CN112505624B - Positioning system based on environment backscattering - Google Patents

Positioning system based on environment backscattering Download PDF

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CN112505624B
CN112505624B CN202011425053.XA CN202011425053A CN112505624B CN 112505624 B CN112505624 B CN 112505624B CN 202011425053 A CN202011425053 A CN 202011425053A CN 112505624 B CN112505624 B CN 112505624B
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梁应敞
朱贤明
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University of Electronic Science and Technology of China
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention belongs to the technical field of wireless communication, and particularly relates to a positioning system based on environmental backscattering. The invention calculates the arrival angle of the signals through a spatial domain signal processing technology according to the fact that the signals received by a receiver comprise direct link signals from an environment radio frequency source and environment signals which are backscattered by a backscatter body, the calculation result comprises the arrival angles of the direct link signals and the backscatter signals, the arrival angles of the direct link signals and the backscatter signals are distinguished by utilizing the characteristic that the backscatter signals are subjected to twice fading compared with the direct link signals, and the coordinates of the backscatter body are calculated according to the arrival angles of the backscatter signals to realize positioning. The method is suitable for indoor plane positioning scenes such as logistics warehouses and the like, and the scheme is simple to implement and has high application value.

Description

Positioning system based on environment backscattering
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a positioning system based on environmental backscattering.
Background
With the coming of the 5G era, the internet of things will come to a rapid development stage, and future communication networks will bring huge traffic and huge connection numbers with the rapid growth of internet of things devices. In the current 5G era and even the new 6G vision in the future, efficient utilization of spectrum resources is one of effective means for solving the challenge of huge traffic and huge connection of the internet of things. The environment backscattering technology replaces a special radio frequency source of a traditional backscattering communication system with an environment radio frequency source, so that the cost for deploying the special radio frequency source can be reduced, the utilization rate of frequency spectrum resources is improved, and the positioning system has the potential of realizing high spectrum efficiency and low energy consumption.
In a practical application scene, the radio frequency source signal and the environmental backscatter signal generally come from different directions, and by utilizing the characteristic, the radio frequency source signal and the environmental backscatter signal can be distinguished in a space domain, so that the corresponding signal arrival direction can be obtained. In some application scenarios, the signal direction of the backward scatterer can be accurately estimated, and then the backward scatterer can be positioned.
Disclosure of Invention
The invention mainly provides a positioning system design based on an environment backscattering technology, and realizes the positioning of an environment backscattering body.
The invention uses a receiver to receive signals, the received signals generally comprise direct link signals from an environmental radio frequency source and environmental signals which are backscattered by a backscatter, the receiver calculates the arrival angle of the signals by a space domain signal processing technology, and the calculation result generally comprises two angles, namely the arrival angles of the direct link signals and the backscatter signals. The invention can distinguish the arrival angle of the direct link and the backscattering signal by utilizing the characteristic that the backscattering signal can experience twice fading compared with the direct link signal, and can solve the coordinate of the backscattering body with low cost and high efficiency through a system scheme after the arrival angle of the backscattering signal is obtained.
The technical scheme of the invention is as follows:
a positioning system based on environmental backscattering comprises a radio frequency source, a plurality of receivers with M antennas and a backscattering device, wherein M is more than or equal to 3; the receiver receives the direct link signal and the environmental signal which is backscattered by the backscatter device, the receiver obtains the arrival angles of the direct link signal and the backscatter signal respectively, and the coordinates of the backscatter device are obtained according to the arrival angles of the backscatter signal and the known position coordinates of the plurality of receivers.
The specific method for the receiver to respectively obtain the arrival angles of the direct link signal and the backscatter signal is as follows:
assume that the signal received by the receiver is:
y(t)＝y d (t)+y b (t)+ω(t)
wherein, y d (t) is the received direct link signal, y b (t) is the received backscatter signal, ω (t) is the noise subject to a circularly symmetric gaussian distribution; the arrival angles of the direct link signal and the backscatter signal are obtained through a DOA estimation algorithm, and the arrival angles of the direct link signal and the backscatter signal are distinguished according to the characteristic that the backscatter signal is subjected to fading twice compared with the direct link signal.
