Study On Wireless Power Transfer Mechanism In IoT

Internet of Things(IoT)is a crucial component of the next generation of wireless communication.It tends to improve the quality of services by connecting various mobile devices,sensing devices,and relays through internet without additional human operations.To this end,we need to provide for the various sensing devices with the long-term and stable energy support,which is one of the biggest bottleneck of the IoT commercialization.Among different energy sources,harvesting energy from the radio frequency signal has many advantages,which has been the most promising green energy solution.In this paper,we will focus on the wireless energy harvesting based IoT system and investigate the incentive mechanism of the wireless power transfer based on the contract theory.We consider an IoT system that consist of the RF energy source,the IoT information gateway,and the various IoT sensors.More specifically,the RF energy source benefits from providing wireless power transfer services through different transmission powers.Each IoT sensor does not has the constant energy but can harvest energy from the RF signal by paying the RF energy source some reward.Moreover,the IoT sensor will utilize the harvested energy to transmit its sensing data to the IoT information gateway.Furthermore,we take into account the asymmetric information.That is,the IoT sensors have some private information(i.e.,channel state and energy harvesting efficiency)that the RF energy source only knows the statistically.We first consider the single dimensional private information,i.e.,the IoT sensors are heterogeneous in their channel state.To maximize the profit,the RF energy source needs to design a contract that consists of different transmission powers together with different rewards,one for each type of sensors.Therefore,the contract is feasible if and only if it satisfies the incentive compatibility and individual rationality conditions.This optimal contract problem is non-convex,hence challenging to solve.We first derive the optimal rewards given a feasible transmission power allocation by analyzing the necessary and sufficient conditions.Then we propose two methods to solve the optimal power allocation.Furthermore,we take into account the multi-dimensional private information where the IoT sensors are heterogeneous in both the channel state and the energy harvesting efficiency.The multi-dimensional private information increases the difficulty of achieving the global incentive compatibility.We take advantage of the indifference curve in economics and find that the slope of the IoT sensor's indifference curve(i.e.,the marginal rate of substitution)indicates the sensor's willingness to pay.Moreover,the RF energy source should allocate a larger power to the type of sensors with a high marginal rate of substitution.With this property,we are able to transform the multi-dimensional contract problem back into the single-dimensional case and obtain the optimal wireless power transfer solution through the aforementioned approach.