Research Article Discrete Multiwavelet Critical-Sampling Transform-Based OFDM System over Rayleigh Fading Channels Sameer A. Dawood, 1 F. Malek, 2 M. S. Anuar, 1 and Suha Q. Hadi 1 1 School of Computer and Communication Engineering, University Malaysia Perlis (UniMAP), 02000 Arau, Perlis, Malaysia 2 School of Electrical Systems Engineering, University Malaysia Perlis (UniMAP), 02000 Arau, Perlis, Malaysia Correspondence should be addressed to Sameer A. Dawood; sameer.ad80@yahoo.com Received 31 December 2014; Accepted 10 May 2015 Academic Editor: Lotfi Senhadji Copyright © 2015 Sameer A. Dawood et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Discrete multiwavelet critical-sampling transform (DMWCST) has been proposed instead of fast Fourier transform (FFT) in the realization of the orthogonal frequency division multiplexing (OFDM) system. e proposed structure further reduces the level of interference and improves the bandwidth efficiency through the elimination of the cyclic prefix due to the good orthogonality and time-frequency localization properties of the multiwavelet transform. e proposed system was simulated using MATLAB to allow various parameters of the system to be varied and tested. e performance of DMWCST-based OFDM (DMWCST- OFDM) was compared with that of the discrete wavelet transform-based OFDM (DWT-OFDM) and the traditional FFT-based OFDM (FFT-OFDM) over flat fading and frequency-selective fading channels. Results obtained indicate that the performance of the proposed DMWCST-OFDM system achieves significant improvement compared to those of DWT-OFDM and FFT-OFDM systems. DMWCST improves the performance of the OFDM system by a factor of 1.5–2.5 dB and 13–15.5 dB compared with the DWT and FFT, respectively. erefore the proposed system offers higher data rate in wireless mobile communications. 1. Introduction One of the appealing multicarrier modulation schemes to accomplish the requirement of high data rate is orthogonal frequency division multiplexing (OFDM). e OFDM system divides the high data rate stream into a number of lower rate streams that are transmitted together over a number of orthogonal subcarriers to achieve frequency flat fading [1]. However, in wireless communication systems, the depend- ability of OFDM is restricted because of the time-varying characteristics of the channel, which causes intersymbol interference (ISI) and intercarrier interference (ICI). ISI and ICI can be averted effectively by inserting a cyclic prefix (CP) before each block of OFDM data symbols. However, CP introduces a loss in transmission power and reduction in the bandwidth efficiency [2, 3]. Inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) are normally used in the implementa- tion of OFDM systems to create and detect the different orthogonal subcarriers. Although these transforms reduce the implementation complexity and are more computation- ally efficient, they have drawbacks that create rather high side lobes due to the use of a rectangular window. Moreover, the pulse shaping function used to modulate each subcarrier extends to infinity in the frequency domain, which leads to high interference and lower performance levels [4, 5]. Moreover, one major problem of the FFT-based OFDM (FFT-OFDM) system is the high peak-to-average power ratio (PAPR), which causes intermodulation distortion in the transmitted signal [6, 7]. Given the weak points of the FFT-OFDM system, many researchers have examined the use of wavelet-based OFDM to substitute Fourier-based OFDM; they found that the former has more advantages than the Fourier-based OFDM [8–11]. In OFDM based on wavelet transform, the IFFT and FFT blocks are merely replaced by inverse discrete wavelet transform (IDWT) and discrete wavelet transform (DWT), respectively. Wavelet transform offers much lower side lobes in the transmitted signal, which reduces its sensitivity to ICI. e most significant difference between FFT-OFDM and Hindawi Publishing Corporation Mathematical Problems in Engineering Volume 2015, Article ID 676217, 10 pages http://dx.doi.org/10.1155/2015/676217