Environment backscatter communication transmission method

Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to an environment backscatter communication transmission method. According to the invention, a sending symbol of a reflection device at each moment is set as a constellation point symbol, antennas of the reflection device of the Internet of Things are divided into two groups, and two continuous symbol transmission moments of the reflection device of the Internet of Things are set as a moment period; sending symbols of the first group of antennas and the second group of antennas are respectively in a complex conjugate form of sending signals of each other at two transmission moments, correspondingly, receiving signals of one moment period need to be processed at the same time when a receiving end demodulates, and finally, the receiving signals at the two moments are processed at the same time to obtain the receiving signals. Compared with a traditional transmission method, the method has the advantages that the bit error rate performance is remarkably improved, and particularly, a better diversity gain effect is shown in a backscattering link.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to an environmental backscatter communication transmission method. Background Art

[0002] As an important part of the new generation of information technology, the Internet of Things has been widely used in smart cities, smart transportation, health care and other fields, but its development faces two major challenges. The first is the problem of low-power transmission. Most IoT devices rely on batteries for power supply, so reducing the transmission power consumption of the device and achieving long-term low-power operation have become important issues that need to be solved urgently. The second is the issue of spectrum resources. With the rapid growth of the number of IoT devices, the existing spectrum resources are difficult to meet the connection needs of massive devices, resulting in reduced communication quality and increased latency. How to improve spectrum utilization and ensure reliable connection of large-scale IoT systems is another major challenge that needs to be solved urgently.

[0003] Ambient Backscatter Communication (AmBC) is a low-power communication technology that can effectively address the challenges of low-power transmission and spectrum resources mentioned above. AmBC uses existing RF signals in the environment (such as cellular and WiFi signals) to transmit information, so that the backscatter device (BD) does not need internal high-energy RF devices, but uses external RF sources for communication. This not only eliminates the need for a dedicated carrier transmitter, but also makes full use of existing RF signals for modulation and reflection, thereby significantly reducing the overall communication power of the system, extending the service life of the equipment, and reducing maintenance requirements, showing great potential in IoT applications.

[0004] Symbol constellation point design is crucial in backscatter communication systems. It determines the modulation mode of BD and directly affects the bit error rate of transmission and the reliability of the system. Reasonable constellation point design can improve transmission efficiency and reduce bit error rate in limited energy and complex environments, thereby enhancing system performance and signal link stability. In environmental backscatter communication, constellation point design needs to adapt to complex reflection paths and uncertain channel conditions, achieve signal link enhancement and transmission diversity, and ensure the robustness of communication. Therefore, symbol constellation point design is a key technology to improve system transmission performance and efficiency.

[0005] In environmental backscatter communications, multi-antenna reflection technology can obtain higher reflection energy and enhance the stability and transmission performance of the signal link by configuring multiple antennas on the BD. The multi-antenna configuration enables the reflection device to effectively utilize the RF energy in the environment through spatial diversity, improving the coverage and reliability of the signal. Combined with space-time coding technology, multiple antennas further increase the diversity gain of transmission and significantly improve the system's ability to resist channel fading, thereby ensuring reliable communication under complex channel conditions. Summary of the invention

[0006] Based on the prior art, the present invention proposes an environmental backscatter communication transmission method, which specifically includes three designs: one is the symbol constellation point design of the reflection device, the second is the multi-antenna reflection transmission method of the reflection device, and the third is the joint reception design of the environmental signal and the reflected signal on the receiver side.

[0007] The technical solution adopted by the present invention is:

[0008] An environmental backscatter communication transmission method, the communication system includes a main transmitter, a main receiver and an Internet of Things reflection device, wherein the main transmitter sends a signal to the main receiver and the Internet of Things reflection device, the Internet of Things reflection device uses reflection to modulate the main transmitter signal to achieve the transmission of its own signal, and the main receiver has multiple antennas; the transmission method includes:

