ITERATIVE FOCUSED MILLIMETER WAVE INTEGRATED COMMUNICATION AND SENSING METHOD

Abstract

Provided is an iterative focused millimeter wave integrated communication and sensing method, which converts an environmental sensing problem into a compressed sensing reconstruction problem, and realizes the initial coarse sensing of the environment based on an approximate message passing algorithm; according to a background determining method, the present disclosure divides and determines a target object, removes the influence of background scatters on a receiving signal, and removes the background scatters repeatedly and iteratively, so as to obtain a more accurate focus sensing result of the target object. Compared with existing environment sensing reconstruction algorithms, the iterative focused millimeter wave environment sensing algorithm of the present disclosure significantly improves the accuracy of environment sensing, solves the problem that a large-scale environment cannot be accurately sensed due to limited system resources, and provides an efficient environment sensing method for the future design of integrated sensing and communication systems.

Description

TECHNICAL FIELD

The present disclosure belongs to the technical field of wireless communication, and particularly relates to an iterative focused millimeter wave integrated communication and sensing method.

BACKGROUND

In the current wireless communication field, the emergence of innovative wireless communication technologies, such as ultra-large-scale multiple-input multiple-output (MIMO) technology, intelligent reflecting surface (IRS) and wireless artificial intelligence (AI), provides more possibilities for the design of future wireless communication systems. In the foreseeable future wireless communication present disclosure scenarios, technologies such as autonomous driving, intelligent robot navigation and unmanned aerial vehicle control need not only wireless broadband connection, but also accurate environmental information, including the position, shape and electromagnetic characteristics of objects in the environment. Therefore, as the research hotspot of the 6th generation (6G) wireless communication system, the integrated sensing and communication (ISAC) technology aims to realize environmental sensing by using wireless communication equipment and infrastructure.

In an uplink wireless communication scenario, users send communication signals to the base station for reception, and the transmitted signals are reflected and scattered by objects in the environment, such that the receiving signals of the base station contain environmental information. The design of the integrated system of sensing and communication has a great difficulty: how to deal with a large number of potential unknown variables in the environment, therefore the sparsity of the target environment itself shall be utilized. For example, in the urban wireless communication scene, buildings are sparsely distributed in the block. In addition, in the wireless communication application scenario, electromagnetic waves spread widely, and any environmental scatterer covered by wireless signals will affect the propagation of electromagnetic waves. However, the resources available for environmental sensing, such as the number of users, the number of base station receiving antennas and the number of subcarriers, are limited. Even taking advantage of the sparsity of environmental information, environmental sensing still faces the problem of large system resource expenditure caused by a large number of environmental information variables. At present, the existing integration method of millimeter wave communication and sensing does not take into account the influence of limited system resources on sensing algorithms. Under the condition of limited system resources, only a coarse sensing of the environment can be achieved, and fuzzy imaging results can be obtained. It is urgent to focus on specific targets with limited resources, so as to obtain accurate environmental sensing results. To sum up, how to use limited system resources to achieve accurate sensing of specific targets has high research difficulty and practical significance.

SUMMARY

In view of the shortcomings of the prior art, the object of the present disclosure is to realize environment sensing by a base station using uplink data sent by multiple users in an uplink wireless communication scenario. The present disclosure uses the pilot signal of the existing communication system or other known data sequences for sensing, and can be compatible with the existing communication system to realize the integration of sensing and communication. Considering that the system resources used for sensing are limited, it is impossible to sense all the environment in a large range, an iterative focused millimeter wave environment sensing method for specific targets is proposed.

The object of the present disclosure is achieved by the following technical solution:

Provided is an iterative focused millimeter wave integrated communication and sensing method. In an uplink wireless communication scenario, active users send communication signals to the base station for reception, and the sent signals are transmitted to the base station via multipath channel. The method includes the following steps:

S1, in any time slot, receiving, by a base station, pilot frequency sequence signals with a certain length sent by all active users in an environment to obtain receiving signals, wherein the receiving signals are signals after the pilot frequency sequence signals are influenced by the environment.

S2, converting an environmental sensing problem of a specific target into a compressed sensing reconstruction problem by using the receiving signals in the step S1 based on a multi-beam multi-carrier millimeter wave channel model.

S3, solving the compressed sensing reconstruction problem in step S2 based on an approximate message passing method to obtain a coarse initial result of environment sensing.

S4, selecting a predetermined region as a focused region of interest from the whole environment based on the coarse initial result of environmental sensing, and dividing and determining an target object in the region of interest according to a background determining method and removing the influence of background scatters outside the region of interest on the receiving signals to obtain receiving signals corresponding to the target object.

S5, calculating an environmental sensing result based on the receiving signals corresponding to the target object obtained in the step S4.

S6, repeating step S4 and step S5 in sequence until the algorithm convergence to obtain a final environment sensing result.

Further the step S2 specifically includes the following steps:

S21, discretizing environmental information in the receiving signals in step S1 into pixels; here, each pixel represents environmental information in a small square with a surrounding size of l_s×w_s, and if an environmental size of a whole range is L_s×W_s, a total number of the pixels is N_s=L/l_s×W/w_s; an interior of each pixel may be empty, or there may be scatters; a scattering coefficient x_ns, is used to represent the scattering coefficient of a small cube where a n_s^th point cloud is located; if an interior of the small cube is empty, then x_ns=0; therefore, the environmental information of a whole room can be expressed as x=[x₁, x₂, . . . , x_Ns]^T.

S22, using a multi-beam multi-carrier millimeter wave channel model, wherein at an n_f^th subcarrier frequency, the receiving signals received by a receiving antenna of the base station are expressed as follows:

y _{n f} =w _{n f} (H_nf^s→Bdiag(δx)H_nf^u→s+H_nf^LOS)s_nf+n=w_nf(H_nf^NLOS+H_nf^LOS)s_nf+n

where y_nfε^NcxK represents the receiving signals with a length of K code elements of RF links of N_c base stations, w_nfε^NcxNR is a beam forming vector of N_R uniform linear array receiving antennas of the base stations, δ is a normalized coefficient of a scattering coefficient, which is selected according to a pixel size l_s×w_s and describes the physical relationship between an electromagnetic wave receiving region and a receiving power s_nfε^NuxK represents pilot frequencies with a length of K code elements sent by N_u users, n is noise; H_nf^LOS represents a free-space propagation channel from N_u users to N_R receiving antennas at an n_f^th subcarrier frequency; H_nf^NLOS is a Non-Line-of-Sight (NLOS) channel on a n_f^th subcarrier;

