An amplitude-phase differential modulation and demodulation method for MIMO system

Abstract

The application discloses a kind of amplitude-phase difference modulation and demodulation method for MIMO system.The method is mapped in amplitude and the phase difference of adjacent symbol on source bit data at transmitting end, then according to known CSI information, SVD decomposition is carried out to channel matrix, and the optimal channel capacity power distribution is carried out using singular value matrix control signal amplitude, so that all effective channels in the same symbol period transmit the same symbol, finally, all transmitting symbols are obtained according to precoding scheme and transmitted through radio frequency chain.After synchronization is carried out to the received signal at receiving end, amplitude and phase difference value are obtained and phase wrap is demodulated, signal power of different receiving antennas is estimated, MRC is combined to amplitude and phase difference, and finally, source bit data is obtained by reflection mapping.The method combines the advantages of traditional DPSK modulation and ASK modulation, can flexibly adjust modulation index to adapt to different conditions, and the optimal energy efficiency can be obtained at transmitting end, and the complexity can also be reduced at receiving end.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wireless communication, and relates to a baseband digital modulation and preprocessing method in the communication field, in particular to an amplitude-phase differential modulation and demodulation method for a MIMO system. BACKGROUND

[0002] In the past four decades, mobile communication systems have developed rapidly, and the fifth generation mobile communication system (5G) has been widely used. Massive multiple-input multiple-output (MIMO) is a key technology of 5G, and MIMO technology improves the utilization rate of spatial resources in wireless communication, provides greater capacity and diversity gain by effectively utilizing multiple channels, and can improve transmission rate without increasing bandwidth. At the same time, massive MIMO technology is also one of the important technologies of the next generation of mobile communication.

[0003] MIMO technology can be used in 5G communication to realize spatial diversity, spatial multiplexing and waveform beamforming. The most commonly used space-time block code (STBC) and vertical layered space-time coding (V-BLAST) respectively realize the maximum gain of diversity and multiplexing, but both of them need to estimate the complete channel state information (CSI) information at the receiving end. With the increase of the number of antennas, the complexity of channel estimation will gradually increase, and a large amount of spectrum resources will be wasted, which is one of the key problems of the application of super large scale MIMO technology in the next generation of mobile communication. In the MIMO system, SVD decomposition is a common method for analyzing the channel, which analyzes the number and strength of the channel through SVD decomposition, and then optimizes the power allocation and precoding to improve the channel capacity and eliminate the interference between channels. However, in order to ensure that the codebook of each antenna at the receiving end is the same and the reliability of the receiving end, the optimal power allocation technology with high energy efficiency is difficult to be applied.

[0004] Differential phase shift keying (DPSK) uses the change of the relative phase of the carrier between the previous and subsequent symbols of the modulated signal to transmit information. Because the phase difference carries information, the phase rotation caused by channel multipath can be eliminated. When using DPSK modulation, the receiving end does not need to perform complex channel estimation, and the complexity of the receiver is low, but DPSK modulation is sensitive to noise. Amplitude shift keying (ASK) uses the amplitude of the modulated signal to carry information, and does not use the phase to carry information, so the complexity of the receiver is low, but it is easily affected by multipath effect.

[0005] In summary, the prior art lacks a modulation and demodulation scheme with low receiving end complexity and high spectrum utilization rate for MIMO systems. SUMMARY

[0006] In view of the deficiencies of the prior art, the amplitude-phase differential modulation and demodulation method for MIMO system is proposed, in which the source bit data is sequentially mapped to the phase difference and amplitude to form A-DPM constellation diagram at the transmitting end, the channel is decomposed and analyzed by using SVD, and then the A-DPM signal is subjected to optimal power distribution and SVD precoding and is transmitted from the multiple antennas through the radio frequency chain. The maximum signal power can be received at the receiving end under the limited transmitting power of the transmitter.

