CN113708813B - Multi-user space modulation method based on beam forming - Google Patents
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- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
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- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
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Abstract
The invention discloses a multiuser spatial modulation method based on beam forming, and belongs to the technical field of wireless communication. First, on the base station side, based on the principle of spatial modulation, the base station selects an active antenna transmission signal according to information bits to be transmitted for each user. The base station then beamforms each of the user's transmitted signals using all of the remaining inactive antennas for each user, where the beamforming vector is derived based on zero forcing criteria. Finally, at the user end, the user adopts maximum likelihood detection to decode. The invention combines the beam forming technology and the space modulation technology, thereby not only eliminating the interference among multiple users, but also playing the role of beam enhancement for target users, and realizing the popularization of the space modulation technology from single user to multiple users.
Description
Technical Field
The invention relates to a multi-user space modulation method, in particular to a multi-user space modulation method based on beam forming, which is applicable to the technical field of wireless communication.
Background
The Multiple-input Multiple-Output (MIMO) technology refers to a technology in which a plurality of transmitting antennas and receiving antennas are used at a transmitting end and a receiving end, respectively, and signals are transmitted and received through the plurality of antennas at the transmitting end and the receiving end. In a wireless communication system, MIMO technology can provide diversity gain, array gain and space division multiplexing gain, thereby improving the spectrum utilization rate of the whole system and effectively combating the problems of channel fading, etc., and has been widely used in the wireless communication field.
The spatial modulation technique is a modulation scheme proposed based on a multi-antenna architecture. Compared with the traditional modulation mode, the spatial modulation technology further improves the system capacity by introducing spatial dimension. There are many spatial modulation schemes that have been proposed so far, for example: space shift keying (SSK: space Shift Modulation) modulation scheme [2] The modulation idea is as follows: the transmitting end selects one antenna from a plurality of transmitting antennas as an active antenna to transmit information according to information bits to be transmitted, namely, the transmitting end transmits information by utilizing an antenna sequence number; space Modulation (SM) scheme [3] In this scheme, the transmitting end divides the information bits to be transmitted into two parts: one part of information bits are used for selecting active antennas, and the other part of information bits are used for selecting patterns of transmitting symbols, and the system capacity is effectively improved by combining a space domain and a constellation domain; generalized spatial modulation (GSM: generalised Spatial Modulation) scheme [4] The scheme is popularized to an SM scheme, and a plurality of active antennas are allowed to transmit signals in the same time slot, so that the number of space patterns is greatly increased, and the frequency spectrum utilization rate is improved; orthogonal space modulation (QSM: quadrature Spatial Modulation) scheme [5] The modulation concept is similar to the SM scheme, but the QSM transmits the real and imaginary parts of the modulation symbols independently using two antennas. Compared with the SM scheme, the QSM effectively improves the system performance under the condition of not increasing the computational complexity.
A new spatial modulation scheme has recently been proposed: progressive coded space shift keying (SC-SSK: successive Coded Spatial Shift Keying) has the modulation idea that the antennas at the transmitting end are divided into multiple stages, the number of antennas in each stage being equal. An active antenna is selected in each stage to transmit signals, and the signals transmitted in different stages are different from each other. Compared with the traditional spatial modulation scheme, the SC-SSK shows the superiority of the performance of the SC-SSK in terms of both error code performance and reachable rate. However, the SC-SSK scheme is proposed for a single-user scene, is not suitable for a multi-user scene, and has relatively few researches on multi-user spatial modulation schemes at present, and the performance of only some multi-user spatial modulation schemes is very limited.
Disclosure of Invention
The invention aims to: aiming at the defects of the prior art, the multi-user space modulation method based on the beam forming, which can realize the popularization of space modulation schemes meeting the conditions from single user to multi-user, such as SC-SSK, is provided, and can not only eliminate the interference among users, but also play the beam enhancing effect on target users.
The technical scheme is as follows: in order to achieve the above objective, according to the multi-user spatial modulation method based on beam forming of the present invention, firstly, a base station selects a plurality of active antennas to transmit signals to a plurality of users based on a spatial modulation principle, the signals transmitted on each active antenna are different, and the active antennas are selected by information bits to be transmitted; then, the base station uses all the rest inactive antennas to carry out beam forming on each transmitting signal, so that the transmitting signal obtains an ideal channel state, interference among multiple users is eliminated while beam enhancement is realized, the single-user scene is promoted to the multiple-user scene on the basis of the existing spatial modulation scheme, and a beam forming vector is obtained through a zero forcing criterion; and finally, the user receiving the signals directly carries out maximum likelihood detection on the signal vector, and the specific positions of the active antennas are distinguished according to the estimated difference of the signals sent by each antenna at the base station end, so that the signals are correctly decoded.
