Bit error rate performance of high-speed tunnel communication

[[abstract]]The bit error rate performance for high-speed personal communication service in tunnels with and without traffic is investigated. The impulse response of the tunnel is computed by shooting and bouncing ray/image techniques. Binary data with phase shift keying modulation are transmitted over the multipath channel and coherent match filters are used as receivers. The bit error rate for communication in tunnels with and without traffic is calculated. Numerical results have showed that the multipath effect by the vehicles in the tunnel is an important factor for bit error rate performance. In addition, the effect of space diversity techniques on mitigating the multipath fading is also investigated[[conferencetype]]國際[[conferencedate]]19970811~19970814[[conferencelocation]]Natal, Brazi

Time Domain Inverse Problem of a Buried Dielectric Cylinder

[[abstract]]This paper presents an image reconstruction approach based on the time-domain and particle swarm optimization (PSO) for a 2-D homogeneous dielectric cylinder buried in a half-space. The computational method combines the finite difference time domain (FDTD) method and the particle swarm optimization (PSO) to determine the shape and location of the underground scatterer with arbitrary cross section. The subgirdding technique is implemented in the FDTD code for modeling the shape of the cylinder more closely. In order to describe an unknown cylinder with arbitrary shape more effectively, the shape function is expanded by closed cubic-spline function instead of frequently used trigonometric series. The inverse problem is resolved by an optimization approach, and the global searching scheme PSO is then employed to searching the parameter space. In order to reduce the number of the unknown parameters for the inverse scattering, the shape function of the cylinder is interpolated in terms of the closed cubic-spline. Numerical results demonstrate that, even when the initial guess is far away from the exact one, good reconstruction can be obtained.[[conferencetype]]國際[[conferencedate]]20090323~20090327[[conferencelocation]]Berlin, German

Improving the outage probabilities of rake receivers for ultra-wideband outdoor communication

[[abstract]]The BER performance for ultra-wide band (UWB) outdoor communication is investigated. By using the impulse response of multipath channels, the BER performance for binary pulse amplitude modulation (BPAM) communications over the radio UWB system is evaluated. Numerical results have shown that the multi-path effect caused by moving vehicles in the outdoor environment has a great impact on BER performance. Rake receivers are used to improve the outage probability.[[notice]]需補地點及國別[[conferencetype]]國際[[conferencedate]]20121010~2012101

Comparison of Particle Swarm Optimization and Asynchronous Particle Swarm Optimization for Inverse Scattering of a Two- Dimensional Perfectly Conducting Cylinder

[[abstract]]This paper reports a two dimensional time domain inverse scattering algorithm based upon the finite-difference time domain method for determining the shape of perfectly conducting cylinder. Finite difference time domain method (FDTD) is used to solve the scattering electromagnetic wave of a perfectly conducting cylinder. The inverse problem is resolved by an optimization approach and the global searching scheme asynchronous particle swarm optimization (APSO) is then employed to search the parameter space. By properly processing the scattered field, some EM properties can be reconstructed. One is the location of the conducting cylinder, the others is the shape of the perfectly conducting cylinder. This method is tested by several numerical examples; numerical results indicate that the APSO outperforms the PSO in terms of reconstruction accuracy and convergence speed. Both techniques have been tested in the case of simulated measurements contaminated by additive white Gaussian noise.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙

Frequency dependence on image reconstruction for a buried conductor

[[abstract]]The frequency dependence of image reconstruction for a buried imperfectly conducting cylinder is investigated. A conducting cylinder of unknown shape and conductivity is buried in one half-space and scatters the incident wave from another half-space. By using the measured scattered field, the image problem is reformulated into an optimization problem and solved by the genetic algorithm. The frequency dependence of image reconstruction is investigated and numerical results show that the reconstruction is quite good in the resonant frequency range. On the contrary, if the frequency is too high or too low the reconstruction becomes bad. It is worth noting that the present work provides not only comparative information but quantitative information[[conferencetype]]國際[[conferencedate]]20010521~20010523[[iscallforpapers]]Y[[conferencelocation]]Budapest, Hungar

Electromagnetic scattering of metallic cylinders of arbitrary shape by using asynchronous particle swarm optimization and non-uniform steady state genetic algorithm

[[abstract]]Two techniques for the shape reconstruction of multiple metallic cylinders from scattered fields are investigated in this paper, in which two-dimensional configurations are involved. After an integral formulation, the method of moment (MoM) is applied to solve it numerically. Two separate perfect-conducting cylinders of unknown shapes are buried in one half-space and illuminated by the transverse magnetic (TM) plane wave from the other half space. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equation is derived and the imaging problem is reformulated into optimization problem. The non-uniform steady state genetic algorithm (NU-SSGA) and asynchronous particle swarm optimization (APSO) are employed to find out the global extreme solution of the object function. Numerical results demonstrate even when the initial guesses are far away from the exact shapes, and the multiple scattered fields between two conductors are serious, good reconstruction can be obtained. In addition, the effect of Gaussian noise on the reconstruction results is investigated and the numerical simulation shows that the reconstruction results are good and acceptable, as long as the SNR is greater than 20 dB.[[incitationindex]]SCI[[booktype]]電子版[[booktype]]紙

