Relay-Aided PDMA with Dynamic Power Control for Cell-Edge User Fairness

Abstract

Cell-edge users in wireless communication networks often suffer from poor performance due to weak channel conditions. To address this issue, we propose a relay-assisted communication system that employs Pattern Division Multiple Access (PDMA). This approach enhances efficiency and capacity for cell-edge users while maintaining acceptable relay performance. The proposed scheme includes a Base Station (BS), a Relay (R) with better channel conditions, and a cell-edge user. Transmission occurs over two time slots: In the first time slot, the base station (BS) transmits a superimposed signal to both the relay and the cell-edge user. In the second time slot, the relay forwards only the decoded information intended for the cell-edge user. The cell-edge user then applies successive interference cancellation (SIC) to recover the desired signal.To further optimize system performance, we implement an optimal power allocation strategy at the base station that: (1) assigns power to both the signal intended for the relay and the cell-edge user in the superimposed transmission, while (2) allocating higher transmit power to the relay compared to the BS, leveraging the relay's superior channel conditions. This approach enhances the overall system capacity and reliability, particularly benefiting cell-edge users with weak direct links. This approach enhances the overall capacity and reliability of the relay-assisted transmission, thereby improving the quality of service (QoS) for cell-edge users with weak direct links to the BS. As a result, the cell-edge user benefits from both the BS and relay transmissions, enabling the decoding of the superimposed signal by using SIC and ultimately improving spectral efficiency. Furthermore, we introduce a fairness metric to assess the received capacity relative to the actual capacity of each user, providing insights into the equitable distribution of resources. The fairness metric is calculated as the ratio of the received capacity to the actual capacity for each user, allowing for a comparison of how fairly the system allocates resources under different schemes.

Keywords

• Relay
• Non-orthogonal multiple access
• Superposition coding
• Decode and forward

References

1. Alsakarnah, R., Masoud, M., & Slehat, S., (2025). Relay-aided PDMA with dynamic power control for celledge user fairness. The Eurasia Proceedings of Science, Technology, Engineering and Mathematics (EPSTEM), 33, 73-79.