CN105227226B - The multi-user reception method of force zero and serial interference elimination based on interference synthesis - Google Patents

Abstract

The invention discloses a multi-user receiving method based on interference synthesis, zero-forcing and serial interference elimination. Modulation mode information, first use interference synthesis to reduce the number of signals at the receiving end to the number of receiving antennas, then calculate the zero-forcing receiving filter matrix according to different signal synthesis conditions, and filter the mixed signals separately, and compare the filtering performance. Judging the received symbols, using the serial interference cancellation method to eliminate the influence of the decoded symbols on the reception of the remaining components of the mixed signal, and then repeatedly using the combined interference, calculating the filter matrix, and comparing and judging the remaining mixed signals until all the transmitted symbols are recovered. The invention is based on interference synthesis, adopts zero-forcing and serial interference elimination, can restore all transmission symbols under the condition of fewer receiving antennas, and increases the number of users that the system can accommodate.

Description

Multi-user reception method based on interference synthesis, zero-forcing and serial interference cancellation

technical field

The invention belongs to a signal receiving method in the technical field of mobile communication, in particular to a multi-user receiving method based on interference synthesis based zero-forcing and serial interference cancellation (Successive Interference Cancellation, SIC), which is used for a receiver to recover from co-channel interference Scenarios for multiple signals, such as multiple access channels.

Background technique

With the development of mobile communication technology, the traditional time-frequency signal design has been difficult to meet people's requirements for higher and higher transmission rates of wireless links. People began to try to explore communication opportunities from multiple dimensions, and airspace resources are one of them. important aspect. Multiple Input Multiple Output (MIMO) technology is a breakthrough technology in the field of wireless communication in recent years, which can realize the utilization of airspace resources.

With the development of MIMO technology research, the research on point-to-point single-user MIMO system is close to saturation, and single-user MIMO technology can no longer meet the increasing number of users. Multi-user MIMO (Multiple-User MIMO, MU-MIMO) is increasingly more attention. In the current MU-MIMO research, when the number of signals to be solved is greater than the number of antennas at the receiving end, the receiving end does not have enough degrees of freedom to receive all signals without interference, such as Zero Forcing (ZF) reception method. The number of receiving antennas has become an important factor restricting the receiving capability of the receiver, and it is also the main aspect limiting the system capacity.

Interference alignment cancellation (IAC) can be used for multi-user data reception in MU-MIMO system. Li Z, Shen B, Li J D. Interference alignment and cancellation based concurrent transmission and scheduling scheme formultiuser CR-MIMO system. China Communications. 2013, 10(8): 36-43 Concurrent transmission and scheduling scheme) In the cognitive MIMO (Cognitive Radio Multiple-Input Multiple-Output, CR-MIMO) system, an IAC-based transmission scheduling scheme is designed, by using IA to reduce the dimension of the received signal, and using IC to eliminate the existing The effect of restoring the signal. This method can realize the reception of multiple concurrent signals, but requires mutual cooperation of the receiving end.

Multi-channel data reception can also be achieved by using adaptive filtering. Matched filter (MF) is designed to maximize the output signal-to-noise ratio. It is not limited by the number of receiving antennas and can restore all transmitted symbols. However, this method cannot Eliminate interference. When the interference is strong, the signal-to-interference-noise ratio deteriorates, and the data transmission performance deteriorates.

Since the number of signals that can be processed by the receiver is limited by the receiving antenna, a scheduling algorithm can also be used to constrain the number of concurrent signals. Li Zhao, Liu Ruixue, Wang Lin, et al. A priori user scheduling based on correlated interference in MU-MIMO downlink. Journal of Electronics and Information Technology, 2014,36(1):67-73Selecting a group from multiple users Communicate with the base station to realize full utilization of communication resources. But the scheduling algorithm will hinder the information transmission of unscheduled users, and does not support burst communication.

In summary, how to use limited receiving antennas to recover as many signals as possible and improve the transmission performance of a multi-user communication system has become an urgent problem to be solved.

Contents of the invention

The purpose of the present invention is to provide a multi-user reception method based on interference synthesis based on zero-forcing and serial interference cancellation, which aims to break through the constraint of traditional zero-forcing reception that the number of receiving antennas is not less than the number of signal components to be solved, and realize the use of limited reception The antenna recovers as many signals as possible to increase the number of users that the system can accommodate.