H_nf^LOS is expressed as

H _{n f} ^LOS =e _{n f} ^LOS G _{n f} ^LOS

where e_nf^LOS is a steering vector of N_u users and G_nf^LOS is a channel gain from N_u users to the base station;

$e_{n_f}^{\mathrm{LOS}}\left(n_R,n_u\right)=e^{j\frac{2\pi }{{\lambda }_{n_f}}\left(n_R-1\right)\mathrm{dsin}{\theta }_{n_u}^{\mathrm{LOS}}}/\sqrt{N_R}$

where j represents a complex code element, n_R is a serial number of the receiving antenna, θ_nu^LOS is an arrival angle of a n_u^th user, and d is a uniform linear array antenna spacing deployed by the base station, λ_nf is a wavelength; G_nf^LOS is expressed as follows:

$G_{n_f}^{\mathrm{LOS}}=\mathrm{diag}\left(\left[g_{n_f,1}^{\mathrm{LOS}}{e}^{j{\phi }_{n_f,1}^{\mathrm{LOS}}},\dots ,g_{n_f,N_u}^{\mathrm{LOS}}{e}^{j{\phi }_{n_f,N_u}^{\mathrm{LOS}}}\right]\right)$

where g_nfⁿ_u^LOS and φ_nfⁿ_u^LOS are a channel amplitude gain and a phase shift from the n_u^th user to the base station, respectively.

At the n_f^th subcarrier frequency, a free-space propagation channel H_nf^u→s(n_s, n_u) from the n_u^th user to a n_s^th pixel is expressed as:

$H_{n_f}^{u\to s}\left(n_s,n_u\right)=g_{n_f}^{u\to s}\left(n_s,n_u\right)e^{j{\phi }_{n_f}^{u\to s}\left(n_s,n_u\right)}$

where g_nf^u→s(n_s, n_u) and φ_nf^u→s(n_s, n_u) are a channel amplitude gain and a phase shift from n_u^th user to the n_s^th pixel, respectively.

At the n_f^th subcarrier frequency, a free-space propagation channel H_nf^s→B∈^NRxN_s from N_s pixels to N_R receiving antennas is expressed as:

H _{n f} ^s→B =e _{n f} ^s→B G _{n f} ^s→B

where e_nf^s→B is a steering vector of N_s pixels and G_nf ^s→B is a channel gain from N_s pixels to the base station;

$e_{n_f}^{s\to B}\left(n_R,n_s\right)=e^{j\frac{2\pi }{{\lambda }_{n_f}}\left(n_R-1\right)\mathrm{dsin}{\theta }_{n_s}^{s\to B}}/\sqrt{N_R}$

where n_R is a receiving antenna number, θ_ns^s→B an arrival angle of the n_s^th pixel, and G_nf^s→B is expressed as follows:

$G_{n_f}^{s\to B}=\mathrm{diag}\left(\left[g_{n_f,1}^{s\to B}{e}^{j{\phi }_{n_f,1}^{s\to B}},\dots ,g_{n_f,N_s}^{s\to B}{e}^{j{\phi }_{n_f,N_s}^{s\to B}}\right]\right)$

where g_nfⁿ_s^s→b and φ_nfⁿ_s^s→b are a channel amplitude gain and a phase shift from the n_s^th pixel to the base station, respectively.

S23, expressing an estimation result of the environmental information as {circumflex over (X)}, which is expressed as follows:

{circumflex over (x)}=argmin_xROI||X||₀s.t.||y−w(H^LOS+H^LOS)s||₂≤ε

where y is a receiving signal of all subcarriers, w is a beam forming vector of the uniform linear array receiving antenna of all subcarriers, x_ROI is environmental information in a region of interest, H^NLOS is a NLOS channel of all subcarriers, H^LOS is a LOS channel of all subcarriers, s is a transmitted signal of the NLOS channel of all subcarriers, and ε is a relaxation variable.

Since a free-space channel coefficient of a direct-view channel can be estimated by a numerical model, at the n_f^th subcarrier frequency, part of the receiving signal {tilde over (y)}_nf containing unknown environmental information is expressed as follows:

{tilde over (y)} _{n f} =w _{n f} H _{n f} ^s→Bdiag(δx)H_nf^u→ss_nf+n

By combining data of N_f subcarriers, an iterative focused environmental sensing problem of a specific target is converted into a compressed sensing reconstruction problem equation as follows:

${\left[\begin{array}{c}{\tilde{y}}_1\left(:,1\right)\\ ⋮\\ {\tilde{y}}_1\left(:,K\right)\\ ⋮\\ {\tilde{y}}_{N_f}\left(:,1\right)\\ ⋮\\ {\tilde{y}}_{N_f}\left(:,K\right)\end{array}\right]}_{N_c{N}_{f}K\times 1}={{\delta \left[\begin{array}{c}{w}_1{H}_1^{s\to B}\mathrm{diag}\left(H_1^{u\to s}{s}_1\left(:,1\right)\right)\\ ⋮\\ w_1{H}_1^{s\to B}\mathrm{diag}\left(H_1^{u\to s}{s}_1\left(:,K\right)\right)\\ ⋮\\ w_{N_f}{H}_{N_f}^{s\to B}\mathrm{diag}\left(H_{N_f}^{u\to s}{s}_{N_f}\left(:,1\right)\right)\\ ⋮\\ w_{N_f}{H}_{N_f}^{s\to B}\mathrm{diag}\left(H_{N_f}^{u\to s}{s}_{N_f}\left(:,K\right)\right)\end{array}\right]}_{N_c{N}_{f}K\times N_s}\left[x\right]}_{N_s\times 1}+n\Rightarrow \tilde{y}=\mathrm{Ax}+n.$

Further, the step S3 specifically includes the following steps:

S31, firstly setting an initial coarse environmental sensing prior probability, and letting the environmental information be a Bernoulli-Gaussian distribution, wherein a probability density function p_x(x|q) is expressed as:

p _x(x|q)=(1−λ)δ(x)+λN(x|θ^x,σ^x)

where x represents an element in the environmental information x, all parameters are expressed as q[λ,θ^x, σ^x], δ(·) is an impulse function, λ is a sparse coefficient; θ^x∈[0,1] and σ^x are a mean value and a variance of environmental information distribution, respectively, and N( represents a standard normal distribution;

S32, initializing approximate message passing algorithm parameters, and letting input functions g_in(·), g′_in (·) and output functions g_out(·), g′_out(·) be the following respectively

