PROPOSED APPROACHES TO ENHANCE THE ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEM | ||
| JES. Journal of Engineering Sciences | ||
| Article 6, Volume 42, No 4, July and August 2014, Pages 983-1001 PDF (792.42 K) | ||
| Document Type: Research Paper | ||
| DOI: 10.21608/jesaun.2014.115042 | ||
| Authors | ||
| Usama Sayed Mohammed1; Ahmed Tohamy2 | ||
| 1Electrical Engineering Department,Faculty of Engineering,Assiut University, Assiut, Egypt | ||
| 2Communications & Electronics Eng Dept., Faculty of Eng., Assiut University, Egypt | ||
| Abstract | ||
| In the Orthogonal Frequency Division Multiplexing (OFDM) systems, where the data symbols are transmitted in parallel on different carriers, the length of a symbol is extended. This extension of the symbol length causes the OFDM system to be less sensitive to channel dispersion than a single carrier system transmitting data symbols at the same data rate. However, at the edges of the OFDM symbol, the channel dispersion still causes distortion, and hence introduces interference between successive symbols (i.e. Inter-Symbol Interference, ISI) and interference between different carriers within the same symbol (i.e. Inter-Carrier Interference, ICI). Different guard interval techniques for the OFDM transmission were suggested to reduce the interference between successive symbols. The most commonly used guard interval is the cyclic prefix (CP). In this paper, the impact of replacing the CP by zero insertion (ZI) before the Inverse Fast Fourier Transform (IFFT) process on the OFDM transmitter is studied. The motivation of using the ZI instead of the CP is the reduction in the transmission rate and the high performance in reducing the channel distortion. Moreover, the proposed ZI-OFDM system is suitable to minimize the effect of the fading channel when the channel characteristics are unknown or difficult to be estimated. Another approach to enhance the OFDM system is also introduced in this paper. A signal denoising approach is suggested to be added in the receiver to reduce the effect of the additive white Gaussian noise (AWGN) channel. In this approach, the Radio Frequency signal (RF) is enhanced using a wavelet thresholding technique instead of enhancing the baseband signal. The simulation results show that the proposed ZI approach provides better transmission performance than the recent techniques and achieves a 20 % reduction in the data redundancy relative to the redundancy in the CP-OFDM system. Moreover, the results show that the proposed thresholding approach significantly removed the noise and the signal power is enhanced by almost 30 db with different values of the channel signal-to-noise ratio (SNR). The overall system performance of the proposed ZI approach in the transmitter together with the thresholding approach in the receiver is tested in this paper. | ||
| Keywords | ||
| wavelet thresholding; Gaussian noise; signal denoising; Inter-Symbol Interference (ISI); Inter-Carrier Interference (ICI); cyclic prefix | ||
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