Subcarrier space arrangement index method for MIMO-OFDM system

Abstract

The application discloses a sub-carrier space arrangement index method of MIMO-OFDM system. The method groups source bits of a transmitting end, and respectively carries out QAM modulation and index modulation. The bits after index modulation are mapped into a sub-carrier space arrangement matrix, multiplied with a constellation diagram after QAM modulation, and then subjected to space-time mapping to obtain data to be transmitted by sub-carriers of each transmitting antenna. Then, time domain signals to be transmitted by each antenna are generated through IDFT conversion. At a receiving end, the signals are demodulated through a corresponding mode to obtain a sub-carrier space arrangement matrix and a QAM symbol, and the source bit data is obtained through mapping of the sub-carrier space arrangement matrix and index bits, serial-parallel conversion. The method starts from utilization of space resources, can improve frequency spectrum utilization rate, realizes a certain degree of receiving diversity, and is superior to prior art in bit error rate and demodulation complexity, so that communication quality and frequency spectrum utilization rate reach a balance.

Description

Technical Field

[0001] This invention belongs to the field of wireless communication technology and relates to a digital signal processing method for index modulation in baseband modulation, specifically a subcarrier spatial arrangement indexing method for a MIMO-OFDM system. Background Technology

[0002] The massive user base of 5G wireless networks will significantly increase energy consumption. Therefore, high data rates and high energy efficiency are high priorities in the design of wireless communication systems, including inter-device communication, spectrum sharing, ultra-dense networks, millimeter-wave networks, IoT communication, and multiple-input multiple-output (MIMO) systems. The advent of MIMO technology has enabled better utilization of spatial resources, significantly improving channel capacity and error performance, and is the foundation of next-generation wireless communication systems. MIMO systems increase throughput and coverage area, while providing capacity and diversity gains by utilizing multi-channel capabilities. MIMO systems make the utilization of spatial resources a reality, and one of the key objectives is to improve data transmission rates and spectrum utilization by utilizing distinguishable spatial information. Traditional space-time block codes (STBC) or vertical layered space-time coding (V-BLAST) can maximize diversity and multiplexing gains, but they place very stringent requirements on the channel, and severe inter-carrier interference (ICI) occurs when channel conditions are not met.

[0003] Spatial modulation (SM) is an important MIMO technique that has emerged in recent years. In SM schemes, to achieve spatial diversity in a rich scattering environment, both the receiver and transmitter are equipped with multiple antennas. However, in each transmission time slot, the transmitter only activates one antenna, thus eliminating inter-antenna synchronization problems, avoiding inter-channel interference, and significantly reducing the complexity of the communication system. Furthermore, in SM schemes, in addition to transmitting data symbols, the transmitter's active antenna specifications are used to transmit information. This scheme allows the data rate to increase logarithmically with the number of transmit antennas. However, in multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, since the data transmitted by a single OFDM symbol is much larger than the data carried by the transmitter's active antenna specifications, the improvement in data transmission rate brought by SM modulation in MIMO-OFDM systems is negligible, while the transmitter and receiver become relatively more complex. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a subcarrier spatial arrangement indexing method for MIMO-OFDM systems. By grouping the subcarriers of the OFDM signal according to the number of antennas, and transmitting the subcarriers in each group on different antennas according to different arrangement methods, the data transmission rate can be increased and the bandwidth utilization can be improved without increasing the bandwidth.

[0005] A novel spatial index modulation method for MIMO-OFDM systems specifically includes the following steps:

[0006] Step 1: In a P×Q antenna MIMO-OFDM system, the channel-coded source data is first divided into m groups, where... And m is an integer. For each set of source data... If each data point is mapped to a QAM symbol, then m groups will result in N QAM symbols carried by subcarriers {s1,s2,…,s…}. N}, where N QAM The QAM modulation index is given. The initial space-frequency arrangement data block matrix M, consisting of the i-th group of subcarriers, is... i for:

[0007]

[0008] The matrix M i The size is P*P, where i = 1, 2, ..., m, s n This represents the QAM data carried by the nth subcarrier of OFDM, where n = 1, 2, ..., N.

