Efficient MIMO-OCDM transmission method based on index modulation

Abstract

The invention discloses a high-efficiency MIMO-OCDM transmission method based on index modulation, and the method comprises the steps: constructing a multi-antenna MIMO-OCDM system, carrying out the grouping of needed transmission bit information, and carrying out the processing of each group of information bits in each branch of a transmitter through an index modulator of each transmission antenna of the MIMO-OCDM; carrying out OCDM modulation on the sending signal, and sending the sending signal to a receiving end through a multipath channel; performing channel equalization processing on the time domain signal received by the receiving end; and on the basis of the probability value of each subcarrier, summing the probability values of the carriers in each combination according to c conditions in a table look-up method table, adopting the condition of the combination with the maximum sum of the probability values as an activated subcarrier sequence number combination estimation value, detecting index bit sum and modulation bit information, and completing the whole communication link. According to the invention, the frequency efficiency of a traditional OCDM system can be effectively improved, and the bit error rate is reduced.

Description

Technical Field

[0001] The invention belongs to the field of communication technology, and in particular relates to a high-efficiency MIMO-OCDM transmission method based on index modulation. Background Art

[0002] The Sixth Generation Mobile Communication (6G) technology is currently at the forefront of wireless communication research and development, with the goal of achieving unprecedented data transmission speeds, ultra-low latency, and ultra-large-scale connections. To achieve this goal, academia and industry have conducted extensive research and exploration, especially in the field of coding and waveform modulation technology.

[0003] In the fifth generation mobile communication (5G) network, multiple-input multiple-output (MIMO) combined with orthogonal frequency division multiplexing (OFDM) is the most widely used air interface technology in wireless communication today, enabling high-speed broadband wireless access services. However, OFDM is susceptible to burst errors caused by channel zeros or interference, which seriously affects its average error performance. This may not guarantee that it meets the reliability constraints of ultra-reliable low-latency communication. In addition, since massive machine-type communication networks operate on unlicensed frequency bands, the operation of OFDM systems will inevitably be limited by interference, and the use of OFDM modulation will also have significant out-of-band leakage problems. For the above reasons, industry and academia have vigorously promoted the exploration of transitional variants of OFDM modulation to cope with the increasing traffic and lower tolerance to interference that will be encountered in future generations of wireless networks. Spread spectrum schemes, such as orthogonal chirp division multiplexing (OCDM) technology, have shown considerable application prospects in solving these problems. At the same time, OCDM technology combined with multi-antenna MIMO broadband system can make full use of time and space diversity, and can better resist the impact of multipath effects and Doppler frequency domain, make up for the serious problems existing in the current MIMO-OFDM system, and become a potential air interface technology in the current 6G network.

[0004] Meanwhile, the new index modulation (IM) has been widely used in the field of broadband communications. Specifically, unlike traditional multi-carrier schemes, IM only sends part of the resources (such as subcarriers, antennas, time slots or channel states) for data transmission. This not only does not waste resources and space, but also can achieve higher high throughput and low energy performance, because the additional information bits can be implicitly conveyed by selecting the index of the resource. Therefore, IM can not only transmit modulated information bits based on amplitude or phase modulation, but also harvest additional index bits without consuming energy, thereby significantly improving spectrum and energy efficiency. In addition, due to the flexible structure of the IM-assisted frame, considerable diversity gain can be obtained from the activation mode of the index resource, the type of constellation alphabet or the selection of the channel state, which all contribute to significant performance gains. However, due to the physical limitations of the IM mechanism, existing IM-assisted systems suffer from throughput losses.

[0005] As a multi-carrier communication technology based on chirp spread spectrum (CSS), OCDM has strong anti-multipath interference capability and has become a potential waveform for the next generation of communication networks. However, few studies have been conducted on MIMO-OCDM systems combined with index modulation. Therefore, the present invention proposes a MIMO-OCDM transmission system based on index modulation (IM). Summary of the invention

[0006] In view of the above technical problems, the present invention proposes an efficient MIMO-OCDM transmission method based on index modulation, which can effectively improve the frequency efficiency of the traditional OCDM system and reduce the bit error rate.

[0007] Technical solution:

[0008] An efficient MIMO-OCDM transmission method based on index modulation, the efficient MIMO-OCDM transmission method comprising the following steps:

[0009] S1, construct a multi-antenna MIMO-OCDM system, group the required transmission bit information, and each group of information bits is processed by the index modulator of each transmission antenna of the MIMO-OCDM in each branch of the transmitter to obtain the transmission signal of each antenna;

[0010] S2, performs OCDM modulation on the transmission signal and sends it to the receiving end through a multipath channel;

[0011] S3, performing channel equalization processing on the time domain signal received by the receiving end;

[0012] S4, based on the probability value of each subcarrier, the probability values ​​of each carrier in each combination are summed according to the c cases in the table of the lookup method, and the combination with the largest total probability value is used as the estimated value of the activated subcarrier sequence combination, the index bit and the modulation bit information are detected, and the entire communication link is completed.