[0007] An amplitude-phase differential modulation and demodulation method for MIMO system, specifically comprising the following steps:

[0008] Step 1, in the MIMO system of N T transmitting antennas and N R receiving antennas, assuming that the amplitude modulation order is M A and the phase difference modulation order is M P , the source bit data subjected to channel coding is continuously mapped to the amplitude and phase difference symbols, one amplitude symbol carries log2M A bit information, and one phase difference symbol carries log2M P bit information. The mapped phase and amplitude information b is:

[0009]

[0010] wherein, is the initial phase, is the i-th phase difference modulation symbol, A i is the i-th amplitude modulation symbol. K is the number of symbols of the source bit data after modulation. Then the amplitude and phase difference are combined to form A-DPM complex signal s:

[0011]

[0012] Since the initial phase does not carry information, the first A-DPM symbol only carries log2M A bit information, and the remaining A-DPM symbols carry log2M A + log2M P bit information.

[0013] Step 2, the SVD decomposition is performed on the known channel matrix H:

[0014] H = U∑V T (3)

[0015] wherein the size of the channel matrix H is N R × N T, U is a left singular matrix, ∑ is a singular value matrix, and V is a right singular matrix. The A-DPM complex signal s is extended using a zero vector to have the same number of rows as the dimension of the right singular matrix V:

[0016]

[0017] represents the extended A-DPM complex signal. The extended signal is left multiplied by the right singular matrix V to obtain a matrix X composed of the transmission vectors of all the transmission antennas:

[0018]

[0019] Step 3: After the transmission vectors of all the transmission antennas are IQ modulated, they are transmitted:

[0020]

[0021] wherein, is a vector composed of the transmission signal sampling values of all the transmission antennas at time t. Re() represents taking the real part. X i represents the i-th column of the matrix X, and is a vector composed of the i-th transmission symbol of all the transmission antennas. f c is a carrier frequency, g(t-iT) is a baseband pulse shape, T is a symbol period, ξ is a power control coefficient, and is used to keep the total transmission power constant at P s :

[0022]

[0023] Step 4: The complex signal Y received at the receiving end is:

[0024] Y = HX + N (8)

[0025] wherein, the size of the complex signal Y is N R × K, N is additive white Gaussian noise. Substituting formula (5) and (3) into formula (8) obtains:

[0026]

[0027] wherein, σ is the largest singular value in the SVD decomposition of the channel, is the first column of U, and satisfies

[0028] Step 5: The complex signal Y is subjected to a coordinate transformation to obtain the amplitude and phase of the received signal:

[0029]

[0030]

[0031] where Y A is the received signal amplitude matrix of all receiving antennas, Y P is the signal phase matrix, both of which are of size N R abs(·) represents the absolute value of a complex number, angle(·) represents the angle of a complex number, N A is the additive equivalent amplitude noise, N P is the additive equivalent phase noise, N P , N A The size of the matrix is related to the signal-to-noise ratio.

[0032] Step 6, estimate the signal power of each receiving antenna according to Y A , and calculate the MRC combining coefficients of each receiving antenna. According to the MRC combining principle, the combining coefficient is proportional to the signal-to-noise ratio. Assuming that the noise power of all receiving antennas is the same:

[0033]

[0034] where w r is the MRC combining coefficient of receiving antenna r, Y A (r,i) is the element value of the rth row and ith column of matrix Y A .

[0035] Step 7, the first column of matrix Y P remains unchanged, and the other adjacent columns are sequentially subtracted to obtain the phase difference matrix ΔY P :

[0036]

[0037] As can be seen from equation (13), after subtraction, all receiving antennas obtain the original phase difference sign plus equivalent phase noise and the phase noise power after subtraction is twice that before subtraction, i.e.

[0038] After obtaining the phase difference, since the phase difference may be greater than π or less than -π, the phase difference is unwrapped:

[0039]

[0040] Step 8, using the combining coefficients w r calculated in equation (12), weight and combine the amplitudes and phase differences received by all receiving antennas:

[0041]

[0042]

[0043] The combined signal can reach the maximum received signal-to-noise ratio, and then the amplitude and bit demapping is performed on r A The phase difference and bit demapping is performed on r P After grouping, arrangement and parallel-serial conversion, the original bit data is obtained.

