CN109274411B - Spatial modulation method for massive MIMO system and massive MIMO system - Google Patents
Spatial modulation method for massive MIMO system and massive MIMO system Download PDFInfo
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Abstract
The invention provides a spatial modulation method combining array gain control and analog beamforming, and a large-scale multiple-input multiple-output (MIMO) system based on the spatial modulation method. The method maps the spatial information bit and the emission pattern, can effectively utilize the spatial freedom degree and improve the transmission rate of the system; the array gain control scheme adopted by the invention for a plurality of adjacent antenna subarrays effectively improves the channel gain diversity of the antenna subarrays and reduces the channel correlation of the adjacent subarrays; the analog beam forming method provided by the invention based on the signal-to-leakage-and-noise ratio criterion can effectively reduce the using quantity of radio frequency links in a multi-user large-scale MIMO system and simultaneously reduce the interference among users. The system provided by the invention is not only suitable for a single-user mixed structure large-scale MIMO system, but also suitable for a multi-user mixed structure large-scale MIMO downlink transmission system.
Description
Technical Field
The invention belongs to the wireless communication technology, and particularly relates to a spatial modulation method combining array gain control and analog beamforming, and a large-scale MIMO system based on the spatial modulation method.
Background
Compared with the traditional MIMO, the number of the antennas of the large-scale MIMO is increased by a plurality of orders, the large-scale MIMO has very high array gain, the path loss can be effectively resisted, and the robustness of the system is improved. However, in conventional MIMO systems, precoding is typically performed at digital baseband and requires dedicated baseband and rf hardware for each antenna. For large-scale MIMO systems, it is difficult to achieve all-digital communication due to the high cost and power consumption of the rf link. The use of the analog beam forming technology can effectively reduce the use number of radio frequency links, reduce the hardware implementation cost and reduce the system complexity and the power loss. In a massive MIMO downlink multiuser system, if the number of transmit antennas at the base station is much larger than the number of receive antennas of the users, the channel between the base station and each user is close to orthogonal. Because the larger the number of base station antennas is, the smaller the interference among users is, the interference among users in the massive MIMO system tends to be zero. At this time, the optimal beamforming vector can be selected to reduce the inter-user interference by performing analog beamforming based on the signal-to-leakage-and-noise ratio criterion to maximize the power of the target user and minimize the power leaked to the channel direction of other users.
Spatial modulation is one way to achieve multiple antenna gains. In a MIMO system based on transmit antenna spatial modulation, the transmitter transmits signals only on one antenna or on several antennas at the same time. Thus, the transmitter can realize that the bit data corresponds to the antenna transmission mode, thereby adding extra transmission information. The receiver demodulates the data by determining the mode of transmission. The invention applies the spatial modulation technology to the large-scale MIMO system with the mixed structure, and improves the transmission rate of the system.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to provide a spatial modulation method combining array gain control and analog beamforming and a large-scale MIMO system based on the spatial modulation method so as to improve the transmission rate of the system.
The technical scheme is as follows: in order to achieve the purpose, the invention adopts the following technical scheme:
a spatial modulation method for a massive MIMO system, comprising the steps of:
(1) carrying out spatial modulation on transmitted bit data, dividing the transmitted bit data into two parts, using one part as an information symbol to carry out modulation according to a set modulation mode, using the other part as a spatial information bit, wherein transmitting antennas are grouped, each group of antennas is an antenna sub-array, each antenna sub-array comprises a plurality of transmitting antennas, and a base station selects a transmitting antenna sub-array according to the spatial information bit corresponding to a user terminal;
(2) different array gains are given to different transmitting antenna sub-arrays corresponding to a certain user; in addition, the array gain corresponding to each antenna sub-array is kept unchanged in each frame transmission time and is different in the transmission time of different frames, so that the channel correlation of the adjacent antenna sub-arrays is reduced;
(3) a user side transmits signals to a base station, the base station receives the signals by using a selected antenna sub-array, and estimates an arrival angle of a direct path of an uplink signal by using an arrival angle estimation algorithm, and then, the transmission angle of the signals in a downlink is obtained according to reciprocity of an uplink and a downlink of a channel to form an analog beam forming vector, so that beam forming is carried out on the selected antenna sub-array;
(4) the transmitter transmits signals through the antenna subarrays determined by spatial modulation;
(5) and the user terminal estimates information symbols according to the received signals, calculates error vectors, determines a transmitting mode according to a minimum error criterion and demodulates the spatial information.
Preferably, in the step (2), an array gain factor of the m-th transmitting antenna sub-array of a certain user satisfies
Wherein
And in the transmission time of the T frame, the array gain factor is given to the m transmitting antenna sub-array, and T is the total frame number.
Preferably, in the step (3), the analog beamforming vector of the mth transmit antenna sub-array is represented as:
wherein the transmission angle of the direct path of the signal in the downlink is phi, j is an imaginary constant, k0Where λ is the carrier wavelength, μ is the number of antennas in the transmit antenna sub-array, and d represents the antenna spacing.
