2327-4662 (c) 2020 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JIOT.2020.3028434, IEEE Internet ofThings Journal1Performance Analysis and Optimization of NOMAwith HARQ for Short Packet Communications inMassive IoTFatemeh Ghanami, Ghosheh Abed Hodtani, Branka Vucetic, Mahyar ShirvanimoghaddamAbstract—In this paper, we consider the massive non-orthogonal multiple access (NOMA) with hybrid automatic re-peat request (HARQ) for short packet communications. To reducethe latency, each user can perform one re-transmission providedthat the previous packet was not decoded successfully. The systemperformance is evaluated for both coordinated and uncoordinatedtransmissions. We first develop a Markov model (MM) to analyzethe system dynamics and characterize the packet error rate(PER) and throughput of each user in the coordinated scenario.The power levels are then optimized for two scenarios, includingthe power constrained and reliability constrained scenarios. Asimple yet efficient dynamic cell planning is also designed forthe uncoordinated scenario. Numerical results show that bothcoordinated and uncoordinated NOMA-HARQ with a limitednumber of retransmissions can achieve the desired level ofreliability with the guaranteed latency using a proper powercontrol strategy. Results also show that NOMA-HARQ achievesa higher throughput compared to the orthogonal multiple accessscheme with HARQ under the same average received powerconstraint at the base station.I

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