$g_{\mathrm{in}}\left(\hat{v},{\sigma }^v,q\right)=\arg \underset{x}{\max }{F}_{\mathrm{in}}\left(x,\hat{v},{\sigma }^v,q\right)F_{\mathrm{in}}\left(x,\hat{v},{\sigma }^v,q\right)=\log p_x\left(x❘q\right)-\frac{1}{2{\sigma }^v}{\left(\hat{v}-x\right)}^2{g}_{\mathrm{in}}^{\prime }\left(\hat{v},{\sigma }^v,q\right)=\frac{1}{1-{\sigma }^v\frac{{\partial }^2}{\partial x^2}\log \left[p_x\left(x❘q\right)\right]}{g}_{\mathrm{out}}\left(y,\hat{p},{\sigma }^z\right)=\frac{y-\hat{p}}{{\sigma }^w+{\sigma }^z}{g}_{\mathrm{out}}^{\prime }\left(y,\hat{p},{\sigma }^z\right)=-\frac{1}{{\sigma }^w+{\sigma }^z}$

where, {circumflex over (v)}, σ^v, {circumflex over (p)}, σ^z are input variables and σ^w is a noise variance;

let a number of iterations t_G=0, a residual ŝ(−1)=0, a sparse vector estimated mean value {circumflex over (x)}_ns(t_G)>0, and a sparse vector estimated variance σ_ns(t_G)>0;

S33, letting M=N_cN_fK, where N_c is a number of base stations, a is a number of code elements, N_f is a number of subcarriers; for m=1,2, . . . , M, calculating estimated mean value {circumflex over (z)}_m(t_G) and variance σ_m^z(t_G) of a variable z_m:

σ_m^z(t_G)=Σ_nsA_m,ns²σ_ns^x(t_G)

{circumflex over (p)}m(t_G)=Σ_nsA_m,ns(t_G)−σ_m^z(t)ŝ_m(t_G−1)

{circumflex over (z)} _m(t_G)=Σ_nsA_m,ns{circumflex over (x)}_ns(t_G)

S34, for m=1,2, . . . , M, calculating a mean value ŝ_m(t_G) and a variance σ_m^s(t_G) of the residual:

ŝ _m(t_G)=g_out(t_G, y_m, {circumflex over (p)}_m(t_G), σ_m^z(t_G))

σ_m^s(t_G)=−g′_out(t_G, y_m, {circumflex over (p)}_m(t_G), σ_m^z(t_G))

where y_m is the m^th element of the receiving signal;

S35, for n_s=1,2, . . . , N_s, calculating observed mean value {circumflex over (v)}_ns(t_G) and variance σ_ns^v(t_G) of {circumflex over (x)}_ns(t_G):

{circumflex over (v)} _{n s} (t_G)={circumflex over (x)}_ns(t_G)+σ_ns^v(t_G)Σ_mA_m,nsŝ_m(t_G)

σ_ns(t_G)=[Σ_nsA_m,ns²σ_ns^s(t_G)]⁻¹

S36, for n_s=1,2, . . . , N_s, calculating observed mean value {circumflex over (x)}_ns(t_G+1) and variance σ_ns^x(t_G+1) of x_ns:

{circumflex over (x)} _{n s} (t_G+1)=g_in(t_G, {circumflex over (v)}_ns(t_G), σ_ns^v(t_G), q)

σ_ns^x(_G+1)=σ_ns^v(t_G)g′_in(t_G, {circumflex over (v)}_ns(t_G), σ_ns^r(t_g), q)

S37, executing step S33 to step S36 repeatedly until a convergence condition Σ_m|y_m−{circumflex over (z)}_m(t_G)|>ε_G is satisfied, where ε_G is an error tolerance;

S38, taking a sparse variable {circumflex over (x)}_ns(t_G) as a coarse environmental sensing initial result of the environmental information x.

Further, the step S4 specifically incudes the following steps:

S41, selecting a predetermined region as a focused region of interest from the whole environment according to the coarse environmental sensing initial result and actual needs, wherein the target object is in the region of interest;

S42, in an ith iteration, detecting a background scatterer {circumflex over (x)}_back⁽ⁱ⁾(n_s) outside the region of interest as follows:

${\hat{x}}_{\mathrm{back}}^{\left(i\right)}\left(n_s\right)=\{\begin{array}{cc}0,& {\hat{x}}^{\left(i\right)}\left(n_s\right)\le {\gamma }_i\mathrm{or}{\hat{x}}^{\left(i\right)}\left(n_s\right)\mathrm{inside}\mathrm{ROI}.\\ {\hat{x}}^{\left(i\right)}\left(n_s\right),& {\hat{x}}^{\left(i\right)}\left(n_s\right)\ge {\gamma }_i\end{array}$

where {circumflex over (x)}⁽ⁱ⁾(n_s) represents a result in the ith iteration, y_i is a detection threshold of the background scatterer, and the detection threshold y_i shall decrease with the increase of the number of iterations;

S43, removing a background scattering part from the receiving signal to obtain a receiving signal ŷ_ROI⁽ⁱ⁺¹⁾ of the target object in a region of interest (ROI) of an i+1^st iteration:

ŷ _ROI ⁽ⁱ⁺¹⁾=(1+a){tilde over (y)}+a(ŷ_ROI⁽ⁱ⁾−Ax_back⁽ⁱ⁾)

where a is a weight variable, which is used to enhance the robustness of iterative algorithm, and the weight variable a should increase with the increase of the number of iterations.

Further, the step S5 specifically incudes the following steps:

S51, setting the prior probability of the environmental information in an iterative focused process, wherein in the i^th iteration, it is assumed that the background scatterer obeys Bernoulli Gaussian distribution, and a prior probability formula p(x_back) is as follows:

p(x_back)=(1−λ)δ(x_back)+δ(x_back; θ_back,i, σ_back)

where θ_back,i and σ_back represent the mean value and the variance of the background environmental information distribution, respectively, λ is a sparse coefficient, N(·) represents a standard normal distribution and x_back represents the background scatterer.

