Abstract
Improving spectral efficiency under a certain energy limitation is an important design metric for future wireless communications as a response to the growing transmission demand of wireless devices. In order to improve spectral efficiency for communication systems without increasing energy consumption, this paper considers a non-orthogonal multiple access (NOMA)–based cognitive radio network, with the assistance of a wireless-powered relay station (RS), and then analyzes the system outage performance under amplified-and-forward (AF) and decoded-and-forward (DF) cooperative transmission modes. Specifically, the base station (BS) has the opportunity to cooperate by transmitting information through the RS, depending on whether the RS can harvest sufficient RF energy for cooperative transmission. That is to say, when the energy stored by the RS is sufficient for cooperative transmission, the RS will assist the BS to forward information; otherwise, the BS will send information through direct links, while the RS converts the radio frequency (RF) signals sent by the BS into energy for future transmission. Moreover, the transmission power required by the RS for cooperative transmission is usually relatively large, while the amount of harvested energy by the RS in a transmission slot is usually low, so it takes several consecutive time slots to accumulate enough transmission energy. To this end, we utilize a discrete-time Markov chain to describe the processes of charging and discharging of the RS. Subsequently, we derive the closed-form outage probabilities of both the primary and secondary systems for the considered system in AF and DF modes through mathematical analysis, and verify the accuracy of the analyses through Monte Carlo simulation. The simulation results show that the two proposed cooperative transmission schemes with AF and DF relaying techniques outperform both direct transmission and other similar schemes in both the primary and secondary system, while the DF scheme can provide better performance than the AF scheme within the range of setting values.
Highlights
IntroductionWith non-orthogonal multiple access (NOMA), user equipments (UE) superpose the messages in the same time/frequency/code/power domain and impose inter-user interference simultaneously at the transmitter side, while the receivers side employs the successive interference cancellation (SIC) technique [2,3]
The cooperative non-orthogonal multiple access (NOMA) (C-NOMA) [5,6] scheme can further enhance the performance of NOMA, where one NOMA user acts as a relay to help the other one for reliable transmission
The qualitative numerical results showed that the proposed optimal resource allocation strategy can significantly enhance the sum transmission rate and transmission performance of the secondary system when compared to a traditional cognitive radio network (CRN)-NOMA system
Summary
With NOMA, user equipments (UE) superpose the messages in the same time/frequency/code/power domain and impose inter-user interference simultaneously at the transmitter side, while the receivers side employs the successive interference cancellation (SIC) technique [2,3]. All these attractive characteristics of NOMA can provide higher spectrum efficiency for the overall system and better fairness for users [4]. The combination of CRN, C-NOMA, and energy harvesting techniques obviously provide the higher spectrum efficiency and better outage performance
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