[0013] Step S1 further comprises:

[0014] S11, construct a multi-antenna MIMO-OCDM system, there are N T transmit antennas, and send N R The root received signal sends a modulated signal, and each antenna sends an OCDM signal with N orthogonal Chirp subcarriers;

[0015] S12, for each frame of information transmission, mN T The information bits are divided into N T Each group of information bits is processed by the index modulator of each transmitting antenna of the MIMO-OCDM in each branch of the transmitter; the processing process includes:

[0016] The m bits of information to be transmitted are divided into p groups using a splitter. Each group contains g bits, p = m / g. The transmitted signal in each group is α=1,2,...,g, where l=1,2,...,n; Represents the set of constellation points of the M-order signal.

[0017] In each OCDM group, only k subcarriers out of n Chirp subcarriers are activated to transmit modulation symbols. At the same time, the first p1 bits of information in the input OCDM transmission subblock are used to activate the subcarrier index, and the symbols on the unactivated Chirp subcarriers are set to 0. The other p2 bits of information are used to modulate the M-order signal, and the transmission signal of the i-th antenna is obtained as follows:

[0018]

[0019] Where N represents the total number of chirp subcarriers, x i (t), t = 1, 2, ..., N represents the transmitted symbol on the tth subcarrier.

[0020] Step S2 further comprises:

[0021] The transmitted signal of each antenna is processed by discrete Fresnel transform and parallel-to-serial transform to obtain the converted transmitted signal:

[0022]

[0023] in represents the transmitted signal of the i-th antenna, i=1,2,...,N T ; Φ represents the discrete Fresnel transformation matrix, and its (i,z) elements are defined as:

[0024]

[0025] At the receiving end, the time domain signal received by the pth antenna is expressed as:

[0026]

[0027] where h p,q is the multipath channel impulse response between the qth transmitting antenna and the pth receiving antenna, is the superimposed noise on the pth receiving antenna, s q It is the transmission signal of the qth transmitting antenna after parallel-to-serial conversion.

[0028] Step S3 further comprises:

[0029] The time domain signal received at the receiving end is processed by serial-to-parallel conversion, and the time domain received signal of the pth antenna after conversion is:

[0030]

[0031] Among them, r p =[r p (1),r p (2),…,r p (N)] T is the received signal in the time domain, H p,q is the circulant matrix corresponding to the channel impact from the qth transmitting antenna to the pth receiving antenna;

[0032] Write the time domain received signal in matrix form:

[0033] Y T =HS T +N T

[0034] in They represent the signal vector received by the receiving antenna, the symbol vector sent by the transmitting antenna, and the Gaussian white noise vector at the receiving antenna, respectively. dimensional matrix, is the time domain channel transfer matrix:

[0035]

[0036] A ZF equalizer or an MMSE equalizer is used to perform channel equalization processing on the time domain received signal.

[0037] As a preferred example, in step S3, if ZF balancing is adopted, then:

[0038]

[0039] G ZF E s

[0040] Wherein represents the ZF equalization matrix, represents the power limit of the transmitted signal.

[0041] As a preferred example, in step S3, if MMSE equalization is adopted, then:

[0042]

[0043] Where ρ is the signal-to-noise ratio, G MMSE is the MMSE equalization matrix.

[0044] Step S4 further comprises:

[0045] Give the logarithmic formula of the ratio of the posterior probability corresponding to each index:

[0046]

[0047] in is an M-order modulated signal, x'(l) is the corresponding received signal after channel equalization on each subcarrier, l = 1, ..., N;

[0048] Using Bayesian formula and p(x'(l)=0)=(nk) / n, the logarithmic formula can be re-expressed as:

[0049]

[0050] N 0,F is the frequency domain noise variance.

[0051] S42, for each OCDM sub-block, the probability value of each subcarrier is calculated using a logarithmic formula, and then the total probability value of each combination is obtained according to the table lookup method, and the combination with the largest total probability value is used as the estimated value of the activated subcarrier sequence number combination, and the index bit is obtained according to the estimated value of the activated subcarrier sequence number combination to detect the M-order constellation point modulation symbol on the corresponding subcarrier.