[0044] The present application has the following beneficial effects:

[0045] 1. The receiver does not need complex channel estimation and equalization, which greatly reduces the complexity of the receiver and reduces the waste of pilot on spectrum resources. Through the pre-coding and power allocation of the transmitter and the MRC combination of the receiver, the low-complexity demodulation machine of the receiver can still obtain the maximum diversity gain and has high energy efficiency.

[0046] 2. The amplitude and phase difference joint modulation solves the problem of low modulation order and low spectrum efficiency when used alone, and can also flexibly configure the modulation order of amplitude and phase difference according to the channel and noise. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 It is a system block diagram of amplitude-phase difference modulation and demodulation system for MIMO system;

[0048] Figure 2 It is the result of the influence of antenna combination on the error rate of small-scale MIMO system under the fixed modulation order in embodiment 1;

[0049] Figure 3 It is the result of the influence of antenna combination on the error rate of large-scale MIMO system under the fixed modulation order in embodiment 1;

[0050] Figure 4 It is the result of the influence of different antenna combinations on the total received signal-to-noise ratio in embodiment 1;

[0051] Figure 5 It is the result of the influence of different modulation orders on the error rate of the same MIMO system in embodiment 2. DETAILED DESCRIPTION

[0052] The present application will be further explained in combination with the accompanying drawings;

[0053] Figure 1 It is a system block diagram of amplitude-phase difference modulation and demodulation method for MIMO system, and the source bit data is binary data after source encoding and interleaving. In the method, the source bit data is mapped to phase and phase difference, assuming that M A = M P = 8, the mapping table of amplitude and phase difference and bit information is as follows:

[0054]

[0055] After that, the constellation of A-DPM is formed by rotation and coordinate conversion through CORDIC algorithm, the channel matrix is decomposed by SVD, the A-DPM signal to be sent is precoded by SVD, so that it is sent only in the highest quality channel, and finally transmitted after IQ modulation by the radio frequency transmitter. The constellation is obtained after the received signal of all receiving antennas is received by the radio frequency receiver, the phase and amplitude are calculated by using CORDIC algorithm, the signal power of each receiving antenna is detected according to the amplitude, the phase difference and phase wrapping are calculated, then the amplitude and phase difference are combined by MRC according to the signal power, and then the source bit data is obtained after the combined signal is inverse mapped and parallel-serial converted.

[0056] Embodiment 1

[0057] In this embodiment, 4A-8DPM modulation is used in the environment of Gaussian white noise, the rate is equivalent to that of the conventional 32QAM modulation, the value of the transmitting power P s is kept constant, that is, the total signal-to-noise ratio is unchanged, and the bit error rate performance in different antenna combinations is compared, as shown in Figure 2 , it can be seen that in the case of small-scale antennas, increasing the number of transmitting antennas and receiving antennas can significantly improve the bit error rate, and increasing the number of receiving antennas has greater improvement on the system in the case of small number of transmitting antennas. In the case of large-scale antennas, the result is shown in Figure 3 , with the increase of the number of transmitting antennas, the system performance gradually improves. Figure 4 It shows the improvement of the total signal-to-noise ratio of the system with the increase of the number of transmitting antennas in different receiving antennas, it can be seen that when the number of transmitting antennas is small, increasing the number of receiving antennas has greater improvement on the system signal-to-noise ratio, and vice versa, the greater the number of transmitting antennas, the smaller the improvement of the system signal-to-noise ratio by increasing the number of receiving antennas.

[0058] Embodiment 2

[0059] In this embodiment, the number of antennas is fixed in the environment of Gaussian white noise, 8x2 MIMO system is used, and the influence of different amplitude modulation order and phase difference modulation order combination on the bit error rate is compared when the total modulation order is 16 and 64. The result is shown in Figure 5 , it can be seen that in the case of the same rate, when the total modulation order is small, the bit error rate is lower when the modulation order of the phase difference modulation is higher, and when the total modulation order is large, the bit error rate is lower when the modulation order of the amplitude modulation is higher.