The specific method for obtaining the coordinates of the backscatter device is as follows:
suppose the position coordinates are (x) 0 ,y 0 ) Is obtained by the receiver at an angle of arrival theta 0 In the position coordinate of (x) 1 ,y 1 ) Obtained arrival of receiverAngle theta 1 Obtaining the coordinates of the backscatter means
Figure GDA0002895465040000021
Comprises the following steps:
Figure GDA0002895465040000022
Figure GDA0002895465040000023
the above solution may be implemented by calculating coordinates of the backscatter device according to an arrival angle of the backscatter signal obtained by the receiver at different position coordinates for a case of using a plurality of receivers and a case of using one receiver, specifically:
assume that the receiver is at position coordinate (x) 0 ,y 0 ) To obtain an angle of arrival of theta 0 Moving the receiver to a position coordinate (x) 1 ,y 1 ) To obtain an angle of arrival of theta 1 Obtaining the coordinates of the backscatter means
Figure GDA0002895465040000024
Comprises the following steps:
Figure GDA0002895465040000025
Figure GDA0002895465040000026
the invention has the beneficial effects that: by utilizing the characteristic that the radio frequency source signal and the reflected signal in the environment backscattering communication system usually do not reach the receiver at the same angle, the arrival angle of the reflected signal is separately estimated, and then the specific position of the backscattering body is estimated. The scheme is suitable for indoor plane positioning scenes such as logistics warehouses, is simple to implement and has high application value.
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FIG. 1 is a schematic diagram of the system of the present invention;
FIG. 2 is a schematic flow chart of the present invention;
FIG. 3 is a diagram illustrating a relationship between an estimation accuracy of an angle of arrival of a backscatter link and a signal-to-noise ratio of the backscatter link in simulation;
FIG. 4 is a schematic diagram of the results of a positioning simulation Monte Carlo experiment.
Detailed Description
The invention is described in detail below with reference to the figures and simulation examples.
As shown in FIG. 1, the positioning system of the present invention comprises an ambient radio frequency source, one or more receivers with M (M ≧ 3) antennas, and a backscatter. The environment radio frequency source does not need to be deployed independently, and nearby base stations and WiFi hotspots can be used as radio frequency signal sources. A single antenna may be deployed on the backscatter, or multiple antennas may be deployed. Each receiver device is provided with M receiving antennas, and if two or more receivers are used for receiving, the receivers are arranged at different known positions, and a plurality of arrival angles of the backscatter signals are calculated at the same time, so that the coordinates of the backscatter body are calculated. If one receiver is used for receiving, the receiver can be moved to a known position according to a fixed rule, signals received by multiple receivers are simulated through the moving process, and then the coordinates of the backscattering body are calculated.
Where h represents the channel parameters of the ambient radio source to the backscatter scatterers, f represents the channel parameters of the ambient radio source to the receiver, and g represents the channel parameters of the backscatter scatterers to the receiver.
In the invention:
transmitting radio frequency source signal by environment radio frequency source
Figure GDA0002895465040000031
Where s (t) is the ambient radio source baseband signal with transmit power p s ，f c Is the carrier frequency of the ambient radio source signal.
The bandpass form of the ambient radio frequency source signal received by the array element with the receiver serial number 0 is:
Figure GDA0002895465040000032
wherein f represents the channel parameter of the channel from the environmental radio frequency source to the receiver, and the numerical subscript thereof represents the antenna corresponding to the number of the receiver.
The reception process is illustrated with a uniform linear array: the propagation delay of the array element numbered m with respect to the array element numbered 0 is
Figure GDA0002895465040000041
Where c is the speed of light, d is the interval of array elements, theta is the plane angle between the signal arrival direction and the array element orientation, i.e. the signal incidence angle, and tau is the propagation delay of the array element numbered 1 relative to the array element numbered 0
The band-pass form of the environment radio frequency source signal received by the receiver with the serial number of m array elements is as follows:
Figure GDA0002895465040000042
according to the practical application scenario, the following assumptions can be made:
1. the ambient radio frequency source is far away from the receiver, the incident wave is a plane wave, and the array element interval is small. Thus the channel parameter f m For all m E [0,M-1]The same is true.