And each signal sent by the base station to the user is beamformed by the base station, wherein the number of the antennas for beamforming the signal is equal to the number of non-active antennas which are not selected by the base station and the active antenna which originally sends the signal, and the active antenna and other non-active antennas can jointly perform beamforming when sending the signal, so that the user side can conveniently distinguish the positions of the active antennas from a plurality of antennas participating in beamforming.
The method for distinguishing the active antenna of the base station end by the user specifically comprises the following steps: the multiple active antennas of the base station transmit different single signals, and the inactive antennas of the base station transmit the sum of the signals transmitted by all active antennas.
Is suitable for communication between a transmitting end and a plurality of receiving ends, wherein the transmitting end is provided with N t Base station with root antenna and N receiving end R The number of users of the root antenna is N, each user activates m antennas simultaneously in one time slot, the value of m is only influenced by the selected spatial modulation scheme, and m is more than 1 and less than N t Respectively transmitting m signals with different signal patterns, and representing the j signal transmitted by the base station to the user i as s ij Transmitting a signal s ij The sequence number set of all antennas of (a) is alpha ij Signal s ij Is the precoding vector of (a)Dimension is (N) t -m+1) x 1, transmit signal s ij Channel matrix for all antennas to user n isDimension N R ×(N t -m+1)；
The method comprises the following specific steps:
step 1), a base station divides information bits to be transmitted into a plurality of information blocks with the same length, wherein the length of the information blocks is determined by the dimension of a space pattern, and the space pattern refers to which antennas can be selected by the base station to transmit signals and is influenced by the selected existing space modulation scheme;
step 2) based on the selected existing spatial modulation scheme, the base station transmits signals to the user according to the antennas corresponding to the divided information blocks, and the antennas transmitting the signals are active antennas;
step 3) based on zero forcing criterion, the base station uses the non-active antenna of the unselected transmission signal and the active antenna of the transmission signal to carry out wave beam shaping on each transmission signal transmitted to the user, and realizes the popularization from single user scene to multi-user scene on the basis of the existing spatial modulation technology; .
Step 4), the signals received by each user have no interference among other users, and the signals only contain Gaussian white noise; based on a maximum likelihood detection algorithm, a user estimates a signal pattern transmitted by each antenna at a base station end, and obtains all antenna sequence sets of each received signal corresponding to the base station and transmitting the signal;
step 5) utilizing the antenna sequence set of each base station corresponding to each received signal, and distinguishing the specific position and corresponding number of the active antenna by the user according to the different signals sent by each antenna of the estimated base station end;
and 6) the user performs conventional information decoding according to the spatial modulation scheme adopted by the base station, and the original information bits are recovered.
The existing spatial modulation scheme needs to meet the following requirements: in the spatial modulation scheme, each user activates multiple antennas at the base station side simultaneously in one time slot, and signals transmitted on the active antennas are different from each other; the space modulation scheme SC-SSK including progressive code space shift keying is satisfactory: successive Coded Spatial ShiftKeying.
User 1 has selected m active antennas to transmit signals s respectively 11 ,s 12 ,…,s 1m The base station side uses the remaining (N t -m) pairs s of inactive antennas and the antenna that originally transmitted the signal 11 ,s 12 ,…,s 1m Respectively carrying out beam forming; namely: using the remaining (N) t -m) non-active antennas and transmissions s 11 Is to the signal s 11 Beamforming is performed using the remaining (N t -m) non-active antennas and transmissions s 12 Is to the signal s 12 Performing beam forming, repeating the steps, and performing the steps for s 13 ,…,s 1m Carrying out wave beam forming on each sending signal; and repeating the steps by other (N-1) users to realize the beam forming of each signal sent by each user.
First, the base station estimates the channel matrix H of all antennas at the base station to user N (n=1, 2, …, N) n The dimensions are all N r ×N t The method comprises the steps of carrying out a first treatment on the surface of the Then, the base stationAccording to signal s ij Selected antenna combination alpha ij From H i Is selected to form a matrixRepresenting signal s ij Channel matrix from selected antenna to user i with dimension N R ×(N t -m+1); the base station then extracts the remaining channel matrix H 1 ,H 2 ,…,H j ,…,H N (j+.i) selecting the appropriate column vector to form the interference matrix for user iI.e. signal s ij Channel matrix of selected antennas to other (N-1) users with dimensions (N-1) N R ×(N t -m+1); finally, the base station uses->And->Solving for the signal s ij Corresponding precoding vector->
Solving precoding vectors based on zero forcing criteriaAfter the signal is required to be subjected to beam forming, nulls can be formed in the direction of interfering users, so that the interference among the users is eliminated, and meanwhile, constructive interference is realized for a target user, so that the beam enhancement effect is achieved; precoding vector->The solution of (2) can be converted into the solution of the following optimization problem:
wherein:representing signal s ij Is of a dimension (N t -m+1)×1；/>Representing the transmitted signal s ij Channel matrix from all antennas of (a) to user i with dimension N R ×(N t -m+1)；/>The interference matrix representing user i, i.e. the channel matrix of all active antennas selected by user i to other (N-1) users, has dimensions (N-1) N R ×(N t -m+1)；
Because the base station can serve and transmit signals to multiple users simultaneously, the signals of different users can be transmitted together on the same antenna to eliminate the transmission signal s ij For other (N-1) users, calculateOrthogonal to the channel matrix of other (N-1) users, namely: />Fall at +.>And ensure that: (N) t -m+1)≥(N-1)N R I.e. transmit signal s ij The number of antennas is greater than all the antennas of other (N-1) users, and +.>Rank of (c) satisfies:this means +.>At least k= (N) is present in the orthogonal subspace of (c) t -m+1)-(N-1)N R Orthogonal bases; by linear combination of these k orthogonal bases +.>Interference between users can be eliminated.
