Adaptive Modulation for Orthogonal Frequency Division Multiplexing

Abstract

Orthogonal frequency division multiplexing (OFDM) is one of the promising technologies to improve the spectral efficiency, enhance system capacity and mitigate inter-symbol interference in the wireless communication system. Adaptive modulation (AM) with OFDM has been suggested as a bandwidth efficient transmission technique in wireless fading environments. In this paper, adaptive modulation techniques is used with OFDM system to improve the throughput performance of the system using four modulation schemes BPSK, QPSK, 8QAM, and 16QAM. Two algorithms to estimate SNR are suggested. The first algorithm is to estimate the SNR for each OFDM symbol in the frame. The second algorithm is to estimate the channel SNR for each subcarrier in the OFDM symbol. The comparison between the results of the two algorithms on the performances of BER and throughput for OFDM system is shown. Furthermore, the effect of various types of channel equalization on performances of system will be determined. The obtained results show that a significant improvements in terms of bit error rate (BER) and throughput can be achieved demonstrating the superiority of the adaptive modulation schemes compared to fixed transmission schemes.