Efficient RAN Overload Control Mechanism for NR based mMTC by Dynamic SCMA for RACH

Concurrent Random Access Channel attempts (RACH attempts) in a massive Machine Type Communication (mMTC) system during critical situations create a radio access network (RAN) overload that reduces network accessibility. In Long Term Evolution (LTE) system, Extended Access Class Barring (EAB) is used to mitigate RAN overload by randomizing RACH attempts in the time domain. However, EAB mitigates the RAN overload at the cost of increased access delay for the mMTC transmission, with the access delay impact increasing exponentially with increasing number of devices. Since mMTC is one of the primary usage scenarios for 5G where multi-fold increase in device density is expected, a solution for RAN overload control that does not increase the access delay is essential. In this paper, we propose a RAN overload control mechanism based on Sparse Code Multiple Access (SCMA). In the event of massive RACH attempt scenarios resources for SCMA access are dynamically activated and controlled based on congestion estimation. Simulation results show that the proposed mechanism reduces the mean access delay by 88% and mean RACH attempts by 14% compared to EAB for concurrent access scenarios thereby improving the device capacity of the mMTC system.