CN112954792B - Multi-reflection device joint positioning and communication method based on environment backscattering - Google Patents

Abstract

The invention belongs to the technical field of wireless communication, and in particular relates to a joint positioning and communication method for multi-reflection equipment based on environmental backscattering. The present invention uses a receiver to receive a signal, and the received signal usually includes a direct link signal from an ambient radio frequency source and a backscattered signal from L reflective devices. Through the spatial signal processing technology, the positioning of multiple reflection devices can be realized at the same time. At the same time of positioning, a low-complexity solution for demodulating reflected signals under an OFDM radio frequency source is provided without demodulating radio frequency source information. That is, while positioning the reflection device, the communication between the reflection device and the receiver is realized. The reflection device transmits the pilot frequency, and the receiving end knows the corresponding relationship between the pilot frequency and the reflection device in advance. By performing a correlation operation between the pilot frequency known at the receiving end and the pilot frequency of the received signal, the reflected signal and the reflection device can be determined. Corresponding relationship, and finally realize the information demodulation and positioning of a certain reflective device.

Description

A method for joint positioning and communication of multi-reflection devices based on environmental backscattering

technical field

The invention belongs to the technical field of wireless communication, and in particular relates to a joint positioning and communication method for multi-reflection equipment based on environmental backscattering.

Background technique

Environmental backscattering technology is one of the IoT solutions proposed in recent years. It uses the RF source already existing in the environment as the signal source, and does not need to configure the RF signal source separately like the traditional backscattering technology. Backscattering technology itself has the advantages of low power consumption and low cost. Based on the application of environmental backscattering technology, the deployment of dedicated RF signal sources is eliminated, which further reduces costs and improves spectral efficiency.

With the development of science and technology, the demand for simultaneous communication and positioning of IoT devices is becoming more and more extensive. Designing a system that can simultaneously realize the communication and positioning of multiple reflection devices in the environmental backscatter communication system has broad application prospects. For example, in logistics management, there is an increasing demand for using robots instead of manual operations. Only after robots know the information and location of the logistics parts can they take corresponding actions. Therefore, it is required that logistics parts using IoT devices need both The information is decoded correctly, and its location also needs to be known, so that it is more convenient to use equipment such as robots to replace tedious manual operations.

However, since the environmental backscattering technology uses the radio frequency signal source that already exists in the environment, compared with the traditional backscattering technology, it brings new advantages in eliminating the interference of the radio frequency source signal and demodulating the backscattered signal. challenge. OFDM technology is widely used in today's commercial communication systems. Therefore, OFDM signals are commonly used environmental signals in environmental backscatter communication systems. It has a cyclic prefix structure. Therefore, according to the characteristics of this common RF source signal, the design based on environmental feedback The combined positioning and communication system of the multi-reflection equipment for the scattering also has important practical significance.

SUMMARY OF THE INVENTION

The main content of the present invention is to propose a joint positioning and communication method for multiple reflection devices based on environmental backscattering, which realizes the simultaneous positioning and communication of multiple reflection devices.

The present invention uses a receiver to receive a signal, and the received signal usually includes a direct link signal from an ambient radio frequency source and a backscattered signal from L reflective devices. Through the spatial signal processing technology, the positioning of multiple reflection devices can be realized at the same time. The present invention provides a low-complexity solution for demodulating reflected signals under an OFDM radio frequency source while realizing the positioning of multiple reflected signals, without demodulating radio frequency source information. That is, while positioning the reflection device, the communication between the reflection device and the receiver is realized. The reflection device transmits the pilot frequency, and the receiving end knows the corresponding relationship between the pilot frequency and the reflection device in advance. By performing a correlation operation between the pilot frequency known at the receiving end and the pilot frequency of the received signal, the reflected signal and the reflection device can be determined. Corresponding relationship, and finally realize the information demodulation and positioning of a certain reflective device.

