En Cheng

An underwater acoustic implementation of DFT-spread OFDM

This paper presents a design of DFT-spread OFDM system applied to an underwater acoustic channel. It does not only combine all the advantages of a conventional OFDM system but also reduces the peak-to-average power ratio of the transmit signal. Besides, the scheme spreads the information over several subcarriers as a result of the application of an additional DFT operation and leads to a diversity gain in a frequency-selective fading channel, which is one of the many challenges of communicating data through an underwater acoustic channel. Simulation results show that our proposal possesses good bit-error-rate performance. The system has been tested in a real underwater acoustic channel—the experimental pool in Xiamen University. The experimental results show that the DFT-spread OFDM system can achieve better results than a simple OFDM system in a benign underwater channel.

A comparison of modulation in underwater acoustic DFT-SOFDM system

The DFT-SOFDM is a high speed underwater acoustic communication technology even for underwater military communication. In this paper, different kinds of modulation schemes were compared in the underwater acoustic DFTSOFDM communication system. The comparison results in real underwater acoustic channels showed that, when the underwater acoustic channels were static, each scheme had the same BER performance; when the channels were changing quickly, the BER performances of different modulation scheme were different.

Narrowband interference suppression in underwater acoustic OFDM system

Orthogonal Frequency Division Multiplexing (OFDM) is well known as a very attractive technology for communication. However, because of the spectral leakage in discrete Fourier transform, the spectrum of narrowband interference is spreaded to impact adjacent sub-carriers in OFDM system. Receiver window function was previously implemented to suppress narrow-band interference. In this paper, different kinds of receiver window functions were compared in the underwater acoustic OFDM system. The results of simulation and experiment show that the raised cosine window can suppress NBI and reduce the BER.

Impulsive noise suppression in DFT-SOFDM system

The DFT-SOFDM is a high date rate underwater acoustic transmission scheme even for underwater military communication. It has been widely studied to overcome the complexity of underwater acoustic channels. Generally speaking, multi-carrier transmission systems have many obvious advantages. They are less sensitive to impulsive noise than single-carrier systems. The longer symbol duration provides an advantage in a presence of impulsive noise. Nevertheless, it was recently recognized that this advantage turns into a disadvantage, if the impulsive noise energy exceeds a certain threshold. In this paper, nonlinearity methods for impulsive noise suppression in DFT-SOFDM receivers are considered. The experimental results of this comparative study show that the blanking nonlinearity performs better than the clipping nonlinearity.