Adaptive Interference Cancellation Method for Radar-Communication Integrated Base Station

Abstract

The present invention discloses an adaptive interference cancellation method for a radar-communication integrated base station, belonging to the field of wireless communication. By separating communication signals and radar signals from the mixed signals at the receiving end, the performance of radar detection and uplink communication is improved. Thus, the problems that in a radar-communication integrated base station, the radar echo signal will interfere with the uplink communication signal, and the interference cancellation of the communication integrated base station is imperfect and insufficiently considered are solved.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and particularly to an adaptive interference cancellation method for a radar-communication integrated base station. Background Art

[0002] The large-scale commercialization of the 5th Generation Mobile Communication System (5G) is accelerating the promotion of the economic society towards digitalization, networking, and intelligent transformation, and driving the network into a new era of all things interconnected. However, due to the explosive growth of communication devices, the wireless spectrum resources are becoming increasingly tense. To meet the demand for additional spectrum resources, the industry and academia are exploring the integration of detection functions represented by traditional radars into communication signals, enabling communication and detection to share the same spectrum resources integrally.

[0003] Currently, a collaborative method called DFRC (Dual-Functional Radar-Communication) occupies the mainstream research direction of radar-communication integrated waveforms. This method designs modern integrated technologies such as signals, waveforms, and coding into a complete joint unit, having broad research prospects. In a radar-communication integrated system constructed based on DFRC, the signals transmitted by the base station can be used for both communication and radar, enabling simultaneous operation at the same frequency without occupying additional resources. A large number of scholars have studied the waveform design methods for radar-communication integration to achieve a performance compromise between radar and communication functions. However, since the base station not only needs to receive the echo signals of the radar-communication integrated signals it transmits itself but also the uplink communication signals from communication users, there will inevitably be severe mutual interference between these two different signals at the receiving end. Many studies focus on signal design at the transmitting end but ignore interference cancellation at the receiving end, or directly use time division multiplexing to receive echo signals and uplink communication signals at different times, seriously reducing the overall performance of the radar-communication integrated system. Summary of the Invention

[0004] The present invention provides an adaptive interference cancellation method for a radar-communication integrated base station, which separates communication signals and radar signals from the mixed signals at the receiving end to improve the performance of radar detection and uplink communication. It solves the problems that in a radar-communication integrated base station, the radar echo signals will interfere with the uplink communication signals, and the interference cancellation of the communication integrated base station is imperfect and insufficiently considered.

[0005] The first aspect embodiment of the present invention provides an adaptive interference cancellation method for a radar-communication integrated base station, including the following steps:

[0006] When there is no radar detection target, the base station transmitter sends a pilot to the communication user, so that the communication user receiver calculates the communication channel through the pilot and feeds back the communication channel to the base station through the control link;

[0007] When detecting a radar target, while the base station transmitter sends a radar-communication integrated signal, the base station receiver receives a mixed signal composed of a radar echo signal and an uplink communication signal sent by the communication user;

[0008] Regarding the uplink communication signal in the mixed signal as an interference signal, by minimizing the mean square between the mixed signal and the radar echo signal, an adaptive filter is constructed to obtain an estimation of the radar channel;

[0009] According to the radar channel, the distance information of the detection target is obtained. The distance information of the detection target is detected by multiple adjacent base stations, and the precise positioning of the detection target is obtained based on the relative positions of the multiple adjacent base stations and the obtained distance information of the detection target;

[0010] Reconstruct the radar echo signal using the radar channel;

[0011] Calculate the difference between the mixed signal and the reconstructed radar echo signal to obtain the uplink communication signal passing through the communication channel, perform frequency-domain equalization and symbol decision on the uplink communication signal passing through the communication channel, and obtain the symbols of the uplink communication signal.