The technical scheme of the present invention is:

A method for joint positioning and communication of multi-reflection devices based on environmental backscatter, comprising an ambient radio frequency source, L reflective devices, and a receiver with M antennas, and the number of the reflective devices is l=0,1,... L-1, the receiver coordinates are (x _r , y _r ), M≥L+1; it is characterized in that the joint positioning and communication method includes the following steps:

S1. The ambient radio frequency source transmits the radio frequency source signal, and the reflection device backscatters the ambient radio frequency source signal. The waveform design method of the reflection device is as follows:

Assuming that the symbol period of the reflection device is K times the symbol period of the OFDM radio frequency source, the binary information sent by each reflection device is represented by B _l (m), B _l (m)=±1, when a certain symbol in the transmission chip is transmitted When B(m)=-1, in the corresponding kth OFDM symbol period, design the following reflection device waveform:

Among them, N _c is the length of the cyclic prefix of the OFDM radio frequency source symbol, N is the length of the data part, N+N _c constitutes the length of a complete OFDM symbol, k=1,...K represents the symbol in the same reflection device The sequence number of the OFDM radio source symbol in the period;

When a certain symbol B(m)=1 of the transmission chip, the waveform of the reflection device is always 1;

S2. The receiver receives the signal, performs DOA estimation, and obtains the estimated angles of arrival of the direct link signal and multiple backscattered signals θ _d and θ _L =[θ ₀ ,θ ₁ ,θ ₂ ,...,θ _l , ...θ _L-1 ];

S3. Perform spatial filtering once for all the estimated angle of arrival signals. In each spatial filtering, design a weight vector to perform beamforming, process the received signals, keep only the signals of one angle, suppress the power of signals in other directions, and obtain Direction signals corresponding to all angles of arrival;

S4. Calculate the power of the signal _z (n) after spatial filtering. Suppose the signal has N sampling points, and the calculation method of the power Pz of the signal is:

和反射信号功率

通过直射信号功率

计算射频源到接收机的距离d_f：S5. After obtaining the power corresponding to the direction signals of all the angles of arrival, according to the characteristic that the backscattered signal will experience two fading compared with the direct link signal, the power of the direct signal is distinguished.

and reflected signal power

through direct signal power

Calculate the distance d _f from the RF source to the receiver:

Among them, n represents the attenuation coefficient of the environment, β is a constant, which is determined by the carrier frequency and the environment, both n and β can be obtained in the actual measurement, and _ps is the transmit power;

The rest of the signals are reflected link signals, and the power is used to estimate the product D of the distance from the RF source to the reflecting device and the distance from the reflecting device to the receiver:

为环境射频源到第l个反射设备的距离，

为第l个反射设备到接收机的距离，α_l为第l个反射设备的反射系数；in,

is the distance from the ambient RF source to the lth reflecting device,

is the distance from the lth reflection device to the receiver, α _l is the reflection coefficient of the lth reflection device;

S6. Estimate the distance from the reflection device to the receiver through geometric principles, specifically establishing the following equation according to the cosine theorem of the triangle:

和

Among them, Δθ is the angle between the direct radiation diameter and the reflected diameter, Δθ=|θ _d -θ _l |, which can be obtained by solving the equation

and

计算反射设备的坐标(x_l,y_l)：S7. Use the angle of arrival information θ _l of the backscattered signal and the distance information from the reflection device to the receiver

Calculate the coordinates of the reflective device (x _l , y _l ):

achieve positioning;

S8, demodulate the information of the reflected signal:

Assuming K=1, that is, the duration of one cycle of the reflection device waveform c(n) is the same as the duration of one OFDM symbol, while ignoring noise, within one OFDM symbol cycle, establish:

Among them, L _h is the delay spread of the channel, which represents the number of samples polluted by inter-symbol crosstalk, and these samples are discarded; then there are:

u(m)=|K _l | ² |s(n)| ² B(m)

是一个常数，p_l＝1，s(n)是射频源信号，解调时对B(m)判决法则如下：in,

is a constant, p _l =1, s(n) is the radio frequency source signal, the decision rule for B(m) during demodulation is as follows:

Thereby, the symbols transmitted by the reflection device are recovered;

S9. Use the known pilot sequence to perform a correlation operation with the pilot part of the decoded reflected signal. When the result of the correlation operation between the demodulated signal and a certain known pilot sequence is the largest, it is determined that the signal is related to The corresponding relationship of the pilot frequency is known, so it is determined which reflection device the signal belongs to while transmitting the information.

