A Contention Transmission Unit Allocation Scheme for Uplink Grant-free SCMA Systems

In order to satisfy the requirement of supporting massive connectivity accompanied by the cost of transmission latency and signaling overhead, uplink (UL) grant-free Sparse Code Multiple Access (SCMA) design has been proposed. Contention transmission unit (CTU) is the basic resource for contention transmission for UL SCMA. Most CTU allocation schemes allocate CTU just by the UE_ID, which may bring about high packet loss rate due to the collision of CTUs when the activeness of UEs is not similar. In this paper, we first study the equation of the average packet loss rate, where the optimization of average packet loss rate is proved to be a NP-hard problem as a function of the allocation scheme. In this paper, we proposed a novel scheme based on activeness via dynamic programming transforming the NP-hard problem to a solvable and low complexity problem, which can obtain the Pareto optimal solution ultimately. Simulation results demonstrate that the proposed CTU allocation scheme can greatly reduce the packet loss rate with extremely low complexity.