An efficient MIMO-OCDM transmission method based on index modulation

Abstract

This invention discloses an efficient MIMO-OCDM transmission method based on index modulation, comprising: constructing a multi-antenna MIMO-OCDM system; grouping the required transmit bit information into groups; processing each group of information bits by the index modulator of each transmit antenna of the MIMO-OCDM system in each branch of the transmitter; performing OCDM modulation on the transmit signal and transmitting it to the receiver through a multipath channel; performing channel equalization processing on the time-domain signal received at the receiver; summing the probability values ​​of each carrier in each combination according to c cases in the lookup table, using the combination with the largest sum of probability values ​​as the estimated value of the active subcarrier sequence number combination, detecting the index bits and modulation bit information, and completing the entire communication link. This invention can effectively improve the frequency efficiency of traditional OCDM systems and reduce the bit error rate.

Description

Technical Field

[0001] This invention belongs to the field of communication technology, and in particular relates to an efficient MIMO-OCDM transmission method based on index modulation. Background Technology

[0002] Sixth-generation mobile communication (6G) technology is currently at the forefront of wireless communication research and development, aiming to achieve unprecedented data transmission speeds, ultra-low latency, and massive connectivity. To achieve this goal, academia and industry have conducted extensive research and exploration, particularly in the areas of coding and waveform modulation techniques.

[0003] In fifth-generation mobile communication (5G) networks, Multiple-input Multiple-output (MIMO) systems combined with Orthogonal Frequency Division Multiplexing (OFDM) are the most widely used air interface technologies in wireless communication today, enabling high-speed broadband wireless access services. However, OFDM is susceptible to burst errors caused by channel nulls or interference, severely impacting its average bit error rate (ABER). This may prevent it from meeting the reliability constraints of ultra-reliable low-latency communication. Furthermore, since massive machine-type communication networks operate in unlicensed frequency bands, the operation of OFDM systems is inevitably limited by interference, and OFDM modulation also suffers from significant out-of-band leakage. For these reasons, industry and academia are actively exploring transitional variants of OFDM modulation to address the increasing traffic and lower tolerance for interference that future generations of wireless networks will encounter. Spread spectrum schemes, such as Orthogonal Chirp Division Multiplexing (OCDM), have shown considerable promise in solving these problems. At the same time, OCDM technology combined with multi-antenna MIMO broadband systems can make full use of spatiotemporal diversity and better resist the effects of multipath effects and Doppler frequency domain, making up for the serious problems existing in the current MIMO-OFDM system and becoming a potential air interface technology in the current 6G network.

[0004] Meanwhile, novel index modulation (IM) has been widely applied in broadband communications. Specifically, unlike traditional multicarrier schemes, IM only transmits a portion of the resources (e.g., subcarriers, antennas, time slots, or channel states) for data transmission. This not only avoids resource and space waste but also achieves higher throughput and lower energy consumption, as the additional information bits are implicitly conveyed through the selection of resource indices. Therefore, IM can transmit not only amplitude- or phase-modulated information bits but also additional index bits without consuming energy, significantly improving spectral and energy efficiency. Furthermore, the flexible structure of IM auxiliary frames allows for considerable diversity gains from the selection of index resource activation modes, constellation alphabet types, or channel states, all contributing to significant performance gains. However, due to the physical limitations of the IM mechanism, existing IM-assisted systems suffer from throughput loss.

[0005] OCDM, a multi-carrier communication technology based on chirp spread spectrum (CSS), has strong resistance to multipath interference and has become a potential waveform for next-generation communication networks. However, few studies have focused on combining MIMO-OCDM systems with index modulation. Therefore, this invention proposes a MIMO-OCDM transmission system based on index modulation (IM). Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes an efficient MIMO-OCDM transmission method based on index modulation, which can effectively improve the frequency efficiency of traditional OCDM systems and reduce the bit error rate.

[0007] Technical solution:

[0008] A high-efficiency MIMO-OCDM transmission method based on indexed modulation, the high-efficiency MIMO-OCDM transmission method comprising the following steps:

[0009] S1. Construct a multi-antenna MIMO-OCDM system, group the required transmit bit information into groups, and process each group of information bits in each branch of the transmitter by the index modulator of each transmit antenna of the MIMO-OCDM to obtain the transmit signal of each antenna.

[0010] S2 modulates the transmitted signal using OCDM and transmits it to the receiving end via a multipath channel;

[0011] S3 performs channel equalization processing on the time-domain signal received by the receiver.

[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 lookup table. The combination with the largest sum of probability values ​​is used as the estimated value of the active subcarrier sequence number combination. The index bit and modulation bit information are detected, and the entire communication link is completed.

