Relay-Assisted Wireless Energy Transfer for Efficient Spectrum Sharing in Harsh Environments

Abstract

With exponential growth in the number of wireless devices and limited available spectrum, the problem of spectrum sharing remains in forefront of the research community. Due to the large number of wireless sensing devices, even a small percentage of savings can translate into significant spectrum efficiencies. One of the main hurdles in efficient spectrum sharing in wireless sensor networks (WSN) is the problem of power management at the node level to promote longevity without polluting the spectrum, while promoting collaboration. This problem is even more challenging in extreme (harsh) environments where access to power and battery replacement and charging is limited, if not impossible. Passive sensor technology can be used to eliminate the need for batteries, but it suffers from short communication range. Recently, wireless energy transfer (WET) for powering remote sensor nodes in a WSN has drawn considerable research attention, since it can charge sensing circuits remotely and relieve the need for battery replacement. Modeling the charging and power utilization processes can help with smart transmission decisions, which can eliminate unnecessary transmissions and not only save limited battery power at the node level, but also efficiently utilize the shared spectrum. In this paper, we consider a general relay energy assisted scenario, where a transmitter is powered by an energy source through both direct and relay links. We model data and energy channels separately, transmit energy to power the transmitter battery and schedule data transmission based on stochastic models for data. We also consider various static, mobile and highly scattered channel models. We will set a threshold on required transmission energy and channel quality to decide whether the transmission can be successful (efficient use of spectrum) or the packet may not reach the destination (polluting the spectrum unnecessarily). An energy efficient scheduling method is proposed for the system model to determine whether to transmit data or stay silent based on the stored energy level and channel state. An analytical expression has been derived to approximate outage probability of the system in terms of energy and data thresholds. All theoretical results are validated by numerical simulations and verify the effectiveness of energy relaying and proposed energy efficient scheduling method in reducing the outage probability of the system