission vector to the receiving antenna, and the number of transmitting antennas, and performs spatial modulation.

As described above, among the various problems of the generalized space modulation technique, there is a signal processing technique which suggests a solution to reduce the system operation amount or the calculation amount. However, as a means of solving the signal processing, a sphere search (SS) No configuration has been proposed to optimize the computational complexity by searching only the error vector.

The present invention proposes a low complexity adaptive space modulation method using sphere search that can improve the system implementation easiness by lowering the computational complexity of finding the optimal modulation scheme of adaptive space modulation.

The present invention relates to an Adaptive Space Modulation (ASM) method for adaptively selecting a modulation scheme for each transmission antenna in a multi-antenna system according to a channel state. In searching for an optimal modulation scheme for adaptive space modulation, (SS-ASM) method characterized in that only some error vector is searched using a sphere search (SS) which is reduced to an error vector in the SS search method.

According to an aspect of the present invention, the sphere search is modified and applied to a sphere decoding receiver for generalized space modulation.

According to an aspect of the present invention, the sphere search is performed by setting a threshold value and applying a search early termination method.

According to another aspect of the present invention, there is provided a multiple input / output (MIMO) system using the SS-ASM method.

According to the present invention, the complexity of the calculation is reduced by 90% or more by narrowing down the error vector search area using the searched search without searching all the error vectors to find the optimal modulation scheme.

It can be applied to next-generation communication systems such as low-power IoT technology, which is a communication technology having advantages of low complexity and low power of space modulation by improving spatial modulation performance and improving complexity through adaptive modulation.

1 is an algorithm of a sphere search adaptive space modulation (SS-ASM) method according to the present invention.

In order to reduce computational complexity while maintaining the system performance of the ASM algorithm, the present invention proposes an ASM (SS-ASM) technique using sphere search, which effectively reduces the search space of error vectors in each ASM mode.

This is because in the ASM where each error vector contains only up to two nonzero inputs, the search process of the error vector is similar to the symbol search of generalized space modulation (GSM).

Based on this fact, it is possible to search the error vector and calculate the free distance efficiently by applying an SS process similar to that in the case of the GSM receiver. Further, in order to further reduce the calculation amount, the present invention proposes a threshold for early termination of the SS process.

Hereinafter, an adaptive space modulation (SS-ASM) method using the spherical search according to the present invention will be described in detail.

의 최대값을 가진 ASM 모드를 결정하기 위해, 최적의 ASM 알고리즘은 모든 ASM모드를 검사하고, 각 ASM 모드에 대해 모든 가능한 전송 신호 벡터를 위한 ES를 수행하는바, 이는 상당한 계산량을 요구한다.FD person

The optimal ASM algorithm checks all ASM modes and performs an ES for all possible transmission signal vectors for each ASM mode, which requires a significant amount of computation.

Therefore, in the adaptive space modulation (ASM) method of adaptively selecting the modulation scheme for each transmission antenna in the multi-antenna system according to the channel state, in order to reduce computational complexity, the search space is set as an error vector in the sphere And the FD for each ASM mode is efficiently calculated using a sphere search (SS) technique in which only some error vector is searched.

 Before describing the SS-ASM algorithm according to the present invention, SD for a GSM system is described.

Although the SD-GSM scheme was originally designed to effectively search for symbols in the GSM system, it will be appreciated that the present invention can be applied to search for FDs for ASMs with minor modifications.

1. SD-GSM

개의 송신 안테나와

개의 수신안테나를 가진 MIMO 시스템을 전제로 한다.For GSM, similar to the system model for ASM,

≪ / RTI >

Lt; RTI ID = 0.0 > MIMO < / RTI >

개의 송신 안테나 중

가 동시에 구동되고, 그리고 나서, 송신 신호

는

개의 비 제로 요소를 포함한다. 그리고 수신 신호는 아래 식으로 주어진다.In GSM, however, multiple transmit antennas are driven at each instantaneous value. Specifically, the present invention provides

Of the transmitting antennas

Are simultaneously driven, and then the transmission signal

The

Zero nonzero elements. The received signal is given by the following equation.

<Formula 1>

×

채널 행렬을 나타내며, 각 요소들은 영평균과 단위 변동량을 가진 독립적이고 동일하게 분산된 복합 가우시안 랜덤 변수로 가정한다.Where H is

×

Channel matrix, and each element is assumed to be an independent, equally distributed complex Gaussian random variable with zero mean and unit variance.

를 가진 영평균 복합 가우시안 입력으로 구성된 노이즈 벡터이다.n is the variation per dimension

Is a noise vector composed of zero mean complex Gaussian inputs with.

