Zhang Dianlun

Performance of differential chaos-shift-keying digital communication systems over several common channels

Using chaotic signals in spread-spectrum communications has a few clear advantages over traditional approaches. Chaotic signals are nonperiodic, wide-band, and more difficult to predict, reconstruct, and characterize than periodic carriers. These properties of chaotic signals make it more difficult to intercept and decode the information modulated upon them. The differential chaos shift keying (DCSK) is a non-coherent modulation scheme, and has good anti-noise performance. In this paper, based on the fundamental theories and with some recent researches of others, the DCSK performance is analyzed and the expressions of the bit error rates are derived for DCSK under AWGN channel, Rayleigh fading channel and Ricean fading channel. In the end, the Logistic mapping with zero mean is used for chaos generation in simulation and compared with simulation results.

Hybrid Genetic Algorithm Applied to Wave Directional Spectrum Estimation by Array

array estimation of wave directional spectrum needs to measure the same quantity of the different locations, then the cross-spectrum of different locations is calculated, finally wave direction distribution is estimated based on nonlinear equation between cross-spectrum and wave direction distribution. In the paper, a hybrid genetic algorithm is applied to modified MEM algorithm, the algorithm avoids the complicated Bessel function calculation and also eigenvalue and eigenvector calculation. Simulation result shows that the hybrid genetic algorithm has better precision and also high calculation speed.

A Study of Detecting and Imaging Small Targets On Seabed

The most effective approach to detect underwater targets is to use the sound wave. The reason for this is that the propagating absorption of sound wave in water is much smaller than the other kinds of waves, and a greater working distance can be reached. The problems faced with detecting the small targets on seabed, are fully different from that in detecting underwater target for the general purpose. First, because of the small size of targets, the target strength is small and received echo amplitudes are unlikely great. Second, to decide the presence of small targets and classify them, both the azimuth and range resolution are required to be high for a system. Third, it perhaps is the most important that the main background is the bottom reverberation. All of these imply that there are some particularities in detecting and imaging small targets on seabed. The purpose of this paper is to present such a kind of system. The signal to reverberation ratio and the reverberation to noise ratio related to detecting small targets on seabed, beamforming and focusing in the near field, signal processing and display technique are discussed. Some experiments have been done on lake with the developed system and the obtained results are satisfactory.

Automatically Combining a Geomorphologic Map Using 2-D Imaging Sonar Data

By using a multibeam image sonar, the return signals from the targets on seabed and background can be stored and displayed in the form of distance-azimuth, so that the location and classification for underwater targets are realized. When the sonar is to be evaluated or tested on a specified area, it is generally needed to know the feature of the seabed in the tested area. This is usually done by a side scan sonar1. However, when the ship used in the experiment is fixed, we can’t employ the side scan sonar to get the geomorphologie map. In this case, this task can also be performed by the imaging sonar itself.