CN105099625B - A kind of keying optimum coordinates combinatorial search method during sky for multi-dimensional modulation - Google Patents

Abstract

The present invention is a space-time keying optimal coordinate combination search method for multi-dimensional modulation. The search method provided uses the product of the non-zero eigenvalues of the difference matrix formed by the difference between two different space-time codewords to construct A search method for optimal coordinate combination. The method is based on the multi-dimensional modulation STSK system architecture using coordinate combination. For a specific multi-dimensional constellation diagram, two different space-time code words are calculated in the corresponding space-time code word set formed by a specific coordinate combination method. DMD value, and find out the minimum DMD value D _min . By finding the corresponding combination with the maximum value in the D _min set calculated for all possible coordinate combinations, the upper bound of the pairwise error probability of the space-time codeword can be minimized, and then the optimal coordinate The combined three-dimensional modulation STSK system has better bit error rate performance.

Description

A Space-Time Keying Optimal Coordinate Combination Search Method for Multidimensional Modulation

technical field

The invention faces the technical field of multi-antenna wireless communication, and proposes a search method for optimizing a space-time keying system using multi-dimensional modulation based on coordinate combination, which can effectively improve its bit error rate performance.

Background technique

Space Time Shift Keying (STSK) [1] is a new multiple input multiple output (Multiple Input Multiple Output, MIMO) modulation scheme, and its transmitter structure is shown in Figure 1.

Specifically, the source generates serial B=B ₁ +B ₂ bits, after serial/parallel conversion, a discrete matrix A _q is selected from the discrete matrix set of size Q according to the B ₂ bits of the upper branch , select an information symbol s _l from L-PSK/QAM according to B ₁ bits of the lower branch. Then the information symbol scalar is multiplied by the discrete matrix and dispersed in the two dimensions of time and space, thereby obtaining the STSK codeword. Finally, the STSK codeword is sent out through the space-time mapper. Since STSK only transmits one symbol at a time, there will be no inter-channel interference (Inter Channel Interference, ICI) between multiple physical channels, and the receiving end can use a low-complexity maximum likelihood detector based on a single data stream for demodulation. STSK can take advantage of space and time dimensions, and can achieve a balance between the maximum achievable diversity order and throughput by adjusting STSK parameters, thereby improving the overall performance of the system.

Compared with low-dimensional constellation diagrams of the same size (that is, containing the same number of constellation points), multidimensional constellation diagrams have a larger Minimum Euclidean Distance (MED), so using multidimensional constellation diagrams in STSK can further improve the performance of the system. performance. There are many specific implementations of multidimensional constellation diagrams. Among them, literature [2] provides a method of coordinate combination, which is suitable for three-dimensional signals. The coordinates representing two multidimensional constellation points are combined to form three possible A two-dimensional (2-D, 2-Dimensional) complex signal transmitted on a traditional channel. But this method is not suitable for STSK, because assuming that the value set of each coordinate point is the same and the size is M, then the constellation size of the 2-D symbols combined by this method is M ² . If the value sets are different, the total number of combinations will be more, which may lead to the problem that a higher-order equivalent constellation diagram than the original constellation diagram needs to be demodulated, that is, the complexity of demodulation is increased. In addition, since the constellation point may contain coordinate 0, that is, the complex signal may be 0. After multiplying it with the discrete matrix, the STSK code word obtained is a zero matrix, which will not be able to effectively use the diversity effect, and the receiving end will not be able to Determining which discrete matrix is used will produce a bit error rate flat.

Based on the above considerations, the present invention is aimed at the STSK system based on multi-dimensional modulation, and adopts the coordinate combination in the symbol to realize that the coordinates representing a multi-dimensional symbol are combined in pairs, and the multiple complex symbols formed are formed after the action of a discrete matrix. The STSK codeword. It is worth noting that the combination of coordinates of a multidimensional symbol is not unique. Taking the three-dimensional symbol (x, y, z) as an example, the possible coordinate combinations are (x+jy, z), (y+jx, z), (x+jz, y), (z+jx, y) , (z+jy,x), (y+jz,x) and other 6 types. Signal sets with different MED values will be formed based on different coordinate combinations, and the use of these signal sets in the STSK architecture will have different impacts on performance.

The present invention finds out the coordinate combination that can obtain the best bit error rate performance by finding the optimal coordinate combination method, so that the multi-dimensional modulation STSK system realized by using the optimal coordinate combination can make full use of the performance advantages provided by the multi-dimensional constellation diagram, and Compared with the original STSK system without the optimal coordinate combination, the performance improvement can be obtained.

