Özet:

While continuously increasing demand for high data rates, to develop more efficient wireless communication systems will always be needed. Orthogonal Frequency Division Multiplexing (OFDM) is a promising multi-carrier wireless communication system for high-speed data transmission with spectral efficiency and fading immunity. Conventional OFDM systems use Fourier filters with the help of the inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT) for modulation and demodulation in transmitter and receiver, respectively. On the other hand, wavelet based OFDM system uses orthonormal wavelets which are derived from a multistage tree-structured wavelet family. Discrete wavelet transform (DWT), reducing inter symbol interference (ISI) and inter carrier interference (ICI), can be used due to better orthogonality and more bandwidth efficiency for OFDM systems. In this paper, performance of the OFDM system based on low complexity DWT (DWT-OFDM) has been compared with FFT based OFDM (FFT-OFDM) system. In DWT based OFDM system, the IFFT and FFT blocks in conventional FFT based OFDM system are simply replaced by an IDWT and DWT, respectively. Computer simulations have been performed to verify the effectiveness of both methods and compare the performance of the DWT-OFDM and FFT-OFDM system in additive white Gaussian noise (AWGN) channel and AWGN plus frequency flat Rayleigh fading channels for different modulation types. The obtained simulation results using HIPERLAN/2 standard have demonstrated that the DWT-OFDM system has considerably better performance than the conventional FFT-OFDM system in all modulation types and also provides high SNR improvement of approximately 6 dB for a BER value of 1E-3.

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