Adaptive multi-PHY IEEE802.15.4 TSCH in sub-GHz industrial wireless networks

Abstract

To provide wireless coverage in challenging industrial environments, IEEE802.15.4 Time-Slotted Channel Hopping (TSCH) presents a robust medium access protocol. Using multiple Physical Layers (PHYs) could improve TSCH even more in these heterogeneous environments. However, TSCH only defines one fixed-duration timeslot structure allowing one packet transmission. Using multiple PHYs with various data rates therefore does not yield any improvements because of this single-packet limitation combined with a fixed slot duration. We therefore defined two alternative timeslot structures allowing multiple packets transmissions to increase the throughput for higher data rate PHYs while meeting a fixed slot duration. In addition, we developed a flexible Link Quality Estimation (LQE) technique to dynamically switch between PHYs depending on the current environment. This paper covers a theoretical evaluation of the proposed slot structures in terms of throughput, energy consumption and memory constraints backed with an experimental validation, using a proof-of-concept implementation, which includes topology and PHY switching. Our results show that a 153 % higher net throughput can be obtained with 84 % of the original energy consumption and confirm our theoretical evaluation with a 99 % accuracy. Additionally, we showed that in a real-life testbed of 33 nodes, spanning three floors and covering 2550 m 2 , a compact multi-PHY TSCH network can be formed. By distinguishing between reliable and high throughput PHYs, a maximum hop count of three was achieved with a maximum throughput of 219 kbps. Consequently, using multiple (dynamic) PHYs in a single TSCH network is possible while still being backwards compatible to the original fixed slot duration TSCH standard.

g6TiSCH: Generalized 6TiSCH for Agile Multi-PHY Wireless Networking

“…The proposal by Van Leemput et al [20] is the state-of-the-art in multi-PHY integration in TSCH networking. The authors propose using slower PHYs for unicast links in case the Received Signal Strength Indicator (RSSI) is persistently below a certain threshold.…”

Parent and PHY Selection in Slot Bonding IEEE 802.15.4e TSCH Networks

“…While how to exactly integrate the different modulations in TSCH is not discussed, the proposed policies should be considered as PHY selection mechanisms that can be applied on top of our slot bonding approach. Another recent interesting approach is presented by Van Leemput et al, who take into account the different data rates possible for different PHYs [ 4 ]. The authors defined two alternative timeslot structures allowing multiple packet transmissions to increase the throughput for higher data rate PHYs while maintaining a fixed slot duration.…”

“…When no transmission attempts are available for a certain possible parent, a default ETX value can be chosen (e.g., representing an average link quality). In this case, where link reliability is learned over time and a node has to find a fast and reliable PHY for the current preferred parent (as proposed in Algorithm 1), a node can apply a Link Quality Estimation (LQE) technique as proposed by Van Leemput et al to iterate through the different PHYs [ 4 ]. The necessary score values of possible parents can be distributed throughout the network using the Metric Container option in RPL DIO messages, similar to the metrics distributed for the MRHOF OF [ 19 , 21 ].…”

“…The implementation can be extended to support more PHY radio configurations. As indicated in the work of Van Leemput et al and as seen in Table 2 , taking into account the strict regulation of the sub-GHz spectrum, 44 channels of 200 kHz and 4 channels of 1667 kHz are possible (with frequency overlap) in the 7 sub-GHz bands divided over the European Union 863-870 MHz and 873-920 MHz spectra [ 4 , 24 ]. Such a channel allocation with frequency overlap actually avoids wasting bandwidth and allows for a rich frequency diversity.…”

“…Nevertheless, the 6TiSCH Industrial Internet of Things (IIoT) stack is still limited by the characteristics of the chosen physical (PHY) layer, which is often challenged by the harsh conditions of industrial environments filled with other wireless devices and metal obstacles. To overcome this limitation, the TSCH and 6TiSCH community is shifting research efforts to the support of multiple PHY layers [ 3 , 4 , 5 , 6 ].…”