Performance Of Non-orthogonal Multiple Access Research Articles

Secure Transmission in NOMA-Aided Multiuser Visible Light Communication Broadcasting Network With Cooperative Precoding Design

In this paper, we study the secrecy performance of non-orthogonal multiple access (NOMA) enabled visible light communication (VLC) broadcast channels in the presence of an active eavesdropper (Eve). The considered VLC system consists of multiple separately distributed light-emitting diodes arrays and multiple randomly located users (UEs) in an indoor room. User clustering is conducted to reduce the implementation complexity of successive interference cancellations. Two cooperative precoding strategies based on zero-forcing (ZF) and maximum ratio transmission (MRT) are designed using the effective channel of each cluster. Based on each precoding strategy, a sum secrecy rate maximization problem is developed to obtain the near-optimal power allocation (PA) to strengthen UEs’ confidential transmission and degrade Eve’s reception under minimum secrecy rate requirement, peak amplitude, non-negativity, and power constraints. To tackle the challenging non-convex problem for each precoding strategy, equivalent transformations and arithmetic-geometric mean approximation are conducted to convert the original problem into a series of geometric programming (GP) problems. Based on the reformulated problems, iterative algorithms are proposed to obtain near-optimal solutions by solving the GP problems through successive convex approximations. The convergence and complexity analysis of the proposed algorithms are studied. Simulation results show that the sum security performance of the proposed PA approach outperforms the conventional PA approaches in both ZF-based and MRT-based precoder schemes. The effectiveness of applying NOMA compared with the orthogonal multiple access-based scheme is also validated for the proposed system.

Deep Learning Approaches for Overcoming Nonorthogonal Multiple Access Challenges in 5G Networks: A Review

Nonorthogonal multiple access (NOMA) is a promising multiple access scheme for 5G wireless networks. However, NOMA faces several challenges that still need to be solved optimally. Deep learning algorithms have been proposed as a potential solution to address these challenges. This review provides an overview of the use of deep learning algorithms to optimize NOMA performance in 5G networks. An investigation is conducted on how deep learning methods are applied in NOMA systems for resource allocation, channel estimation and detection, successive interference cancellation, and user clustering.They can learn optimal user clustering, optimal allocation, and interference alignment strategies, eventually boosting the network performance. In addition, deep learning algorithms can learn the complex relationships between the transmitted symbols and the received signal, leading to accurate detection of the superimposed signals. Opportunities and challenges in NOMA can be identified based on existing research showing how applying deep learning algorithms is better than conventional approaches. The main contribution of this review is to provide insights into the potential of deep learning algorithms to remarkably improve NOMA performance in 5G networks. This article is also a valuable resource for researchers and practitioners interested in using deep learning algorithms for NOMA in 5G networks.

A Downlink RIS-Aided NOMA System With Hardware Impairments: Performance Characterization and Analysis

Reconfigurable intelligent surface (RIS) has recently been envisioned to provide an adaptable channel for futuristic wireless communication networks. This work characterized the impact of hardware impairments in the downlink RIS-aided non-orthogonal multiple access (NOMA) wireless networks. We considered the hardware impairments in the transceivers of the base station (BS) and users, phase error at the RIS and the imperfect successive interference cancellation (SIC) for the NOMA users. Specifically, the performance is evaluated by deriving the closed-form expressions for the outage probability (OP), spectral efficiency (SE) and energy efficiency (EE). Additionally, the performance of the orthogonal multiple access (OMA) system is also evaluated and compared with its NOMA counterpart. The RIS-aided NOMA outperforms OMA for the ideal hardware scenario. However, the hardware impairments significantly deteriorate RIS-aided NOMA's performance compared to RIS-aided OMA. Further, we have also compared the proposed RIS-aided NOMA with the baseline full-duplex relaying (FDR) based NOMA. The results show that the gains are more significant for a RIS-aided system than FDR.