The beneficial effects of the present invention are as follows: the present invention proposes a joint positioning and communication method for multi-reflection devices based on environmental backscattering. It reflects the information of the equipment and has strong application value.

Description of drawings

Fig. 1 shows the system composition of the present invention

Fig. 2 shows the waveform design of a reflection device considered by the present invention

Figure 3 shows an illustration of a signal structure considered by the present invention

Fig. 4 shows the simulation result of the signal of the technical solution considered by the present invention being correctly judged to the correct reflection device

Fig. 5 shows the simulation result of the information demodulation performance of the reflection device of the technical solution considered by the present invention

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings.

其中s(t)是功率归一化射频源基带信号，发射功率为p_s。信道是强LOS径，图中

代表环境射频源到反向散射体的信道参数，

代表环境射频源到接收机的信道参数，

代表反向散射体到接收机的信道参数。n代表该环境的衰减系数，可以通过在某一具体环境实测而得，一般在2到4之间。d_f为环境射频源到接收机的距离，d_h为环境射频源到反向散射体的距离，d_g为反向散射体到接收机的距离。As shown in FIG. 1, the environmental backscattering system based on the present invention includes an environmental radio frequency source, L reflection devices, and a receiver with M antennas, M≥L+1; the environmental radio frequency source transmits the radio frequency source signal

where s(t) is the power-normalized RF source baseband signal, and the transmit power is p _s . The channel is a strong LOS path, as shown in the figure

represents the channel parameters from the ambient RF source to the backscatterer,

represents the channel parameters from the ambient RF source to the receiver,

Represents the channel parameters from the backscatterer to the receiver. n represents the attenuation coefficient of the environment, which can be obtained by actual measurement in a specific environment, generally between 2 and 4. d _f is the distance from the ambient RF source to the receiver, _dh is the distance from the ambient RF source to the backscatterer, and _dg is the distance from the backscatterer to the receiver.

Taking a uniform linear array as an example to illustrate the model of receiver reception, the number of reflection devices is L, and the number of reflection devices is l=0,1,...L-1, and the arrival angle of the direct signal is θ _d , The angle of arrival of the reflected signal from the reflecting device numbered l is θ _l .

The received signal can be expressed as

是带通噪声，

是射频源到编号为l的反射设备的距离，

是编号为l的反射设备到接收机的距离。c_l(t)为编号为l的反射设备的要传输的基带信号，α_l为反射系数。

和

为方向矢量，其中

为空间相位，f_c是载波频率，d是天线间距，c是光速，λ是载波波长。where l=0,1,...L-1.

is the bandpass noise,

is the distance from the RF source to the reflecting device numbered l,

is the distance from the reflective device numbered l to the receiver. c _l (t) is the baseband signal to be transmitted by the reflection device numbered l, and α _l is the reflection coefficient.

and

is the direction vector, where

is the spatial phase, f _c is the carrier frequency, d is the antenna spacing, c is the speed of light, and λ is the carrier wavelength.

The digital baseband form of the received signal can be expressed as

σ²是噪声功率。where ω(n) is the complex baseband noise, which follows a cyclic symmetric complex Gaussian distribution

σ ² is the noise power.

The present invention designs the waveform of the reflected signal, and the specific waveform design scheme is as follows:

It is assumed that the reflecting device symbol period is K times the OFDM radio source symbol period. The binary information emitted by each reflective device is denoted by B1(m), where B1 ₍ m)=± ₁ . When a certain symbol B(m)=-1 in the transmission chip, the following reflection device waveform is designed

N _c is the length of the cyclic prefix of the OFDM radio frequency source symbol, N is the length of the data part, and N+N _c constitutes the length of a complete OFDM symbol.

When a certain symbol of the transmission chip B(m)=1, the reflection device waveform is constant at 1.