2.s (t) has a much smaller bandwidth than the carrier frequency, so the delay between array elements is negligible compared to the symbol interval. Thus s (t) is the same for all receiving elements at the same time, i.e. s (t) ≈ s (t- τ) m )
Thus, the signal arriving at the ambient rf source of each array element of the receiver can be written as:
Figure GDA0002895465040000043
due to time delays, the signals arriving at each array element differ only in phase. The phase difference between the array element with the number m and the array element with the number 0 to the received environmental radio frequency source signal is
Figure GDA0002895465040000044
Wherein f is c Is the carrier frequency, tau, of the ambient radio source signal m The propagation delay of the array element numbered m relative to the array element numbered 0.
The array element spacing d is set to half the wavelength of the carrier, i.e.
Figure GDA0002895465040000045
λ is the carrier wavelength and the direction of arrival of the signal is θ, then
Figure GDA0002895465040000046
Thus, the device
Figure GDA0002895465040000047
Order to
Figure GDA0002895465040000048
Representing a phase shift of the direct signal received by the array element numbered m with respect to the direct signal of the array element numbered 0, then
Figure GDA0002895465040000049
Wherein theta is d Is the direction of incidence of the ambient radio source signal (direct signal). Defining a direction vector as a f (θ d )＝[1,a f,1 (θ d ),...,a f,M-1 (θ d )] T Then, the ambient rf source signals received by all array elements from the direct link are:
Figure GDA0002895465040000051
the signal from the ambient radio source will reach the receiver after being reflected by the backscatter. The ambient radio source signal received by the back scatterer is:
Figure GDA0002895465040000052
where h represents the channel parameter between the ambient radio source to the back scatterer.
The backscatter will modulate its own baseband signal c (t) to
Figure GDA0002895465040000053
Up and reflected, and the reflection coefficient is set as α, so that the reflected signal emitted by the backscatter body to the receiver is:
Figure GDA0002895465040000054
receiver uniform linear array reception of reflected signals, as derived for ambient radio source signal reception, channel parameter g m For all m E [0,M-1]The same is true. The reflected signals received by different array elements have phase differences due to the difference of the arrival directions of the signals. The reflected signal received by the array element with the receiver number m is as follows:
Figure GDA0002895465040000055
where h represents the channel parameters between the ambient radio source and the backscatter, g represents the channel parameters between the backscatter and the receiver, and the subscript represents the correspondingly numbered antenna of the receiver.
Figure GDA0002895465040000056
Representing the phase shift, θ, of the reflected signal received by the array element numbered m relative to the reflected signal of the array element numbered 0 b Is the angle of arrival of the reflected signal. Defining a direction vector as a g (θ b )＝[1,a g,1 (θ b ),...,a g,M-1 (θ b )] T All array elements are connectedThe received backscatter signal is:
Figure GDA0002895465040000057
the signals received by the receiver are:
y(t)＝y d (t)+y b (t)+ω(t)
where ω (t) is the noise following a circularly symmetric Gaussian distribution.
The receiver performs digital signal processing on the received signals to obtain reliable estimation of the arrival angle of each component of the received signals, obtains a plurality of angles of the reflected signals of the reverse scatterers by designing a specific receiving scheme, and further calculates to obtain two-dimensional coordinate data of the reverse scatterers.
As more algorithms for estimating the DOA by the received signal, one is exemplified below:
the bandpass form of the signal received by the known receiver is as follows:
y(t)＝y d (t)+y b (t)+ω(t)
wherein the content of the first and second substances,
Figure GDA0002895465040000061
ω (t) is the noise following a circularly symmetric Gaussian distribution with a variance σ 2 。a f (θ d )＝[1,a f,1 (θ d ),...,a f,M-1 (θ d )] T ，a g (θ b )＝[1,a g,1 (θ b ),...,a g,M-1 (θ b )] T Is a vector of the direction of the light,
Figure GDA0002895465040000062
Figure GDA0002895465040000063
the digital signal obtained after the receiver performs coherent reception, sampling and digital signal processing is
Figure GDA0002895465040000064
s (n) represents the symbol corresponding to the ambient radio source signal, and c (n) represents the symbol generated by the backscatter itself. The carrier wave is removed from the received and processed digital signal, but the phase offset between the received signals of different array elements still exists.