[0052] Beneficial effects:

[0053] The high-efficiency MIMO-OCDM transmission method based on index modulation of the present invention can effectively improve the frequency efficiency of the traditional OCDM system and reduce the bit error rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a principle diagram of the efficient MIMO-OCDM transmission method based on index modulation of the present invention;

[0055] Figure 2 Schematic diagram of bit error rate performance of OCDM-IM, OFDM-IM, OCDM, and OFDM systems under 4×4 MIMO;

[0056] Figure 3 Schematic diagram of bit error rate performance of OCDM-IM, OFDM-IM, OCDM, and OFDM systems under 8×8 MIMO;

[0057] Figure 4 Schematic diagram of the bit error rate performance of OCDM-IM, OFDM-IM, OCDM, and OFDM systems with different k values ​​under 4×4 MIMO. DETAILED DESCRIPTION

[0058] The following examples will enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0059] The present invention discloses an efficient MIMO-OCDM transmission method based on index modulation, and the efficient MIMO-OCDM transmission method comprises the following steps:

[0060] S1, construct a multi-antenna MIMO-OCDM system, group the required transmission bit information, and each group of information bits is processed by the index modulator of each transmission antenna of the MIMO-OCDM in each branch of the transmitter to obtain the transmission signal of each antenna;

[0061] S2, performs OCDM modulation on the transmission signal and sends it to the receiving end through a multipath channel;

[0062] S3, performing channel equalization processing on the time domain signal received by the receiving end;

[0063] S4, based on the probability value of each subcarrier, the probability values ​​of each carrier in each combination are summed according to the c cases in the table of the lookup method, and the combination with the largest total probability value is used as the estimated value of the activated subcarrier sequence combination, the index bit and the modulation bit information are detected, and the entire communication link is completed.

[0064] See also Figure 1 The efficient MIMO-OCDM transmission method specifically includes the following steps:

[0065] Step 1: Information bit grouping

[0066] Step 1.1: Consider a multi-antenna MIMO-OCDM system with a total of N T transmit antennas, and send N R Each antenna sends a modulated signal with N orthogonal chirp subcarriers. IM is used to enhance the performance of the MIMO-OCDM system. For each frame of information transmission, there are a total of mN T information bits enter the MIMO-OCDM-IM transmitter. These bits are first divided into N T The corresponding bits are processed by the index modulator of each transmit antenna of the MIMO-OCDM in each branch of the transmitter.

[0067] Step 1.2: For each antenna, the transmitted m bits of information are divided into p groups by the divider, each group contains g bits, that is, p = m / g. For each OCDM group, we set only k subcarriers out of n Chirp subcarriers to be activated to transmit modulation symbols. At the same time, the information of the first p1 bits in the input OCDM transmission subblock is used to activate the subcarrier index. The IM-OCDM scheme sets the symbols on the unactivated Chirp subcarriers to 0, that is, they are not used to transmit data.

[0068] Step 1.3: The sending signal in each group is α=1,2,...,g, where l=1,2,...,n. Then p2 bits of information are used to modulate the M-order signal. The transmission signal of the i-th antenna is

[0069]

[0070] Step 2: After this, the transmission signal is converted from IDFnT to parallel-to-serial conversion to obtain the transmission signal

[0071]

[0072] where Φ represents the discrete Fresnel transform (DFnT) matrix, whose (m,n) elements are defined as

[0073]

[0074] Similar to OFDM-based systems, a cyclic prefix is ​​appended to the OCDM block to combat multipath propagation. Assume that the receiver can synchronously obtain channel state information through a specific channel estimation method. The received time domain signal can be expressed as

[0075]

[0076] where h p,qis the multipath channel impulse response from the qth transmitting antenna to the pth receiving antenna, is the superimposed noise on the pth receiving antenna.

[0077] Step 3: Channel Equalizer Design Process

[0078] Step 3.1: After the serial-to-parallel (S / P) conversion, the time domain received signal of the pth antenna is

[0079]

[0080] Among them, r (p) =[r (p) (1),r (p) (2),…,r (p) (N)] T is the received signal in the time domain, H p,q is the circulant matrix corresponding to the channel impact from the qth transmitting antenna to the pth receiving antenna. Its first column is

[0081] H p,q =[h p,q (0),h p,q (1),...,h p,q (L-1),0...0] T

[0082] Step 3.2: The received signal is written in matrix form as:

[0083] Y T =HS T +N T

[0084] in They are dimensional matrix, is the time domain channel transfer matrix, and its specific expression can be written as

[0085]

[0086] If ZF equilibrium is adopted, then

[0087]

[0088] If MMSE equalization is used, then

[0089]

[0090] where ρ is the signal-to-noise ratio (SNR).