Realize the object method of the present invention comprises the following steps:

In the first step, each transmitter is equipped with N _T transmitting antennas, N _T ≥ 2, and transmits one channel of data using beamforming transmission mode. The transmitter calculates the precoding vector p _k according to the respective channel information, and obtains each channel of transmitted data and take L as the modulation method information with the largest modulation order among the modulation methods used, the number of K transmitters sending signals K is greater than the number of receiver antennas _NR , and the transmission power of each transmitter is _PT ;

In the second step, the transmitter estimates the channel state information h _k , k=0,1,...,K-1, and reports it to the receiver together with the modulation information L;

In the third step, the receiver receives the mixed signal y,

where x _k represents the symbol sent by transmitter k, n represents additive white Gaussian noise, and the variance of the noise component is The spatial characteristics of the signal sent by the transmitter k at the receiving end are e _k = h _k p _k , and all the signals at the receiving end form a set A, then the number of signals contained in the initial state set A is K, that is, card(A) =K, where card( ) represents the number of elements in the set;

The fourth step is to compare the size of card(A) and _NR , if card(A) _≤NR , the receiver design zero-forcing receiving filter matrix μ∈card(A) filters y, where, means to find the pseudo-inverse of the matrix, and output card(A) decoded symbols; if card(A)> _NR , the receiver randomly selects _NR -1 signals in the set A to form the signal set C to be solved, then card( C)=N _R -1, the spatial characteristics e _i =h _i p _i ,i∈C of all the signals in the set C, the rest of the signals in the set A form the interference set I, and the signals in the set I are synthesized to synthesize the interference The spatial characteristics of There are many situations after the transmitted symbols are modulated, so there are L ^card(I) synthetic situations for the combined interference. Assuming that the modulation constellation diagram has central symmetry, only need to consider An interference combination situation, that is, e _ε has possible values;

In the fifth step, the receiver first performs Schmidt-orthogonalization on the spatial feature e _i = _hi p _i ,i∈C of the signal to be solved and the spatial feature e _ε of the synthetic interference, and obtains a set of orthonormal basis and Then calculate each filter vector f _i , i∈C in the zero-forcing receiving filter matrix G according to the orthonormal basis,

Conjugate and transpose this N _R -1 column vectors to get G ^H , based on the diversity of e _ε , G has a total types, only one of which corresponds to the actual transmitted symbols;

In the sixth step, the receiver first divides the mixed signal y into way, and then adopt the fifth step designed A filter matrix G ^H filters each mixed signal separately, and compares the signal-to-noise ratio/signal-to-interference-noise ratio SNR/SINR of the received signal, and selects the best decision to output N _R -1 received symbols,

In the seventh step, the receiver uses the decoded symbols and channel information to reconstruct the signal, and then uses serial interference cancellation to convert the decoded _NR -1 symbols in the mixed signal y The signal corresponding to i∈C Eliminate, reduce the number of signals processed by the receiver, and get:

In the eighth step, the receiver deletes the decoded signal from the set A, updates the set A by assigning sets A-C to A, and returns to the fourth step.

The further technical solution of the present invention is: when the number of antennas configured by each transmitter is different, each transmitter transmits data in a different manner, and when the number of transmitting antennas N _T =1, the transmitter uses an omnidirectional transmission mode to send one path of data, here When , the h _k p _k corresponding to the transmitter with the number of transmitting antennas equal to 1 should be replaced by h _k , and the spatial characteristics of the transmitted signal corresponding to the transmitter at the receiving end become e _k =h _k ; when the number of transmitting antennas N _T ≥ 2 , the transmitter sends a channel of data using beamforming transmission mode.

Compared with the prior art, the present invention has the following characteristics:

1. The traditional zero-forcing reception method requires that the number of receiving antennas is not less than the number of signals to be resolved, so when the number of signals is greater than the number of receiving antennas, it cannot be received by the traditional zero-forcing reception method. The present invention can realize receiving all sent data under the condition that the number of receiving antennas is limited, increases the number of users that the system can accommodate, and obtains good data rate performance;

2. The present invention designs an interference synthesis method. When the number K of transmitted symbols is greater than the number _NR of receiving antennas, _NR -1 signals are selected as interference signals and synthesized to reduce the number of signals at the receiving end to N _R , calculate the zero-forcing receiving filter matrix according to different signal synthesis conditions, and use the obtained zero-forcing receiving filter matrix to filter the mixed signal respectively, and compare the filtering performance to determine the correct receiving symbol;

3. The present invention adopts serial interference elimination technology, by subtracting the recovered signal from the received mixed signal, thereby reducing the burden on the receiver from the decoded signal, and then combining zero-forcing reception to make all transmitters The sent symbols are recovered.