Preferably, in the step (3), for a multi-user scenario, the user terminals respectively transmit mutually orthogonal signals to the base station.
Preferably, in the step (3), for a multi-user scenario, for an active antenna sub-array, after obtaining the transmission angle of the signal in the downlink of each user, an analog beamforming vector is obtained based on a criterion of maximizing the signal-to-leakage-noise ratio,
wherein, the signal-to-leakage-and-noise ratio of the kth ue is represented as:
wherein,
a steering vector corresponding to a transmitting angle from a transmitting antenna subarray of a kth user terminal to a direct path of the kth user terminal is represented,
a guide vector rho corresponding to a transmitting angle from a transmitting antenna subarray of a kth user terminal to a direct path of a qth user terminal of the base stationk,kAnd ρq,kEach of which represents a corresponding path gain, respectively,
is variance, in denominator
Term represents the power leakage from the beamforming direction of the target user terminal k to other user terminals by maximizing the SLNRkTo obtain the optimal beamforming vector f of the kth user terminalk。
Preferably, in step (5), the transmission pattern is determined according to a minimum error criterion, and performing spatial information demodulation further includes the receiver jointly estimating the transmission pattern and the information symbols according to the following criterion by using a maximum likelihood estimation method or a minimum euclidean distance estimation method according to the received signal:
wherein the error vector epsilonn,m＝y-βmHmfmsnY is the signal vector received by the receiver, HmRepresenting the channel matrix, beta, from the m-th sub-array of transmit antennas to the receivermArray gain factor, s, for the mth transmit antenna sub-arraynInformation corresponding to the nth constellation point in the set N-dimensional information constellation diagramAnd (4) a symbol.
In another embodiment, the present invention provides a massive MIMO system based on spatial modulation, comprising a transmitter end device and a receiver end device, wherein:
the transmitter end device comprises a space modulation unit, an array gain control unit and an analog beam forming unit, wherein,
the space modulation unit performs space modulation on the transmitted bit data, and divides the transmitted bit data into two parts, one part is used as an information symbol to be modulated according to a set modulation mode, the other part is used as a space information bit, wherein the transmitting antennas are grouped, each group of antennas is an antenna sub-array, each antenna sub-array comprises a plurality of transmitting antennas, and the base station determines the transmitting antenna sub-array according to the space information bit corresponding to the user terminal;
the array gain control unit endows different array gains to different transmitting antenna sub-arrays corresponding to a certain user, and the array gain of each antenna sub-array is kept unchanged in each frame transmission time and is different in the transmission time of different frames;
the analog beam forming unit adopts an arrival angle estimation algorithm to estimate an arrival angle of a direct path of an uplink signal, and then obtains a transmission angle of a signal in a downlink according to reciprocity of an uplink and a downlink of a channel to form an analog beam forming vector so as to form beam forming on a selected antenna subarray;
the receiver end device is used for estimating information symbols according to the received signals and demodulating spatial information.
Preferably, for a multi-user scenario, for an active antenna sub-array, the analog beamforming unit obtains an analog beamforming vector based on a maximized signal-to-leakage-noise ratio criterion after obtaining an emission angle of a signal in a downlink of each user,
wherein, the signal-to-leakage-and-noise ratio of the kth ue is represented as:
wherein,
a steering vector corresponding to a transmitting angle from a transmitting antenna subarray of a kth user terminal to a direct path of the kth user terminal is represented,
a guide vector rho corresponding to a transmitting angle from a transmitting antenna subarray of a kth user terminal to a direct path of a qth user terminal of the base stationk,kAnd ρq,kEach of which represents a corresponding path gain, respectively,
is variance, in denominator
Term represents the power leakage from the beamforming direction of the target user terminal k to other user terminals by maximizing the SLNRkTo obtain the optimal beamforming vector f of the kth user terminalk。
Preferably, the array gain control unit enables the array gain factor of the m-th transmitting antenna sub-array of a certain user to satisfy
Wherein
And in the transmission time of the T frame, the array gain factor is given to the m transmitting antenna sub-array, and T is the total frame number.
Preferably, the receiver-side apparatus includes:
a pattern estimation unit for estimating information symbols according to the received signals, calculating error vectors, and determining a transmission pattern according to a minimum error criterion;
a spatial demodulation unit for performing spatial information demodulation according to the transmission pattern; and
and the symbol estimation unit is used for determining the information symbols by adopting a maximum likelihood estimation method or according to the Euclidean distance between the received signal on each antenna and the constellation point.
Has the advantages that:
the invention provides a spatial modulation method combining array gain control and analog beamforming and a large-scale MIMO system based on the spatial modulation method. The method maps the spatial information bit and the emission pattern, can effectively utilize the spatial freedom degree and improve the transmission rate of the system; the array gain control scheme adopted by the invention for a plurality of adjacent antenna subarrays effectively improves the channel gain diversity of the antenna subarrays and reduces the channel correlation of the adjacent subarrays; the analog beam forming method provided by the invention based on the signal-to-leakage-and-noise ratio criterion can effectively reduce the using quantity of radio frequency links in a multi-user large-scale MIMO system and simultaneously reduce the interference among users. The system provided by the invention is not only suitable for a single-user mixed structure large-scale MIMO system, but also suitable for a multi-user mixed structure large-scale MIMO downlink transmission system.
