Opportunistic Overlapping: Joint scheduling of uplink URLLC/eMBB traffic in NOMA based Wireless Systems

We consider the joint scheduling of uplink URLLC and eMBB user traffic in a cellular system. The central challenge is coordinating URLLC uplink user transmissions for traffic requiring extremely low latency, high reliability, and in the absence of knowledge of instantaneous URLLC channel qualities, albeit with knowledge of channel distributions. To avoid collisions and meet latency and reliability constraints, we propose to pre optimize layouts of non-overlapping transmission opportunities for URLLC users’, which may, or may not, be used depending on their traffic. To increase overall throughput we propose to leverage Non-Orthogonal Multiple Access (NOMA) based opportunistic scheduling of overlapping eMBB user traffic and propose power control policies, i.e. eMBB transmit power backoff, to protect possible URLLC transmissions from overlapping eMBB traffic. We derive the sum-rate optimal power control for eMBB traffic, and propose a linear approximation that simplifies the later scheduling task. Utilizing an outage capacity model for the unknown URLLC channel qualities, we assign the URLLC allocations as a greedy first fit decreasing packing problem. We then apply an opportunistic overlapping scheduler that, subject to meeting URLLC users' latency constraints, optimizes eMBB users’ sum utility. Substantial discrete event simulations were conducted to explore the performance impact of system parameters associated with URLLC traffic requirements, eMBB power control, etc. Depending on the traffic scenarios, we show gains reaching 75% in the sum eMBB throughput and/or 5th percentile throughput relative to an orthogonal multiple access baseline.