Multi-user MIMO-OFDM communication perception integration method and system

Abstract

The invention discloses a multi-user MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) communication sensing integrated method and system, and belongs to the technical field of wireless communication. According to the invention, all communication time-frequency resources are completely multiplexed for the sensing task, and the transmitting beam forming is cooperatively designed, so that the communication quality requirements of multiple users and the sensing requirements of the target are met at the same time; and target information is extracted by combining an optimized two-stage sensing signal processing algorithm including spatial denoising, high-resolution angle estimation and time delay Doppler estimation, so that high-efficiency communication and high-precision sensing under zero sensing special time-frequency resource overhead are realized. According to the method, the core problems that the communication spectrum efficiency is reduced and the sensing performance is limited due to division of special sensing time-frequency resources in a traditional communication sensing integrated system are solved, the sensing resolution and the parameter estimation accuracy can be effectively improved on the premise of not sacrificing the capacity of the communication system, and the system performance is improved. The method is especially suitable for application scenes with high requirements for communication and sensing performance, such as low-altitude unmanned aerial vehicles.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a resource allocation, beamforming and perception method in a multi-user multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) integrated communication and perception (ISAC) system with zero perception time-frequency resource overhead. Background Art

[0002] Low-altitude drones (UAVs) have broad application prospects in precision agriculture, aerial delivery, and surveillance, placing higher demands on communication and perception capabilities. Integrated Sensing and Communication (ISAC) technology, by sharing hardware platforms and spectrum resources, can efficiently provide both services and is a key enabling technology for the large-scale deployment of UAVs.

[0003] Traditional ISAC systems typically allocate dedicated time-frequency resources for sensing tasks, for example, allocating 10%-20% of time-frequency resources specifically for sensing. While this approach is simple to implement, it has the following problems:

[0004] Reduced communication spectrum efficiency: Dedicated sensing resources squeeze out available communication resources, resulting in a decrease in communication rate.

[0005] Limited perception performance: The resources allocated to perception are limited, which affects the accuracy, resolution, and unambiguous range of perception.

[0006] Low resource utilization: Especially in scenarios where drones serve as both communication user equipment (UE) and sensing targets, communication signals and sensing signals are not completely isolated in space. If orthogonal time-frequency resource allocation is used, time-frequency resource utilization will be severely reduced and additional power consumption will be incurred.

[0007] Although some studies have considered reusing communication time-frequency resources for perception, most existing work focuses on specific aspects (such as beamforming or perception algorithms) and lacks a design framework for an integrated communication and perception system for UAV ISAC scenarios. This is especially true when supporting three-dimensional ISAC and four-dimensional parameter estimation (azimuth, pitch angle, distance, and radial velocity). The existing algorithms are highly complex and have limited practicality.

[0008] In order to solve the above problems, the present invention proposes a new ISAC framework, which can improve both communication performance and perception performance without allocating dedicated perception resources. Summary of the Invention

[0009] The present invention provides a multi-user MIMO-OFDM communication and perception integration method and system with zero perception time-frequency resource overhead. The method is aimed at the demand for efficient integration of communication and perception functions in low-altitude unmanned aerial vehicle applications, and solves the problems of reduced communication spectrum efficiency and limited perception performance caused by the allocation of dedicated perception resources in traditional communication and perception integration systems. By multiplexing all communication time-frequency resources for perception and carefully designing the transmit beamforming to simultaneously meet the communication and perception tasks, zero perception time-frequency resource overhead is achieved, thereby simultaneously improving communication and perception performance.

[0010] The present invention provides a multi-user MIMO-OFDM zero-perception time-frequency resource overhead communication perception integrated method for low-altitude unmanned aerial vehicles, comprising the following steps:

[0011] Allocate all available time-frequency resources to one or more communication users for data transmission, and do not allocate dedicated time-frequency resources for sensing tasks;

[0012] Designing transmit beamforming for the one or more communication users so that the transmitted signal meets the communication service quality requirements of each communication user while also meeting the perception requirements of one or more perception targets or perception areas;

[0013] The base station receives the reflected / scattered signal from the sensing target or sensing area, and uses the reflected / scattered signal and transmit beamforming information to perform sensing processing to obtain target information.

