Issues of data reliability in indoor channel: Impact on the energy efficiency of battery powered wireless sensor nodes

Wireless sensors are constrained by a limited supply of energy when powered by batteries. They also have limited memory and limited computational power. The challenge of a network based on such constrained infrastructure is twofold; maintaining data reliability and energy efficiency. Availability of the instantaneous channel side or state information (CSI) at the transmitter can help it to set transmission parameters, such as power, data rate and encoding technique, to achieve optimum results. However in an indoor environment, when the movement of objects between a transmitter and a receiver is random, the estimated CSI may not be sufficient to obtain desired results. This paper evaluates the impact of channel fading on data reliability due to multipath transmission. Simulation results q the number of retransmissions required for an indoor fading channel and its impact on battery life. Although adaptive transmission techniques have been proposed and implemented to maximize throughput in several technologies including WIMAX, the primary focus of this paper is on research related to improve energy efficiency of sensor nodes rather than throughput. This is because sensors used for surveillance and monitoring are not designed for high data rates, but are meant to send data to the central station with a certain threshold bit error rate and acceptable latency. This paper proposes a transmission strategy to increase energy efficiency of fading radio channels for improved data reliability. It also emphasizes the need to introduce an opportunistic transmission strategy to meet these goals.