[0012] Optionally, in an embodiment of the present invention, regarding the uplink communication signal in the mixed signal as an interference signal, by minimizing the mean square between the mixed signal and the radar echo signal, an adaptive filter is constructed to obtain an estimation of the radar channel, including:

[0013] Taking the minimization of the mean square between the mixed signal and the radar echo signal output by the adaptive filter as the optimization objective, construct the adaptive filter;

[0014] Calculate the gradient of the optimization objective with respect to the tap coefficients of the adaptive filter. According to the principle of the steepest descent method, the tap coefficients move along the negative gradient direction with a preset step size;

[0015] Calculate the tap coefficients for all frames received by the base station, and average the obtained tap coefficients to complete the estimation of the radar channel.

[0016] Optionally, in an embodiment of the present invention, obtaining the distance information of the detection target according to the radar channel includes: setting a target detection threshold, determining the taps of the adaptive filter whose tap coefficients are greater than the target detection threshold, and multiplying the delay time corresponding to the taps by the speed of light and dividing by 2 to obtain the distance information between the detection target and the base station.

[0017] Optionally, in an embodiment of the present invention, reconstructing the radar echo signal by using the radar channel includes: performing linear convolution on the estimated radar channel and the radar communication integrated signal transmitted by the transmitting end of the base station to obtain the radar echo signal.

[0018] Optionally, in an embodiment of the present invention, performing frequency domain equalization and symbol decision on the uplink communication signal passing through the communication channel to obtain the symbols of the uplink communication signal includes:

[0019] Using the fast discrete Fourier transform, converting both the uplink communication signal passing through the communication channel and the communication channel to the frequency domain, completing the frequency domain equalization of the uplink communication signal through the least squares algorithm, and performing decision on the equalized uplink communication signal through maximum likelihood estimation to obtain the uplink communication symbols.

[0020] The adaptive interference cancellation method of the radar communication integrated base station in the embodiment of the present invention first reconstructs the radar echo signal, and then performs frequency domain equalization and maximum likelihood decision on the communication signal, so that the radar communication integrated base station can simultaneously perform target detection and uplink and downlink communication, obtaining better radar performance and communication performance.

[0021] The additional aspects and advantages of the present invention will be partly given in the following description, partly will become obvious from the following description, or will be understood through the practice of the present invention. Description of the Drawings

[0022] The above-mentioned and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0023] Figure 1 is a flowchart of an adaptive interference cancellation method for a radar communication integrated base station according to an embodiment of the present invention;

[0024] Figure 2 is a schematic diagram of the execution process of an adaptive interference cancellation method for a radar communication integrated base station according to an embodiment of the present invention;

[0025] Figure 3 is a system block diagram of an adaptive filter according to an embodiment of the present invention;

[0026] Figure 4A radar channel estimation diagram provided according to an embodiment of the present invention. Detailed implementation manners

[0027] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as a limitation on the present invention.

[0028] The adaptive interference cancellation method of a radar-communication integrated base station according to an embodiment of the present invention will be described below with reference to the accompanying drawings. Aiming at the problem mentioned in the above background technology that in a radar-communication integrated base station, the radar echo signal will interfere with the uplink communication signal, the present invention provides an adaptive interference cancellation method for a radar-communication integrated base station. In this method, the reconstruction of the radar echo signal is first completed, and then the frequency-domain equalization and maximum likelihood decision are performed on the communication signal, so that the radar-communication integrated base station can simultaneously perform target detection and uplink and downlink communication, and obtain better radar performance and communication performance.

[0029] Specifically, Figure 1 A flowchart of an adaptive interference cancellation method for a radar-communication integrated base station provided according to an embodiment of the present invention.

[0030] As Figure 1 shown, the adaptive interference cancellation method of the radar-communication integrated base station includes the following steps:

[0031] In step S101, when there is no radar detection target, the base station transmitter sends a pilot to the communication user, so that the communication user receiver calculates the communication channel through the pilot and feeds back the communication channel to the base station through the control link.

[0032] In the case of no radar detection target, the base station transmitter sends a pilot, and the communication user receiver calculates the communication channel through the received pilot and feeds it back to the base station through the control link, so as to obtain the communication channel.

