CN113225117A - Multi-user Massive MIMO system signal transmitting and receiving method - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a signal transmitting and receiving method of a multi-user Massive MIMO system. The scheme of the invention directly carries out beamforming on the CSI (channel State information) of a channel, and carries out beamforming or precoding operation on a signal through a beamforming technology based on zero forcing. Under the framework, a transmitting end can put all information bits into one data stream for transmission, and can obtain beamforming gain at the transmitting end and receiving end through all antennas at the transmitting end and receiving end, and obtain receiving diversity gain at the receiving end through combined detection of all receiving antennas. The invention realizes the transmitting beam forming gain of the transmitter and the space diversity gain of the receiver in a multi-user SM-MIMO system, and can inject more bits into a single data stream, thereby realizing higher transmission data rate and good performance.

Description

Multi-user Massive MIMO system signal transmitting and receiving method

Technical Field

The invention belongs to the technical field of wireless communication, and particularly relates to a signal transmitting and receiving method of a multi-user Massive MIMO system.

Background

Multiple-input multiple-output (MIMO) technology can significantly improve spectral efficiency without increasing transmit power and spectral resources. Among them, spatial multiplexing and spatial diversity are attracting attention, such as vertical layered space-time (V-BLAST) and Alamouti space-time block coding (STBC). In addition, the beam forming technology is an efficient MIMO transmission technology, originates from an array signal processing technology, forms an energy focusing beam by weighing and combing transmission signals of different antennas, transmits a directional strong beam to reduce high transmission loss of a receiver so as to improve the signal-to-noise ratio of the receiver, is an important means of spatial filtering, and has become a key technology and a research hotspot of mobile communication systems beyond 5G and 5G. Currently, the most commonly used beamforming methods in the mobile communication system include Maximum Ratio Transmission (MRT), Zero Forcing (ZF), Minimum Mean Square Error (MMSE), Block Diagonalization (BD), and Signal to Leakage and Noise Ratio (SLNR). To date, there has been extensive research into the design and optimization of beamforming vectors in different MIMO scenarios. Meanwhile, spatial modulation, a new MIMO technology, has been widely discussed in recent years, and it has a single rf characteristic and a unique switch structure, simplifying the implementation of transmission and reception. Furthermore, Spatial Shift Keying (SSK) is a similar but more simplified approach to SM, using only the index of the antenna to modulate information at a single radio frequency, resulting in lower practical implementation complexity and cost. The performance of the SM system can be further improved by preprocessing at the transmitting end using Channel State Information (CSI).

Considering performance, computational complexity and practical application, especially in massive MIMO scenarios, how to improve the spectrum efficiency and performance of SM-MIMO systems by using beamforming technology, while achieving its practical application is still a hot and pending issue.

Disclosure of Invention

Aiming at the problems, the invention provides a zero forcing beamforming auxiliary single-layer transmission technology for a multi-user SM/SSK MIMO system based on the great advantages of a CSI auxiliary MIMO system, the zero forcing beamforming auxiliary single-layer transmission technology is defined as MU-SZF-SM/MU-SZF-SSK in the invention, the scheme of the invention directly carries out beamforming on CSI (channel State information) of a channel, and carries out beamforming or precoding operation on a signal through a zero forcing-based beamforming technology. Under the framework, a transmitting end can put all information bits into one data stream for transmission, and can obtain beamforming gain at the transmitting end and receiving end through all antennas at the transmitting end and receiving end, and obtain receiving diversity gain at the receiving end through combined detection of all receiving antennas.

The technical scheme of the invention is as follows:

the basic technical scheme adopted by the invention is to adopt a binary digital signal space modulation method of a multi-input multi-output system and assume that a transmitting end knows channel state information. The system has s users, each user having N_tRoot transmitting antenna, N_rRoot receiving antennas for transmitting each group b₁+b₂A digital signal of bits. Wherein front b₁Bit mapping to antenna number, i.e. antenna to be activated after spatial modulation, and finally b₂And mapping the bits into APM symbols, carrying out precoding processing on the obtained signals, carrying out maximum likelihood detection at a receiving end, and decoding and outputting.