[0013] Step S1 further includes:

[0014] S11, Construct a multi-antenna MIMO-OCDM system. The multi-antenna MIMO-OCDM system has a total of N... T One transmitting antenna, simultaneously transmitting to N R The root receive signal transmits a modulated signal, and each antenna transmits an OCDM signal with N orthogonal Chirp subcarriers;

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

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

[0017] In each OCDM packet, only k subcarriers out of n Chirp subcarriers are activated to transmit modulation symbols. Simultaneously, the first p1 bits of information from the input OCDM transmit subblock are used to activate the subcarrier index, and the symbols on the inactive Chirp subcarriers are set to 0. The remaining p2 bits are used to modulate the M-order signal, resulting in the transmitted signal of the i-th antenna:

[0018]

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

[0020] Step S2 further includes:

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

[0022]

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

[0024]

[0025] At the receiving end, the time-domain signal received by the p-th antenna is represented as:

[0026]

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

[0028] Step S3 further includes:

[0029] The time-domain signal received at the receiving end is processed by serial-to-parallel conversion. The converted time-domain received signal of the p-th antenna is as follows:

[0030]

[0031] Where, r p =[r p (1),r p (2),…,r p (N)] T For time-domain received signals, H p,q It is the cyclic matrix corresponding to the channel impulse from the q-th transmitting antenna to the p-th receiving antenna;

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

[0033] Y T =HS T +N T

[0034] in Let represent the signal vector received by the receiving antenna, the symbol vector transmitted by the transmitting antenna, and the Gaussian white noise vector at the receiving antenna, respectively. 3D matrix It is the time-domain channel transfer matrix:

[0035]

[0036] Channel equalization processing of the time-domain received signal is performed using a ZF equalizer or an MMSE equalizer.

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

[0038]

[0039] G ZF E s

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

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

[0042]

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

[0044] Step S4 further includes:

[0045] The logarithmic formula for the ratio of posterior probabilities for each index is given:

[0046]

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

[0048] Using Bayes' theorem And p(x'(l)=0)=(nk) / n, the logarithmic formula can be rewritten as:

[0049]

[0050] N 0,F This represents 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 the sum of the probability values ​​of each combination is obtained by looking up a table. The combination with the largest sum of probability values ​​is used as the estimated value of the active subcarrier sequence number combination, and the index bit is obtained based on the estimated value of the active subcarrier sequence number combination to detect the M-order constellation point modulation symbol on the corresponding subcarrier.

[0052] Beneficial effects:

[0053] The efficient MIMO-OCDM transmission method based on index modulation of the present invention can effectively improve the frequency efficiency of traditional OCDM systems and reduce the bit error rate. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the high-efficiency MIMO-OCDM transmission method based on index modulation of the present invention;

[0055] Figure 2 The diagram illustrates the bit error rate performance of OCDM-IM, OFDM-IM, OCDM, and OFDM systems under 4×4 MIMO.

[0056] Figure 3 The diagram illustrates the bit error rate performance of OCDM-IM, OFDM-IM, OCDM, and OFDM systems under 8×8 MIMO.

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

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

[0059] This invention discloses a high-efficiency MIMO-OCDM transmission method based on indexed modulation, the high-efficiency MIMO-OCDM transmission method comprising the following steps:

[0060] S1. Construct a multi-antenna MIMO-OCDM system, group the required transmit bit information into groups, and process each group of information bits in each branch of the transmitter by the index modulator of each transmit antenna of the MIMO-OCDM to obtain the transmit signal of each antenna.

[0061] S2 modulates the transmitted signal using OCDM and transmits it to the receiving end via a multipath channel;

[0062] S3 performs channel equalization processing on the time-domain signal received by the receiver.

[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 lookup table. The combination with the largest sum of probability values ​​is used as the estimated value of the active subcarrier sequence number combination. The index bit and modulation bit information are detected, and the entire communication link is completed.

[0064] See 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 One transmitting antenna, simultaneously transmitting to N R The received signal is transmitted as a modulated signal, with each antenna transmitting an OCDM signal having 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 10 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 a splitter, each group containing g bits, i.e., p = m / g. Within each OCDM group, we configure it to activate only k subcarriers out of the n chirp subcarriers to transmit modulation symbols. Simultaneously, the first p1 bits of information from the input OCDM transmit subblock are used to activate the subcarrier index. The IM-OCDM scheme sets the symbols on inactive chirp subcarriers to 0, meaning they are not used for data transmission.

[0068] Step 1.3: The transmitted signal within 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. Thus, the transmitted signal of the i-th antenna is obtained as follows:

[0069]

[0070] Step 2: After this, the transmitted signal, after undergoing IDFnT and parallel-to-serial conversion, becomes the transmitted signal.