[0033] In step S102, when performing radar detection of a target, while the base station transmitter sends a radar-communication integrated signal, the base station receiver receives a mixed signal composed of the radar echo signal and the uplink communication signal sent by the communication user.

[0034] The radar-communication integrated signal sent by the base station transmitter can be used for both target detection and downlink communication. At the same time, the transmitted signal needs to perform beamforming to meet the different requirements of the radar and communication dual functions.

[0035] In step S103, the uplink communication signal in the mixed signal is regarded as an interference signal, and an adaptive filter is constructed by minimizing the mean square between the mixed signal and the radar echo signal to obtain an estimation of the radar channel.

[0036] The power of the uplink communication signal in the mixed signal is small while the power of the radar echo signal is large. Therefore, the uplink communication signal is regarded as an interference signal, and the radar echo signal is preferentially processed. Using the least mean square algorithm, with the mean square between the mixed signal and the radar echo signal as the optimization function, the gradient is calculated to construct an adaptive filter, and the tap coefficients of the adaptive filter correspond to the estimation of the radar channel.

[0037] In an embodiment of the present invention, regarding the uplink communication signal in the mixed signal as an interference signal, and constructing an adaptive filter by minimizing the mean square between the mixed signal and the radar echo signal to obtain an estimation of the radar channel, includes:

[0038] Taking minimizing the mean square between the mixed signal and the radar echo signal output by the adaptive filter as the optimization objective, an adaptive filter is constructed;

[0039] Calculating the gradient of the optimization objective with respect to the tap coefficients of the adaptive filter, and according to the principle of the steepest descent method, the tap coefficients move along the negative gradient direction with a preset step size;

[0040] Calculating the tap coefficients for all frames received by the base station, and averaging the obtained tap coefficients to complete the estimation of the radar channel.

[0041] In step S104, according to the radar channel, the distance information of the detection target is obtained. The distance information of the target is detected by multiple adjacent base stations, and the precise location of the detection target is obtained based on the relative positions of the multiple adjacent base stations and the obtained distance information of the detection target.

[0042] In an embodiment of the present invention, obtaining the distance information of the detection target according to the radar channel includes: setting a target detection threshold, determining the taps for which the tap coefficients of the adaptive filter are greater than the target detection threshold, and multiplying the delay time corresponding to the tap by the speed of light and dividing by 2 to obtain the distance information between the detection target and the base station. The delay time corresponding to the tap is the time that the radar signal experiences from transmission to reception.

[0043] The above steps of multiple base stations respectively complete the distance estimation of the same detection target. Under the condition that the positions of multiple base stations are fixed and known, the coordinates of the detection target can be solved by an overdetermined equation.

[0044] In step S105, the radar echo signal is reconstructed using the radar channel.

[0045] In an embodiment of the present invention, a radar echo signal is reconstructed by using a radar channel, including: linearly convolving the estimated radar channel with a radar communication integrated signal transmitted by a base station transmitter to obtain a radar echo signal.

[0046] In step S106, the difference between the hybrid signal and the reconstructed radar echo signal is calculated to obtain an uplink communication signal passing through the communication channel. The uplink communication signal passing through the communication channel is subjected to frequency domain equalization and symbol decision to obtain the symbols of the uplink communication signal.

[0047] In an embodiment of the present invention, subjecting the uplink communication signal passing through the communication channel to frequency domain equalization and symbol decision to obtain the symbols of the uplink communication signal includes: using a fast discrete Fourier transform to convert both the uplink communication signal passing through the communication channel and the communication channel to the frequency domain, completing the frequency domain equalization of the uplink communication signal through a least squares algorithm, and making a decision on the equalized uplink communication signal through maximum likelihood estimation to obtain the uplink communication symbols.

[0048] The adaptive interference cancellation method of the radar communication integrated base station of the present invention will be described in detail below through a specific embodiment.

[0049] As Figure 2 shown, the execution process of the adaptive interference cancellation method of the radar communication integrated base station in the embodiment of the present invention is presented.

