Efficient Random-Access Scheme for Massive Connectivity in 3GPP Low-Cost Machine-Type Communications

In order to facilitate low-cost network connection of many devices, machine-type communication (MTC) has evolved to low-cost MTC (LC-MTC) in the third-generation partnership project standard. LC-MTC should be able to effectively handle intensive accesses through multiple narrowband random-access channels (RACHs) assigned within the bandwidth of a long-term evolution system. As the number of MTC devices and their congestion rapidly increase, the random-access scheme for the LC-MTC RACH needs to be improved. This paper presents a novel random-access scheme that introduces virtual preambles of LC-MTC devices and associates them with RACH indexes to effectively discern LC-MTC devices. In comparison with the sole use of preambles, our scheme allows an LC-MTC device to better choose a unique virtual preamble. Thereby, the probability of successful accesses of LC-MTC devices increases in contention-based random-access environments. We experimentally assessed our scheme, and the results show that our scheme performs better than the existing preamble-based scheme in terms of collision probability, access delay, and access blocking probability.