Qunfei Zhang

Single Carrier Frequency Domain Equalizer for Underwater Wireless Communication

Single carrier modulation with frequency domain equalizer is proposed for underwater acoustic channel. An unique training sequence, viewed as cyclic prefix, is inserted into transmitted sequences so that low complexity minimum mean square error (MMSE) frequency domain equalization (FDE) is used for combating the inter-symbol interference in the receivers. Maximum likelihood estimation for robust initial phase error and Doppler shift are derived by using training sequence. The receiver estimates the initial phase error, Doppler shift and underwater acoustic channelblock-by-block. Compare to zero padding or cyclic prefix of single carrier modulation, training sequence has the potential to provide more accurate estimation than decision-directed methods and alleviate the time-scale effect caused by significant Doppler shiftfor wideband acoustic signal. The proposed UWA communication system with single transmitter and single receiver has been tested in practical South China Sea on June 2007.xa0xa0At a distance of 30 km, the data rates of 450 bps and 900 bps are achieved with uncoded bit error rates of 4 out of 8333 (BPSK) and 103 out of 16666 (QPSK).

Reliable Mobile Underwater Wireless Communication Using Wideband Chirp Signal

Acoustic communication between fast-moving underwater vehicles is difficult due to the fact the ratio of the vehicle speed to the sound speed many times exceeds its counterpart in the mobile radio channels. Hence, symbol synchronization, as important as carrier frequency identification, is critical for mobile underwater wireless communication. In this paper, we propose a reliable mobileunderwater wireless communication using wideband chirp signals and a novel symbol self-synchronization method. The use of chirp signals takes advantage of the low Doppler sensitivity as well as their good autocorrelation properties. Several lake experiments and computer simulations have been carried out to verify the proposed system over different distances. Phenomenon of synchronization error accumulation caused by Doppler shift is presented. Our works show that the developed system is able to provide a reliable wireless link between fast-moving underwater vehicles. The achieved data rateis 300 bps with uncoded bit error rate around

Detecting the Number of Sources Using Modified EGM

10^{-3}

High-speed underwater acoustic communication based on OFDM

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M-ary Chirp Spread Spectrum Modulation for Underwater Acoustic Communication

10^{-5}

A novel joint estimator of direction-of-arrival and time-delay for multiple source localization

when the relative speed is as large as 18 m/s (36 knots).

Ship wakes 3D simulation based on OSG

In the array signal process field, to estimate the direction of arrival (DOA) of sources, it is a key problem to estimate the number of signal source correctly. Luo Jingqing proposed a set of eigenvalue gradient methods (EGMs), which showed better performances of number-detection than traditional AIC and MDL method. However, EGMs doesnt take the false-alarm probability (PFA) into account, which causes high PFA while no source exists. In this paper, after some analysis to the average eigenvalue-gradient distribution of the pure noise auto-correlation matrix, a modification is introduced to improve the PFA performance of EGMs. Computer simulation results shows that the modification is efficient, and bring only tiny loss of number-detection probability in very low SNR

Self-differential joint frequency and phase modulation for long-range underwater acoustic communications

Due to multipath propagation and frequency selective fading, there are many obstacles for reliable and high data rate underwater acoustic (UWA) communication. OFDM is an attractive technique beginning used in UWA communication with three obvious advantages: good performance against multipath interference, ability to combat the frequency selective fading and the high frequency band efficiency. Recently, the researches of Refs. 1, 2, 3, 4, 5 focus on short-range UWA communication. In this paper, we pay attention to medium-range (10 km) UWA communication based on OFDM. An OFDM system is designed and realized. Several important problems are described in which the characteristics of UWA channel is analyzed, Doppler frequency shift is estimated by using cyclic prefix and compensated by resampling the received signal. Experiments in a lake were conducted and its performance is investigated. Experimental results show that the data rate reach 9 kbps and 2.8 kbps at a distance of 5 km and 10 km respectively with the bit error rate (BER) below 10/sup -4/.

Maximum Likelihood DOA Estimator Based On Importance Sampling

M-ary chirp spread spectrum modulation (MCSS) for medium range underwater acoustic (UWA) communication is proposed in this paper. The method of MCSS uses M-ary different chirp signals to represent message at the transmitter and a bank of correlators to demodulate the message at the receiver. There are three advantages for MCSS applied to UWA communication: good performance against multipath interference and channel fading, higher data transmission rate with robustness and larger processing gain. Experimental results in the lake show the efficiency for MCSS that is in the distance of 25 km, the data rate can reach 300 bps with BER below 10-4.

Coherent signal-subspace focusing to frequency dependent modeling for DOA estimation of wide-band sources

Source localization is one of the important topics in signal processing, in which a key problem is to jointly estimate direction-of-arrival (DOA) and time-delay for multiple sources. In this paper, a novel and efficient algorithm of joint DOA and time-delay estimation (named as ESPRIT-TDF algorithm) is proposed. Based on constructing two special types of covariance matrixes for two identical subarrays, both DOA and time-delay can be estimated simultaneously via rotational invariance technique and high-resolution time-delay frequency (TDF) technique. This algorithm is not only easy to be implemented with low computation but also suitable for multiple source localization where the non-minimum phase signal is frequently employed. Computer simulations and experiments in water tank are conducted to show the improved performance in precision and resolution by using the ESPRIT-TDF algorithm.