OFDM sound source distance depth estimation method based on single hydrophone

Abstract

The invention relates to the technical field of underwater acoustic positioning, discloses an OFDM (Orthogonal Frequency Division Multiplexing) sound source distance and depth estimation method based on a single hydrophone, and aims to realize parallel processing of communication positioning tasks and efficient utilization of underwater time-frequency resources and promote development of light-weight and low-energy-consumption equipment adaptive to an underwater unmanned small platform. According to the OFDM sound source distance and depth estimation method based on the single hydrophone, the frequency domain input and output relation of a communication system under a multi-path channel is combined, an observation model used for target positioning is constructed through comb-shaped pilot frequency, a multi-snapshot measurement matrix is constructed through a space domain smoothing means, multi-path time delay estimation is achieved based on a rotation invariant subspace algorithm, and the estimation accuracy is improved. And then target positioning is realized by adopting a channel time delay feature matching method. The OFDM sound source distance and depth estimation method based on the single hydrophone provided by the invention is suitable for integrated information processing of the single hydrophone, has the advantages of miniaturization, light weight and portability, and is suitable for an underwater unmanned small platform.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic positioning, and in particular to an OFDM sound source distance depth estimation method based on a single hydrophone. Background Art

[0002] Communication and positioning are basic requirements in underwater acoustic applications. Although they have been studied comprehensively over the years, they are often regarded as independent technical systems. In recent years, the integrated integration of communication and positioning functions in underwater acoustic wireless transmission systems has attracted a lot of research interest. Compared with the traditional independent technical route, the integrated solution can deeply couple communication and perception capabilities through the introduction of dual-function waveforms. On the one hand, it promotes the full utilization of spectrum resources and adapts to underwater acoustic channels with limited available bandwidth; at the same time, it is conducive to the parallel processing of communication and positioning tasks, and improves the operating efficiency of the traditional time division system. At the hardware level, the integrated waveform can use a set of equipment to complete the transmission and reception processing, which reduces the volume, weight and power consumption of the system and is highly adapted to underwater unmanned platforms. One trend is that the application of miniaturized equipment (such as single vector or single scalar sensors) on submersibles has become a research hotspot.

[0003] Based on this, the present invention is oriented to the integrated information processing of a single hydrophone, adopts the OFDM signal with efficient spectrum utilization as the dual-function waveform, and proposes an OFDM sound source distance depth estimation method based on a single hydrophone. While meeting the high-speed communication requirements, the embedded pilot subcarrier provides effective environmental perception capability. Summary of the invention

[0004] In order to achieve the deep integration of communication and positioning functions, the present invention proposes an OFDM sound source distance depth estimation method based on a single hydrophone. Specifically, based on the OFDM frequency domain input-output relationship under a multipath channel, a measurement model for source positioning is constructed using pilot information. A multi-snap measurement matrix is ​​constructed by spatial domain smoothing, and multipath delay estimation is achieved based on the rotationally invariant subspace algorithm. In order to reduce the communication system's demand for high collaboration between the transmitter and receiver, the channel relative delay feature matching method is used to achieve target positioning.

[0005] To achieve the purpose of the present invention, the technical solution of the present invention is as follows: The OFDM sound source distance depth estimation method based on a single hydrophone provided by the present invention comprises the following steps: S1. Use ray acoustics to develop a three-path propagation channel model in shallow water scenarios, including the direct sound path and the surface and bottom reflected sound paths; S2, based on the frequency domain input-output relationship of the OFDM system, a measurement model for source location is constructed using pilot information; S3, construct a multi-snapshot measurement matrix through spatial domain smoothing, and realize multipath delay estimation based on rotation invariant subspace algorithm; S4. Use channel relative delay feature matching method to achieve target positioning.

[0006] Preferably, the three-path propagation channel model assumes that the water bottom and the water surface in the observation area remain horizontal, the sound speed is evenly distributed, and the sound line propagates in a straight line.

[0007] Preferably, the measurement model is based on coarse synchronization before OFDM demodulation to obtain signal arrival time and construct a frequency domain input-output relationship.

[0008] Preferably, the multi-snap measurement matrix is ​​constructed by dividing the observation vector into overlapping sub-vectors, utilizing the Vandermonde form and translation invariance properties of frequency-domain equally spaced pilots.

