Implementation of Ofdm System by Using Convolutional Coding and Bch Coding With Adaptive Modulation

Abstract

WhenOrthogonal Frequency Division Multiplexing (OFDM) is a used it has several benefits for high speed data transmission over wireless as it is multicarrier transmission scheme. OFDM uses a large number of narrow bandwidth carriers. In an OFDM, individually each subcarrier is attenuated under the frequency-selective and fast fading channel if the same fixed transmission scheme is used for all OFDM subcarriers therefore it gets results in highest attenuation leads to performance is poor. The main aim of this paper is the introduction of the adaptive modulation to get an understanding of the differences between fixed & adaptive modulations schemes. Basically in this paper work, adaptive modulation is implemented by dividing whole subcarriers into blocks of adjacent subcarriers. By calculating average instantaneous signal to noise (SNR) same modulation scheme is applied to all subcarriers of same block. Here we observed average bit error rate (BER) performance of OFDM system under fixed modulation and adaptive modulation. Average BER performance of these modulation techniques is observed with various inverse fast Fourier transform (IFFT) size and using simpler adaptive Quadrature amplitude modulation (QAM) schemes. The simulation results show that BER performance of OFDM system using adaptive modulation is better than fixed modulation. The proposed adaptive modulation and coding Technique for OFDM maintains fixed BER under changing channel condition.