ABSTRACT
The last decade has witnessed a rapid increase in the number of mobile subscribers with portable devices like smart phones and tablets to enjoy a wide range of services from simple voice to interactive multimedia. Due to scarcity of the spectrum, the current wireless systems are still unable to meet the ever-increasing subscribers’ demands for bandwidth and resource-hungry applications, with a vigorous requirement of seamless connectivity, anywhere and anytime, despite the fast-growing 4th-generation systems. This motivates the wireless industry and academia researchers to define new paradigm technologies and structures for future 5th-generation (5G) wireless systems. In this regard, many enabling technologies and potential solutions are proposed, among which non-orthogonal multiple access (NOMA) is considered as a promising multiple access technology for 5G. In this chapter, we first briefly describe the classifications of NOMA. We then focus on power domain NOMA and discuss its operational principle and possible system architecture for downlink (DL). In the context of issues related to the DL NOMA system, we provide a review of recent advancements in the topic. We highlight some critical factors related to the current NOMA receiver, which inevitably limit the NOMA performance and operation. As a remedy, we suggest an alternative receiver design that may be adopted for 5G NOMA. We justify our proposal by presenting performance comparison results between the existing and proposed receiver for 5G NOMA. Finally, we provide recommendations for future research, followed by the conclusion.