Drawings
FIG. 1(a) is a schematic diagram of a transmitter end of a single-user massive MIMO system using the method of the present invention.
FIG. 1(b) is a schematic diagram of a receiver end of a single-user massive MIMO system according to the method of the present invention.
Fig. 2(a) is a schematic diagram of a base station (transmitter) end of the method of the present invention for a multi-user massive MIMO downlink transmission system.
Fig. 2(b) is a schematic diagram of a user k (receiver) end of the multi-user massive MIMO downlink transmission system according to the method of the present invention.
Detailed Description
The technical solution of the present invention is described in detail below, but the scope of the present invention is not limited to the embodiments.
The embodiment of the invention discloses a spatial modulation method combining array gain control and analog beamforming, which comprises the following steps:
in a large-scale MIMO downlink transmission system with a multi-user hybrid structure, a transmitter divides transmitted bit data into two parts, one part is used as an information symbol to be modulated according to a set modulation mode, and the other part is used as a spatial information bit to be spatially modulated; the transmitter groups transmitting antennas, and each group of antennas is a subarray; each user corresponds to one radio frequency link, wherein each radio frequency link adopts a separated sub-architecture model and is connected with a plurality of antenna sub-arrays, and each sub-array comprises a plurality of transmitting antennas. The separated sub-architecture model is defined as an antenna sub-array for transmitting signals is determined according to the transmission pattern of each user at a certain determined moment, and the antenna sub-array is connected with a radio frequency link corresponding to the user through a phase shift network; the transmission pattern is defined as the transmission condition of an antenna sub-array determined by the spatial information bits of a certain user at a certain moment.
And the transmitter transmits signals according to the antenna sub-arrays determined by the spatial modulation.
Preferably, the transmitting end of the present invention does not need to know the full channel state information. For a single-user scene, the base station determines a transmitting antenna sub-array according to the spatial information bit corresponding to the user. The user side transmits a Signal to the base station, the base station receives the Signal by using the selected antenna subarray, and meanwhile, an arrival angle estimation algorithm, such as a Multiple Signal Classification (MUSIC) algorithm, is adopted to estimate an arrival angle of a direct path of an uplink Signal. Then, according to the reciprocity of the uplink and downlink of the channel, the transmission angle of the signal in the downlink can be obtained to form an analog beamforming vector.
Further, when the correlation between the antenna sub-arrays of the transmitter is strong, a plurality of antenna sub-arrays of a certain user are distinguished by adopting an array gain control mode. In the same frame transmission time, different array gains are given to different antenna sub-arrays of the user; in addition, the array gain of each antenna sub-array is respectively kept constant in the transmission time of each frame and is different in the transmission time of different frames.
Further preferably, for a multi-user scenario, the base station determines the transmit antenna sub-array according to the spatial information bits corresponding to each user. And each user side respectively sends mutually orthogonal signals to the base station, the base station receives the signals by using the transmitting antenna sub-array of each user, and estimates the arrival angle of the direct path of the uplink signal of each user by adopting an MUSIC algorithm. And similarly, according to the reciprocity of the uplink and downlink of the channel, obtaining the transmitting angle of the signal in the downlink of each user to form an analog beamforming vector.
Further, for a multi-user scenario, the spatial information bit corresponding to each user controls the transmission condition of the antenna array. For active antenna subarrays, the invention obtains the analog beamforming vector based on the maximized signal-to-leakage-noise ratio criterion.
Further, when the correlation between the antenna sub-arrays of the transmitter corresponding to a certain user is strong, the antenna sub-arrays of the user are distinguished by adopting an array gain control mode. In the same frame transmission time, different array gains are given to different antenna sub-arrays of the user; in addition, the array gain of each antenna sub-array is respectively kept constant in the transmission time of each frame and is different in the transmission time of different frames.
The receiver estimates the information symbols and the transmission pattern from the received signal, performs spatial information demodulation, and determines the information symbols.
Preferably, each user estimates information symbols from the received signal, calculates an error vector, determines a transmission pattern according to a minimum error criterion, and performs spatial information demodulation.
Further preferably, each user determines an information symbol according to the euclidean distance between the received signal and the constellation point on each antenna, calculates an error vector, and determines a transmission pattern according to a minimum error criterion, thereby performing spatial information demodulation.
The method is not only suitable for the single-user mixed structure large-scale MIMO system, but also suitable for the multi-user mixed structure large-scale MIMO downlink transmission system, can effectively utilize the spatial freedom degree, and improves the transmission rate of the system.
