Power-domain non orthogonal multiple access (PD-NOMA) in cooperative networks: an overview Mahrukh Liaqat 1 • Kamarul Ariffin Noordin 1 • Tarik Abdul Latef 1 • Kaharudin Dimyati 1 Ó Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Non-orthogonal multiple access (NOMA) scheme is emerging as a favourable multiple access scheme for future 5G networks. Compared to orthogonal multiple access techniques, NOMA provides spectral efficiency, user fairness, better connectivity, enhanced data rate and reduced latency. Thus, NOMA can be a suitable multiple access technique for 5G networks. On the other hand, in wireless networks, cooperation is a well-recognized proven technique for performance enhancement. Cooperative networks offer multiple desirable advantages, including high performance, reliability and greater coverage area. It is believed that in future 5G systems, many existing wireless technologies will be combined with new technologies. Power domain-NOMA (PD-NOMA) has features that can provide opportunities of improved perfor- mance and better spectral utilization for downlink cooperative networks. Recently, research works of incorporating PD- NOMA in cooperative networks have gained attention of researchers around the globe. This article surveys the recent research trends in PD-NOMA based cooperative network by reviewing related recent research on performance analysis of cooperative PD-NOMA systems, resources allocation, and impact of relay selection. Additionally, this review article discusses the performance of cooperative PD-NOMA networks when they are integrated with other 5G technologies including cognitive radio, full duplex radio and wireless energy harvesting. Furthermore, some unaddressed issues are highlighted for future research in this area. Keywords Non-orthogonal multiple access (NOMA) Á Cooperation Á Cooperative relay networks Á Cooperative NOMA 1 Introduction The 5th generation (5G) wireless networks are expected to fulfil the growing demands of mobile data. With the fast growth of internet of things, fifth generation networks have to support immense connectivity of devices or/and con- sumers. Compared to existing fourth generation (4G) of cellular network, 5G is expected to meet the following key features: 10–100 times increased data rate, up to 99.99% availability, reduced delays, 10–100 times greater number of connected devices, guaranteed coverage, 10 times reduced energy consumption, and efficient incorporation of existing wireless technologies with new 5G techniques [1–3]. Advanced technologies are required to meet these expected requirements. Over the past two decades, multiple access techniques have been considered very important in designing wireless generation networks and they are considered very impor- tant in describing the efficiency of any communication systems. Radio access technology defines the basic physi- cal connection in a cellular network. Radio access tech- nology is applied by using a radio access network, which provides connection of mobile terminals to the core net- work; this is accomplished by channel access technique. Multiple access (MA) schemes enable multiple users to share the resources. These access techniques can be broadly divided into two types which are, non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA). OMA schemes eliminate interfering signals by assigning orthogonal resources to users. Time division multiple access (TDMA), frequency division multiple access (FDMA) and code division multiple access & Kamarul Ariffin Noordin kamarul@um.edu.my 1 Department of Electrical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia 123 Wireless Networks https://doi.org/10.1007/s11276-018-1807-z