Scheduling of Heterogeneous Services by Resolving Conflicts

Fifth generation (5G) new radio introduced flexible numerology to accommodate heterogeneous services. However, optimizing the scheduling of heterogeneous services with differing delay and throughput requirements over 5G new radio is a challenging task. In this paper, we investigate near optimal, low complexity scheduling of radio resources for ultra-reliable low-latency communications (URLLC) when coexisting with enhanced mobile broadband (eMBB) services. We demonstrate that maximizing the sum throughput of eMBB services while servicing URLLC users over a fixed length time-frequency grid, is, in the long-term, equivalent to minimizing the number of URLLC placements in the time-frequency grid; this is the consequence of reducing the number of infeasible placements for eMBB, to which we refer to as “conflicts.” To meet this new objective, we evaluate the performance of new, conflict-aware heuristics, consisting of a family of “greedy” and a lightweight heuristic inspired by bin packing optimization, all of near optimal performance. Moreover, having shed light on the impact of conflict in layer-2 scheduling, we investigate non-orthogonal multiple access (NOMA) as a potential approach for conflict resolution leveraging superposition coding. The superior performance of NOMA with respect to OMA, thanks to resolving conflicts, is showcased by extensive numerical results.

Power allocation to enhance non-orthogonal multiple access performance

Power allocation to enhance non-orthogonal multiple access performance

Power allocation to enhance non-orthogonal multiple access performance

Power allocation to enhance non-orthogonal multiple access performance

Performance Analysis of IRS-Aided NOMA Communications in the Presence of Imperfect SIC

The intelligent reflecting surface (IRS) is expected to be a promising technique to achieve a robust spectrum and energy efficiency. This paper investigates the advantages of IRS in enhancing performance of non-orthogonal multiple access (NOMA) communications in the presence of imperfect successive-interference-cancellation (SIC) and phase distortion (PD) caused by a non-ideal IRS. Specifically, average achievable rates (AARs) of the users are the target performance metrics. For performance evaluation, the probabilistic characterizations of signal-to-interference-plus-noise ratios (SINRs) at the users are studied. These results allow for deriving the theoretical formulas for the AAR. Monte Carlo simulations are adopted to verify the accuracy of these theoretical results. The numerical results show the effects of various key system parameters, such as source transmit power, NOMA power allocation (PA) factors, reflecting tile (RTs) allocation, the SIC imperfection factor, and the PD factor, on the AAR that provide useful information for the system’s design.

A Cat Swarm Optimization based transmission power minimization for an aerial NOMA communication system

This article underlines the inclusion of Non-Orthogonal Multiple Access (NOMA) aerial network nodes to rapidly serve a mass deployment of devices in the next-generation networks. The analysis of an aerial NOMA deployment is conducted considering the objective of minimization of the required transmission power in comparison to an aerial deployment employing Orthogonal Multiple Access (OMA). The findings of the study highlight the inter-dependency among the considered optimization variables of user pairing, altitude, and power allocation as well as stress the implication of their joint optimization for improved performance of the aerial NOMA system. The formulated mixed-integer non-linear programming problem is solved utilizing a joint optimization technique. Meanwhile, the employment of Cat Swarm Optimization (CSO) framework for NOMA user pairing optimization marks the first work of its kind in the literature. Subsequently, the altitude of the NOMA Unmanned Aerial Vehicle Base Station (UAV-BS) is computed using tools of convex optimization. The obtained results of the proposed methodology solved iteratively substantiate the better performance of NOMA compared to an equivalent OMA UAV-BS deployment. Subsequently, the presented results demonstrate the efficacy of the proposed CSO approach in reducing the required transmission power as well as the operating altitude attributed to lower flying energy consumption of the UAV-BS compared to random and particle swarm optimization based user pairing techniques.

Link and System-Level NOMA Simulator: The Reproducibility of Research

This study focuses on the design of a MATLAB platform for non-orthogonal multiple access (NOMA) based systems with link-level and system-level analyses. Among the different potential candidates for 5G, NOMA is gaining considerable attention owing to the many-fold increase in spectral efficiency as compared to orthogonal multiple access (OMA). In this study, a NOMA simulator is presented for two and more than two users in a single cell for link-level analysis; whereas, for system-level analysis, seven cells and 19 cells scenarios were considered. Long-term evolution (LTE) was used as the baseline for the NOMA simulator, while bit error rate (BER), throughput and spectral efficiency are used as performance metrics to analyze the simulator performance. Moreover, we demonstrated the application of the NOMA simulator for different simulation scenarios through examples. In addition, the performance of multi-carrier NOMA (MC-NOMA) was evaluated in the presence of AWGN, impulse noise, and intercell interference. To circumvent channel impairments, channel coding with linear precoding is suggested to improve the BER performance of the system.