[0050] Step 1: In this embodiment, the number of antennas M T at the base station transmitter is 4, and the number of antennas M R at the base station receiver is 2. The antenna arrays at the base station transmitter and receiver are uniform linear arrays, and the spacing between adjacent antennas is 0.5 wavelengths. The downlink signal carrier frequency of the base station is 5.7 GHz, and the detection target is a point target. The number of transmitting antennas of the communication user is N T = 2. The signal-to-noise ratio of the communication signal at the base station receiver is 20 dB. The communication channel satisfies the standard complex Gaussian distribution.

[0051] In this example, the uplink communication channel obtained by the base station through the control link is denoted as h r,t (m,n):

[0052]

[0053] where y r,com (m,n) represents the signal passing through the communication channel at the nth discrete time sampling point in the mth subframe received by the rth receiving antenna of the base station, and s t (m,n) is the uplink communication signal at the nth discrete time sampling point in the mth subframe transmitted by the tth antenna of the communication user transmitter. represents the linear convolution operation on the discrete time dimension, N is the length of one frame of the signal, and M is the total number of transmitted frames.

[0054] Step 2: The integrated radar communication signal x(m,n) transmitted by the base station can be expressed as:

[0055]

[0056] where, (·) T represents matrix transpose, and x i (m,n) is the signal at the nth discrete time sampling point in the mth sub-frame transmitted by the ith antenna of the base station.

[0057] In the case where there may be detection targets, the echo signal received by the radar receiver can be expressed as:

[0058]

[0059] where, y r,rad (m,n) represents the radar echo signal at the nth discrete time sampling point in the mth sub-frame received by the rth receiving antenna of the base station, and α r,t,p represents the fading coefficient from the tth antenna of the base station transmitter to the rth antenna of the base station receiver through the pth detection target, and τ r,t,p represents the time delay from the tth antenna of the base station transmitter to the rth antenna of the base station receiver through the pth detection target, and P is the total number of detection targets.

[0060] The mixed signal y(m,n) composed of the uplink communication signal and the radar echo signal received by the base station receiver can be expressed as:

[0061]

[0062] y r (m,n) = y r,com (m,n) + y r,rad (m,n) (5)

[0063] where, y r (m,n) is the mixed signal at the nth discrete time sampling point in the mth sub-frame received by the rth receiving antenna of the base station receiver.

[0064] Step 3: The mixed signal in formula (5) is composed of the uplink communication signal and the radar echo signal. In most cases, the power of the radar echo signal is much greater than the power of the uplink communication signal received by the receiver. Therefore, in this step, the communication signal is temporarily regarded as interference signal, and the radar echo signal is separated from the mixed signal first.

[0065] Using an adaptive filtering scheme, a filter is established with a total number of taps being M T ×M R ×(L + 1), where L + 1 is the number of filter taps corresponding between a single receiving antenna and a single transmitting antenna. For the r-th receiving antenna, the taps used are as Figure 3 shown. The mixed signal received by the r-th receiving antenna (temporarily ignoring the uplink communication signal) is obtained by adding the signals transmitted by M T transmitting antennas with different time delays and attenuations. Therefore, M T ×(L + 1) taps are used to reconstruct it. Figure 3 The output signal after addition in the filter can be expressed as y r,op (m,n), and there is:

[0066]

[0067] where, w r,i,l (m,n) is the tap coefficient with a delay of l between the r-th receiving antenna and the i-th transmitting antenna at the n-th discrete time sampling point in the m-th subframe. Perform dimensionality reduction on w r,i,l (m,n), and the expression after dimensionality reduction is w r,β (m,n) = w r,i,l (m,n), where the new index β after dimensionality reduction is β = i×(L + 1) + l. At this time, the tap array w r (m,n) corresponding to the r-th receiving antenna can be written as:

[0068]

[0069] Similarly, perform dimensionality reduction on x i (m,n - l) as well, and denote the expression after dimensionality reduction as where β = i×(L + 1) + l. Denote the vector form of as There is:

[0070]

[0071] At this time, formula (6) can be rewritten as:

