Precoding transmission method and device based on RIS auxiliary Internet of Vehicles communication system

Abstract

The invention discloses a precoding transmission method and device based on an RIS auxiliary Internet of Vehicles communication system. The method comprises the following steps: constructing an orthogonal LFM waveform based on channel characteristics and multi-user transmission requirements of the RIS auxiliary Internet of Vehicles communication system; obtaining a pre-coded cascade channel matrix of the RIS auxiliary Internet of Vehicles communication system based on a preset pre-coding matrix; converting the pre-coded RIS auxiliary Internet of Vehicles communication system into a real number field pre-coding linear model; setting a pre-coding equivalent channel matrix of the real number field pre-coding linear model as a unit matrix to obtain a pre-coding matrix of the Internet of Vehicles communication system; estimating a real number field precoding equivalent channel of the real number field precoding linear model based on a linear channel estimation algorithm; and carrying out data demodulation on the transmission information based on a multi-antenna combined minimum Euclidean distance algorithm to complete information transmission. According to the invention, the channel estimation overhead can be reduced, and the high reliability of information transmission and the anti-interference capability among multiple users can be improved.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a precoding transmission method and device based on a RIS-assisted vehicle networking communication system. Background Art

[0002] With the development of 6G communication systems, the demand for vehicle-to-everything (V2X) applications continues to increase, especially in terms of ultra-high data rates, low latency and high reliability. Against this background, intelligent reflective surface (RIS) technology has emerged as an important means to improve signal propagation conditions. By flexibly adjusting the reflection path of the signal, RIS can optimize communications between vehicles and with infrastructure, significantly enhance signal coverage and strength, and thus effectively reduce multi-user interference. This technology is particularly suitable for high-density traffic environments and helps to achieve more efficient real-time information transmission between vehicles.

[0003] In IoV communications, high-mobility vehicle users may be interfered by base stations transmitting information for other high-mobility vehicle users while receiving their own information. However, due to the limited processing capabilities of the user end, it is difficult to completely eliminate these interferences. In high-speed mobile scenarios, the relative motion between vehicles will cause Doppler frequency shift, affecting the transmission quality of the signal. In addition, since RIS lacks signal processing capabilities and has a large number of passive reflection units, it becomes difficult to obtain channel state information in real time in IoV systems. This leads to high channel estimation overhead in delay-sensitive high-mobility scenarios, which increases the delay of data transmission and cannot meet the robustness requirements of high-mobility IoV transmission. Summary of the invention

[0004] In order to overcome the defects and shortcomings of the prior art, the present invention provides a precoding transmission method and device based on a RIS-assisted Internet of Vehicles communication system. According to the virtual line-of-sight (LoS) path provided by RIS and the ability to create a Rice fading environment, the present invention redesigns a linear frequency modulation (LFM) signal (i.e., Chirp signal) with good anti-Doppler and long-distance low power consumption characteristics, and precodes the transmission waveform to meet the needs of Internet of Vehicles information transmission. The characteristics of the transmission waveform are utilized to convert the RIS-assisted Internet of Vehicles communication system into a Doppler robust real domain linear model based on a differential detection algorithm. Based on the ease of implementation and low complexity of the real domain linear model, the channel estimation complexity of the RIS-assisted Internet of Vehicles communication system can be simplified, and the pilot design overhead can be reduced, thereby improving the high reliability and low-latency communication capability of the information transmission of the Internet of Vehicles communication system.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a precoding transmission method based on a RIS-assisted vehicle networking communication system, comprising the following steps:

[0007] Based on the channel characteristics of the RIS-assisted Internet of Vehicles communication system and the multi-user transmission requirements, the corresponding transmission waveform is constructed, and the bit data transmitted by the transmitter is mapped into a multi-level amplitude complementary orthogonal LFM waveform after space-time coding;

[0008] Presetting a precoding matrix, and obtaining a precoded RIS-assisted Internet of Vehicles communication system cascade channel matrix based on the preset precoding matrix;

[0009] Based on the orthogonal LFM waveform and the cascade channel matrix of the RIS-assisted vehicle network communication system, and combined with the Ricean channel characteristics of the RIS-assisted vehicle network communication system, the precoded RIS-assisted vehicle network communication system is transformed into a real-domain precoded linear model with Doppler robustness.

[0010] The precoding equivalent channel matrix in the real-domain precoding linear model is set to the unit matrix to obtain the precoding matrix of the Internet of Vehicles communication system;

[0011] The real-domain precoding equivalent channel of the real-domain precoding linear model is estimated based on a linear channel estimation algorithm;

[0012] Based on the multi-antenna joint minimum Euclidean distance algorithm, data demodulation is performed on the transmission information in the RIS-assisted Internet of Vehicles communication system to complete the information transmission.

