A differential fraction spread spectrum LoRa communication method and system based on RIS

Abstract

The application relates to the technical field of Internet of Things wireless communication, and discloses a differential fraction spread spectrum LoRa communication method and system based on RIS. A transmitter divides input bits into RIS permutation matrix bits, RIS phase bits and signal bearing bits; a differential matrix is constructed through differential coding, the permutation matrix and phase information are embedded into the signal bearing, and a transmission signal matrix is generated by stacking. A receiver demodulates the signal bearing through de-chirping and discrete Fourier transform, obtains estimated signal bearing bits, and decodes the estimated RIS permutation matrix bits and the estimated RIS phase bits based on maximum likelihood detection without channel state information. The application realizes fine adjustment of data rate and noise resistance performance through a fraction spread spectrum factor, obtains spatial modulation gain through adjustment of the number of RIS reflection modes, significantly improves spectral efficiency and throughput without channel estimation, and is suitable for 6G Internet of Things, low-power wide-area networks and other scenes.

Description

Technical Field

[0001] This invention relates to the field of Internet of Things (IoT) wireless communication technology, and in particular to a differential fractional spread spectrum LoRa communication method and system based on RIS. Background Technology

[0002] The rapid development of the Internet of Things (IoT) is driving transformation in numerous fields such as smart transportation, smart cities, and smart agriculture. These application scenarios place core demands on wireless networks, including low power consumption, long-distance transmission, and reliable communication. Low-power wide-area networks (LPWANs), as a key technology meeting these needs, have become a research hotspot in the IoT field. Among them, LoRa modulation technology, based on chirped spread spectrum (CSS) technology, has achieved significant commercial success in low-power long-distance communication scenarios due to its excellent link budget and anti-interference capabilities. It can effectively resist the effects of noise, multipath fading, and frequency offset, making it the mainstream choice for low-data-rate long-distance wireless communication.

[0003] However, as IoT applications increasingly demand higher data transmission rates, traditional LoRa modulation technology has gradually revealed its performance bottlenecks, making it difficult to meet the high throughput requirements of next-generation IoT (especially in 6G scenarios). Its core limitations are mainly reflected in the following aspects:

[0004] On the one hand, traditional LoRa uses integer spreading factors (SF) for signal modulation. This design inherently limits its spectral efficiency (SE), making it difficult to increase data transmission rates and unsuitable for high-speed applications such as over-the-air upgrades, video surveillance sensor data transmission, and real-time data aggregation. To overcome this limitation, the academic community has proposed various improvement schemes. For example, Interleaved Chirped Spread Spectrum LoRa (ICS-LoRa) carries additional data bits by constructing interleaved chirped signals; Phase Shift Keying LoRa (PSK-LoRa) embeds additional information into the signal phase; Slope Keying LoRa (SSK-LoRa), Indexed Modulation (IM)-based LoRa, and Orthogonal Chirped Indexed Modulation (IQCIM) schemes improve spectral efficiency by utilizing time, frequency, and orthogonal domains, respectively. However, these solutions generally suffer from common drawbacks: most rely on coherent detection or accurate channel state information (CSI), which requires a complex channel estimation process. This not only increases system overhead and computational costs, but also reduces the stability of the system in fast fading channels, violating the core design philosophy of LoRa technology: low complexity and high energy efficiency.

[0005] On the other hand, traditional LoRa systems are susceptible to interference in fading channels, posing challenges to communication reliability, and existing improvement schemes have failed to fully exploit the transmission potential in the spatial dimension. In recent years, reconfigurable smart surfaces (RIS) have been introduced into the field of wireless communication as a promising technology. Through a planar structure composed of a large number of electrically controllable passive reflective elements, RIS can intelligently regulate the wireless propagation environment, construct strong signal transmission paths, effectively overcome obstruction problems, and improve communication coverage, providing a new approach to solving the performance bottlenecks of LoRa systems.

[0006] LoRa-assisted communication schemes based on RIS are mainly divided into two categories: coherent detection and incoherent detection. Due to the stringent requirements of IoT applications for low power consumption and low complexity, incoherent detection schemes that do not require channel state information are more practical. Among the existing RIS-assisted LoRa-related schemes, some achieve low-overhead communication by combining differential modulation and reflection pattern training, while others transmit information without the need for CSI through differential phase shift keying (such as LoRa-RIS-DPSK). However, these schemes still have significant shortcomings: first, they have not broken through the limitations of the traditional LoRa integer spreading factor, resulting in limited room for improvement in spectral efficiency; second, most of them use uniform phase modulation for all reflection units of the RIS, failing to fully utilize the rich combinational gains brought by a large number of independent and controllable reflection units, and not fully exploring the spatial modulation capabilities of the RIS.

