OFDM SYSTEM PERFORMANCE ENHANCEMENT USING DISCRETE WAVELET TRANSFORM AND DS-SS SYSTEM OVER MOBILE CHANNEL

摘要

OFDM system is a promising system. However, it faces problems of information rate reduction due to cyclic prefix together with some imperfections. These imperfections destroy sub-carrier orthogonality and introduce inter-carrier interference (ICI) among sub-carrier in addition to attenuation and rotation of each of the sub-carriers phase. In this paper a discrete wavelet transform OFDM, DWT-OFDM, system was proposed to improve the bandwidth efficiency of an OFDM system by removing the cyclic prefix and enhance the orthogonality. In the proposed system, IDWT and DWT replace the IFFT and FFT, respectively. For further performance enhancement of the proposed system has been combined with direct sequence spread spectrum (DS/SS). Computer simulations were presented to show the performance enhancement over selective Rayleigh fading channel. The results show that the proposed DWT-OFDM system gives 5 dB performance enhancement compared to FFT-OFDM system together with avoiding the reduction in the bandwidth efficiency. Furthermore, the performance of DWT-OFDM can be more enhanced by about 14 dB using the DS/SS system.