Power-Domain Non-Orthogonal Multiple Access (NOMA) in 5G Systems: Potentials and Challenges

Abstract

Abstract-Non-orthogonal multiple access (NOMA) is one of the promising radio access techniques for performance enhancement in next-generation cellular communications. Compared to orthogonal frequency division multiple access (OFDMA), which is a well-known high-capacity orthogonal multiple access (OMA) technique, NOMA offers a set of desirable benefits, including greater spectrum efficiency. There are different types of NOMA techniques, including power-domain and code-domain. This paper primarily focuses on power-domain NOMA that utilizes superposition coding (SC) at the transmitter and successive interference cancellation (SIC) at the receiver. Various researchers have demonstrated that NOMA can be used effectively to meet both network-level and user-experienced data rate requirements of fifth-generation (5G) technologies. From that perspective, this paper comprehensively surveys the recent progress of NOMA in 5G systems, reviewing the state-of-the-art capacity analysis, power allocation strategies, user fairness, and user-pairing schemes in NOMA. In addition, this paper discusses how NOMA performs when it is integrated with various proven wireless communications techniques, such as cooperative communications, multiple-input multiple-output (MIMO), beamforming, space-time coding, and network coding, among others. Furthermore, this paper discusses several important issues on NOMA implementation and provides some avenues for future research. I. INTRODUCTIONFrom analog phone calls through to all Internet Protocol services, including voice and messaging, each transition has been encouraged by the need to meet the requirements of the new generation of mobile technology. Subsequently, mobile communications technology is presently facing a new challenge, giving birth to a hyper-connected society through the emergence of fifth-generation (5G) services. With enormous potential for both consumers and industry, 5G is expected to roll out by 2020. From the next-generation radio access technology viewpoint, a step change in data speed and a significant reduction in end-to-end latency is a major concern for 5G, since the rapid development of the mobile Internet and the Internet of Things (IoT) exponentially accelerates the demand for high data-rate applications. In particular, many of the industry initiatives that have progressed with work on 5G declare that the network-level data rate in 5G should be 10-20 Gbps (that is, 10-20 times the peak data rate in 4G), and the user-experienced data rate should be 1 Gbps (100 times the user-experienced data rate in 4G). They also set the latency (end-to-end round-trip delay) at 1 millisecond (one-fifth of the latency in 4G).The underlying physical connection in a cellular network is called radio access technology, which is implemented by a radio access network (RAN). A RAN basically utilizes a channel access technique to provide the mobile terminals with a connection to the core network. The design of a suitable multiple access technique is one of the most important aspects in improvi...

Non-Orthogonal Multiple Access: A Unified Perspective

“…Recently, the PD-NOMA with SPC at the transmitter and SIC receiver was analyzed theoretically and attracted extensive attention [7], [10]- [12]. In PD-NOMA, the symbol vector of multiple users is directly multiplied by the power allocation matrix P without any need for spreading, and the system model of PD-NOMA is identical to the aforementioned unified model.…”

IoT’s Tiny Steps towards 5G: Telco’s Perspective

“…It is contemplated in two ways: (1) peak data rate-defined as the maximum achievable data rate by the user; and (2) minimum guaranteed user data rate-defined as the minimum experience data rate by the user [16]. New mobile technologies are primarily driven by users' needs for higher data rates, as discussed in [8,16,99,215,216]. The expected values in 5G networks are 10 Gbps for minimum peak data rate and 100 Mbps as minimum guaranteed user data rate [5].…”

“…They include several non-orthogonal multiple access (NOMA) forms: multi-user shared multiple access (MUSA) [145][146][147][148], resource spread multiple access (RSMA) [149], sparse code multiple access (SCMA) [150][151][152], pattern division multiple access (PDMA) [153][154][155], interleave-division multiple access (IDMA) [156,157], and NOMA by power domain [158]. The NOMA is a radio access technology design for enabling greater spectrum efficiency [56,[159][160][161][162]207], higher cell-edge throughput, relaxed channel feedback, and low transmission latency [99]. NOMA can be employed to enhance user fairness and to support massive connections with diverse QoS requirements [163].…”

NOMA for Multinumerology OFDM Systems

“…To guarantee the fairness among NOMA users, more power is required for users with poor channel conditions and less power for users with better channel conditions [8]. However, if the users have similar channel conditions, OMA can guarantee better fairness and conventional power domain NOMA cannot strictly guarantee the users' quality of service (QoS) targets [9], which could be critical for some scenarios with strict fairness constraints.…”