In conventional zero-forcing based multi-user MIMO techniques (MIMO-ZF), it is adapted to full stream transmission, i.e. the number of transmitted streams per user is equal to the number of receiving antennas, so its spectral efficiency, i.e. the constellation order of each stream multiplied by the total number of streams. When the number of transmission streams per user of the conventional MIMO-ZF is smaller than the number of receiving antennas, some antennas at the receiving end cannot receive signals, and the receiving antennas cannot be fully utilized. Especially when the conventional multi-user MIMO-ZF performs its single stream transmission, it is even impossible to achieve the receive diversity gain because only one target antenna can receive the signal in this case, and thus joint detection cannot be performed on all the received signals. The innovation of the scheme is that a spatial modulation technology is integrated in the traditional multi-user MIMO-ZF technology, the CSI information of a channel is directly subjected to beam forming, all information bits are put into one data stream for transmission for each user, the signal is subjected to precoding operation through a zero-forcing beam forming technology, and all antennas are utilized to perform combined detection at a receiving end.

Transmitting terminal

In MU-SZF-SM, bit information is mapped into transmitting antenna serial number and constellation point symbol through grouping, and the frequency spectrum efficiency B of the system is s (log) at the moment, assuming that M-order modulation is adopted₂(N_t)+log₂(M)), where s is the number of users. Front log₂(N_t) Binary to decimal conversion of the bit, the converted value being used to select the transmitting antenna i which activates the 1 st user₁In the next log₂(M) bit binary to decimal conversion, the converted value being used to select the constellation point symbol x sent_1jLog of next₂(N_t) Bit mapping to select the transmit antenna i that activates the 2 nd user₂Serial number of (2), log₂(M) bit binary to decimal, the converted value is mapped to the constellation point symbol x selected and sent by the user 2_2jAnd so on, the transmitting antenna i of the s-th user_sActivated, and selects the constellation point symbol to be transmitted as x_sjThese conventional modulation constellations may be multilevel phase shift keying constellations (PSK) or quadrature amplitude modulation constellations (QAM), and the activated transmit antenna matrix and the constellation point symbol matrix selected for transmission are then represented as follows:

i＝[i₁,i₂,…,i_m,…i_s]^T#(1)

under the multi-user MIMO configuration, the channel matrix H of the whole system has N_tRoot transmitting antenna (N)_rS) receiving antennas, wherein N is configured per user_rRoot receiving antenna, and is thus one (N)_r*s)*N_tA matrix of dimensions, represented as follows:

H＝[H₁,H₂,…,H_m,…H_s]^T#(3)

the transmitted symbols of this system before beamforming are represented as follows:

x＝[x₁,x₂,…x_m,…,x_s]^T#(6)

wherein in the formula

Is the ith user of the mth user_mA channel column vector from the root transmit antenna to all receive antennas.

Each element in (a) obeys an independent gaussian distribution CN (0,1),

is a mapping symbol of the APM constellation of the mth user,

is the transmit power. If it is not

Then it is the MU-SZF-SSK system if

Is a conventional APM symbol, and is then a MU-SZF-SM system. Transmission signal x of mth user under MU-SZF-SM/MU-SZF-SSK MIMO system_mIs a number N_rA vector of x 1, which is a vector consisting of log₂(N_t) And log₂A single stream signal of (M) bits. It is noted that for each user, all information bits are placed in one data stream

In this regard, it is different from conventional multi-user MIMO-ZF full stream transmission. In particular, for the scheme proposed by the invention, the transmission layer of each user does not follow N_rIs increased, which is much different from the conventional multi-user MIMO-ZF system, because the transmission layer of each user in the conventional multi-user MIMO-ZF is generally identical to the receiving antenna N_rAnd (4) correlating. For the receiving antenna is N_rFor each user in a multi-user MIMO-ZF system, generating N_rX 1 dimensional transmission vector of N_rA different APM symbol composition, considered as N_rStreaming, the amount of information transmitted being N_r×log₂M bits. However, the number of transmission streams per user in MU-SZF-SM/MU-SZF-SSK proposed by the present invention does not follow N_rBecause of the log of the transmitted signal₂(N_t)+log₂(M) bit information associated only with the number N of transmitting antennas_tAnd modulation order M. Thus, the transmission signal x is a vector in the MU-SZFSM/MU-SZF-SSK MIMO system, which transfers s logs₂(N_t)+log₂A single-layer data stream of (M) bits, which avoids severe interference and thus achieves good performance. In addition, for each user, the signal sent out includes not only the APM symbol

Also includes spatial channels

The transmitter transmits the channel information

Sent directly to the receiver, yet still utilize the spatial channels to convey information.

