A time domain array processing method for underwater acoustic single-carrier communication based on ultra-short baseline array

Abstract

The present invention discloses a time-domain array processing method for underwater acoustic single-carrier communication based on an ultra-short baseline array, which belongs to the field of underwater acoustic communication. Specifically, each array element in the ultra-short baseline array uses a copy-related frame synchronization technology to process the single-carrier signal received simultaneously and estimate the integer delay portion. Then, each array element refines the integer delay through a three-point interpolation method to accurately calculate the fractional delay. After the signal is down-converted, phase compensation is performed on the fractional delay. Next, each array element estimates its own signal-to-noise ratio and performs weighted processing, adaptively adjusting the weighting factor. Finally, the signals that have undergone delay compensation and weighted processing are added and combined, and a single-carrier time-domain equalization method is applied to eliminate multipath interference. A decision feedback equalizer (DFE) is used to equalize the signal to further improve the reliability of the signal. The present invention improves the accuracy of signal reception. The method is simple, has low complexity, and is suitable for practical applications.

Description

Technical Field

[0001] The present invention belongs to the field of underwater acoustic communication, and in particular relates to a time domain array processing method for underwater acoustic single-carrier communication based on an ultra-short baseline array. Background Art

[0002] The ultrashort baseline array is composed of a transmitting transducer and a receiving hydrophone array. Its characteristics are that the array size is extremely small, only a few centimeters to tens of centimeters, and it has the advantages of integrated communication and positioning. The integration of the receiving part reduces the use of unmanned platforms and is particularly suitable for UUVs (unmanned underwater vehicles). Based on the above characteristics, the ultrashort baseline array has become an important part of underwater detection and communication technology.

[0003] With the continuous development of underwater acoustic communication technology, how to achieve high-quality signal reception and stable communication transmission in complex and changing underwater acoustic environments has become a technical problem that needs to be solved urgently.

[0004] The underwater acoustic communication environment is characterized by complex characteristics such as multipath propagation, noise interference, and channel fading. This results in severe signal delay, attenuation, and multipath interference during signal propagation. These issues pose significant challenges to traditional underwater acoustic communication systems in terms of signal processing and transmission reliability. This is especially true when using ultra-short baseline arrays for underwater acoustic communication, where multi-channel signal delay errors and noise interference have a particularly significant impact on the results. Therefore, effectively compensating for delay errors and enhancing the signal-to-noise ratio (SNR) have become key to improving the performance of underwater acoustic communication systems.

[0005] In existing underwater acoustic communication systems, such as the multi-channel equalization processing method proposed in the literature [1]. Stojanovic, M., JACatipovic and J.G. Proakis, Phase-coherent digital communications for underwater acoustic channels [J]. IEEE journal of oceanic engineering, 1994. 19(1): p. 100-111., although it can improve signal quality to a certain extent, its equalizer length is usually long and the system complexity is high, which makes it difficult to meet the needs of practical applications. For example, the signal processing steps based on the traditional equalization algorithm are numerous, the computational complexity is high, and the real-time performance is poor, making it impossible to achieve efficient and stable communication in a complex underwater acoustic environment. In addition, the influence of multipath interference and noise often leads to a significant decrease in signal reception quality and system reliability, limiting the practical application effect of the underwater acoustic communication system. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention proposes a time-domain array processing method for underwater acoustic single-carrier communication based on an ultra-short baseline array. The method accurately estimates and compensates for the time delay through a fractional delay estimation method, performs weighted processing on the array elements using a signal-to-noise ratio weighting method, then combines the signals, and finally processes them through a time-domain equalizer, thereby significantly improving the performance of single-carrier time-domain array processing.

[0007] The underwater acoustic single-carrier communication time domain array processing method based on an ultra-short baseline array comprises the following steps:

[0008] Step 1: Each element in the ultra-short baseline array simultaneously receives the same single-carrier signal for underwater communication and performs pre-processing;

[0009] Step 2: Each array element uses the copy-correlation frame synchronization technology to process the received single-carrier signal and estimate the integer delay part;

[0010] For the kth array element, the received signal is copied and correlated with the synchronization header signal to find the time t corresponding to the peak point of the output waveform. k , which is used as the estimated integer delay corresponding to the array element.

[0011] The waveform of the copy-related output is expressed as

[0012]

[0013] When τ=t0, Taking the maximum value, near the peak, it is approximately a cosine function; B(τ) is the signal amplitude, ω0 is the signal angular frequency;

[0014] Step 3: Each array element refines the integer delay using the three-point interpolation method to accurately calculate the fractional delay;

[0015] Step 4: After the signal is down-converted, phase compensation for fractional delay is performed on each array element signal to ensure that the phases of the signals in each channel are aligned after delay compensation.

