Bit and subcarrier allocation for OFDM transmission using adaptive modulation

OFDM is one of the promising modulation candidates for a fourth generation broadband mobile communication system because of its robustness against intersymbol interference (ISI). The OFDM transmission technique has the inherent flexibility to adapt the modulation scheme on each subcarrier according to the signal-to-noise ratio (SNR) on a subcarrier. We propose the bit allocation algorithm in order to increase the transmission rate by changing the channel modulation scheme according to the estimated channel state information. In the proposed algorithm, the subcarriers are clustered in blocks, which are allocated the same modulation scheme. This way, the signaling overhead can be reduced in comparison with the standard subcarrier bit loading algorithms. In this paper, we presents an evaluation for the effects of various modulation scheme combination, target BER, and the various number of subcarriers in the subband block on the performance of adaptive OFDM.