New CAP Reduction Mechanisms for IEEE 802.15.4 DSME to Support Fluctuating Traffic in IoT Systems

TL;DR

This paper introduces two extensions to IEEE 802.15.4 DSME that dynamically adapt the CFP/CAP ratio, enhancing responsiveness to traffic fluctuations while maintaining high throughput in IoT systems.

Contribution

The paper proposes novel mechanisms for real-time adjustment of the CFP fraction in DSME, improving flexibility and performance under variable traffic conditions.

Findings

Extensions enable dynamic CFP/CAP ratio adaptation.

Simulations show improved responsiveness to traffic changes.

High throughput is maintained despite traffic fluctuations.

Abstract

In 2015, the IEEE 802.15.4 standard was expanded by the Deterministic and Synchronous Multi-Channel Extension (DSME) to increase reliability, scalability and energy-efficiency in industrial applications. The extension offers a TDMA/FDMA-based channel access, where time is divided into two alternating phases, a contention access period (CAP) and a contention free period (CFP). During the CAP, transmission slots can be allocated offering an exclusive access to the shared medium during the CFP. The fraction $\tau$ of CFP's time slots in a dataframe is a critical value, because it directly influences agility and throughput. A high throughput demands that the CFP is much longer than the CAP, i.e., a high value of the fraction $\tau$, because application data is only sent during the CFP. High agility is given if the expected waiting time to send a CAP message is short and that the length of the CAPs are sufficiently long to accommodate necessary (de)allocations of GTSs, i.e., a low value of the fraction $\tau$. Once DSME is configured according to the needs of an application, the fraction $\tau$ can only assume one of two values and cannot be changed at run-time. In this paper, we propose two extensions of DSME that allow to adopt $\tau$ to the current traffic pattern. We show theoretically and through simulations that the proposed extensions provide a high degree of responsiveness to traffic fluctuations while keeping the throughput high.