| Underwater acoustic communication technology,as the only long-distance and efficient underwater communication mode,is the key technology to ensure information transmission in the underwater work process,and is widely used in military and civil fields.OFDM technology is a multi-carrier modulation technology with high spectral efficiency and anti-multipath fading characteristics,and is one of the key technologies in the fourth generation mobile communication.Because the underwater acoustic channel is a time-varying,space-varying and frequency-varying channel,the severe expansion,Doppler phenomenon and complex environmental noise bring great challenges to the application of OFDM technology in the underwater acoustic channel.The research of high-speed communication technology in complex underwater acoustic environment has important significance and broad application prospects.Based on the OFDM-MFSK communication system,focusing on the engineering problems in practical applications,this paper conducts research on communication system modeling,channel estimation technology and peak-to-average ratio suppression technology.Firstly,the thesis studies the OFDM-MFSK underwater acoustic communication system.The characteristics of underwater acoustic channel are analyzed and a simplified model is proposed.According to the characteristics of underwater acoustic channel,combined with MFSK modulation,a model of OFDM-MFSK communication system is proposed.Aiming at the problem of low frequency band utilization in OFDM-MFSK system,an OFDM-MFSK-DPSK communication system combined with differential phase modulation is proposed.The simulation results show that the two systems have excellent performance in corresponding channels.Secondly,this paper studies the channel estimation technology in underwater acoustic OFDM-MFSK-DPSK system.The channel estimation method based on the inserted pilot symbol in the non-blind channel estimation is mainly studied.In the OFDM-MFSK-DPSK underwater acoustic communication system,the channel estimation performance is analyzed by simulation from the pilot form,the estimation algorithm,the inserted pilot interval and the pilot value.Finally,this paper studies the peak-to-average ratio suppression technology in OFDM-MFSK-DPSK underwater acoustic communication system.The relationship between the peak-to-average power ratio(PAPR)of OFDM-MFSK-DPSK system and the total number of subcarriers in the system,the decimal number of MFSK modulation and the decimal number of DPSK is studied.Based on the selective mapping algorithm,the MG-SLM algorithm is proposed.The simulation results show that the MG-SLM algorithm can better reduce the PAPR of the system.Proposed μ-MGSLM algorithm,which combines MG-SLM algorithm and μ-law companding transformation can further improve the PAPR performance of OFDM-MFSK-DPSK system.Combined with channel estimation,the effect of algorithm is analyzed from three aspects : calculation complexity,PAPR suppression performance and bit error rate performance. |