[0013] As a preferred technical solution, the bit data transmitted by the transmitting end is mapped into a multi-base amplitude complementary orthogonal LFM waveform after space-time coding, which is specifically expressed as:

[0014]

[0015] Among them, s n ∈{0,1,…M-1} represents the bit data transmitted by the nth transmitting antenna, With s n A complementary signal is formed and the amplitude sum of the two signals is M-1, T represents the duration of the signal transmission symbol, f0 represents the center carrier frequency, μ represents the frequency modulation slope of the LFM signal, when μ>0 represents a positive slope, when μ<0 represents a negative slope, the positive and negative slopes are orthogonal to each other, is the Up-Chirp signal, It is a Down-Chirp signal. The Up-Chirp signal and the Down-Chirp signal are orthogonal to each other.

[0016] As a preferred technical solution, the conversion of the precoded RIS-assisted Internet of Vehicles communication system into a real-domain precoded linear model with Doppler robustness specifically includes:

[0017] The received signal at the receiving end is processed by matched filtering, and the orthogonal LFM waveform is passed through the Up-Chirp matched filter and the Down-Chirp matched filter to obtain the corresponding matched filtering result;

[0018] The corresponding matched filtering results are differentially detected, and the precoded RIS-assisted Internet of Vehicles communication system is converted into a real-domain precoded linear model with Doppler robustness, which is specifically expressed as:

[0019]

[0020] Among them, d m represents the precoded cascade channel vector from the base station to the mth mobile vehicle user after RIS reflection, represents the output vector of the orthogonal waveform after the Up-Chirp matched filter, represents the output vector of the orthogonal waveform after the Down-Chirp matched filter, The Doppler frequency shift f d The phase rotation caused by mj ,θ mj Represent the amplitude and phase of the precoding cascade channel, g m is the real domain equivalent channel vector from the base station to the mth mobile vehicle user after RIS reflection in the real domain precoding linear model, N t represents the total number of transmitting antennas of the base station, is the real-domain equivalent transmitted signal vector of the real-domain precoding linear model, n1, n2 represent the noise after the matched filter, v is the equivalent noise of the real-domain precoding linear model, B represents the signal bandwidth, and ρ represents the mutual correlation coefficient between the Up-Chirp signal and the Down-Chirp signal.

[0021] As a preferred technical solution, the orthogonal LFM waveform is passed through an Up-Chirp matched filter and a Down-Chirp matched filter to obtain a corresponding matched filtering result, which is specifically expressed as:

[0022]

[0023] As a preferred technical solution, the mutual correlation coefficient of the Up-Chirp signal and the Down-Chirp signal is specifically expressed as:

[0024]

[0025] Among them, a(·) and b(·) represent the Fresnel cosine function and the Fresnel sine function, respectively.

[0026] As a preferred technical solution, the precoded cascade channel vector d between the base station and the mth mobile vehicle user after RIS reflection m , specifically expressed as:

[0027] The cascade channel matrix of the RIS-assisted IoV communication system after precoding is: D = FH;

[0028] Where D = [d1,…d m ,…d K ] T , d m is the mth row of the cascaded channel matrix D, and F represents the precoding matrix;

[0029] The cascade channel matrix from the base station to K mobile vehicle users after RIS reflection is:

[0030] H=[h1,…h m ,…h K ] T

[0031] Among them, h m is the mth row of the cascaded channel matrix H, (·) T Represents a transpose operation;

[0032] The cascade channel from the base station to the mth mobile vehicle user after RIS reflection is:

[0033] h m =r m ΘQ

[0034]

[0035] in, They represent the LoS part of the subchannel from the base station to the RIS and from the RIS to the mth mobile vehicle user, respectively. They represent the NLoS part of the subchannel from the base station to the RIS and from the RIS to the mth mobile vehicle user, respectively. C and V represent the Rice factor represents the phase control matrix of the RIS array, α n represents the phase shift of the nth reflection unit in the RIS array, and N represents the number of units in the RIS array.

[0036] As a preferred technical solution, the precoding equivalent channel matrix in the real domain precoding linear model is set to the unit matrix to obtain the precoding matrix of the Internet of Vehicles communication system, specifically including:

[0037] The real domain equivalent channel vector g between the base station and the mth mobile vehicle user after RIS reflection in the real domain precoding linear model m for:

[0038]

[0039] The equivalent channel matrix in the real-domain precoding linear model is:

[0040]

[0041] Where G=[g1,…g m ,…g K ] T , d m is the mth row of the precoding cascade channel matrix D, Re(·) represents the real part operation, Γ represents the diagonal matrix, (·) * represents the conjugation operation;

[0042] The precoding equivalent channel matrix in the real-domain precoding linear model is set to the identity matrix, expressed as:

[0043]

[0044] Where I represents the identity matrix;

[0045] The precoding cascade channel matrix D is defined as:

[0046] |D|=|FH|=I

[0047] When D=FH=I, the precoding matrix F of the Internet of Vehicles communication system is:

[0048] F=H H (HH H ) -1

[0049] in,(·) H ,(·) -1 denote the conjugate transpose and inverse operations respectively, and H denotes the cascade channel matrix from the base station to the K mobile vehicle users after RIS reflection.