Obtaining the signal s by solving an optimization problem ij Is a precoding vector of (a)
(1) Interference matrix for user iSVD decomposition is carried out to obtain:
wherein:is->The dimension of the left singular matrix of (a) is: (N-1) N R ×(N-1)N R ；/>Is a diagonal matrix whose diagonal values form the matrix +.>Is of the singular value of (N-1) N R ×(N t -m+1); matrix->Constitutes->Right singular matrices of (2) which correspond to +.>The dimensions are respectively: (N) t -m+1)×(N t -m+1-k)、(N t -m+1)×k；
②Constitutes +.>Is set in the same way as the set of orthogonal bases of (1), at this time, precoding vector +.>The writing is as follows:
wherein:representing the combined coefficient vector, the dimensions are: kx1, in order to ensure->Need to ensure->
(3) Bringing formula (3) into formula (1), the optimization problem is rewritten as follows:
using the definition of the matrix norm, equation (4) is rewritten as follows:
wherein,is a Hermite matrix, where the optimization problem is translated into a vector of combined coefficients +.>Is a solution to (c). So long as the optimal +.>The optimal precoding vector can be obtained using equation (3)>
(4) Equation (5) is a constrained nonlinear convex optimization problem, solved using the interior point method.
Further, the base station performs beam forming on the transmission signal and then transmits the transmission signal, and the user detects and decodes the noise-containing signal after receiving the noise-containing signal; wherein the signals received by the user 1 are:
wherein: y is 1 Is the signal vector received by user 1, with dimension N R X 1; n is an additive white gaussian noise vector with a dimension N R X 1, wherein each component obeys a mean of zero and a variance ofIs a complex gaussian distribution of (c).
Further, the maximum likelihood detection of user 1 is expressed as:
wherein: I.I F Representing the Frobenius norm, alpha 1j Representing the transmitted signal s 1j Is set of sequence numbers for all antennas of a pair,representing the maximum likelihood decoding ML detection of the transmitted signal s 1j Sequence number set estimates for all antennas of (a).
The beneficial effects are that:
1. the invention adopts the wave beam forming technology based on zero forcing criterion, which not only can form zero sink in the direction of interfering users to eliminate the interference among users, but also can realize constructive interference to the target users to play the role of wave beam enhancement;
2. the invention skillfully selects the inactive antenna to carry out beam forming on the signal, thereby not only playing the role of beam forming, but also enabling the user end to distinguish the position of the active antenna, thereby smoothly decoding and effectively solving the contradiction between the spatial modulation technology and the beam forming technology;
3. the multi-user space modulation method based on beam forming has strong applicability and can be applied to the multi-user popularization problem of the space modulation scheme meeting the conditions.
Drawings
Fig. 1 is a schematic block diagram of a multi-user spatial modulation method based on beamforming according to the present invention;
fig. 2 is a schematic block diagram of an embodiment of a multi-user spatial modulation method based on beamforming according to the present invention;
FIG. 3 is a graph of single user versus multi-user bit error rate performance;
FIG. 4 is a graph of the number of transmit antennas versus bit error rate performance;
fig. 5 is a graph of bit error rate performance versus different schemes.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
The invention relates to a multiuser space modulation method based on beam forming, firstly, a base station selects a plurality of active antennas to send signals to a plurality of users based on a space modulation principle, the signals sent by each active antenna are different, and the active antennas are selected through information bits to be transmitted; then, the base station uses all the rest inactive antennas to carry out beam forming on each transmitting signal, so that the transmitting signal obtains an ideal channel state, interference among multiple users is eliminated while beam enhancement is realized, the single-user scene is promoted to the multiple-user scene on the basis of the existing spatial modulation scheme, and a beam forming vector is obtained through a zero forcing criterion; and finally, the user receiving the signals directly carries out maximum likelihood detection on the signal vector, and the specific positions of the active antennas are distinguished according to the estimated difference of the signals sent by each antenna at the base station end, so that the signals are correctly decoded. And each signal sent to the user by the base station, the number of the antennas for beamforming the signal by the base station is equal to the number of non-active antennas which are not selected by the base station and the active antenna which originally sends the signal, and the active antenna and other non-active antennas perform beamforming simultaneously when sending the signal, so that the user side can conveniently distinguish the positions of the active antennas from a plurality of antennas which participate in beamforming.
