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, which is a well-known high-capacity orthogonal multiple access 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 at the transmitter and successive interference cancellation 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, 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.

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

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.

/pdf/nonorthogonal-multiple-access-for-5g-and-beyond-4vzewzi5qj.pdf

Nonorthogonal Multiple Access for 5G and Beyond

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.

In the fifth generation (5G) of wireless communication systems, hitherto unprecedented requirements are expected to be satisfied. As one of the promising techniques of addressing these challenges, non-orthogonal multiple access (NOMA) has been actively investigated in recent years. In contrast to the family of conventional orthogonal multiple access (OMA) schemes, the key distinguishing feature of NOMA is to support a higher number of users than the number of orthogonal resource slots with the aid of non-orthogonal resource allocation. This may be realized by the sophisticated inter-user interference cancellation at the cost of an increased receiver complexity. In this paper, we provide a comprehensive survey of the original birth, the most recent development, and the future research directions of NOMA. Specifically, the basic principle of NOMA will be introduced at first, with the comparison between NOMA and OMA especially from the perspective of information theory. Then, the prominent NOMA schemes are discussed by dividing them into two categories, namely, power-domain and code-domain NOMA. Their design principles and key features will be discussed in detail, and a systematic comparison of these NOMA schemes will be summarized in terms of their spectral efficiency, system performance, receiver complexity, etc. Finally, we will highlight a range of challenging open problems that should be solved for NOMA, along with corresponding opportunities and future research trends to address these challenges.

/pdf/a-survey-of-non-orthogonal-multiple-access-for-5g-47blcczlam.pdf

A Survey of Non-Orthogonal Multiple Access for 5G

This paper considers the application of multiple-input multiple-output (MIMO) techniques to nonorthogonal multiple access (NOMA) systems. A new design of precoding and detection matrices for MIMO-NOMA is proposed and its performance is analyzed for the case with a fixed set of power allocation coefficients. To further improve the performance gap between MIMO–NOMA and conventional orthogonal multiple access schemes, user pairing is applied to NOMA and its impact on the system performance is characterized. More sophisticated choices of power allocation coefficients are also proposed to meet various quality-of-service requirements. Finally, computer simulation results are provided to facilitate the performance evaluation of MIMO–NOMA and also demonstrate the accuracy of the developed analytical results.

The Application of MIMO to Non-Orthogonal Multiple Access

Non-orthogonal transmission, although not entirely new to the wireless industry, is gaining more attention due to its promised throughput gain and unique capability to support a large number of simultaneous transmissions within limited resources. In this article, several key techniques for non-orthogonal transmission are discussed. The downlink technique is featured by MUST, which is being specified in 3GPP for mobile broadband services. In the uplink, grantfree schemes such as multi-user shared access and sparse code multiple access, are promising in supporting massive machine-type communication services. The multi-antenna aspect is also addressed in the context of MUST, showing that MIMO technology and non-orthogonal transmission can be used jointly to provide combined gain.

Non-orthogonal transmission technology in LTE evolution

This paper investigates the system-level performance of downlink non-orthogonal multiple access (NOMA) combined with single user MIMO (SU-MIMO) for future LTE (Long-Term Evolution) enhancements. The goal is to clarify the performance gains of NOMA combined with SU-MIMO transmission, taking into account the LTE radio interface such as frequency-domain scheduling, adaptive modulation and coding (AMC), and NOMA specific functionalities such as multi-user pairing/ordering and transmit power allocation. In particular, we propose practical schemes to efficiently combine NOMA with open-loop SU-MIMO (Transmission Mode 3: TM3) and closed-loop SU-MIMO (Transmission Mode 4: TM4) specified in LTE. Based on computer simulations, we compare NOMA performance gains for different granularities of scheduling and MCS (modulation and coding scheme) selection, for both genie-aided channel quality information (CQI) estimation and approximated CQI estimation, and using different number of power sets. Evaluation results show that NOMA can still provide a hefty portion of its expected gains even with approximated CQI estimation and limited number of power sets, and also when LTE compliant subband scheduling and wideband MCS are applied.

System-level performance of downlink NOMA combined with SU-MIMO for future LTE enhancements

As a promising downlink multiple access scheme for LTE enhancements and 5G, non-orthogonal multiple access (NOMA) has been attracting a lot of attention in recent years. This paper introduces an overview of the concept, performance evaluation gains, our ongoing experimental trials and current standardization status. The goal is to clarify the benefits of NOMA over orthogonal multiple access (OMA) such as OFDMA adopted by Long-Term Evolution (LTE), also its combination with MIMO is discussed. Using computer simulations, NOMA performance gains are assessed from both link-level and system-level perspectives. Also, our NOMA testbed and the measurement results are explained. Finally, we summarize the current status of ongoing standardization of downlink NOMA, which is currently under study in 3GPP LTE Release 13.

NOMA: From concept to standardization

Multiple access (MA) technology is of most importance for 5G. Non-orthogonal multiple access (NOMA) utilizing power domain and advanced receiver has been considered as a promising candidate MA technology recently. In this paper, the NOMA concept is presented toward future enhancements of spectrum efficiency in lower frequency bands for downlink of 5G system. Key component technologies of NOMA are presented and discussed including multiuser transmission power allocation, scheduling algorithm, receiver design and combination of NOMA with multi-antenna technology. The performance gains of NOMA are evaluated by system-level simulations with very practical assumptions. Under multiple configurations and setups, the achievable system-level gains of NOMA are shown promising even when practical considerations were taken into account.

Non-orthogonal multiple access (NOMA) for future downlink radio access of 5G

Disclosed are a base station device and a user terminal that provide a favourable search space in a communication system which expands bandwidth by gathering a plurality of basic frequency blocks. A base station device (20) comprises: a selection unit (302) which selects a single basic frequency block from the system band; a downlink control information generation unit (306) which generates downlink control information for demodulating a data channel transmitted discretely on the selected basic frequency block, and provides a search space with aggregated downlink control information for a plurality of basic frequency blocks on a downlink control channel of a designated basic frequency block among the plurality of basic frequency blocks; and a transmission means (203) which transmits on the downlink control channel provided in the aggregated downlink control information in the search space.

Anxin Li

Papers

Non-orthogonal transmission technology in LTE evolution

System-level performance of downlink NOMA combined with SU-MIMO for future LTE enhancements

NOMA: From concept to standardization

Non-orthogonal multiple access (NOMA) for future downlink radio access of 5G

Base station apparatus and user terminal