[0050] As a preferred technical solution, the real-domain precoding equivalent channel of the real-domain precoding linear model is estimated based on a linear channel estimation algorithm, which is specifically expressed as follows:

[0051]

[0052] in, represents the estimated real-domain precoding channel vector, u0 represents the transmitted pilot symbol used for channel estimation, and z0 represents the received pilot symbol.

[0053] As a preferred technical solution, data demodulation is performed on the transmission information in the RIS-assisted Internet of Vehicles communication system based on a multi-antenna combined minimum Euclidean distance algorithm, which is specifically expressed as follows:

[0054]

[0055] in, Represents the transmission data restored after data demodulation, z m represents the differential detection result of the received signal at the mth receiving antenna, K represents the total number of high-mobility vehicle users with a single antenna, represents the estimated real-domain precoding channel vector, represents the real-domain equivalent transmitted signal vector of the real-domain precoding linear model.

[0056] The present invention also provides a precoding transmission device based on a RIS-assisted vehicle networking communication system, which is used to implement the above-mentioned precoding transmission method based on a RIS-assisted vehicle networking communication system, including: a transmission waveform construction module, a precoding matrix preset module, a cascade channel matrix construction module, a real number domain precoding linear model construction module, a precoding matrix calculation module, a channel estimation module, and a data demodulation module;

[0057] The transmission waveform construction module is used to construct a corresponding transmission waveform based on the channel characteristics of the RIS-assisted vehicle networking communication system and the multi-user transmission requirements, and map the bit data transmitted by the transmitter into a multi-base amplitude complementary orthogonal LFM waveform after space-time coding;

[0058] The precoding matrix preset module is used to preset the precoding matrix;

[0059] The cascade channel matrix construction module is used to obtain a pre-coded RIS-assisted Internet of Vehicles communication system cascade channel matrix based on a preset pre-coding matrix;

[0060] The real-domain precoding linear model construction module is used to convert the precoded RIS-assisted vehicle networking communication system into a real-domain precoding linear model with Doppler robustness based on the orthogonal LFM waveform and the RIS-assisted vehicle networking communication system cascade channel matrix and in combination with the Ricean channel characteristics of the RIS-assisted vehicle networking communication system;

[0061] The precoding matrix calculation module is used to set the precoding equivalent channel matrix in the real domain precoding linear model to the unit matrix to obtain the precoding matrix of the Internet of Vehicles communication system;

[0062] The channel estimation module is used to estimate the real-domain precoding equivalent channel of the real-domain precoding linear model based on a linear channel estimation algorithm;

[0063] The data demodulation module is used to perform data demodulation on the transmission information in the RIS-assisted Internet of Vehicles communication system based on a multi-antenna joint minimum Euclidean distance algorithm to complete information transmission.

[0064] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0065] (1) According to the requirements of the Internet of Vehicles communication system for reliable transmission and multi-user interference suppression, the present invention reconstructs the LFM signal with good matching properties and performs precoding processing on the transmission waveform, effectively solving the problem of unstable signal transmission of the RIS-assisted Internet of Vehicles communication system when driving at high speed and the problem of information crosstalk between mobile users.

[0066] (2) The present invention utilizes the characteristics of the transmitted waveform and transforms the RIS-assisted IoV communication system into a Doppler-robust real-domain linear model based on a differential detection algorithm. The real-domain linear model is easy to implement and has low complexity. A simple and efficient linear estimation is used to effectively solve the real-time tracking problem of channel phase information in high-speed mobile scenarios, significantly reducing the channel estimation overhead and improving the effectiveness and reliability of signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 It is a flow chart of a precoding transmission method based on a RIS-assisted Internet of Vehicles communication system of the present invention;

[0068] Figure 2 This is a schematic diagram of precoding transmission of the RIS-assisted Internet of Vehicles communication system of the present invention;

[0069] Figure 3 It is a schematic diagram of the architecture of the RIS-assisted Internet of Vehicles communication system of the present invention;

[0070] Figure 4 Schematic diagram of the normalized time domain waveform of the LFM signal of the present invention;

[0071] Figure 5 It is a time domain schematic diagram of the matched output of the LFM signal after the matched filter of the present invention;

[0072] Figure 6 It is a time domain schematic diagram of the mismatch output of the LFM signal after passing through the matched filter of the present invention;

[0073] Figure 7 It is a schematic diagram of the performance simulation comparison between precoded transmission and non-precoded transmission based on the RIS-assisted Internet of Vehicles communication system of the present invention;

[0074] Figure 8 It is a simulation diagram of the output signal-to-noise ratio of the pre-coded transmission of the RIS-assisted vehicle networking communication system of the present invention changing with the number of base station antennas;

[0075] Fig. 9 It is a schematic diagram of the performance simulation comparison of the precoding transmission method of the RIS-assisted Internet of Vehicles communication system of the present invention. DETAILED DESCRIPTION