[0014] Optionally, in one embodiment of the present invention, the design of the transmit beamforming in the target search phase aims to minimize the transmit power while satisfying the user communication signal-to-noise ratio constraint and the perception power constraint in the preset perception scanning direction.

[0015] Optionally, in one embodiment of the present invention, the design of the transmit beamforming in the target tracking phase aims to minimize the transmit power while satisfying the user communication signal-to-noise ratio constraint and the perception signal-to-noise ratio constraint for the known perception target.

[0016] Optionally, in one embodiment of the present invention, the design method of the transmit beamforming includes an SDR-based optimization method or a low-complexity closed-form solution method.

[0017] Optionally, in one embodiment of the present invention, the perception processing includes spatial denoising, two-dimensional angle estimation, and delay-Doppler estimation based on the estimated angle.

[0018] Optionally, in one embodiment of the present invention, the two-dimensional angle estimation algorithm adopts a MUSIC algorithm.

[0019] Optionally, in one embodiment of the present invention, the spatial domain denoising utilizes the sparse characteristics of the signal in the delay-Doppler domain and removes the noise component by setting an energy threshold.

[0020] Optionally, in one embodiment of the present invention, the base station is equipped with a UPA antenna to support full-dimensional beamforming and sensing.

[0021] The present invention also provides a communication and perception integrated system, comprising:

[0022] A resource allocation module is used to allocate all available time-frequency resources to communication users to transmit communication signals, and not to allocate dedicated sensing time-frequency resources for sensing tasks;

[0023] a transmit beamforming module, configured to design transmit beamforming for the communication user so that the communication signal meets the communication service quality requirements of each communication user while also meeting the perception requirements of the perception target or perception area;

[0024] A sensing receiving module, configured to receive, at a base station, an echo signal of the communication signal reflected or scattered from the sensing target;

[0025] A perception processing module is used to process the echo signal and estimate the parameters of the perception target in combination with the transmission beamforming information of the communication signal.

[0026] Optionally, in one embodiment of the present invention, the transmit beamforming module is configured to: in the target search phase, perform beam scanning for a preset perception scanning direction, and for each perception scanning direction, design transmit beamforming to minimize the transmit power while satisfying the user communication service quality constraint, and at the same time satisfy the perception power constraint in the perception scanning direction; in the target tracking phase, utilize previously obtained prior information about the known perception target to design transmit beamforming to minimize the transmit power while satisfying the user communication service quality constraint, and at the same time satisfy the perception signal-to-noise ratio constraint on the known perception target.

[0027] Optionally, in one embodiment of the present invention, the perception processing module is configured to perform the following operations: process the received echo signal to estimate the two-dimensional arrival angle of the perception target; and perform two-dimensional delay-Doppler estimation on the perception target based on the estimated two-dimensional arrival angle.

[0028] The present invention has the following beneficial effects:

[0029] Improved communication performance: By using all time-frequency resources for communication, dedicated sensing resources are avoided from occupying communication resources, thereby significantly increasing the overall communication rate.

[0030] Enhanced perception capability: Reusing all communication time-frequency resources for perception increases the effective perception bandwidth and observation time, thereby improving the perception delay-Doppler resolution, unambiguous range, and parameter estimation accuracy.

[0031] Achieve efficient system operation: The proposed low-complexity beamforming algorithm and two-stage super-resolution sensing algorithm ensure low-overhead and high-efficiency implementation of the system.

[0032] Optimizing drone application scenarios: This effectively solves the problem of inefficient resource allocation in traditional communication and perception integration when drones serve as both communication users and perception targets, thereby improving the overall utilization efficiency of wireless resources.

