Automatic real-time frame synchronization method of frequency-modulated hydro-acoustic communication system

Abstract

The invention discloses an automatic real-time frame synchronization method of a frequency-modulated hydro-acoustic communication system, and relates to hydro-acoustic communication. The automatic real-time frame synchronization method of the frequency-modulated hydro-acoustic communication system comprises the following steps: at a transmitting terminal, sequentially transmitting a coarse synchronizing signal and a fine synchronizing signal both fixed in time length; and at a receiving end, performing sliding FFT (Fast Fourier Transform) on hydro-acoustic signals which are acquired from a transducer terminal in real time by a step size L at first, automatically judging coarse synchronization according to the first-increase and later-reduction trend of a F (f1) value in each spectrogram, calculating the attenuation coefficient a(t) of a channel to signals by using the received coarse synchronizing signal, automatically adjusting a fine synchronization threshold b and estimating the approximate time start c of the fine synchronizing signal, and finally, performing mutual correlation operation on the hydro-acoustic signals acquired from the start c according to the adjusted fine synchronization threshold b to obtain fine synchronization. A DMA (Direct Memory Access) module of a DSP (Digital Signal Processor) is used for setting a ping-pong buffer in which the hydro-acoustic signals acquired by an AD (Acquisition Device) can be stored without DSP intervention; as a result, automatic real-time tracking on synchronizing signals in up-and-down hydro-acoustic channels is realized; the quantity of operation is low and few memory resources are occupied.

Description

technical field [0001] The invention relates to underwater acoustic communication, in particular to an automatic real-time frame synchronization method of a frequency modulation underwater acoustic communication system. Background technique [0002] The propagation characteristics of sound waves in seawater are significantly superior to electromagnetic waves and visible light waves, making underwater acoustic technology one of the main research fields of marine high technology. The underwater acoustic communication technology is an important means of information transmission between various underwater vehicles, underwater robots, and between command ships, and is a key technology in underwater acoustic communication equipment. [0003] Ocean acoustic channel data transmission requires the system to have a high transmission rate and low bit error rate, but the underwater acoustic channel is an extremely complex random time-space-frequency variable parameter channel (Xu Xiaome...

AI Technical Summary

Problems solved by technology

First, when the single-frequency pulse signal is desynchronized, the amplitude spectrum value after FFT transformation is used for judgment, but the amplitude spectrum can only reflect the frequency domain information of the signal, and cannot reflect the time domain information of the signal. At the same time, signals with different time domains are transformed by FFT It can be exactly the same in the frequency domain. In principle, it can be seen that this method has poor anti-interference performance

Second, a fixed threshold is used for synchronous judgment of the two types of signals, ignoring the strong fluctuations caused by the underwater acoustic channel, which greatly reduces the probability of correct detection of synchronous signals in practical applications.

Third, in underwater acoustic communication, with the change of communication distance and the random time-space-frequency change of the channel, the signal-to-noise ratio of the receiving end changes randomly, while the fixed threshold can only satisfy the synchronization under the condition of a specific range of signal-to-noise ratio. Detection, when the signal-to-noise ratio is low, if you want to detect synchronization, you need to lower the threshold, which requires human intervention in practical applications, and the effect of real-time applications is greatly reduced

It can be seen that the traditional synchronization method makes it difficult to realize real-time and stable detection of synchronization signals in complex and changeable underwater acoustic channels.

Images