Design of degrees of distribution of LDS-OFDM

In this paper, we study the design of low density signature-orthogonal frequency division multiple access (LDS-OFDM). Compare to the conventional OFDMA system, LDS system has some desirable properties that allows system operating at overloaded conditions. LDS-OFDM system has been shown that outperforms the corresponding OFDMA system. In this paper, we focus on the design of the LDS degrees distribution, which has not been addressed in the literature. The goal is to achieve the optimum system load. We propose an iterative optimization procedure by utilizing the EXIT chart. Optimized load has been given in this paper with corresponding LDS spreading parameters. The performance of the designed LDS-OFDM system is evaluated. Monte Carlo based simulations further confirm that the designed LDS-OFDM outperforms the corresponding OFDMA system by up to 10 dB.