An Improved Random Access Scheme Using Directional Beams for 5G Massive Machine-Type Communications

In the 5th generation (5G) massive machine-type communication (mMTC), random access is the limiting factor of performance because there may be massive user equipments (UEs) up to 1 million unit competing for the access opportunities. Existing random access schemes in the 4th generation (4G) or 5G systems are not able to handle such a large amount of concurrent random access requests. This article proposes a random access scheme based on directional beams, which offers a new spatial degree of freedom to improve the random access performance in 5G mMTC. In this scheme, a cell is divided into Beam Zones in the space domain. UEs in different Beam Zones choose a certain physical random access channel (PRACH) resource with a different probability. When preamble collision occurs, uplink radio resource is allocated to the Beam Zone which has low collision probability. We provide theoretical performance analysis of the proposed scheme using different performance metrics. Comparisons are carried out between the proposed and several existing random access schemes. The proposed scheme can be easily deployed without any modification to the 5G framework. Existing random access optimizing algorithms can also be applied to the proposed scheme.