Claims

1. A method for amplitude-phase differential modulation and demodulation for MIMO systems, characterized by: In one N T transmit antenna and N R receive antenna MIMO system, the amplitude modulation order is set to M A , and the phase difference modulation order is set to M P ; At the transmitting end, the source bit data after channel coding is continuously mapped into amplitude symbol and phase difference symbol, and the mapped phase and amplitude information b is: wherein, is the initial phase, is the i-th phase difference modulation symbol, A i is the i-th amplitude modulation symbol; K is the number of symbols obtained after the source bit data is modulated; the amplitude symbol and the phase difference are combined to form an A-DPM complex signal s: The first A-DPM symbol s(1) carries log2M A bits of information, the remaining A-DPM symbols carry log2M A + log2M P bits of information; The channel matrix is decomposed by SVD, and the A-DPM complex signal s is pre-coded by SVD, and then transmitted after IQ modulation by the radio frequency transmitter; At the receiving end, the received signal is demodulated according to the modulation method of the transmitting end, and the phase difference and amplitude symbol are calculated, and the source bit data is reflected.

2. The amplitude-phase differential modulation and demodulation method for MIMO systems according to claim 1, characterized in that: The channel matrix H is decomposed by SVD: H = U∑V T (3) where the channel matrix H has size N R x N T , U is a left singular matrix, ∑ is a singular value matrix, and V is a right singular matrix.

3. The amplitude and phase differential modulation and demodulation method for MIMO system according to claim 1, wherein: The A-DPM complex signal s is pre-coded by SVD to obtain the transmitting signal of the transmitting end, and the specific method is: The A-DPM complex signal s is extended by using zero vector, so that the number of rows is the same as the dimension of the right singular matrix V after the decomposition of the channel matrix: represents the extended A-DPM complex signal; the extended complex signal is left multiplied by the right singular matrix V to obtain the matrix X composed of the transmission vectors of all the transmission antennas: The transmitting vectors of all transmitting antennas are IQ modulated: wherein is the vector of transmit signal sample values of all transmit antennas at time t; Re() denotes taking the real part; X i denotes the i-th column of matrix x, is the vector of i-th transmit symbol of all transmit antennas; f c is the carrier frequency, g(t - iT) is the baseband pulse shape, T is the symbol period, and ξ is a power control coefficient used to keep the total transmit power constant at P s :

4. The amplitude-phase differential modulation and demodulation method for MIMO systems according to claim 3, wherein: According to the pre-coding mode of the transmitting end, the received complex signal Y is rewritten as: wherein σ is the largest singular value of the channel SVD decomposition, satisfies The complex signal Y is coordinate transformed to obtain the amplitude and phase of the received signal: where Y A is the received signal amplitude matrix, Y P is the signal phase matrix; abs(·) denotes the complex absolute value, angle(·) denotes the complex angle, N A is the additive equivalent amplitude noise, N P is the additive equivalent phase noise; The first column of matrix Y P is kept unchanged, and the other adjacent columns are subtracted in turn to obtain the phase difference matrix ΔY P : wherein represents the equivalent phase noise; further unwrapping operations are performed:

5. The amplitude and phase differential modulation and demodulation method for MIMO system according to claim 4, wherein: Assuming that the noise power of all receiving antennas is the same, the received signal amplitude matrix Y is calculated as A The signal power of each receiving antenna is estimated, and the MRC combining coefficients of each receiving antenna are calculated: where w r is the MRC combining coefficient of the receive antenna r, Y A (r,i) is the element value of the rth row, ith column of the receive signal amplitude matrix Y A . Using the combined coefficients w r The amplitude and phase difference of all received antennas are weighted and combined: For r A Perform an inverse mapping between amplitude and bits, for r P The phase difference is inversely mapped to the bits, and the original bit data is obtained after grouping, arranging, and parallel-to-serial conversion.

6. The amplitude and phase differential modulation and demodulation method for MIMO system as claimed in claim 1, wherein: When M A = M P = 8, the mapping of the amplitude sign and the phase difference sign is done according to the following table:

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