Fairness-aware Joint Pattern and Power Design for Downlink PDMA Systems

Abstract

Pattern division multiple access (PDMA) is recognized as a promising non-orthogonal multiple access technique for overloaded wireless systems, capable of being used for multiplexing multiple users over a limited set of resources. However, the real performance of PDMA is determined not only by the access principle itself, but also by the joint interaction between pattern design, transmit power allocation, and receiver interference cancellation. This paper proposes a fairness PDMA scheme for overloaded downlink systems based on joint pattern assignment, power allocation, and adaptive successive interference cancellation (SIC). The design aims to improve spectral efficiency and user fairness under real residual-interference conditions. Simulation results show that the proposed PDMA consistently outperforms orthogonal multiple access (OMA) and fixed-pattern PDMA techniques. At 30 dB, the proposed scheme achieves an average sum rate of approximately 14.5 bit/s/Hz under ideal SIC, compared with nearly 12 bit/s/Hz for OMA and approx. 8.5 bit/s/Hz for fixed-pattern PDMA. In terms of fairness, at an overload factor of \textlambda = 1.5, the proposed method attains a Jain's fairness index of approx. 0.84, whereas OMA and fixed-pattern PDMA achieve nearly 0.58 and 0.44, respectively. These results confirm that an adaptive joint design allows to obtain both high throughput and balanced user performance in overloaded PDMA systems.