[0009] Step 2: Extract the remaining D values ​​from the i-th group of source data. imb Bit data is mapped to a subcarrier spatial arrangement index matrix I i D imb satisfy The index matrix I i The size is P*P, consisting of P mutually orthogonal unit vectors, and each arrangement of the P unit vectors corresponds to a D. imb Bit data.

[0010] Step 3: Transfer the initial space frequency data block M i With index matrix I i Multiplying them together yields the space-frequency data block matrix X carrying index information. i Index matrix I i Different arrangements of unit vectors do not change the QAM symbols carried by the subcarriers; they only change the transmit antennas corresponding to the subcarriers. Each space-frequency data block X i Carrying D imb +N QAM *P bits of data. The m space-frequency data block matrices are concatenated in ascending order of subcarriers to obtain a space-frequency data matrix S = [X1X2X3…X…] for P antennas. m ].

[0011] Step 4: Perform IDFT calculation on each row of the space frequency data matrix S in sequence. In order to make the result of IDFT calculation pure real numbers, before performing IDFT calculation, each row of matrix S needs to be constructed into a conjugate symmetric matrix form as shown in formula (4):

[0012]

[0013] In the above formula This represents the QAM symbol carried by the nth subcarrier on the p-th antenna. s* represents the conjugate of s. It is a 1×N zp A matrix of all zeros. The oversampling rate C is set based on the number of zeros, where C = N. DFT / (N DFT -N zp ), where N DFT The oversampling rate is the computation length for IDFT and DFT; a large oversampling rate can reduce the system's bit error rate. After IDFT computation, the discrete form of the OFDM real signal x to be transmitted by the p-th antenna can be obtained. p :

[0014]

[0015] Where k = 0, 1, 2, ..., N DFT -1. S[p][n] represents the data in the p-th row and n-th column of the space-frequency data matrix S. p = 1, 2, ..., P. After IDFT operation, the space-frequency data matrix S to be transmitted by the antenna is mapped into space-time matrix blocks, x1, x2, ..., x... P They are transmitted simultaneously through P antennas.

[0016] Step 5: Group the received data according to the transmit subcarrier grouping method. After receiving the signal, the receiver first performs OFDM demodulation and conversion to the frequency domain using DFT. In a MIMO-OFDM system, assuming perfect channel estimation, a good scattering environment in the MIMO channel, spatially uncorrelated channels, and a channel coherence time much longer than the duration of a space-time block, after passing through a frequency-selective fading channel, the transmission system model is:

[0017]

[0018] in The signal carried by the nth subcarrier received by the receiving antenna q. This represents the channel response corresponding to the nth subcarrier on the transmitting antenna p and the receiving antenna q. It is the QAM signal carried by the nth subcarrier of the transmitting antenna p. This represents the additive noise of the nth subcarrier of the receiving antenna q.

[0019] According to the space-frequency data matrix S, each subcarrier exists only on one antenna, that is... Only one of them is not zero. Therefore It can be represented as:

[0020]

[0021] in This indicates that the number t is... n The nth subcarrier data transmitted by the antenna, [t1t2t3…t N ] represents the subcarrier spatial arrangement index information, t n ∈[1,2,…,P]. This refers to the receiving antenna q, numbered t. n The channel response of the nth subcarrier under the transmit antenna. Since the N subcarriers of OFDM are divided into m groups, each group has P subcarriers, the data received by each group of subcarriers can be considered as a vector:

[0022]

[0023] This indicates that the m-th subcarrier packet received by the receiving antenna q is numbered t. p The channel response of the p-th subcarrier of the transmitting antenna. This represents the data vector of the m-th packet received by the receiving antenna q. The QAM symbol carried by the p-th subcarrier in the m-th subcarrier group.

[0024] Step 6: Perform antenna and QAM symbol detection on the data vectors of the received m subcarrier packets using a maximum likelihood (ML) detector.

[0025]

[0026] in The data vector for the m-th subcarrier carries spatial index information and QAM symbols. It carries QAM data. The subcarriers are numbered as The antenna transmits.

[0027] Step 7: Perform QAM inverse mapping on each group of data information after ML demodulation, demap the antenna index information, and finally obtain the restored source bit stream after data sorting.

