Study Of Hydroacoustic Chirp-rate Modulation Based On Differential Pattern Encoding

Underwater acoustic communication technology is one of underwater equipmentcommunications,navigation underlying technology. The realization of real-time, high-speed,steady underwater acoustic communication in remarkable multi-path effect, obviousdoppler effect and bandwidth-limited underwater acoustic channel is significant. In thispaper, a underwater acoustic communication scheme which combines chirp spreadspectrum and differential Pattern delay coding is proposed, due to the impact caused bybandwidth-limited underwater acoustic channel signal multipath and doppler effect.Firstly, the paper introduces the basics of underwater acoustic communication,including the basic components of the system and a classic multi-path acoustic channelmodel. It details principles of the Pattern delay coding and differential Pattern delay coding,and analyzes its anti-multipath performance, anti-doppler performance and interference,and further on validate its performance trough simulation on Matlab platform.Then, the paper proposes the modulation algorithm which combines spread spectrumand differential Pattern delay difference coding, which spread uses Chirp-Rate Modulation(CRM) chirp spread spectrum. On the one hand, CRM has a strong anti-multipath capability,and anti-doppler effect. On the other hand, it can increase the width of symbols for limitedbandwidth acoustic channel, when using the Chirp signal as a differential Pattern time delaycoding pattern. A further aspect, the rate of underwater acoustic communications has beengreatly improved33.3%compared to Pattern time delay coding, as one information symbolwill simultaneously transmit two-dimensional information with the information carried bythe delay difference and information with Chirp signal.Finally, the paper also proposes a new demodulation algorithm to realize the twodimensional decoding including delay information and Chirp information, by focusingeffect on Chirp signal of different frequency modulation slope in different u fractionaldomain using the fractional Fourier transform (FRFT). On Matlab platform, through a largenumber of system simulation experiments, under the premise of SNR0dB and the dopplershift is greater than30Hz, the error can be controlled account to10e5as opposed to acopy of the relevant decodes. The simulation results confirms the CRM-DPDS underwater acoustic communication system has strong resistance of multiplicity, doppler resistance,anti-jamming performance and it has a strong robustness.