The scatterer distribution in the selected ROI is a Gaussian distribution, and there is no sparsity.

p(x_ROI)=(x_ROI; θ_ROI, σ_ROI)

where θ_ROI and σ_ROI represent the mean value and variance of ROI environmental information distribution, respectively;

S52, according to the prior probability formula obtained in step S51, setting the prior probability p(x) of environmental information inside and outside the region of interest in the current i+1^st iteration, x={x_ROI, x_back};

S53, initializing the approximate message passing algorithm parameters, and letting the input functions g_in(·), g′_in(·) and the output functions g_out(·), g′_out(·) be as follows:

$g_{\mathrm{in}}\left(\hat{v},{\sigma }^v,q\right)=\arg \underset{x}{\max }{F}_{\mathrm{in}}\left(x,\hat{v},{\sigma }^v,q\right)F_{\mathrm{in}}\left(x,\hat{v},{\sigma }^v,q\right)=\log p_x\left(x❘q\right)-\frac{1}{2{\sigma }^v}{\left(\hat{v}-x\right)}^2{g}_{\mathrm{in}}^{\prime }\left(\hat{v},{\sigma }^v,q\right)=\frac{1}{1-{\sigma }^v\frac{{\partial }^2}{\partial x^2}\log \left[p_x\left(x❘q\right)\right]}{g}_{\mathrm{out}}\left(y,\hat{p},{\sigma }^z\right)=\frac{y-\hat{p}}{{\sigma }^w+{\sigma }^z}{g}_{\mathrm{out}}^{\prime }\left(y,\hat{p},{\sigma }^z\right)=-\frac{1}{{\sigma }^w+{\sigma }^z}$

Let the number of iterations t_G=0, the residual ŝ(−1)=0, the sparse vector estimated mean value {circumflex over (x)}_ns(t_G)>0 and the sparse vector estimate variance σ_ns^x(t_G)>0;

S54, letting M=N_cN_fK, and for m=1,2, . . . , M, calculating estimated mean value {circumflex over (z)}_m(t_G) and variance σ_m^z(t_G) of z_m, which is specifically as follows:

σ_m(t_G)=Σ_nsA_m,ns²σ_ns^x(t_G)

{circumflex over (p)} _m(t_G)=Σ_nsA_m,ns{circumflex over (x)}_ns(t_G)−σ_m^z(t)ŝ_m(t_G−1)

{circumflex over (z)} _m(t_G)=Σ_nsA_m,ns{circumflex over (x)}_ns(t_G)

S55, for m=1,2, . . . , M, calculating a mean value ŝ_m(t_G) and a variance σ_m^s(t_G) of the residual, which is specifically as follows:

ŝ _m(t_G)=g_out(t_G, ŷ_ROI,m⁽ⁱ⁺¹⁾, {circumflex over (p)}_m(t_G), σ_m^z(t_G))

σ_m^s(t_G)=−g′_out(t_G, ŷ_ROI,m⁽ⁱ⁺¹⁾, {circumflex over (p)}_m(t_G), σ_m^z(t_G))

where ŷ_ROI,m⁽ⁱ⁺¹⁾ is a m^th element of the receiving signal obtained in S43;

S56, for n_s=1,2, calculating observed mean value {circumflex over (v)}_ns(t_G) and variance σ_ns^v(t_G) of {circumflex over (x)}_ns(t_G) as follows:

{circumflex over (v)} _{n s} (t_G)=(t_G)+σ_ns(t_G)Σ_mA_m,nsŝ_m(t_G)

σ_ns^v(t_G)=[Σ_nsA_m,ns²σ_ns^s(t_G)]⁻¹;

S57, for n_s=1,2, . . . , N_s, calculating observed mean value {circumflex over (x)}_ns(t_G+1) and variance σ_ns^x(t_G+1) as follows:

{circumflex over (x)} _{n s} (t_G+1)=g_in(t_G, {circumflex over (v)}_ns(t_G), σ_ns^v(t_G),q)

σ_ns^x(t_G+1)=σ_ns^v(t_G)g′_in(t_G,{circumflex over (v)}_ns(t_G), σ_ns^r(t_G),q)

S58, repeating steps S54 to S57 until the convergence condition Σ_m|y_m−{circumflex over (z)}_m(t_G)|>ε_G is satisfied;

S59, taking the sparse variable {circumflex over (x)}_ns(t_G) estimated in the above steps as a final environment sensing result of the current iteration.

The present disclosure has the following beneficial effects: in the uplink wireless communication scene, the present disclosure provides a design method for integrated millimeter wave sensing and communication system by using the existing communication equipment, and fully utilizes different system resources to realize focused environmental sensing based on data sent by users; the iterative focused environmental sensing method provided by the present disclosure solves the problem of low accuracy of large-scale environmental sensing due to insufficient system resources; the present disclosure overcomes the defect that the traditional compressed sensing algorithm cannot focus on a specific range of environmental variables, while in the iterative process of the algorithm, the prior probability of environmental variables is estimated step by step according to the reconstruction result of compressed sensing in each step, thus realizing an iterative progressive compressed sensing sparse reconstruction for a specific target. On the basis of the same system resource overhead, the algorithm of the present disclosure significantly improves the sensing accuracy of a specific target and is superior to the existing algorithms.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a two-dimensional focused millimeter wave environment sensing scenario provided by an exemplary embodiment;

FIG. 2 is a flowchart of an iterative algorithm provided by an exemplary embodiment;

FIG. 3 is a diagram showing the relationship between the number of users and the environmental sensing accuracy MSE when comparing the present disclosure with other compressed sensing reconstruction algorithms provided by an exemplary embodiment;

FIG. 4 is a diagram showing the relationship between the number of subcarriers and the environmental sensing accuracy MSE when comparing the present disclosure with other compressed sensing reconstruction algorithms provided by an exemplary embodiment.

DESCRIPTION OF EMBODIMENTS

In order to better understand the technical solution of the present disclosure, the embodiments of the present disclosure will be described in detail with reference to the attached drawings.

It should be clear that the described embodiments are only part of, not all of the embodiment of this present disclosure. Based on the embodiments in this present disclosure, all other embodiments obtained by those skilled in the art without creative work belong to the protection scope of this present disclosure.

A single-cell uplink communication system is taken into consideration, in which a multi-antenna BS serves multiple single-antenna users. In order to sense a specific target, all users send uplink communication signals to the base station at the same time. Due to a large amount of scattering in the environment, the transmitted signal of each user propagates through multiple paths. Therefore, the signal received by the base station contains abundant environmental scattering information in order that the base station can process the receiving signal to realize environmental sensing. As shown in FIG. 1, considering a simplified two-dimensional scene model, the analysis method of three-dimensional scenario can also be deduced. Gray target scatters are scatters to be imaged accurately, and the rest are background scatters that will not be considered.

The present disclosure provides an iterative focused millimeter wave integrated communication and sensing method, which includes the following steps:

S1, in any time slot, a base station receives pilot frequency sequence signals with a certain length sent by all active users in an environment to obtain receiving signals; the receiving signals are signals after the pilot frequency sequence signals are influenced by the environment.

S2, an environmental sensing problem of a specific target is converted into a compressed sensing reconstruction problem by using the receiving signals in the step S1 based on a multi-beam multi-carrier millimeter wave channel model.

