Enhanced spatial group based random access for cellular M2M communications

We have proposed a spatial group based random access (SGRA) scheme which is a novel RA scheme to effectively increase the number of available preambles for future cellular M2M communications. In the SGRA scheme, a machine node in the cell should determine its own spatial group (SG) by estimating the distance between the eNodeB and itself through any distance estimation methods. At the moment, the distance estimation error may inevitably occur in the distance estimation and may cause a group-mismatch problem, which affects the performance of the SGRA scheme in terms of RA collision probability and delay. Therefore, in this paper, we propose a group-reselection solution and a shared distance solution in order to resolve the group-mismatch problem in the SGRA scheme. Through numerical results, it is shown that the combination of the proposed solutions provides a significant robustness against the distance estimation errors, which leads to accommodating a significantly larger number of machine nodes with very lower collision probabilities and shorter average RA delay in more practical M2M deployment environments.