[0028] The present invention has the following beneficial effects:

[0029] For the transmitter of a MIMO-OFDM system, a subcarrier spatial arrangement method is used to ensure that the number of OFDM subcarriers transmitted on each antenna is consistent. By rationally configuring the subcarrier grouping, bandwidth utilization can be effectively improved, making the data rate in the MIMO-OFDM system increase logarithmically with the number of transmit antennas, and also reducing the PAPR (Packet Reduction Proportion) on each transmit antenna. The receiver can demodulate using a maximum likelihood (ML) demodulator to obtain the transmit antenna index and QAM data. Alternatively, an MMSE (Multi-Level Multi-Screen Equalizer) can be used for noise removal and channel equalization, avoiding adverse effects on system transmission reliability. Attached Figure Description

[0030] Figure 1 A schematic diagram of a MIMO-OFDM system based on subcarrier spatial permutation index;

[0031] Figure 2 The examples provide system bit error rate results for different antenna combinations under rich scattering environment channels;

[0032] Figure 3 The system bit error rate results for different antenna combinations in the weak scattering environment channel in the examples. Detailed Implementation

[0033] The present invention will be further explained below with reference to the accompanying drawings;

[0034] Example 1

[0035] This embodiment assumes that the 24 original binary bits of data after source coding are {011110110100_110011011101}, using 4QAM modulation, with N=8 subcarriers, P=4 transmit antennas, and m=2 packets in OFDM. The original binary bits are then divided into {10110100_11011101} and {0111_1100}. {10110100_11011101} is then 4QAM modulated and mapped into two initial space-frequency arranged data blocks M1 and M2.

[0036]

[0037]

[0038] {0111_1100} is mapped to subcarrier space permutation index matrices I1, I2:

[0039]

[0040]

[0041] The mapping relationships are shown in Table 1:

[0042] Table 1

[0043]

[0044] The initial space frequency data block M i With index matrix I i Multiplying them together yields the space-frequency data block matrix X carrying index information. i :

[0045]

[0046]

[0047] Each space frequency data block matrix X i Carrying 12 bits of data. Rearranging [X1X2] according to the subcarrier positions yields the space-frequency data matrix S to be transmitted by the antenna:

[0048]

[0049] Each row of matrix S represents the data to be transmitted by one antenna. After receiving the signal, the receiver can estimate the transmitted spatial arrangement index matrix I and the QAM modulated data M through maximum likelihood estimation, and then obtain the original sequence through inverse mapping.

[0050] Example 2

[0051] In this embodiment, after channel coding, QAM mapping, index matrix mapping, and space-time mapping, the source bit sequence of the MIMO-OFDM system is used to construct a conjugate sequence for the signal of each antenna. This sequence is then processed by IDFT to generate the OFDM signal for each antenna, which is finally transmitted via the RF transmit antenna. At the receiver, a corresponding MMSE frequency domain equalizer is designed, followed by a QAM demodulator. The signal is first demodulated by QAM and then fed into the ML subcarrier spatial arrangement decoder. Finally, the search bits and data bits are combined and channel decoded to obtain the source bit stream. Specifically, the oversampling rate C = 4, the IFFT and FFT lengths are 1024, and the number of subcarriers N = 400.

[0052] The bit error rate of the above method under different signal-to-noise ratios in a Rayleigh fading channel with 10 multipath paths was calculated, and the performance of the MISO-OFDM system, the dual-transmit dual-receive MIMO-OFDM system, and the dual-transmit quad-receive system were compared. The results are as follows: Figure 2 As shown, increasing the number of receiving antennas can significantly improve the bit error rate. It can be seen that MIMO-OFDM subcarrier spatial arrangement index modulation can effectively achieve receiver diversity, and in rich scattering environments, it can improve spectral efficiency while maintaining reliable communication quality using spatial information. Figure 3For a Rayleigh fading channel with two multipath paths, the bit error rate of this method is calculated at different signal-to-noise ratios. Figure 2 In comparison, it can be seen that this system has better communication quality when the multipath effect is weak. Compared with V-BLAST coding, this method reduces the requirements for the scattering environment, improves spectral utilization, and achieves better communication quality. It can be applied to various channel environments. This method can achieve a certain degree of receive diversity, and its bit error rate is better than that of spatial indexing (SM-OFDM) and V-BLAST-based MIMO systems, while its demodulator complexity is lower than that of SM-OFDM and V-BLAST-based MIMO systems.

