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The popularity of concurrent transmissions (CT) has soared after recent studies have shown their feasibility on the four physical layers specified by BLE 5, hence providing an alternative to the use of IEEE 802.15.4 for the design of reliable and efficient low-power wireless protocols. However, to date, the extent to which physical layer properties affect the performance of CT has not yet been investigated in detail. This paper fills this gap and provides an extensive study on the impact of the physical layer on CT-based solutions using IEEE 802.15.4 and BLE 5. We first highlight through simulation how the impact of errors induced by relative carrier frequency offsets on the performance of CT highly depends on the choice of the underlying physical layer. We then confirm these observations experimentally on real hardware and with varying environmental conditions through an analysis of the bit error distribution across received packets, unveiling possible techniques to effectively handle these errors. We further study the performance of CT-based data collection and dissemination protocols in the presence of RF interference on a large-scale testbed, deriving insights on how the employed physical layer affects their dependability., Comment: arXiv admin note: substantial text overlap with arXiv:2005.13816

Flooding protocols based on concurrent transmissions are regarded as the most reliable way to collect or disseminate data across a multi-hop low-power wireless mesh network. Recent works have shown that such protocols are effective for narrowband communication not only over IEEE 802.15.4, but also over the BLE 5 physical layers (PHYs). However, to date, existing literature has only built synchronous flooding solutions on top of a single PHY, and there has been no attempt to leverage different PHYs at runtime to increase performance. This paper fills this gap and presents OSF, an open-source framework that enables the design of multi-PHY synchronous flooding solutions thanks to a novel radio driver and middle-ware architecture capable of dynamically switching the underlying physical layer. This allows exploitation of the specific benefits of each PHY (e.g., higher data-rate, increased robustness) on-demand during each flood, increasing performance. We tailor OSF to the off-the-shelf nRF52840 platform, and showcase its benefits by comparing single-PHY and multi-PHY synchronous flooding solutions on a real-world testbed.

Targeting dependable communications for industrial Internet of Things applications, IETF 6TiSCH provides mechanisms for efficient scheduling, routing, and forwarding of IPv6 traffic across low-power mesh networks. Yet, despite an overwhelming body of literature covering both centralized and distributed scheduling schemes for 6TiSCH, an effective control solution for large-scale multi-hop mesh networks remains an open challenge. This paper addresses this with a novel approach that eliminates much of the routing and link-layer overhead incurred by centralized schedulers, and provides a robust mechanism for data dissemination synchronization within 6TiSCH. Specifically, we leverage the physical layer (PHY) switching capabilities of modern low-power wireless platforms to build on recent work demonstrating the viability of Concurrent Transmission (CT)-based flooding protocols across the Bluetooth 5 (BT 5) PHYs. By switching the PHY and MAC layer at runtime, we inject a BT 5-based CT flood within a standard IEEE 802.15.4 TSCH slotframe, thereby providing a reliable, low-latency scheme for 6TiSCH control messaging. We present an analytical model and experimental evaluation showing how our solution not only exploits the BT 5 high data-rate PHY layers for rapid data dissemination, but can also provide reliable 6TiSCH association and synchronization even under external radio interference. We further discuss how the proposed technique can be used to address other open challenges within the standard.

The popularity of concurrent transmissions (CT) has soared after recent studies have shown their feasibility on the four physical layers specified by BLE 5, hence providing an alternative to the use of IEEE 802.15.4 for the design of reliable and efficient low-power wireless protocols. However, to date, the extent to which physical layer properties affect the performance of CT has not yet been investigated in detail. This paper fills this gap and provides the first extensive study on the impact of the physical layer on CT-based solutions using IEEE 802.15.4 and BLE 5. We first highlight through simulation how the impact of errors induced by de-synchronization and beating on the performance of CT highly depends on the choice of the underlying physical layer. We then confirm these observations experimentally on real hardware through an analysis of the bit error distribution across received packets, unveiling possible techniques to effectively handle these errors. We further study the performance of CT-based flooding protocols in the presence of radio interference on a large-scale, and derive important insights on how the used physical layer affects their dependability., Comment: Paper submitted at ICNP 2020

Wireless low-power transceivers used in sensor networks such as IEEE 802.15.4 typically operate in unlicensed frequency bands that are subject to external interference from devices transmitting at much higher power. Communication protocols should therefore be designed to be robust against such interference. A critical building block of many protocols at all layers is agreement on a piece of information among a set of nodes. At the MAC layer, nodes may need to agree on a new time slot or frequency channel; at the application layer nodes may need to agree on handing over a leader role from one node to another. Message loss caused by interference may break agreement in two different ways: none of the nodes use the new information (time slot, channel, leader) and stick with the previous assignment, or - even worse - some nodes use the new information and some do not. This may lead to reduced performance or failures. In this paper we investigate the problem of agreement under interference and point out the limitations of the traditional message-based n-way handshake approach. We propose novel protocols that use jamming instead of message transmissions and show that they outperform the n-way handshake in terms of agreement probability, energy consumption, and time-to-completion both in the unicast case (two neighboring nodes agree) as well as in the broadcast case (any number of neighboring nodes agree).