The embodiment of the invention discloses a large-scale MIMO system based on spatial modulation, which comprises a transmitter end device and a receiver end device;
the transmitter end device is used for dividing the transmitted bit data into two parts, one part is used as an information symbol to be modulated according to a set modulation mode, and the other part is used as a spatial information bit to be spatially modulated; the transmitter groups transmitting antennas, and each group of antennas is a subarray; each user corresponds to one radio frequency link, wherein each radio frequency link adopts a separated sub-architecture model and is connected with a plurality of antenna sub-arrays, and each sub-array comprises a plurality of transmitting antennas. The separated sub-architecture model is defined as an antenna sub-array for transmitting signals is determined according to the transmission pattern of each user at a certain determined moment, and the antenna sub-array is connected with a radio frequency link corresponding to the user through a phase shift network; the transmission pattern is defined as the transmission condition of an antenna sub-array determined by the spatial information bits of a certain user at a certain moment.
The receiver end device is used for estimating information symbols according to the received signals and demodulating spatial information.
Preferably, the receiver-side apparatus includes:
a pattern estimation unit for estimating information symbols according to the received signals, calculating error vectors, and determining a transmission pattern according to a minimum error criterion;
a spatial demodulation unit for performing spatial information demodulation according to the transmission pattern;
and the symbol estimation unit is used for determining the information symbols according to the Euclidean distance between the received signals on each antenna and the constellation points.
The following describes the embodiments of the present invention in detail for two scenarios, i.e., single-user and multi-user, respectively.
The invention relates to a massive MIMO wireless communication system, which comprises a transmitter and a receiver.
Scene one: single-user mixed structure large-scale MIMO system
In the single-user massive MIMO system, as shown in FIGS. 1(a) and 1(b), a transmitter is configured with ntRoot antenna, receiver configuration nrA root antenna. At a certain moment, after the transmitting antenna sub-array is determined by the space information bits, in the transmitting antenna sub-array, from the ith rootThe channel coefficient from the transmitting antenna to the p-th receiving antenna is hp,i. The signal vector received by the receiver can be represented as:
y＝Hmgmx+w (1)
wherein HmRepresenting the channel matrix between the mth transmit antenna sub-array determined by the spatial information bits and the receiving end, HmThe element of the p-th row and the i-th column is hp,i，gmRepresenting the analog beamforming vector of the mth transmitting antenna sub-array, x is the transmitted symbol, w is the noise vector, the mean value of the elements of w is zero, and the variance is
Complex gaussian distribution.
In the present embodiment, let n be assumedtη μ, where η and μ are positive integers. The antennas of the transmitter are divided into η groups of uniform linear antenna sub-arrays, each group having μ antennas. And each time the signal is transmitted, the transmitter selects one group of antenna sub-arrays to transmit the signal according to the spatial information bits. In this case, the transmitter has
A transmission pattern in which
Representing a combinational operation. Each respective emission pattern may be in accordance with
Bit information is mapped, wherein
Indicating a rounding down operation.
In the present embodiment, it is assumed that a narrowband cluster channel model is employed. If there are L transmission paths in the mm wave channel, the narrowband cluster channel model may be expressed as:
wherein L represents the number of paths, αlA gain factor representing the ith path, obeying a complex gaussian distribution with a mean of 0 and a variance of 1; thetalAnd
respectively representing the arrival angle and emission angle of the ith path, obeying (0,2 pi)]Is uniformly distributed. a isr(θl) And
and antenna array response vectors of the l path of the base station and the user terminal are respectively represented.
In the present embodiment, the antenna arrays of the base station and the user terminal are uniform linear antenna arrays. At this time, ar(θl) And
can be further respectively represented as
Wherein k is02 pi/λ, λ is the carrier wavelength, and d denotes the antenna spacing.
In this embodiment, the base station determines the transmit antenna sub-array according to the spatial information bits corresponding to the user. Assuming that the base station does not know the channel state information, the user terminal needs to transmit a signal to the base station, and the transmitting antenna sub-array of the base station estimates the arrival angle of the direct path of the uplink signal by adopting an MUSIC algorithm according to the received signal. Then, according to the reciprocity of the uplink and downlink of the channel, the transmitting angle of the signal in the downlink is obtained to form an analog beam forming vector, so that the beam direction is aligned to the direction of the optimal path.
Assuming that the estimated transmission angle of the direct signal path in the downlink is phi, the analog beamforming vector of the mth transmit antenna sub-array can be expressed as:
in this embodiment, when the spatial channel correlation is strong, an array gain control method is adopted for different antenna sub-arrays selected by spatial information bits at different times by the same user, so as to realize channel distinction, that is, different array gains are given to η groups of antenna sub-arrays of a base station within a certain frame transmission time; and the array gain corresponding to each antenna sub-array is kept unchanged in each frame transmission time and is different in the transmission time of different frames, so that the high channel correlation caused by the close spatial distance of the large-scale antenna arrays at the transmitting end is reduced. The array gain allocation can be represented by:
y＝βmHmgmx+w (6)
where m is the antenna sub-array number (m is 1,2, eta), beta, selected by the spatial information bits at a certain timemIs the array gain factor of the m-th group of antenna sub-arrays and satisfies E { | betam|21. Array gain factor betamThe transmission time of each frame is kept constant and is different in the transmission time of different frames.