[0007] Furthermore, the Fractional Spread Factor LoRa (FSF-LoRa) scheme extends the spreading factor from integers to non-integer ranges. By introducing fractional coefficients, it makes fine adjustments based on the integer spreading factor of traditional LoRa, optimizing the trade-off between data rate and noise immunity. However, this scheme does not combine the spatial control advantages of RIS technology, resulting in limited reliability improvement in fading channels and failing to further expand the dimensions of data transmission. Summary of the Invention

[0008] This invention provides a RIS-based differential fractional spread spectrum LoRa communication method and system that requires no channel state information and has low overhead.

[0009] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: This invention provides a RIS-based differential fractional spread spectrum LoRa communication method, comprising the following steps: S1. At the transmitter, the input bits are divided into RIS permutation matrix bits, RIS phase bits, and bearer signal bits; the RIS permutation matrix bits are integrated into the RIS permutation matrix selection, and the RIS phase bits are... M-PSK modulation is converted into phase information, and the bearer signal bits are obtained by LoRa modulation based on fractional spreading factor; a difference matrix is ​​constructed by combining the permutation matrix and the phase information, each column element of the difference matrix contains a phase information, and the arrangement of non-zero elements in each column of the difference matrix contains RIS reflection mode information. The phase information of the difference matrix is ​​embedded into the carrying signal to generate a transmission signal matrix; wherein, the sequence of non-zero elements of the difference matrix generates the positions of the non-zero elements of the transmission signal matrix. S2. The transmitter sends the transmission signal matrix to the receiver so that the receiver obtains the received signal matrix; S3. At the receiver, the received signal matrix is ​​demodulated on the bearer signal to obtain the estimated bearer signal bits. The estimated RIS permutation matrix bits and the estimated RIS phase bits are obtained by removing the bearer signal and performing differential detection, thus completing the information decoding.

[0010] A RIS-based differential fractional spread spectrum LoRa communication system includes: A transmitter is used to divide input bits into RIS permutation matrix bits, RIS phase bits, and bearer signal bits; the RIS permutation matrix bits are integrated into the RIS permutation matrix selection, and the RIS phase bits are... M -PSK modulation is converted into phase information, and the bearer signal bits are obtained by LoRa modulation based on fractional spreading factor; a difference matrix is ​​constructed by combining the permutation matrix and the phase information, each column element of the difference matrix contains a phase information, and the arrangement of non-zero elements in each column of the difference matrix contains RIS reflection mode information. The phase information of the difference matrix is ​​embedded into the carrying signal to generate a transmission signal matrix; wherein, the sequence of non-zero elements of the difference matrix generates the positions of the non-zero elements of the transmission signal matrix. A transmission channel is used to transmit the transmission signal matrix from the transmitter to the receiver so that the receiver obtains the received signal matrix. The receiver is used to demodulate the received signal matrix on the bearer signal to obtain estimated bearer signal bits, and to obtain estimated RIS permutation matrix bits and estimated RIS phase bits by removing the bearer signal and performing differential detection, thereby completing information decoding.

[0011] Compared with existing technologies, its advantages are as follows: This invention combines molecular spread spectrum LoRa and differential reflection technology. By introducing a fractional spreading factor, it extends the integer spreading factor of traditional LoRa to a non-integer range. Adjusting the fractional coefficients of the fractional spreading factor increases the chirp number for each LoRa symbol, and the differential reflection mechanism allows each LoRa symbol to carry more bits. This invention reduces the system's bit error rate by adjusting the number of RIS reflection modes, and allows for flexible throughput selection by adjusting the fractional spreading factor, achieving flexible configuration of data rate and noise immunity. At the receiver, optimal maximum likelihood detection can be used to jointly decode the RIS reflection modes and phase information without acquiring instantaneous channel state information. This invention synergistically utilizes the fine-tuning capabilities of the fractional spreading factor and the spatial modulation advantages of RIS technology to meet the next-generation Internet of Things' demands for high throughput, high reliability, and low power consumption communication. Attached Figure Description

[0012] Figure 1 This is a flowchart illustrating the steps of a RIS-based differential fractional spread spectrum LoRa communication method provided by the present invention. Figure 2 This is a block diagram of the transmitter in a RIS-based differential fractional spread spectrum LoRa communication method provided in Embodiment 1 of the present invention; Figure 3 This is a block diagram of the concatenated channel in a RIS-based differential fractional spread spectrum LoRa communication method provided in Embodiment 1 of the present invention; Figure 4 This is a block diagram of the receiver in a RIS-based differential fractional spread spectrum LoRa communication method provided in Embodiment 1 of the present invention; Figure 5 This is a comparison of the bit error rate performance of different systems provided in Embodiment 2 of the present invention; Figure 6 This is a comparison of the throughput performance of different systems provided in Embodiment 2 of the present invention. Detailed Implementation