는 다음 식2와 같다.Maximum maximum likelihood (ML)

Is expressed by Equation 2 below.

<Formula 2>

는 GSM시스템에서의 모든 가능한 송신 신호벡터 집합이다. ML 해는 다음 식3과 같이도 나타낼 수 있다.here,

Is a set of all possible transmit signal vectors in the GSM system. The ML solution can also be expressed as in Equation 3 below.

<Formula 3>

는 영강압 추정치를 나타낸다. Cholesky 분해를 통해, 상 삼각의

×

행렬인 U를 얻을 수 있고, 이는

를 만족한다.here,

Represents the zero-step-down estimate. Through Cholesky decomposition, the upper triangular

×

We can get the matrix U,

.

Therefore, Equation 3 can be rewritten as Equation 4 below.

<Formula 4>

To reduce computational complexity to find the ML solution, the SD receiver only checks for vectors in the sphere of radius d. That is, the present invention only needs to inspect the signal vector satisfying the constraint of Equation 5 below.

&Lt; EMI ID =

If the above equation is expanded, it can be expressed as the following Equation 6.

&Lt; EMI ID =

는 s의 i번째 입력이고,

는 U의 i번째 행 j번째 열 입력이다.here,

Is the i-th input of s,

Is the i-th row and j-th column input of U.

에서 시작하고, 레벨 i에서 식7의 조건을 검사한다.In SD, a depth-first tree search is performed to find a symbol vector satisfying the constraint of Equation (5). That is,

And checks the condition of Equation 7 at level i.

Equation (7)

이며,

는 레벨 i에서의 구 반지름을 나타내고, 이는 다음 식8에 의해 반복적으로 계산된다.here,

Lt;

Represents the radius of the sphere at level i, which is iteratively calculated by Equation 8 below.

<Formula 8>

는 d로 설정된다. 상기 식7의 조건이 만족되면, 탐색 프로세스는 레벨 1에 도달할 때까지 레벨 i-1로 진행한다.here,

Is set to d. If the condition of Equation 7 is satisfied, the search process proceeds to level i-1 until level 1 is reached.

 In contrast to SD for spatial multiplexing, the SD-GSM scheme must consider the non-transmittance from each transmit antenna in the tree search process.

레벨로부터의 레벨(

)은

= 0이라는 심볼 값을 갖고, 남아있는

레벨은 비 제로 신호

을 갖는다. 반면

은 컨스텔레이션 집합을 가리킨다. 가능한 심볼 후보를 추적하기 위해, GSM-SD기법은 레벨i에서의 조합 행렬(식9)을 적용한다.Especially all

Level from level (

)silver

= 0, and the remaining

Level is a non-zero signal

Respectively. On the other hand

Refers to a constellation set. To track possible symbol candidates, the GSM-SD scheme applies a combination matrix at level i (Equation 9).

Equation (9)

개의 가능한 활성 안테나 조합을 포함하고, 여기서

이진벡터인

는 유효한 안테나 조합을 나타낸다.this is

&Lt; / RTI &gt; of possible active antenna combinations, where

Binary vector

Represents a valid antenna combination.

인 동안,

는 다음 식10과 같이 4개의 가능한 안테나 조합으로 구성된다.E.g,

While,

Is composed of four possible antenna combinations as shown in Equation 10 below.

<Formula 10>

을 가리키고, 0은

= 0을 가리킨다.Here, in the i-th row,

0 &lt; / RTI &gt;

= 0.

로 갱신된다. 위 예에서

가 선택된다면, 본 발명은 네 번째 입력을 위해 0을 갖는 열과 같이 무효한 안테나 조합을 배제함으로써

을 얻을 수 있다.After selecting the symbol candidates at level i, the combination matrix &lt; RTI ID = 0.0 &gt;

. In the above example

The present invention excludes invalid antenna combinations, such as columns with zeros for a fourth input

Can be obtained.

은 다음 식11과 같이 표현된다.As a result,

Is expressed as Equation 11 below.

<Formula 11>

= 0이 선택된다면,

이 아래 식12로 설정된다.In contrast,

= 0 is selected,

Lt; / RTI &gt;

<Formula 12>

= 0이 레벨 3에서 선택되는 경우,

를 얻을 수 있고, 이는 레벨 1과 레벨 2에서 오직

의 심볼만이 유효함을 의미한다. 그러므로

= 0 과

= 0은 탐색 지역에서 배제된다.Continuing with equation 12,

= 0 is selected at level 3,

, Which means that at level 1 and level 2 only

&Quot;&lt; / RTI &gt; therefore

= 0 and

= 0 is excluded from the search area.

