Home > News > Thesis defense — Liviu Octavian Varga — December 16

Thesis defense — Liviu Octavian Varga — December 16

Wednesday 16 December 2015

The goal of the thesis is to enable IPv6 harvested and autonomous wireless sensor networks with very low duty-cycle. It is part of an industrial project, GreenNet, hosted by STMicroelectronics with the goal of being a pioneer in the Internet of Things. The new platform differentiates from its existing competitors by a small size, which implies small battery capacity. However, a photovoltaic cell is capable of recharging the battery even under low light conditions. On top of this, we aim at nodes that sleep for very long periods. Hence, the existing solutions were not completely suited for our needs.
The thesis proposes to analyze the possible challenges that one can meet while developing a harvested low-duty cycle platform. The most important contribution of this work is that we implement and evaluate the performance of our solutions on real hardware platforms in conditions very close to real-life.
In this dissertation, we first of all develop and implement a basic solution based on the IEEE 802.15.4 beacon-enabled standard. We choose the synchronized mode because it allows nodes to reach duty-cycles as low as 0.01%. A more difficult step was to bring multi-hop: we design a new routing scheme inside our network, and a time based access for routers and devices to eliminate interferences as much as possible. The routing scheme is meant to be simple and efficient.
We go even further to optimize the total time the nodes are on: we proposed to shut down coordinators before their standardized end of slot when there is no communication. Devices that do not need to send data can skip beacons and only need to wake up to synchronize their clock or to send data. In the same time we solve the problem of multicast for long sleeping nodes by converting these packets into unicast traffic. We also improved the duty-cycle of routers that do no have associated devices by forcing them to beacon at a slower rate, as long as they do not have any associated devices.
To improve the network performance we also propose a backward compatible multi- channel solution. Such a scheme is useful when a link between two nodes achieves very bad performance on a certain channel but better results on a different frequency.
All the solutions presented above and discussed in the dissertation were implemented and tested on the GreenNet platform. We also realized measurements of the nodes efficiency while in harvested conditions and showed that it is possible to handle har- vested routers, when there is enough available light.

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