[0076] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0077] Example 1

[0078] like Figure 1 As shown, this embodiment provides a precoding transmission method based on a RIS-assisted Internet of Vehicles communication system, which solves the transmission reliability problem, multi-user co-channel interference problem and high channel estimation overhead problem existing in the RIS-assisted Internet of Vehicles communication system in the prior art. The precoding transmission method improves the high reliability and low latency communication capability of the Internet of Vehicles communication system in a fast fading environment. This embodiment is applied to an Internet of Vehicles communication system in a high-speed mobile scenario with RIS assistance, and the Internet of Vehicles communication system includes at least one having N t A base station (BS) having a transmitting antenna, at least one RIS array having N reflecting units, and K high-mobility vehicle users with single antennas, the method comprises the following steps:

[0079] S1: Based on the channel characteristics and multi-user interference suppression requirements of the RIS-assisted IoV communication system, perform transmitter signal processing suitable for the IoV communication system;

[0080] In this embodiment, RIS can provide a virtual LoS path and create a Ricean fading environment in the IoV communication system, so the channel characteristics of the RIS-assisted IoV communication system can be modeled as a Ricean channel model based on the LoS path;

[0081] In this embodiment, the sub-channels from the base station to the RIS and from the RIS to the m-th mobile vehicle user both present Rice channel characteristics dominated by the LoS path, which are respectively expressed as:

[0082]

[0083] Among them, C, V represent Rice factors, represents the LoS portion of the channel, represents the NLoS portion of the channel;

[0084] The cascade channel from the base station to the mth mobile vehicle user after RIS reflection is:

[0085] h m =r m ΘQ

[0086] in represents the phase control matrix of the RIS array, α nrepresents the phase shift of the nth reflection unit in the RIS array;

[0087] The cascade channel matrix from the base station to K mobile vehicle users after RIS reflection is:

[0088] H=[h1,…h m ,…h K ] T

[0089] where h m is the mth row of the channel matrix H, (·) T Represents a transpose operation;

[0090] Based on the Ricean channel characteristics and multi-user interference suppression requirements of the RIS-assisted Internet of Vehicles communication system, an LFM signal (i.e., Chirp signal) with good matching properties is selected as the transmitting waveform, and the transmitter signal processing suitable for the Internet of Vehicles communication system is performed according to the waveform characteristics.

[0091] Specifically, the basic characteristics of the LFM signal are as follows:

[0092] The time domain expression of Chirp signal is:

[0093]

[0094] Among them, f0 represents the center carrier frequency, T represents the duration of the signal transmission symbol, μ represents the frequency modulation slope of the LFM signal, when μ>0, it represents a positive slope, when μ<0, it represents a negative slope, and the positive and negative slopes are orthogonal to each other.

[0095] In the LFM signal, the impulse response of the matched filter is:

[0096] d(t)=c(-t) *

[0097] in(·) * represents the conjugation operation.

[0098] The Chirp signal is processed by matched filtering and non-matched filtering, respectively, as follows:

[0099]

[0100] Where B represents the signal bandwidth, a(·) and b(·) represent the Fresnel cosine function and the Fresnel sine function, respectively, which are:

[0101]

[0102] After matched filtering, the narrow pulse signal is approximately a Sinc function and the output amplitude is enlarged. The output after non-matched filtering is a small-amplitude signal with a relatively gentle amplitude. The matched filtering properties of the Chirp signal are beneficial to constructing a signal detection algorithm suitable for the Internet of Vehicles communication system.

[0103] Then, according to the transmission requirements of the RIS-assisted Internet of Vehicles communication system in terms of anti-multi-user interference and anti-Doppler frequency deviation, as well as the basic characteristics of the LFM signal, the transmitter signal processing suitable for the Internet of Vehicles communication system is carried out.

[0104] like Figure 2 As shown, the bit data transmitted by the transmitter is mapped into a multi-base amplitude complementary orthogonal LFM waveform after space-time coding, as follows:

[0105]

[0106] where s n ∈{0,1,…M-1} represents the bit data transmitted by the nth transmitting antenna, With s n The complementary signals are formed and the amplitude sum of the two signals is M-1. In order to simplify the analysis, it is assumed in this embodiment that M=2. In addition, since the positive and negative frequency modulation slopes of the LFM signal are orthogonal to each other, x n (t) are orthogonal.

[0107] In the orthogonal waveform x n (t), is the Up-Chirp signal, is a Down-Chirp signal. The two signals are orthogonal to each other, and the mutual correlation coefficient of the two signals is:

[0108]

[0109] The impulse response of the Up-Chirp matched filter is the Down-Chirp signal, and the impulse response of the Down-Chirp matched filter is the Up-Chirp signal.

[0110] In the RIS-assisted multi-user downlink vehicle network communication system, multiple mobile vehicle user terminals communicate with the base station on the same time slot, frequency and code channel, which inevitably produces co-channel interference; since the mobile terminals are limited in power consumption and size, it is difficult to bear the overhead of interference elimination, so interference suppression is achieved through precoding processing at the base station transmitter.

[0111] The precoding matrix is ​​defined as F, which acts on the cascade channel of the RIS-assisted Internet of Vehicles communication system to eliminate the co-channel interference between multiple users. The precoded cascade channel matrix is:

[0112] D=FH

[0113] Where D=[d1,…d m ,…d K ] T , d m is the mth row of the channel matrix D.

