Abstract
This paper presents a traffic-adaptive contention-free period (CFP) extension (TaCFPext) protocol for IEEE 802.15.4 deterministic and synchronous multichannel extension (DSME) medium access control (MAC), which aims to satisfy the traffic adaptability requirement of industrial wireless sensor networks (IWSNs). The legacy DSME standard has limitations in accommodating highly varying traffic load in IWSNs due to its fixed multi-superframe structure. TaCFPext enables a node to adaptively use a contention access period (CAP) as an extended CFP (extCFP) on the demands of traffic loads in a distributed manner. The node starts TaCFPext when it determines that the CFP of the current multi-superframe is insufficient to accommodate the traffic load. Then, the node selects a CAP to be used as an extCFP, on which it is allocated an extended guaranteed time slot (extGTS). When the traffic load decreases, the extGTS is deallocated before the GTS in CFP, and the extCFP returns to CAP again. An experimental simulation was performed to verify the superiority of TaCFPext. The results demonstrated that TaCFPext outperforms the legacy DSME for aggregate throughput and average delay under various traffic conditions.
Highlights
Industrial wireless sensor network (IWSN) is a key component for the Industrial Internet of Things (IIoT) framework, which can be widely adopted in various industrial applications such as environmental sensing, monitoring, control and automation
The channel frequency used during the extGTS (i.e., C_ext) is derived as follows: C_ext HoppingSequenceList_ext[m], m (i j l macChannelOffset where HoppingSequenceList_ext[m] represents the m-th channel frequency in the modified hopping sequence for extGTS, i is the index of the slot in an extCFP, j is the Superframe duration (SD) index that represents the index of the superframe in a beacon interval (BI), k is the number of slots within an extCFP (i.e., 8), macChannelOffset is the channel offset of the receiver node, macPanCoordinatorBsn is the sequence number of enhanced beacon (EB) sent by the PAN coordinator, and macHoppingSequenceLength is the hopping sequence length of the existing hopping sequence
TaCFPext achieves 41.61% and 16.85% shorter average delay compared to legacy deterministic and synchronous multichannel extension (DSME) and DSME with contention access period (CAP) reduction, respectively
Summary
Industrial wireless sensor network (IWSN) is a key component for the Industrial Internet of Things (IIoT) framework, which can be widely adopted in various industrial applications such as environmental sensing, monitoring, control and automation. Battaglia et al [28] proposed the concept of shareable GTS for DSME networks, which can be redundantly allocated to one or more periodic traffics having a period longer than the length of the multi-superframe, thereby improving the usability of the CFP These studies commonly use the fixed multisuperframe structure of DSME standard, and it is difficult to adapt to highly-varying traffic load. The coordinator calculates the number of GTSs required in the network, by which it toggles the CAP reduction option and adjusts the length of the multisuperframe In these studies, it is assumed that nodes constantly transmit the same amount of traffic.
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