[0072]

[0073] where, (·) H represents the conjugate transpose operation. Denote the difference between the output signal of the r-th receiving antenna in the adaptive filter and the mixed signal in (5) as e r (m,n), and there is:

[0074]

[0075] The mean square that minimizes this difference is taken as the optimization objective of the filter, and the mean square expression is:

[0076]

[0077] where (·) * denotes taking the conjugate. J r (m,n) is the mean square objective function. The gradient of the objective function with respect to the tap coefficients is:

[0078]

[0079] According to the principle of the steepest descent method, the tap coefficients obtained in each iteration move along the negative gradient direction with a step size μ, that is:

[0080]

[0081] When n = N, the iteration ends. Repeat step 3 for all the frames received by the base station, and averaging the finally obtained tap coefficients can complete the estimation of the radar channel. The estimation of the radar channel corresponding to the r-th receiving antenna and the i-th transmitting antenna of the base station is denoted as There is:

[0082]

[0083] For different base station receiving antenna numbers r = 0, 1, …, M R -1, repeat step 3, and the estimation of the radar channel corresponding to each receiving antenna can be obtained.

[0084] Step 4: Arbitrarily select the r-th receiving antenna and the i-th transmitting antenna of the base station, estimate the radar channel between these two antennas according to step 3 as Figure 4 shown, set the target detection threshold, find out the taps whose tap coefficients of the adaptive filter in step 3 are greater than this threshold, and determine that there is a target. The delay time corresponding to the tap is the time that the radar signal experiences from transmission to reception, and multiplying this time by the speed of light and dividing by 2 corresponds to the distance between the detected target and the base station.

[0085] Step 5: Reconstruct the radar echo signal received by the base station receiving antenna according to the estimation of the radar channel obtained by formula (14) in step 3. For the r-th receiving antenna, the reconstructed echo signal is denoted as y r,re (m,n), and the calculation method is:

[0086]

[0087] Step 6: Calculate the difference between the signal obtained in formula (15) in step 5 and the mixed signal obtained in step 2, and denote the difference signal corresponding to the r-th receiving antenna of the base station as y r,gap(m,n), there is:

[0088] y r,gap (m,n) = y r (m,n) - y r,re (m,n) (16)

[0089] Convert y r,gap (m,n) into vector form y gap (m,n), there is:

[0090]

[0091] For y r,com (m,n) in formula (1) of step 1, convert it into vector form y com (m,n), there is:

[0092]

[0093] For s t (m,n) in formula (1) of step 1, convert it into vector form s(m,n), there is:

[0094]

[0095] Convert h r,t (m,n) in formula (1) of step 1 into matrix form H(m,n), and the (r,t) - th element of H(m,n) is equal to h r,t (m,n).

[0096] For y gap (m,n), y com (m,n), s(m,n) and H(m,n) are respectively subjected to fast discrete Fourier transform in the time dimension to obtain y gap (m,k), y com,fft (m,k), s fft (m,k) and H fft (m,k), where k is the discrete frequency point subscript, there is:

[0097] y com,fft (m,k) = H fft (m,k)s fft (m,k) (20)

[0098] y gap,fft (m,k) = H fft (m,k)s fft (m,k) + δ (21)

[0099] Since y gap (m,k) is the difference signal obtained after adaptive filtering, it is different from the true value ycom,fft (m, k) has an error, which is denoted as δ.

[0100] Using the least squares method, estimate the vector s fft (m, k), and the estimation formula is:

[0101]

[0102] Among them, is the estimation result of the frequency-domain form of the uplink communication signal. Perform a fast discrete inverse Fourier transform on this result, and then perform a maximum likelihood decision to obtain the communication symbol.

