QBT: Queue-Size Based Busy Tones for Protecting Multihop Low-Power Networks

Cross-technology interference in the ISM band is a prevalent and challenging problem. Prior work has proposed to use busytone signaler that can protect Zigbee transmissions from WiFi interference, but only in a single-hop setting. In this work, we propose Queue-size based Busy Tone (QBT) scheme that uses novel multihop busytone scheduling and priority path selection algorithms to protect multihop Zigbee network under heavy WiFi traffic. We adopt the busytone idea from prior work, but extend it to multihop networks where data is collected from and forwarded by a number of low-power nodes. We implement QBT on a lowpower embedded platform, and evaluate through experimental measurements on a real multihop LLN testbed consisting of 30 low-power embedded nodes and one gateway with two radios, the sink and the signaler, respectively. We show that QBT improves the performance of Zigbee network under WiFi interference dramatically in terms of both reliability (up to 66.4%) and energy efficiency (up to 24.4%). We also report our findings on adjacent-channel interference among Zigbee channels, and investigate the effect of busytone on WiFi traffic as well.