Assuming that the base station side has 5 antennas, the user 1 selects the 1 st antenna and the 2 nd antenna as active antennas to respectively transmit the signal s 1 、s 2 User 2 selects the 2 nd and 3 rd antennas as active antennas to respectively transmit signals s 3 、s 4 The base station side transmission signal configuration is as shown in fig. 2. Taking user 1 as an example, for signal s 1 The base station uses the four antennas 1, 3, 4 and 5 to carry out beam forming on the base station; for signal s 2 The base station uses the four antennas of the 2 nd, 3 rd, 4 th and 5 th antennas to beam-form the base station. Since s is transmitted on the 1 st and 2 nd antennas respectively 1 、s 2 The two single signals, and the sum s of all active antenna transmission signals are transmitted on the 3 rd, 4 th and 5 th antennas 1 +s 2 Through maximum likelihood detection, the user 1 can distinguish the 1 st antenna and the 2 nd antenna as active antennas according to different signals transmitted on each antenna, and the user 1 can decode correctly according to the selected spatial modulation scheme.
The method for distinguishing the active antenna of the base station end by the user specifically comprises the following steps: the multiple active antennas of the base station transmit different single signals, and the inactive antennas of the base station transmit the sum of the signals transmitted by all active antennas.
As shown in fig. 1, the present invention is applicable to communication between a transmitting end and a plurality of receiving ends, wherein the transmitting end has N t Base station with root antenna and N receiving end R The number of users of the root antenna is N, each user activates m antennas simultaneously in one time slot, the value of m is only influenced by the selected spatial modulation scheme, and m is more than 1 and less than N t Respectively transmitting m signals with different signal patterns, and representing the j signal transmitted by the base station to the user i as s ij Transmitting a signal s ij The sequence number set of all antennas of (a) is alpha ij Signal s ij Is the precoding vector of (a)Dimension is (N) t -m+1) x 1, transmit signal s ij The channel matrix from all antennas to user n is +.>Dimension N R ×(N t -m+1)；
The method comprises the following specific steps:
step 1), a base station divides information bits to be transmitted into a plurality of information blocks with the same length, wherein the length of the information blocks is determined by the dimension of a space pattern, and the space pattern refers to which antennas can be selected by the base station to transmit signals and is influenced by the selected existing space modulation scheme;
step 2) based on the selected existing spatial modulation scheme, the base station transmits signals to the user according to the antennas corresponding to the divided information blocks, and the antennas transmitting the signals are active antennas;
step 3) based on zero forcing criterion, the base station uses the inactive antenna of the unselected transmission signal and the active antenna of the transmission signal to carry out wave beam shaping to each transmission signal transmitted to the user, thus realizing the popularization from single user scene to multi-user scene based on the existing space modulation technology;
step 4), the signals received by each user have no interference among other users, and the signals only contain Gaussian white noise; based on a maximum likelihood detection algorithm, a user estimates a signal pattern transmitted by each antenna at a base station end, and obtains all antenna sequence sets of each received signal corresponding to the base station and transmitting the signal;
step 5) utilizing the antenna sequence set of each base station corresponding to each received signal, and distinguishing the specific position and corresponding number of the active antenna by the user according to the different signals sent by each antenna of the estimated base station end;
and 6) the user performs conventional information decoding according to the spatial modulation scheme adopted by the base station, and the original information bits are recovered.
The existing spatial modulation scheme needs to meet the following requirements: in the spatial modulation scheme, each user activates multiple antennas at the base station side simultaneously in one time slot, and signals transmitted on the active antennas are different from each other; the space modulation scheme SC-SSK including progressive code space shift keying is satisfactory: successive Coded Spatial Shift Keying.