Description of drawings

Fig. 1 is the multi-user uplink communication system model provided by the present invention;

Fig. 2 is a flow chart of a multi-user receiving method based on interference synthesis-based zero-forcing and serial interference cancellation provided by the present invention;

Fig. 3 is a schematic diagram of designing filter vectors of a multi-user reception method based on interference synthesis, zero-forcing and serial interference cancellation provided by the present invention;

Fig. 4 is a receiver structure diagram of a multi-user receiving method based on interference synthesis based zero-forcing and serial interference cancellation provided by the present invention;

Fig. 5 is a simulation diagram of the system data rate performance obtained based on _NT = 2, _NR = 2 and K = 3 in Embodiment 1 of the present invention, while providing a fixed receiving antenna and changing the number of transmitters (or the number of concurrent signals) System data rate simulation diagram;

Fig. 6 is a simulation diagram of system data rate performance based on _NT = 1, _NR = 2 and K = 3 in Embodiment 2 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit it. this invention.

The embodiment of the present invention is mainly based on multiple access channel (Multiple Access Channel, MAC) for research and description, and aims to provide a multi-user receiving method based on interference synthesis, zero forcing and serial interference cancellation.

Example 1

Fig. 1 is the system model of embodiment 1. For simplicity of implementation, only a communication system consisting of three transmitters and one receiver is studied, the receiver is configured with _NR = 2 receiving antennas, each transmitter is configured with _NT = 2 antennas, and each transmitter only transmits One channel of data, then the number of sent data K=3, the embodiment of the present invention only studies that all transmitters use binary phase shift keying modulation (Binary Phase-Shift Keying, BPSK), and the modulation mode information L=2, what needs to be explained Yes, the present invention is not limited to the case where all transmitters use the same modulation method. When different transmitters use different modulation methods, L is taken as the modulation method information with the largest modulation order among the modulation methods used.

As shown in Figure 2, the receiving method in Embodiment 1 of the present invention specifically includes the following steps:

In the first step, each transmitter is equipped with N _T = 2 transmitting antennas, and transmits one channel of data using beamforming transmission mode. The transmitters calculate the precoding vector p _k according to their respective channel information, assuming that all transmitters follow the main If the eigenmode is transmitted, the precoding vector is selected as the main right singular vector of the channel matrix, which corresponds to the maximum singular value of the channel matrix. Each transmission is modulated by BPSK mode, and the modulation mode information is L=2. Each transmitter The transmit power of is equal to P _T ;

In the second step, the transmitter estimates the channel state information h _k , k=0, 1, 2, and reports it to the receiver together with the modulation mode information L=2;

In the third step, the receiver receives the mixed signal y;

where x _k represents the symbol sent by transmitter k, n represents additive white Gaussian noise, and the variance of the noise component is The spatial characteristics of the signal sent by the transmitter k at the receiving end are e _k =h _k p _k , and all the signals at the receiving end form a set A, then the number of signals contained in the initial state set A is 3, that is, card(A) =3, where card( ) represents the number of elements in the set;

The fourth step is to compare the size of card(A) and the number of receiving antennas 2, if card(A)≤2, the receiver design zero-forcing receiving filter matrix μ∈card(A) filters y, where, It means to find the pseudo-inverse of the matrix, and output card(A) decoded symbols to compare the size of card(A) and _NR ; if card(A)>2, the receiver randomly selects _NR -1=1 in the set A signals constitute the signal set C to be solved, then card(C)=1, the spatial characteristics e _i =h _i p _i , i∈C of the signals in the set C, and the rest of the signals in the set A form the interference set I, then card( I)=2, the signals in the set I are synthesized, and the spatial characteristics of the synthesized interference are Because the transmitted symbols all adopt BPSK modulation, so there are 2 ^card(I) = 4 kinds of signal synthesis situations, assuming that the modulation constellation diagram has central symmetry, then only need to consider An interference combination situation, that is, e _ε has two possible values;

In the fifth step, the receiver first performs Schmidt-orthogonalization of the spatial features e _i , i∈C of the signal to be solved and the synthetic interference e _ε , and obtains a set of orthonormal basis Then calculate each filter vector f _i , i∈C in the zero-forcing receiving filter matrix G according to the orthonormal basis,

This zero-forcing receiving filter matrix G is carried out conjugate transposition, obtains G ^H , the diversity of e _ε causes zero-forcing receiving filter matrix G to have 2 ^card(I)-1 =2 kinds, and wherein only one kind is with the actual transmission The symbols match. Figure 3 describes the design method of the filter vector f ₀ in the zero-forcing receiving filter matrix G when the signal x ₀ belongs to the set C and the rest of the signals belong to the set I. The receiver first synthesizes the signals in I and obtains the space for the combined interference feature e _ε ; then perform Schmidt orthogonalization on e _ε to obtain the orthonormal basis Finally, using the construction method of the filter vector in the zero-forcing receiving filter matrix G described in this step to get It should be noted that _, according to the fourth step of Embodiment 1 of the present invention, e _ε has two possible values _{e ε1} and e _ε2 .