In an embodiment, step S2 specifically includes the following steps:

S21, environmental information in the receiving signals in step S1 is discretized into pixels; each pixel represents environmental information in a small square with a surrounding size of l_s×w_s, and if an environmental size of a whole range is L_s×W_s, a total number of the pixels is N_s=L/l_s×W/w_s; an interior of each pixel may be empty, or there may be scatters; a scattering coefficient x_ns is used to represent the scattering coefficient of a small cube where a n_s^th point cloud is located; if an interior of the small cube is empty, then x_ns=0; therefore, the environmental information of a whole room can be expressed as x=[x₁,x₂, . . . , x_Ns]^T.

S22, a multi-beam multi-carrier millimeter wave channel model is used, and at an n_f^th subcarrier frequency, the receiving signals received by a receiving antenna of the base station are expressed as follows:

y _{n f} =w _{n f} (H_nf^s→Bdiag(δx)H_nf^u→s+H_nf^LOS)s_nf+n=w_nf(H_nf^NLOS+H_nf^LOS)s_nf+n

where y_nf∈^NcxK represents the receiving signals with a length of K code elements of RF links of N_c base stations w_nf∈^{NcxN R} is a beam forming vector of N_R uniform linear array receiving antennas of the base stations, δ is a normalized coefficient of a scattering coefficient, which is selected according to a pixel size l_s×w_s and describes the physical relationship between an electromagnetic wave receiving region and a receiving power s_nf∈^NuxK represents pilot frequencies with a length of K code elements sent by N_u users, n is noise; H_nf^LOS represents a free-space propagation channel from N_u users to N_R receiving antennas at an n_f^th subcarrier frequency; and H_nf^NLOS is a NLOS channel on a nfth subcarrier.

H _{n f} ^LOS is expressed as

H _{n f} ^LOS =e _{n f} ^LOS G _{n f} ^LOS

where e_nf^LOS is a steering vector of N_u users and G_nf^LOS is a channel gain from N_u users to the base station;

$e_{n_f}^{\mathrm{LOS}}\left(n_R,n_u\right)=e^{j\frac{2\pi }{{\lambda }_{n_f}}\left(n_R-1\right)\mathrm{dsin}{\theta }_{n_u}^{\mathrm{LOS}}}/\sqrt{N_R}$

where j represents a complex code element, n_R is a serial number of the receiving antenna, θ_nu^LOS is an arrival angle of a n_u^th user, and d is a uniform linear array antenna spacing deployed by the base station, λ_nf is a wavelength; G_nf^LOS is expressed as follows:

$G_{n_f}^{LOS}=\mathrm{diag}\left(\left[g_{n_f,1}^{LOS}{e}^{j{\phi }_{n_f,1}^{LOS}},\dots ,g_{n_f,N_u}^{LOS}{e}^{j{\phi }_{n_f,N_u}^{LOS}}\right]\right)$

where g_nf,nu^LOS and φ_nf,nu^LOS are a channel amplitude gain and a phase shift from the n_u^th user to the base station, respectively.

At the n_f^th subcarrier frequency, a free-space propagation channel H_nf^u→s(n_s, n_u) from the n_u^th user to a n_s^th pixel is expressed as:

$H_{n_f}^{u\to s}\left(n_s,n_u\right)=g_{n_f}^{u\to s}\left(n_s,n_u\right)e^{j{\phi }_{n_f}^{u\to s}\left(n_s,n_u\right)}$

where g_nf^u→s(n_s, n_u) and φ_nf^u→s(n_s, n_u) are a channel amplitude gain and a phase shift from n_u^th user to the n_s^th pixel, respectively.

At the n_f^th subcarrier frequency, a free-space propagation channel H_nf^s→B∈^NRxNs from N_s pixels to N_R receiving antennas is expressed as:

H _{n f} ^s→B =e _{n f} ^s→B G _{n f} ^s→B

where e_nf^s→B is a steering vector of N_s pixels and G_nf^s→B is a channel gain from N_s pixels to the base station.

$e_{n_f}^{s\to B}\left(n_R,n_s\right)=e^{j\frac{2\pi }{{\lambda }_{n_f}}\left(n_R-1\right)\mathrm{dsin}{\theta }_{n_s}^{s\to B}}/\sqrt{N_R}$

where n_R is a receiving antenna number, θ_ns^s→B an arrival angle of the n_s^th pixel, and G_nf^s→B is expressed as follows:

$G_{n_f}^{s\to B}=\mathrm{diag}\left(\left[g_{n_f,1}^{s\to B}{e}^{j{\phi }_{n_f,1}^{s\to B}},\dots ,g_{n_f,N_s}^{s\to B}{e}^{j{\phi }_{n_f,N_s}^{s\to B}}\right]\right)$

where g_nfns^s→B and φ_nfns^s→B are a channel amplitude gain and a phase shift from the n_s^th pixel to the base station, respectively.

S23, an estimation result of the environmental information is expressed as {circumflex over (x)}, which is expressed as follows:

{circumflex over (x)}=argmin_xROI||x||₀s.t. ||y−w(H^NLOS+H^LOS)s||₂≤ε

where y is a receiving signal of all subcarriers, w is a beam forming vector of the uniform linear array receiving antenna of all subcarriers, x_ROI is environmental information in a region of interest, H^NLOS is a NLOS channel of all subcarriers, H^LOS is a LOS channel of all subcarriers, s is a transmitted signal of the NLOS channel of all subcarriers, and ε is a relaxation variable.

Since a free-space channel coefficient of a direct-view channel can be estimated by a numerical model, at the n_f^th subcarrier frequency, part of the receiving signal ŷ_nf containing unknown environmental information is expressed as,

{tilde over (y)} _{n f} =w _{n f} H _{n f} ^s→Bdiag(δx)H_nf^u→ss_nf+n

by combining data of N_f subcarriers, an iterative focused environmental sensing problem of a specific target is converted into a compressed sensing reconstruction problem equation as follows:

${\left[\begin{array}{c}{\tilde{y}}_1\left(:,1\right)\\ ⋮\\ {\tilde{y}}_1\left(:,K\right)\\ ⋮\\ {\tilde{y}}_{N_f}\left(:,1\right)\\ ⋮\\ {\tilde{y}}_{N_f}\left(:,K\right)\end{array}\right]}_{N_c{N}_{f}K\times 1}={{\delta \left[\begin{array}{c}{w}_1{H}_1^{s\to B}\mathrm{diag}\left(H_1^{u\to s}{s}_1\left(:,1\right)\right)\\ ⋮\\ w_1{H}_1^{s\to B}\mathrm{diag}\left(H_1^{u\to s}{s}_1\left(:,K\right)\right)\\ ⋮\\ w_{N_f}{H}_{N_f}^{s\to B}\mathrm{diag}\left(H_{N_f}^{u\to s}{s}_{N_f}\left(:,1\right)\right)\\ ⋮\\ w_{N_f}{H}_{N_f}^{s\to B}\mathrm{diag}\left(H_{N_f}^{u\to s}{s}_{N_f}\left(:,K\right)\right)\end{array}\right]}_{N_c{N}_{f}K\times N_s}\left[x\right]}_{N_s\times 1}+n\Rightarrow \tilde{y}=\mathrm{Ax}+n.$

