Novel Protocol For Efficient MTC Transmission Over Massive MIMO Enabled 2-Step RACH

The 2-step Random Access Channel (2S-RACH) protocol introduced in 5G New Radio (NR) halves the number of steps compared to 4G. This achieves significant energy efficiency for MTC devices as the small MTC data transmission can be completed within 2 steps of RACH procedure itself. Limited number of preambles used in RACH can result in collision leading to back-off and retransmissions. Collision probability increases with an increasing number of MTC devices attempting transmission. The RACH attempts in mMTC system typically have periodic patterns of low number of attempts, which can change dynamically to extremely high in case of emergencies when all device attempts for RACH access simultaneously. In such cases, severe congestion for RACH resources leads to recursive retransmissions leading to service outage. Enabling massive MIMO-based physical uplink shared channels (mPUSCH) for the 2S-RACH can be an effective solution for reducing the congestion, provided the resources are allocated dynamically. In this paper, we propose a novel 2S-RACH protocol; Dynamic Grant Controlled RACH Access (DGCmRACH) that dynamically assigns the massive MIMO resources based on the estimated number of random access users during preamble transmission. The simultaneous transmission for non-colliding and collision based data transmission proposed in this protocol significantly improves the resource efficiency without access delay impacts. The compact control channel design of DGCmRACH also achieves shorter access delay compared to 25-RACH by 32%. The DGC-mRACH protocol shows a 30% reduction in resource overloading conditions in RAN compared to static resource allocation for mass concurrent access scenario.