In the sixth step, the receiver first divides the mixed signal y into two channels, and then uses the two zero-forcing receiving filter matrices G designed in step 5 to filter the mixed signal respectively, and compares the SNR/SINR of the received signal, and outputs a receiving symbols, i∈C;

In the seventh step, the receiver reconstructs the signal by using the decoded symbol and channel information, and then uses serial interference cancellation to convert a decoded symbol in the mixed signal y The signal corresponding to i∈C eliminate, get,

In the eighth step, the receiver deletes the decoded signal from the set A, updates the set A by assigning sets A-C to the set A, and returns to the fourth step.

FIG. 4 shows a specific receiver structure diagram of Embodiment 1 of the present invention, which illustrates the operation process of filter reception, serial interference elimination and residual signal recovery in Embodiment 1 of the present invention. Figure 4. First, x ₀ is used as the desired signal to be solved, and other signals are used as interference and interference synthesis is performed. According to the sixth step, the receiver divides the mixed signal y at the receiving end into two channels, and adopts the zero-forcing receiving filter matrix G ₁ and G ₂ filter and receive the mixed signal, compare the SNR/SINR of the received signal, and choose the best decision output and will Feedback to the receiver; then according to the seventh step, the decoded corresponding signal get rid of Finally design the zero-forcing receiving filter matrix W _ZF receiving output

Example 2

On the basis of Embodiment 1, when the number of antennas configured by each transmitter is different, each transmitter transmits data in a different manner. When the number of transmitting antennas N _T =1, the transmitter transmits one channel of data in an omnidirectional transmission mode. At this time, the h _k p _k corresponding to the transmitter with the number of transmitting antennas equal to 1 in Embodiment 1 should be replaced by h _k , the transmitting The spatial characteristics of the transmitted signal corresponding to the transmitter at the receiving end become e _k =h _k ; when the number of transmitting antennas N _T ≥ 2, the transmitter transmits one channel of data in a beamforming transmission mode, as described in Embodiment 1 above.

The embodiment of the present invention also lies in that in the fifth step, when the number of transmitted signals is greater than the number of receiving antennas _NR , the interference synthesis is performed first, so that the number of signals at the receiving end is reduced to _NR , and then zero-forcing and serial interference cancellation are used to perform The reception of multi-user data; there are many situations in the modulated transmission symbols, which lead to a variety of composite situations in the composite interference. The present invention designs the corresponding zero-forcing reception filter matrix G according to different composite situations, and divides the mixed signal y at the receiving end into Multi-channel, use the designed G to filter each mixed signal separately, compare the SNR/SINR of the received signal, and choose the best to judge and output the correct received symbol.

The application effect of the present invention is further illustrated by the following simulation experiments:

Figure 5 shows the system data rate performance obtained based on _NT = 2, _NR = 2 and K = 3 in Embodiment 1. Similarly, according to the method of Embodiment 1, the number of antennas at the fixed receiving end _NR = 2 is simulated, and the transmitting When the number of symbols K∈{3,4,5}, the data rate performance of the method of the present invention. The traditional zero-forcing reception method requires that the number of concurrent signals does not exceed the number of receiver antennas, so when K> _NR , zero-forcing reception cannot be used to process the mixed signal, and the method proposed by the present invention can be used when the number of antennas at the receiving end is limited All the sent data can be recovered under the button. As shown in Figure 5, when K∈{3,4,5} and K> _NR , the sum rate of all the data that can be received by the proposed method of the present invention changes with the signal-to-noise ratio. With the increase of the noise ratio, the system data rate performance is also gradually improved; since the proposed method can recover all the transmitted signals, as K increases, the number of signals recoverable by the receiver increases, and the system data rate performance also gradually improves.