The invention is further described below with reference to the accompanying drawings. Referring to fig. 1, fig. 1 is a schematic block diagram of multi-user spatial modulation based on beamforming according to one embodiment;
without loss of generality, assume that the base station side has N t The number of users is N, each user has N R The antenna, based on the selected spatial modulation scheme, activates m antennas simultaneously in one time slot for each user, and transmits m different signals respectively, s ij The j-th signal transmitted by the user i, that is, the signal transmitted by the user 1 is: s is(s) 11 ,s 12 ,…,s 1m The signals sent by the user 2 are: s is(s) 21 ,s 22 ,…,s 2m The signal sent by the user N is: s is(s) N1 ,s N2 ,…,s Nm Wherein: s is(s) ij ≠s i'j' I+.i 'or j+.j'. Alpha ij Representing the transmitted signal s ij Is set of sequence numbers for all antennas of a pair,representing signal s ij Is of a dimension (N t -m+1)×1。Representing the transmitted signal s ij Channel matrix from all antennas to user N with dimension N R ×(N t -m+1)。
The multiuser spatial modulation method based on beam forming can be implemented by the following four processes:
(1) Spatial modulation process
Step 1), a base station divides information bits into a plurality of information blocks with the same length, wherein the length of the information blocks is determined by the dimension of a space pattern;
step 2) based on the selected spatial modulation scheme, the base station selects active antennas to transmit signals according to the divided information blocks. Here, it is assumed that each user selects m active antennas to transmit signals;
(2) Beam forming process
Step 3), for each user, the base station uses all non-active antennas which are not selected by the user to carry out beam forming on each signal sent by the user;
take user 1 as an example. User 1 has selected m active antennas to transmit signals s respectively 11 ,s 12 ,…,s 1m So that the base station side can use the remaining (N t -m) pairs of inactive antennas s 11 ,s 12 ,…,s 1m And respectively carrying out beam forming. Namely: using the remaining (N) t -m) non-active antennas and transmissions s 11 Is to the signal s 11 And carrying out beam forming. Make the following stepsWith the remainder (N) t -m) non-active antennas and transmissions s 12 Is to the signal s 12 And carrying out beam forming. Repeating the steps, and the steps can be respectively carried out on s 13 ,…,s 1m And carrying out beam forming. The other (N-1) users repeat the steps, and each signal sent by each user can be subjected to wave beam forming.
Step 4) based on zero forcing criterion, the base station solves out the corresponding precoding vector, carries out beam forming on the signal, and then sends out the signal through an antenna;
first, the base station estimates the channel matrix H of all antennas at the base station to user N (n=1, 2, …, N) n The dimensions are all N r ×N t The method comprises the steps of carrying out a first treatment on the surface of the Then, the base station generates a signal s ij Selected antenna combination alpha ij From H i Is selected to form a matrixRepresenting signal s ij Channel matrix from selected antenna to user i with dimension N R ×(N t -m+1). The base station then extracts the remaining channel matrix H 1 ,H 2 ,…,H j ,…,H N (j+.i) selecting the appropriate column vector to form the interference matrix for user iI.e. transmit signal s ij Channel matrix of antennas to other (N-1) users, dimension (N-1) N R ×(N t -m+1); finally, the base station uses->And->Solving for the signal s ij Corresponding precoding vector->Here, we solve for the precoding vector +_ based on zero forcing criterion>That is, after the signal is required to be subjected to beam forming, nulls can be formed in the direction of the interfering user, so that the interference among users is eliminated, and meanwhile, the constructive interference to the target user is realized, so that the beam enhancement effect is achieved. Thus, precoding vector +.>The solution of (2) can be converted into the solution of the following optimization problem:
wherein:representing signal s ij Is of a dimension (N t -m+1)×1；/>Representing the transmitted signal s ij Channel matrix from all antennas of (a) to user i with dimension N R ×(N t -m+1)；/>Representing the interference matrix of user i, i.e. the transmitted signal s ij Channel matrix of (N-1) to other (N-1) users, dimension (N-1) N R ×(N t -m+1)。
To cancel the signal s ij Interference to other (N-1) users, we requireOrthogonal to the channel matrix of other (N-1) users, namely: />Fall at +.>Is used for the orthogonal subspace of the matrix. At this time, we want to ensure: (N) t -m+1)≥(N-1)N R I.e. transmit signal s ij The number of antennas is greater than all the antennas of the other (N-1) users, so +.>Orthogonal subspaces exist. At the same time->Rank of (c) satisfies: />This means +.>At least k= (N) is present in the orthogonal subspace of (c) t -m+1)-(N-1)N R Orthogonal bases. By linear combination of these k orthogonal bases we can get +.>Thereby eliminating interference between users.
Next, we obtain the signal s by solving an optimization problem ij Is a precoding vector of (a)
(1) Interference matrix for user iSVD decomposition is carried out to obtain:
wherein:is->The dimension of the left singular matrix of (a) is: (N-1) N R ×(N-1)N R ；/>Is a diagonal matrix whose diagonal values form the matrix +.>Is of the singular value of (N-1) N R ×(N t -m+1); matrix->Constitutes->Right singular matrices of (2) which correspond to +.>The dimensions are respectively: (N) t -m+1)×(N t -m+1-k)、(N t -m+1)×k。
②Constitutes +.>Is set in the same way as the set of orthogonal bases of (1), at this time, precoding vector +.>The method can be written as follows:
wherein:representing the combined coefficient vector, the dimensions are: kx1. Here, to ensureWe require->
(3) Bringing formula (3) into formula (1), the optimization problem can be rewritten as follows:
using the definition of the matrix norm, equation (4) can be rewritten as follows:
wherein,is a Hermite matrix. At this point our optimization problem is transformed into +.>Is a solution to (c). So long as the optimal +.>The optimal precoding vector can be obtained using equation (3)>
(4) From observation of equation (5), this is a constrained nonlinear optimization problem, and is a convex optimization problem. We can solve using the interior point method. There is a built-in optimization function library in Matlab, we can also solve the above-mentioned optimization problem using fmincon functions.
