Asymmetrical PS Scheme For Maximizing Capacity In A Two-Way Relaying Network With Energy Harvesting

Two-way relaying technology can improve the spectrum efficiency and extend the coverage area by making full use of time slot resources,so it is usually used for information exchange between sensor nodes in the Internet of Things(IoT).Nevertheless,the relay nodes in the network are mostly energy-constrained and randomly deployed around the terminals.Thus how to provide energy for relay nodes with low overhead while guaranteeing reliable communication is crucial.Driven by this demand,the technology of relaying network with energy harvesting emerges by utilizing the characteristics of radio frequency(RF)signals that can not only carry energy but also transmit information.This paper aims at three-step two-way relaying network based on power-splitting(PS)receiver.Different from existing studies,we make full use of the channel statistical characteristics of different links in the two-way relaying system to study how to design appropriate asymmetrical PS scheme from the perspective of outage capacity.The main contributions are as follows.Firstly,the outage performance under asymmetrical PS scheme is studied by considering a linear energy harvesting(EH)model.For the expression of the outage probability with the transcendental integral,the result error will be relatively large if the upper and lower bounds are given to approximate the simulation value of outage capacity.Therefore,this paper approximates the transcendental integral to the sum of M closed-form expressions.On this basis,the expression of outage capacity is given,and the influence of system parameters(such as distance between terminals and relay nodes)and PS coefficient on outage capacity is studied.Finally,an iterative algorithm is proposed to determine the optimal PS coefficient,so as to obtain the maximum outage capacity.Secondly,a practical energy harvester circuit consists of the non-linearity components such as diodes and inductors,etc.Thus,the energy conversion efficiency gradually decreases with the increase of RF power and finally tends to zero.If the research results based on the linear EH model are directly applied to the actual communication system,it will lead to resource mismatch and be failure to achieve optimal transmission performance.Therefore,it is necessary to restudy the outage performance of our considered system and redesign the corresponding asymmetrical PS ratios based on the characteristics of non-linear EH model.Toward this end,we first introduce a non-linear EH model,which is characterized by multi-segment linear function,and the parameters of the multi-segment linear function are obtained by fitting with the actual test data.By means of the total probability formula and random process knowledge,we then obtain the expressions of the outage probability and outage capacity.Finally,the influence of relay network parameters and PS coefficient on outage capacity is studied by combining the derived formula.The theoretical results are verified by Monte Carlo simulation and the proposed asymmetrical PS scheme is compared with the existing symmetric PS schemes.The results show that the asymmetric PS scheme can make full use of the channel statistical characteristics between terminals and relay nodes,thus effectively reducing the outage probability and increasing the total outage capacity of the three-step two-way relaying network.