A Comparison of Energy-Efficient HARQ Protocols for M2M Communication in the Finite Block-Length Regime

Hybrid Automatic Repeat reQuest (HARQ) techniques are largely used in the context of wireless communications systems especially in the last few years, being employed in the latest cellular systems, including the Long Term Evolution (LTE) standard. Such schemes have been widely studied in literature; however, in this paper we are interested in applying the results of Polyanskiy-Poor-Verdu on the finite block-length regime, comparing the performance of Type-I and Type-II HARQ schemes in the context of green communication, i.e., in a scenario in which the energy efficiency is a key performance indicator. A prominent example of this context is the Machine-to-Machine (M2M) communication, which is foreseen to play a fundamental role as an enabler of the Internet of Things (IoT) paradigm. We derive a novel, optimal, power allocation strategy and we provide simulation results showing that a minimum 40% energy saving can be achieved if we enable packet combining at the receiver side.