[0114] S2: Based on the transmitter signal suitable for the Internet of Vehicles communication system and combined with the Ricean channel characteristics of the RIS-assisted Internet of Vehicles communication system, a precoded linear system model with Doppler interference suppression capability is constructed, specifically:

[0115] Combination Figure 2 As shown, first, the received signal is processed by matched filtering at the receiving end, and the orthogonal waveform x n (t) The output results of Up-Chirp and Down-Chirp matched filters are:

[0116]

[0117] Then, the matched filtering results are differentially detected at the receiving end, and the precoded RIS-assisted IoV communication system is converted into a real-domain precoded linear model with Doppler robustness:

[0118]

[0119] Among them, d m represents the precoded cascade channel vector from the base station to the mth mobile vehicle user after RIS reflection, represents the output vector of the orthogonal waveform after the Up-Chirp matched filter, Represents the output vector of the orthogonal waveform after passing through the Down-Chirp matched filter; The Doppler frequency shift f d The phase rotation caused by Doppler is approximately constant within one symbol period. After being equivalent to a linear model, the phase rotation caused by Doppler is is eliminated, ensuring the robustness of the RIS-assisted IoV communication system in high mobility scenarios; d mj ,θ mj represent the amplitude and phase of the precoding cascade channel respectively, is the real domain equivalent transmitted signal vector of the linear model, n1, n2 represent the noise after the matched filter, and v is the equivalent noise of the linear model.

[0120] g in real domain precoding linear model m is the real domain equivalent channel vector from the base station to the mth mobile vehicle user after RIS reflection:

[0121]

[0122] The equivalent channel matrix in the real-domain precoding linear model is:

[0123]

[0124] Where G=[g1,…g m ,…g K ] T , d m is the mth row of the precoding cascade channel matrix D, Re(·) represents the real part operation, Γ is a diagonal matrix, and the diagonal elements can be expressed as:

[0125]

[0126] S3: Based on the equivalent real-domain linear model of the RIS-assisted IoV communication system and the signal processing at the transmitter, the precoding matrix F of the IoV communication system is obtained, which specifically includes:

[0127] In order to eliminate the co-channel interference of mobile vehicle users in the RIS-assisted IoV communication system, the precoding equivalent channel matrix in the equivalent real domain linear model in step S2 is set to the unit matrix:

[0128]

[0129] Where I is the identity matrix.

[0130] Since Γ is a diagonal matrix, in order to satisfy the precoding equivalent channel matrix G is a unit matrix, the precoding cascade channel matrix D must also be a diagonal matrix, and:

[0131]

[0132] Since D is a diagonal matrix, The above formula can be re-expressed as:

[0133]

[0134] The precoding cascade channel matrix D can be further defined as:

[0135] D|=|FH|=I

[0136] When only D=FH=I is considered, the precoding matrix F of the Internet of Vehicles communication system is:

[0137] F=H H (HH H ) -1

[0138] Through the above precoding processing, the precoding equivalent channel matrix of the RIS-assisted vehicle networking communication system can be set to the unit matrix, thereby eliminating the co-channel interference between multiple users, where (·)H ,(·) -1 denote conjugate transpose and inverse operations respectively.

[0139] After precoding, the system output signal-to-noise ratio is approximately:

[0140]

[0141] where σ 2 is the noise variance. It can be seen from the above formula that increasing the number of transmitting antennas can improve the output signal-to-noise ratio of the system, thereby improving the information transmission quality of the Internet of Vehicles system.

[0142] S4: Based on the equivalent real-domain linear model of the RIS-assisted IoV communication system, a low-complexity channel estimation algorithm and data demodulation algorithm are constructed, including:

[0143] According to the characteristics of the linear model, a low-complexity linear channel estimation algorithm (least squares method) can be used to estimate the real-domain precoding equivalent channel of the linear model, effectively avoiding the real-time tracking of the instantaneous channel information in the complex domain, thereby reducing the high channel estimation overhead problem caused by the introduction of the RIS array. Specifically:

[0144]

[0145] in, represents the estimated real-domain precoding channel vector, u0 represents the transmitted pilot symbol used for channel estimation, and z0 represents the received pilot symbol;

[0146] Based on the Doppler-robust real-domain precoding linear model and low-complexity channel estimation method, a multi-antenna joint minimum Euclidean distance algorithm is used to demodulate the transmission information in the RIS-assisted vehicle network communication system:

[0147]

[0148] in, Represents the transmission data restored after data demodulation, z m It represents the differential detection result of the received signal at the mth receiving antenna.

[0149] In this embodiment, the specific parameters are set as follows:

[0150] like Figure 3 As shown in the figure, the initial configuration of the RIS-assisted vehicle networking communication system is:

[0151] Assume that all location information is based on a three-dimensional Cartesian coordinate system with x, y, and z as coordinate axes. The initial coordinate positions of the base station and RIS are (20, -15, 25) m and (-5, 45, 10) m, respectively. In addition, L represents the coverage area of ​​RIS, and the vehicle travels in this area at a speed of 50 m / s and communicates with the base station, where N t =128, N = 64, K = 8. The center carrier frequency of the LFM signal is f0 = 3.5 GHz, the signal bandwidth is B = 2.5 MHz, and the Rice factor in Rice fading is set to 10.