[0009] The IoT reflection device is set to modulate the reflection device signal by antenna impedance, and the transmission symbol of the IoT reflection device at each moment is a constellation point symbol. The antenna of the IoT reflection device is divided into two groups, and two consecutive IoT reflection device symbol transmission moments are set as a moment period. In a moment period, the transmission symbols of the first group of antennas and the second group of antennas are respectively the complex conjugate forms of the signals transmitted by the other party at the two transmission moments. Specifically, at the first moment, the transmission symbol of the first group of antennas is defined as c(a), and the transmission symbol of the second group of antennas is defined as c(b). At the second moment, the transmission symbol of the first group of antennas is defined as c(a). * (a), the transmitted symbol of the second group of antennas is c * (b), each subsequent time period is transmitted according to this encoding method;

[0010] The main receiver jointly demodulates the signals from the main transmitter and the IoT reflector device. The main receiver needs to process the received signals of a time period at the same time during demodulation. Specifically, in one time period, the main receiver receives the signal at the first moment, then receives the signal at the second moment and performs conjugate processing, and finally processes the received signals at the two moments simultaneously to obtain the received signal.

[0011] Furthermore, the main receiver uses a maximum likelihood detector for joint demodulation, specifically:

[0012] Define the kth signal y received by the mth antenna of the main receiver at the first moment m,k (0) is:

[0013]

[0014] Among them, f m is the channel coefficient between the main transmitter and the main receiver, m=1,…,M, M is the number of antennas of the main receiver, Ps is the average transmission power at the main transmitter, s k (0) is the signal sent by the main transmitter at the first moment, c(0) is the signal sent by the IoT reflection device at the first moment, α is the reflection coefficient of the IoT reflection device, v1 is the channel coefficient between the main transmitter and the first group of antennas of the IoT reflection device, v2 is the channel coefficient between the main transmitter and the second group of antennas of the IoT reflection device, g 1,m is the channel coefficient between the first antenna group of the IoT reflector device and the mth receiving antenna of the main receiver, g 2,m is the channel coefficient between the second group antenna of the IoT reflector device and the mth receiving antenna of the main receiver, u m,k (0) is the receiving noise of the main receiver, which has a mean of 0 and a variance of σ 2 The cyclically symmetric complex Gaussian distribution of

[0015] Define the kth signal y received by the mth antenna of the main receiver at the second moment m,k (1) is:

[0016]

[0017] Among them, s k (1) is the signal sent by the main transmitter at the second moment, c(1) is the signal sent by the IoT reflector at the second moment, u m,k (1) is the receiving noise of the main receiver, which has a mean of 0 and a variance of σ 2 The cyclically symmetric complex Gaussian distribution of

[0018]

[0019] Assume that the average power of v1 and v2 is the same, g 1,m and g 2,m The average power of the direct link and the backscatter link is the same, and the average received signal-to-noise ratio of the direct link and the backscatter link is defined as in The relative signal-to-noise ratio between the backscatter link and the direct link is defined as

[0020] Simplify the received signal and define H1=[h0,h1,h2], The received signal vector at the first moment is y k (0) = [y 1,k (0),…,y M,k (0)] T , the received signal vector at the second moment is y k (1) = [y 1,k (1),…,y M,k (1) T , let x k (0)=[s k (0),s k (0)c(0),s k (0)c(1)] T , u k (0)=[u 1,k (0),…,u M,k (0)] T and Thus the received signal model is simplified to:

[0021] y k (0) = h0s k (0)+h1s k (0)c(0)+h2s k (0)c(1)+u k (0) = H1x k (0)+u k (0)

[0022]

[0023] The result of the maximum likelihood detector is:

[0024]

[0025] Right now

[0026]

[0027] Furthermore, the detection of the maximum likelihood detector is simplified as follows:

[0028] For each master transmitter signal s k (0), the reflected device signal c(0) remains unchanged. For each main transmitter signal s k (1), the reflected device signal c(1) remains unchanged; therefore, under the conditions of selecting c(0) and c(1), we first obtain s k (0) and s kThe maximum likelihood estimate of (1) is denoted as and where c = [c(0), c(1)] T ; Based on all the estimated conditions

[0029] and Get the maximum likelihood estimate of c(0) and c(1), denoted as Estimation based on the best reflection device’s own information Re-estimate s(0) and s(1) to obtain the optimal estimation result.

