Precoding transmission method and device based on RIS-assisted vehicle network communication system

Abstract

The present invention discloses a precoding transmission method and device based on a RIS-assisted vehicle networking communication system. The method includes the following steps: constructing an orthogonal LFM waveform based on the channel characteristics of the RIS-assisted vehicle networking communication system and the multi-user transmission requirements; obtaining a precoded RIS-assisted vehicle networking communication system cascade channel matrix based on a preset precoding matrix; converting the precoded RIS-assisted vehicle networking communication system into a real-domain precoding linear model; setting the precoding equivalent channel matrix of the real-domain precoding linear model to a unit matrix to obtain a precoding matrix of the vehicle networking communication system; estimating the real-domain precoding equivalent channel of the real-domain precoding linear model based on a linear channel estimation algorithm; and performing data demodulation on the transmitted information based on a multi-antenna combined minimum Euclidean distance algorithm to complete information transmission. The present invention can reduce channel estimation overhead, improve the high reliability of information transmission, and enhance the anti-interference capability between multiple users.

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 network 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 backdrop, intelligent reflective surface (RIS) technology has emerged as a key means of improving signal propagation conditions. By flexibly adjusting the signal reflection path, RIS can optimize communication between vehicles and with infrastructure, significantly enhancing signal coverage and strength, thereby effectively reducing multi-user interference. This technology is particularly suitable for high-density traffic environments and helps achieve more efficient real-time information transmission between vehicles.

[0003] In IoV communications, high-mobility vehicle users, while receiving their own information, may experience interference from base stations transmitting information for other high-mobility vehicle users. However, due to limited processing capabilities on the user side, it is difficult to completely eliminate this interference. In high-speed scenarios, the relative motion between vehicles can induce Doppler shift, affecting signal transmission quality. Furthermore, due to the RIS's lack of signal processing capabilities and its large number of passive reflectors, real-time acquisition of channel state information becomes difficult in IoV systems. This results in high channel estimation overhead in latency-sensitive high-mobility scenarios, increasing data transmission latency and failing to meet the robustness requirements of high-mobility IoV transmission. Summary of the Invention

[0004] 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. Based on the virtual line-of-sight (LoS) path provided by RIS and the ability to create a Ricean fading environment, the present invention redesigns a linear frequency modulation (LFM) signal (i.e., a Chirp signal) with excellent Doppler resistance and long-distance low power consumption characteristics, and precodes the transmitted waveform to meet the needs of Internet of Vehicles information transmission. Utilizing the characteristics of the transmitted waveform, the RIS-assisted Internet of Vehicles communication system is converted into a Doppler-robust real-domain linear model based on a differential detection algorithm. Due to 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, the pilot design overhead can be reduced, and the high reliability and low-latency communication capability of the information transmission of the Internet of Vehicles communication system can be improved.

[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 network communication system, comprising the following steps:

[0007] Based on the channel characteristics and multi-user transmission requirements of the RIS-assisted vehicle network communication system, a corresponding transmission waveform is constructed. The bit data transmitted by the transmitter is mapped into a multi-ary 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 cascaded channel matrix of the RIS-assisted IOV communication system, and combined with the Ricean channel characteristics of the RIS-assisted IOV communication system, the precoded RIS-assisted IOV 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 identity 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 vehicle network 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 follows:

[0014]

[0015] Among them, s n ∈{0,1,…M-1} represents the bit data transmitted by the nth transmitting antenna, With s n Complementary signals are formed and the sum of the amplitudes 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, and 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 Doppler robust real-domain precoded linear model specifically includes:

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

[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 precoding linear model with Doppler robustness, which is specifically expressed as:

[0019]

[0020] Among them, d m represents the precoded concatenated 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, Indicated by 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 between the base station and the mth mobile vehicle user after RIS reflection in the real domain precoding linear model, N t Indicates 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 and 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 cross-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 the corresponding matched filtering results, which are specifically expressed as follows:

[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] Where 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 is 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 concatenated 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 cascade 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 between the base station and RIS and the RIS to the mth mobile vehicle user, respectively. C and V represent the Rice factors represents the phase control matrix of the RIS array, α n It represents the phase shift of the nth reflector element in the RIS array, and N represents the number of elements 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 identity 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 is 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, which is expressed as:

