Home-Area Sensor Networks

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Chenyang Lu (PI), Mo Sha,Greg Hackmann

Home area networks (HANs) consisting of wireless sensors have emerged as the enabling technology for important applications such as smart energy and assisted living. A key challenge faced by HANs is maintaining reliable operation in real-world residential environments. This work performs two in-depth empirical studies on the wireless channels in real homes. The spectrum study analyzes spectrum usage in the 2.4 GHz band where wireless sensor networks based on the IEEE 802.15.4 standard must coexist with existing wireless devices. We characterize the ambient wireless environment in six apartments through passive spectrum analysis across the entire 2.4 GHz band over seven days in each of the apartments. Notably, we find that the wireless conditions in these residential environments can be much more complex and varied than in a typical office environment. Moreover, while 802.11 signals play a significant role in spectrum usage, there also exist non-negligible noise from non-802.11 devices. The multi-channel link study measures the reliability of different 802.15.4 channels through active probing with motes. We discover that there is not always a persistently reliable channel over 24 hours; that reliability is strongly correlated across adjacent channels; and that link reliability does not exhibit cyclic behavior at daily or weekly timescales. Nevertheless, reliability can be maintained through a small number of channel hops per day, suggesting channel diversity as a key tool for designing robust HANs in residential environments. Based on the empirical study, we propose the Adaptive and Robust Channel Hopping (ARCH) protocol: a lightweight receiver-oriented protocol which handles the dynamics of residential environments by reactively channel hopping when channel conditions have degraded. Our results demonstrate that ARCH can reduce packet retransmissions by a median of 42.3% compared to using a single, fixed wireless channel, and can enable up to a 2.2X improvement in delivery rate on the most unreliable links in our experiment. Under a multi-hop routing scenario, ARCH reduced radio usage by 31.6% on average, by reducing the ETX of each link by up to 83.6%. Due to ARCH's lightweight reactive design, most links achieve this improvement in reliability with 10 or fewer channel hops per day.


Publications


If you have any questions or comments, feel free to email Mo Sha at msha@wustl.edu.

Acknowledgements

This work is supported by the Grant from Broadcom and Emerson.

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