Cogent Computing's Pervasive Computing Laboratory is the hub of our work with state-of-the-art software and hardware in the area of wireless sensor networks and embedded systems design. Off-the-shelf systems such as Crossbow's MICA2 series of sensor nodes enable us to rapidly prototype novel, practical techniques for core sensor network capabilities, such as ad-hoc locationing.
In addition to working with off-the-shelf hardware, we develop novel embedded systems. The Pervasive Computing Laboratory contains complete resources to do this, including Altera EPXA1 development kits, a digital storage oscilloscope, an arbitrary signal generator and a logic analyser. Our work in novel sensing hardware makes use of the Gumstix Linux platform with Bluetooth and Zigbeewireless technology.
We use a wide variety of software development resources, from operating systems for embedded systems, such as TinyOS, to high-level languages like Python for simulation and visualisation, as in our work on self-organising maps. We also develop novel system development tools, such as the SenSor simulator for wireless sensor networks.
The testbed’s main function is to facilitate the design, implementation, evaluation and testing of sensor network applications as well as protocols prior to full-scale deployment. Once complete it will allow the implementation of various architectures in order to allow decisions on which is best for the application under construction. The testbed will also maintain tools for easy debugging as testing proceeds.
The current implementation boasts a hierarchical architecture although the configuration is flexible enough to allow a flat, fully-distributed architecture if the application calls for it. The initial iteration of the testbed consists of 16 nodes (deployed end of Dec. 2007) with 40 nodes in the next implementation cycle (due to be launched in March 2008). A basic flooding protocol has already been implemented with plans to implement a cluster-based protocol like Leach in the near future.
A service for collection and dissemination of sensed data has already been implemented and tested on temperature sensory inputs.
The Bluetoothradio provides a convenient means of establishing a small network between the devices. Bluetooth personal area networks (PANs) involve the creation of picoNets, which are composed of up to 8 devices, one of which is designated the master. By interconnecting these Bluetooth picoNets, scatterNets which are composed of more than the standard 8 devices, devices from different picoNets can perform bridging by switching between different picoNets to allow communication in a larger network. The initial iteration uses Bluetooth for communication with the next iteration to include even more nodes or using a combination of Bluetooth with a wifi backbone for expanding the size the network. A Zigbeeimplementation is also planned given its more reliable communication model.
Sensor node hardware
In use are the Connex 400xm-bt and Verdex 400xm-bt motherboards developed by Gumstix Inc. These run Linux and feature the Marvell® PXA270 with XScale™ 400Mhz processor. There are 16Mb of Flash memory and 64Mb of RAM on board ideal for supporting applications that have greater memory requirements. Communication capabilities include Bluetooth(TM) communications, WiFI (802.11G standard) and Zigbee. Board dimensions are 80mm x 20mm with 60 pin and 92 pin connectors for expansion boards.
Multi-type sensing capability is hosted on an in-house designed expansion board allowing up to sensors per node for multi-point data capture. Currently, the boards interface with temperature sensors. In the second phase (starting Jan. 2008) the sensor load will be extended to include accelerometers, humidity and light sensors.