Implementation of Adaptive Modulation in OFDM System

Abstract

This paper investigates various modulation techniques for OFDM including BPSK, QPSK, 8 QAM, 16 QAM,
32 QAM, 64 QAM, 128 QAM, 256 QAM and 512 QAM and system performance is improved with high folds by choosing
the modulation technique based on the channel conditions. In this paper, transmitter and receiver models are simulated
according to the parameters established by the standard IEEE 802.11a, to evaluate the performance. Also, convolution
coding is used to improve the system performance. Use of adaptive modulation can effectively control the BER of the
transmission, as sub carriers that have a poor Eb /No (db) can be allocated a low modulation scheme such as BPSK. For
good Eb /No (db), the high modulation scheme giving priority to spectral efficiency can be considered. Eb/No of the
channel is estimated before the transmission. The modulation scheme is set based on the SNR of the channel. The
proposed adaptive modulation for OFDM maintains fixed BER under changing channel condition