[0152] The effect of this embodiment is illustrated by comparing the performance of the precoding transmission method based on the RIS-assisted vehicle networking communication system proposed in this embodiment with other transmission methods in related technologies in a high mobility scenario through the MATLAB platform:

[0153] like Figure 4 As shown in the figure, it is the time domain waveform of the transmitted symbol of the LFM signal, and the transmitted code element is 0011. When the transmitted code element is 1, the signal is modulated into an Up-Chirp waveform, and the modulation frequency increases linearly with time; when the transmitted code element is 0, the signal is modulated into a Down-Chirp waveform, and the modulation frequency decreases linearly with time. In the LFM signal, the signal frequency changes linearly within a certain period of time. Since the frequency modulation slopes of different polarities have good orthogonality, different frequency modulation slopes can be used to represent different data, thereby realizing information transmission.

[0154] like Figure 5 , Figure 6 As shown, this is the time domain diagram of the LFM signal after passing through the matched filter. Figure 5 The matching output result of the LFM signal is shown. After matched filtering, the signal is approximately a narrow pulse of the Sinc function with relatively concentrated energy. Figure 6 is the mismatched output result of the LFM signal, and the amplitude is relatively flat. The matched filtering characteristics of the LFM signal can be used to perform differential detection on the output result after filtering, and a real domain linear model with Doppler robustness can be derived. From the above results, it can be seen that the LFM signal has good matching correlation, concentrated energy after pulse compression, and is insensitive to frequency deviation and Doppler effect. When applied to the Internet of Vehicles communication system, it can enhance the system's ability to resist frequency deviation and multipath fading.

[0155] like Figure 7As shown, the performance of the highly robust precoding system designed by the present invention is compared with that of the non-precoding system. The precoding transmission method proposed by the present invention uses the estimated cascade channel matrix to implement a simple linear precoding design at the transmitting end, which effectively reduces the channel multiplexing interference between multiple users in the Internet of Vehicles communication system, improves the system detection performance, and reduces the detection complexity at the user end. In the non-precoding system, as the vehicle speed increases, the mutual interference between adjacent vehicle users gradually intensifies, resulting in a decrease in its performance compared to the precoding system.

[0156] like Figure 8 As shown in the figure, it is a simulation diagram of the output signal-to-noise ratio of the highly robust RIS-assisted Internet of Vehicles precoding communication system designed by the present invention changing with the number of base station antennas. Under different transmission bit signal-to-noise ratios, the output signal-to-noise ratio of the system after precoding increases linearly with the number of transmitting antennas, and the overall performance of the system can be further improved by increasing the number of base station antennas.

[0157] like Fig. 9 As shown, in the RIS-assisted high-mobility Internet of Vehicles communication scenario, the comparison between the precoding transmission method designed by the present invention based on the RIS-assisted Internet of Vehicles communication system and the prior art in terms of transmission reliability. As the user's moving speed increases, the communication performance of the prior art gradually decreases; while the precoding transmission method proposed in the present invention can maintain relatively stable communication capabilities within a larger speed variation range, which verifies that the precoding transmission method of the present invention has the advantage of maintaining relatively reliable communication capabilities in a high-mobility Internet of Vehicles communication system. The present invention combines precoding technology with RIS to provide a new solution for reducing interference between multiple users and improving Doppler robustness in a high-mobility environment. The precoding technology can optimize the signal transmission method in a targeted manner, reduce interference and improve system performance.

[0158] Example 2

[0159] This embodiment provides a precoding transmission device based on a RIS-assisted vehicle networking communication system, which is used to implement the precoding transmission method based on a RIS-assisted vehicle networking communication system of the above-mentioned embodiment 1, including: a transmission waveform construction module, a precoding matrix preset module, a cascade channel matrix construction module, a real number domain precoding linear model construction module, a precoding matrix calculation module, a channel estimation module, and a data demodulation module;

[0160] In this embodiment, the transmission waveform construction module is used to construct a corresponding transmission waveform based on the channel characteristics of the RIS-assisted vehicle networking communication system and the multi-user transmission requirements, and map the bit data transmitted by the transmitter into a multi-base amplitude complementary orthogonal LFM waveform after space-time coding;

[0161] In this embodiment, the precoding matrix preset module is used to preset the precoding matrix;

[0162] In this embodiment, the cascade channel matrix construction module is used to obtain the precoded RIS-assisted Internet of Vehicles communication system cascade channel matrix based on a preset precoding matrix;

[0163] In this embodiment, the real-domain precoding linear model construction module is used to convert the precoded RIS-assisted Internet of Vehicles communication system into a Doppler-robust real-domain precoding linear model based on the orthogonal LFM waveform and the RIS-assisted Internet of Vehicles communication system cascade channel matrix, and in combination with the Ricean channel characteristics of the RIS-assisted Internet of Vehicles communication system;

[0164] In this embodiment, the precoding matrix calculation module is used to set the precoding equivalent channel matrix in the real domain precoding linear model to the unit matrix to obtain the precoding matrix of the Internet of Vehicles communication system;

[0165] In this embodiment, the channel estimation module is used to estimate the real-domain precoding equivalent channel of the real-domain precoding linear model based on a linear channel estimation algorithm;

[0166] In this embodiment, the data demodulation module is used to perform data demodulation on the transmission information in the RIS-assisted Internet of Vehicles communication system based on a multi-antenna joint minimum Euclidean distance algorithm to complete information transmission.