[0103] Step 7: Multiple base stations respectively complete the distance estimation of the same detection target in the manner of Steps 2-4. Denote the total number of base stations as Q (Q >> P), establish a plane rectangular coordinate system from a top-down perspective, and denote the rectangular coordinates of the q-th base station as (x q , y q )(known). Denote the distance to the p-th detection target obtained according to Step 4 as d p,q (known). Denote the rectangular coordinates of the p-th detection target as (x p , y p )(unknown), and the following system of equations can be obtained:

[0104]

[0105] This equation is an overdetermined equation in most cases, and the least squares method can be used to obtain the coordinates of all detection targets.

[0106] According to the adaptive interference cancellation method of the integrated radar and communication base station proposed in the embodiment of the present invention, first complete the reconstruction of the radar echo signal, and then perform frequency-domain equalization and maximum likelihood decision on the communication signal, so that the integrated radar and communication base station can simultaneously perform target detection and uplink / downlink communication, and obtain better radar performance and communication performance.

[0107] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or N embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0108] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0109] Any process or method description in a flowchart or otherwise described herein can be understood to represent a module, segment, or portion of code including one or N executable instructions for implementing a customized logical function or process, and the scope of the preferred embodiments of the present invention includes additional implementations, where the functions may be performed in a substantially simultaneous manner or in an order opposite to that shown or discussed, according to the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention pertain.

Claims

1. An adaptive interference elimination method for a radar communication integrated base station, characterized in that: The following steps are involved: When there is no radar detection target, a base station transmitter sends a pilot signal to a communication user, so that the communication user receiver calculates a communication channel through the pilot signal and feeds back the communication channel to the base station through a control link; When performing radar detection on a target, the base station transmitting end sends a radar communication integrated signal, while the base station receiving end receives a mixed signal consisting of a radar echo signal and an uplink communication signal sent by the communication user; An uplink communication signal in the mixed signal is regarded as an interference signal, and an adaptive filter is constructed by minimizing the mean square between the mixed signal and the radar echo signal to obtain an estimate of the radar channel; Acquiring distance information of a detection target according to the radar channel, detecting the distance information of the target through a plurality of adjacent base stations, and accurately positioning the detection target according to the relative positions of the plurality of adjacent base stations and the acquired distance information of the detection target; reconstructing the radar echo signal using the radar channel; The difference between the mixed signal and the reconstructed radar echo signal is calculated to obtain an uplink communication signal passing through the communication channel, and frequency domain equalization and symbol decision are performed on the uplink communication signal passing through the communication channel to obtain a symbol of the uplink communication signal.

2. The method according to claim 1, characterized in that The uplink communication signal in the mixed signal is regarded as an interference signal, and an adaptive filter is constructed by minimizing the mean square between the mixed signal and the radar echo signal to obtain an estimation of the radar channel, including: constructing the adaptive filter with minimizing the mean square between the mixed signal and the radar echo signal output by the adaptive filter as an optimization goal; Calculating the gradient of the optimization target with respect to the tap coefficients of the adaptive filter, and moving the tap coefficients in a negative gradient direction with a preset step size according to the principle of steepest descent method; The tap coefficients are calculated for all frames received by the base station, and the obtained tap coefficients are averaged to complete the estimation of the radar channel.

3. The method according to claim 2, characterized in that Acquiring distance information of a detected target according to the radar channel includes: A target detection threshold is set, a tap coefficient of the adaptive filter is determined to be greater than a tap of the target detection threshold, and the delay time corresponding to the tap is multiplied by the speed of light and divided by 2 to obtain the distance information between the detected target and the base station.

4. The method according to claim 1, wherein Reconstructing the radar echo signal using the radar channel includes: The estimated radar channel is linearly convolved with the radar communication integrated signal transmitted by the base station transmitting end to obtain the radar echo signal.

5. The method according to claim 1, wherein Performing frequency domain equalization and symbol decision on an uplink communication signal passing through the communication channel to obtain a symbol of the uplink communication signal includes: The uplink communication signal passing through the communication channel and the communication channel are converted into the frequency domain by using the fast discrete Fourier transform, the frequency domain equalization of the uplink communication signal is completed by the least squares algorithm, and the equalized uplink communication signal is judged by the maximum likelihood estimation to obtain the uplink communication symbol.

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