An adaptive modulation method based on bit preassign for HF OFDM systems

Adaptive HF OFDM system can improve the transmission performance by bit and power loading based on the characteristic of subchannel. Greedy algorithm is the optimal method for finite granularity bit allocation, but it has high computational complexity. A new improved bit and power loading algorithm is proposed for HF OFDM systems in this paper, some bits is pre-allocated to some subchannels based on SNR, the spare bits are allocated by greedy algorithm in new method. The results of simulation reveal that the BER performance of the new method approaches to greedy algorithm when the adjustable coefficient is 0.5, and the computational complexity is lower than greedy algorithm.