Time Domain Microwave Imaging for a Buried Dielectric Cylinder by Dynamic Differential Evolution

[[abstract]]This paper presents the studies of time domain inverse scattering for a two dimensional homogeneous dielectric cylinder buried in a half-space which are based on the finite difference time domain (FDTD) method and the dynamic differential evolution (DDE). For the forward scattering, the FDTD method is employed to calculate the scattered E fields, while for the inverse scattering the DDE scheme is utilized to determine the shape, location and the permittivity of the buried cylindrical scatterer with arbitrary cross section. The subgirdding technique is implemented for the FDTD code in order to model the shape of the cylinder more smoothly. In additions, in order to describe an unknown cylinder with arbitrary cross section more effectively during the course of searching, the closed cubic-spline expansion is adopted to represent the scatterer contour instead of the frequently used trigonometric series. Numerical results demonstrate that, even when the initial guess is far away from the exact one, good reconstruction can be obtained. In addition, the effects of Gaussian noise on the reconstruction results are investigated. Numerical results show that even the measured scattered fields are contaminated with Gaussian noise, DDE is able to yield good reconstructed quality.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙

Bit Error Rate Reduction by Smart UWB Antenna Array in Indoor Wireless Communication

[[abstract]]In this paper, a new ultra wideband circular antenna array (UCAA) combining genetic algorithm to minimize the bit error rate (BER) is proposed. The ultra wideband (UWB) impulse responses of the indoor channel for any transmitter-receiver location are computed by applying shooting and bouncing ray/image (SBR/Image) techniques, inverse fast Fourier transform and Hermitian processing. By using the impulse response of multipath channel, the BER performance of the binary pulse amplitude modulation (B-PAM) impulse radio (IR) UWB system with circular antenna array can be calculated. Based on the topography of the antenna and the BER formula, the array pattern synthesis problem can be reformulated into an optimization problem and solved by the genetic algorithm. Our approach is not only choosing BER as the object function instead of sidelobe level of the antenna pattern, but also considering the antenna feed length effect of each array element. The strong point of the genetic algorithm is that it can find out the solution even if the performance index cannot be formulated by simple equations. Simulation results show that the synthesized antenna array pattern is effective to focus maximum gain to the LOS path which scales as the number of array elements. In other words, the receiver can increase the received signal energy to noise ratio. The synthesized array pattern also can mitigate severe multipath fading in complex propagation environment. As a result, the BER can be reduced substantially in indoor UWB communication system.[[notice]]補正完畢[[journaltype]]國際[[incitationindex]]SCI[[ispeerreviewed]]Y[[booktype]]電子版[[countrycodes]]TW

Image reconstruction of inhomogeneous biaxial dielectric cylinders buried in a slab medium

100學年度研究獎補助論文[[abstract]]The image reconstruction of inhomogeneous biaxial dielectric cylinders buried in a slab medium is investigated. A biaxial dielectric cylinder of unknown permittivities buried in a slab scatters a group of unrelated incident waves from outside. The scattered field is recorded outside the slab. By proper arrangement of the various unrelated incident fields, the difficulties of ill-posedness and nonlinearity are circumvented, and the permittivity distribution can be reconstructed through simple matrix operations. The algorithm is based on the moment method and the unrelated illumination method. Numerical results are given to demonstrate the capability of the inverse algorithm. Good reconstructed results are obtained even in the presence of additive Gaussian random noise in measured data. In addition, the effect of noise on the reconstruction result is also investigated.[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙

Electromagnetic Imaging for Inhomogeneous Dielectric Cylinder Buried in a Slab Medium

[[abstract]]The electromagnetic imaging of inhomogeneous dielectric cylinders buried in a slab medium is investigated. Dielectric cylinders of unknown permittivities are buried in second space and scattered a group of unrelated waves incident from first space where the scattered field is recorded. By proper arrangement of the various unrelated incident field, the difficulties of ill-posedness and nonlinearity are circumvented, and the permittivity distribution can be reconstructed through simple matrix operations. The algorithm is based on the moment method and the unrelated illumination method. Numerical results are given to demonstrate the capability of the inverse algorithm. They also show that the permittivity distribution of the cylinders can be successfully reconstructed even when the permittivity is fairly large. Good reconstructed results are obtained even in the presence of additive Gaussian noise in measured data. In addition, the effect of noise on the reconstruction result is also investigated.[[notice]]補正完畢[[incitationindex]]EI[[booktype]]紙