Damien O'Rourke

Heterogeneous traffic performance comparison for 6LoWPAN enabled low-power transceivers

We study the suitability of IPv6/6LowPan protocols under heterogeneous traffic loads in environmental sensor networks: microclimate nodes generating periodic but low-bandwidth data, while multimedia nodes generating high-bandwidth data streams on demand, for example. We further study the performance tradeoffs we can achieve by varying the radio frequency or data rate of radio transceivers in both indoor and outdoor environments. We use one legacy and two new IEEE 802.15.4 compliant transceivers, in the 900 MHz and 2.4 GHz bands. We show that, surprisingly, the 2.4 GHz radio outperforms the 900 MHz radio outdoors in terms of the maximum range, but performs worse indoors at higher data rates. We show, however, that irrespective of the radio band used, the Berkeley low-power IP network stack supports high-bandwidth data transmissions (up to 120 kbps), while handling heterogeneous traffic well --- at 99.9% reliability.

An Energy-efficient Rate Adaptive Media Access Protocol (RA-MAC) for Long-lived Sensor Networks

We introduce an energy-efficient Rate Adaptive Media Access Control (RA-MAC) algorithm for long-lived Wireless Sensor Networks (WSNs). Previous research shows that the dynamic and lossy nature of wireless communications is one of the major challenges to reliable data delivery in WSNs. RA-MAC achieves high link reliability in such situations by dynamically trading off data rate for channel gain. The extra gain that can be achieved reduces the packet loss rate which contributes to reduced energy expenditure through a reduced numbers of retransmissions. We achieve this at the expense of raw bit rate which generally far exceeds the application’s link requirement. To minimize communication energy consumption, RA-MAC selects the optimal data rate based on the estimated link quality at each data rate and an analytical model of the energy consumption. Our model shows how the selected data rate depends on different channel conditions in order to minimize energy consumption. We have implemented RA-MAC in TinyOS for an off-the-shelf sensor platform (the TinyNode) on top of a state-of-the-art WSN Media Access Control Protocol, SCP-MAC, and evaluated its performance by comparing our implementation with the original SCP-MAC using both simulation and experiment.

Practical packet combining for use with cooperative and non-cooperative ARQ schemes in resource-constrained wireless sensor networks

An improved implementation of a post-detection packet combining scheme, which is especially applicable to low power, resource-constrained sensor networks, is developed and practically implemented on popular off-the-shelf wireless motes. The algorithm can be used as part of protocols such as cooperative communications and hybrid-ARQ schemes which have been shown to be of major benefit for wireless communications. Using the packet combining implementation developed in this paper more than an 85% reduction in energy costs are possible over previous, similar approaches. Both simulated and practical experiments are developed in which packet combining is shown to offer up to approximately 2.5dB reduction in the required Signal-to-Noise Ratio (SNR) for a desired Packet Error Rate (PER). This is a welcome result as complex schemes, such as maximal-ratio combining, are not implementable on many of the resource constrained devices under consideration.

A Practical Implementation of an Improved Packet Combining Scheme for Wireless Sensor Networks

An improvement to a recently proposed packet combining procedure based on the use of a CRC is developed. Upon receiving two packets, sent over independent channels, a large error burst may appear in one; however, it is unlikely that the same situation will have occurred for its pair. By making an intelligent choice as to which packet the burst is most likely to be in, and choosing the other packet for correction, the decoding time can be reduced significantly. A practical implementation is provided with real results that show not only can this decision be made correctly on the majority of occasions but, once the correct packet is chosen, an intelligent search operation can be performed further reducing overhead.

Towards a framework for a versatile wireless multimedia sensor network platform

We describe our current work towards a framework that establishes a hierarchy of devices (sensors and actuators) within a wireless multimedia node and uses frequent sampling of cheaper devices to trigger the activation of more energy-hungry devices. Within this framework, we consider the suitability of servos for Wireless Multimedia Sensor Networks (WMSNs) by examining their functional characteristics and energy consumption [2].