[0013] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0014] Example 1 like Figure 1 As shown, this embodiment provides a RIS-based differential fractional spread spectrum LoRa communication method, including the following steps: S1. At the transmitter, the input bits are divided into RIS permutation matrix bits, RIS phase bits, and bearer signal bits; the RIS permutation matrix bits are integrated into the RIS permutation matrix selection, and the RIS phase bits are... M-PSK modulation is converted into phase information, and the carrier signal bits are obtained by LoRa modulation based on fractional spreading factor; a difference matrix is ​​constructed by combining the permutation matrix and the phase information, each column element of the difference matrix contains a phase information, and the arrangement of non-zero elements in each column of the difference matrix contains the RIS reflection mode information. The phase information of the difference matrix is ​​embedded into the carrying signal to generate a transmission signal matrix; wherein, the sequence of non-zero elements of the difference matrix generates the positions of the non-zero elements of the transmission signal matrix. S2. The transmitter sends a transmission signal matrix to the receiver so that the receiver can obtain the received signal matrix; S3. At the receiver, the received signal matrix is ​​demodulated on the bearer signal to obtain the estimated bearer signal bits. By removing the bearer signal and performing differential detection, the estimated RIS permutation matrix bits and the estimated RIS phase bits are obtained, thus completing the information decoding.

[0015] The transmitter and receiver of the method in this embodiment constitute a RIS-assisted differential molecular spread spectrum LoRa communication system. The RIS-assisted differential molecular spread spectrum LoRa communication system of the present invention is referred to as FSF-LoRa-RIS-DRM in the embodiment.

[0016] In step S1, the design block diagram of the transmitter is as follows: Figure 2 As shown, the signal transmission process at the transmitter is as follows: First, the input bits are divided into RIS permutation matrix bits, RIS phase bits, and bearer signal bits; the RIS permutation matrix bits are integrated into the RIS permutation matrix selection, and the RIS phase bits are... M -PSK modulation is converted into phase information, and the carrier signal bits obtain the carrier signal based on the fractional spreading factor.

[0017] Secondly, a difference matrix is ​​constructed by combining the permutation matrix and phase information. Specifically, using differential encoding, the permutation matrix and phase information are represented as a difference matrix, where each column contains a phase information element, and the arrangement of non-zero elements in each column contains the RIS reflection mode information.

[0018] Finally, the phase information of the difference matrix is ​​embedded into the carrier signal to generate the transmission signal matrix; wherein, the sequence of non-zero elements of the difference matrix generates the positions of the non-zero elements of the transmission signal matrix.

[0019] RIS possesses A legal A permutation matrix of dimension, where , Indicates the number of reflection modes in RIS. express The factorial. In the method proposed in this embodiment, a frame is divided into... A block composed of symbol time slots, because of RIS Each reflection mode is activated in permutation order during the block, occupying [a certain position / occupancy]. The 1st symbol slot. Due to the properties of binary bits, the RIS permutation matrix bits are mapped to the 1st symbol slot. t During each block period Permutation matrix ,in t It is an integer greater than 0, and in the proposed method, it is only from... Select from a list of valid permutation matrices There are matrices, which are defined as follows: , , …, This constitutes a set of permutation matrices. It is important to note that the permutation matrix used is not fixed, but is selected based on the actual modulation requirements.

[0020] To illustrate the mapping process more intuitively, Table 1 lists... and Examples, where, The bits are RIS permutation matrix bits, and ;— indicates that the corresponding permutation matrix is ​​not used for information transmission. For the given example, only 4 permutation matrices are selected to carry the RIS permutation matrix bits, while 2 permutation matrices do not participate in information carrying, and the permutation matrix for the corresponding bit is not fixed.

[0021] Table 1. Bit-mapped encoding of permutation matrix, applicable to... , K =3

[0022] RIS phase bits through M -PSK modulation is converted into phase information, and the phase information is further diagonalized to obtain a permutation matrix carrying the phase. The RIS phase bits are... r 2 bits, and To match the permutation matrix In the dimension, the RIS phase bits are mapped to K indivual M -PSK symbols, which are stacked into a vector By further diagonalization get ,Right now Further based on and permutation matrix The permutation matrix carrying the phase can be obtained. Permutation matrix carrying phase The expression is:

[0023] in, This is the permutation matrix carrying the phase; Let be the permutation matrix; This refers to the diagonalized phase information; Let K be a set of complex matrices of size K×K.

