Abstract: Wireless communications is the fastest growing segment of the communication industry. The most widely used wireless communication is mobile communication. But, there are many technical challenges that must be overcome. A signal transmitted on a wireless channel is subject to Fading, Shadowing, Interference, Propagation path loss etc. There is always a greater demand for capacity with the high quality service. In this situation, orthogonal frequency division multiplexing (OFDM) is well defined technique, which is a suitable option for high band width data transmission, by converting the wideband signal into narrow band signals for transmission. The transmission of these individual narrow band signals are executed with orthogonal carrier. In this paper, the performance of transmission mode are evaluated by Bit Error Rate versus the Signal to Noise Ratio under frequently used three channel modes, Additive White Gaussian Noise, Rayleigh Fading and Rician Fading channel. In order to investigate, first we derive the mathematical modelling for bit error rate and signal to noise ratio of OFDM over AWGN, Rayleigh and Rician fading channels then, OFDM is design and implemented. Here we have assumed AWGN channel, Rician and Rayleigh fading channel as noise channel and also built BPSK, QPSK and QAM modulation technique. OFDM transmitters and receivers are implemented here using Inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT) of size 64 with 52 sub carriers to convert the spectra to time domain & vice versa. The signal frequency is 8MHz and sub-carrier frequency is 0.125MHz. The performance has been concluded based on BER vs. SNR output for BPSK, QPSK and QAM using AWGN, Rayleigh & Rician channel is that BPSK is better than QPSK and QAM in all channel because over AWGN channel at SNR=4dB, BER=0.01 and same BER is achieved by QPSK at SNR=8 and give better performance over AWGN as compare to Rayleigh and Rician channel. And Rician channel is better than Rayleigh channel, BER in Rician is 1/4th of Rayleigh for BPSK, for QPSK, 5/4 for 16-QAM.

Keywords: OFDM, AWGN, Rayleigh, Rician, BER, SNR, IFFT, BPSK, QPSK and QAM.