Two Step Random Access Latency Improvement in Congested beyond 5G Networks

Abstract

It has been recently proposed to enhance the performance of random access procedure (RAP) by downsizing the current four step RAP (4s-RAP) to two step RAP (2s-RAP) in order to address ultra reliable low latency communications (URLLC) in 5G and beyond 5G wireless networks. 2s-RAP reduces latency and signaling overhead by manifesting only one round trip between gNB (5G base station) and the UE (user equipment). However, the low latency goal of 2s-RAP is challenged by the increase in the number of UEs in the future wireless networks. Numerous UEs competing for limited random access resources would result in frequent collisions followed by multiple random access reattempts, resulting in increased delay. In this paper, we propose novel algorithms to improve the performance of 2s-RAP in a congested environment. In the proposed algorithms, the UEs can perform RAP reattempts in either 2s-RAP or 4s-RAP based on the channel conditions such that the chances of RAP failure due to poor channels are reduced. They can also transit to 4s-RAP from the initially selected 2s-RAP in order to alleviate the congestion in 2s-RAP. The proposed algorithms are probabilistically analyzed based on collision probabilities and success rates. We employ our derived mathematical equations, as well as carry out simulation evaluations, to present the performance results effectively.