[0033] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0035] Figure 1 Schematic diagram of a multi-user MIMO-OFDM ISAC scenario for low-altitude UAVs provided by an embodiment of the present invention;

[0036] Figure 2 A schematic diagram comparing OFDM resource grids for a zero-aware time-frequency resource overhead solution and a dedicated awareness resource solution provided in an embodiment of the invention;

[0037] Figure 3 A schematic diagram of the distribution of the perception search and tracking stages provided by an embodiment of the invention;

[0038] Figure 4 This is a flowchart of the perception signal processing proposed by the present invention, including steps such as spatial denoising, angle perception, and delay-Doppler perception;

[0039] Figure 5 2D MUSIC spectrum without spatial domain denoising method for comparison;

[0040] Figure 6 2D MUSIC spectrum corresponding to the spatial domain denoising method proposed in this invention;

[0041] Figure 7 A block diagram of a MIMO-OFDM synaesthesia integrated system provided by an embodiment of the invention. DETAILED DESCRIPTION

[0042] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0043] Example 1

[0044] 1. Signal Model

[0045] Reference Figure 1 , the present invention considers a downlink multi-user MIMO-OFDM communication perception integration system. The base station (BS) is equipped with two M×N units of UPA for downlink signal transmission and uplink perception signal reception. The use of UPA is intended to support full-dimensional MIMO communication perception integration for low-altitude UAVs. The system simultaneously serves U single-antenna communication UEs and perceives K targets. It is worth noting that the perception target can also be a communication UE, for example Figure 1 Target 1 and UE1 in the figure are the same drone.

[0046] The expression of a frame of OFDM signal sent by the base station can be written as:

[0047] s(t)=s c (t)+s s (t)

[0048] in

[0049]

[0050] It is a communication signal.

[0051]

[0052] is a dedicated sensing signal. Where Δf is the subcarrier spacing, T CP is the duration of the cyclic prefix (CP), T O is the total duration of the OFDM symbol including the CP. Contains PQ independent and identically distributed (iid) modulation symbols, where element b p,q represents the symbol on the p-th subcarrier and the q-th OFDM symbol, and satisfies Γ u represents the set of resource elements allocated to user u, and satisfies Sometimes Γ s Represents a set of resource elements dedicated to perception. In addition, f u,q and f s,qThey represent the user beamforming vector and perception beamforming vector corresponding to all subcarriers on the qth OFDM symbol. Where Γ represents the set of all available resource elements.

[0053] The core of the present invention is to achieve zero sensing time-frequency resource overhead. This means that no dedicated time-frequency resources are allocated for the sensing task. Figure 2 In (b), all available TF resources Γ are allocated to communication users for data transmission. The sensing function is completely realized by multiplexing these signals carrying communication data. Therefore, the total signal s(t) transmitted by the base station is only composed of the communication signal s c (t) constitutes a dedicated perception signal s s (t) is zero. This mechanism is different from the traditional allocation of dedicated sensing resources ( Figure 2 This is in contrast to the solution in (a).

[0054] 2. Search and Tracking Phase

[0055] In the communication perception integration method of the present invention, the perception process of the base station can generally be divided into two main stages: the target search stage and the target tracking stage. Figure 3 shown.

[0056] During the target search phase, the base station performs beam scanning within an OFDM frame to proactively discover and identify potential new targets. Because prior information about the target is limited or nonexistent, beamforming design focuses on achieving sufficient sensing coverage in all scanning directions while ensuring communication quality.

[0057] Target Tracking: Once a target is detected and preliminary track information (such as position and velocity) is established, the base station enters the target tracking phase. During this phase, the base station uses prior information about the target to adjust beam pointing, continuously monitor the identified target, and update parameters. Target search can be performed periodically to detect new targets, while target tracking continues between search intervals.