[0043]

[0044] Where I represents the identity matrix;

[0045] The precoding concatenated 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 of the transmission information in the RIS-assisted Internet of Vehicles communication system is performed based on a multi-antenna combined minimum Euclidean distance algorithm, which is specifically expressed as follows:

[0054]

[0055] in, Represents the transmission data recovered 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 the RIS-assisted vehicle networking communication system, which is used to implement the above-mentioned precoding transmission method based on the 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-domain precoding linear model construction module, a precoding matrix calculation module, a channel estimation module, and a data demodulation module;

[0057] The transmit waveform construction module is used to construct a corresponding transmit waveform based on the channel characteristics and multi-user transmission requirements of the RIS-assisted vehicle network communication system, and map the bit data transmitted by the transmitter into a multi-ary 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-to-vehicle communication system into a Doppler-robust real-domain precoding linear model based on the orthogonal LFM waveform and the cascaded channel matrix of the RIS-assisted vehicle-to-vehicle communication system, in combination with the Ricean channel characteristics of the RIS-assisted vehicle-to-vehicle 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 combined 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) Based on the requirements of the IoV communication system for reliable transmission and multi-user interference suppression, the present invention reconstructs an LFM signal with good matching properties and precodes the transmission waveform, effectively solving the problem of unstable signal transmission at high speeds and the problem of information crosstalk between mobile users in the RIS-assisted IoV communication system.

[0066] (2) The present invention utilizes the characteristics of the transmitted waveform and transforms the RIS-assisted vehicle network communication system into a Doppler-robust real-domain linear model based on the 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 Schematic diagram of the flow of the precoding transmission method based on the 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 vehicle networking communication system of the present invention;

[0069] Figure 3 This 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 This is a time domain schematic diagram of the matched output of the LFM signal after passing through the matched filter of the present invention;

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

[0073] Figure 7 Schematic diagram showing the performance simulation comparison between precoded transmission and non-precoded transmission based on the RIS-assisted vehicle networking communication system of the present invention;

[0074] Figure 8 This 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] Figure 9 Schematic diagram of performance simulation comparison of the precoding transmission method of the RIS-assisted vehicle network communication system of the present invention. DETAILED DESCRIPTION

[0076] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to 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 vehicle network communication system, which solves the transmission reliability problems, multi-user co-channel interference problems, and high channel estimation overhead problems of the RIS-assisted vehicle network communication system in the prior art. The precoding transmission method improves the high reliability and low latency communication capability of the vehicle network communication system in a fast fading environment. This embodiment is applied to a vehicle network communication system in a high-speed mobile scenario with RIS assistance. The vehicle network 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 elements, and K highly mobile vehicle users having single antennas, the method comprising 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. Therefore, 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 exhibit Ricean 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 reflector element 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 vehicle-to-vehicle communication system, an LFM signal (i.e., Chirp signal) with good matching properties is selected as the transmission waveform, and the transmitter signal processing suitable for the vehicle-to-vehicle communication system is performed according to the waveform characteristics.

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

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

[0093]

[0094] Wherein, f0 represents the center carrier frequency, T represents the duration of the signal transmission symbol, and μ represents the frequency modulation slope of the LFM signal. When μ>0, it represents a positive slope, and when μ<0, it represents a negative slope. 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, as follows:

[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 flat 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 shift, as well as the basic characteristics of LFM signals, the transmitter signal processing suitable for the Internet of Vehicles communication system is carried out.

[0104] like Figure 2 As shown in FIG, the bit data transmitted by the transmitter is space-time coded and mapped into a multi-base amplitude complementary orthogonal LFM waveform, 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 two signals form complementary signals and the sum of their amplitudes is M-1. To simplify the analysis, in this embodiment, it is assumed 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 a multi-user downlink vehicle-to-vehicle communication system assisted by RIS, multiple mobile vehicle user terminals communicate with the base station on the same time slot, frequency, and code channel, inevitably generating co-channel interference. Due to the power consumption and size limitations of mobile terminals, the overhead of interference cancellation is difficult to bear. Therefore, interference suppression is achieved through precoding processing at the base station transmitter.

