Digital Signal Processing 92 (2019) 223–233 Contents lists available at ScienceDirect Digital Signal Processing www.elsevier.com/locate/dsp Cognitive radio inspired NOMA with SWIPT for green multicasting in next generation wireless networks Sangeeta Bhattacharjee a , Tamaghna Acharya a,∗ , Uma Bhattacharya b a Department of Electronics and Telecommunication Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, 711103, India b Department of Computer Science and Technology, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, 711103, India a r t i c l e i n f o a b s t r a c t Article history: Available online 28 June 2019 Keywords: Energy-efficient multicast Cognitive radio inspired NOMA SWIPT Outage analysis This paper investigates an application of simultaneous wireless information and power transfer (SWIPT) in a cognitive radio (CR) inspired non-orthogonal multiple access (NOMA) framework with an aim to support simultaneous multicast services of delay sensitive traffic to a high priority multicast group and a low priority multicast group, modeled as primary user (PU) and secondary user (SU) respectively. A cooperative NOMA protocol is proposed where the nodes in the SU multicast group (SU-MG), located in between a common base station (BS) and the PU multicast group (PU-MG), act as relays. As an incentive, a provision is made such that the BS could support exclusive downlink transmission to the SU-MG. In view of the challenge of supporting sustainable network operation with their limited battery power, the SU relays are equipped with requisite harvesting hardware to harvest energy from the NOMA signal transmitted by the BS, using the principle of SWIPT. Closed form expressions of outage probabilities of PU-MG and SU-MG and their approximations under high SNR regime are derived to characterize the performance of the proposed protocol. Furthermore, allocation of exclusive time interval to SU-MG and power sharing of NOMA signal are optimized jointly with an aim to minimize the outage probability of SU-MG under the outage constraint of PU-MG. Simulation results are presented to validate the accuracy of the analytical expressions. Results highlight that proposed scheme performs much better in terms of energy efficiency of PU-MG as compared to that of traditional orthogonal multiple access and non- cooperative NOMA, both without SWIPT.  2019 Elsevier Inc. All rights reserved. 1. Introduction Non-orthogonal multiple access (NOMA) [1] is a promising technology to ameliorate the spectrum utilization of 5G cellu- lar networks as well as other emerging wireless networks such as smart grid [2], radar communication [3], etc. NOMA provides paradigm shift from the conventional orthogonal multiple access (OMA) techniques, where users are served by orthogonal resource blocks. It achieves higher system throughput and accommodates massive connectivity by allowing multiple users to share frequency and temporal resources over a common spectrum through power or code domain multiplexing [4]. The key idea of power domain NOMA is to serve multiple users, with heterogeneous channel con- ditions, concurrently by superimposing their signals at the trans- mitter with different power levels. This enables delivery of lesser * Corresponding author. E-mail addresses: sangeeta.bhatta@gmail.com (S. Bhattacharjee), t_acharya@telecom.iiests.ac.in (T. Acharya), ub@cs.iiests.ac.in (U. Bhattacharya). power to the users with stronger channel conditions in compar- ison to that of the users with poorer channel conditions [5]. At each receiver, successive interference cancellation (SIC) technique [4] is used to recover the individual users’ signal from the su- perimposed one by eliminating multiuser interference. Although conventional power-domain NOMA ensures user fairness, it cannot guarantee reception reliability due to inherent interference present in the transmitted signal [6]. Cognitive radio (CR) inspired NOMA (CR-NOMA) is a varia- tion of power-domain NOMA, which facilitates intelligent spectrum sharing by minimizing multiuser interference while guaranteeing the required heterogeneous quality of service (QoS) for multiple users. In downlink CR-NOMA, the base station (BS) serves multiple users by prioritizing them according to their QoS requirements [7]. Specifically, the users with stronger channel conditions, referred to as secondary users (SUs), are granted opportunistic access to the spectrum of primary users (PUs) with poorer channel condi- tions subject to the satisfaction of QoS requirements of the latter. However, a situation may arise, that PUs, because of their strin- gent QoS requirements, may deny spectrum access to the SUs due https://doi.org/10.1016/j.dsp.2019.06.011 1051-2004/ 2019 Elsevier Inc. All rights reserved.