Abstract
Driven by the rapid escalation of the wireless capacity requirements imposed by advanced multimedia applications (e.g., ultrahigh-definition video, virtual reality, etc.), as well as the dramatically increasing demand for user access required for the Internet of Things (IoT), the fifth-generation (5G) networks face challenges in terms of supporting large-scale heterogeneous data traffic. Nonorthogonal multiple access (NOMA), which has been recently proposed for the third-generation partnership projects long-term evolution advanced (3GPP-LTE-A), constitutes a promising technology of addressing the aforementioned challenges in 5G networks by accommodating several users within the same orthogonal resource block. By doing so, significant bandwidth efficiency enhancement can be attained over conventional orthogonal multiple-access (OMA) techniques. This motivated numerous researchers to dedicate substantial research contributions to this field. In this context, we provide a comprehensive overview of the state of the art in power-domain multiplexing-aided NOMA, with a focus on the theoretical NOMA principles, multiple-antenna-aided NOMA design, on the interplay between NOMA and cooperative transmission, on the resource control of NOMA, on the coexistence of NOMA with other emerging potential 5G techniques and on the comparison with other NOMA variants. We highlight the main advantages of power-domain multiplexing NOMA compared to other existing NOMA techniques. We summarize the challenges of existing research contributions of NOMA and provide potential solutions. Finally, we offer some design guidelines for NOMA systems and identify promising research opportunities for the future.
Highlights
The recent literature of power-domain multiplexing aided Non-orthogonal multiple access (NOMA) proposed for 5G systems has been surveyed with an emphasis on the following aspects: the basic principles of NOMA, the amalgams of multiple antenna techniques and NOMA, the interplay of NOMA and cooperative communications, the resource control of NOMA, its coexistence with other key 5G techniques, and the implementation challenges and standadization
Investigating the inherent integration of multiple-antenna aided and cooperative techniques with NOMA is important, since they are capable of providing extra spatial diversity, either with the aid of centralized or distributed beamforming designs
It is worth pointing that when designing centralized beamformers, the most influential factor is the appropriate ordering of the matrix based channels
Summary
Following the pioneering contributions of Maxwell and Hertz, Marconi demonstrated the feasibility of wireless communications across the Atlantic at the end of the 19th century. The classic orthogonal multiple access (OMA) schemes, such as time division multiple access (TDMA) ‘Street’, frequency division multiple access (FDMA), orthogonal variable spreading factor based code division multiple access (OVSF-CDMA), interleave division multiple access (IDMA) and orthogonal frequency division multiple access (OFDMA) ‘Street’ converged to OMA/nonorthogonal multiple access (NOMA) ‘Square’ of Fig. 1 They have evolved further along spatial division multiple access (SDMA) and multi-functional antenna array ‘Street’ - these solutions have found their way into the 4G OFDMA systems. The often-quoted albeit potentially unrealistic expectations include 1,000 times higher system capacity, 10 times higher system throughput and 10 times higher energy efficiency per service than those of the fourth generation (4G) networks [6] Several key directions such as ultra-densification, mmWave communications, massive MIMO arrangements, D2D and machine-to-machine (M2M) communication, full-duplex (FD) solutions, energy harvesting (EH), cloud-based radio access networks (C-RAN), wireless network virtualization (WNV), and software defined networks (SDN) have been identified by researchers [7]–[9].
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