Performance of Uplink NOMA with User Mobility Under Short Packet Transmission

The scenario of an uplink two-user non-orthogonal multiple access (NOMA) communication system is analytically studied when it operates in the short packet transmission regime. The considered users support mobility and each is equipped with a single antenna, while they directly communicate with a multi-antenna base station. Power-domain NOMA is adopted for the signal transmission as well as the successive interference cancellation approach is performed at the receiver for decoding. The packet error rate (PER) is obtained in simple closed formulae under independent Rayleigh faded channels and for arbitrary user mobility profiles. The practical time variation and correlation of the channels is also considered. Moreover, useful engineering insights are manifested in short transmission time intervals, which define a suitable setup for the forthcoming ultra-reliable and low latency communication systems. Finally, it turns out that the optimal NOMA power allocation can be computed in a straightforward cost-effective basis, capitalizing on the derived PER expressions.

Numerous Factors Affecting Performance of NOMA for Massive Machine Type Communications in B5G Systems

Massive machine type communications (mMTC) are one of the critical requirements for beyond fifth generation (B5G) communication systems. Services for a huge number of user terminals should be provided simultaneously due to the explosive development of mMTC. It is proved that non-orthogonal multiple access (NOMA) is effective in satisfying such a requirement. In this paper we evaluate the impacts of numerous factors, such as channel encoding, channel decoding, repetition number, multi-user detector, and number of receiver antennas, on the performance of NOMA. It is surprised to find that some conclusions drawn from orthogonal multiple access system may do not hold anymore for NOMA systems. The factors which have significant impact on the performance of NOMA should be paid more attention to in the system design. The analysis and evaluation results shine more light on how to design an effect NOMA scheme by considering both transmitter and receiver to fulfill the requirements of mMTC for B5G systems.

Deep-Learning-Enhanced NOMA Transceiver Design for Massive MTC: Challenges, State of the Art, and Future Directions

Non-orthogonal multiple access (NOMA) is a promising evolution path to meet the requirements of massive machine type communications (mMTC) in 5G and beyond. However, the deployment of NOMA is hindered by the non-unified signal processing architectures of various NOMA schemes and the inflexibility resulting from the offline design paradigm. The block-wise optimized transceivers make its performance far from the limit. The recent breakthrough of deep learning and its positive applications to wireless communications have paved the way to tackle these challenges. This article studies the effectiveness and efficiency of deep learning in enhancing NOMA performance. Specifically, we first present the deep neural network (DNN), which is constructed via a uniform signal processing architecture, and use it as the unified multiuser receiver in both data and model-driven approaches. This enables the end-to-end optimization of NOMA transceivers due to the universal function approximation property of DNN. On the other hand, with DNN we can automatically extract the user access behaviors out of the time-series signals and optimize the transceivers to match these cross-lay-er behaviors. We further analyze the integration of non-orthogonal communication and neural computation to accomplish high-efficiency data transmission at low cost. Finally, we identify some essential future directions of deep-learning-enhanced NOMA from the perspectives of online reconfigurability and adaptability toward the ever changing environment in future mMTC.

Rayleigh Sönümlemeli Kanalda NOMA Üstünlük Koşulunun Belirlenmesi

Non-orthogonal Multiple Access (NOMA) is a new generation multiple access technique in which multiple users simultaneously share the same frequency band. In the implementation of NOMA, the choice of user pairs that will use the same frequency is a determining factor for the NOMA superiority condition due to Successive Interference Cancellation (SIC) mechanism on the receiver. However, performance of NOMA depends on SIC mechanism which relies on the order of the user in a NOMA cluster. In the literature, it has been shown that utilizing distance based order of the users for user pairing outperforms over the random pairing and an analytical boundary distance is derived for NOMA superiority condition for a path loss based channel model. In this study, the path loss based NOMA superiority condition respect to the Orthogonal Multiple Access (OMA) was investigated in terms of the spectral efficiencies for Rayleigh channel model in a cellular uplink and the results were compared with an analytical boundary value derived for a path loss based channel model in the literature. In addition, the effect of power ratio of the users on the NOMA superiority condition is investigated and accuracy of the derived analytical model is validated with numerical results for both channel models. The results reveal that the NOMA superiority condition based on distance changes depend on the assumed channel model, but assuming the channel as Rayleigh fading or path loss based channel does not make a significant difference. In addition, it is observed that the accuracy of the derived NOMA superiority condition changes with the power ratios for both channel models and the gap between numerical and analytical results is larger in Rayleigh channel compared to path loss based channel model.

