Zhiyong Xu

Research and implementation of an improved 800BPS speech coding algorithm

An improved 800bps speech coding algorithm is presented in this paper. Several methods are exploited to reduce the bit rate, such as dynamic bit allocation, multi-frame joint vector quantization and parameter interpolation. The 800 bps speech coding algorithm has been implemented on TMS320VC5416. The PESQ scores obtained with GL VQT are over 2.9, which show that the speech coding system can meet actual communication requirements.

Online evolution reconstruction from a single measurement record with random time intervals for quantum communication

Online reconstruction of a time-variant quantum state from the encoding/decoding results of quantum communication is addressed by developing a method of evolution reconstruction from a single measurement record with random time intervals. A time-variant two-dimensional state is reconstructed on the basis of recovering its expectation value functions of three nonorthogonal projectors from a random single measurement record, which is composed from the discarded qubits of the six-state protocol. The simulated results prove that our method is robust to typical metro quantum channels. Our work extends the Fourier-based method of evolution reconstruction from the version for a regular single measurement record with equal time intervals to a unified one, which can be applied to arbitrary single measurement records. The proposed protocol of evolution reconstruction runs concurrently with the one of quantum communication, which can facilitate the online quantum tomography.

Pulse width modulation and demodulation scheme in long-distance scattering optical communication

In order to satisfy the source demand of long-distance scattering optical communication system, pulse width modulation scheme is proposed, which aim at the characteristics of high power laser. A wireless optical communication experiment system is built and the pulse width which generated by the same drive electric is tested. Based on the experiment, the distribution of the optical pulse width which is obtained by fitting method is presented. Furthermore, the performance of pulse width modulation and demodulation which is based on pulse width distribution is researched.

Error performance analysis in short and long wavelength infrared free space optical communication

Based on the line-of-sight channel model of atmosphere established through the photon tracing method, the impact of SNR, bit rate and visibility to the bit error rate of free space optical communication (FSO) is analyzed. The comparative analysis is accomplished by using two wavelengths laser 1.55^μm and 10.6^μm. The results show that the error bit rates of 1.55^μm and 10.6^μm increase with SNR decreasing or bit rate increasing. In low visibility, the error performance of 10.6^μm laser is better than that of 1.55^μm, and the superiority is much more obvious in lower SNR and higher bit rate. Furthermore, error performances of the two wavelengths are almost the same.

Study on the characteristics of different infrared transmission in atmospheric turbulence

It is known theoretically that the long wavelength infrared has better performance when transmitting in atmospheric turbulence. In order to evaluate the influence of the atmospheric turbulence quantificationally, the characteristics of different infrareds transmission in atmospheric turbulence are simulated and studied. A series of time relevant phase screens of atmospheric turbulence are simulated based on Fourier transform method proposed by McGlamery. Wind speed and direction are introduced in the meantime. Wavefront distortion, image spot dancing and spreading, receive loss of different wavelengths (0.85μm, 3.6μm, 10.6μm) are simulated respectively and compared to each other. The results show that the performances of long wavelength infrared (10.6μm) are the best, mid wavelength infrared (3.6μm) takes the second place and short wavelength infrared (0.85μm) is the worst.

A novel dispersion flattened and single-mode terahertz photonic crystal fiber with material-filled structure

A novel kind of terahertz (THz) photonic crystal fibers (PCFs) based on the material-filled structure is proposed in this paper. Different materials can be selectively filled into parts of air-holes in the designed THz PCFs, and then perfect features such as single-mode transmission and ultra-flattened dispersion are obtained easily in large frequency ranges near 1THz. Employing full-vectorial finite element method (FEM) and plane wave expansion method (PWE), confinement losses and modal dispersion with different structural parameters and diverse refractive indices of the filled materials are investigated respectively. Numerical results show that the proposed PCFs have acceptable confinement losses, low and flattened dispersions whose absolute values are lower than 1ps/nm*km. Moreover, its structure is simple and its feature is insensitive to variations of parameters. It is helpful for PCFs design and real fabrication in the potential THz applications.