[0016] For the kth array element, after down-converting the signal, the estimated integer delay t is first used k To intercept the signal, k Intercept to the end of the signal. Then multiply the kth channel by the corresponding where f c is the center frequency of the signal, is the fractional delay estimated for the kth array element.

[0017] Step 5: Each array element estimates the signal-to-noise ratio of the received single-carrier signal;

[0018] The signal-to-noise ratio is:

[0019]

[0020] P n To estimate the noise power using pure noise segment; P s is the power of the noise-free signal.

[0021] Step 6: Perform weighted processing on each signal-to-noise ratio and adaptively adjust the weighting factor of each array element to maximize the output signal-to-noise ratio;

[0022] Assume that the receiving end receives M diversity channels, and the received signal of channel m is r m (t), then the output signal R(t) after merging is

[0023]

[0024] where ω m Represents the weighting factor of each diversity branch, and adaptively adjusts the weighting factor of each branch:

[0025] ω m ∝SNR m

[0026] Where SNR m is the signal-to-noise ratio of the mth channel.

[0027] Step 7: Add and combine the signals after delay compensation and weighting processing;

[0028] Step 8: Apply single-carrier time-domain equalization to the combined signal to eliminate multipath interference; use a decision feedback equalizer (DFE) to equalize the signal to further improve signal reliability.

[0029] The advantages of the present invention are:

[0030] 1) The present invention provides a time-domain array processing method for underwater acoustic single-carrier communication based on an ultra-short baseline array, which accurately estimates and compensates for time delay through a fractional delay estimation method, thereby improving the accuracy of signal reception;

[0031] 2) The present invention provides a time-domain array processing method for underwater acoustic single-carrier communication based on an ultrashort baseline array. The method uses a signal-to-noise ratio weighting method to perform weighted processing on array elements, and then performs signal merging, thereby enhancing the contribution of high signal-to-noise ratio signals and maximizing the output signal-to-noise ratio.

[0032] 3) The present invention provides a time-domain array processing method for underwater acoustic single-carrier communication based on an ultra-short baseline array, which is ultimately processed by a single-carrier time-domain equalizer, thereby reducing the impact of multipath interference and improving signal reliability;

[0033] 4) The present invention provides a time-domain array processing method for underwater acoustic single-carrier communication based on an ultra-short baseline array. The method is simple, low in complexity, and suitable for practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a flow chart of a time domain array processing method for underwater acoustic single-carrier communication based on an ultra-short baseline array according to the present invention.

[0035] Figure 2 This is a frame structure diagram of the signal transmitted in the present invention.

[0036] Figure 3 This is a block diagram of the receiver used in the present invention.

[0037] Figure 4 This is a simulation diagram of the fractional delay estimation and compensation method in the present invention. DETAILED DESCRIPTION

[0038] To facilitate understanding and implementation of the present invention by those skilled in the art, the present invention is further described below in detail with reference to the accompanying drawings and embodiments. It is apparent that the embodiments described are merely partial embodiments of the present invention, not all embodiments. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0039] The time-domain array processing method for underwater acoustic single-carrier communications using an ultra-short baseline array aims to achieve superior signal reception performance and system reliability through a series of simplified and efficient signal processing steps. By receiving signals from multiple array elements and performing precise time delay estimation and compensation, combined with signal-to-noise ratio weighted processing and single-carrier time-domain equalization, the accuracy and reliability of signal reception can be significantly improved in complex underwater acoustic communication environments. This novel time-domain array processing method not only maintains low system complexity while providing more efficient signal processing performance, but also has important practical application value and broad prospects.

[0040] The time domain array processing method for underwater acoustic single-carrier communication based on ultra-short baseline array is as follows: Figure 1 As shown, the following steps are included:

[0041] Step 1: Use an ultra-short baseline array to receive underwater communication single-carrier signals;

[0042] Each element in the ultra-short baseline array receives the same single-carrier signal for underwater communication at the same time, but due to different positions, the received signals will have slight delay differences and different noise interference.

[0043] The received signal is preprocessed, including filtering and downsampling; the purpose of preprocessing is to reduce noise and interference, improve signal quality, and lay the foundation for subsequent delay estimation and signal processing.

[0044] The transmission and reception frame structure is as follows Figure 2 As shown, it is composed of a synchronization header signal and a data part, with a blank part in the middle. The specific structure of the data part is the alternation of three training sequences and two information sequences;

[0045] Step 2: Each array element processes its received single-carrier signal using a copy-correlation frame synchronization technique to estimate the arrival time and initial integer sampling point delay of each array element signal.