[0024] based on By combining the permutation matrix and phase information, a difference matrix is ​​constructed. The expression for the difference matrix is:

[0025] in, The difference matrix is ​​the given value. It is the difference matrix generated by the previous block; It is the identity matrix used for initialization. This can be further represented as a permutation matrix and M The product of diagonal matrices with -PSK notation, i.e.

[0026] in, yes The permutation matrix in It is a diagonal matrix whose diagonal elements come from M -PSK symbol. Therefore. elements and The sequence at each non-zero element position in the matrix carries RIS permutation matrix bits and RIS phase bits, respectively. The difference matrix can be further represented as...

[0027] in, Indicates the first The basis vector, the th basis vector The elements are non-zero. , This represents the index within that range, and yes In the A non-zero element at position 1 is a M -PSK symbol, representing , According to and The corresponding non-zero element position, the RIS's first Reflection modes In the t The first block k It is activated during each time slot, among which NThis indicates the number of elements in the RIS. The diagonal elements can be represented as , ,in Indicates the first i The on / off state of a reflective element. Indicates the first i The phase shift angle of each reflecting element.

[0028] The bearer signal bits are obtained based on a fractional spreading factor, which is the sum of an integer spreading factor and fractional coefficients. Bit, and In order to carry the difference matrix The phase and reflection mode activation sequence, carrying signal bits are converted K A number of bearer symbols containing the same number of bits, wherein F The fractional spreading factor proposed in this invention is the integer spreading factor in traditional LoRa. and fractional coefficient The sum. Fractional coefficient. The expression can be written as

[0029] in, It is a non-negative integer. Therefore, when At that time, that is The fractional spreading factor in the proposed system is comparable to the integer spreading factor of traditional LoRa. It's important to note that the fractional spreading factor increases the chirp count per symbol without changing the number of bits per symbol, which determines the number of bits per symbol. Include Bit, i.e. For each transmitted signal sample, the time interval is... ,in BW This represents the signal bandwidth. In the discrete-time domain, the sampling ratio is... In the case of, corresponding bearer signal It can be represented as

[0030] in, n It is a sample index. , E Energy is represented by the symbol "unit". , Represents the imaginary unit. This represents the LoRa basic chirped signal. A signal vector $ From 0 to ofn bearer signal Composition can be represented as

[0031] In obtaining K After each signal vector, the difference matrix The phase of each column is embedded into the sequence. K In each carrier signal vector, and according to the difference matrix The arrangement of non-zero elements, through stacking K A transmission signal matrix is ​​generated from each carrier signal vector. This process can be represented as

[0032] in, This is represented as the Kronecker product. Specifically, for the sampling time... n , No. t The first block k Transmission signal matrix of each time slot The expression is:

[0033] in, For transmission signal matrix; To carry signals; It is a difference matrix; It represents the imaginary unit.

[0034] And it is located The positions of non-zero elements. Therefore, the receiver actually receives and superimposes data continuously. K The received signal matrix is ​​obtained by transmitting samples from each symbol time slot.

[0035] In step S2, the transmitter sends a transmission signal matrix to the receiver so that the receiver obtains the received signal matrix. The transmitter sends the transmission signal matrix to the receiver through a transmission channel, which is a cascaded channel. The cascaded channel includes a channel from the transmitter to the RIS, a channel from the RIS to the receiver, and a direct link channel from the transmitter to the receiver. Figure 3 As shown, These represent the Rayleigh fading channel vectors between the transmitter and RIS, between the RIS and the receiver, and in the direct link, respectively, whose elements follow the rules of... For the sake of brevity, we introduce the following matrix:

[0036] Therefore, the expression for the equivalent cascaded channel of the proposed method is:

[0037] in, For the cascaded channel; This refers to the channel matrix from the transmitter to the RIS; The channel matrix from the RIS to the receiver; This is the direct link channel matrix from the transmitter to the receiver.

[0038] It should be noted that, for the sake of simplicity, path loss is not considered in the channel.

[0039] for The reflection mode of RIS is based on The position of the column in which it is located is active, as analyzed in the transmitter section. Therefore, the equivalent channel of the system is... .

[0040] In step S3, the receiver demodulates the received signal matrix on the bearer signal to obtain the estimated bearer signal bits. By removing the bearer signal and performing differential detection, the receiver obtains the estimated RIS permutation matrix bits and the estimated RIS phase bits, thus completing the information decoding.

