Latency-Energy Tradeoff based on Channel Scheduling and Repetitions in NB-IoT Systems

TL;DR

This paper develops a model to analyze how channel scheduling and repetitions in NB-IoT systems affect latency and energy consumption, providing insights for optimizing system performance.

Contribution

It introduces a tractable model of NB-IoT protocol operation to analyze the latency-energy tradeoff influenced by channel scheduling and coverage class interactions.

Findings

Channel scheduling significantly impacts latency and battery life.

The model accurately predicts system performance, validated by simulations.

Optimal operation points balance latency and energy consumption.

Abstract

Narrowband IoT (NB-IoT) is the latest IoT connectivity solution presented by the 3GPP. NB-IoT introduces coverage classes and introduces a significant link budget improvement by allowing repeated transmissions by nodes that experience high path loss. However, those repetitions necessarily increase the energy consumption and the latency in the whole NB-IoT system. The extent to which the whole system is affected depends on the scheduling of the uplink and downlink channels. We address this question, not treated previously, by developing a tractable model of NB-IoT access protocol operation, comprising message exchanges in random-access, control, and data channels, both in the uplink and downlink. The model is then used to analyze the impact of channel scheduling as well as the interaction of coexisting coverage classes, through derivation of the expected latency and battery lifetime for each coverage class. These results are subsequently employed in investigation of latency-energy tradeoff in NB-IoT channel scheduling as well as determining the optimized operation points. Simulations results show validity of the analysis and confirm that there is a significant impact of channel scheduling on latency and lifetime performance of NBIoT devices.