Comprehensive Throughput Analysis of Unslotted ALOHA for Low Power Wide Area Networks

Unslotted ALOHA has been often employed by several low power wide area networks (LPWANs) for Internet-of-Things (IoTs) as a random access (RA) protocol. This work analyzes the performance of unslotted ALOHA systems in terms of throughput and RA delay, and investigates their optimization. Our analysis consists of 1) two-heterogeneous user case, whose backoff rate and packet length are different, 2) N-homogeneous user case, whose backoff rate and packet length are identical, and 3) homogeneous users of infinite population model. In the two-user case, we investigate the throughput region of unslotted ALOHA by using a multiobjective optimization problem (MOOP) and derive the Laplace Stieltjes transform (LST) of the probability density function (PDF) of RA delay. For N-homogeneous user case, we show how the throughput behaves according to the population size, packet length, and backoff rate. Our work may provide a comprehensive analytical framework for unslotted ALOHA systems.