The transmitted symbols then need to be precoded, assuming the simplest zero-forcing (ZF) precoding algorithm is used, with the precoding matrix as follows:

W＝H^H(HH^H)^-1#(8)

therefore, the transmitted signal of each user after zero-forcing beamforming can be expressed as

Wherein, W is a precoding matrix, and H is a channel matrix of the whole system. In addition, if the power normalization is performed on the transmitted symbol and α is the power normalization factor, then

Receiving end

For each user, the signal obtained by the receiving end after passing through the channel can be expressed as follows:

wherein N is (s N)_r) X 1-dimensional gaussian white noise vector, elements obeying CN (0,1),

for transmitting power, matrix

Is N in MIMO system_r×N_rOf the power normalization matrix, here

Is considered to be a modified transmitted sparse signal vector. After the power is normalized, the signals obtained by the receiving end are detected by a maximum likelihood method:

for conventional beamforming of MIMO-ZF, it is difficult to achieve a reception diversity gain even in the case where a receiving end has multiple antennas. This is because the pre-processing of multi-user MIMO-ZF for multi-stream transmission is achieved by pre-canceling the interference at the transmitter without requiring joint detection between multiple antennas at the receiving end. Thus, MIMO-ZF employs multi-stream transmission, each receive antenna obtaining the target APM symbol previously formed at the transmitter without interference.

The invention has the beneficial effects that: the MU-SZF-SM/MU-SZF-SSK provided by the invention is elaborately designed for single stream transmission, and not only realizes the transmit beam forming gain of a transmitter, but also realizes the space diversity gain of a receiver in a multi-user SM-MIMO system. Since MU-SZF-SM/MU-SZF-SSK has significant beamforming gain and receive diversity gain, more bits can be injected in a single data stream, thereby achieving higher transmission data rates and good performance.

Drawings

FIG. 1 is a schematic diagram of a MIMO configuration system model according to the present invention;

FIG. 2 is a diagram comparing the MU-MIMO-ZF and MU-SZF-SSK received by 32-sender 2-user 4.

Detailed Description

The technical scheme of the invention is described in detail in the following with reference to the accompanying drawings and embodiments:

as shown in fig. 1, a MIMO configuration system model of MU-SZF-SM/MU-SZF-SSK proposed by the present invention is briefly shown, and the model is roughly divided into four modules, a precoding module, a CSI-structured space symbol module, a transmitting end module, and a receiving end module.

Examples

In this example, the system adopts SSK modulation, and the number of transmitting antennas N_t32, the number of users is 2, the number of receiving antennas is N _r4, the total spectral efficiency of the system is therefore B ═ s (log)₂(N_t)+log₂(M)) -10 bps/Hz, then the activated transmit antenna matrix and the constellation point symbol matrix selected for transmission are represented as follows:

i＝[i₁,i₂]^T#(12)

in MU-MIMO configuration, the channel matrix H of the entire system has 32 transmit antennas and 8 receive antennas, where 4 receive antennas are configured per user, and thus is an 8 × 32 dimensional matrix. The transmitting end learns that the channel state information is as follows through the feedback link:

H＝[H₁,H₂]^T#(15)

if the bit data to be transmitted by the 2 nd user is b 00101, the 5 bits 00101 are spatial bits and are mapped to a spatial symbol h according to the mapping rule₂₅＝[h_1,25 h_2,25 … h_4,25]^TSince SSK modulation is employed, it is determined

The symbol to be transmitted is

Wherein, in the formula h₂₅Channel column vectors from the 5 th transmit antenna to all receive antennas for the 2 nd user. h is₂₅Each element in (a) obeys an independent gaussian distribution CN (0,1),

is a mapping symbol of the APM constellation of the 2 nd user,

is the transmit power.Transmission signal x of 2 nd user under MU-SZF-SM/MU-SZF-SSK MIMO system₂Is a 4 x 1 vector consisting of₂(32) 5 and log₂(2) 1-bit single stream signal. It is noted that for user 2, all information bits are placed in one data stream

In this regard, it is different from conventional multi-user MIMO-ZF full stream transmission. In particular, in the MU-SZF-SSK example presented above, because of the log of the transmitted signal₂(32)+log₂(2) The bit information is related only to the number of transmit antennas and the modulation order. Thus, the transmit signal x is a vector in the MU-SZFSM/MU-SZF-SSK MIMO system, which delivers 2 logs₂(32)+log₂(2) A single layer stream of bits, which avoids severe interference and thus achieves good performance. In addition, for user 2, the signal sent out includes not only the APM symbol

And also includes a spatial channel h₂₅The transmitter transmits the channel information h₂₅Sent directly to the receiver, yet still utilize the spatial channels to convey information.