[0009] Preferably, the multipath delay estimation is implemented by singular value decomposition and rotationally invariant subspace algorithm to obtain a time offset parameter estimation value.

[0010] Preferably, the target positioning is based on a relative time delay feature matching method, and source direction estimation is achieved by minimizing an objective function.

[0011] Compared with the related art, the OFDM sound source distance depth estimation method based on single hydrophone provided by the present invention has the following beneficial effects: Compared with the existing positioning schemes based on long baseline, (ultra) short baseline, towed array and vertical array, the single hydrophone source positioning scheme proposed in the present invention does not require array correction and high-precision clock synchronization. The equipment used has the advantages of miniaturization, lightness and portability, and can be installed on small underwater unmanned platforms, further reducing the data processing burden.

[0012] The solution proposed in the present invention can realize sound source positioning while performing OFDM communication. Compared with the existing time-division communication and positioning system, the overall operation efficiency of the system is higher and the direction information is updated more frequently. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The overall processing flow chart of an OFDM sound source distance depth estimation method based on a single hydrophone provided by the present invention; Figure 2 This is a schematic diagram of the communication and positioning integration scenario in the present invention; Figure 3 It is a schematic diagram of the water tank test results in the present invention. DETAILED DESCRIPTION

[0014] The present invention will be further described below in conjunction with the accompanying drawings.

[0015] See also Figure 1 The present invention proposes an OFDM sound source distance depth estimation method based on a single hydrophone, which comprises the following steps: S1. Use ray acoustics to develop a three-path propagation channel model in shallow water scenarios, including the direct sound path and the surface and bottom reflected sound paths; S2, based on the frequency domain input-output relationship of the OFDM system, a measurement model for source location is constructed using pilot information; S3, construct a multi-snapshot measurement matrix through spatial domain smoothing, and realize multipath delay estimation based on rotation invariant subspace algorithm; S4. Use channel relative delay feature matching method to achieve target positioning.

[0016] The specific implementation of the solution of the present invention will be further described below with reference to the accompanying drawings.

[0017] (1) As shown in the figure below, it is assumed that the bottom and surface of the water in the observation area remain level and the water depth is , speed of sound Evenly distributed, the sound line propagates in a straight line. Assume that the heights of the receiving end and the transmitting end from the bottom of the water are and , the horizontal distance is , A three-path propagation channel consists of a direct acoustic path, a water surface reflection path, and a water bottom reflection path. The above assumption is approximately valid for short-range transmission in shallow water.

[0018] (2) Assume that both the transmitter and receiver are stationary during the positioning period, and the position of the transmitter relative to the receiver is For underwater high-frequency communication signals, ray acoustics theory is used to model them. If the channel state is relatively stable, there is transmission paths (mainly considering The time-invariant channel impulse response can be expressed as: (1); In the above formula is the impulse function, are multipath delays arranged from small to large and different from each other, Indicates the path strength.

[0019] (3) The receiver needs to perform coarse synchronization to obtain the signal arrival time before performing OFDM demodulation , if the signal transmission time is , the resulting time offset is . Characterizing the multipath structure of the channel is the basis for realizing single hydrophone source positioning.

[0020] (4) For an OFDM symbol, let The baseband frequency of the equally spaced comb pilot subcarriers is , the training symbol carried is After preprocessing such as down-conversion, low-pass filtering, and OFDM demodulation, the frequency domain input-output relationship of the communication system can be obtained. Since the channel is time-invariant, it is assumed that no inter-subcarrier interference is generated during OFDM demodulation. Subsequently, only the pilot subcarriers are considered and the input and output vectors are divided by the training symbols at the same time, and a typical frequency domain measurement model can be obtained: (2); in To measure the noise ( represents a complex domain), , , l = 1, 2,… , L It is time bias The phase shift generated on each pilot subcarrier ( is the transpose symbol), The complex-valued path gain Composition, of which is the carrier frequency.

[0021] (5) Considering that Equation (2) is a single snapshot model, in order to apply the subspace method, it is necessary to construct a rank greater than Note that the equally spaced pilots in the frequency domain make It has a Vandermonde form. Based on its translation invariance, the spatial domain smoothing method can be used to restore the rank of the matrix. Assume that the smoothing times are ( ), then the observation vector Divide into Overlapping subvectors , Include No. arrive elements. Then it is constructed as follows : (3).

