Hybrid Non-orthogonal Multiple Access Research Articles

Non-Orthogonal Multiple Access: Achieving Sustainable Future Radio Access

NOMA has been recognized as a highly promising FRA technology to satisfy the requirements of the fifth generation era on high spectral efficiency and massive connectivity. Since the EE has become a growing concern in FRA from both the industrial and societal perspectives, this article discusses the sustainability issues of NOMA. We first thoroughly examine the theoretical power regions of NOMA to show the minimum transmission power with fixed data rate requirement, demonstrating the EE performance advantage of NOMA over orthogonal multiple access. Then we explore the role of energy-aware resource allocation and grant-free transmission in further enhancing the EE performance of NOMA. Based on this exploration, a hybrid NOMA strategy that reaps the joint benefits of resource allocation and grant-free transmission is investigated to simultaneously accomplish high throughput, large connectivity, and low energy cost. Finally, we identify some important and interesting future directions for NOMA designers to follow in the next decade.

Millimeter-Wave Communications With Non-Orthogonal Multiple Access for B5G/6G

In order to further improve the system capacity, we explore the integration of non-orthogonal multiple access (NOMA) in millimeter-wave communications (mmWave-NOMA) for future B5G and 6G systems. Compared with the conventional NOMA, the distinguishing feature of mmWave-NOMA is that, it is usually characterized by transmit/receive beamforming with large phased arrays. In this paper, we focus on the design challenges of mmWave-NOMA due to beamforming. Firstly, we study how beamforming affects the sum-rate performance of mmWave-NOMA, and find that with conventional single-beam forming, the performance may be offset by the relative angle between NOMA users. Then, we consider multi-beam forming for mmWave-NOMA, which is shown to be able to achieve promising performance enhancement as well as robustness. Next, we investigate the challenging joint design of the intertwined power allocation and user pairing for mmWave-NOMA. Relevant challenges are discussed and some potential solutions are proposed in detail. We further consider hybrid spatial division multiple access (SDMA) and NOMA in mmWave communications, where some possible system configurations and the corresponding solutions are discussed to address the multi-user issues including multi-user precoding and multi-user interference mitigation. Finally, we present future directions in mmWave-NOMA and summarize the paper.

Optimal Power Allocation and Scheduling for Non-Orthogonal Multiple Access Relay-Assisted Networks

The emerging non-orthogonal multiple access (NOMA), which enables mobile users (MUs) to share same frequency channel simultaneously, has been considered as a spectrum-efficient multiple access scheme to accommodate tremendous traffic growth in future cellular networks. In this paper, we investigate the NOMA downlink relay-transmission, in which the macro base station (BS) first uses NOMA to transmit to a group of relays, and all relays then use NOMA to transmit their respectively received data to an MU. In specific, we propose an optimal power allocation problem for the BS and relays to maximize the overall throughput delivered to the MU. Despite the non-convexity of the problem, we adopt the vertical decomposition and propose a layered-algorithm to efficiently compute the optimal power allocation solution. Numerical results show that the proposed NOMA relay-transmission can increase the throughput up to 30 percent compared with the conventional time division multiple access (TDMA) scheme, and we find that increasing the relays’ power capacity can increase the throughput gain of the NOMA relay against the TDMA relay. Furthermore, to improve the throughput under weak channel power gains, we propose a hybrid NOMA (HB-NOMA) relay that adaptively exploits the benefit of NOMA relay and that of the interference-free TDMA relay. By using the throughput provided by the HB-NOMA relay for each individual MU, we study the multi-MUs scenario and investigate the multi-MUs scheduling problem over a long-term period to maximize the overall utility of all MUs. Numerical results demonstrate the performance advantage of the proposed multi-MUs scheduling that adopts the HB-NOMA relay-transmission.

Dynamic IoT Device Clustering and Energy Management With Hybrid NOMA Systems

Fog computing, as a promising technique, is with huge advantages in dealing with large amounts of data and information with low latency and high security. We introduce a promising multiple access technique entitled nonorthogonal multiple access to provide communication service between the fog layer and the Internet of Things (IoT) device layer in fog computing, and propose a dynamic cooperative framework containing two stages. At the first stage, dynamic IoT device clustering is solved to reduce the system complexity and the delay for the IoT devices with better channel conditions. At the second stage, power allocation based energy management is solved using Nash bargaining solution in each cluster to ensure fairness among IoT devices. Simulation results reveal that our proposed scheme can simultaneously achieve higher spectrum efficiency and ensure fairness among IoT devices compared to other schemes.

Evaluating the Ergodic Rate in SWIPT-Aided Hybrid NOMA

This letter studies a hybrid non-orthogonal multiple access (NOMA)-based wireless system, in which the users harvest energy from the received downlink signals in order to transmit on the uplink. We argue that the use of energy harvesting helps in maintaining distinct power levels when the users commence uplink NOMA transmissions. To evaluate the performance of the proposed model, we derive closed-form mathematical expressions of the average ergodic rate of the system. The results illustrate that: 1) this scheme is capable of establishing NOMA-based uplink communication solely on the basis of harvested energy and 2) power-splitting parameter shows positive correlation on the uplink rate performance, whereas the choice of time-splitting parameter favors either uplink or downlink data rate.