(3) Detection process
Step 5) estimating the transmitted space pattern by a user according to the coding process;
the base station performs wave beam forming on the signals and then sends out the signals, and the user detects and decodes the signals after receiving the signals containing noise. Taking user 1 as an example, the signals received by user 1 are as follows:
wherein: y is 1 Is the signal vector received by user 1, with dimension N R X 1; n is an additive white gaussian noise vector with a dimension N R X 1, wherein each component obeys a mean of zero and a variance ofIs a complex gaussian distribution of (c).
Because the precoding vector is obtained based on zero forcing rule, the interference between users is completely eliminated, so that the user 1 only receives the signals of the user and can not receive the signals of other users.
Step 6), the user estimates the signal sent by each antenna at the base station end based on the maximum likelihood detection algorithm as in step 5);
taking user 1 as an example, its maximum likelihood detection can be expressed as:
wherein: I.I F Representing the Frobenius norm, alpha 1j Representing the transmitted signal s 1j Is set of sequence numbers for all antennas of a pair,representation ofFor the transmitted signal s under ML detection 1j Sequence number set estimates for all antennas of (a).
(4) Decoding process
Step 7), according to the signals processed in the step 6), the user identifies the specific position of the active antenna;
and 8) according to the spatial modulation scheme adopted by the base station, the user decodes the information by using the detected position of the active antenna, and restores the original information bit.
Take user 1 as an example. Through ML detection, user 1 can estimate the transmitted signal s 11 ,s 12 ,…,s 1m Sequence number set of all antennas of (a), namely:user 1 then identifies the location of the active antenna based on the set of sequence numbers for these antennas. We note that: when the base station performs beam forming, each active antenna only transmits s 11 ,s 12 ,…,s 1m Is to transmit s simultaneously with the inactive antenna 11 ,s 12 ,…,s 1m The m signals. By using the difference of the antenna transmission signals, the user 1 can successfully distinguish the position of the active antenna, namely: using estimated->User 1 can know which signals are transmitted by each antenna at the base station end, and those only transmit s 11 ,s 12 ,…,s 1m The antenna of a certain signal is an active antenna, and the rest antennas are inactive antennas. Finally, user 1 can decode smoothly by the position of the active antenna based on the selected spatial modulation scheme.
(5) Simulation results
In the simulation, we randomly generate a complex Gaussian random channel matrix, the real part and the imaginary part of each element in the channel matrix obey the mean value of 0, and the variance of 0Is a gaussian distribution of (c). We select hereThe spatial modulation scheme used meets the previously mentioned requirement that multiple antennas are activated at a time, each transmitting a different signal. In addition, all multi-user scenes in the following simulation refer to scenes containing two users, and the user side adopts ML demodulation.
First, we compare the bit error rate performance of a single user scenario with a multi-user scenario based on this patent. For comparison fairness, the number of antennas of the base station in two scenes is 5, the number of receiving antennas of each user is 2, and the power of signals sent by each user is 1.
As shown in fig. 3, when the signal-to-noise ratio is less than or equal to 10dB, the bit error rate performance of the multi-user scene is almost consistent with that of the single-user scene, and the total transmission rate of the multi-user scene can reach 8 bits/transmission, which is twice that of the single-user scene; when the signal-to-noise ratio is greater than 10dB, the error rate performance of the single-user scene is better than that of the multi-user scene. For example, at ber=1×10 -3 When the signal-to-noise ratio required for a single user scenario is about 20.5dB, the signal-to-noise ratio required for a multi-user scenario is about 23dB, and the single user has a gain of 2.5dB over the multi-user scenario. Note, however, that the overall transmission rate of the multi-user scenario is now twice that of the single-user scenario.
Then, we have studied the bit error rate performance impact of the number of base station side antennas on the multi-user scenario. Here, the number of antennas of the base station is 5 and 15, the number of receiving antennas of each user is 2, the power of the signal sent by each user is 1, and the total transmission rate is 8 bits/transmission in both scenes.
As shown in fig. 4, under the condition that the transmission rate is unchanged, when the number of base station antennas is increased from 5 to 15, the average bit error rate performance of the system is obviously improved. For example, at ber=1×10 -2 The signal-to-noise ratio required for 15 transmit antennas is approximately 12dB and for 5 transmit antennas is approximately 16.5dB, the former having a gain of 4.5dB over the latter. This is because the more the number of antennas at the base station, the more the number of antennas used for beamforming, the better the signal enhancement effect, and the lower the bit error rate.
Finally, we compare the bit error rate performance of different multi-user schemes. We have chosen a multiuser spatial modulation scheme based on antenna grouping as the comparison object. In order to ensure fairness, the number of base station antennas in the two schemes is 15, two users are arranged in each scheme, the number of antennas of each user is 2, and the total transmission rate of the system is 8 bits/transmission.