[0111] Define the precoding matrix as F, which acts on the cascade channel of the RIS-assisted Internet of Vehicles communication system to eliminate co-channel interference between multiple users. The cascade channel matrix after precoding 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 precoding linear system model with Doppler interference suppression capability is constructed. Specifically:

[0115] Combine 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 the Up-Chirp and Down-Chirp matched filters are:

[0116]

[0117] Then, at the receiving end, the matched filtering results are differentially detected to transform the precoded RIS-assisted vehicle network communication system into a real-domain precoded linear model with Doppler robustness:

[0118]

[0119] Among them, d m represents the precoded concatenated 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; Indicated by 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; mj ,θ mj represent the amplitude and phase of the precoding concatenated 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 transmitter signal processing, 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 vehicle network communication system, the precoding equivalent channel matrix in the equivalent real domain linear model in step S2 is set to the identity 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 we have:

[0131]

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

[0133]

[0134] The precoding concatenated 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 network communication system can be set to the identity matrix, thereby eliminating the co-channel interference between multiple users, where (·)H ,(·) -1 denote the 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. As can be seen from the above formula, 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. Specifically, the algorithms include:

[0143] Based on 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 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 a Doppler-robust real-domain precoding linear model and a low-complexity channel estimation method, a multi-antenna joint minimum Euclidean distance algorithm is used to demodulate the data transmitted in the RIS-assisted vehicle network communication system:

[0147]

[0148] in, Represents the transmission data recovered 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 network communication system is:

[0151] Assume that all location information is based on a three-dimensional Cartesian coordinate system with x, y, and z as the 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 the RIS. The vehicle travels through 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 Ricean factor in Ricean fading is set to 10.

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

[0153] like Figure 4 Figure 2 shows the time domain waveform of the transmitted symbol of an LFM signal, with the transmitted symbol being 0011. When the transmitted symbol is 1, the signal is modulated into an up-chirp waveform, with the modulation frequency increasing linearly over time. When the transmitted symbol is 0, the signal is modulated into a down-chirp waveform, with the modulation frequency decreasing linearly over time. In an LFM signal, the signal frequency varies linearly over time. Because frequency modulation slopes of different polarities are orthogonal, different frequency modulation slopes can be used to represent different data, thereby achieving information transmission.

[0154] like Figure 5 、 Figure 6 As shown in FIG, it is the time domain diagram of the LFM signal after passing through the matched filter. Figure 5 The matching output 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 This is the mismatched output of the LFM signal, with a relatively flat amplitude. LFM signals can be used to perform differential detection on the filtered output using the matched filtering properties of the signal, deriving a real-domain linear model that is Doppler-robust. These results demonstrate that LFM signals exhibit good matching correlation, concentrated energy after pulse compression, and are insensitive to frequency offset and Doppler effects. Application of these signals in connected vehicle communication systems can enhance the system's robustness against frequency offset and multipath fading.

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

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

[0157] like Figure 9 As shown, in the RIS-assisted high-mobility vehicle network communication scenario, the comparison of the precoding transmission method designed by the present invention based on the RIS-assisted vehicle network communication system and the existing technology in terms of transmission reliability is shown. As the user's movement speed increases, the communication performance of the existing technology gradually decreases; while the precoding transmission method proposed by 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 vehicle network communication system. The combination of precoding technology and RIS in the present invention provides a new solution for reducing interference between multiple users and improving Doppler robustness in a high-mobility environment. The precoding technology can specifically optimize the signal transmission method, reduce interference and improve system performance.