Then precoding is carried out, and the precoding matrix is W ═ H^H(HH^H)^-1And if α is a power normalization factor, then α ═ Wh₂₅|₂Therefore, the final transmission signal form of the transmitting end is:

the modulation and precoding process of the system is realized through the steps, and the form of the received signal after the power normalization factor is removed after the signal passes through the channel is as follows:

where n is an 8 x 1 dimensional Gaussian white noise vector, the elements obey CN (0,1),

for transmitting power, matrix

Is a 4 x 4 power normalization matrix in MIMO systems, where

After the power is normalized, the signals obtained by the receiving end are detected by a maximum likelihood method:

it can be seen from the final equation that the system is a MIMO system with 2 users 32 transmitting and 4 receiving, performance gain is introduced by combining the beamforming technology, and only the ith user is seen from the receiving end₂The root antenna needs to be detected. The scheme has no limit on the number of the receiving and transmitting antennas, is flexible and can bring greater performance improvement. The improvement of the error code performance of the invention is specifically analyzed by combining the simulation result.

Fig. 2 shows the comparison of the error rates of the proposed scheme of the present invention under the conditions of 32 transmitting antennas, 2 users and 4 receiving antennas, and the SSK modulation is adopted to make the spectral efficiency B ═ s (log)₂(N_t)+log₂(M)) -10 bps/Hz, while for MU-MIMO-ZF systems in this case full-stream transmission, the spectral efficiency is B-s N _r8 bps/Hz. Generally, the change of the bit error rate is slowly changed along with the signal-to-noise ratio, the spectral efficiency of the scheme is higher than that of the traditional MU-MIMO-ZF under the condition of low signal-to-noise ratio (below 6 dB), the bit error rate is lower than that of the traditional MU-MIMO-ZF, and the performance of the scheme is better.

Claims (1)

1. A multi-user Massive MIMO system signal transmitting and receiving method, wherein the system has s users, each user has N_tRoot transmitting antenna, N_rRoot receiving antennas for transmitting each group b₁+b₂Digital signal of bits, in which the front b₁Bit mapping to antenna number, post b₂Mapping bits into APM symbols; it is characterized by comprising:

transmitting terminal

Assuming that M-order modulation is used, the spectral efficiency B of the system is s (log)₂(N_t)+log₂(M)), front log₂(N_t) Binary to decimal conversion of the bit, the converted value being used to select the transmitting antenna i which activates the 1 st user₁In the next log₂(M) bit binary to decimal conversion, the converted value being used to select the constellation point symbol x sent_1jLog of next₂(N_t) Bit mapping to select the transmit antenna i that activates the 2 nd user₂Log of (2), then₂(M) bit binary to decimal, the converted value is mapped to the constellation point symbol x selected and sent by the user 2_2jAnd so on, the transmitting antenna i of the s-th user_sActivated, and selects the constellation point symbol to be transmitted as x_sjThe modulation constellation can be a multilevel phase shift keying constellation or a quadrature amplitude modulation constellation, and the activated transmitting antenna matrix and the constellation point symbol matrix selected to be transmitted are represented as follows:

i＝[i₁，i₂，…，i_m，…i_s]^T

the channel matrix H of the system is:

H＝[H₁，H₂，…，H_m，…H_s]^T

the transmitted symbols before beamforming are:

x＝[x₁，x₂，…x_m，…，x_s]^T

wherein the content of the first and second substances,

is the ith user of the mth user_mThe channel column vectors for the root transmit antenna to all receive antennas,

each element in (a) obeys an independent gaussian distribution, x_jmIs a mapping symbol of the APM constellation of the mth user,

is the transmit power; transmission signal x of mth user_mIs a number N_rA vector of x 1, which is a vector consisting of log₂(N_t) And log₂Composed of a single stream of (M) bits, all information bits being placed in a data stream for each user

The above step (1);

precoding the transmission symbol to obtain a transmission signal

W＝H^H(HH^H)^-1

Wherein, alpha is a power normalization factor,

receiving end

For each user, the signals obtained by the receiving end after passing through the channel are:

wherein N is (s x N)_r) X 1-dimensional Gaussian white noise vector, matrix

Is N in MIMO system_r×N_rThe power of the power normalization matrix of (a),

is the modified transmitted sparse signal vector;

carrying out maximum likelihood method detection on signals obtained by a receiving end:

Images