[0030] Furthermore, the main receiver uses a detector based on successive interference cancellation for joint demodulation, specifically:

[0031] Define the symbol period of the IoT reflection device as K times the symbol period of the main transmitter. The block diagonal channel matrix of the first IoT reflection device symbol transmission time is Transmit signal vector Noise Vector Received signal vector The block diagonal channel matrix at the symbol transmission time of the second IoT reflection device Transmit signal vector Noise Vector Received signal vector The received signal expression is written as:

[0032]

[0033] First, estimate the transmission signals s(0) and s(1) of the main transmitter in a time period:

[0034] Define the primary receiver to apply a block diagonal decoding matrix at the first IoT reflection device symbol transmission instant Applying a block diagonal decoding matrix at the second IoT reflection device symbol transmission instant Define linear detectors including maximum ratio combining MRC, zero forcing ZF and minimum mean square error MMSE detectors, decoding matrix Each matrix and decoding matrix Each matrix They are as follows, k=0,...,K-1:

[0035]

[0036] in, The channel fading coefficient of the direct link from the main transmitter to the main receiver It represents the channel fading coefficient of the backscatter link from the first group of antennas of the IoT reflector device to the main receiver. represents the channel fading coefficient of the backscatter link from the second group of antennas of the IoT reflector device to the main receiver, P s is the average transmission power of the main transmitter signal s(n), σ 2 is the receiver noise power, I is the unit matrix;

[0037] After applying the decoding matrix, the signal is extracted from the received signal and and The expressions are:

[0038]

[0039] After linear detection, the signal of the main transmitter is recovered:

[0040]

[0041] in Represents vector The 3k+1th component of Represents vector The 3k+1th component in ;

[0042] get and After that, the interference between the direct link and the main transmitter signal is weakened, and the following intermediate signal is obtained:

[0043]

[0044] Define the intermediate signal vector At the same time, define the decoding matrix H3(1:2:2M,:)=[h1,h2], For the intermediate vector signal After applying the decoding matrix H3, the intermediate vector signal Extract BD signal but:

[0045]

[0046] After decoding, the IoT reflection device signal is restored:

[0047]

[0048] Re-estimate s(0) and s(1), and first rewrite the received signal as:

[0049]

[0050] where c = [c(0), c(1)] T , equivalent channel and When getting and After that, construct and and re-estimate s k (0) and s k (1):

[0051]

[0052] Finally, joint demodulation is achieved.

[0053] The beneficial effect of the present invention is that the present invention has a significant improvement in bit error rate performance compared to traditional transmission methods, especially showing a better diversity gain effect in a backscatter link. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Schematic diagram of environmental backscatter communication considered by the present invention;

[0055] Figure 2 It is a schematic diagram of the BD reflection transmission method proposed by the present invention;

[0056] Figure 3 Schematic diagram of the bit error rate curve of the PT main signal s(n) and the BD secondary signal c(n) using the ML detector. DETAILED DESCRIPTION

[0057] The present invention is described in detail below in conjunction with the accompanying drawings:

[0058] The present invention considers Figure 1 The communication transmission process shown in the figure, in which the primary transmitter (PT) sends a signal to the primary receiver (PR) and the IoT reflector device (BD), and then the BD uses the reflection to modulate the PT signal to transmit its own signal, wherein the BD has multiple antennas. The primary transmitter (PT) has a single antenna, the IoT reflector device (BD) has two antennas, and the primary receiver (PR) has multiple antennas M (M>1). BD changes the amplitude and phase of the received environmental signal by intentionally changing its antenna reflection coefficient, and loads the encoded self-information on the received broadcast signal s k (n) to realize information transmission from BD to PR.