[0167] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A precoding transmission method based on a RIS-assisted vehicle networking communication system, characterized in that: The steps include: Based on the channel characteristics of the RIS-assisted Internet of Vehicles communication system and the multi-user transmission requirements, the corresponding transmission waveform is constructed, and the bit data transmitted by the transmitter is mapped into a multi-level amplitude complementary orthogonal LFM waveform after space-time coding; Presetting a precoding matrix, and obtaining a precoded RIS-assisted Internet of Vehicles communication system cascade channel matrix based on the preset precoding matrix; Based on the orthogonal LFM waveform and the cascade channel matrix of the RIS-assisted vehicle network communication system, and combined with the Ricean channel characteristics of the RIS-assisted vehicle network communication system, the precoded RIS-assisted vehicle network communication system is transformed into a real-domain precoded linear model with Doppler robustness. The precoding equivalent channel matrix in the real-domain precoding linear model is set to the unit matrix to obtain the precoding matrix of the Internet of Vehicles communication system; The real-domain precoding equivalent channel of the real-domain precoding linear model is estimated based on a linear channel estimation algorithm; Based on the multi-antenna joint minimum Euclidean distance algorithm, data demodulation is performed on the transmission information in the RIS-assisted Internet of Vehicles communication system to complete the information transmission.

2. The precoding transmission method based on the RIS-assisted vehicle networking communication system according to claim 1 is characterized in that: The bit data transmitted by the transmitting end is mapped into a multi-base amplitude complementary orthogonal LFM waveform after space-time coding, which is specifically expressed as: Among them, s n ∈{0,1,…M-1} represents the bit data transmitted by the nth transmitting antenna, With s n A complementary signal is formed and the amplitude sum of the two signals is M-1, T represents the duration of the signal transmission symbol, f0 represents the center carrier frequency, μ represents the frequency modulation slope of the LFM signal, when μ>0 represents a positive slope, when μ<0 represents a negative slope, the positive and negative slopes are orthogonal to each other, is the Up-Chirp signal, It is a Down-Chirp signal. The Up-Chirp signal and the Down-Chirp signal are orthogonal to each other.

3. The precoding transmission method based on the RIS-assisted vehicle networking communication system according to claim 2 is characterized in that: The method of converting the precoded RIS-assisted Internet of Vehicles communication system into a real-domain precoded linear model with Doppler robustness specifically includes: The received signal at the receiving end is processed by matched filtering, and the orthogonal LFM waveform is passed through the Up-Chirp matched filter and the Down-Chirp matched filter to obtain the corresponding matched filtering result; The corresponding matched filtering results are differentially detected, and the precoded RIS-assisted Internet of Vehicles communication system is converted into a real-domain precoded linear model with Doppler robustness, which is specifically expressed as: Among them, d m represents the precoded cascade channel vector from the base station to the mth mobile vehicle user after RIS reflection, represents the output vector of the orthogonal waveform after the Up-Chirp matched filter, represents the output vector of the orthogonal waveform after the Down-Chirp matched filter, The Doppler frequency shift f d The phase rotation caused by mj ,θ mj Represent the amplitude and phase of the precoding cascade channel, g m is the real domain equivalent channel vector from the base station to the mth mobile vehicle user after RIS reflection in the real domain precoding linear model, N t represents the total number of transmitting antennas of the base station, is the real-domain equivalent transmitted signal vector of the real-domain precoding linear model, n1, n2 represent the noise after the matched filter, v is the equivalent noise of the real-domain precoding linear model, B represents the signal bandwidth, and ρ represents the mutual correlation coefficient between the Up-Chirp signal and the Down-Chirp signal.

4. The precoding transmission method based on the RIS-assisted vehicle networking communication system according to claim 3 is characterized in that: The orthogonal LFM waveform passes through the Up-Chirp matched filter and the Down-Chirp matched filter to obtain the corresponding matched filtering results, which are specifically expressed as:

5. The precoding transmission method based on the RIS-assisted vehicle networking communication system according to claim 3 is characterized in that: The mutual correlation coefficient of the Up-Chirp signal and the Down-Chirp signal is specifically expressed as: Among them, a(·) and b(·) represent the Fresnel cosine function and the Fresnel sine function, respectively.