[0058] 3. Transmit beamforming design

[0059] In order to ensure the dual performance of communication and perception while multiplexing communication signals for perception, the design of transmit beamforming is crucial. In the framework of zero perception time-frequency resource overhead, all transmitted signals are communication signals, and their beamforming f u,q (Target search phase, beamforming of user u on OFDM symbol q) or f u (During the target tracking phase, beamforming does not change with q) It is necessary to take into account both communication and perception requirements.

[0060] In the target search phase, the base station adjusts its beam pointing to different angles (φ s,q ,θ s,q ) to scan. For each scanning direction a s,q and the user u served by the current symbol, transmits the beamforming vector f u，q The design goal is to meet the minimum communication service quality (minimum signal-to-noise ratio) of user u. ), minimize the total transmission power of the base station while ensuring that in the current scanning direction a s，q There is enough sensing energy (such as the minimum sensing power ε min ). The optimization problem can be expressed as:

[0061]

[0062] Constrained by:

[0063]

[0064] Among them, h u and They are the statistical channel correlation matrix R of user u u The principal eigenvector and maximum eigenvalue, σ 2 is the noise power. This problem is a quadratically constrained quadratic programming (QCQP) problem and can be solved using the semidefinite relaxation (SDR) technique. To reduce computational complexity, the present invention also provides a low-complexity closed-form suboptimal beamforming solution, expressed as a linear combination of the communication channel direction and the sensing scan direction:

[0065]

[0066] The coefficient a u , b u,q and phase It is derived based on the communication SNR constraint and the perception power constraint. Specifically:

[0067]

[0068] During the target search phase, the scanning beam angle can be designed as follows:

[0069]

[0070] in is the perceived beam angle of the qth symbol. In this design, OFDM symbols with the same beam direction form a block structure. Q should be designed to be larger than the number of beams, MN, to ensure full coverage, and should be an integer multiple of MN to keep the number of symbols per beam equal.

[0071] In the target tracking phase, the base station has obtained the target of interest k∈Ω trk Prior information, such as the estimated angle of arrival (Corresponding to the steering vector ) and scattering coefficient At this time, the beamforming vector f u The design goal is to meet the communication service quality of user u (such as minimum signal-to-noise ratio). ) and the perceived service quality of all tracked targets k (such as the minimum perceived signal-to-noise ratio ), minimize the transmission power. The optimization problem can be expressed as:

[0072]

[0073] Constrained by:

[0074]

[0075] This problem can also be solved by SDR.

[0076] 4. Perception Algorithm

[0077] This paper proposes a low-complexity two-stage super-resolution perception algorithm, such as Figure 4 As shown in FIG, the method mainly includes three steps: spatial domain denoising, two-dimensional angle estimation, and delay-Doppler estimation based on the estimated angle.

[0078] In order to improve the performance of subsequent angle estimation algorithms (such as MUSIC) under low SNR, especially when the echo signal may be weak under the zero-perception time-frequency resource overhead system, the received echo signal tensor is first Perform spatial domain denoising. This process first removes the modulation symbols of the received signal. Then it is transformed into the delay-Doppler (DD) domain. In the target search phase, a two-dimensional FFT is performed on the OFDM symbol block corresponding to each sensing beam direction; in the target tracking phase, a two-dimensional FFT is performed on all used OFDM symbols. Since the target signal is usually sparse in the DD domain, and the noise is distributed in the entire DD plane, an energy threshold ε can be set to th , the units with energy below this threshold in the DD domain are regarded as noise and set to zero, thereby retaining the signal components with higher energy

[0079] Then, the denoised signal is used to estimate the 2D arrival angle of the target. First, the spatial autocorrelation matrix of the received signal is constructed. In order to deal with the possible coherent multipath signals, forward-backward spatial smoothing (FBSS) is used to improve the rank property of the autocorrelation matrix. The autocorrelation matrix R of the sub-array is i，j After FBSS, we get

