On Improving the Energy Efficiency of Wireless Sensor Networks under Time-Varying Environment

The adaptive modulation and coding (AMC) schemes has long been adopted at physical layer to combat time-varying properties of the wireless channel. However, transmitting packet over deep fading channel can render extra energy expenditure, due to the incorporation of more error protection or usage of lower modulation mode, which is unaffordable for energy-limited wireless sensor device. To avoid such inefficient energy usage, a simple approach is to temporally buffer the packet when the channel is in deep fading, until the channel quality recovers. Nevertheless, buffering packet can lead to communication performance degradations - communication latency and packet overflow, which should be taken into consideration in sensing applications with QoS requirements. In this paper, by using previously proposed discrete time queuing model, we analyze the effects of Rayleigh fading on the sensor communication system, and propose a cross-layer design on power aware communication of sensor device. Specifically, in such channel adaptive system, each sensor can judiciously accesses the medium according to the channel condition, traffic load, and buffer variation. Simulation and analytical results indicate that, such cross-layer design can lead to energy conservation by as much as 30-40 per cent.