KMote - Design and Implementation of a Low Cost, Low Power Hardware Platform for Wireless Sensor Networks

Wireless Sensor Networks (WSNs), as the name suggests consist of a network of wireless nodes that have the capability to sense a parameter of interest like temperature, humidity, vibration etc. The sensed parameter is often relayed to a base station through the network formed amongst these nodes. The devices used are typically characterized by low cost, low power and are rugged in operation. They are commonly referred to as motes in the WSN domain. The usage of motes was originally intended/ designed for military applications but soon spread to other civilian applications like habitat Monitoring, environment monitoring, monitoring structural health of railway bridges etc. Advances in hardware and wireless technologies have facilitated rapid development of these tiny motes worldwide but their availability in India is not common. Our work has been motivated by the need to develop such motes in India. This report describes the design and implementation of a mote, which we call as KMote. The mote integrates programming, computation, communication, and sensing onto a single system and provides an easy user interface for operating and deploying it. This report discusses the design challenges and hurdles involved in translating a paper design to a working prototype. Simplicity in design, low cost, and low power consumption were the primary considerations that influenced the design of KMote. This being our first effort in hardware design, we opted for a simplistic design and chose programming complexity in favour of hardware simplicity. We have implemented a prototype that is based on the telos design and integrates an MSP430 microcontroller, CC2420 radio, 8 MB flash and an on board temperature sensor. We have tested and proved the operation of the microcontroller and the radio for transfer of data over a wireless channel in 2.4 Ghz spectrum (ISM band). We have also carried out outdoor experimental tests to determine the RF communication range of the KMote. We have obtained a range nearly double that of the TMote, the most popular commercial mote available in the market. At this range we were operating at an average RSSI of -84 dBm and experienced a packet error rate less than 1%. The bill of material cost of KMote is Rs 1625 and is less than one fourth of the selling cost of the Tmote (Rs 7740). Also, the administrative overheads involved and large lead time for procurement of Tmote deters widespread use of motes in India. Therefore, the low cost of development of KMote makes it a viable option for fabricating such boards in India. We believe that the experience and knowledge gained by developing this mote would be beneficial to improve the existing prototype and aid in the easy availability of such motes to research and educational communities in India, thus contributing to the growth of applications in the WSN domain. We also argue in favour of developing such motes in India due to the significant cost benefits offered by such a development.