6. The precoding transmission method based on the RIS-assisted vehicle networking communication system according to claim 3 is characterized in that: The precoded cascade channel vector d between the base station and the mth mobile vehicle user after RIS reflection m , specifically expressed as: The cascade channel matrix of the RIS-assisted IoV communication system after precoding is: D = FH; Where D = [d1,…d m ,…d K ] T , d m is the mth row of the cascaded channel matrix D, and F represents the precoding matrix; The cascade channel matrix from the base station to K mobile vehicle users after RIS reflection is: H=[h1,…h m ,…h K ] T Among them, h m is the mth row of the cascaded channel matrix H, (·) T Represents a transpose operation; The cascade channel from the base station to the mth mobile vehicle user after RIS reflection is: h m =r m ΘQ Among them, Q LoS , represents the LoS part of the subchannel from the base station to the RIS and from the RIS to the mth mobile vehicle user, respectively, Q NLoS , They represent the NLoS part of the subchannel from the base station to the RIS and from the RIS to the mth mobile vehicle user, respectively. C and V represent the Rice factor. represents the phase control matrix of the RIS array, α n represents the phase shift of the nth reflection unit in the RIS array, and N represents the number of units in the RIS array.

7. The precoding transmission method based on the RIS-assisted vehicle networking communication system according to claim 3 is characterized in that: The precoding equivalent channel matrix in the real domain precoding linear model is set to the unit matrix, and the precoding matrix of the Internet of Vehicles communication system is obtained, which specifically includes: The real domain equivalent channel vector g between the base station and the mth mobile vehicle user after RIS reflection in the real domain precoding linear model m for: The equivalent channel matrix in the real-domain precoding linear model is: Where G=[g1,…g m ,…g K ] T , d m is the mth row of the precoding cascade channel matrix D, Re(·) represents the real part operation, Γ represents the diagonal matrix, (·) * represents the conjugation operation; The precoding equivalent channel matrix in the real-domain precoding linear model is set to the identity matrix, expressed as: Where I represents the identity matrix; The precoding cascade channel matrix D is defined as: D|=|FH|=I When D=FH=I, the precoding matrix F of the Internet of Vehicles communication system is: F=H H (HH H ) -1 in,(·) H ,(·) -1 denote the conjugate transpose and inverse operations respectively, and H denotes the cascade channel matrix from the base station to the K mobile vehicle users after RIS reflection.

8. The precoding transmission method based on the RIS-assisted vehicle networking communication system according to claim 1 is characterized in that: The real-domain precoding equivalent channel of the real-domain precoding linear model is estimated based on the linear channel estimation algorithm, which is specifically expressed as: in, represents the estimated real-domain precoding channel vector, u0 represents the transmitted pilot symbol used for channel estimation, and z0 represents the received pilot symbol.

9. The precoding transmission method based on the RIS-assisted vehicle networking communication system according to claim 1 is characterized in that: The data demodulation of the transmission information in the RIS-assisted Internet of Vehicles communication system is performed based on the multi-antenna joint minimum Euclidean distance algorithm, which is specifically expressed as follows: in, Represents the transmission data restored after data demodulation, z m represents the differential detection result of the received signal at the mth receiving antenna, K represents the total number of high-mobility vehicle users with a single antenna, represents the estimated real-domain precoding channel vector, represents the real-domain equivalent transmitted signal vector of the real-domain precoding linear model.

10. A precoding transmission device based on a RIS-assisted vehicle networking communication system, characterized in that: The method for implementing the precoding transmission method based on the RIS-assisted vehicle networking communication system according to any one of claims 1 to 9 comprises: a transmission waveform construction module, a precoding matrix preset module, a cascade channel matrix construction module, a real number domain precoding linear model construction module, a precoding matrix calculation module, a channel estimation module, and a data demodulation module; The transmission waveform construction module is used to construct a corresponding transmission waveform based on the channel characteristics of the RIS-assisted vehicle networking communication system and the multi-user transmission requirements, and map the bit data transmitted by the transmitter into a multi-base amplitude complementary orthogonal LFM waveform after space-time coding; The precoding matrix preset module is used to preset the precoding matrix; The cascade channel matrix construction module is used to obtain a pre-coded RIS-assisted Internet of Vehicles communication system cascade channel matrix based on a preset pre-coding matrix; The real-domain precoding linear model construction module is used to convert the precoded RIS-assisted vehicle networking communication system into a real-domain precoding linear model with Doppler robustness based on the orthogonal LFM waveform and the RIS-assisted vehicle networking communication system cascade channel matrix and in combination with the Ricean channel characteristics of the RIS-assisted vehicle networking communication system; The precoding matrix calculation module is used to set the precoding equivalent channel matrix in the real domain precoding linear model to the unit matrix to obtain the precoding matrix of the Internet of Vehicles communication system; The channel estimation module is used to estimate the real-domain precoding equivalent channel of the real-domain precoding linear model based on a linear channel estimation algorithm; The data demodulation module is used to perform data demodulation on the transmission information in the RIS-assisted Internet of Vehicles communication system based on a multi-antenna joint minimum Euclidean distance algorithm to complete information transmission.

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