[0059] The communication process of the present invention is as follows:

[0060] 1) PT sends a modulated signal s(n). After the signal passes through the PT-PR channel and the PT-BD channel, PR and BD receive the above-mentioned sent signal s(n), where n represents time n;

[0061] 2) BD modulates its signal c(n) by changing the antenna impedance. The signal sends a symbol c at each moment, where c is a set of constellation points. The Q is the number of constellation point symbols. The constellation point transmission design with DC component bias characteristics proposed in the present invention has the specific feature of satisfying the expectation that the constellation point is not equal to 0, that is,

[0062] 3) BD first passes the information it transmits through Figure 2 The coding scheme shown. Specifically, BD divides multiple antennas into two groups, considering two BD symbol transmission moments. At time 0, the first group of antennas sends symbol c(0), and the second group of antennas sends symbol c(1); at time 1, the first group of antennas sends the complex conjugate form of symbol $c(1)$ and takes the symbol, and the second group of antennas sends the complex conjugate form of symbol $c(0)$. At subsequent moments, BD is transmitted according to the above coding method;

[0063] 4) According to the above transmission coding method, BD realizes backscatter modulation by changing its own antenna impedance, and modulates the above space-time coded symbols onto the radio frequency signal sent by PT;

[0064] 5) The primary receiver (PR) needs to receive and jointly demodulate the signals from the PT and BD. The PT and BD signals are jointly demodulated by designing the corresponding demodulation codeword matrix and combining the joint demodulation algorithm. The joint demodulation algorithm may include a maximum likelihood (ML) detector and a suboptimal detector based on successive interference cancellation (SIC).

[0065] The specific joint demodulation method is:

[0066] The present invention considers flat block fading. In each fading block, we define Represents the channel fading coefficient of the direct link from the main transmitter to the main receiver. represents the channel fading coefficient of the BD first antenna to the PR backscatter link, Indicates the channel fading coefficient of the backscatter link from the second antenna of BD to PR.

[0067] Assume that the symbol period of the IoT reflection device is K times (K ≥ 1) that of the main transmitter. Let the signal sent by the reflection device in its nth symbol period be c(n), and the signal sent by the main transmitter be s(n) adopts QPSK modulation. c(n) adopts the constellation point with DC component bias characteristic proposed by the present invention, such as Where j represents a complex number. Since the information of the reflection device itself is encoded, the receiving end needs to process the received signals in the two reflection device symbol periods at the same time during demodulation. The following will take the received signals in the 0th and 1st reflection device symbol periods for specific analysis. Similar operations can be performed on the received signals in the remaining periods. In the 0th reflection device symbol period, the kth signal y received by the mth antenna of the main receiver m,k (0) is:

[0068]

[0069] Among them, P s is the average transmission power at the main transmitter, α is the reflection coefficient of the IoT reflection device, which is generally a complex number with an absolute value less than 1, v1 is the channel coefficient between the main transmitter and the first antenna of the reflection device, v2 is the channel coefficient between the main transmitter and the second antenna of the reflection device, and g 1,m is the channel coefficient between the first antenna of the reflection device and the mth receiving antenna of the main receiver, g 2,m is the channel coefficient between the second antenna of the reflection device and the mth receiving antenna of the main receiver, f m is the channel coefficient between the main transmitter and the main receiver (m=1,...,M), u m,k (0) is the receiving noise of the main receiver, which has a mean of 0 and a variance of σ 2 The cyclically symmetric complex Gaussian distribution of

[0070] In the first reflection device symbol period, the main receiver needs to perform conjugate processing on the received signal, that is, take the conjugate of the received signal. At this time, the kth signal y received from the mth antenna m,k (1) is:

[0071]

[0072] Among them, u m,k (1) is the receiving noise of the main receiver, which has a mean of 0 and a variance of σ 2 The cyclically symmetric complex Gaussian distribution of

[0073] Assuming that the average power of v1 and v2 is the same, g 1,m and g 2,m For convenience, the average received signal-to-noise ratio of the direct link and the backscatter link are defined as and in The relative signal-to-noise ratio between the backscatter link and the direct link is also defined as

[0074] To simplify the expression, let Then we can set H1 = [h0,h1,h2], The received signal vector y in the 0th BD symbol period k (0) = [y 1,k (0),...,y M,k (0)] T , the received signal vector y in the first BD symbol period k (1) = [y 1,k (1),...,y M,k (1) T , x k (0)=[s k (0),s k (0)c(0),s k (0)c(1)] T , u k (0)=[u 1,k (0),...,u M,k (0)] T and In this way, the received signal model can be simplified to

[0075]

[0076] In the present invention, two receiving processing methods are designed, namely the optimal maximum likelihood detector and the suboptimal detector based on successive interference cancellation. The system will operate in a flat fading channel. The two detection methods will be described in detail below.

