Research On Beamforming And Its Application In Underwater Acoustic Communication

Multipath fading, band-limited, and co-channel interference are the major factors that affect the performance and capacity of broadband underwater acoustic communication. OFDM has higher spectral efficiency and favorable ability of anti-multipath interference, which is widely used to solve the problem, the influence of band-limited and multipath fading to the system performance in broadband water acoustic communication. Beamforming is considered as an important way to solve co-channel interference, which major function is making the receiver system to form space directivity, proceed with spatial filtering, suppress interference or noise, increase SNR of receiver, and improve the communication capability of system. When without extra transmitting power or band, applying beamforming technology in OFDM water acoustic communication can further increase the channel capacity of water acoustic communication system, and increase communication distance.The performance of the beamformer is determined by beamforming algorithm. MVDR beamforming algorithm has obvious advantage at interference suppression and azimuth resolution. However, MVDR is a narrowband signal processing method, which is not adapted to modulated broadband signal in OFDM water acoustic communication system. So narrowband MVDR algorithm shall be extended to broadband. This paper first focuses on researching broadband MVDR beamforming algorithm adapting to OFDM water acoustic communication, which includes broadband incoherent MVDR algorithm and STMV algorithm. Consequently, this paper presents an improved algorithm based on the cascade of CBF and STMV, which can solve the problem of interested orientation beam spectrum background heightening of STMV algorithm and effectively decrease the operand of STMV algorithm. The improved algorithm integrates the advantage of CBF and STMV algorithm, which has the characteristics of stable algorithm, high definition, strong anti-interference, etc.Based on the research of broadband MVDR beamforming algorithm, this paper presents and designs OFDM water acoustic communication system integrating CBF, STMV and improved STMV algorithm. Comparing with traditional single hydrophone OFDM system, the simulation result of applying beamforming technology indicates that the communication performance of OFDM system has been greatly improved.That verifies the feasibility and effectiveness of applying beamforming technology in OFDM water acoustic communication, and helps find a new technical way to realize long-distance and high speed water acoustic communication with increased channel capacity of OFDM and improved communication performance.