Contents of the invention

The combined search method provided by the present invention can reduce the upper bound of the pairwise error probability of the space-time codeword to the greatest extent, and then obtain better bit error rate performance.

For realizing above-mentioned purpose of the invention, the technical scheme that adopts is:

A space-time keying optimal coordinate combination search method for multi-dimensional modulation,

It is suitable for finding the optimal combination scheme from the space-time keying system of multi-dimensional modulation using coordinate combination. This method uses the difference formed by two different multi-dimensional space-time code words S _l',q' and S _l,q The product DMD of the non-zero eigenvalues of the difference matrix constructs an optimal coordinate combination search method, where l' and l represent the labels of the modulated signal in its set, and q' and q represent the labels of the discrete matrix in its set ; The relationship between l' and l and q' and q can be divided into three categories:

E ₁ ={l'≠l,q'=q}

E ₂ ={l'=l,q'≠q}

E ₃ ＝{l'≠l,q'≠q}

Among them, E ₁ means that the modulation signals are different, but the discrete matrices are the same; E ₂ means that the modulation signals are the same, but the discrete matrices are different; E ₃ means that the modulation signals are different, but the discrete matrices are different;

The search method includes the following steps:

S1. define the set C that includes all coordinate combinations, and label each element in the set C, N _C is the size of the set, and the loop variable i=1;

S2. Select the coordinate combination form C(i), and calculate the corresponding S _{l', q'} for all possible values of l, l', q and q' that conform to the relationship of E ₁ , E ₂ and E ₃ , S _{1, the DMD value D of q} , the calculated DMD value D forms a set Θ={D|E ₁ or E ₂ or E ₃ };

S3. Select the minimum value D _min (i)=min(Θ) from the set Θ;

S4.i=i+1;

S5. If i>N _C , go to step S6, otherwise skip to step S2;

S6. Select the minimum value contained in it from the N _C sets Θ and make the N _C minimum values form a set D _min , and then find out the label corresponding to the maximum value of its elements from the set D _min

S7. Selecting C(m) as the optimal coordinate optimal combination scheme.

Preferably, in the step S2, the specific process of calculating the DMD value D of S _{1 ', q'} and S _{1, q} is as follows:

where λ _n is a non-zero eigenvalue of matrix A, r is the rank of matrix A, and A is defined as:

A＝ΔΔ ^H ＝(S _l,q -S _l',q' )·(S _l,q -S _l',q' ) ^H

(S _l,q -S _l',q' ) ^H represents the conjugate transpose of (S _l,q -S _l',q' ).

Compared with prior art, the beneficial effect of the present invention is:

The optimal coordinate combination search method provided by the present invention can find the coordinate combination that obtains the best bit error rate performance, so that the multi-dimensional modulation STSK system realized by using the optimal coordinate combination can make full use of the performance advantages provided by the multi-dimensional constellation diagram, and Compared with the original STSK system without the optimal coordinate combination, the performance improvement can be obtained.

Description of drawings

Fig. 1 is the transmitter structure of the traditional CSTSK system.

Figure 2 is a structural diagram of an STSK transmitter based on three-dimensional modulation.

Figure 3 is an example of a 3-D signal coordinate combination.

Figure 4 is a flowchart of the OCCS method.

Fig. 5 is the spatial structure of a common 16-point 3-D constellation used in the test of the present invention: 16RCIC.

Figure 6 shows the symbol error rate performance curves of the 3D-STSK (3,2,2,16,2) system using 16RCIC under different coordinate combinations.

Detailed ways

The accompanying drawings are for illustrative purposes only and cannot be construed as limiting the patent;

The present invention will be further elaborated below in conjunction with the accompanying drawings and embodiments.

Example 1

The focus of the present invention is to find the optimal combination scheme in multi-antenna systems based on multi-dimensional modulation using coordinate combination to achieve optimal performance. This embodiment takes STSK based on 3-dimensional (3-D) modulation as an example to illustrate the specific implementation of the invention, but the method proposed by the invention is also applicable to STSK systems with dimensions greater than 3.

Figure 2 shows the structure diagram of STSK (3-D STSK, traditional STSK is recorded as 2-D STSK) transmitter based on 3-D modulation. It can be seen that the overall structure of Figure 2 and Figure 1 is similar, but the difference is It is the lower branch that is replaced by a 3-D mapper. The specific operation performed in the present invention is to first map the input B ₂ bits into a 3-D symbol according to the selected constellation diagram, and then combine according to the specific coordinates to form two complex numbers that can be transmitted on the channel Signal. Figure 3 shows an example of a coordinate combination, when a 3-D signal is represented by two 2-D signals, while using a sampling rate twice that of the 2-D STSK system, the required bandwidth is 2-D 2 times that of the system, and the relevant technical field names this implementation as "R2 implementation".