S3, the compressed sensing reconstruction problem in step S2 is solved based on an approximate message passing method to obtain a coarse initial result of environment sensing;

in an embodiment, step S3 specifically includes the following steps:

S31, firstly, an initial coarse environmental sensing prior probability is set, and the environmental information is set to be a Bernoulli-Gaussian distribution, wherein a probability density function p_x(x|q) is expressed as:

p _x(x|q)=(1−λ)δ(x)+λN(x|θ^x, σ^x)

where x represents an element in the environmental information x, all parameters are expressed as q[λ, θ^x,σ^x], δ(·) is an impulse function, λ is a sparse coefficient; θ^x∈[0,1] and σ^x are a mean value and a variance of environmental information distribution, respectively, and N(·) represents a standard normal distribution;

S32, approximate message passing algorithm parameters are initialized, and the input functions g_in(·), g′_in(·) and output functions g_out(·), g′_out(·) are as follows:

$g_{\mathrm{in}}\left(\hat{v},{\sigma }^v,q\right)=\arg \underset{x}{\max }{F}_{\mathrm{in}}\left(x,\hat{v},{\sigma }^v,q\right)F_{\mathrm{in}}\left(x,\hat{v},{\sigma }^v,q\right)=\log p_x\left(x❘q\right)-\frac{1}{2{\sigma }^v}{\left(\hat{v}-x\right)}^2{g}_{\mathrm{in}}^{\prime }\left(\hat{v},{\sigma }^v,q\right)=\frac{1}{1-{\sigma }^v\frac{{\partial }^2}{\partial x^2}\log \left[p_x\left(x❘q\right)\right]}{g}_{\mathrm{out}}\left(y,\hat{p},{\sigma }^z\right)=\frac{y-\hat{p}}{{\sigma }^w+{\sigma }^z}{g}_{\mathrm{out}}^{\prime }\left(y,\hat{p},{\sigma }^z\right)=-\frac{1}{{\sigma }^w+{\sigma }^z}$

where {circumflex over (v)}, σ^v, {circumflex over (p)}, σ^z are input variables and σ^w is a noise variance.

Let a number of iterations t_G=0, a residual ŝ(−1)=0, a sparse vector estimated mean value {circumflex over (x)}_ns(t_G)>0, and a sparse vector estimated variance σ_ns^x(t_G)>0.

S33, let M=N_cN_fK, where N_c is a number of base stations, a is a number of code elements, N_f is a number of subcarriers; for m=1,2, . . . , M, estimated mean value {circumflex over (z)}_m(t_G) and variance σ_m^z(t_G) of a variable z_m are calculated:

σ_m^z(t_G)=Σ_nsA_m,ns²σ_ns^x(t_G)

{circumflex over (p)} _m(t_G)=Σ_nsA_m,ns{circumflex over (x)}_ns(t_G)−σ_m^z(t)ŝ_m(t_G−1)

{circumflex over (z)} _m(t_G)=Σ_nsA_m,ns{circumflex over (x)}_ns(t_G)

S34, for m=1,2, . . . , M, a mean value ŝ_m(t_G) and a variance σ_m^s(t_G) of the residual are calculated:

ŝ _m(t_G)=g_out(t_G, y_m, {circumflex over (p)}_m(t_G), σ_m^z(t_G))

σ_m^s(t_G)=−g′_out(t_G, y_m, {circumflex over (p)}_m(t_G), σ_m^z(t_G))

where y_m is the m^th element of the receiving signal;

S35, for n_s=1,2, . . . , N_s, observed mean value {circumflex over (v)}_ns(t_G) and variance σ_ns^v(t_G) of {circumflex over (x)}_ns(t_G) are calculated:

{circumflex over (v)} _{n s} (t_G)={circumflex over (x)}_ns(t_G)+σ_ns^v(t_G)Σ_mA_m,nsŝ_m(t_G)

σ_ns^v(t_G)=[Σ_nsA_m,n,nsσ_ns^s(t_G)]⁻¹

S36, for n_s=1,2, . . . , N_s, observed mean value {circumflex over (x)}_ns(t_G+1) and variance σ_ns^x(t_G+1) of x_ns are calculated:

{circumflex over (x)} _{n s} (t_G+1)=g_in(t_G, {circumflex over (v)}_ns(t_G), σ_ns^v(t_G), q)

σ_ns^x(t_G+1)=σ_ns^v(t_G)g′_in(t_G, {circumflex over (v)}_ns(t_G), σ_ns^r(t_G), q)

S37, step S33 to step S36 are repeatedly executed until a convergence condition Σ_m|y_m−{circumflex over (z)}_m(t_G)|>ε_G is satisfied, where ε_G is an error tolerance;

S38, a sparse variable {circumflex over (x)}_ns (t_G) is taken as a coarse environmental sensing initial result of the environmental information x.

S4, a predetermined region is selected as a focused region of interest from the whole environment based on the coarse initial result of environmental sensing, and the target object in the region of interest is divided and determined according to a background determining method and the influence of background scatters outside the region of interest on the receiving signals is removed to obtain receiving signals corresponding to the target object;

In an embodiment, step S4 is specifically:

S41, a predetermined region as a focused region of interest from the whole environment according to the coarse environmental sensing initial result and actual needs; the target object is in the region of interest;

S42, in an ith iteration, a background scatterer {circumflex over (x)}_back⁽ⁱ⁾(n_s) outside the region of interest is detected as follows:

${\hat{x}}_{\mathrm{back}}^{\left(i\right)}\left(n_s\right)=\{\begin{array}{cc}0,& {\hat{x}}^{\left(i\right)}\left(n_s\right)\le {\gamma }_i\mathrm{or}{\hat{x}}^{\left(i\right)}\left(n_s\right)\mathrm{inside}\mathrm{ROI}.\\ {\hat{x}}^{\left(i\right)}\left(n_s\right),& {\hat{x}}^{\left(i\right)}\left(n_s\right)\ge {\gamma }_i\end{array}$

where {circumflex over (x)}⁽ⁱ⁾(n_s) represents a result in the ith iteration, y_i is a detection threshold of the background scatterer, and the detection threshold y_i shall decrease with the increase of the number of iterations;

S43, a background scattering part from the receiving signal is removed to obtain a receiving signal ŷ_ROI⁽ⁱ⁺¹⁾ of the target object in ROI of an i+1^st iteration:

Ŷ _ROI ⁽ⁱ⁺¹⁾=(1−a){tilde over (y)}+a(ŷ_ROI⁽ⁱ⁾−Ax_back⁽ⁱ⁾)

where a is a weight variable, which is used to enhance the robustness of iterative algorithm, and the weight variable a should increase with the increase of the number of iterations.