Figure 6 shows the system data rate performance obtained based on _NT = 1, _NR = 2 and K = 3 in Embodiment 2 of the present invention. When the transmitted symbol K is greater than the number of receiving antennas _NR , the receiving antenna designed in the present invention The method can break through the traditional zero-forcing receiving method that requires the number of receiving antennas to be no less than the limit of the number of signals to be solved, and receive all the transmitted symbols. As can be seen from Figure 6, as the signal-to-noise ratio increases, the obtained method of the present invention The system data rate performance has also gradually improved.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (3)

1. A multi-user receiving method of zero-forcing and serial interference elimination based on interference synthesis, which is realized in an uplink communication system with multiple concurrent transmitters and a common receiver, and the system receiver obtains the communication with each transmitter For the channel state information and the modulation mode information used by the transmitter, first use interference synthesis to reduce the number of signals processed by the receiving end to the number of receiving antennas, and then calculate the corresponding zero-forcing receiving filter matrix according to different signal synthesis conditions, and respectively The signal is filtered, and the received symbols are judged by comparing the filtering performance, and the serial interference cancellation method is used to eliminate the influence of the decoded symbols on the reception of the remaining components in the mixed signal, and then repeatedly use the synthetic interference and calculate the filter matrix for the remaining mixed signal , comparison and judgment, until the symbols sent by all transmitters are recovered, the receiving method includes the following steps: In the first step, each transmitter is equipped with N _T transmitting antennas, N _T ≥ 2, and transmits one channel of data using beamforming transmission mode. The transmitter calculates the precoding vector p _k according to the respective channel information, and obtains each channel of transmitted data and take L as the modulation method information with the largest modulation order among the modulation methods used, the number of K transmitters sending signals K is greater than the number of receiver antennas _NR , and the transmission power of each transmitter is _PT ; In the second step, the transmitter estimates the channel state information h _k , k=0,1,...,K-1, and reports it to the receiver together with the modulation mode information L; In the third step, the receiver receives the mixed signal y, where x _k represents the symbol sent by transmitter k, n represents additive white Gaussian noise, and the variance of the noise component is The spatial characteristics of the signal sent by the transmitter k at the receiving end are e _k = h _k p _k , and all the signals at the receiving end form a set A, then the number of signals contained in the initial state set A is K, that is, card(A) =K, where card( ) represents the number of elements in the set; The fourth step is to compare the size of card(A) and _NR , if card(A) _≤NR , the receiver design zero-forcing receiving filter matrix μ∈card(A) filters y, where, means to find the pseudo-inverse of the matrix, and output card(A) decoded symbols; if card(A)> _NR , the receiver randomly selects _NR -1 signals in the set A to form the signal set C to be solved, then card( C)=N _R -1, the spatial characteristics e _i =h _i p _i ,i∈C of all the signals in the set C, the rest of the signals in the set A form the interference set I, and the signals in the set I are synthesized to synthesize the interference The spatial characteristics of There are many situations after the transmitted symbols are modulated, so there are L ^card(I) synthetic situations for the combined interference. Assuming that the modulation constellation diagram has central symmetry, only need to consider An interference synthesis situation, that is, possible values; In the fifth step, the receiver first performs Schmidt-orthogonalization on the spatial feature e _i = _hi p _i ,i∈C of the signal to be solved and the spatial feature e _ε of the synthetic interference, and obtains a set of orthonormal basis and Then calculate each filter vector f _i , i∈C in the zero-forcing receiving filter matrix G according to the orthonormal basis, Conjugate and transpose this N _R -1 column vectors to get G ^H , based on the diversity of e _ε , G has a total types, only one of which corresponds to the actual transmitted symbols; In the sixth step, the receiver first divides the mixed signal y into way, and then adopt the fifth step designed A filter matrix G ^H filters each mixed signal separately, and compares the signal-to-noise ratio/signal-to-interference-noise ratio SNR/SINR of the received signal, and selects the best decision to output N _R -1 received symbols, In the seventh step, the receiver uses the decoded symbols and channel information to reconstruct the signal, and then uses serial interference cancellation to convert the decoded _NR -1 symbols in the mixed signal y corresponding signal Eliminate, reduce the number of signals processed by the receiver, and get: In the eighth step, the receiver deletes the decoded signal from the set A, updates the set A by assigning sets A-C to A, and returns to the fourth step. 2. the multi-user receiving method of zero-forcing and serial interference elimination based on interference synthesis according to claim 1 is characterized in that, in the 5th step, when the number of transmitted signals is greater than the number of receiving antennas _NR , the interference is performed first Combining, the number of signals at the receiving end is reduced to _NR , and then zero-forcing and serial interference elimination are used to receive multi-user data. 3. The multi-user receiving method of zero-forcing and serial interference cancellation based on interference synthesis according to claim 1, characterized in that, when there are multiple situations in the modulated transmission symbol causing the composite interference to have multiple composite situations, Then design the corresponding zero-forcing receiving filter matrix G according to different synthesis situations, and divide the mixed signal y at the receiving end into multiple channels, use the designed G to filter each mixed signal separately, and compare the SNR/SINR of the received signal , the optimal decision outputs the correct received symbol.