As shown in Figure 2, when -1 is transmitted, the waveform is designed to perform a transition in the middle of an OFDM radio frequency source symbol, from 1 to -1, while when 1 is transmitted, the waveform is designed to have no transition.

Using the DOA estimation algorithm, L+1 angles of arrival can be estimated. Here, the Root-MUSIC algorithm (Barabell, "Improving the resolution performance of eigenstructure-based direction-finding algorithms," ICASSP'83. IEEE International Conference on Acoustics, Speech, and Signal Processing, Boston, Massachusetts, USA, 1983, pp.336-339, doi: 10.1109/ICASSP.1983.1172124) as an example to illustrate the estimation algorithm:

1. According to the set sampling number N, perform N sampling to obtain the sample sequence y(n), where

2. Calculate the y(n) autocorrelation matrix R, R=E{y(n)y ^H (n)}, where time average can be used instead of statistical average, that is

3. Perform eigenvalue decomposition on R. Since the number of target signals is L+1, the normalized eigenvector ui corresponding to the smallest ML-1 eigenvalue is obtained, where _i =L+2, L+3... , M.

u _i =[u _i0 ,u _i1 ,...u _i(m-1) ] ^T

4. Construct the vector a(z), a(z)=[1, z ^-1 ,...,z- ^(M-1) ] ^T .

Construct the following function:

乘以自身共轭转置，得到

Multiplying by the self-conjugate transpose, we get

i＝3,4,...,M。

i=3,4,...,M.

5. Define Polynomials

Set it to 0 and solve the equation. Find the value of z.

6. The number of target signals is L+1, and the z value is modulo subtracted by 1, and then the absolute value is sorted from small to large. This will find the 2L+2 closest roots modulo 1 (multiple roots will occur). Since the signal reflected by the backscatterer undergoes two attenuations, its signal strength is much smaller than that of the direct signal. The roots closest to the unit circle belong to the direct link signal. The angle of arrival of the reflected link signal can be obtained after the rest of the roots are deduplicated.

7. Since z=e ^jφ , φ is the spatial angular frequency, φ=−πsinθ. therefore

The calculation obtains an estimate of the direction of arrival of the signal.

和反射信号到达角度估计值

后，进行空域滤波。目的是只保留某一个方向的信号，将其他方向信号置零。Obtain the estimated value of the angle of arrival of the direct signal

and the estimated angle of arrival of the reflected signal

Afterwards, spatial filtering is performed. The purpose is to keep only the signals in a certain direction, and set the signals in other directions to zero.

方向的反射信号，将其他估计出来的方向的信号置零为例说明：There are many kinds of spatial filtering algorithms. Here is an example of a spatial filtering algorithm to preserve the

The reflected signal of the direction, and the signal of other estimated directions is set to zero as an example to illustrate:

代表要迫零的方向的集合。提出优化问题：write out the matrix

Represents a collection of directions to zero forcing. Ask the optimization problem:

st w ^H A = 0

The specific algorithm steps are as follows:

1. For the direction you want to force zero, construct a matrix through the direction vector

2. Solving B ^H A=0 can be solved by A ^H B=0

其中B⁺是B矩阵的M-P广义逆矩阵。3.

where B ⁺ is the MP generalized inverse of the B matrix.

的反射信号为例，空域滤波完成后，信号形式为：Here, only the arrival angle is retained as

The reflected signal of , for example, after the spatial filtering is completed, the signal form is:

z(n)=w ^H y(n)

That is, the signal is:

Among them, w is the weight vector designed in the spatial filtering process, p ₀ =w ^H a(θ ₀ ), ε _l =w ^H a(θ _l )ε _d =w ^H a(θ _d ) represents the power of each signal component The degree of inhibition depends on the accuracy of the DOA estimation. If the DOA estimation is very accurate, then p ₀ ≈1, ε _l and ε _d are both small values, about 0, which can be classified as noise. The following discussion is based on such a situation, that is, p ₀ =1, ε = 0 .

