Haixin Sun

Joint carrier frequency offset and impulse noise estimation for underwater acoustic OFDM with null subcarriers

Multicarrier modulation in the form of orthogonal frequency division multiplexing (OFDM) has been actively studied for underwater acoustic communications. In this paper, we investigate the OFDM performance in the presence of impulse-like noises. We present one method that estimates the carrier frequency offset (CFO) and the impulse noise separately, based on existing approaches, and one method that estimates them jointly. Simulation results in both time-invariant and time-varying channels have verified the receiver performance.

Driver fatigue detection through pupil detection and yawing analysis

Detecting driver fatigue is an important method to improving transportation safety. This paper presents a fatigue detection system based on pupil detection and yawning analysis. The parameters used for detecting fatigue are: eye closure duration measured through eye state information and yawning analyzed through mouth state information. Because of the IR illuminator, the system works robustly at night time.

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.

Impulsive Noise Mitigation in Underwater Acoustic OFDM Systems

Mitigation of impulsive noise has been extensively studied in wireline, wireless radio, and powerline communication systems. However, its study in underwater acoustic (UWA) systems is quite limited. This paper considers impulsive noise mitigation for underwater orthogonal frequency-division multiplexing (OFDM) systems, where the system performance is severely impacted by the channel Doppler effect. We propose a practical approach based on a least squares formulation: First, the positions of impulsive noise are determined in the time domain based on the signal amplitude, and second, impulsive noise samples are jointly estimated with the Doppler shift based on the measurements of the OFDM null subcarriers. Based on the available channel estimate and tentative data symbol decisions, an iterative receiver is further developed. Data sets have been acquired in a recent sea experiment near Kaohsiung city, Taiwan, in May 2013. Performance results based on extensive simulations and collected data sets demonstrate that the proposed receivers effectively mitigate impulsive noise for UWA OFDM systems.

Impulsive noise suppression in per-survivor processing based DSSS systems

Impulsive noise exists in many underwater acoustic communication environments, while traditional receivers often model it as an additive white Gaussian noise (AWGN). In a previous work, we proposed per-survivor processing (PSP) based receivers for direct sequence spread spectrum (DSSS) systems. In this work, we investigate two algorithms, passband and baseband clipping, for impulsive noise mitigation in PSP based DSSS systems. Simulation results show that both the passband and baseband clipping approaches can get better performance than the conventional receiver without clipping. Based on noise data collected from a sea test, the semi-experimental results show that both approaches can yield more than 1 dB gain if clipping ratios are properly selected, and that the passband clipping approach slightly outperforms the baseband clipping approach.

Dynamic network coded cooperative OFDM for underwater data collection

In this paper, we consider an underwater data collection problem, where multiple underwater nodes need to send data to one common destination. With the conventional ARQ protocol, the destination requests retransmission from each node individually without any node cooperation. We propose two protocols, selective relay cooperation and dynamic network coded cooperation, utilizing the fact that underwater nodes can overhear the transmission of others. In the selective relay cooperation, one node can be selected as a relay to transmit the data from another undecoded node in the retransmission round. In the network coded cooperation, the selected relay nodes transmit network coded packets, combining the packets from several undecoded nodes to the destination. The relay nodes participating the cooperation are selected by the destination based on the measured pilot signal to noise ratio of the underlying OFDM modulation. Simulation results based on one specific underwater topology show that the proposed schemes can achieve significant gains compared with the conventional ARQ scheme.

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.

A low complexity clustering optimization algorithm for underwater sensor networks

Aiming at issues of load imbalance and low energy efficiency in the existing underwater sensor network clustering algorithm, a novel global optimal clustering algorithm with the low complexity and parallel processing is proposed. The algorithm is based on the basic idea of particle swarm optimization algorithm (PSO). After the binary initial code of the sensor nodes, the particle code is adjusted by mutation to satisfy the ideal number of cluster heads. In the iterative process, new particles are generated by random recombination of the surviving nodes. In order to screen out the optimal particle, three optimization objectives are considered in the particle fitness function, which are cluster head energy, cluster head load and cluster range. Simulation results show that the proposed algorithm can effectively improve the load balance and prolong the network lifetime.

Detection of underwater moving object based on the compressed sensing

This paper proposes method of detecting the motion state of underwater targets based on compression sensing. A Linear frequency modulation signal is influenced by the moving state of the target under test, and its echo parameters such as the initial frequency, frequency modulation rate, and phase, will change according to the moving state of the target. Firstly, this method uses the characteristics of the high order LFM Chirplet Transform matrix, which has the bending effect, and energy accumulation in the time-frequency domain, in order to sparse the linear frequency modulated echo signal. Secondly, based on compression sensing, the characteristic parameters of an echo signal, such as the initial frequency and frequency modulation rate, have been reconstructed. At the same time, the interference by background noise in the underwater acoustic channel is eliminated. As a result, we can determine the motion state of an underwater object according to the physical characteristics of the linear frequency modulation signal echo. Simulations and experiments show that the higher order Chirplet Transform has very high resolution without cross-term inference, and is suitable for analyzing non-stationary underwater acoustic signals. After obtaining the characteristics of the time-frequency of an echo signal, the main characteristics of the data are extracted by compressed sensing based on the Noiselets matrix, and the noise interference from the underwater acoustic channel is eliminated. This technique can improve measurement of the physical parameters of underwater moving targets, and has a high detection probability under low SNR, so the validity of the theoretical analysis has been proved.

Research of Cooperative Diversity Applied in OFDM System

In recent years cooperative diversity has been widely used in wireless network, and Orthogonal frequency division multiplexing (OFDM) is a key technique of multi-carrier transmission to meet high data rate requirement of wireless communication. The aim of this project is to combine the technology of OFDM with cooperative diversity techniques, in this project, we have done simulation in matlab and compare the performances of the system while the cooperation node employs AF cooperative scheme contrast with DF cooperative scheme. The simulation results show that the OFDM system with Cooperative Diversity has a better performance when the cooperation node employs DF cooperative scheme.