Jingwei Yin

This paper describes a three-step frequency-domain equalization scheme for multiple-input multiple-output (MIMO) underwater acoustic communication. First, an iterative least-squares channel estimation method is developed to enhance the accuracy of channel estimation in MIMO communication. The interference rejection combining method is then adopted to suppress co-channel interference based on the estimated MIMO channels. This technique exploits the correlation between the interference received through different channels. Finally, a decision feedback equalizer embedded with a digital phase-lock loop is cascaded before the final determination of equalized symbols to compensate the phase rotation. Experimental results show that the bit error rates of the proposed scheme can be several orders of magnitude lower than those of conventional frequency-domain equalization schemes.

In this paper, the authors address the design of optimal waveform for target detection and parameter estimation based on the features analysis of the whistle of Indo-pacific humpback dolphins. A set of types of waveforms exist in the sequence of whistle calls. Considering the perfect performance of non-linear frequency modulated and multi-harmonics structure in anti-range sidelobe and anti-reverberation, several fusion schemes of several kinds of waveforms are explored and fusion results are studied analytically and from simulation. It is concluded that the bionic harmonic fused signal shows good time resolution, and improve the performance of suppressing reverberation. Research result provides nice reference and application value in underwater sonar based on bionic acoustic signal.

In the field of multistatic remote detection for underwater target, as a time-variant and multi-path channel interfered by environmental noise, underwater acoustic environment limits the spatial share of channel and poses a great challenge against spatial-division-multiplexing(SDM) in multistatic detection. In this paper, a kind of method of spatial-division-multiplexing(SDM) in time-variant channel based on vector adaptive time-reversal technique is proposed. By using time-reversal technique, multi-path structure of channel is efficiently restrained ; Applied adaptive filtering, time-variant characteristic of channel is effectively suppressed; With single vector hydrophone, spatial focus of target echoes and noise interference suppression is accomplished by spatial filtering. Finally, excellent results are performed in spatial-division-multiplexing(SDM) of multistatic detection, supported by the experimental simulation.

Information is carried by the time delay between adjacent code elements in differential pattern time delay shift coding system. It has an ability of anti inter-symbol interference and the Doppler effects. In order to obtain higher communication rate and reduce the interference between channels, this paper proposes a dual-channel orthogonal modulation differential pattern time delay shift coding underwater acoustic communication method and selects the balance Gold sequence as Patterns. At the transmitter end, divide input bits into two channels to differential pattern time delay shift encode and modulate orthogonally. Then add the encoded signal of two channels together to transmit. At the receiver end, demodulate the received signal orthogonally, search the correlation peak position of patterns. And estimate time delay to restore the original input information. Dual parallel channel transmission mode effectively improves communication rate of differential Pattern time delay shift coding and the orthogonal modulation method greatly reduces the interference between channels. Simulation research is carried on for the method, at transmission data 2x10^4bit and SNR -5dB, information is recovered at a communication rate 205 bit/s with very low bit error rate.

With the increase of of marine resource and underwater users, developing a high-bit-rate underwater acoustic communication has become a hot topic. APSK (Amplitude and Phase-shift Keying) is a modulation technique having high efficiency in spectrum utilization, it attracts more and more attention in high-bit-rate underwater acoustic communication. Differential APSK (DAPSK) is modulated using differential amplitude and phase code in time domain, and it has higher bandwidth efficiency and be easier to realize the system than APSK. A transmission system based on DAPSK modulation and OFDM is presented to solve the problems of effectiveness and reliability in high-bit-rate underwater acoustic communication. Simulation results show that the system using DAPSK modulation has a better performance than those using APSK and QAM modulation.

With the development of underwater acoustic communication in military and commercial field and the urgent need for underwater wireless Ad Hoc networks, developing an intelligent and high-bit-rate underwater communication system is imminent. OFDM(Orthogonal Frequency Division Multiplexing) technology could be a good platform for cognitive underwater communication, which has advantages including high efficiency in spectrum utilization, faster communication speed and flexibility in choosing frequencies. A design scheme of the OFDM based cognitive underwater communication and block diagram are given. The system can intelligently choose NC-OFDM (Non-Contiguous OFDM), DOFDM (Differential OFDM) or Pilot-added OFDM communication schemes in order to meet different channel conditions and different rate requirements and to overcome the problem of data conflict and the waste of spectrum resources in multi-users’ competitive communication. Meanwhile, the system also can intelligently choose parameters in each scheme, such as sub-channel, pilot interval and error-correcting codes. The simulation results prove the feasibility and effectiveness of the OFDM based cognitive underwater communication.

With the increasing demands of underwater source development and the increase of users, underwater transfer information has also greatly increased and high-bit-rate underwater acoustic communication has become a hot topic in underwater acoustic communication research. MDAPSK (Multilevel Differential Amplitude and Phase-shift Keying) is a modulation technique having high efficiency in spectrum utilization, which transfers information by using differential amplitude and phase code, demodulates information by adopting coherent demodulation. It reduces the difficulty of system, and improves the speed of transmission. While OFDM (Orthogonal Frequency Division Multiplexing) has advantages including high efficiency in spectrum and faster communication speed. After describing the schemes of the two technologies, a design scheme which concerns application of MDAPSK in the OFDM based underwater communication was given. The convolutional codes are also used in this system to realize the effectiveness and reliability in high-bit-rate underwater wireless communication. The computer simulation and the channel pool experimentation show that the system has a better performance. Key words: MDAPSK; OFDM; convolution coding; high-bit-rate communication