[0080] Then, the smoothed autocorrelation matrix is ​​analyzed using the MUSIC algorithm. Perform eigenvalue decomposition to separate the signal subspace and the noise subspace. By searching the MUSIC spectrum function at all possible angles (φ, θ) The peak value of the target is used to estimate the AoA of the target, where a(φ, θ) is the steering vector corresponding to the angle, E n is the eigenvector matrix corresponding to the noise subspace. Figure 5 and Figure 6 The comparison of 2D MUSIC spectra with and without spatial domain denoising shows that denoising can significantly enhance the peak height, thereby improving the angle estimation performance under low signal-to-noise ratio.

[0081] After obtaining the target's AoA estimation, subsequent delay and Doppler shift estimation is performed for each estimated angle direction. First, for the kth A The estimated AoA is used to design a zero-forcing (ZF) receive beamforming vector This vector is designed to enhance the signal coming from that direction while suppressing interference from signals coming from other estimated angular directions.

[0082] Then, use ZF receive beamforming Extract the signal component corresponding to the angle from the total received signal Since the present invention adopts zero-perception time-frequency resource overhead, the transmitted signal is a communication signal carrying user data, and its beamforming f u,q (or f u ) is designed for communication users and is related to the subcarrier index p and symbol index q. Therefore, before performing delay-Doppler estimation, it is necessary to accurately remove the modulation symbol b p,q and the effect of transmit beamforming on a specific sensing path. This is achieved by calculating the equivalent modulation symbols, In the tracking phase in It corresponds to user u on resource (p,q) and covers the kth A The extracted signal is beamformed with AoA. Divide by the corresponding equivalent modulation symbol to get

[0083] Finally, the processed signal Perform a two-dimensional Fourier transform (i.e. calculate its periodogram) to jointly estimate the target delay and Doppler shift Based on these estimates, the target's range and radial velocity can be further calculated. At the same time, the target's radar cross section or complex scattering coefficient can also be estimated. Used to update target information and assist in beamforming in the subsequent tracking phase.

[0084] During the target search phase, delay-Doppler estimation is usually performed on a subset of symbols covering a specific scan angle. In the target tracking phase, it can be performed on all TF resources Γ allocated to the user to obtain better accumulation gain.

[0085] Example 2

[0086] This embodiment provides a communication perception integrated system, such as Figure 7 Shown, including:

[0087] A resource allocation module is used to allocate all available time-frequency resources to communication users to transmit communication signals, and not to allocate dedicated sensing time-frequency resources for sensing tasks;

[0088] The transmit beamforming module is used to design transmit beamforming for the communication user, so that the communication signal can meet the communication service quality requirements of each communication user while also meeting the perception requirements of the perception target or perception area. The transmit beamforming module is configured as follows: in the target search phase, beam scanning is performed for a preset perception scanning direction, and for each perception scanning direction, transmit beamforming is designed to minimize the transmit power while meeting the user's communication service quality constraints, while meeting the perception power constraints in the perception scanning direction; in the target tracking phase, the transmit beamforming is designed using the previously obtained prior information about the known perception target to minimize the transmit power while meeting the user's communication service quality constraints, while meeting the perception signal-to-noise ratio constraints of the known perception target.

[0089] A sensing receiving module, configured to receive, at a base station, an echo signal of the communication signal reflected or scattered from the sensing target;

[0090] A sensing processing module is configured to process the echo signal and, in combination with transmit beamforming information of the communication signal, estimate parameters of the sensing target. The sensing processing module is configured to: process the received echo signal to estimate the two-dimensional angle of arrival of the sensing target; and perform two-dimensional delay-Doppler estimation on the sensing target based on the estimated two-dimensional angle of arrival.

[0091] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions 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 any one or N embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0092] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "N" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0093] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code comprising one or N executable instructions for implementing a custom logical function or step of a process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may be performed out of the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention pertain.

