Spatial clustering in slotted ALOHA two-hop random access for machine type communication

The LTE random access procedures proposed in 3GPP for Machine Type Communication in current cellular systems may become overwhelmed when too many machine devices attempt to upload their data. In this paper, we propose a two-hop cluster random access based on slotted ALOHA communication. In each cluster, a cluster head (CH) is selected according to the channel gains. The CH aggregates data from cluster members and then initiates the LTE random access procedure to the base station. Due to the offloading from the random access channel to the slotted ALOHA, the number of contending devices is reduced, which alleviates the collision problem and results in better performance. The simplification of access procedure can also significantly decrease the energy consumption. We define a clustering metric for machine locations and we examine the impact of the metric on the performance. The simulation results show that as machine locations become more clustered, the overall performance improves