[0041] The FSF-LoRa-RIS-DRM receiver block diagram is as follows: Figure 4 As shown, the received signal matrix It can be represented as

[0042] in, , It is a complex Gaussian noise matrix. Let a value have zero mean and covariance be . The complex Gaussian noise vector, express An identity matrix of dimension 1 This represents the noise power spectral density.

[0043] Step S3 includes: S3.1 The received signal matrix is ​​demodulated on the bearer signal to obtain the estimated bearer signal bits; Step S3.1 includes: S3.1.1, Take a 1× K The unit vector and the downchirped signal vector are multiplied by the Kronecker product to obtain the downchirped signal matrix; S3.1.2 The dechirped signal matrix and the received signal matrix are subjected to a Hadamard product operation to obtain the dechirped signal matrix; S3.1.3, for each of the dechirped signal matrices The stacked matrix is ​​obtained by performing a discrete Fourier transform on each point; S3.1.4. Select the maximum output of the Fourier transform of the stacked matrix to obtain the estimated bearer symbol, and perform symbol-to-bit conversion on the estimated bearer symbol to obtain the estimated bearer signal bits.

[0044] Specifically, in step S3.1, in order to obtain the estimated bearer symbol, a The unit vector and the down-chirped signal vector Perform the Kronecker product, where the lower chirped signal The lower chirped signal matrix is ​​obtained, i.e.:

[0045] Through calculation and The Hadamard product, used to dechirp the signal matrix. It can be represented as:

[0046] in,

[0047] and, It is also a complex AWGN matrix. Then, for each Applying the Discrete Fourier Transform (DFT) to each point yields the following signal:

[0048] in, It is the specific operation matrix of DFT. This represents the transpose operator. It is an integer. Therefore, It can be expanded into

[0049] in, , It is the phase shift generated by the channel. The magnitude is given by the following formula.

[0050] in, The above operations can be represented as a stacking matrix. The carrying symbol is estimated by selecting the maximum output of the DFT. The calculation method is as follows:

[0051] Through the By executing the above formula, the estimated bearing symbols are obtained sequentially. Finally, through the analysis of... Perform symbol-to-bit conversion to obtain the estimated number of bearer signal bits.

[0052] Step S3 also includes: S3.2, Obtain the estimated RIS permutation matrix bits and the estimated RIS phase bits by removing the bearer signal and performing differential detection; Step S3.2 includes: S3.2.1. The estimated bearer signal vector is obtained from the modulated estimated bearer symbols; S3.2.2. Calculate the received signal matrix and K The Hadamard product of the estimated carrier signal vectors is used to remove the carrier signal from the received signal matrix, resulting in the decarrier signal matrix. S3.2.3. Based on the removed signal matrix, the estimated permutation matrix carrying phase information is obtained through the optimal maximum likelihood detector, and then the estimated RIS permutation matrix bits and the estimated RIS phase bits are decoded.

[0053] Specifically, in step S3.2, after obtaining the estimated bearer signal bits, the RIS permutation matrix bits and RIS phase bits of the differential reflection section can be further decoded. This is achieved by modulating an estimated bearer symbol. In order to obtain an estimated bearer signal vector. ,in This is an estimated carrying signal. Further, through corresponding calculations... and K We obtain the de-bearing signal matrix by taking the Hadamard product of the estimated bearer signal vectors and removing the bearer signal from the received signal matrix. It can be represented as:

[0054] in, It is the first t The first block k The decarrier signal vector during each time slot. Based on the orthogonality of LoRa signals, i.e.:

[0055] It can be represented as:

[0056] therefore, This can be further expressed as:

[0057] in, It is also a complex Gaussian noise matrix.

[0058] Based on the construction of the difference matrix, Further, it is given by the following formula:

[0059] Therefore, the estimated phase permutation matrix is This can be obtained using an optimal maximum likelihood (ML) detector that does not require CSI, i.e.:

[0060] in, It is all legal The set whose cardinality is . Finally, it is possible to decode the code generated by... The carried RIS permutation matrix bits and RIS phase bits are shown in Table 1.

