Contention Based Uplink Transmission with NOMA for Latency Reduction

Contention based uplink (CB UL) access has been proposed as an effective way to simplify uplink access signaling interactions and reduce access latency compared with traditional dedicated scheduling request (DSR) based approach. Although being effective for low traffic load, CB UL suffers a lot when traffic load increases and even not workable when traffic load is high because of the collision problem. Non-orthogonal multiplexing access (NOMA) has been proposed as a promising approach for 5G multiple access, which enables multiple user terminals (UEs) to share the same resource at the same time and exploits the collisions for better resource utilization efficiency. In this paper, we propose novel methods to extend NOMA for CB UL focusing on the problem that how to enable good "collisions" (signals with large enough power difference) without knowing which UEs will conduct the CB UL transmissions so as for effective SIC processing and good NOMA performance. Two methods have been proposed by exploiting downlink signal-noise-ratio (SNR) information at UE and scheduling information at evolved-Node-B (eNodeB) to form good user pairing for NOMA. Simulation results show that the proposed NOMA based CB UL is very effective and can greatly reduce access latency of CB UL.