And then processing y (n) to obtain DOA information of two signal components in y (n).
The specific DOA estimation algorithm is implemented as follows:
1. according to the set sampling number N, sampling for N times to obtain a sample sequence y (N), wherein
Figure GDA0002895465040000066
2. Calculating y (n) autocorrelation matrix R, R = E { y (n) y H (n) where the statistical average may be replaced by a time average, i.e.
Figure GDA0002895465040000065
3. Decomposing the characteristic value of R, and obtaining the minimum normalized characteristic vector u corresponding to M-2 characteristic values because the number of target signals is only 2 i Where i =3,4 …, M.
u i ＝[u i0 ,u i1 ,...u i(m-1) ] T
4. Construct vector a (z), a (z) = [1,z = -1 ,...,z -(M-1) ] T 。
The following function is constructed:
Figure GDA0002895465040000071
Figure GDA0002895465040000072
multiplying by self conjugate transpose to obtain f i (z)＝a H (z)u i u i H a(z)＝|a H (z)u i | 2 ,i＝3,4,...,M。
5. Defining polynomial
Figure GDA0002895465040000073
Let it be 0, solve the equation. And obtaining the value of z.
6. The number of target signals is 2, the z value is subjected to modulo subtraction by 1, and then the absolute value is taken to be sorted from small to large. This will find the 4 roots closest to modulo 1 (heavy roots will appear). Since the signal reflected by the back scatterer undergoes two attenuations, its signal strength is much less than the direct signal. The first root, i.e. the root with the mode closest to 1, represents the angle of arrival of the direct signal and the 4 th root represents the angle of arrival of the signal reflected by the back scatterer.
7. Since z = e jφ Phi is the spatial angular frequency, phi = -pi sin theta. Thus, it is possible to provide
Figure GDA0002895465040000074
And calculating to obtain the signal arrival direction estimation.
After the arrival angle of the backscatter signal is obtained, the coordinates of the backscatter device can be calculated, and the complete process is shown in fig. 2, since the environmental radio frequency source is a signal source existing in the environment, no other setting is needed, taking the reception of one receiver as an example:
1. starting the backward scatterer, activating an internal circuit, and controlling the internal impedance switching state of the backward scatterer by the symbol c (n) of the backward scatterer to reflect the environment radio-frequency signal.
2. Starting the receiver at a known coordinate point, which is set to (x) 0 ,y 0 )。
3. And the receiver receives the signals and collects N sampling points to estimate the arrival direction of the primary reverse scatterer signals.
4. The receiver moves to another known coordinate point, which is set to (x) 1 ,y 1 ). The receiver antenna orientation is unchanged.
5. And the receiver receives the signals and collects N sampling points to estimate the arrival direction of the primary reverse scatterer signals.
6. And calculating the coordinates of the reverse scatterer according to the two measurement results.
According to the principle of triangulation, assuming that the antenna is oriented in the positive y-axis direction, the signal incident from the left side is at a positive angle, the signal incident from the right side is at a negative angle, and the estimated arrival angle of the signal is in the range of θ e [ -90 °,90 °]When Tag is in the position of
Figure GDA0002895465040000081
When, set the receiver at (x) 0 ,y 0 ) The estimated angle is theta 0 In (x) 1 ,y 1 ) The estimated angle is theta 1 . Then there are:
Figure GDA0002895465040000082
Figure GDA0002895465040000083
the above is a system scheme proposed for one receiver, and two receivers can be used instead of the mobile operation of the receiver to obtain two measurements to calculate the backscatter coordinates.