2. SS-ASM

The FD of the k-th ASM mode can be expressed by Equation 13 below.

Equation (13)

는 k번째 ASM 모드를 위한 모든 가능한 송신 신호 벡터의 집합이다.here,

Is a set of all possible transmit signal vectors for the k-th ASM mode.

로 설정될 때 식13이 식2와 같아짐을 나타낸다.The comparison of Equation 13 and Equation 2 is shown in Equation 2

The equation (13) becomes equal to the equation (2).

That is, the process of finding FD in Equation 13 can be converted into the ML symbol search process of Equation 14. [

<Formula 14>

는 k번째 ASM 모드를 위한 모든 가능한 오류 벡터

이고,

이다. 오류 벡터는 오직 두 개의 비 제로 입력만을 갖고 있는데 xi 와 xj는 단일 비 제로 입력을 가지며, 이는 오류 벡터가 GSM의 송신 신호에서와 유사한 구조를 갖고 있기 때문이다.here,

Is the sum of all possible error vectors for the k-th ASM mode

ego,

to be. The error vector has only two nonzero inputs, xi and xj have a single nonzero input because the error vector has a similar structure to that of the GSM transmission signal.

Therefore, according to the present invention, by applying the SS process developed by modifying the above-described SD-GSM to apply to the ASM by modifying a sphere decoding receiver for generalized space modulation (GSM) for searching the sphere, The solution of Eq. 14 can be obtained efficiently. This implies that FD of Equation 13 can be calculated with low complexity.

By reusing or modifying Equations 5 through 8 above, the SS process for each ASM mode can be expressed as:

When applying SS to ASM, the following two cases need to be considered.

와

에서의 비 제로 요소가 같은 위치에 있다면, 오류 벡터

는 오직 단일 비 제로 입력을 가진다. 그러므로 식14를 풀기 위한 프로세스는

을 가진 SD-GSM 탐색기에서와 같아진다.Case 1:

Wow

If the nonzero elements in the vector are in the same position,

Has only a single non-zero input. Therefore, the process for solving Equation 14 is

Lt; RTI ID = 0.0 &gt; SD-GSM &lt; / RTI &gt;

와

에서의 비 제로 요소가 다른 위치에 있다면, s는 두 개의 비 제로 입력을 포함하고, 그로 인해 식 14를 푸는 프로세스는

를 가진 SD-GSM 탐색기에서와 같아진다.Case 2:

Wow

If the nonzero element in () is in a different position, then s contains two nonzero inputs, and so the process of solving Equation 14 is

Gt; &lt; RTI ID = 0.0 &gt; SD-GSM &lt; / RTI &gt;

를 가진 ASM시스템의 예를 든다. For case 1 and case 2, the combination matrix should be properly designed, and to illustrate the combination matrix design,

An example of an ASM system with.

At the initial level, the combination matrix for case 1 can be expressed as:

<Formula 15>

On the other hand, for Case 2,

<Formula 16>

Two possible approaches can be considered in order to obtain the SS solution considering case 1 and case 2.

In the first approach, called direct search, C1 and C2 are combined to construct a construction combination matrix as shown in Eq. (17).

<Formula 17>

는 i = 1, 2, ···,

인 탐색프로세스 동안,

유효값을 검사하기 위해 적용된다.after,

I = 1, 2, ...,

During the seek process,

It is applied to check valid values.

In contrast, in the second approach, called the two-step search, the search is first performed in the search area corresponding to case 1 to find the distance from the initial solution to the center of the sphere.

]은 식18에 의해 재구성될 수 있다.Note that solutions for case 1 can be found at low complexity. Specifically, if we limit the search space to an error vector with a single nonzero value at the 1-th input, then l ∈ [1 ...

] Can be reconstructed by Eq. (18).

<Formula 18>

은 U의 l번째 열을 나타낸다. 식18에서, 최소 진폭 오류 신호

만이 경우 1을 위한 탐색 프로세스 동안 l번째 비 제로 오류 위치로 고려될 필요가 있다.here,

Represents the lth column of U. In Equation 18, the minimum amplitude error signal

Only need to be considered as the lth non-zero error location during the search process for Case 1.

개의 오류 벡터만이 경우 1의 해로서 검사되어야 하며, l번째 오류 위치를 위한 다중 최소 진폭 오류 신호가 존재할 수 있음을 유의해야 한다. As a result, when compared to the total number of error vectors, significantly fewer error vectors,

It should be noted that only one error vector should be checked in the case of case 1, and there may be multiple minimum amplitude error signals for the lth error position.

