Two paradigms in cellular Internet-of-Things access for energy-harvesting machine-to-machine devices: push-based versus pull-based

Equipping communication apparatuses with energy-harvesting technology could achieve system sustainability without human intervention. Though the harvested energy of existing techniques is limited and intermittent, it is sufficient to power devices in low-power-consuming machine-to-machine (M2M) communications. However, due to the large number of devices with time-varying energy arrival, the medium access control protocol should be redesigned. This study focuses on studying energy-harvesting M2M uplink cellular communications from the protocol design perspective, considering the properties of M2M and energy harvesting. The authors first explore the performance of two fundamental schemes: push-based and pull-based random access channel (RACH) procedures in terms of preamble collision probability, throughput, energy efficiency, and packet delay. In the push-based scheme, devices are self-energy-aware and there is no schedule signalling cost. However, the performance degrades as the device number increases. The pull-based scheme is an alternative to have stable throughput and energy efficiency, with sacrifice of the extra scheduling cost and increasing latency. As a result, a hybrid scheme is proposed to adaptively select the preamble transmission schemes based on the estimated device number. The hybrid scheme guarantees adequate packet delay under different traffic loads and varying energy levels.