Error Rate Analysis of Non-Orthogonal Multiple Access With Residual Hardware Impairments

In this letter, the impact of residual hardware impairment (RHI) on the performance of non-orthogonal multiple access (NOMA) is investigated by taking into account the effect of imperfect successive interference cancellation (ipSIC). The new exact and asymptotic pairwise error probability (PEP) expressions with RHI under ipSIC are derived over Rayleigh fading channels. The asymptotic PEP expression is subsequently utilized to quantify the diversity orders achieved by NOMA users in the presence of RHI. In particular, we show that the effective diversity order of each NOMA user equals to user’s order for both ideal and non-ideal (RHI) scenarios. Leveraging the derived PEP, the union bound on the bit error rate of NOMA users are further evaluated. We demonstrate that the impact of RHI with ipSIC on each user’s error rate performance is negligible. In contrast, when perfect SIC is considered, such effects are significant. Numerical and Monte Carlo simulation results are presented to corroborate the analysis.

Performance Analysis of NOMA in Vehicular Communications Over i.n.i.d Nakagami-m Fading Channels

This paper investigates the performance of non-orthogonal multiple access (NOMA) in vehicular networks where a base station (BS) communicates with the vehicles moving away from the BS with single-input multiple-output. To combine the signals received at the antennas, diversity combining techniques such as maximal ratio combining (MRC) and selection combining (SC) are performed at the receiver of each vehicle. However, in practice, the expected performance from the diversity techniques may not be achieved due to the fact that all the diversity branches are not independent and identically distributed (i.i.d) all the time. In this context, analytical expressions of the outage probability and ergodic sum rate are derived for the considered vehicular networks with the assumption of independent but not necessarily identically distributed (i.n.i.d) Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${m}$ </tex-math></inline-formula> fading channels. The performance analysis of NOMA vehicular networks is also extended for multiple-input multiple-output antenna configurations and evaluated in the presence of successive interference cancellation (SIC) error propagation. The obtained analytical results are validated by Monte Carlo simulations. Furthermore, the performance of NOMA is verified with conventional orthogonal multiple access (OMA) for fading parameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m=1$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m=2$ </tex-math></inline-formula> with perfect channel knowledge and channel estimation. Numerical results show that NOMA outperforms the conventional OMA by approximately 20% and has high sum rate with i.n.i.d as well as i.i.d channel consideration. However, i.n.i.d consideration degrades the performance of NOMA and OMA as the diversity gain achieved with i.n.i.d consideration is less as compared to i.i.d consideration. The performance is further deteriorated with SIC error and channel estimation.

Power-Tolerant NOMA Using Data-Aware Adaptive Power Assignment for IoT Systems

Nonorthogonal multiple access (NOMA) is a promising candidate for future wireless networks due to its ability to improve the spectral efficiency and network connectivity. Nevertheless, the error rate performance of NOMA depends significantly on the power assignment for each user, which requires accurate knowledge of the channel state information (CSI) at the transmitter, which can be challenging for several applications, such as wireless sensor networks (WSNs) and Internet of Things (IoT). Therefore, this article proposes a power-tolerant NOMA by adaptively changing the signal power of each user to reduce the system sensitivity to inaccurate power assignment. The power adaptation in the power-adaptive NOMA (PANOMA) is performed based on the transmitted data, and it does not require accurate CSI. To quantify its potential, the bit error rate (BER) and the lower bound capacity performance, over Rayleigh fading channels, are derived in exact closed forms for two and three users scenarios. The results demonstrate that PANOMA provides a tangible BER performance improvement over conventional power-domain NOMA when both schemes use suboptimal power assignment, which is typically experienced in practical scenarios involving channel time variation and CSI estimation errors. Specifically, it will be shown that both schemes provide similar BERs using optimal assignment, but the PANOMA offers BER reduction by a factor of 10 for certain scenarios when suboptimal power values are assigned. The integrity of the analytical results is verified via matching extensive Monte Carlo simulation experiments.

