Research On Chirp-MFCSK Underwater Acoustic Communication System Based On Orthogonal Chirp Pilot

In the 2020s,as humans entered the 5G era,the development of wireless communications has brought great convenience to humans.Compared with wireless communications,underwater acoustic communications are far from meeting human needs in underwater communications.Underwater acoustic communication technology is a popular direction with high demand and large development space at present.According to the development history and current situation of underwater acoustic communication,this paper finds that the underwater acoustic communication modulation technology has the disadvantages of low communication rate,low frequency band utilization,and high bit error rate.In addition,the multipath effect and time-varying characteristics of underwater acoustic channels are also greatly restrict the development of underwater acoustic communication technology.This paper proposes a"Chirp-MFCSK system under orthogonal chirp pilots" and analyzes and simulates its performance under this background.The "Chirp-MFCSK system under orthogonal chirp pilots" proposed in this paper is mainly divided into two parts.The first is the "Chirp-MFCSK system".This system is a two-dimensional digital modulation technology based on a Chirp signal with good correlation characteristics and spreading gain.The Chirp-MFCSK system in this paper uses the time-frequency gain characteristics of the Chirp signal.And the system digitally modulate the Chirp signal in two mutually orthogonal dimensions,which are the frequency dimension and the delay dimension.This two-dimensional modulation method is different from the traditional frequency shift keying(FSK)and cyclic shift keying(CSK).It combines the two dimensions to increase the resource utilization of the communication system without interfering with each other and increase the communication rate without reducing system performance.In this paper,the ChirpMFCSK system is simulated under AWGN channel and underwater acoustic multipath channel.The results show that Chirp-MFCSK has better bit error rate performance than traditional single-dimensional modulation under both channels.This paper also proposes an "orthogonal chirped pilot" method in order to adapt to the time-varying underwater acoustic channel better.This method takes advantage of the good orthogonality of the Chirp signal and uses two independent branches respectively.One of the branches sends orthogonal signals to communicate and the other sends orthogonal chirped pilot to estimate channel.This mechanism not only improves the real-time performance of the channel estimation results,but also saves the pilot transmission time for channel estimation and improve the communication rate.According to the research in this paper,the Chirp-MFCSK under the orthogonal chirp pilot method can accurately obtain the impulse response of the channel by using the"short-time iterative matching correlation channel estimation method" proposed in this paper.Finally,the system performance is further improved after the VTRM processing.