S5, an environmental sensing result is calculated based on the receiving signals corresponding to the target object obtained in the step S4;

In an embodiment, step S5 specifically includes the following steps:

S51, the prior probability of the environmental information in an iterative focused process is set; in the i^th iteration, it is assumed that the background scatterer obeys Bernoulli Gaussian distribution, and a prior probability formula p(x_back) is as follows:

p(x_back)=(1−λ)δ(x_back)+λ(x_back; θ_back,i, σ_back)

where θ_back,i and σ_back represent the mean value and the variance of the background environmental information distribution, respectively, λ is a sparse coefficient, N(·) represents a standard normal distribution and x_back represents the background scatterer.

The scatterer distribution in the selected ROI is a Gaussian distribution, and there is no sparsity.

p(x_ROI)=(x_ROI; θ_ROI, σ_ROI)

where θ_ROI and σ_ROI represent the mean value and variance of ROI environmental information distribution, respectively;

S52, according to the prior probability formula obtained in step S51, the prior probability p(x) of environmental information inside and outside the region of interest in the current i+1^st iteration is set, x={x_ROI, x_back}.

S53, the approximate message passing algorithm parameters are initialized, and let the input functions g_in(·), g′_in(·) and the output functions g_out(·), g′_in(·) be as follows:

$g_{\mathrm{in}}\left(\hat{v},{\sigma }^v,q\right)=\arg \underset{x}{\max }{F}_{\mathrm{in}}\left(x,\hat{v},{\sigma }^v,q\right)F_{\mathrm{in}}\left(x,\hat{v},{\sigma }^v,q\right)=\log p_x\left(x❘q\right)-\frac{1}{2{\sigma }^v}{\left(\hat{v}-x\right)}^2{g}_{\mathrm{in}}^{\prime }\left(\hat{v},{\sigma }^v,q\right)=\frac{1}{1-{\sigma }^v\frac{{\partial }^2}{\partial x^2}\log \left[p_x\left(x❘q\right)\right]}{g}_{\mathrm{out}}\left(y,\hat{p},{\sigma }^z\right)=\frac{y-\hat{p}}{{\sigma }^w+{\sigma }^z}{g}_{\mathrm{out}}^{\prime }\left(y,\hat{p},{\sigma }^z\right)=-\frac{1}{{\sigma }^w+{\sigma }^z}$

Let the number of iterations t_G=0, the residual Ŝ(−1)=0, the sparse vector estimated mean value {circumflex over (x)}_ns(t_G)>0 and the sparse vector estimate variance σ_ns^x(t_G)>0;

S54, let M=N_cn_fK, and for m=1,2, . . . , M, estimated mean value {circumflex over (z)}_m(t_G) and variance σ_m^z(t_G) of z_m are calculated, which is specifically as follows:

σ_m^z(t_G)=Σ_nsA_m,ns^x(t_G)

{circumflex over (p)} _m(t_G)=Σ_nsA_m,ns{circumflex over (x)}_ns(t_G)−σ_m^z(t)ŝ_m(t_G−1)

{circumflex over (z)} _m(t_G)=Σ_nsA_m,ns{circumflex over (x)}_ns(t_G)

S55, for m=1,2, . . . , M, calculating a mean value ŝ_m(t_G) and a variance σ_m^s(t_G) of the residual, which is specifically as follows:

ŝ _m(t_G)=g_out(t_G, ŷ_ROI,m⁽ⁱ⁺¹⁾, {circumflex over (p)}_m(t_G), σ_m^z(t_G))

σ_m^s(t_G)=−g′_out(t_G, ŷ_ROI,m⁽ⁱ⁺¹⁾, {circumflex over (p)}_m(t_G), σ_m^z(t_G))

where ŷ_ROI,m⁽ⁱ⁺¹⁾ is a m^th element of the receiving signal obtained in S43;

S56, for n_s=1,2, N_s, observed mean value {circumflex over (v)}_ns(t_G) and variance σ_ns^v(t_G) of {circumflex over (x)}_ns(t_G) as follows:

{circumflex over (v)} _{n s} (t_G)={circumflex over (x)}_ns(t_G)+σ_ns(t_G)Σ_mA_m,nsŝ_m(t_G)

σ_ns^v(t_G)=[Σ_nsA_m,ns²σ_ns^s(t_G)]⁻¹;

S57, for n_s=1,2, . . . , N_s, observed mean value {circumflex over (x)}_ns(t_G+1) and variance σ_ns^x(t_G+1) as follows:

{circumflex over (x)} _{n s} (t_G+1)=g_in(t_G, {circumflex over (v)}_ns(t_G), σ_ns^v(t_G),q)

σ_ns^x(t_G+1)=σ_ns^v(t_G)g′_in(t_G,{circumflex over (v)}_ns(t_G), σ_ns^r(t_G),q)

S58, steps S54 to S57 are repeated until the convergence condition Σ_m|y_m−{circumflex over (z)}_m(t_G)|>ε_G is satisfied;

S59, the sparse variable {circumflex over (x)}_ns(t_G) estimated in the above steps is taken as a final environment sensing result of the current iteration.

S6, step S4 and step S5 are repeated in sequence until the algorithm convergence, the iterative flow chart is shown in FIG. 2, and the final environment sensing result is obtained.

As can be seen from computer simulation: as shown in FIGS. 3 and 4, the imaging effect between the focused method of the present disclosure and the large-scale imaging algorithm is compared. Compared with large-scale imaging, the algorithm of the present disclosure significantly improves the imaging accuracy of objects in ROI. FIG. 3 shows that with the increase of the number of users, the environmental sensing effect of the method of the present disclosure is gradually improved and superior to the existing algorithms. FIG. 4 shows that with the increase of the number of subcarriers, the environmental sensing effect of the method of the present disclosure is gradually improved and superior to the existing algorithms.