[0071]

[0072] Where Φ represents the Discrete Fresnel Transform (DFnT) matrix, and its (m,n) elements are defined as follows:

[0073]

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

[0075]

[0076] Where h p,qIt is the multipath channel impulse response between the q-th transmitting antenna and the p-th receiving antenna. It is the superimposed noise on the p-th receiving antenna.

[0077] Step 3: Channel Equalizer Design Process

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

[0079]

[0080] Where, r (p) =[r (p) (1),r (p) (2),…,r (p) (N)] T For time-domain received signals, H p,q It is the cyclic matrix corresponding to the channel impulse from the q-th transmitting antenna to the p-th 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 follows:

[0083] Y T =HS T +N T

[0084] in They are respectively 3D matrix It is the time-domain channel transfer matrix, and its specific expression can be written as:

[0085]

[0086] If ZF equilibrium is used, then we have

[0087]

[0088] If MMSE equalization is used, then...

[0089]

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

[0091] Step 4: Design of an indexed modulated reML detector

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

[0093]

[0094] in It is an M-order modulated signal. The received signal after channel equalization on each subcarrier, l = 1,...,N. A larger λ(l) indicates a greater probability that subcarrier l will be activated by the transmitter's index selector. Using Bayes' theorem... And p(x(l)=0)=(nk) / n. The above equation can be reformulated as

[0095]

[0096] Step 4.2: For each OCDM sub-block, first calculate the LLR value of each subcarrier using the above formula, then sum the LLR values ​​of each carrier in each combination according to the c cases in the lookup table, and thus obtain the formula expression.

[0097]

[0098] Where ω = 1,...,c. If, for the cases in Table 1, the α-th OCDM sub-block has... After calculating the LLR values ​​for all c cases in the table (c=4 for Table 1), the receiver uses the combination with the largest LLR value as the estimated value for the active subcarrier number combination, i.e. Based on this estimate, the index bit is obtained, and the M-order constellation point modulation symbol on the corresponding subcarrier is detected.

[0099] Example

[0100] This example uses Monte Carlo simulation on a relatively practical communication system to verify the effectiveness of the proposed IM-OCDM scheme in terms of efficiency and superiority compared to traditional OFDM and OCDM-based systems. To verify the efficiency and applicability of IM, this example presents a simulation analysis of an IM-based multi-antenna MIMO-OCDM system. The simulation environment is set as follows: the system defaults to the number of transmit antennas equal to the number of receive antennas, N... T =N R={4,8}. Each transmitted OCDM symbol uses N=128 orthogonal chirp subcarriers superimposed, with a CP length of 1 / 8 of the subcarrier number. The transmitter uses 4-QAM and 16-QAM modulation for symbol mapping. Furthermore, the channel model used is a quasi-static multipath channel, and the multipath channel changes every 10 symbols, with its channel coefficients following a standard Gaussian distribution. The system traverses 10 reachable wireless communication paths, and the noise used is additive white Gaussian noise. The receiver assumes perfect CSI. Both the OCDM and OFDM systems use the aforementioned ZF and MMSE single-tap frequency domain equalizers for channel equalization.

[0101] The IM-MIMO-OCDM and IM-MIMO-OFDM systems are consistent with the single-antenna IM-OCDM scheme. At the transmitting end, the index selector uses a combinational number method to select active subcarriers. At the receiving end, the reML scheme is used to detect the active subcarriers, thereby obtaining the IM index bit information. First, we set n=4 within the IM-MIMO-OCDM packet and k=2 of the active subcarriers. Table 1 shows the lookup table for index mapping when n=4, k=3, and c=4.

[0102]

[0103]

[0104] Simulation results show a comparison of the bit error rate performance of OCDM and OFDM systems using IM under 4×4 MIMO. With the introduction of IM, both MIMO-OCDM and MIMO-OFDM achieve certain performance gains. Specifically, Figure 2 This demonstrates that, under 4-QAM transmission conditions, the MIMO-OCDM system using the MMSE equalizer can achieve a 3dB SNR gain compared to a conventional MIMO-OCDM system.

[0105] Figure 3 This paper presents a comparison of the bit error rate performance of OCDM and OFDM systems using IM under 8×8 MIMO. As mentioned earlier, increasing the number of antennas further widens the performance difference between IM-MIMO-OCDM and MIMO-OCDM systems. Simulations demonstrate that an 8×8 IM-MIMO-OCDM system can achieve a 4dB SNR gain relative to a conventional MIMO-OCDM system when transmitting 4-QAM.