[0061] Example 2 This embodiment provides a RIS-based differential fractional spread spectrum LoRa communication system, including: A transmitter is used to divide input bits into RIS permutation matrix bits, RIS phase bits, and bearer signal bits; the RIS permutation matrix bits are integrated into the RIS permutation matrix selection, and the RIS phase bits are... M -PSK modulation is converted into phase information, and the bearer signal bits are obtained by LoRa modulation based on fractional spreading factor; a difference matrix is ​​constructed by combining the permutation matrix and the phase information, each column element of the difference matrix contains a phase information, and the arrangement of non-zero elements in each column of the difference matrix contains RIS reflection mode information. The phase information of the difference matrix is ​​embedded into the carrying signal to generate a transmission signal matrix; wherein, the sequence of non-zero elements of the difference matrix generates the positions of the non-zero elements of the transmission signal matrix. A transmission channel is used to transmit the transmission signal matrix from the transmitter to the receiver so that the receiver obtains the received signal matrix. The receiver is used to demodulate the received signal matrix on the bearer signal to obtain estimated bearer signal bits, and to obtain estimated RIS permutation matrix bits and estimated RIS phase bits by removing the bearer signal and performing differential detection, thereby completing information decoding.

[0062] Example 3 Based on the RIS-based differential fractional spread spectrum LoRa communication system described in Embodiment 2, this embodiment provides a comparison of the bit error rate performance and throughput performance of this system with other systems, including conventional LoRa, PSK-LoRa, and LoRa-RIS-DPSK. This embodiment includes: A transmitter is used to divide input bits into RIS permutation matrix bits, RIS phase bits, and bearer signal bits; the RIS permutation matrix bits are integrated into the RIS permutation matrix selection, and the RIS phase bits are... M -PSK modulation is converted into phase information, and the bearer signal bits are obtained by LoRa modulation based on fractional spreading factor; a difference matrix is ​​constructed by combining the permutation matrix and the phase information, each column element of the difference matrix contains a phase information, and the arrangement of non-zero elements in each column of the difference matrix contains RIS reflection mode information. The phase information of the difference matrix is ​​embedded into the carrying signal to generate a transmission signal matrix; wherein, the sequence of non-zero elements of the difference matrix generates the positions of the non-zero elements of the transmission signal matrix. A transmission channel is used to transmit the transmission signal matrix from the transmitter to the receiver so that the receiver obtains the received signal matrix. The receiver is used to demodulate the received signal matrix on the bearer signal to obtain estimated bearer signal bits, and to obtain estimated RIS permutation matrix bits and estimated RIS phase bits by removing the bearer signal and performing differential detection, thereby completing information decoding.

[0063] Comparison of bit error rate performance of different systems, such as Figure 5 As shown, Figure 5 This paper presents a comparison of the bit error rate (BER) performance of the system in this embodiment with other systems under Rayleigh fading channels, where the parameters are set to... , , ,as well as Furthermore, for fair comparison, all performance comparisons are based on bit signal-to-noise ratio. It is carried out on a scale.

[0064] It can be observed that when using and At this time, the bit error rate performance of FSF-LoRa-RIS-DRM is inferior to that of PSK-LoRa, comparable to but slightly worse than LoRa-RIS-DPSK, but significantly better than traditional LoRa. For example, at a bit error rate of... At that time, PSK-LoRa and LoRa-RIS-DPSK achieved gains of approximately 1.5 dB and 0.8 dB, respectively, compared to FSF-LoRa-RIS-DRM.

[0065] First, PSK-LoRa demodulation requires pilot signals for channel estimation, but this perfect channel estimation scenario is an idealized condition and difficult to achieve in real-world dynamic fading environments. In stark contrast, FSF-LoRa-RIS-DRM, through its unique differential reflection mechanism, completely avoids the significant overhead of acquiring instantaneous CSI required by PSK-LoRa, greatly contributing to reduced communication costs and improved system real-time performance. Second, the slight difference between LoRa-RIS-DPSK and FSF-LoRa-RIS-DRM is negligible in practical engineering applications, fully demonstrating their nearly equivalent bit error rate performance. Furthermore, it can be observed that when... and At this time, FSF-LoRa-RIS-DRM outperforms PSK-LoRa and LoRa-RIS-DPSK in terms of bit error rate performance. For example, at a bit error rate of... At that time, FSF-LoRa-RIS-DRM achieved gains of approximately 0.2 dB and 1.1 dB compared to PSK-LoRa and LoRa-RIS-DPSK, respectively. This performance advantage stems from the increased... K This results in a unique spatial modulation gain. K Increasing the number of RIS reflection modes from 2 to 3 significantly enriches the permutation diversity of RIS, which adds additional spatial degrees of freedom and can more effectively mitigate deep fading in Rayleigh channels. Unlike traditional methods that improve SE by extending bandwidth or reducing symbol spacing, this RIS mode permutation method is a green and efficient spectrum enhancement scheme tailored for LPWAN scenarios.

[0066] Comparison of throughput performance of different systems, such as Figure 6 As shown, Figure 6 This example demonstrates a comparison of throughput performance between the system in this embodiment and other systems under Rayleigh fading channels, where the parameters are set to... , , , ,as well as .

