Collision Resolution Algorithm for Multi-user NOMA Random Access Systems

This paper considers the collision resolution algorithm when multiple packets transmit simultaneously in each slot in a non-orthogonal multiple access (NOMA) systems. Packets are divided into two groups and two different received powers can be selected. Packets in each group can select one power level as their received power. As more than one packet may transmit in a time slot in each group, collision will happen and throughput may decrease at the same time. We introduce the collision resolution period (CRP) algorithm and the collided packets will transmit in the CRP. By controlling the transmission probability in each group, we can make a big different comparing to the system without a CRP. This paper will show the optimal transmission probability and the maximum throughput. Numerical results show that our proposed algorithm yields the maximum throughput of 0.6489.