Assuming an equivalent gain beta of the receiver-known channelmHmgmThe receiver may jointly estimate the transmission pattern and the information symbols by maximum likelihood detection based on the received signal, thereby demodulating the spatial information and determining the transmitted information symbols. Assuming that a signal is transmitted using the m-th group of antenna sub-arrays of the transmitter (corresponding to the m-th transmission pattern), an error vector is defined:
εn,m＝y-βmHmgmsn (7)
wherein HmRepresenting the channel moment from the m-th transmit antenna sub-array to the receiverArray, betamArray gain factor, s, for the mth transmit antenna sub-arraynFor the information symbol corresponding to the nth constellation point in the set N-dimensional information constellation diagram, a maximum likelihood estimation method or a minimum euclidean distance estimation method may be correspondingly adopted. Then, the transmission pattern and the information symbols are jointly estimated according to the following criteria:
the transmission pattern and information symbols are determined from the estimates of m and n so that the spatial information and symbol information can be demodulated.
The estimate of the transmitted information symbol s is:
the transmission rate of the embodiment in the single-user massive MIMO system based on spatial modulation is as follows:
R＝log2(N)+log2(Γt) (10)
where N is the modulation order of the information, ΓtIs the number of transmission patterns.
Scene two: large-scale MIMO downlink transmission system with multi-user hybrid structure
Here, downlink multi-user transmission is considered, i.e. the base station transmits different data to multiple users simultaneously. As shown in fig. 2(a) and 2(b), a base station (transmitter) is configured with n for each usertA root antenna, a k user receiving end configured with nkA root antenna, K users in total. At a certain moment, after a transmitting antenna sub-array is determined by the spatial information bits of the kth user, the channel coefficient from the ith transmitting antenna to the pth receiving antenna of the kth user in the transmitting antenna sub-array is
The signal received by the kth user can be expressed as:
wherein Hk,kAnd Hk,qRespectively representing the channel matrix from the transmitting antenna sub-array of the kth user and the transmitting antenna sub-array of the qth user of the base station to the kth user, fkAnd fqRespectively representing the analog beamforming vectors, x, of the kth and qth userskAnd xqSymbols, w, transmitted for the k and q users respectivelykIs a noise vector, wkSubject to a mean of zero and a variance of
Complex gaussian distribution.
In the present embodiment, it is assumed that the base station is configured with n for each usertA root antenna, and ntη μ, where η and μ are positive integers. The antennas of each user are divided into η groups of uniform linear antenna sub-arrays, each group having μ antennas. Each time a signal is transmitted, the transmitter selects one of the antenna sub-arrays to transmit the signal. At this time, the k-th user has
A transmission pattern in which
Representing a combinational operation. Each respective emission pattern may be in accordance with
Bit information is mapped, wherein
Indicating a rounding down operation.
In this embodiment, a narrowband cluster channel model is employed. Assuming that there are L transmission paths in the mm wave channel, the narrow band cluster channel model between the k-th user's transmitting antenna sub-array and the user's receiving end can be expressed as:
wherein L iskIndicates the number of paths for the k-th user,
the gain factor of the ith path of the kth user is represented, and the kth user follows a complex Gaussian distribution with the mean value of 0 and the variance of 1;
and
respectively representing the arrival angle and the emission angle of the ith path of the kth user, obeying (0,2 pi)]Is uniformly distributed.
And
and respectively representing antenna array response vectors of a transmitting antenna sub array of a kth user of the base station and the ith path of the kth user terminal.
In the present embodiment, the antenna arrays of the base station and the user terminal are uniform linear antenna arrays. At this time, the process of the present invention,
and
can be further respectively represented as
Wherein k is02 pi/λ, λ is the carrier wavelength, and d denotes the antenna spacing.
In this embodiment, for each user, the base station determines a transmit antenna sub-array according to the spatial information bits corresponding to each user. Assuming that the base station does not know the channel state information, each user side respectively sends mutually orthogonal signals to the base station, the base station receives the signals by using the transmitting antenna sub-array of each user, and estimates the arrival angle of the direct path of the uplink signal of each user by adopting an MUSIC algorithm. And similarly, acquiring the transmission angle of the signal in the downlink of each user according to the reciprocity of the uplink and the downlink of the channel. Then, for the active antenna subarray, the invention obtains the analog beam forming vector f based on the signal-to-leakage-noise ratio criterionkMaximizing the power of the target user and minimizing the power leakage to other users.
Further, the signal-to-leakage-and-noise ratio of the kth user can be expressed as:
wherein,
a steering vector corresponding to a transmitting angle from a transmitting antenna sub-array of a kth user to a direct path of the kth user of the base station is represented,
a steering vector rho corresponding to the transmitting angle from the transmitting antenna sub-array of the kth user to the direct path of the qth user of the base stationk,kAnd ρq,kRespectively representing the corresponding path gain, in denominator
The term represents the power that leaks from the beamforming direction of the target user k to the other users. By maximizing SLNRkThat is, the k-th user can be obtainedOptimal beamforming vector fk. By analogy, the optimal beamforming vectors of all users of the base station can be obtained.
