FADING MINIMIZATION WITH OFDM TECHNIQUES AND MAXIMUM LIKELIHOOD FUNCTION

INTRODUCTION As technology and system requirements in field of computer science and telecommunications are changing very fast. Over the previous years, since the transition from analog to digital communications, and from wired to wireless, different standards and solutions have been adopted, developed, implemented and modified, often to deal with new and different business requirements. OFDM (Orthogonal Frequency Division Multiplexing) has been shown to be an effective technique to combat multipath fading in wireless communications. OFDM is a modulation scheme that allows digital data to be efficiently and reliably transmitted over a radio channel, even in multipath medium. It transmits data by using a large number of narrow bandwidth carriers with regularly spaced in frequency, forming a block of spectrum. The separation of the subcarriers is such that there is a very compact spectral utilization. Using OFDM, it is possible to have overlapping sub channels in the frequency domain, therefore increasing the transmission rate. OFDM makes possible to use Maximum Likelihood (ML) decoding with reasonable complexity. OFDM is computationally efficient with FFT techniques. ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING As wireless communication evolves towards broadband systems to support high data rate applications, therefore a technology is needed that can efficiently handle frequency selective fading. The widely used solution to this context is OFDM system. The key idea of OFDM is to divide the whole transmission band into a number of parallel subchannels (also called subcarriers) so that each subchannel is a flat fading RESEARCH ARTICLE ISSN: 2321-7758