Performance Analysis of NOMA-Based Underlay Cognitive Radio Networks With Partial Relay Selection

This paper investigates outage and throughput performance of non-orthogonal multiple access (NOMA) based underlay cognitive radio (i.e., CR-NOMA) network under partial relay selection (PRS) scheme. Here NOMA is used in the secondary network, where K half duplex, decode-and-forward (DF) relays are available for assisting the secondary base station (SBS) to deliver information to the secondary users (SUs). We derive analytical expressions for the outage probabilities experienced by the SUs under imperfect successive interference cancellation (i-SIC) conditions. The interference threshold constraint of the primary receiver and the maximum transmit power constraint of the secondary nodes are considered for the analysis. To provide more insights on the outage performance, we obtain expressions for the asymptotic outage probabilities of the SUs in the high transmit power region. Next, we derive analytical expressions for the optimal power allocation (OPA) factors at the SBS and at the selected relay that independently maximize the delay limited throughput of the secondary network in CR-NOMA system. We also determine the jointly optimal power allocation factors that maximize the throughput. We use numerical and simulation investigations to establish that the outage probabilities of the SUs reduce significantly while the throughput improves under the considered PRS scheme, compared to random relay selection and fixed relaying strategies. Further, it is established that the proposed OPA factors can significantly reduce the outage probabilities experienced by the SUs and improve the system throughput compared to equal/random power allocation schemes.

Performance Analysis of Filtered OFDM Based Downlink and Uplink NOMA System over Nakagami-m Fading Channel

Efficient consumption of available resources and fulfillment of increasing demands are the two main challenges which are addressed by exploring advanced multiple access schemes along with efficient modulation techniques. To this end, non-orthogonal multiple access (NOMA) is discussed as a promising scheme for future 5G traffic. NOMA enables the users to share same resource block, permitting certain level of interference. In this paper, we propose filtered OFDM (F-OFDM) as a transmission waveform for NOMA systems, as it offers all the advantages of OFDM with the additional provision of sub-band filtering to satisfy the diverse services of the users. We examine F-OFDM in both downlink and uplink NOMA systems. Error-related performances of both downlink and uplink F-OFDM NOMA systems are analyzed and compared with conventional OFDM NOMA system over Nakagami-m fading channel. The results show that the error performance of F-OFDM NOMA is better than that of OFDM NOMA. An improvement of about 2 dB and 1 dB in bit error rate is achieved in downlink and uplink F-OFDM NOMA, respectively. Monte Carlo simulations are conducted for different values of fading parameter m, supporting the obtained analytical results

On the Performance of Downlink NOMA in Underlay Spectrum Sharing

Non-orthogonal multiple access (NOMA) and spectrum sharing are two potential technologies for providing massive connectivity in beyond fifth-generation (B5G) networks. In this paper, we present the performance analysis of a multi-antenna-assisted two-user downlink NOMA system in an underlay spectrum sharing system. We derive closed-form expressions for the average achievable sum-rate and outage probability of the secondary network under a peak interference constraint and/or peak power constraint, depending on the availability of channel state information (CSI) of the interference link between secondary transmitter (ST) and primary receiver (PR). For the case where the ST has a fixed power budget, we show that performance can be divided into two specific regimes, where either the interference constraint or the power constraint primarily dictates the performance. Our results confirm that the NOMA-based underlay spectrum sharing system significantly outperforms its orthogonal multiple access (OMA) based counterpart, by achieving higher average sum-rate and lower outage probability. We also show the effect of information loss at the ST in terms of CSI of the link between the ST and PR on the system performance. Moreover, we also present closed-form expressions for the optimal power allocation coefficient that minimizes the outage probability of the NOMA system for the special case where the secondary users are each equipped with a single antenna. A close agreement between the simulation and analytical results confirms the correctness of the presented analysis.

Outage performance of NOMA with interference over [formula omitted] shadowed faded channels

Non-orthogonal multiple access (NOMA) is an emerging multiple access technique to provide higher spectral efficiency and data rates for future wireless communications. In this paper, outage probability expressions are obtained for NOMA over κ-μ shadowed faded channel, which can be applied to analyze the performance in mobile, satellite and underwater communication. Initially we observed the signal to interference ratio (SIR) at user equipment (UE) by considering the inter and intra cellular interference. The outage probability expressions are obtained for NOMA with maximum ratio and selection combining. In this paper, we also calculated the outage results with random number of interferers. The analytical results are presented for two users which are at near and edge positions of a Voronoi cell. Finally, simulated results are presented to validate the analytical expressions.