A Novel Power Distribution Scheme Combined with Adaptive Modulation Based on Subcarrier Grouping for OFDM Systems

In this paper, we propose to adapt both the modulation scheme and the transmit power in the frequency domain using a heuristic evaluation of the bit error rate (BER) for each subcarrier. The proposed method consists in ordering in terms of fading impact, grouping a certain number of subcarriers and performing local power adaptation in each subcarrier group. The subcarrier grouping is performed in order to equalize the average channel condition of each subcarrier group. Grouping and local power adaptation allow us to take advantage of the channel variations and to reduce the computational complexity of the proposed power distribution scheme, while avoiding the performance degradation due to the suboptimum power adaptation as much as possible. Compared to the conventional power distribution methods, the proposed scheme does not require any iterative process and the power adaptation is directly performed using an analytical formula. Simulations show a gain in terms of BER performance compared to equal power distribution and existing algorithms for power distribution. In addition, due to the subcarrier group specificity, the trade-off between the computational complexity and the performance can be controlled by adjusting the size of the subcarrier groups. Simulation results show significant improvement of BER performance compared to equal power allocation. key words: OFDM, adaptive modulation, Lagrangian method, global BER optimization