As shown in fig. 5, the multi-user spatial modulation scheme based on beamforming proposed in this patent is superior to the scheme based on antenna grouping in terms of bit error rate performance. For example, at ber=1×10 -2 The required signal-to-noise ratio for this scheme is about 12dB, and the required signal-to-noise ratio for the packet-based scheme is about 15.5dB, with a 3.5dB gain over the packet-based scheme. This highlights the superiority of the performance of the solution. Meanwhile, when the base station has 15 antennas, the scheme can fully support the transmission of higher speed.
Claims (7)
1. A multiuser space modulation method based on beam forming is characterized in that: firstly, a base station selects a plurality of active antennas to transmit signals to a plurality of users based on a spatial modulation principle, the signals transmitted by each active antenna are different, and the active antennas are selected through information bits to be transmitted; then, the base station uses all the rest inactive antennas to carry out beam forming on each transmitting signal, so that the transmitting signal obtains an ideal channel state, interference among multiple users is eliminated while beam enhancement is realized, the single-user scene is promoted to the multiple-user scene on the basis of the existing spatial modulation scheme, and a beam forming vector is obtained through a zero forcing criterion; finally, the user receiving the signals directly carries out maximum likelihood detection on the signal vector, and the specific positions of the active antennas are distinguished according to the difference of the signals sent by each antenna of the estimated base station end, so that the signals are correctly decoded;
each signal sent by the base station to the user, the number of the antennas for carrying out beam forming on the signal by the base station is equal to the number of non-active antennas which are not selected by the base station and the active antenna which originally sends the signal, and the active antenna and other non-active antennas can carry out beam forming simultaneously when sending the signal, so that the user side can conveniently distinguish the positions of the active antennas from a plurality of antennas which participate in beam forming;
the method for distinguishing the active antenna of the base station end by the user specifically comprises the following steps: the multiple active antennas of the base station transmit different single signals, and the inactive antennas of the base station transmit the sum of the signals transmitted by all active antennas.
2. The beam-forming-based multi-user spatial modulation method according to claim 1, wherein: is suitable for communication between a transmitting end and a plurality of receiving ends, wherein the transmitting end is provided with N t Base station with root antenna and N receiving end R The number of users of the root antenna is N, each user activates m antennas simultaneously in one time slot, the value of m is only influenced by the selected spatial modulation scheme, and m is more than 1 and less than N t Respectively transmitting m signals with different signal patterns, and representing the j signal transmitted by the base station to the user i as s ij Transmitting a signal s ij The sequence number set of all antennas of (a) is alpha ij Signal s ij Is the precoding vector of (a)Dimension is (N) t -m+1) x 1, transmit signal s ij The channel matrix from all antennas to user n is +.>Dimension N R ×(N t -m+1)；
The method comprises the following specific steps:
step 1), a base station divides information bits to be transmitted into a plurality of information blocks with the same length, wherein the length of the information blocks is determined by the dimension of a space pattern, and the space pattern refers to which antennas can be selected by the base station to transmit signals and is influenced by the selected existing space modulation scheme;
step 2) based on the selected existing spatial modulation scheme, the base station selects corresponding antennas to send signals to users according to the divided information blocks, and the antennas for sending signals are active antennas;
step 3) based on zero forcing criterion, the base station uses the non-active antenna of the unselected transmission signal and the active antenna of the transmission signal to carry out wave beam shaping on each transmission signal transmitted to the user, and realizes the popularization from single user scene to multi-user scene on the basis of the existing spatial modulation technology;
step 4), the signals received by each user have no interference among other users, and the signals only contain Gaussian white noise; based on a maximum likelihood detection algorithm, a user estimates a signal pattern transmitted by each antenna at a base station end, and obtains all antenna sequence sets of each received signal corresponding to the base station and transmitting the signal;
step 5) utilizing the antenna sequence set of each base station corresponding to each received signal, and distinguishing the specific position and corresponding number of the active antenna by the user according to the different signals sent by each antenna of the estimated base station end;
and 6) the user performs conventional information decoding according to the spatial modulation scheme adopted by the base station, and the original information bits are recovered.
3. The method for multiuser spatial modulation based on beam forming according to claim 2, wherein: in the spatial modulation scheme, each user activates multiple antennas at the base station side simultaneously in one time slot, and signals transmitted on the active antennas are different from each other; the space modulation scheme SC-SSK including progressive code space shift keying is satisfactory: successive Coded Spatial Shift Keying.