[0046] For the kth array element, the received signal is copied and correlated with the synchronization header signal to find the time t corresponding to the peak point of the output waveform. k , which is used as the estimated integer delay corresponding to the array element.

[0047] Step 3: Each array element refines the initially estimated integer delay using the three-point interpolation method to accurately calculate the fractional delay;

[0048] The three-point interpolation method is as follows:

[0049] The synchronization head signal is generally a Doppler-insensitive linear frequency modulation signal or a hyperbolic frequency modulation signal. Taking the linear frequency modulation signal as an example, its copy-related output waveform can be expressed as

[0050]

[0051] When τ=t0, Taking the maximum value, near the peak, it is approximately a cosine function; B(τ) is the signal amplitude, ω0 is the signal angular frequency;

[0052] Assume the fitting function is

[0053] r(τ)=A r cosω r τ+B r sinω r τ

[0054] Using the peak point r(τ2)=r2 estimated in step 2, select a point (τ1,r1) and a point (τ3,r3) before and after the point (τ2,r2), then we have

[0055]

[0056] Since τ2-τ1=τ3-τ2=t s ,but

[0057] r3sinωr t s =r2sin2ω r t s -r1sinω r t s

[0058] Divide both sides of the equation by sinω r t s , we can estimate the value of the oscillation frequency by sorting:

[0059]

[0060] The fitting curve can be expressed as:

[0061]

[0062] in and

[0063]

[0064] so

[0065]

[0066] When r When τ=kπ+φ (k is a non-negative integer), |r(τ)| takes the maximum value. At this time,

[0067]

[0068] This is the estimated delay.

[0069] Step 4: After down-conversion, phase compensation is performed on each element signal to ensure that the phases of the signals in each channel are aligned after delay compensation, thus preventing phase deviation from affecting the beamforming results.

[0070] For the kth array element, after down-converting the signal, the estimated integer delay t is first used k To intercept the signal, k Intercept to the end of the signal. Then multiply the kth channel by the corresponding where f c is the center frequency of the signal, is the fractional delay estimated for the kth array element.

[0071] Step 5: Each array element estimates the signal-to-noise ratio of the received single-carrier signal;

[0072] Assume that the noisy signal of a channel at the receiving end can be expressed as the sum of the noise-free signal s(t) and the noise n(t)

[0073] r(t)=s(t)+n(t)

[0074] The power of the received noisy signal is:

[0075]

[0076] Estimate the power of the noise using a pure noise segment:

[0077]

[0078] The power of the noise-free signal is:

[0079] P s =P r -P n

[0080] The signal-to-noise ratio of the received signal is:

[0081]

[0082] P n To estimate the noise power using pure noise segment; P s is the power of the noise-free signal.

[0083] Step 6: Perform weighted processing based on the estimated signal-to-noise ratio of the signal received by each array element. Adaptively adjust the weighting factor of each array element to maximize the output signal-to-noise ratio and improve signal quality.

[0084] The specific method of weighting based on the signal-to-noise ratio is:

[0085] Assume that the receiving end receives M diversity channels, and the received signal of channel m is r m (t), then the output signal R(t) after merging is

[0086]

[0087] where ω m Represents the weighting factor of each diversity branch. According to the SNR weighting criterion, the SNR of the combined output signal can reach the theoretical maximum. Based on the criterion of maximizing the output SNR, the weighting factor of each branch is adaptively adjusted:

[0088]

[0089] where α m is the signal amplitude, N m is the noise power.

[0090] The weighting factor is related to the signal-to-noise ratio of each channel. Channels with high signal-to-noise ratios have larger weighting factors. If the signal amplitudes of each channel are equal, the weighting factor is determined by the power of the noise received by each branch. These characteristics enable signal-to-noise ratio weighting to maximize the output signal-to-noise ratio under any fading characteristics.

[0091] Step 7: Add and combine the signals after delay compensation and weighting processing;

[0092] Merge the delay-aligned and weighted channels to further improve the signal-to-noise ratio after processing and enhance the reception quality of the target signal.

[0093] Step 8: Apply single-carrier time-domain equalization to the combined signal to eliminate multipath interference. A decision feedback equalizer (DFE) is used to equalize the signal to further improve signal reliability.

[0094] The signal is equalized using a decision feedback equalizer and RLS algorithm, and a second-order digital phase-locked loop is added to enhance system performance.

