To Sense or Not To Sense: A Delay Perspective

With massive access of Machine-to-Machine (M2M) communications, the delay performance of random access networks has become a major concern, which crucially depends on the access parameter setting and sensing capability of nodes. To facilitate the increasing demand for low-latency services, it is of vital importance to study how to optimize the delay performance by tuning the access parameters, and understand which type of random access, sensing-free Aloha or sensing-based Carrier Sense Multiple Access (CSMA), performs better in terms of the optimal delay performance. In this paper, the minimum mean queueing delay of data packets and the corresponding optimal transmission probability of each node are derived for Aloha and CSMA, based on which the upper bound of sensing time for CSMA to outperform Aloha in terms of the minimum mean queueing delay is characterized. The analysis is applied to the 2-step Random Access-based Small Data Transmission (RA-SDT) scheme in the Fifth-Generation (5G) system, and offers important insights for the optimal access design of M2M communications.