In the uplink wireless communication scenario, the design method for integrated millimeter wave sensing and communication system by using the existing communication equipment fully utilizes different system resources to realize focused environmental sensing based on the data sent by users, converts the environmental sensing problem into a compressed sensing reconstruction problem, and then realizes the initial coarse sensing of the environment based on an approximate message passing algorithm. According to a background determining method, in the present disclosure, the target object is divided and determined, and the influence of the background scatterer on the receiving signal is removed, and finally, the background scatterer is repeatedly removed, so as to obtain a more accurate focused sensing result of the target object. Compared with the existing environmental sensing reconstruction algorithms, the iterative focused environmental sensing method provided by the present disclosure solves the problem of low precision of large-scale environmental sensing due to insufficient system resources, improves the defect that the traditional compressed sensing algorithm cannot focus on a specific range of environmental variables, thereby providing an efficient environment sensing method for the future design of integrated sensing and communication system. In the iterative process of the algorithm, according to the results of each step of compressed sensing reconstruction, the prior probability of environmental variables is estimated step by step, and an iterative progressive compressed sensing sparse reconstruction is realized for a specific target. On the basis of the same system resource overhead, the algorithm of the present disclosure significantly improves the sensing accuracy of a specific target and is superior to the existing algorithms.

The above is only preferred embodiments of one or more embodiments of this specification, and is not intended to limit one or more embodiments of this specification. Any modification, equivalent substitution, improvement and the like made within the spirit and principle of one or more embodiments of this description shall be included in the scope of protection of one or more embodiments of this description.

Claims

1. An iterative focused millimeter wave integrated communication and sensing method, which is applied to uplink wireless communication, comprising the following steps: S1, in any time slot, receiving, by a base station, pilot frequency sequence signals with a certain length sent by all active users in an environment to obtain receiving signals, wherein the receiving signals are signals after the pilot frequency sequence signals are influenced by environment;S2, converting an environmental sensing problem of a specific target into a compressed sensing reconstruction problem using the receiving signals in the step S1 based on a multi-beam multi-carrier millimeter wave channel model;S3, solving the compressed sensing reconstruction problem in the step S2 based on an approximate message passing method to obtain a coarse initial result of environment sensing;S4, selecting a predetermined region as a focused region of interest from whole environment based on the coarse initial result of environmental sensing, and dividing and determining a target object in the region of interest according to a background determining method and removing influence of background scatters outside the region of interest on the receiving signals to obtain receiving signals corresponding to the target object;S5, calculating an environmental sensing result based on the receiving signals corresponding to the target object obtained in the step S4; andS6, repeating the steps S4 and S5 in sequence until the algorithm convergence, to obtain a final environment sensing result.

2. The method according to claim 1, wherein the step S2 comprises the following sub-steps: S21, discretizing environmental information in the receiving signals in the step S1 into pixels, wherein each of the pixels represents environmental information in a small square with a surrounding size of ls×ws, letting an environmental size of a whole range is Ls×Ws, a total number of the pixels being Ns−L/ls×W/ws; each of the pixels is empty, or has scatters inside, wherein a scattering coefficient xns is used to represent a scattering coefficient of a small cube where a nsth point cloud is located, when an interior of the small cube is empty, xns=0, and environmental information of a whole room is expressed as x=[x1, x2, . . . , xns]T;S22, constructing a multi-beam multi-carrier millimeter wave channel model, wherein at an nfth subcarrier frequency, the receiving signals received by a receiving antenna of the base station are expressed as follows: ynf=wnf(Hnfs→Bdiag(δx)Hnfu→s+HnfLOS)snf+n=wnf(HnfNLOS+HnfLOS)snf+n where ynf∈NcxK represents the receiving signals with a length of K code elements of RF links of Nc base stations, wnfεNcxNR represents a beam forming vector of NR uniform linear array receiving antennas of the base stations, δ represents a normalized coefficient of a scattering coefficient, selected according to a pixel size is×ws, wherein a normalized coefficient defines a physical relationship between an electromagnetic wave receiving region and a receiving power, snfεNuxK represents pilot frequencies with a length of K code elements sent by Nu users, n represents noise; HnfLOS represents a free-space propagation channel from Nu users to NR receiving antennas at an nfth subcarrier frequency; and HnfLOS represents a Non-Line-of-Sight (NLOS) channel on an nfth subcarrier;wherein HnfLOS is expressed as follows: HnfLOS=enfLOSGnfLOS where enfLOS represents a steering vector of Nu users and GnfLOS represents a channel gain from Nu users to the base station;wherein enfLOS is expressed as follows:

3. The method according to claim 2, wherein the step S3 comprises the following steps: S31, firstly setting an initial coarse environmental sensing prior probability, and letting the environmental information be a Bernoulli-Gaussian distribution, wherein a probability density function px(x|q) is expressed as: px(x|q)=(1−λ)δ(x)+λN(x|θx,σx)where x represents an element in environmental information x, all parameters are expressed as q[λ,θx, σx], δ(·) represents an impulse function, λ represents a sparse coefficient; θx∈[0,1] and σx represent a mean value and a variance of environmental information distribution, respectively, and N(·) represents a standard normal distribution;S32, initializing approximate message passing algorithm parameters, and letting input functions gin(·), g′in(·) and output functions gout(·), g′out(·) be as follows, respectively

4. The method according to claim 3, wherein the step S4 comprises the following steps: S41, selecting a predetermined region as a focused region of interest from the whole environment according to the coarse environmental sensing initial result and actual needs, wherein the target object is in the region of interest;S42, in an ith iteration, detecting a background scatterer {circumflex over (x)}back(i)(ns) outside the region of interest as follows:

5. The method according to claim 1, wherein the step S5 comprises the following steps: S51, setting the prior probability of the environmental information in an iterative focused process, wherein in the ith iteration, assuming that the background scatterer obeys Bernoulli Gaussian distribution, and a prior probability formula p(xback) is expressed as follows: p(xback)=(1−λ)δ(xback)+λ+(xback; θback,i, σback)where θback,i and σback represent a mean value and a variance of a background environmental information distribution, respectively, λ represents a sparse coefficient, N(·) represents a standard normal distribution, and xback represents the background scatterer;wherein scatterer distribution in the selected ROI is a Gaussian distribution, with no sparsity: p(xROI)=(xROI; θROI, σROI)where θROI and σROI represent a mean value and a variance of ROI environmental information distribution, respectively;S52, setting, according to the prior probability formula obtained in step S51, the prior probability p(x) of environmental information inside and outside the region of interest in an (i+1)st iteration, wherein x={xROI, xback};S53, initializing approximate message passing algorithm parameters, and letting input functions gin(·), g′in(·) and output functions gout(·), g′out(·) be as follows: