A time delay scale inversion method under broadband mobile underwater acoustic communication

Abstract

The application provides a time delay scale inversion method under wideband mobile underwater acoustic communication, which can effectively focus each path energy, enhance the receiving signal-to-noise ratio and improve the performance of the communication system by inverting along the time delay dimension and taking the reciprocal of the scale dimension. The application can effectively focus the multi-path energy and improve the receiving signal-to-noise ratio under the multi-scale time delay spread mobile underwater acoustic channel by using the two-dimensional sparse representation of the wideband mobile underwater acoustic channel in the time delay-scale dimension and inverting in the time and scale dimensions, solves the problem that the time inversion technology cannot realize energy focusing under the multi-scale time delay spread mobile underwater acoustic channel by one-dimensional time inversion, and effectively improves the performance of the wideband mobile underwater acoustic communication system.

Description

Technical Field

[0001] This invention relates to the field of signal processing, specifically to broadband mobile underwater acoustic communication technology, orthogonal frequency division multiplexing technology, time reversal technology, etc. Background Technology

[0002] Due to the relative motion between communication devices and the influence of factors such as wind, waves, and ocean currents, the signal received by the receiver is a superposition of multiple signals with different time delays and Doppler spreads. Furthermore, because the bandwidth of underwater acoustic communication is severely limited, the transmission bandwidth B and the center frequency f are affected. c The ratio is usually greater than 0.2, which does not satisfy the narrowband approximation condition (B / f). c <<1), therefore, the time-domain signal scaling caused by the Doppler effect cannot be ignored. The mobile underwater acoustic channel exhibits multi-scale delay spread fading characteristics. How to achieve reliable transmission under broadband mobile underwater acoustic communication is a current research challenge at home and abroad.

[0003] Currently, the main processing methods for multi-scale delay-spread fading channels can be divided into two categories. The first category is to select the optimal resampling factor. However, since the Doppler spread factor of each path is different, this method can only reduce the impact of average Doppler spread, and the residual interference still seriously limits the performance of the communication system. The second category is to perform multi-channel resampling technology, which mainly involves resampling each path according to the corresponding Doppler spread factor and then weighting and combining them. However, this technology will generate significant additional interference and has limited focused energy. To address the above problems, this invention proposes a delay-scale inversion technology, similar to time reversal technology. The proposed delay-scale inversion technology inverts the delay dimension and takes the reciprocal of the scale dimension, which can effectively focus the energy of each path in broadband mobile underwater acoustic channels to enhance the received signal-to-noise ratio and effectively solve the problem that traditional time reversal technology cannot achieve energy focusing under broadband mobile conditions. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a delay-scale inversion method for broadband mobile underwater acoustic communication. By inverting the delay dimension and taking the reciprocal of the scale dimension, this invention effectively focuses energy along each path in a broadband mobile underwater acoustic channel, enhancing the received signal-to-noise ratio and thus improving the performance of the communication system.

[0005] The steps of the technical solution adopted by the present invention to solve its technical problem are as follows:

[0006] Step 1: Use Orthogonal Frequency Division Multiplexing (OFDM) communication, where the subcarrier spacing is Δf and the OFDM symbol length is T = 1 / Δf;

[0007] Step 2: Generate a sequence by modulating the information sequence to be transmitted using Binary Phase Shift Keying (BPSK). That is, when the transmitted symbol information is 1, When the transmitted symbol information is 0 BPSK modulation generates a sequence Mapped onto the corresponding frequency domain subcarrier, we obtain the frequency domain subcarrier symbol X[m], m = 0, 1, ..., N-1, where m refers to the m-th subcarrier and N is the number of subcarriers;

[0008] Step 3: Convert the frequency domain subcarrier symbol X[m] into a continuous time domain signal s(t) for transmission using the Inverse Fast Fourier Transform (IFFT);

[0009] Step 4: The continuous time-domain signal s(t) is passed through the time-delay-scale spread channel h(τ,α) to obtain the received signal r(t);

[0010] Step 5: Construct the delay-scale inversion channel h DSR (τ',α');

[0011] Step 6: Combine the received signal r(t) with the time-delay-scale inversion channel h DSR Substituting (τ',α') into equation (5) yields the time-domain signal y(t);

[0012] Step 7: Map the time-domain signal y(t) to the frequency-domain Y[m], m=0,1,...,N-1 using Fast Fourier Transform (FFT);

[0013] Step 8: Perform BPSK demodulation on the frequency domain signal Y[m], m=0,1,...,N-1 to recover the original information sequence.

[0014] In step 3, the continuous time-domain signal s(t) is:

[0015]

[0016] Where t is a continuous time scale. Let j be the imaginary part of the pulse to be emitted, and m = 0, 1, ..., N-1.

[0017] The received signal r(t) is:

[0018]

[0019]

[0020] Where n(t) is additive white Gaussian noise, P is the number of propagation paths, τ and α are the path delay and Doppler spread factor of channel h(τ,α), respectively. i τ i and α i Let be the channel gain, path delay, and Doppler spread factor of the i-th path in channel h(τ,α), respectively, and δ(·) be the Dirac function.

