Mitigation techniques for wireless communications over fading channels

Abstract

In a wireless communication system, there are usually many obstacles between the transmitter and the receiver, so a superposition of numerous reflected components will be the signal the receiver received. This multipath propagation causes inevitable changes in the amplitude, phase and angle of the signal reaching the receiver, resulting in multipath fading. Two main typical types of fading are Rayleigh fading and Rician fading. To mitigate the fading, we adopt orthogonal frequency division multiplexing (OFDM) technology. OFDM can divide a big data stream with a high transmission rate into N parallel data streams, and each is modulated. Accordingly, the final signal can resist distortion and fading to a certain extent. In this dissertation, we introduce the additive white Gaussian noise (AWGN) channel model, Rayleigh channel model and Rician channel model. Then we calculate the ideal bit-error rate (BER) of Quadrature-phase-shift keying (QPSK) signals in these channels. In order to mitigate fading, we design a parameter-based OFDM system, and add channel estimation, spread spectrum and other modules to the OFDM system for optimization. The result is analyzed by the final BER curve. All the process is simulated in MATLAB.