[0158] Example 2

[0159] This embodiment provides a precoding transmission device based on a RIS-assisted vehicle network communication system, which is used to implement the precoding transmission method based on the RIS-assisted vehicle network communication system of the above-mentioned embodiment 1, including: a transmission waveform construction module, a precoding matrix preset module, a cascaded channel matrix construction module, a real-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 transmit waveform construction module is used to construct a corresponding transmit waveform based on the channel characteristics and multi-user transmission requirements of the RIS-assisted vehicle network communication system, and map the bit data transmitted by the transmitter into a multi-ary 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 vehicle-to-vehicle communication system into a Doppler-robust real-domain precoding linear model based on the orthogonal LFM waveform and the cascaded channel matrix of the RIS-assisted vehicle-to-vehicle communication system, in combination with the Ricean channel characteristics of the RIS-assisted vehicle-to-vehicle 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 identity 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 combined 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 considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A precoding transmission method based on a RIS-assisted vehicle network communication system, characterized in that: The steps include: Based on the channel characteristics and multi-user transmission requirements of the RIS-assisted vehicle network communication system, a corresponding transmission waveform is constructed. The bit data transmitted by the transmitter is mapped into a multi-ary 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 cascaded channel matrix of the RIS-assisted IOV communication system, and combined with the Ricean channel characteristics of the RIS-assisted IOV communication system, the precoded RIS-assisted IOV 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 identity 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. The linear channel estimation algorithm adopts the least squares method and is specifically expressed as follows: in, represents the estimated real-domain precoding channel vector, u0 represents the transmitted pilot symbol used for channel estimation, (·) T represents the transposition operation, z0 represents the received pilot symbol; Based on the multi-antenna joint minimum Euclidean distance algorithm, the data transmission information in the RIS-assisted vehicle network communication system is demodulated to complete the information transmission; 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 recovered 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 real-domain equivalent transmitted signal vector of the real-domain precoding linear model.

2. The precoding transmission method based on the RIS-assisted vehicle network 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 Complementary signals are formed and the sum of the amplitudes 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, and 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 network communication system according to claim 2 is characterized in that: The method of converting the precoded RIS-assisted IoV communication system into a Doppler robust real-domain precoded linear model specifically includes: The received signal at the receiving end is processed by matched filtering. The orthogonal LFM waveform passes through the Up-Chirp matched filter and the Down-Chirp matched filter to obtain the corresponding matched filtering results. The corresponding matched filtering results are differentially detected, and the precoded RIS-assisted Internet of Vehicles communication system is converted into a real-domain precoding linear model with Doppler robustness, which is specifically expressed as: Among them, d m represents the precoded concatenated 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, Indicated by the Doppler frequency shift f d The phase rotation caused by mj ,θ mj denote the amplitude and phase of the precoded cascade channel from the jth transmitting antenna of the base station to the mth mobile vehicle user, d mn ,θ mn They represent the amplitude and phase of the precoded cascade channel from the nth transmitting antenna of the base station to the mth mobile vehicle user, g m is the real domain equivalent channel vector between the base station and the mth mobile vehicle user after RIS reflection in the real domain precoding linear model, N t Indicates 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 and 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 cross-correlation coefficient between the Up-Chirp signal and the Down-Chirp signal; 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: 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 is m for:

4. The precoding transmission method based on the RIS-assisted vehicle network 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: Where a(·) and b(·) represent the Fresnel cosine function and the Fresnel sine function, respectively.

5. The precoding transmission method based on the RIS-assisted vehicle network communication system according to claim 3 is characterized in that: The precoded concatenated 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 = [d 1, …d m, …d K ] T , d m is the mth row of the concatenated 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=[h 1, …h m, …h K ] T Among them, h m is the mth row of the cascade 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 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 It represents the phase shift of the nth reflector element in the RIS array, and N represents the number of elements in the RIS array.

6. The precoding transmission method based on the RIS-assisted vehicle network 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 identity matrix to obtain the precoding matrix of the Internet of Vehicles communication system, specifically including: 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, which is expressed as: Where I represents the identity matrix; The precoding concatenated 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.

7. A precoding transmission device based on a RIS-assisted vehicle network communication system, characterized in that: The method for implementing the precoding transmission method based on the RIS-assisted vehicle network communication system according to any one of claims 1 to 6 comprises: a transmission waveform construction module, a precoding matrix preset module, a cascade channel matrix construction module, a real domain precoding linear model construction module, a precoding matrix calculation module, a channel estimation module, and a data demodulation module; The transmit waveform construction module is used to construct a corresponding transmit waveform based on the channel characteristics and multi-user transmission requirements of the RIS-assisted vehicle network communication system, and map the bit data transmitted by the transmitter into a multi-ary 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-to-vehicle communication system into a Doppler-robust real-domain precoding linear model based on the orthogonal LFM waveform and the cascaded channel matrix of the RIS-assisted vehicle-to-vehicle communication system, in combination with the Ricean channel characteristics of the RIS-assisted vehicle-to-vehicle 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 combined minimum Euclidean distance algorithm to complete information transmission.

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