Study On Cooperative Communication Of Cognitive Radio Networks With Simultaneously Wireless Information And Power Transfer

Wireless communication systems are faced with unprecedented challenges, such as the scarcity of the spectrum resources, the energy constrainment of wireless networks and the point to point communication approaching the Shannon limit, and so on. A variety of solutions have been put forward to address these challenges. Especially, the cognitive radio(CR), proposed by Dr. Joseph Mitola, has been considered as a promising approach to mitigating spectrum scarcity by enabling unlicensed/secondary users(SUs) to opportunistically access the licensed but underutilized spectrum of primary users(PUs). Meanwhile, energy harvesting technology provides a promising way to power energy constrained wilreless networks because of its convient depolyment and pollution-free characteristics 。 What’s more, as cooperative communication can enhance the reliability of conventional wireless transmission and expand its coverage, cooperative orthogonal frequency division multiplexing(OFDM) has been extensively studied and gradually incorporated into CRNsIn this thesis, we consider user cooperation in a cognitive radio network(CRN) which is operated in orthogonal frequency division multiplexing(OFDM) scheme in the context of simultaneous wireless information and power transfer(SWIPT). In particular, the secondary transmitter(ST) can not only forward the received primary signals to assist primary transmission and earn more opportunities to utilize the primary spectrum, but also extract energy from part of those signals to power both the relay transmission and its own secondary transmission.In our work, we accordingly combine the information cooperation with the energy cooperation in the CRN, and propose two joint information and energy cooperation schemes corresponding to two practical receiver architectures at ST, namely, the time switching scheme and the power splitting scheme, both of which involve time and power allocation for cooperative transmission.In the power splitting scheme, the RF signal is divided into two streams, one for forwarding to the PU and the other for energy harvesting, which achieves better tradeoff between information and energy transfer. Meanwhile, another cooperative coommunicaion scheme is proposed with the consideration of subcarrier matching, in which the spectrum band of the ST is separated into two portions, one portion for primary information relaying and the other for sencondary information transferring. This cooperation scheme balances the primary transmission and secondary transmission in a better fashion.For each scheme, efficient algorithms are devised to tackle such non-trivial tradeoffs. Simulation results demonstrate that the proposed user cooperation schemes significantly improve the achievable throughput.