Chaotic hybrid spread spectrum secure underwater acoustic communication method

Abstract

The invention discloses a chaotic hybrid spread spectrum secure underwater acoustic communication method. The method comprises the following steps: 1) a transmitting end uniformly groups a binary sequence sent by an information source, each group is divided into three blocks, the first block is subjected to BPSK modulation and Gray mapping, the second block is subjected to M-element chaotic phase modulation CPM spread spectrum sequence mapping, and the third block is modulated into a chaotic frequency modulation spread spectrum CFM signal; mixing and modulating the output three types of orthogonal signals to obtain a chaotic mixed spread spectrum CHSS signal to be transmitted, and converting the CHSS signal into an analog signal for transmission; 2) converting the received underwater acoustic analog signal into a digital signal by the receiving end, using an in-phase branch BPSK spread spectrum signal in chaotic phase modulation spread spectrum as a pilot signal, and performing time-frequency two-dimensional search on the signal by using the spread spectrum gain of the chaotic phase modulation spread spectrum code to complete time-frequency synchronization; and demodulating the signal after time-frequency synchronization, adopting an incoherent maximum likelihood demodulation algorithm for M-element CPM and CFM spread spectrum, and adopting a coherent demodulation algorithm for BPSK to complete M-element despreading and coherent demodulation, thereby obtaining a binary sequence.

Description

technical field [0001] The invention relates to the technical field of underwater acoustic communication, in particular to a method for secure underwater acoustic communication with chaotic mixing and spread spectrum. Background technique [0002] With the increase of people's ocean development and the increase of demand for marine resources, the realization of robust and confidential underwater acoustic communication has become a new research hotspot. The strong attenuation characteristics of the seawater medium lead to the narrow transmission bandwidth of the underwater channel. The complex and changeable underwater acoustic environment and the low propagation speed of the underwater acoustic signal make the underwater acoustic channel one of the most complex channels. Due to the existence of spread spectrum gain, spread spectrum communication has good anti-noise and anti-multipath interference characteristics, and is widely used in the field of long-distance underwater ac...

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Problems solved by technology

However, the strong anti-noise performance of spread spectrum communication is at the expense of spectrum utilization, and the communication data rate is usually very low; the conventional pseudo-random (Pseudo-Noise, PN) sequence used in traditional spread spectrum communication has obvious periodicity Once the signal is intercepted, the corresponding features such as chip rate and code period are easy to be extracted and used by the enemy, resulting in information leakage

[0003] In the prior art, the M-element direct-sequence spread spectrum (Direct-Sequence Spread Spectrum, DSSS) communication method utilizes the combination of multiple spread spectrum sequences to carry information bits, which improves the data rate of spread spectrum communication to a certain extent; combined spread spectrum communication The data rate can be further improved on the basis of the M element, but it is difficult to ensure complete orthogonality between the superimposed spreading codes, so there is mutual interference, which reduces the bit error rate performance of the system; the cyclic shift of the double orthogonal channel The Cyclic Shift Keying (CSK) spread spectrum communication method modulates information on the symbol phase, and uses the size of the symbol phase to represent information. On the one hand, it improves the bandwidth utilization of the spread spectrum communication system. Traffic lanes solve the problem of inter-channel interference, but bandwidth utilization is still limited

[0004] The above-mentioned communication methods are all communication methods in a non-secure environment, without considering the anti-interception ability of the signal, using chaotic sequences instead of conventional Gold codes or Kasami sequences, using chaotic sequences that are noise-like, pseudo-random, aperiodic, and extremely sensitive to initial values. Sensitive characteristics solve the problem of regular PN code periodicity and greatly improve the security of communication. However, due to the binary quantization of the original chaotic sequence during the signal generation process, the processed chaotic sequence is different from the ordinary PN sequence. The essence is the same, and the quantization causes the correlation to decrease, and the available quantity decreases; the probability of signal detection is reduced by using burst communication. Although the probability of interception can be reduced to a certain extent, this method will greatly reduce the effective communication rate.

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