当p₀≈1，反射系数α₀已知，n和β实现进行实地测量后已知的情况下，则可以估计出

的值，即射频源到反射设备的距离和反射设备到接收机的距离的乘积D。The power of the measured z ₀ (n) signal is

When p ₀ ≈ 1, the reflection coefficient α ₀ is known, and n and β are known after field measurements, then it can be estimated that

The value of , that is, the product D of the distance from the RF source to the reflective device and the distance from the reflective device to the receiver.

Retain the signal of the direct link, suppress all reflected signals to estimate the distance from the RF source to the receiver, and perform spatial filtering in a similar way to the above, we can get

计算出d_f的值，以估计出射频源到接收机的距离。In the formula, p _d =w ^H a(θ _d ), p _d ≈1, and ε _l is a very small value, about 0, which can be classified as noise. Therefore, the power of the signal z _d (n) can be found

Calculate the value of d _f to estimate the distance from the RF source to the receiver.

Therefore, the positioning problem of the reflected signal can be modeled as the following geometric problem:

作为两条径距离的乘积也可以估计出来。那么由三角形的余弦定理。直射径和反射径之间的夹角为Δθ＝|θ_d-θ₀|，可以建立如下方程：θ _d and θ ₀ can be obtained after performing DOA estimation, and d _f can be estimated by keeping only the direct path signal,

It can also be estimated as the product of the two radial distances. Then by the cosine law of triangles. The angle between the direct diameter and the reflected diameter is Δθ=|θ _d -θ ₀ |, and the following equation can be established:

和

这样，反射设备到达接收机的距离

即可估计出来，同时已知信号到达角θ₀，则可以估计出反射设备的位置。In this equation, D and Δθ and d _f are known, and the two equations can be solved as

and

In this way, the distance from the reflecting device to the receiver

can be estimated, and at the same time the signal arrival angle θ ₀ is known, the position of the reflecting device can be estimated.

The calculation method of the coordinates of the reflection device is as follows. Assume that the coordinates of the known receiver are (x _r , y _r ), the coordinates of the reflection device are (x, y), and the angle of arrival is θ

Finally, the positioning result of the reflected signal is obtained.

The method to locate and demodulate the reflected signal at the same time is as follows:

For the convenience of analysis, it is assumed that K=1, that is, the duration of one cycle of the reflection device waveform c(n) is the same as the duration of one OFDM symbol. This assumption also does not affect the correctness of the theoretical derivation. That is, a complete OFDM symbol corresponds to a symbol B _l (m) of a reflection device, that is, there are N+N _c c(n) samples in a B _l (m) symbol period.

The spatially filtered signal is as follows:

The model can be simplified to the following form:

z ₀ (n)=K ₀ s(n)c ₀ (n)+ω(n)

是一个常数，

和

由于空域滤波已经置零，将其归入ω(n)项内。in

is a constant,

and

Since the spatial filtering has been zeroed, it is included in the ω(n) term.

As shown in Fig. 3 , assuming that the delay spread of channel h is L _h , a certain amount of intersymbol interference will be caused to the symbols of the CP, and the length of the CP is greater than the delay spread, so there are still some symbols of the CP that will not cause code If the inter-symbol crosstalk is detected, the sample points of the part where the inter-symbol crosstalk is not generated are used for processing. That is, ISI does not affect the correctness of the derivation.

Due to the nature of cyclic prefixes:

s(n)=s(n+N), n=0,...,N _c -1

Due to the nature of the designed waveform:

In one OFDM symbol period, that is, one B ₀ (m) symbol period, ignoring the influence of noise, as shown in Figure 3, the z ₀ (n) signal has the following properties: when n=L _h -1,..., When N _c -1

To process the signal, let:

ω_cross(n)为共轭相乘运算中产生的交叉项，也归于噪声项。but

ω _cross (n) is the cross term produced in the conjugate multiplication operation, which is also attributed to the noise term.

Therefore, if noise is ignored, u(m)=|K _o | ² |s(n)| ² B(m), that is, the processed u(m) is the original transmitted symbol B(m) multiplied by a constant.