In this embodiment, when the correlation between the antenna sub-arrays of the transmitter corresponding to a certain user is strong, an array gain control manner is adopted to realize channel differentiation. In other words, within a certain frame transmission time, different array gains are given to the η groups of antenna sub-arrays of the kth user, and the array gain corresponding to each antenna sub-array is kept unchanged within each frame transmission time and is different within the transmission time of different frames, so that the high channel correlation caused by the proximity of the large-scale antenna array spatial distance of the transmitting end is reduced. The array gain allocation for the kth user can be represented by:
where m is an antenna sub-array ( m 1, 2.. eta.), β selected by spatial information bits at a certain timek,mIs the array gain factor of the mth group antenna sub-array in the kth user and satisfies E { | betak,m|21, array gain factor βk,mThe transmission time of each frame is kept constant and is different in the transmission time of different frames.
Assuming an equivalent gain beta of the receiver-known channelmHmfmThe receiver may jointly estimate the transmission pattern and the information symbols using maximum likelihood detection based on the received signal, thereby demodulating the spatial information and determining the transmitted information symbols. Because the multi-user channels of the large-scale MIMO are gradually orthogonal, and each user carries out analog beam forming based on the signal-to-leakage-and-noise ratio criterion, the beams among all users at the transmitting end can be assumed to have strong directivity, and the interference among all users is almost zero. Similar to a single user, multiple users can be independently demodulated, respectively. Assuming that the mth group of antenna sub-arrays of the kth user transmitter transmits (corresponding to the mth transmission pattern), an error vector is defined:
εn,m＝y-βmHmfmsn (17)
wherein HmRepresenting the channel matrix, beta, from the m-th sub-array of transmit antennas to the receivermFor the array gain, s, of the m-th transmit antenna sub-arraynFor the information symbol corresponding to the nth constellation point in the set N-dimensional information constellation diagram, a maximum likelihood estimation method or a minimum euclidean distance estimation method may be correspondingly adopted. Then, the transmission pattern and the information symbols are jointly estimated according to the following criteria:
the transmission pattern and information symbols are determined from the estimates of m and n so that the spatial information and symbol information can be demodulated.
The estimate of the transmitted information symbol s is:
in a multi-user multi-input multi-output system, the transmission rate of the kth user in the multi-user large-scale MIMO system based on spatial modulation is as follows:
Rk＝log2(Nk)+log2(Γk,t) (20)
wherein N iskModulation order, Γ, for the kth user informationk,tIs the number of transmission patterns corresponding to the kth user.
The following describes a single-user and multi-user spatial modulation massive MIMO system combining array gain control and analog beamforming proposed by the present invention with reference to specific examples.
Example 1: a single-user spatial modulation massive MIMO system combining array gain control and analog beamforming. Suppose nt＝400，n r2; the transmitter transmits an information stream using BPSK modulation. The antennas of the transmitter are divided into 4 antenna sub-arrays with 100 antennas each. Therefore, it is alwaysThere are 4 transmission patterns, each of which is mapped with 2 bits of spatial information, and the mapping relationship is shown in table one.
Table one: mapping relation of single user information bit and transmitting pattern and information symbol
When the information bit is 001, the received signal may be expressed as:
y＝β1H1f1x+w (21)
wherein, beta1Is the array gain factor of the 1 st group antenna sub-array and satisfies E { | beta1|2}＝1。H1Is the channel matrix between the 1 st group of transmitting antenna subarrays and the receiving end. f. of1The optimal analog beamforming vector for the antenna sub-array of group 1. x is the transmitted symbol. w is a noise vector, the elements of w obey a mean of zero and a variance of
Complex gaussian distribution.
Further, the array gain factor β1The transmission time of each frame is kept constant and is different in the transmission time of different frames. For example, during the first frame transmission time,
during the transmission time of the second frame,
by analogy, array gain control is carried out, and the requirements are met
Equivalent gain beta of known channel of receivermHmfmThen the error vector can be expressed as:
εn,m＝y-βmHmfmsn (22)
jointly estimating the transmission pattern and the information symbols according to the following criteria by using a maximum likelihood estimation method or a minimum Euclidean distance estimation method:
the spatial information bits are demapped with reference to the table. And the estimate of the transmitted information symbol s is:
example 2: a multi-user spatial modulation massive MIMO system combining array gain control and analog beamforming. Assuming that the number K of users is 2, each user is connected with a communication radio frequency link, and the transmitting end configures n for each usertThe antenna array is divided into 2 antenna sub-arrays with 100 antennas in each array, where η is 200 antennas. Each user receiver configures n k1 antenna; the information stream to each user is QPSK formatted. Each user may use 2 transmission patterns, and the corresponding may be mapped with 1-bit spatial information. The mapping relationship between the spatial information bits of the total users and the transmission pattern is shown in table two.