[0067] It can be observed that the throughput performance of FSF-LoRa-RIS-DRM is superior to other systems, and as... K Increasing from 2 to 4 significantly expands its advantages. For example, in At 5 dB, using The FSF-LoRa-RIS-DRM achieves a throughput of approximately 9800 b / s, which is about 12.5% ​​higher than LoRa-RIS-DPSK and nearly 50% higher than traditional LoRa. Even at lower levels At 0 dB, using The system still maintains a throughput gain of approximately 10% relative to LoRa-RIS-DPSK and approximately 40% relative to conventional LoRa, demonstrating robust throughput performance even under adverse channel conditions. Furthermore, since this significant throughput improvement stems from the differential reflection mechanism, this gain is achieved without any inherent trade-offs; unlike traditional methods that increase data rates by reducing symbol spacing or extending bandwidth, the RIS mode arrangement mechanism of FSF-LoRa-RIS-DRM adds an additional data-carrying dimension in the spatial domain. It can also be observed that this embodiment provides a more refined throughput adjustment mechanism compared to other systems. For example, when… SF When increasing from 7 to 8, the throughput of traditional LoRa drops sharply, making it difficult to adjust... SF To achieve optimal throughput. In contrast, FSF-LoRa-RIS-DRM utilizes a flexible fractional spreading factor to provide finer throughput tuning. As can be seen from the figure, even when hour F The throughput decreased more significantly than with traditional LoRa, even as it increased from 7 to 7.15. SF The increase from 7 to 8 is much smoother.

[0068] The FSF-LoRa-RIS-DRM system in this embodiment combines molecular spread spectrum LoRa and differential reflection technology. By adjusting the fractional coefficient of the spreading factor, the chirp number of each LoRa symbol is increased, and through the differential reflection mechanism, each LoRa symbol carries more bits. The bit error rate of the system can be reduced by adjusting the number K of the RIS reflection modes, and flexible throughput selection can be achieved by adjusting the spreading factor.

[0069] In summary, addressing the shortcomings of existing LoRa technologies in terms of spectral efficiency, fading resistance, and data transmission dimensionality expansion, this invention provides a RIS-based differential fractional spread spectrum LoRa communication method and system that requires no channel state information, has low complexity, and high spectral efficiency. This invention employs a differential reflection modulation mechanism, eliminating the need for the receiver to acquire instantaneous channel state information and avoiding a complex channel estimation process. This invention achieves spatial modulation gain by adjusting the number of RIS reflection modes, reducing the bit error rate; it increases the chirp number for each LoRa symbol by adjusting the fractional coefficient of the spreading factor, and through the differential reflection mechanism, allows each LoRa symbol to carry more bits. These two synergistic configurations enable the system to adapt to different channel conditions and service requirements. This invention can synergistically utilize the fine-tuning capabilities of the fractional spreading factor and the spatial modulation advantages of RIS technology to meet the next-generation Internet of Things' demands for high throughput, high reliability, and low power consumption communication.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A differential fractional spread spectrum LoRa communication method based on RIS, characterized in that, Includes the following steps: S1. At the transmitter, the input bits are divided into RIS permutation matrix bits, RIS phase bits, and bearer signal bits; the RIS permutation matrix bits are integrated into the RIS permutation matrix selection, and the RIS phase bits are... M -PSK modulation is converted into phase information, and the bearer signal bits are obtained by LoRa modulation based on fractional spreading factor; a difference matrix is ​​constructed by combining the permutation matrix and the phase information, each column element of the difference matrix contains a phase information, and the arrangement of non-zero elements in each column of the difference matrix contains RIS reflection mode information. The phase information of the difference matrix is ​​embedded into the carrying signal to generate a transmission signal matrix; wherein, the sequence of non-zero elements of the difference matrix generates the positions of the non-zero elements of the transmission signal matrix. S2. The transmitter sends the transmission signal matrix to the receiver so that the receiver obtains the received signal matrix; S3. At the receiver, the received signal matrix is ​​demodulated on the bearer signal to obtain the estimated bearer signal bits. The estimated RIS permutation matrix bits and the estimated RIS phase bits are obtained by removing the bearer signal and performing differential detection, thus completing the information decoding.

2. The method according to claim 1, characterized in that, In step S1, the RIS phase bit is passed through M -PSK modulation is converted into phase information, and the phase information is further diagonalized to obtain a permutation matrix carrying the phase. The expression for the permutation matrix carrying the phase is: in, This is the permutation matrix carrying the phase; Let be the permutation matrix; This refers to the diagonalized phase information; for K × K The set of complex matrices.