As shown in fig. 3, for the performance simulation result, the angle estimation deviation value is set to be not more than 1 ° as an effective estimation, and the probability of effective estimation under different conditions is calculated through several monte carlo experiments. The signal-to-noise ratio of the back scatterer reflected signal to the noise is set to be in the range of-10 dB to-28 dB, and the ratio of the direct link signal-to-noise ratio to the reflected link signal-to-noise ratio is fixed to be 10dB. Thus, the direct link signal-to-noise ratio ranges between 0dB to-18 dB. The environment signal is set to be a signal which is subjected to Gaussian distribution, the channel parameter is a channel parameter which is subjected to block fading and is subjected to Rayleigh distribution, the reflection symbol period is set to be 8 times of the symbol period of the environment signal, 10000 sample points are set to be acquired in each calculation, and the number of array elements of the receiver is 8.
According to simulation results, more accurate estimation (the accuracy is more than 95%) can be obtained when the signal-to-noise ratio is more than-18 dB, and the estimation performance is seriously deteriorated when the signal-to-noise ratio is lower than the value.

Claims (2)

1. A positioning system based on environmental backscattering is characterized by comprising a radio frequency source, a plurality of receivers with M antennas and a backscattering device, wherein M is more than or equal to 3; the receiver receives a direct link signal and an environment signal which is backscattered by the backscatter device, the receiver respectively obtains the arrival angles of the direct link signal and the backscatter signal, and the coordinates of the backscatter device are obtained according to the arrival angles of the backscatter signal and the known position coordinates of the plurality of receivers;
the specific method for the receiver to respectively obtain the arrival angles of the direct link signal and the backscatter signal is as follows:
assume that the signal received by the receiver is:
y(t)＝y d (t)+y b (t)+ω(t)
wherein, y d (t) is the received direct link signal, y b (t) is the received backscatter signal, ω (t) is the noise subject to a circularly symmetric gaussian distribution; respectively obtaining the arrival angles of the direct link signal and the backscatter signal through a DOA estimation algorithm, and distinguishing the arrival angles of the direct link signal and the backscatter signal according to the characteristic that the backscatter signal is subjected to fading twice compared with the direct link signal;
the specific method for obtaining the coordinates of the backscatter device is as follows:
suppose the position coordinates are (x) 0 ,y 0 ) The receiver obtains an angle of arrival of theta 0 In the position coordinate of (x) 1 ,y 1 ) The receiver obtains an angle of arrival of theta 1 Obtaining the coordinates of the backscatter means
Figure FDA0003863257800000011
Comprises the following steps:
Figure FDA0003863257800000012
Figure FDA0003863257800000013
2. a positioning system based on environmental backscattering is characterized by comprising a radio frequency source, a receiver with M antennas and a backscattering device, wherein M is more than or equal to 3; the receiver receives a direct link signal and an environment signal which is backscattered by the backscatter device, the receiver respectively obtains the arrival angles of the direct link signal and the backscatter signal, and the coordinates of the backscatter device are obtained according to the arrival angles of the backscatter signal obtained by the receiver at different position coordinates;
the specific method for the receiver to respectively obtain the arrival angles of the direct link signal and the backscatter signal is as follows:
assume that the signal received by the receiver is:
y(t)＝y d (t)+y b (t)+ω(t)
wherein, y d (t) is the received direct link signal, y b (t) is the received backscatter signal, ω (t) is the noise subject to a circularly symmetric gaussian distribution; respectively obtaining the arrival angles of the direct link signal and the backscatter signal through a DOA estimation algorithm, and distinguishing the arrival angles of the direct link signal and the backscatter signal according to the characteristic that the backscatter signal is subjected to fading twice compared with the direct link signal;
the specific method for obtaining the coordinates of the backscatter device is as follows:
assume that the receiver is at position coordinate (x) 0 ,y 0 ) To obtain an angle of arrival of theta 0 Moving the receiver to a position coordinate (x) 1 ,y 1 ) Where the obtained angle of arrival is theta 1 Obtaining the coordinates of the backscatter means
Figure FDA0003863257800000021
Comprises the following steps:
Figure FDA0003863257800000022
Figure FDA0003863257800000023
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