Precise frame synchronizing method in hydroacoustic communication

Abstract

The present invention relates to a method for accurate frame synchronization in underwater acoustic communication, which mainly includes the following steps: 1) digitally process the received signal, respectively use s u (t) and s d The copy of (t) performs copy correlation processing on the received signal r(t), and calculates the absolute value of the correlation function |C u (τ)| and |C d (τ)|2)|C u (τ)|, |C d (τ)| is compared with a set threshold, if it is smaller than the threshold, then return to step 1) for related processing, if |C u (τ)| and |C d (τ)| exceeds the threshold, it is judged that there is a synchronous pulse arrival, and the calculation is transferred to step 3; 3) Calculate |C u (τ)| and |C d The time τ corresponding to the maximum value of (τ)| u and τ d , and calculate the interval Δ between the positions of the two correlation peaks, and then calculate the relative Doppler β; 4) calculate the midpoint Λ of the positions of the two correlation peaks, and use this as the time starting point of the synchronization signal. The present invention has the advantages that accurate Doppler estimated value and time-of-arrival estimated value can be provided, and these two estimated values ​​are very important for underwater acoustic communication under certain conditions, which can effectively improve the communication effect, and can also greatly reduce the Small amount of computation for decoding.

Description

technical field [0001] The invention relates to the field of underwater acoustic communication, and mainly relates to a precise frame synchronization method in underwater acoustic communication. Background technique [0002] Underwater acoustic communication refers to the related technology of acoustic communication in seawater medium. Compared with radio communication and wired communication, underwater acoustic communication is a more complex communication method, and its complexity is mainly reflected in the time of communication signals. Dimension broadening and frequency dimension divergence. The factors that cause the signal to broaden in the time dimension include multipath propagation effects, the influence of ocean currents, and the propagation of energy on the seabed, etc. The factors that cause the signal to diverge in the frequency dimension include relative motion between transceiver platforms, ocean currents (such as tides, internal waves, eddies, etc.) Influe...

AI Technical Summary

Problems solved by technology

[0003] There are three main methods of frame synchronization in the past: one method is to use a linear frequency modulation pulse signal (abbreviated as LFM signal) or a pseudo-random sequence signal (such as m sequence) as the frame header, and to process the LFM signal or m sequence in the receiving process. The signal is processed by pulse compression, so that the arrival time of the pulse can be extracted, such as figure 1 As shown, this method is simple and effective, but it cannot estimate the relative Doppler value, and it is only suitable for low Doppler occasions, such as when a fixed platform based on the seabed transmits underwater measurement data to moored buoys on the water surface, because the platform If the relative motion rate between them is very small, you can use this frame header and frame synchronization method

[0004] The second method is to transmit an LFM signal first, and then transmit a single-frequency pulse signal (abbreviated as CW pulse). In the receiving process, the pulse arrival time can be extracted by performing pulse compression processing on the LFM signal. For the CW pulse Spectrum analysis can measure the Doppler frequency deviation value, such as figure 2 As shown, the quasi-synchronous estimation of pulse arrival time and Doppler frequency offset is realized in this way. This method is also relatively simple in implementation, but to achieve higher spectral resolution, it is necessary to use a longer pulse width CW Pulse, which actually takes up the communication time and reduces the communication rate

This method has better performance, but there are difficulties in implementation. The main reason is that it is necessary to save a complete subframe signal before estimating the Doppler frequency offset value, which takes up a lot of computer memory, especially This problem is more prominent when the subframe is longer

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