[0077] 1. ML Detector

[0078] Let the result of ML detector be but

[0079]

[0080] The number of searches for the ML detector is With the modulation order As the number of increases, the number of searches of the ML detector increases exponentially. Therefore, the complexity of the ML detector is extremely high.

[0081] Next, we consider how to significantly reduce the complexity of the ML detector by exploiting the structure of the received signal. For each primary transmitter signal s k (0), k = 0, ... K-1, the reflected device signal c(0) remains unchanged. For each main transmitter signal s k(1), k = 0, ... K-1, the reflected device signal c(1) remains unchanged. Therefore, under the conditions of selecting c(0) and c(1), we can get s k (0) and s k The maximum likelihood estimate of (1) is denoted as and where c = [c(0), c(1)] T . Based on all the conditions and The maximum likelihood estimates of c(0) and c(1) can be obtained, denoted as at last The corresponding conditional estimate and They are k (0) and s k The processing of the low-complexity ML detector is as follows.

[0082] 1) Given c(0) and c(1), estimate s(0) and s(1)

[0083] Under the conditions of selecting c(0) and c(1), the received signal can be written as

[0084]

[0085] where c = [c(0), c(1)] T , equivalent channel and The received signal vector y k (0) and y k (1) By performing maximum ratio combining, s can be estimated k (0) and s k (1) Estimation results and The expression is

[0086]

[0087] 2) Estimate the optimal c(0) and c(1), and then re-estimate s(0) and s(1)

[0088] Let the optimal reflection device self-information estimate be but

[0089]

[0090] Finally, s(0) and s(1) are re-estimated, and the optimal estimation result is and

[0091] The search times for the above low-complexity ML detector are It is lower than the search times of the original ML detector in (4). However, for the case of large K and high-order modulation at PT and BD, the search times of the low-complexity ML detector are still large.

[0092] 2. Detector based on continuous interference cancellation

[0093] For the convenience of expression, the block diagonal channel matrix in the 0th reflection device symbol period is defined as Transmit signal vector Noise Vector Received signal vector and the block diagonal channel matrix in the first reflection device symbol period Transmit signal vector Noise Vector Received signal vector

[0094] Then the received signal expression can be written as

[0095]

[0096] Since the backscatter link channel experiences double fading, the direct link channel h0 is usually stronger than the backscatter link channels h1 and h2. In order to reduce the complexity of the algorithm, it is considered to first use a linear detector to estimate s(0) and s(1), and then use the estimated results to reduce the interference between the direct link and the main transmitter signal. Then, the reflected device signals c(0) and c(1) can be detected. Finally, the recovered reflected device signals are used to obtain s k (0) and s k The details are as follows.

[0097] 1) The first step is to estimate s(0) and s(1)

[0098] For a linear detector, the host receiver applies a block diagonal decoding matrix in the 0th reflection device symbol period Apply the block diagonal decoding matrix in the first reflection device symbol period For maximum ratio combining (MRC), zero forcing (ZF) and minimum mean square error (MMSE) detectors, the decoding matrix Each matrix and decoding matrix Each matrix They are given as follows

[0099]

[0100] After applying the decoding matrix, the signal can be extracted from the received signal and and The expressions are as follows

[0101]

[0102] After linear detection, the signal of the main transmitter can be recovered

[0103]

[0104] in Represents vector The 3k+1th component of Represents vector The 3k+1th component in .

