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PHY Abstraction and System Evaluation for SCMA with UL Grant-Free Transmission

This paper aims to evaluate the system level performance of the newly proposed non-orthogonal multiple access scheme sparse code multiple access (SCMA) with uplink grant-free transmissions for 5G massive machine-type communication (mMTC) scenario. The challenge lies in the modeling and abstraction of physical layer actions as the link-to-system interface, including the features of overloading, grant-free transmission, as well as non-linear receiver. Specifically, we propose to use single bound to simplify the maximum-likelihood (ML) receiver modelling with only linear computational complexity, while still guaranteeing sufficient accuracy requirement. Extensive simulations verify the correctness of the method under a series of practical assumptions. Evaluation results show that non-orthogonal multiple access schemes such as SCMA with grant-free can provide significant system capacity gain over orthogonal multiple access such as grant-free OFDMA (about 3.5 times as shown in the evaluated scenario) in terms of packet arrival rate at given system outage (defined as 1% packet drop rate). It is noted that the proposed method has been just agreed in 3gpp RAN1 86 meeting and included in the technical report.