Compared with Figure 1, another difference in Figure 2 is that the intersection of the upper branch and the lower branch is changed from the original product to the form of the Kronecker product. According to Figure 3, the 3-D signal after combining a coordinate can be expressed in the form of a vector as:

s _l ＝(k _x x _l +jk _y y _l ,k _z z _l ).

In the above formula, in this embodiment, the normalization factor is used and The signals distributed in the two time slots have almost the same average power, which reduces the linear range requirement of the transmitter amplifier. The detailed introduction of the modulation scheme can refer to [3]. Here we use "3D-STSK(N _t ,N _r ,T,Q,2)" to denote a specific 3-D STSK configuration, where N _t represents the number of transmit antennas, N _r represents the number of receive antennas, and T represents a The duration of the 3-D STSK codeword, Q represents the size of the discrete matrix set, and 2 represents twice the sampling rate of the 2-D STSK system, that is, R2 3-DSTSK.

Assuming that the discrete matrix obtained by the upper branch is A _q , then the obtained 3-D STSK codeword is:

For a different 3-D STSK codeword S _l',q' , the relationship between l' and l and q' and q can be divided into three categories:

E ₁ ={l'≠l,q'=q}

E ₂ ={l'=l,q'≠q}

E ₃ ＝{l'≠l,q'≠q}.

The DMD value D of S _l',q' and S _l,q is defined as:

where λ _n is a non-zero eigenvalue of matrix A, r is the rank of matrix A, and A is defined as:

A＝ ^ΔΔH ＝(S _l,q -S _l',q' )·(S _l,q -S _l',q' ) ^H .

According to literature [4], the upper bound of the space-time codeword pair error probability (Pair-wise ErrorProbability, PEP) in the high SNR region can be expressed as:

The minimum value D _min of D determines the upper bound of PEP, so from the 3-D STSK code word set formed by different coordinate combinations, the corresponding D _min values can be calculated respectively, and then from a series of D _min values Select the largest one, and its corresponding coordinate combination can make the system obtain the best bit error rate performance.

Specifically, as shown in Figure 4, the Optimal Coordinate Combination Search (OCCS) method proposed by the present invention can be performed in the following steps:

S1. define the set C that includes all coordinate combinations, and label each element in the set C, N _C is the size of the set, and the loop variable i=1;

S2. Select the coordinate combination form C(i), and calculate the corresponding S _{l', q'} for all possible values of l, l', q and q' that conform to the relationship of E ₁ , E ₂ and E ₃ , S _{1, the DMD value D of q} , the calculated DMD value D forms a set Θ={D|E ₁ or E ₂ or E ₃ };

S3. Select the minimum value D _min (i)=min(Θ) from the set Θ;

S4.i=i+1;

S5. If i>N _C , go to step S6, otherwise skip to step S2;

S6. Select the minimum value contained in it from the N _C sets Θ and make the N _C minimum values form a set D _min , and then find out the label corresponding to the maximum value of its elements from the set D _min

S7. Selecting C(m) as the optimal coordinate optimal combination scheme.

The following is an example to illustrate the specific implementation of the OCCS method proposed by the present invention for a common 3-D constellation diagram, that is, 16RCIC [6] shown in FIG. 5 . According to the rank and determinant criteria [4], several discrete matrix sets can be randomly generated, and the OCCS method is applied to these discrete matrix sets. The obtained results are shown in Table 1. It can be seen from Table 1 that when using the 16RCIC three-dimensional constellation diagram, the optimal coordinate combination is (x+jy, z) or (y+jx, z), both of which have the largest D _min value.

Table 1: Coordinate combinations and corresponding D _min values of 16RCIC three-dimensional constellation diagram

Coordinate combination _Dmin (z+jy,x) 0.0368 (z+jx,y) 0.0368 (y+jz,x) 0.0368 (y+jx,z) 0.0399 (x+jy, z) 0.0399 (x+jz,y) 0.0368

In order to fully illustrate the beneficial effects of the present invention, the effectiveness of the present invention will be further described below in combination with simulation analysis and results.

