Multivariable optimisation approach for power allocation in OFDM-DCSK system

This study proposes some multivariable approaches for power allocation in orthogonal frequency multiple access-based differential chaos shift keying (OFDM-DCSK) system. The objective is to minimise the overall bit error rate (BER) under the total transmission power limit. There is some literature focusing on the power allocation for OFDM-DCSK systems, but all of them have only addressed the case where the power allocated to the reference subcarrier is assumed to be equal to one to simplify the problem to a single-variable optimisation problem. In this study, the authors simultaneously take the reference and data-bearing subcarriers power into consideration. They formulate a multivariable optimisation problem and solve it using Lagrange relaxation to derive a closed form solution. As the main contribution, the problem is converted to a cubic equation which is solved theoretically. Since the equation is non-convex, they solve it again using a genetic algorithm (GA)-based method for additive white Gaussian noise channel as a case study. The heuristic algorithm validates the theoretical approach. As another conclusion, the simulation results indicate that both of the proposed approaches outperform algorithms relaxing the reference power in terms of the BER performance, but the analytical solution leads to less time complexity in comparison with the GA-based method.