4. The method for multiuser spatial modulation based on beam forming according to claim 2, wherein: user 1 has selected m active antennas to transmit signals s respectively 11 ,s 12 ,…,s 1m The base station side uses the remaining (N t -m) pairs s of inactive antennas and the antenna that originally transmitted the signal 11 ,s 12 ,…,s 1m Respectively carrying out beam forming; namely: using the remaining (N) t -m) non-active antennas and transmissions s 11 Is to the signal s 11 Beamforming is performed using the remaining (N t -m) non-active antennas and transmissions s 12 Is to the signal s 12 Performing beam forming, repeating the steps, and respectively performing the steps on s 13 ,…,s 1m Carrying out wave beam forming on each sending signal; and repeating the steps by other (N-1) users to realize the beam forming of each signal sent by each user.
5. The method for multiuser spatial modulation based on beam forming according to claim 2, wherein:
first, the base station estimates the channel matrix H of all antennas at the base station to user N (n=1, 2, …, N) n The dimensions are all N r ×N t The method comprises the steps of carrying out a first treatment on the surface of the Then, the base station generates a signal s ij Selected antenna combination alpha ij From H i Is selected to form a matrix Representing signal s ij Channel matrix from selected antenna to user i with dimension N R ×(N t -m+1); the base station then extracts the remaining channel matrix H 1 ,H 2 ,…,H j ,…,H N (j+.i) selecting the appropriate column vector to form the interference matrix for user iI.e. signal s ij Channel matrix of selected antennas to other (N-1) users with dimensions (N-1) N R ×(N t -m+1); finally, the base station uses->And->Solving for the signal s ij Corresponding precoding vector->
Solving precoding vectors based on zero forcing criteriaAfter the signal is required to be subjected to beam forming, nulls can be formed in the direction of interfering users, so that the interference among the users is eliminated, and meanwhile, constructive interference is realized for a target user, so that the beam enhancement effect is achieved; precoding vector->The solution of (2) is converted into the solution of the following optimization problem:
wherein:representing signal s ij Is of a dimension (N t -m+1)×1；/>Representing the transmitted signal s ij Channel matrix from all antennas of (a) to user i with dimension N R ×(N t -m+1)；/>Representing the interference matrix of user i, i.e. the transmitted signal s ij Channel matrix of (N-1) to other (N-1) users, dimension (N-1) N R ×(N t -m+1)；
Because the base station can serve multiple users and send signals to multiple users simultaneously, the signals of different users can be sent together on the same antenna to eliminate the sending signalsNumber s ij For other (N-1) users, calculateOrthogonal to the channel matrix of other (N-1) users, namely: />Fall at +.>And ensure that: (N) t -m+1)≥(N-1)N R I.e. transmit signal s ij The number of antennas is greater than all the antennas of other (N-1) users, and +.>Rank of (c) satisfies:this means +.>At least k= (N) is present in the orthogonal subspace of (c) t -m+1)-(N-1)N R Orthogonal bases; by linear combination of these k orthogonal bases +.>Interference among users can be eliminated;
obtaining the signal s by solving an optimization problem ij Is a precoding vector of (a)
(1) Interference matrix for user iSVD decomposition is carried out to obtain:
wherein:is->The dimension of the left singular matrix of (a) is: (N-1) N R ×(N-1)N R ；/>Is a diagonal matrix whose diagonal values form the matrix +.>Is of the singular value of (N-1) N R ×(N t -m+1); matrix->Constitutes->Right singular matrices of (2) which correspond to +.>The dimensions are respectively: (N) t -m+1)×(N t -m+1-k)、(N t -m+1)×k；
②Constitutes +.>Is set in the same way as the set of orthogonal bases of (1), at this time, precoding vector +.>The writing is as follows:
wherein:representing the combined coefficient vector, the dimensions are: kx1, in order to ensure->Need to ensure->
(3) Bringing formula (3) into formula (1), the optimization problem is rewritten as follows:
using the definition of the matrix norm, equation (4) is rewritten as follows:
wherein,is a Hermite matrix, where the optimization problem is translated into a vector of combined coefficients +.>Is solved; so long as the optimal +.>The optimal precoding vector can be obtained by using equation (3)(4) Equation (5) is a constrained nonlinear convex optimization problem, solved using the interior point method.
6. The method for multiuser spatial modulation based on beam forming according to claim 2, wherein: the base station carries out beam forming on the transmission signals and then transmits the transmission signals, and a user detects and decodes the noise-containing signals after receiving the noise-containing signals; wherein the signals received by the user 1 are:
wherein: y is 1 Is the signal vector received by user 1, with dimension N R X 1; n is an additive white gaussian noise vector with a dimension N R X 1, wherein each component obeys a mean of zero and a variance ofIs a complex gaussian distribution of (c).
7. The method for multiuser spatial modulation based on beam forming according to claim 2, wherein: the maximum likelihood detection for user 1 is expressed as:
wherein: I.I F Representing the Frobenius norm, alpha 1j Representing transmissionSignal s 1j Is set of sequence numbers for all antennas of a pair,representing the maximum likelihood decoding ML detection of the transmitted signal s 1j Sequence number set estimates for all antennas of (a).
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