The simulation system is a 3-D modulated STSK system configured as 3D-STSK (3, 2, 2, 16, 2) using coordinate combination, using 16RCIC 3-D constellation diagram, and the set of discrete matrices is randomized according to rank and determinant criteria Generated while assuming that the channel is an independent and identically distributed frequency-flat Rayleigh fading channel. The receiver assumes that ideal channel state information can be obtained, and uses a maximum likelihood (ML) detector to estimate the transmitted symbols and the discrete matrix. The simulation results are shown in Figure 6, from which it can be seen that the application of the OCCS method can enable the R2 3-D STSK system to obtain the optimal symbol error rate (SER) performance.

The optimal coordinate combination search method provided by the present invention can find the coordinate combination that obtains the best bit error rate performance, so that the multi-dimensional modulation STSK system realized by using the optimal coordinate combination can make full use of the performance advantages provided by the multi-dimensional constellation diagram, and Compared with the original STSK system without the optimal coordinate combination, the performance improvement can be obtained.

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the implementation of the present invention. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. All modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

references

[1]. S.Sugiura, S.Chen, and L.Hanzo, "A universal space-time architecture for multiple-antenna aided systems (a general space-time architecture based on multi-antenna systems)," IEEECommunications Surveys and Tutorials, vol .14, no.2, pp.401-420, 2012.

[2]. Zhong Yuanhong et al., A Signal Mapping and Demapping Method for Wireless Communication System, CN 101834705, 2010.

[3]. Patent disclosure, "Space-time keying based on multi-dimensional modulation and its joint optimization algorithm".

[4]. H. Jafarkhani, Space-Time Coding: Theory and Practice (Space-Time Coding: Theory and Practice). Cambridge University Press, 2005.

[5].Z.Chen, J.S.Bae, S.-K.Chung, J.-W.Koh, and S.G.Kang, "Multi-envelope3-dimensional constellations for polarization shift keying modulation Envelope three-dimensional constellation), "in 2010International Conference on Information and Communication Technology Convergence (ICTC), 2010, pp.173-174.

[6].S.Cho and S.Park, "Improved 16-ary constellation mapping for threedimensional OFDM systems (16-point improved constellation for three-dimensional OFDM systems)," IET Electronics Letters, vol.48, no.9, pp .530-532, 2012.

Claims (2)

1. A space-time keying optimal coordinate combination search method for multidimensional modulation, suitable for finding the optimal combination scheme from the space-time keying system of multidimensional modulation using coordinate combination, the method utilizes two different multidimensional The product DMD of the non-zero eigenvalues of the difference matrix formed by the difference between the space-time codewords S _l',q' and S _l,q constructs an optimal coordinate combination search method, where l' and l represent the modulation signal The label in its set, q' and q represent the label of the discrete matrix in its set; the relationship between l' and l and q' and q can be divided into three categories: E ₁ ={l'≠l,q'=q} E ₂ ={l'=l,q'≠q} E ₃ ＝{l'≠l,q'≠q} Among them, E ₁ means that the modulation signals are different, but the discrete matrices are the same; E ₂ means that the modulation signals are the same, but the discrete matrices are different; E ₃ means that the modulation signals are different, but the discrete matrices are different; It is characterized in that: the search method includes the following steps: S1. define the set C that includes all coordinate combinations, and label each element in the set C, N _C is the size of the set, and the loop variable i=1; S2. Select the coordinate combination form C(i), and calculate the corresponding S _{l', q'} for all possible values of l, l', q and q' that conform to the relationship of E ₁ , E ₂ and E ₃ , S _{1, the DMD value D of q} , the calculated DMD value D forms a set Θ={D|E ₁ or E ₂ or E ₃ }; S3. Select the minimum value D _min (i)=min(Θ) from the set Θ; S4.i=i+1; S5. If i>N _C , go to step S6, otherwise skip to step S2; S6. Select the minimum value contained in it from the N _C sets Θ and make the N _C minimum values form a set D _min , and then find out the label corresponding to the maximum value of its elements from the set D _min S7. Selecting C(m) as the optimal coordinate optimal combination scheme. 2. The space-time keying optimal coordinate combination search method for multi-dimensional modulation according to claim 1, characterized in that: in the step S2, calculate S _{1 ', q'} , S _{1, the DMD value of q} The specific process of D is as follows: where λ _n is a non-zero eigenvalue of matrix A, r is the rank of matrix A, and A is defined as: A＝ΔΔ ^H ＝(S _l,q -S _l',q' )·(S _l,q -S _l',q' ) ^H (S _l,q -S _l',q' ) ^H represents the conjugate transpose of (S _l,q -S _l',q' ).