NCSMA: A NOMA-Based CSMA/CA Protocol for Ad Hoc Networks

Carrier-sense multiple access with collision avoidance (CSMA/CA) is one of the fundamental medium access control (MAC) protocols for ad hoc networks. As a network increases in size, its throughput degrades substantially due to packet collision. To reduce the collision probability, a nonorthogonal multiple-access (NOMA)-based CSMA/CA (NCSMA) protocol is proposed. The proposed NCSMA protocol employs Zadoff-Chu (ZC) sequences and a NOMA power coefficient allocation (N-PCA) frame to select the NOMA node and schedule the power level, preventing packet collisions caused by random selection. Moreover, the normalized saturation throughput and the average packet delay of the proposed approach are theoretically analyzed, and closed-form expressions are derived. Simulation results show that the proposed protocol improves the normalized saturation throughput by 66.7% and reduces the average packet delay by 35.97% compared to those of the current best CSMA/CA protocol.