[0105] 2) The second step is to estimate c(0) and c(1)

[0106] From formula (12), we can get and After that, the interference between the direct link and the main transmitter signal can be weakened to obtain the following intermediate signal

[0107]

[0108] For the convenience of expression, define the intermediate signal vector So At the same time, define the decoding matrix Then H3(1:2:2M,:)=[h1,h2], In the middle of the vector signal After applying the decoding matrix H3, the intermediate vector signal Extract BD signal but

[0109]

[0110] After decoding, the BD signal can be restored as shown below

[0111]

[0112] 3) The third step is to re-estimate s(0) and s(1)

[0113] The received signal can be rewritten as

[0114]

[0115] where c = [c(0), c(1)] T, equivalent channel and When getting and After that, you can construct and and re-estimate s k (0) and s k (1), as shown below

[0116]

[0117] When the first step uses MRC, ZF and MMSE linear detectors to estimate s k (0) and s k (1), the detectors are called MRC-SIC detector, ZF-SIC detector and MMSE-SIC detector respectively.

[0118] In the following section, simulation results are provided to evaluate the performance of the proposed system detector. Assuming the channel coefficient f m , g 1,m , g 2,m , v1 and v2 are independent Rayleigh fading Each has mean zero and variance β f , β g , β g , β v , β v It is further assumed that when the distances from PT to PR and from PT to BD are large, the channel coefficient variance β f =10 -7 and β v =10 -5 . Channel coefficient variance β g It is related to the short distance from BD to PR and is determined by the relative signal-to-noise ratio △γ. Assume that the BD reflection coefficient α=0.2+0.3j, and the average transmission power of the main transmitter P s =1. The number of receiving antennas on PR is M = 1, and the number of channel realizations is not less than 5×10 6 Second-rate.

[0119] Figure 3 Simulation results show that the proposed method has significant improvement in bit error rate performance compared with traditional transmission methods, especially in backscatter links, showing better diversity gain effect.

Claims

1. An environmental backscatter communication transmission method, wherein the communication system includes a main transmitter, a main receiver and an Internet of Things reflection device, wherein the main transmitter sends a signal to the main receiver and the Internet of Things reflection device, and the Internet of Things reflection device uses reflection to modulate the main transmitter signal to achieve the transmission of its own signal, and the main receiver has multiple antennas; characterized in that, The transmission method comprises: The IoT reflection device is set to modulate the reflection device signal by antenna impedance, and the transmission symbol of the IoT reflection device at each moment is a constellation point symbol. The antenna of the IoT reflection device is divided into two groups, and two consecutive IoT reflection device symbol transmission moments are set as a moment period. In a moment period, the transmission symbols of the first group of antennas and the second group of antennas are respectively the complex conjugate forms of the signals transmitted by the other party at the two transmission moments. Specifically, at the first moment, the transmission symbol of the first group of antennas is defined as c(a), and the transmission symbol of the second group of antennas is defined as c(b). At the second moment, the transmission symbol of the first group of antennas is defined as c(a). * (a), the transmitted symbol of the second group of antennas is c * (b), each subsequent time period is transmitted according to this encoding method; The main receiver jointly demodulates the signals from the main transmitter and the IoT reflector device. The main receiver needs to process the received signals of a time period at the same time during demodulation. Specifically, in one time period, the main receiver receives the signal at the first moment, then receives the signal at the second moment and performs conjugate processing, and finally processes the received signals at the two moments simultaneously to obtain the received signal.

