Throughput Modeling and Analysis of Random Access in Narrowband Internet of Things

Narrowband Internet of Things (NB-IoT) is one of the most promising technologies for low-power, wide-area, and low-traffic applications. In NB-IoT, random access is implemented in media access control layer to resolve the channel contention conflict among multiple user equipments (UEs), and is crucial to the throughput performance of NB-IoT. Previous results in long-term evolution cannot be directly applied due to specification differences. In this paper, we take the first attempt to systematically analyze the performance of random access in NB-IoT. First, after extensively studying the backoff mechanism, we characterize the probability that a UE initiates random access, the probability that a packet is transmitted successfully and the probability that a channel is busy. Then, we define each UE's buffer as a first-in-first-out queue. We employ Markov chain to model retransmission number caused by collisions and the length of the queue simultaneously. By exploiting the characteristic of the steady-state distribution of the Markov chain, the above three probabilities in steady state can be obtained explicitly. Based on these probabilities, we calculate the system throughput in terms of UE number, packet generation rate, retransmission number, and the length of the queue. Finally, we investigate the system throughput and conduct extensive simulations under various parameters, which validate our analysis.