Claims

1. A subcarrier spatial arrangement indexing method for MIMO-OFDM systems, characterized in that: Specifically, the following steps are included: Step 1: At the transmitter of the MIMO-OFDM system with P antennas, the source data after channel coding is first divided into m groups, where... And m is an integer; for each group of source data Each data point is mapped to a QAM symbol, resulting in the QAM symbols {s1, s2, ..., sn} carried by N subcarriers at the transmitter. N }, where N QAM Let M be the QAM modulation index; then the initial space-frequency arrangement data block matrix M composed of QAM symbols on the i-th subcarrier group. i for: The matrix M i The size is P*P, where i = 1, 2, ..., m; Step 2: Extract the remaining D values ​​from the i-th group of source data. imb Bit data is mapped to a subcarrier spatial arrangement index matrix I i D imb satisfy The index matrix I i It consists of P mutually orthogonal unit vectors, with a size of P*P. Each arrangement of the P unit vectors corresponds to a D. imb Bit data; Step 3: Transfer the initial space frequency data block M i With index matrix I i Multiplying them together yields the space-frequency data block matrix X carrying index information. i Each space frequency data block X i Carrying D imb +N QAM *P bits of data; The m space-frequency data block matrices are concatenated according to the forward order of the subcarriers to obtain a space-frequency data matrix S = [X1 X2 X3 … X…] for P antennas. m ]; Step 4: Perform IDFT calculation on the space frequency data matrix S, map it into a timing signal, and then transmit it using the corresponding antenna; at the receiving end, use ML to perform antenna and QAM symbol detection on the received data vector, then perform QAM inverse mapping, and demap the antenna index information according to the index matrix in step 2. Finally, after data sorting, the restored source data is obtained.

2. The subcarrier spatial arrangement indexing method for a MIMO-OFDM system as described in claim 1, characterized in that: Before performing IDFT calculation on the space frequency data matrix S, the following conjugate symmetric matrix is ​​constructed for each row of the matrix: in This represents the QAM symbol carried by the nth subcarrier on the p-th antenna, where p = 1, 2, ..., P; s * Indicates the conjugate of s; It is a 1×N zp A matrix of all zeros; the oversampling rate C and the IDFT computation length N are set according to the number of zeros. DFT C=N DFT / (N DFT -N zp ); Calculate the timing signal x transmitted by the p-th antenna. p : Where S[p][n] represents the data in the p-th row and n-th column of the space frequency data matrix S.

3. The subcarrier spatial arrangement indexing method for a MIMO-OFDM system as described in claim 1, characterized in that: At the receiving end, assuming the number of receiving antennas is Q, the transmission system model is as follows: in, To receive the signal carried by the nth subcarrier received by the receiving antenna q; This indicates that the number t is... n The QAM signal carried by the nth subcarrier transmitted by the antenna, [t1 t2 t3 … t N ] represents the subcarrier spatial arrangement index information, t n ∈[1,2,…,P]; This indicates that the receiving antenna q, numbered t n The channel response of the nth subcarrier under the transmitting antenna; then the data received by the receiving terminal carrier is represented as: in, This indicates that the m-th subcarrier packet received by the receiving antenna q is numbered t. p The channel response of the p-th subcarrier of the transmitting antenna; This represents the data vector of the m-th packet received by the receiving antenna q; The QAM symbol carried by the p-th subcarrier in the m-th subcarrier group.

4. The subcarrier spatial arrangement indexing method for a MIMO-OFDM system as described in claim 3, characterized in that: Antenna and QAM symbol detection are performed on the data vectors of the received m subcarrier packets using a maximum likelihood detector: in The data vector of the m-th subcarrier carries spatial index information and QAM symbols; it also carries QAM data. The subcarriers are numbered as The antenna transmits.

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