Table two: mapping relation between information bit and transmission pattern in multi-user transmission
When the spatial information bit sent by the first user is 0, the user 1 selects the 1 st group of uniform linear antenna sub-arrays to transmit corresponding modulation symbols; when the spatial information bit sent by the second user is 1, user 2 selects the 2 nd group of uniform linear antenna sub-arrays to transmit the corresponding modulation symbols. At this time, the signal to leakage noise ratio of user 1 can be expressed as:
wherein,
a steering vector corresponding to a transmitting angle from a 1 st group transmitting antenna sub-array of a 1 st user to a direct path of the 1 st user at a base station end is represented,
a steering vector, rho, corresponding to the transmitting angle from the 1 st group transmitting antenna subarray of the 1 st user to the direct path of the 2 nd user at the base station end1,1And ρ2,1Each of which represents a corresponding path gain, respectively,
representing the power leaked from the beamforming direction of target user 1 to the 2 nd user. Based on the criterion of maximizing the signal-to-leakage-noise ratio, the optimal analog beam forming vector f of the user 1 can be obtained1。
At this time, due to the progressive orthogonality among the large-scale antenna multi-user channels, the analog beamforming vector f of the user 1 is determined based on the criterion of maximizing the signal-to-leakage-and-noise ratio1After that, can be approximately considered
At this time, the receiving end of user 2 only receives the signal transmitted from base station user 2. Similarly, the receiving end of user 1 only receives the signal transmitted from user 1.
The received signal of the first user may be expressed as:
y1＝β1,1H1,1f1x1+w1 (26)
wherein, beta1,1Array gain, H, of group 1 transmit antenna sub-arrays representing user 11,1Channel matrix representing the 1 st group of transmit antenna sub-arrays of user 1 to the receiving end of user 1, f1For indicatingOptimal analog beamforming vector, x, for group 1 transmit antenna subarrays of USER-11For transmitted symbols, w1Is a noise vector.
For the first user, an error vector is defined:
jointly estimating the transmission pattern and the information symbols according to the following criteria:
and carrying out demapping on the spatial information bits according to the table. And the estimate of the transmitted information symbol s is:
the user 2 can demodulate the spatial information and the data stream information using the same method.
The embodiment of the invention discloses a large-scale MIMO system based on spatial modulation, which comprises a transmitter end device and a receiver end device; the transmitter end device is used for dividing the transmitted bit data into two parts, one part is used as an information symbol to be modulated according to a set modulation mode, and the other part is used as a spatial information bit to be spatially modulated; the transmitter groups the transmitting antennas, and each group of antennas is a subarray; each user corresponds to one radio frequency link, wherein each radio frequency link adopts a separated sub-architecture model and is connected with a plurality of antenna sub-arrays, and each sub-array comprises a plurality of transmitting antennas. And adopting an array gain control mode for different antenna sub-arrays selected by the spatial information bits at different moments of the same user, thereby realizing channel distinction, namely endowing different antenna sub-arrays with different array gains. The array gain factor for each antenna sub-array remains constant during each frame transmission time and varies from transmission frame to transmission frame. The transmitter selects the optimal beamforming vector for each user based on the criterion of maximizing the signal-to-leakage-noise ratio; the receiver estimates information symbols and transmission patterns according to the received signal, and performs spatial information demodulation. The large-scale MIMO system based on spatial modulation of this embodiment and the spatial modulation method combining the array gain control and the analog beamforming described above belong to the same inventive concept, and the specific implementation details are the same as those described above, and are not described herein again.
As will be apparent to those skilled in the art, many modifications can be made to the invention without departing from the spirit and scope thereof, and it is intended that the present invention cover all modifications and equivalents of the embodiments of the invention covered by the appended claims.