The decision rule for B(m) during demodulation is as follows:

In this way, the symbols transmitted by the reflection device can be recovered.

Use the known pilot sequence to perform the correlation operation with the pilot part of the decoded reflected signal. When the result of the correlation operation between the demodulated signal and a certain known pilot sequence is the largest, it can be determined that the signal is related to the already decoded signal. The corresponding relationship of the pilot frequency is known, so it is possible to know which reflecting device the signal belongs to while transmitting the information.

Simulation analysis:

The reflective devices are set to 4, the positioning area is a space of 10 meters × 10 meters, the receiver is in this space, and the ambient radio frequency source is outside this space.

N _c of the OFDM symbol of the ambient radio frequency source is set to 16, N is set to 64, and N+N _c is 80, which is also the number of sampling points for one OFDM symbol. The reflector symbol period is the same as the OFDM symbol period. A total of 80,000 samples are collected, that is, 1,000 symbol sequences for DOA estimation. The transmit power of the source is fixed to 1, the coordinate of the source is set to (-5, 15), and the number of receiver antennas is 8. In the channel parameters, β is set to 1, and the distance attenuation coefficient is set to 2.5. The fixed coordinate of the receiver is (5,0). The arrival angle of the direct signal is -33.7°, and the distance from the source transmitter to the receiver is 18.03 meters. According to the previous signal model, the signal-to-noise ratio of the direct-link signal is related to the signal-to-noise ratio of the transmitted signal. The ratio of the ratios is Δγ _d = -31.4 dB.

The reflection coefficient of the reflecting device is set to α=0.2+0.3j. In the simulation, the coordinates of the reflection device are fixed. The coordinates of the reflection device numbered 0 are (2,3), the coordinates of the reflection device numbered 1 are (4,7), and the coordinates of the reflection device numbered 2 are (6,1). The reflection device with number 3 has coordinates (7,9). That is, the distances from the four reflection devices to the receiver are 4.24 meters, 7.07 meters, 1.41 meters, and 9.22 meters, respectively, and the true directions of the four reflection devices to the receiver are 45.0°, 8.1301°, -45.0°, and -12.53°, respectively. . The length of the pilot sequence of the reflection device is set to 64 symbols of the reflection device.

From the previous signal model, the ratio of the power of the reflected signal of the ith reflecting device with fixed coordinates to the signal-to-noise ratio of the transmitted signal can be calculated as:

Under the simulation conditions, it can be known that the Δγ _i of the four reflection devices are -53.1dB, -57.1dB, -43.9dB, and -61.2dB respectively. It can be seen that the reflected signal power difference of the reflection devices at different positions can reach about 20dB.

Change the signal-to-noise ratio γ _s of the transmit signal power from 30dB to 60dB, the signal-to-noise ratio of the received signal of the direct link is γ _s +Δγ _d , and the signal-to-noise ratio of the received signal of the four reflection devices is γ _s +Δγ _i . Several Monte Carlo experiments are carried out in each round. In each Monte Carlo experiment, the statistical reflection signal is determined as the accuracy of the corresponding reflection device, and the bit error rate of each reflection device is counted.

As shown in Figure 4, this is the simultaneous access of signals of multiple reflection devices, and the reflection signal is judged as the simulation result of the reflection device. It can be seen that when the signal-to-noise ratio of the transmitted signal is greater than 40dB, the probability of a correct decision is very high. Show that the program is effective. At the same time, the lowest decision probability is about 20%. This is because for a signal in one direction, assuming a completely random decision, it may be decided as four reflected signals or direct signals, and the probability of the correct decision is exactly 20%.

Fig. 5 is the simulation result of the bit error rate of the signal demodulation of the multi-reflection device. It can be seen that the bit error rate performance is greatly affected by the signal-to-noise ratio of the received signal. At the same time, when the signal-to-noise ratio is high enough, the bit error rate of the demodulation of the reflection device is also satisfactory, which shows the correctness of the signal demodulation scheme.

