Subcarrier-wise power allocation for OFDM-IDMA systems

Current orthogonal frequency division multiplexing interleave division multiple access (OFDM-IDMA) systems only employ the power optimization process in the user-wise level but the subcarrier-wise level remains untouched. This paper proposes a novel and efficient algorithm for subcarrier-wise power allocation in OFDM-IDMA system, which aims at maximizing the channel capacity under the constraints of user-wise average powers. Different from the widely used channel capacity formula, the objective function is changed from capacity of Gaussian inputs to capacity of quadrature phase shift keying (QPSK) modulated inputs. Comparisons with other alternative algorithms such as equal power allocation algorithm and water filling power allocation algorithm are provided. Simulation results show that the proposed algorithm can achieve better and more robust BER performance.