2. The method for transmitting environmental backscatter communication according to claim 1, characterized in that: The main receiver uses a maximum likelihood detector for joint demodulation, specifically: Define the kth signal y received by the mth antenna of the main receiver at the first moment m,k (0) is: Among them, f m is the channel coefficient between the main transmitter and the main receiver, m = 1, ..., M, M is the number of antennas of the main receiver, P s Average transmit power at the main transmitter, s k (0) is the signal sent by the main transmitter at the first moment, c(0) is the signal sent by the IoT reflection device at the first moment, α is the reflection coefficient of the IoT reflection device, v1 is the channel coefficient between the main transmitter and the first group of antennas of the IoT reflection device, v2 is the channel coefficient between the main transmitter and the second group of antennas of the IoT reflection device, g 1,m is the channel coefficient between the first antenna group of the IoT reflector device and the mth receiving antenna of the main receiver, g 2,m is the channel coefficient between the second group antenna of the IoT reflector device and the mth receiving antenna of the main receiver, u m,k (0) is the receiving noise of the main receiver, which has a mean of 0 and a variance of σ 2 The cyclically symmetric complex Gaussian distribution of Define the kth signal y received by the mth antenna of the main receiver at the second moment m,k (1) is: Among them, s k (1) is the signal sent by the main transmitter at the second moment, c(1) is the signal sent by the IoT reflector at the second moment, u m,k (1) is the receiving noise of the main receiver, which has a mean of 0 and a variance of σ 2 The cyclically symmetric complex Gaussian distribution of Assume that the average power of v1 and v2 is the same, g 1,m and g 2,m The average power of the direct link and the backscatter link is the same, and the average received signal-to-noise ratio of the direct link and the backscatter link is defined as and in The relative signal-to-noise ratio between the backscatter link and the direct link is defined as Simplify the received signal and define H1=[h0,h1,h2], The received signal vector at the first moment is y k (0) = [y 1,k (0),...,y M,k (0)] T , the received signal vector at the second moment is y k (1) = [y 1,k (1),...,y M,k (1) T , let x k (0) = [s k (0),s k (0)c(0),s k (0)c(1)] T , u k (0)=[u 1,k (0),…,u M,k (0)] T and Thus the received signal model is simplified to: y k (0)=h0s k (0)+h1s k (0)c(0)+h2s k (0)c(1)+u k (0)=H1x k (0)+u k (0) The result of the maximum likelihood detector is: Right now 3. The environmental backscatter communication transmission method according to claim 2, characterized in that: The detection of the maximum likelihood detector is simplified as follows: For each master transmitter signal s k (0), the reflected device signal c(0) remains unchanged. For each main transmitter signal s k (1), the reflected device signal c(1) remains unchanged; therefore, under the conditions of selecting c(0) and c(1), we first obtain s k (0) and s k The maximum likelihood estimate of (1) is denoted as and where c = [c(0), c(1)] T ; Based on all the conditions and Get the maximum likelihood estimate of c(0) and c(1), denoted as Estimation based on the best reflection device’s own information Re-estimate s(0) and s(1) to obtain the optimal estimation result.

4. The environmental backscatter communication transmission method according to claim 1, characterized in that: The main receiver uses a detector based on successive interference cancellation for joint demodulation, specifically: Define the symbol period of the IoT reflection device as K times the symbol period of the main transmitter. The block diagonal channel matrix of the first IoT reflection device symbol transmission time is Transmit signal vector Noise Vector Received signal vector The block diagonal channel matrix at the symbol transmission time of the second IoT reflection device Transmit signal vector Noise Vector Received signal vector The received signal expression is written as: First, estimate the transmission signals s(0) and s(1) of the main transmitter in a time period: Define the primary receiver to apply a block diagonal decoding matrix at the first IoT reflection device symbol transmission instant Applying a block diagonal decoding matrix at the second IoT reflector device symbol transmission instant Define linear detectors including maximum ratio combining MRC, zero forcing ZF and minimum mean square error MMSE detectors, decoding matrix Each matrix and decoding matrix Each matrix They are as follows, k=0,...,K-1: in, The channel fading coefficient of the direct link from the main transmitter to the main receiver It represents the channel fading coefficient of the backscatter link from the first group of antennas of the IoT reflector device to the main receiver. represents the channel fading coefficient of the backscatter link from the second group of antennas of the IoT reflector device to the main receiver, P s is the average transmission power of the main transmitter signal s(n), σ 2 is the receiver noise power, I is the unit matrix; After applying the decoding matrix, the signal is extracted from the received signal and and The expressions are: After linear detection, the signal of the main transmitter is recovered: in Represents vector The 3k+1th component of Represents vector The 3k+1th component in ; get and After that, the interference between the direct link and the main transmitter signal is weakened, and the following intermediate signal is obtained: Define the intermediate signal vector At the same time, define the decoding matrix H3(1:2:2M,:)=[h1,h2], For the intermediate vector signal After applying the decoding matrix H3, the intermediate vector signal Extract BD signal but: After decoding, the IoT reflection device signal is restored: Re-estimate s(0) and s(1), and first rewrite the received signal as: where c = [c(0), c(1)] T , equivalent channel and When getting and After that, construct and and re-estimate s k (0) and s k (1): Finally, joint demodulation is achieved.

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