Claims

1. A multi-user MIMO OFDM communication perception integrated method, characterized in that: The following steps are involved: All available time-frequency resources are allocated to communication users for transmitting communication signals, and no dedicated sensing time-frequency resources are allocated for sensing tasks; Designing transmit beamforming for the communication users so that the communication signals meet the communication service quality requirements of each communication user while also meeting the perception requirements of the perception target or perception area; Receiving, by a base station, an echo signal of the communication signal reflected or scattered from the sensing target or sensing area; The echo signal is processed and combined with the transmit beamforming information of the communication signal to estimate the parameters of the sensing target or sensing area.

2. The method according to claim 1, characterized in that The steps of designing transmit beamforming include, in the target search phase: performing beam scanning for a preset perception scanning direction; designing transmit beamforming for each perception scanning direction to minimize transmit power while satisfying user communication service quality constraints, while satisfying the perception power constraints in the perception scanning direction; and in the target tracking phase, utilizing previously obtained prior information about a known perception target; designing transmit beamforming to minimize transmit power while satisfying user communication service quality constraints, while satisfying the perception signal-to-noise ratio constraints for the known perception target.

3. The method according to claim 2, wherein: The beam scanning angles in the search phase are allocated in a block structure, with continuous OFDM symbols allocated to each direction. The number of symbols is greater than the number of beams and is an integer multiple. The beamforming in the tracking phase does not change with the OFDM symbols.

4. The method according to claim 3, characterized in that The transmit beamforming is designed by using an optimization solution method based on semi-definite relaxation or a low-complexity closed-form solution method.

5. The method according to claim 1, wherein The steps of processing the echo signal include: a first stage: performing spatial domain denoising on the echo signal, and using the delay-Doppler domain sparsity to set an energy threshold to remove noise; a second stage: estimating the target two-dimensional arrival angle based on the denoised signal; and a third stage: performing target delay-Doppler estimation based on the estimated target two-dimensional arrival angle.

6. The method according to claim 5, characterized in that The two-dimensional arrival angle estimation adopts a multiple signal classification algorithm.

7. The method according to claim 5, characterized in that Performing target delay-Doppler estimation based on the estimated target two-dimensional arrival angle specifically includes: calculating equivalent modulation symbols according to the transmission beamforming information of the communication signal and the target arrival angle information, and using the equivalent modulation symbols to process the echo signal to eliminate the influence of the modulation information.

8. A communication and perception integrated system based on the method according to any one of claims 1 to 7, characterized in that: include: A resource allocation module is used to allocate all available time-frequency resources to communication users to transmit communication signals, and not to allocate dedicated sensing time-frequency resources for sensing tasks; a transmit beamforming module, configured to design transmit beamforming for the communication user so that the communication signal meets the communication service quality requirements of each communication user while also meeting the perception requirements of the perception target or perception area; A sensing receiving module, configured to receive, at a base station, an echo signal of the communication signal reflected or scattered from the sensing target; A perception processing module is used to process the echo signal and estimate the parameters of the perception target in combination with the transmission beamforming information of the communication signal.

9. The system according to claim 8, characterized in that The transmit beamforming module is configured to: perform beam scanning in a preset sensing scanning direction during a target search phase, and design transmit beamforming for each sensing scanning direction to minimize transmit power while satisfying a user communication quality of service constraint, while satisfying a sensing power constraint in the sensing scanning direction; In the target tracking phase, the transmit beamforming is designed using the previously obtained prior information about the known perceived target to minimize the transmit power while satisfying the user communication service quality constraint and the perceived signal-to-noise ratio constraint of the known perceived target.

10. The system according to claim 8, wherein: The perception processing module is configured to perform the following operations: processing the received echo signal to estimate the two-dimensional arrival angle of the perception target; and performing two-dimensional delay-Doppler estimation on the perception target based on the estimated two-dimensional arrival angle.

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