Performance Analysis for Irregular Repetition Slotted ALOHA with Short Packet Transmissions

Abstract

Irregular repetition slotted ALOHA (IRSA) is regarded as a promising short packet transmission scheme for massive machine-type communications (mMTC). However, few related works have taken into account the effect of finite blocklength. In this paper, we propose an IRSA-based uplink access model that introduces the packet error probability caused by the finite block-length. Considering the Rayleigh channel, a frame-level power allocation strategy is used to ensure that all users achieve the same target power at the access point, which enables the identification of collision-free slots. In particular, for frames with unacceptable channel states, a user will actively choose not to perform transmission to improve device energy efficiency. The varying trends of system throughput and user invalid probability with respect to fading threshold and packet length are effectively analyzed. Numerical results show that by properly setting the controllable parameters, a good compromise can be achieved between the two performance metrics.