A hybrid precoding‐ and filtering‐based uplink MC‐LNOMA scheme for 5G cellular networks with reduced PAPR

AbstractUplink multicarrier localized nonorthogonal multiple access (MC‐LNOMA) is a variant of hybrid nonorthogonal multiple access, where subcarrier mapping is performed in localized mode. MC‐LNOMA is one of the most prominent emerging schemes and likely to be employed in the forthcoming fifth‐generation cellular networks due to its massive connectivity, spectral efficiency, better cell coverage capability, and higher data rate. It may employ orthogonal frequency‐division multiple access due to the technical ripeness. However, schemes based on orthogonal frequency‐division multiple access all suffer from the high peak‐to‐average power ratio problem. Therefore, in this paper, a new finite impulse response filter–based discrete cosine transform–precoded uplink MC‐LNOMA scheme is presented for peak‐to‐average power ratio reduction. MATLAB simulations demonstrate the performance supremacy of the proposed scheme compared to contemporary schemes such as discrete cosine transform–precoded uplink MC‐LNOMA and nonprecoded uplink MC‐LNOMA.

Experimental demonstration of a non-orthogonal multiple access scheme for visible light communications with SCFDM transmission

We experimentally demonstrate a hybrid non-orthogonal multiple access (NOMA) and single carrier division multiplexing (SCFDM) transmission scheme for visible light communications, which offers higher spectral efficiency, improved tolerance against multi-path and a good balance between the data throughput and fairness. Compared with the orthogonal frequency division multiplexing based NOMA, NOMA-SCFDM with lower peak to average power ratio offers enhanced tolerance to the light emitting diode nonlinearity and improved bit error rate performance.

Delay Minimization for NOMA-MEC Offloading

This paper considers the minimization of the offloading delay for non-orthogonal multiple access assisted mobile edge computing (NOMA-MEC). By transforming the delay minimization problem into a form of fractional programming, two iterative algorithms based on Dinkelbach's method and Newton's method are proposed. The optimality of both methods is proved and their convergence is compared. Furthermore, criteria for choosing between three possible modes, namely orthogonal multiple access (OMA), pure NOMA, and hybrid NOMA, for MEC offloading are established.

On the Application of Quasi-Degradation to MISO-NOMA Downlink

In this paper, the design of non-orthogonal multiple access (NOMA) in a multiple-input-single-output (MISO) downlink scenario is investigated. The impact of the recently developed concept, quasi-degradation, on NOMA downlink transmission is first studied. Then, a Hybrid NOMA (H-NOMA) precoding algorithm, based on this concept, is proposed. By exploiting the properties of H-NOMA precoding, a low-complexity sequential user pairing algorithm is consequently developed, to further improve the overall system performance. Both analytical and numerical results are provided to demonstrate the performance of the H-NOMA precoding through the average power consumption and outage probability, while conventional schemes, as dirty-paper coding and zero-forcing beamforming, are used as benchmarking.

Outage Performance for Dynamic Power Allocation in Hybrid Non-Orthogonal Multiple Access Systems

In this letter, we propose a novel dynamic power allocation scheme for hybrid non-orthogonal multiple access (DH-NOMA). The exact expressions for the outage probabilities and their asymptotic approximations at high signal-to-noise ratio are derived in DH-NOMA systems. Both Monte Carlo simulations and analytical results are used to compare the proposed scheme with the existing works, such as NOMA based on fixed power allocation (F-NOMA) and cognitive radio inspired NOMA (CR-NOMA). The provided results demonstrate that the DH-NOMA scheme can always achieve better outage performance than the traditional orthogonal multiple access, and achieve a more balanced tradeoff between the two user individual rates than F-NOMA and CR-NOMA.

Beamforming for Combating Inter-cluster and Intra-cluster Interference in Hybrid NOMA Systems

In this paper, downlink beamforming (BF) for hybrid non-orthogonal multiple access (NOMA) systems is considered, in order to combat inter and intra cluster interference. First, to minimize the inter- and intra-cluster interference, the projection hybrid NOMA (PH-NOMA) BF algorithm is introduced, by combining conventional zero-forcing BF (ZFBF) and hybrid NOMA (H-NOMA) precoding. Second, to further reduce the overall interference, two user pairing algorithms, termed projection-based pairing algorithm (PBPA) and inversion-based pairing algorithm (IBPA), are also proposed, by adopting the properties of quasi-degradation developed previously. Consequently, the proposed BF algorithm is obtained by combining PH-NOMA and PBPA/IBPA. Moreover, the system performance in terms of outage probability and diversity is analyzed for both the proposed BF algorithms and conventional ZFBF. Finally, computer simulations are conducted to demonstrate the efficiency of the proposed BF algorithms and to validate the correctness of the performance analysis.