Performance analysis and enhancement of random access process in cellular-IoT

Narrowband Internet of things(NB-IoT) and enhanced machine-type communications(eMTC) are two new IoT-oriented solutions introduced by the 3 rd generation partnership project(3 GPP) in Rel-13. In order to meet the new requirements(such as long battery life, low device cost, low deployment cost, extended coverage and support for a massive number of devices) of machine-to-machine(M2 M) communication, these two technologies had some improvements on the random access(RA) mechanism compared to traditional long term evolution(LTE). For example, repetition of preamble transmission and coverage enhancement(CE) levels have been proposed to offer communication services in a wider area. In addition, NB-IoT has adopted a new spectrum allocation method and proposed a new type of preamble structure to meet the requirement of big amount of connections. We summarize details and differences of the RA process in LTE, eMTC and NB-IoT. Afterwards, as an improvement, we propose an enhanced access protocol for NB-IoT. Finally, performance analysis and comparison are presented in terms of access success probability, average access delay, access spectrum efficiency and average number of RA attempts.