[0021] The time-delay-scale inversion channel h in step 5 DSR (τ',α') is:

[0022]

[0023] Where τ' and α' are respectively the channel h DSR Path delay and Doppler spread factor of (τ',α').

[0024] In step 6, the time-domain signal y(t) is:

[0025]

[0026] in

[0027] In step 7, the time-domain signal y(t) is mapped to the frequency-domain Y[m], that is:

[0028]

[0029] in To receive pulses, superscript * Indicates conjugate.

[0030] The beneficial effects of this invention are as follows: In multi-scale delay-spread mobile underwater acoustic channels, this invention addresses the shortcomings of existing single-channel and multi-channel resampling techniques. Inspired by time reversal technology, it utilizes the two-dimensional sparse representation of the broadband mobile underwater acoustic channel in the delay-scale dimension to propose a delay-scale inversion technique. By performing two-dimensional inversion in both time and scale dimensions, it can effectively focus multipath energy and improve the received signal-to-noise ratio in multi-scale delay-spread mobile underwater acoustic channels. Furthermore, this invention solves the problem that time reversal technology, which only performs one-dimensional time reversal, cannot achieve energy focusing in multi-scale delay-spread mobile underwater acoustic channels. This invention can effectively improve the performance of broadband mobile underwater acoustic communication systems. Attached Figure Description

[0031] Figure 1 This is a comparative analysis chart of the bit error rate after delay-scale inversion processing under different signal-to-noise ratios according to the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0033] Step 1: This invention uses OFDM communication, with a subcarrier spacing Δf = 5Hz, OFDM symbol time T = 1 / Δf = 0.2s, and the number of subcarriers N = 1024;

[0034] Step 2: Modulate the information sequence to be transmitted using BPSK to generate a sequence X[m], m=0,1,...,N-1 and map it onto the corresponding frequency domain subcarriers;

[0035] Step 3: Convert the frequency domain symbol X[m], m=0,1,...,N-1 to a continuous time domain signal s(t) for transmission using IFFT transformation:

[0036]

[0037] Step 4: The time-domain signal s(t) is passed through a time-delay-scale spread channel h(τ,α) to obtain the received signal r(t), i.e.

[0038]

[0039]

[0040] Step 5: Construct the delay-scale inversion channel h DSR (τ',α'):

[0041]

[0042] Step 6: Combine the received signal r(t) with the time-delay-scale inversion channel h DSR Substituting (τ', α') into equation (11) yields the signal y(t), i.e.:

[0043]

[0044] Step 7: Map the time-domain signal y(t) to the frequency-domain Y[m], m=0,1,...,N-1, i.e.,

[0045]

[0046] in To receive pulses;

[0047] Step 8: Demodulate the frequency domain signal Y[m], m=0,1,...,N-1 using BPSK to recover the original information sequence;

[0048] Figure 1With OFDM modulation of N=1024 and BPSK mapping for the information sequence, the bit error rate analysis under different signal-to-noise ratios obtained from 100 Monte Carlo experiments shows that the system performance is significantly improved after time-delay-multi-scale inversion channel processing.

Claims

1. A delay scale reversal method for broadband mobile underwater acoustic communication, characterized in that... Includes the following steps: Step 1: Use orthogonal frequency division multiplexing (OFDM) communication, where the subcarrier spacing is... OFDM symbol length ; Step 2: Generate a sequence by performing binary phase shift keying modulation on the information sequence to be transmitted. That is, when the transmitted symbol information is 1, When the transmitted symbol information is 0, BPSK modulation generates a sequence Mapped onto the corresponding frequency domain subcarriers, resulting in frequency domain subcarrier symbols. ,in Refers to the first Subcarriers, This represents the number of subcarriers. Step 3: Convert the frequency domain subcarrier symbols using inverse fast Fourier transform. Convert to continuous time domain signal transmission; Step 4: Continuous Time Domain Signal Delay-Scale Spreading Channel The received signal was then obtained. ; Step 5: Construct a delay-scale inversion channel ; The delay-scale inversion channel for: (4) in and Channels Path delay and Doppler spread factor; Step 6: Receive the signal With delay-scale inversion channel Substituting into equation (5) yields the time-domain signal. ; Step 7: Convert the time-domain signal using Fast Fourier Transform. Mapping to the frequency domain ; Step 8: For frequency domain signals BPSK demodulation is performed to recover the original information sequence.

2. The delay scale reversal method for broadband mobile underwater acoustic communication according to claim 1, characterized in that: In step 3, the continuous time-domain signal for: (1) in For continuous time scale, Let j be the imaginary part of the emitted pulse. .

3. The delay scale reversal method for broadband mobile underwater acoustic communication according to claim 1, characterized in that: The received signal for: (2) (3) in It is additive white Gaussian noise. The number of propagation paths, and Channels Path delay and Doppler spread factor, , and Channels The Path channel gain, path delay, and Doppler spread factor. This is the Dirac function.

4. The delay scale reversal method for broadband mobile underwater acoustic communication according to claim 1, characterized in that: In step 6, the time-domain signal for: (5) in .

5. The delay scale reversal method for broadband mobile underwater acoustic communication according to claim 1, characterized in that: In step 7, the time-domain signal Mapping to the frequency domain ,Right now: (6) in To receive pulses, superscript Indicates conjugate.

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