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

[0107] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A high-efficiency MIMO-OCDM transmission method based on indexed modulation, characterized in that, The high-efficiency MIMO-OCDM transmission method includes the following steps: S1. Construct a multi-antenna MIMO-OCDM system by grouping the required transmit bit information into groups. Each group of information bits is processed by the index modulator of each transmit antenna of the MIMO-OCDM in each branch of the transmitter to obtain the transmit signal of each antenna. S2 modulates the transmitted signal using OCDM and transmits it to the receiving end via a multipath channel; S3 performs channel equalization processing on the time-domain signal received by the receiver. S4. Based on the probability value of each subcarrier, the probability values ​​of each carrier in each combination are summed according to the lookup table method. The combination with the largest sum of probability values ​​is used as the estimated value of the active subcarrier sequence number combination. The index bit and modulation bit information are detected, and the entire communication link is completed. Step S1 further includes: S11, Construct a multi-antenna MIMO-OCDM system. The multi-antenna MIMO-OCDM system has a total of N... T One transmitting antenna, simultaneously transmitting to N R The root receive signal transmits a modulated signal, and each antenna transmits an OCDM signal with N orthogonal Chirp subcarriers; S12, for the information transmission of each frame, mN T Each information bit is divided into N T Each group of information bits is processed by the index modulator of each transmit antenna of the MIMO-OCDM in each branch of the transmitter; the processing includes: The m bits of information to be transmitted are divided into p groups using a splitter, each group containing g bits, where p = m / g. The transmitted signal within each group is... α = 1, 2, ..., p, where l = 1, 2, ..., n; where S represents the constellation point set of the M-order signal; In each OCDM packet, only k subcarriers out of n Chirp subcarriers are activated to transmit modulation symbols. Simultaneously, the first p1 bits of information from the input OCDM transmit subblock are used to activate the subcarrier index, and the symbols on the inactive Chirp subcarriers are set to 0. The remaining p2 bits are used to modulate the M-order signal, resulting in the transmitted signal of the i-th antenna: Where N represents the total number of chirp subcarriers, x i (t), t=1,2,…,N represents the transmitted symbol on the t-th subcarrier; Step S2 further includes: The transmitted signal from each antenna is processed by discrete Fresnel transform and parallel-to-serial transform to obtain the transformed transmitted signal: in This represents the transmitted signal of the i-th antenna, where i = 1, 2, ..., N. T Φ represents the discrete Fresnel transformation matrix, and its (i, z) elements are defined as follows: At the receiving end, the time-domain signal received by the p-th antenna is represented as: Where h p,q It is the multipath channel impulse response between the q-th transmitting antenna and the p-th receiving antenna. It is the superimposed noise on the p-th receiving antenna, s q It is the transmitted signal after parallel-to-serial conversion by the qth transmitting antenna; Step S3 further includes: The time-domain signal received at the receiving end is processed by serial-to-parallel conversion. The converted time-domain received signal of the p-th antenna is as follows: Where, r p =[r p (1),r p (2),…,r p (N)] T For time-domain received signals, H p,q It is the cyclic matrix corresponding to the channel impulse from the q-th transmitting antenna to the p-th receiving antenna; Write the received signal in the time domain in matrix form: Y T =HS T +N T in Let represent the signal vector received by the receiving antenna, the symbol vector transmitted by the transmitting antenna, and the Gaussian white noise vector at the receiving antenna, respectively. 3D matrix It is the time-domain channel transfer matrix: Use a ZF equalizer or an MMSE equalizer to perform channel equalization processing on the time-domain received signal; In step S3, if ZF equalization is used, then: G ZF E s Where ZF represents the equalization matrix, and power limitation of the transmitted signal is represented; In step S3, if MMSE equalization is used, then: Where ρ is the signal-to-noise ratio, and G MMSE This is the MMSE equilibrium matrix; Step S4 further includes: The logarithmic formula for the ratio of posterior probabilities for each index is given: in Let x'(l) be the M-order modulated signal, and x'(l) be the received signal after channel equalization on each subcarrier, where l = 1, ..., N; Using Bayes' theorem And p(x'(l)=0)=(nk) / n, the logarithmic formula can be rewritten as: N 0,F The variance of frequency domain noise; S42, for each OCDM sub-block, the probability value of each subcarrier is calculated using a logarithmic formula, and the sum of the probability values ​​of each combination is obtained by looking up a table. The combination with the largest sum of probability values ​​is used as the estimated value of the active subcarrier sequence number combination, and the index bit is obtained based on the estimated value of the active subcarrier sequence number combination to detect the M-order constellation point modulation symbol on the corresponding subcarrier.

Images