Claims (1)

1. A multi-reflection device joint positioning and communication method based on environmental backscatter, comprising an ambient radio frequency source, L reflection devices, and a receiver with M antennas, and the number of the reflection devices is l=0,1,. ..L-1, the receiver coordinates are (x _r , y _r ), M≥L+1; it is characterized in that the joint positioning and communication method comprises the following steps: S1. The ambient radio frequency source transmits the radio frequency source signal, and the reflection device backscatters the ambient radio frequency source signal. The waveform design method of the reflection device is as follows: Assuming that the symbol period of the reflection device is K times the symbol period of the OFDM radio frequency source, the binary information sent by each reflection device is represented by B _l (m), B _l (m)=±1, when a certain symbol in the transmission chip is transmitted When B(m)=-1, in the corresponding kth OFDM symbol period, design the following reflection device waveform:

Among them, N _c is the length of the cyclic prefix of the OFDM radio frequency source symbol, N is the length of the data part, N+N _c constitutes the length of a complete OFDM symbol, k=1,...K represents the symbol in the same reflection device The sequence number of the OFDM radio source symbol in the period; When a certain symbol B(m)=1 of the transmission chip, the waveform of the reflection device is always 1; S2. The receiver receives the signal, performs DOA estimation, and obtains the estimated angles of arrival of the direct link signal and multiple backscattered signals θ _d and θ _L =[θ ₀ ,θ ₁ ,θ ₂ ,...,θ _l , ...θ _L-1 ]; S3. Perform spatial filtering once for all the estimated angle of arrival signals. In each spatial filtering, design a weight vector to perform beamforming, process the received signals, keep only the signals of one angle, suppress the power of signals in other directions, and obtain Direction signals corresponding to all angles of arrival; S4. Calculate the power of the signal _z (n) after spatial filtering. Suppose the signal has N sampling points, and the calculation method of the power Pz of the signal is:

S5. After obtaining the power corresponding to the direction signals of all the angles of arrival, according to the characteristic that the backscattered signal will experience two fading compared with the direct link signal, distinguish the power of the direct signal

and reflected signal power

through direct signal power

Calculate the distance d _f from the RF source to the receiver:

Among them, n represents the attenuation coefficient of the environment, β is a constant, determined by the carrier frequency and the environment, both n and β can be obtained in actual measurement, and _ps is the transmit power; The rest of the signals are reflected link signals, and the power is used to estimate the product D of the distance from the RF source to the reflecting device and the distance from the reflecting device to the receiver:

in,

is the distance from the ambient RF source to the lth reflecting device,

is the distance from the lth reflection device to the receiver, α _l is the reflection coefficient of the lth reflection device; S6. Estimate the distance from the reflection device to the receiver through geometric principles, specifically establishing the following equation according to the cosine theorem of the triangle:

Among them, Δθ is the angle between the direct radiation diameter and the reflected diameter, Δθ=|θ _d -θ _l |, which can be obtained by solving the equation

and

S7. Use the angle of arrival information θ _l of the backscattered signal and the distance information from the reflection device to the receiver

Calculate the coordinates of the reflective device (x _l , y _l ):

achieve positioning; S8, demodulate the information of the reflected signal: Assuming K=1, that is, the duration of one cycle of the reflection device waveform c(n) is the same as the duration of one OFDM symbol, while ignoring noise, within one OFDM symbol cycle, establish:

Among them, L _h is the delay spread of the channel, which represents the number of samples polluted by inter-symbol crosstalk, and these samples are discarded; then there are: u(m)=|K _l | ² |s(n)| ² B(m) in,

is a constant, p _l =1, s(n) is the radio frequency source signal, the decision rule for B(m) during demodulation is as follows:

Thereby, the symbols transmitted by the reflection device are recovered; S9. Use the known pilot sequence to perform a correlation operation with the pilot part of the decoded reflected signal. When the result of the correlation operation between the demodulated signal and a certain known pilot sequence is the largest, it is determined that the signal is related to The corresponding relationship of the pilot frequency is known, so it is determined which reflection device the signal belongs to while transmitting the information.

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