[0091] Step 4: Index-modulated reML detector design

[0092] Step 4.1: The detector of the IM-OCDM scheme provides the logarithm of the ratio of the posterior probabilities of the symbols by considering that the posterior probabilities of the Fresnel domain symbols can be non-zero or zero. The following probability values ​​(LLR values) give the logarithm of the ratio of the posterior probabilities corresponding to each index:

[0093]

[0094] in is the M-order modulation signal, is the received signal after channel equalization corresponding to each subcarrier, l = 1,...,N. The larger λ(l) indicates that the subcarrier l is more likely to be activated by the index selector at the transmitter. Using the Bayesian formula and p(x(l)=0)=(nk) / n. The above equation can be re-expressed as

[0095]

[0096] Step 4.2: For each OCDM sub-block, first use the above formula to calculate the LLR value of each sub-carrier, and then sum the LLR values ​​of each carrier in each combination according to the c cases in the table of the lookup method, and then we can get the formula expression

[0097]

[0098] Where ω=1,...,c. If for the case in Table 1, the αth OCDM sub-block has After calculating the LLR values ​​of all c cases in the table (for Table 1, c = 4), the receiving end uses the combination with the largest LLR value as the estimated value of the activated subcarrier sequence number combination, that is, And according to this estimated value, the index bit is obtained to detect the modulation symbol of the M-order constellation point on the corresponding subcarrier.

[0099] Examples

[0100] This example uses Monte Carlo simulation for a more practical communication system to verify the effectiveness of the proposed IM-OCDM scheme in terms of efficiency and superiority compared to traditional systems based on OFDM and OCDM. In order to verify the efficiency and applicability of IM, this example gives a simulation analysis of a multi-antenna MIMO-OCDM system based on IM. The simulation environment is set as follows: the system defaults to the number of transmitting antennas being equal to the number of receiving antennas, N T =N R={4,8}. The OCDM symbols sent by each transmitting antenna are superimposed with N=128 orthogonal Chirp subcarriers, and the CP length is 1 / 8 of the number of subcarriers. The transmitter uses 4-QAM and 16-QAM modulation to map symbols. In addition, the channel model used is a quasi-static multipath channel, and the multipath channel used here changes once every 10 symbols, and the change law of its channel coefficient obeys the standard Gaussian distribution. The wireless communication channel through which the system passes is set with a total of 10 reachable paths, and the noise used is additive white Gaussian noise. The receiver defaults to knowing the perfect CSI. Both the OCDM system and the OFDM system use the above-mentioned ZF and MMSE single-tap frequency domain equalizers for channel equalization.

[0101] The IM-MIMO-OCDM system and the IM-MIMO-OFDM system are consistent with the single-antenna IM-OCDM scheme. The index selector at the transmitting end uses the combination number method to select the activated subcarrier. The reML scheme is used at the receiving end to detect the activated subcarriers, thereby obtaining the index bit information of the IM. First, n=4 is set in the IM-MIMO-OCDM group, and the number of activated subcarriers is k=2. Table 1 is a lookup table for index mapping when n=4, k=3, and c=4.

[0102]

[0103]

[0104] The simulation results show the comparison of the bit error rate performance of OCDM and OFDM systems using IM under 4×4 MIMO. With the introduction of IM, the performance of MIMO-OCDM and MIMO-OFDM can both achieve certain gain effects. Specifically, Figure 2 It is demonstrated that when the system transmits 4-QAM, the MIMO-OCDM system using the MMSE equalizer can achieve a 3dB SNR gain compared to the ordinary MIMO-OCDM system.

[0105] Figure 3 The BER performance comparison between OCDM and OFDM systems using IM under 8×8 MIMO is shown. As mentioned above, the increase in the number of antennas will further increase the performance difference between IM-MIMO-OCDM and MIMO-OCDM systems. The simulation shows that under the condition of 8×8 IM-MIMO-OCDM system sending 4-QAM, it can obtain 4dB SNR gain compared with ordinary MIMO-OCDM system.

[0106] from Figure 4It can be observed that when the system sends 16-QAM modulation signals, the IM-MIMO-OCDM with n=4 and k=1 has a higher bit error rate of 10 than the systems with k=2 and k=3. -3 This level can produce 4dB and 8dB performance gains respectively.