Claims (4)
1. A spatial modulation method for massive MIMO system, comprising the steps of:
(1) carrying out spatial modulation on transmitted bit data, dividing the transmitted bit data into two parts, using one part as an information symbol to carry out modulation according to a set modulation mode, using the other part as a spatial information bit, wherein transmitting antennas are grouped, each group of antennas is an antenna sub-array, each antenna sub-array comprises a plurality of transmitting antennas, and a base station selects a transmitting antenna sub-array according to the spatial information bit corresponding to a user terminal;
(2) different array gains are given to different transmitting antenna sub-arrays corresponding to a certain user, and the array gain factor of the m-th transmitting antenna sub-array of the certain user meets the requirement
Wherein
An array gain factor is given to the mth transmitting antenna subarray in the transmission time of the tth frame, and T is the total frame number; in addition, the array gain corresponding to each antenna sub-array is within the transmission time of each frameKeeping the antenna subarrays unchanged, and reducing the channel correlation of the adjacent antenna subarrays according to the difference of the transmission time of different frames;
(3) a user side transmits signals to a base station, the base station receives the signals by using a selected antenna sub-array, and estimates an arrival angle of a direct path of an uplink signal by using an arrival angle estimation algorithm, and then, the transmission angle of the signals in a downlink is obtained according to reciprocity of an uplink and a downlink of a channel to form an analog beam forming vector, so that beam forming is carried out on the selected antenna sub-array; the analog beamforming vector for the mth transmit antenna sub-array is represented as:
wherein the transmission angle of the direct path of the signal in the downlink is phi, j is an imaginary constant, k02 pi/lambda, lambda is the carrier wavelength, mu is the number of antennas in the transmitting antenna sub-array, T represents the matrix transposition, d represents the antenna spacing;
for a multi-user scene, the user side respectively sends mutually orthogonal signals to the base station; for a multi-user scene, for an active antenna subarray, after obtaining the transmission angle of a signal in each user downlink, obtaining an analog beamforming vector based on a maximized signal-to-leakage-noise ratio criterion, wherein the signal-to-leakage-noise ratio of a kth user terminal is represented as:
wherein,
a steering vector corresponding to a transmitting angle from a transmitting antenna subarray of a kth user terminal to a direct path of the kth user terminal is represented,
indicating the transmitting day of the kth user terminal of the base stationA steering vector rho corresponding to the emission angle of the direct path from the linear subarray to the qth user terminalk,kAnd ρq,kEach of which represents a corresponding path gain, respectively,
is variance, in denominator
Term represents the power leakage from the beamforming direction of the target user terminal k to other user terminals by maximizing the SLNRkTo obtain the optimal beamforming vector f of the kth user terminalk；
(4) A base station transmitter transmits signals through antenna subarrays determined by spatial modulation;
(5) and the user terminal estimates information symbols according to the received signals, calculates error vectors, determines a transmitting mode according to a minimum error criterion and demodulates the spatial information.
2. The spatial modulation method for massive MIMO system as claimed in claim 1, wherein in said step (5), the transmission pattern is determined according to a minimum error criterion, and performing spatial information demodulation further comprises the receiver jointly estimating the transmission pattern and the information symbols according to the following criteria by using a maximum likelihood estimation method or a minimum euclidean distance estimation method according to the received signals:
wherein the error vector epsilonn,m＝y-βmHmfmsnY is the signal vector received by the receiver, HmRepresenting the channel matrix, beta, from the m-th sub-array of transmit antennas to the receivermArray gain factor, s, for the mth transmit antenna sub-arraynAnd the information symbol corresponding to the nth constellation point in the set N-dimensional information constellation diagram.
3. A massive MIMO system based on spatial modulation comprises a transmitter end device and a receiver end device, and is characterized in that:
the transmitter end device comprises a space modulation unit, an array gain control unit and an analog beam forming unit, wherein,
the space modulation unit performs space modulation on the transmitted bit data, and divides the transmitted bit data into two parts, one part is used as an information symbol to be modulated according to a set modulation mode, the other part is used as a space information bit, wherein the transmitting antennas are grouped, each group of antennas is an antenna sub-array, each antenna sub-array comprises a plurality of transmitting antennas, and the base station determines the transmitting antenna sub-array according to the space information bit corresponding to the user terminal;
the array gain control unit endows different array gains to different transmitting antenna sub-arrays corresponding to a certain user, and the array gain of each antenna sub-array is kept unchanged in each frame transmission time and is different in the transmission time of different frames; the array gain control unit enables the array gain factor of the m-th transmitting antenna sub-array of a certain user to satisfy
Wherein
An array gain factor is given to the mth transmitting antenna subarray in the transmission time of the tth frame, and T is the total frame number;
the analog beam forming unit adopts an arrival angle estimation algorithm to estimate an arrival angle of a direct path of an uplink signal, and then obtains a transmission angle of a signal in a downlink according to reciprocity of an uplink and a downlink of a channel to form an analog beam forming vector so as to form beam forming on a selected antenna subarray; for a multi-user scene and an active antenna subarray, the analog beam forming unit obtains an analog beam forming vector based on a maximized signal-to-leakage-noise ratio criterion after obtaining the emission angle of a signal in each user downlink,
wherein, the signal-to-leakage-and-noise ratio of the kth ue is represented as:
wherein,
a steering vector corresponding to a transmitting angle from a transmitting antenna subarray of a kth user terminal to a direct path of the kth user terminal is represented,
a guide vector rho corresponding to a transmitting angle from a transmitting antenna subarray of a kth user terminal to a direct path of a qth user terminal of the base stationk,kAnd ρq,kEach of which represents a corresponding path gain, respectively,
is variance, in denominator
Term represents the power leakage from the beamforming direction of the target user terminal k to other user terminals by maximizing the SLNRkTo obtain the optimal beamforming vector f of the kth user terminalk；
The receiver end device is used for estimating information symbols according to the received signals and demodulating spatial information.
4. The massive MIMO system based on spatial modulation of claim 3, wherein the receiver-side apparatus comprises:
a pattern estimation unit for estimating information symbols according to the received signals, calculating error vectors, and determining a transmission pattern according to a minimum error criterion;
a spatial demodulation unit for performing spatial information demodulation according to the transmission pattern; and
and the symbol estimation unit is used for determining the information symbols by adopting a maximum likelihood estimation method or according to the Euclidean distance between the received signal on each antenna and the constellation point.
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