[0022] (6) By analogy The sensor The measurement matrix obtained by sampling is as follows. According to the subspace method, Perform eigendecomposition to obtain the characteristic matrix ,in represents the matrix conjugate transpose. The above operation can be simplified to Perform singular value decomposition, and the resulting left singular vector matrix is .

[0023] (7) Order the singular values ​​from large to small The column vectors are sorted. , The first three columns are signal subspace matrices, and the rest are noise subspace matrices. Based on the rotation-invariant subspace algorithm, the estimated value of the time offset parameter can be obtained: .

[0024] (8) If absolute time deviation is used To perform positioning, the time synchronization between the transmitter and receiver is required to ensure that the receiver can obtain the accurate transmission time of the signal. This will limit the application scenarios of the method, and because Generally, it is in the order of milliseconds. The overall time error of the system needs to be controlled at a low level to ensure that For the above considerations, the present invention designs the algorithm based on relative delay. The relative delay of multipath signals with respect to the first-arriving signal can be defined as .

[0025] (9) Note Note that when the sound field is sufficiently predictable, for Therefore, the feature matching method based on relative delay can be expressed as: (4); Let the above formula be the smallest This is the final positioning result.

[0026] (10) Considering the noise-free condition The theoretical minimum value of is 0. To construct a pin-shaped spatial spectrum similar to MUSIC, the objective function can be written as: (5); Based on the above formula, the estimation of the source direction will be completed by spectrum peak searching.

[0027] Compared with the related art, the OFDM sound source distance depth estimation method based on single hydrophone provided by the present invention has the following beneficial effects: Compared with the existing positioning schemes based on long baseline, (ultra) short baseline, towed array and vertical array, the single hydrophone source positioning scheme proposed in the present invention does not require array correction and high-precision clock synchronization. The equipment used has the advantages of miniaturization, lightness and portability, and can be installed on small underwater unmanned platforms, further reducing the data processing burden.

[0028] The solution proposed in the present invention can realize sound source positioning while performing OFDM communication. Compared with the existing time-division communication and positioning system, the overall operation efficiency of the system is higher and the direction information is updated more frequently.

[0029] like Figure 3 The test results of the proposed method in a water pool are shown. The water depth of the water pool is 5 m, and the sound source and the hydrophone are 3 m and 5.7 m away from the bottom of the pool. Since the bottom of the pool and the water surface are not treated with anechoic treatment, the sound waves will produce multipath propagation effects in the pitch angle domain. As can be seen from the figure, the proposed method has a thumbtack-shaped spatial spectrum and gives a relatively accurate positioning result, with a positioning error of about 5% of the slant range.

[0030] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for estimating the distance depth of an OFDM sound source based on a single hydrophone, characterized in that: The following steps are involved: S1. Use ray acoustics to develop a three-path propagation channel model in shallow water scenarios, including the direct sound path and the surface and bottom reflection sound paths; S2, based on the frequency domain input-output relationship of the OFDM system, a measurement model for source location is constructed using pilot information; S3, construct a multi-snapshot measurement matrix through spatial domain smoothing, and realize multipath delay estimation based on rotation invariant subspace algorithm; S4. Use channel relative delay feature matching method to achieve target positioning.

2. The OFDM sound source distance depth estimation method based on a single hydrophone as claimed in claim 1, characterized in that: The three-path propagation channel model assumes that the water bottom and water surface in the observation area remain horizontal, the sound speed is evenly distributed, and the sound line propagates in a straight line.

3. The OFDM sound source distance depth estimation method based on a single hydrophone according to claim 1, characterized in that: The measurement model is based on coarse synchronization before OFDM demodulation, obtains signal arrival time, and constructs frequency domain input-output relationship.

4. The OFDM sound source distance depth estimation method based on a single hydrophone according to claim 1, characterized in that: The multi-snap measurement matrix is ​​constructed by dividing the observation vector into overlapping sub-vectors, utilizing the Vandermonde form and translation invariance of frequency-domain equally spaced pilots.

5. The OFDM sound source distance depth estimation method based on a single hydrophone according to claim 1, characterized in that: The multipath delay estimation is implemented through singular value decomposition and rotation invariant subspace algorithm to obtain the estimated value of the time offset parameter.

6. The OFDM sound source distance depth estimation method based on a single hydrophone according to claim 1, characterized in that: The target positioning is based on a relative time delay feature matching method, and the source direction estimation is achieved by minimizing the objective function.

Images