를 갖고, 그로 인해, 그들 사이의 선택은 PEP 성능에 영향을 미치지 않는다.However,

, So that the choice between them does not affect the PEP performance.

After a search for Case 1, I R is used as the initial radius of SS for Case 2, which is performed using the combination matrix in Equation 16.

In summary, cases 1 and 2 should be considered separately in the search process, and the solution for case 1 is used to reduce the initial radius of SS for case 2, which reduces the computational complexity of SS for case 2 .

Comparing the complexity between these two approaches, we analyze the complexity based on the two - stage search because the two - stage search requires less complexity than the direct search.

로 표기되는 최대 FD를 가진 ASM모드는 최적 ASM 모드로 세팅되고, 이는 신호 전송을 위해 사용된다. After performing the SS for the ASM mode,

, The ASM mode with the maximum FD is set to the optimal ASM mode, which is used for signal transmission.

In the present invention, to further reduce computational complexity, it is contemplated to terminate the SS for each ASM mode early.

3. Early termination

가 대부분의 채널인식의 다른 ASM 모드에서 보다 더 크기 때문이다.Of the various ASM modes, the unified bit allocation mode is most likely to be selected,

Is larger than in other ASM modes of most channel recognition.

는 초기에

으로 세팅되고,

는 더 작은 FD를 가진 ASM 모드가 발견될 때마다 갱신된다.so

In the early days

Lt; / RTI &gt;

Is updated each time an ASM mode with a smaller FD is found.

와

(임계값에 해당함)를 비교한다. During the SS process for ASM mode, the error vector is checked in the sphere until it finds the one with the minimum distance. However, when early termination is applied during the SS process, the distance of each calculated error vector

Wow

(Corresponding to the threshold value).

를 만족한다면, 상응하는 ASM의 FD는

보다 적어야 하므로, 이는 최적 ASM모드가 아님을 의미한다. As described above, in the sphere search according to the present invention, a threshold value is set and an early search termination method is applied.

, The FD of the corresponding ASM is &lt; RTI ID = 0.0 &gt;

Which means it is not the optimal ASM mode.

을 만족한 오류 벡터가 발견되면, 현재 ASM 모드를 위한 SS 프로세스가 즉각적으로 종결되고 다음 ASM모드를 위한 작업이 시작된다.so

Is found, the SS process for the current ASM mode is immediately terminated and the operation for the next ASM mode is started.

보다 더 작다면,

는 이 FD로 갱신된다.In contrast, the FD of the ASM mode

Lt; / RTI &gt;

Is updated with this FD.

The overall process of the SS-ASM according to the present invention can be summarized by the algorithm of FIG.

In steps 1 to 4, the error vectors for the uniform-bit-allocation ASM mode are checked and the minimum distance between them is set to the initial FD.

In step 1, only the error vector corresponding to case 1 in uba is considered to find I R, which is used as the initial radius when performing SS for case 2 in step 2.

In steps 5-10, the ASM mode, excluding the uba, is checked to determine the optimal ASM mode.

의 FD는 초기에 I R로 세팅되고, 이는 단계 6에서 발견된다. 그리고 나서 단계 13에 기재된 바와 같이, 더 작은 거리를 가진 오류 벡터가 발견될 때마다 갱신된다.In step 7,

FD is initially set to IR, which is found in step 6. And then updated whenever an error vector with a smaller distance is found, as described in step 13.

보다 작은 거리를 가진 오류 벡터가 발견될 때 수행된다.The current FD is used as the sphere radius for SS in step 8. In step 11, early termination

Is performed when an error vector with a smaller distance is found.

In steps 17 and 18, the minimum FD and the optimal ASM mode are updated because the new ASM mode with the smaller FD is found without premature termination.

The present invention is a technique for selecting an optimal modulation scheme in a multiple input / output (MIMO) system. The technical scope includes a multiple input / output (MIMO) system applying the SS-ASM method described above.

Claims (4)

An adaptive space modulation (ASM) method for adaptively selecting a modulation scheme for each transmission antenna in a multi-antenna system according to a channel state,
Characterized in that when searching for an optimal modulation method of adaptive space modulation, only a certain error vector is searched using a sphere search (SS) in which the search space is reduced to an error vector in a sphere. (SS-ASM) method. The method according to claim 1,
Wherein the sphere search is modified by applying a sphere decoding receiver for generalized spatial modulation. The method according to claim 1,
Wherein the sphere search is performed by setting a threshold and applying a search early termination method. A multiple input / output (MIMO) system applying the SS-ASM method of any one of claims 1 to 3.

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