[0095] The overall block diagram of the receiver of this underwater acoustic single-carrier communication time domain array processing method based on ultra-short baseline array is as follows: Figure 3 As shown, for n array elements, the rough estimates of their respective delays are time t1, t2, ..., t n , the corresponding delay fine estimation is t'1,t'2,...,t' n After the signal is down-converted, each channel is multiplied by the corresponding The respective signal-to-noise ratio estimates are obtained, added and combined, and then equalized to output the final result.

[0096] Example:

[0097] The time-domain array processing method for underwater acoustic single-carrier communication for ultra-short baseline arrays proposed in this invention was simulated and verified:

[0098] The simulation is for an ultra-short baseline five-element array with an array spacing of half a wavelength. The basic signal parameters are shown in Table 1.

[0099] Table 1 Simulation signal parameters

[0100] parameter set up communication system Single carrier Modulation method BPSK Operating frequency band 20.75-29.25kHz Center frequency 25kHz Communication rate 5kbps Shaping filter Square root of raised cosine, alpha = 0.7, span = 6 Synchronous header HFM signal (20-30kHz bandwidth, 10ms duration) Training sequence N = 255 length m sequence, 5kcps

[0101] Under this simulation condition, a delay of 1.4(k-1) sampling points is added to the kth channel, and the uncompensated and compensated array processing methods are used for processing. The simulated SNR-BER curve is as follows: Figure 4 As shown in the figure, in the case of fractional delay, the fractional delay estimation and compensated array processing method has a lower bit error rate than the original method.

[0102] The time domain array processing method for underwater acoustic single-carrier communication for ultra-short baseline arrays proposed in the present invention is verified by field data processing.

[0103] The field test and simulation have the same signal parameters and receiving array type. The field test has a total of 2590 frames. As shown in the figure, each frame has two information sequences, a total of 5180. The number of packet losses and processing time are shown in Table 2.

[0104] Table 2 Field data array processing results

[0105]

[0106] The results show that the present invention effectively improves the performance of the single-carrier time-domain array processing method through the comprehensive application of methods such as accurate delay estimation and compensation, signal-to-noise ratio weighted merging and time-domain equalizer processing, and has significant technical advantages and broad application prospects.

Claims

1. A time domain array processing method for underwater acoustic single-carrier communication based on an ultra-short baseline array, characterized in that: The specific steps are as follows: Step 1: Each element in the ultra-short baseline array simultaneously receives the single-carrier signal of underwater communication and performs pre-processing; Step 2: Each array element uses the copy-correlation frame synchronization technology to process the received single-carrier signal and estimate the integer delay part; For the kth array element, the received signal is copied and correlated with the synchronization header signal to find the time t corresponding to the peak point of the output waveform. k , which is used as the estimated integer delay corresponding to the array element; Step 3: Each array element refines the integer delay using the three-point interpolation method to accurately calculate the fractional delay; Step 4: After the signal is down-converted, phase compensation for fractional delay is performed on each array element signal to ensure that the phases of the signals in each channel are aligned after delay compensation. For the kth array element, after down-converting the signal, the estimated integer delay t is first used k To intercept the signal, k Intercept to the end of the signal; then multiply the kth channel by the corresponding where f c is the center frequency of the signal, is the fractional delay estimated for the kth array element; Step 5: Each array element estimates the signal-to-noise ratio of the received single-carrier signal; Step 6: Perform weighted processing on each signal-to-noise ratio and adaptively adjust the weighting factor of each array element to maximize the output signal-to-noise ratio; Assume that the receiving end receives M diversity channels, and the received signal of channel m is r m (t), then the output signal R(t) after merging is where ω m Represents the weighting factor of each diversity branch, and adaptively adjusts the weighting factor of each branch: oh m ∝SNR m Where SNR m is the signal-to-noise ratio of the mth channel; Step 7: Add and combine the signals after delay compensation and weighting processing; Step 8: Apply single-carrier time-domain equalization to the combined signal to eliminate multipath interference; A decision feedback equalizer is used to equalize the signal to further improve the reliability of the signal.

2. The method for processing underwater acoustic single-carrier communication time domain array based on ultra-short baseline array according to claim 1, characterized in that: In the step 2, the waveform of the copy-related output is expressed as When τ=t0, Taking the maximum value, near the peak, it is approximately a cosine function; B(τ) is the signal amplitude, and ω0 is the signal angular frequency.

3. The time domain array processing method for underwater acoustic single-carrier communication based on ultra-short baseline array according to claim 1, characterized in that: In step 5, the signal-to-noise ratio is: P n To estimate the noise power using pure noise segment; P s is the power of the noise-free signal.

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