FDTD Analysis of Signal and Interference Characteristics in Multi-channel Propagation over Forests for WiMAX Communication

WiMAX wireless communication has been rapidly developed for broadband mo- bile communication. Mobile WiMAX communication system uses microwave carrier of 2.5GHz frequency band and modulation is OFDM mainly. By using OFDM technique, WiMAX provide high speed and reliable communication against multi pass interferences due to the presence of obstacles in communication channels. To design excellent high performance mobile communica- tion systems, accurate evaluation of communication system is indispensable. By using parallel FDTD, we studied fundamental characteristics of microwave propagation and scattering in ur- ban area (1,2). We also studied wave propagation and scattering by forest and trees using two-dimensional FDTD (3). The efiects of multiple scattering and attenuation of microwave by forest are severe factors of high speed wireless communications. In this paper, signal and interference characteristics of WiMAX communication signal in more realistic forest model are numerically analyzed using three-dimensional FDTD method. The incident wave is a WiMAX communication wave given by equivalent current Jy (rt;t) = s(t)sin((!c + m!0)t)J(rt) (1) where (x0; y0, z0) is a center of incident beam, S is a beamspot size at z = z0, !c = 2…fc, fc = 2:5GHz is a carrier frequency, !0 = 2…f0, f0 = 1=T = 50MHz is a interval of carrier frequency and mf0 is a sub carrier frequency. The OFDM system provides high-speed data rate by synthesizing multi sub carriers. s(t) is a sequence of transmission code. Total analysis region of FDTD is shown in Fig. 1. Fig. 2 shows a block diagram of communication system. h(t) is a transfer function which contains noises generated by propagation channel and interference signals from other user's terminal. In case of WiMAX, multiple sub carrier are used for signal modulation to realize reliable high data rate communication. WiMAX provides connection service to multi users simultaneously, the interference of signals from multi users at base station is considered. For evaluation of transmission characteristics under this environment, SNR, CNR and BER are calculated by time response obtained using FDTD and to improve the transmission characteristics, design of digital signal processing and digital fllter for recognition and separation of each desired signal from received signals contaminated by noise interference are discussed.