[0107] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. An efficient MIMO-OCDM transmission method based on index modulation, characterized in that: The efficient MIMO-OCDM transmission method comprises the following steps: S1, construct a multi-antenna MIMO-OCDM system, group the required transmission bit information, and each group of information bits is processed by the index modulator of each transmission antenna of the MIMO-OCDM in each branch of the transmitter to obtain the transmission signal of each antenna; S2, performs OCDM modulation on the transmission signal and sends it to the receiving end through a multipath channel; S3, performing channel equalization processing on the time domain signal received by the receiving end; S4, based on the probability value of each subcarrier, the probability values ​​of each carrier in each combination are summed according to the c cases in the table of the lookup method, and the combination with the largest total probability value is used as the estimated value of the activated subcarrier sequence combination, the index bit and the modulation bit information are detected, and the entire communication link is completed.

2. The high-efficiency MIMO-OCDM transmission method based on index modulation according to claim 1, characterized in that: Step S1 further comprises: S11, construct a multi-antenna MIMO-OCDM system, there are N T transmit antennas, and send N R The received signal is used to send a modulated signal, and each antenna sends an OCDM signal with N orthogonal Chirp subcarriers. S12, for each frame of information transmission, mN T The information bits are divided into N T Each group of information bits is processed by the index modulator of each transmitting antenna of the MIMO-OCDM in each branch of the transmitter; the processing process includes: The m bits of information to be transmitted are divided into p groups using a splitter. Each group contains g bits, p = m / g. The transmitted signal in each group is in in A constellation point set representing an M-order signal; In each OCDM group, only k subcarriers out of n Chirp subcarriers are activated to transmit modulation symbols. At the same time, the first p1 bits of information in the input OCDM transmission subblock are used to activate the subcarrier index, and the symbols on the unactivated Chirp subcarriers are set to 0. The other p2 bits of information are used to modulate the M-order signal, and the transmission signal of the i-th antenna is obtained as follows: Where N represents the total number of chirp subcarriers, x i (t), t = 1, 2, ..., N represents the transmitted symbol on the tth subcarrier.

3. The high-efficiency MIMO-OCDM transmission method based on index modulation according to claim 1, characterized in that: Step S2 further comprises: The transmitted signal of each antenna is processed by discrete Fresnel transform and parallel-to-serial transform to obtain the converted transmitted signal: in represents the transmitted signal of the i-th antenna, i=1,2,...,N T ; Φ represents the discrete Fresnel transformation matrix, and its (i,z) elements are defined as: At the receiving end, the time domain signal received by the pth antenna is expressed as: where h p,q is the multipath channel impulse response between the qth transmitting antenna and the pth receiving antenna, is the superimposed noise on the pth receiving antenna, s q It is the transmission signal of the qth transmitting antenna after parallel-to-serial conversion.

4. The high-efficiency MIMO-OCDM transmission method based on index modulation according to claim 1, characterized in that: Step S3 further comprises: The time domain signal received at the receiving end is processed by serial-to-parallel conversion, and the time domain received signal of the pth antenna after conversion is: Among them, r p =[r p (1),r p (2),…,r p (N)] T is the received signal in the time domain, H p,q is the circulant matrix corresponding to the channel impact from the qth transmitting antenna to the pth receiving antenna; Write the time domain received signal in matrix form: Y T =HS T +N T in They represent the signal vector received by the receiving antenna, the symbol vector sent by the transmitting antenna, and the Gaussian white noise vector at the receiving antenna, respectively. dimensional matrix, is the time domain channel transfer matrix: A ZF equalizer or an MMSE equalizer is used to perform channel equalization processing on the time domain received signal.

5. The efficient MIMO-OCDM transmission method based on index modulation according to claim 4, characterized in that: In step S3, if ZF equilibrium is adopted, then: G ZF E s Wherein represents the ZF equalization matrix, represents the power limit of the transmitted signal.

6. The high-efficiency MIMO-OCDM transmission method based on index modulation according to claim 4, characterized in that: In step S3, if MMSE equalization is adopted, then: Where ρ is the signal-to-noise ratio, G MMSE is the MMSE equalization matrix.

7. The high-efficiency MIMO-OCDM transmission method based on index modulation according to claim 1, characterized in that: Step S4 further comprises: Give the logarithmic formula of the ratio of the posterior probability corresponding to each index: in is an M-order modulated signal, x'(l) is the corresponding received signal after channel equalization on each subcarrier, l = 1, ..., N; Using Bayesian formula and p(x'(l)=0)=(nk) / n, the logarithmic formula can be re-expressed as: N 0,F is the frequency domain noise variance; S42, for each OCDM sub-block, the probability value of each subcarrier is calculated using a logarithmic formula, and then the total probability value of each combination is obtained according to the table lookup method, and the combination with the largest total probability value is used as the estimated value of the activated subcarrier sequence number combination, and the index bit is obtained according to the estimated value of the activated subcarrier sequence number combination to detect the M-order constellation point modulation symbol on the corresponding subcarrier.

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