International Journal of Emerging Technology and Advanced Engineering Website: www.ijetae.com (ISSN 2250-2459,ISO 9001:2008 Certified Journal, Volume 3, Issue 3, March 2013)678 Performance Evaluation of OFDM System with Rayleigh, Rician and A WGN Ch annels Sai Krishna Borra 1 ; Suman Krishna Chaparala 2 1,2 Student, K L University, Vijayawada Abstract—A Orthogonal Frequency Division Multiplexing (OFDM) scheme offers high spectral efficiency and better resistance to fading environments. In OFDM the data is modulated using multiple number of sub-carriers that are orthogonal to each other because of which the problems associated with other modulation schemes such as Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) are reduced. This paper deals with the analysis ofOFDM System utilizing different modulation techniques (QAM and BPSK) over Rayleigh, Rician and Additive White Gaussian Noise (AWGN) fading environments with the use ofpilot aided arrangement and finally the results are conveyed. Keywords—AWGN Channel, Orthogonal Frequency Division Multiplexing (OFDM), QAM, Rayleigh Fading, Rician Fading.I.I NTRODUCTIONOrthogonal Frequency Division Multiplexing (OFDM) is becoming a very common multi-carrier modulation technique for transmission of signals over wireless channels in diverse environments. OFDM divides the high- rate stream into parallel lower rate data and hence prolongs the symbol duration, thus helping to eliminate Inter Symbol Interference (ISI). In an OFDM system the sub-channels overlap with each other to a certain extent as can be seen in figure.1-1in which leads to the reduced use of bandwidth and since these carriers are orthogonal to each other InterCarrier Interference (ICI) is also reduced [2]. The input data sequence is mapped into symbols, which are distributed and sent over the N parallel sub-channels, one symbol per channel. To permit dense packing and still guarantee that a minimum of interference between the sub- channels is encountered, the carrier frequencies must be chosen carefully. By using orthogonal carriers, which in the Frequency domain can be viewed so as the frequency distance between two sub-carriers is given by the distance to the first spectral null. FIGURE 1-1:(A)Conventional multicarrier technique(FDM)(B)Orthogonal Frequency Division multiplexing Technique. II.SYSTEM MODELThe concept of using parallel-data transmission and Frequency Division Multiplexing (FDM) was first published in the mid of 1960s. The basic idea was to use parallel data and FDM with overlapping sub-channels to avoid the use of high-speed equalization to combat impulsive noise and multipath distortion and fully utilize bandwidth. Although the idea of OFDM was conceived in 1960s, it was not realizable until the advent of FFT. With the advent of FFT/IFFT it became possible to generate OFDM using the digital domain for orthogonality of sub carriers. Figure 2-1 shows a block diagram of a discrete time OFDM system, where an N complex-valued data symbol modulates N orthogonal carriers using the IFFT forming. The transmitted OFDM signal multiplexes N low- rate data streams, each experiencing an almost flat fading channel when transmitted.