3. The method according to claim 2, characterized in that, In step S1, a difference matrix is ​​constructed by combining the permutation matrix and the phase information. The expression of the difference matrix is: in, The difference matrix is ​​the given value. It is the difference matrix generated by the previous block; Let be the permutation matrix carrying phase information.

4. The method according to claim 1, characterized in that, In step S1, the bearer signal bits are obtained by LoRa modulation based on a fractional spreading factor. The fractional spreading factor is the sum of an integer spreading factor and fractional coefficients, and the expression for the fractional coefficients is: in, It is a non-negative integer; The expression for the fractional spreading factor is: Where F is the fractional spreading factor; SF is the integer spreading factor.

5. The method according to claim 4, characterized in that, In step S1, the phase information of the difference matrix is ​​embedded into the bearer signal to generate a transmission signal matrix, the expression of which is: in, The transmission signal matrix; The carrying signal; The difference matrix is ​​the given value. It represents the imaginary unit.

6. The method according to claim 1, characterized in that, In step S2, the transmitter sends the transmission signal matrix to the receiver through a transmission channel, which is a cascaded channel. The cascaded channel includes a transmitter-to-RIS channel, a RIS-to-receiver channel, and a direct link channel from the transmitter to the receiver. The cascaded channel is equivalently represented as follows: in, For the cascaded channel; This refers to the channel matrix from the transmitter to the RIS; The channel matrix from the RIS to the receiver; This is the direct link channel matrix from the transmitter to the receiver.

7. The method according to claim 1, characterized in that, In step S3, the expression for the received signal matrix is: in, , It is a complex Gaussian noise matrix. Let a value have zero mean and covariance be . The complex Gaussian noise vector, express An identity matrix of dimension 1 This represents the noise power spectral density.

8. The method according to claim 1, characterized in that, Step S3 includes: S3.1 The received signal matrix is ​​demodulated on the bearer signal to obtain the estimated bearer signal bits; Step S3.1 includes: S3.1.1, Take a 1× K The unit vector and the downchirped signal vector are multiplied by the Kronecker product to obtain the downchirped signal matrix; S3.1.2 The dechirped signal matrix and the received signal matrix are subjected to a Hadamard product operation to obtain the dechirped signal matrix; S3.1.3, for each of the chirped signal matrices The stacked matrix is ​​obtained by performing a discrete Fourier transform on each point; S3.1.

4. Select the maximum output of the Fourier transform of the stacked matrix to obtain the estimated bearer symbol, and perform symbol-to-bit conversion on the estimated bearer symbol to obtain the estimated bearer signal bit.

9. The method according to claim 8, characterized in that, Step S3 includes: S3.2, Obtain the estimated RIS permutation matrix bits and the estimated RIS phase bits by removing the bearer signal and performing differential detection; step S3.2 includes: S3.2.

1. Modulate the estimated bearer symbols to obtain the estimated bearer signal vector; S3.2.

2. Calculate the received signal matrix and K The Hadamard product of the estimated bearer signal vectors is used to remove the bearer signal from the received signal matrix to obtain the debearer signal matrix; S3.2.

3. Based on the decarrier signal matrix, the estimated permutation matrix carrying phase information is obtained through the optimal maximum likelihood detector, and then the estimated RIS permutation matrix bits and the estimated RIS phase bits are decoded.

10. A differential fractional spread spectrum LoRa communication system based on RIS, characterized in that, include: A transmitter is used to divide input bits into RIS permutation matrix bits, RIS phase bits, and bearer signal bits; the RIS permutation matrix bits are integrated into the RIS permutation matrix selection, and the RIS phase bits are... M -PSK modulation is converted into phase information, and the bearer signal bits are obtained by LoRa modulation based on fractional spreading factor; a difference matrix is ​​constructed by combining the permutation matrix and the phase information, each column element of the difference matrix contains a phase information, and the arrangement of non-zero elements in each column of the difference matrix contains RIS reflection mode information. The phase information of the difference matrix is ​​embedded into the carrying signal to generate a transmission signal matrix; wherein, the sequence of non-zero elements of the difference matrix generates the positions of the non-zero elements of the transmission signal matrix. A transmission channel is used to transmit the transmission signal matrix from the transmitter to the receiver so that the receiver obtains the received signal matrix. The receiver is used to demodulate the received signal matrix on the bearer signal to obtain estimated bearer signal bits, and to obtain estimated RIS permutation matrix bits and estimated RIS phase bits by removing the bearer signal and performing differential detection, thereby completing information decoding.

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