Power-domain Non-orthogonal Multiple Access Research Articles

Power-Optimized NOMA With TXOP Tuning-Based Channel Access Scheme for IEEE 802.11ah Dense IoT Networks

In this letter, we propose a power-optimized NOMA with TXOP tuning based novel channel access scheme for IEEE 802.11ah dense IoT networks. Using the proposed method, we form the NOMA-clusters to mitigate the number of contending nodes in a group. Further, the proposed scheme enables nodes in a NOMA-cluster to transmit simultaneously using power-domain NOMA, as well as multiple frames based on the TXOP limit in single resource block. With an analytical model, we evaluate the throughput and connectivity performance. From the analytical and simulation results, it is evident that the proposed scheme significantly improve the performance of NOMA-IoT networks.

Exploiting hybrid non‐orthogonal multiple access in satellite–terrestrial systems with randomly deployed users

In this letter, a hybrid non-orthogonal multiple access (NOMA) scheme for satellite–terrestrial systems is proposed, which is capable of integrating both power domain NOMA (PD-NOMA) and code domain NOMA (CD-NOMA) design modes. The stochastic geometry method is considered to model the position of the terrestrial NOMA user. Specifically, the closed-form expressions of exact outage probability with imperfect interference cancellation are derived. In order to get more insights, the asymptotic outage probabilities for high SNR conditions are also discussed. Numerical results are provided to confirm the validity of theoretical analysis and reveal the effects of critical parameters on system performance.

Adaptive clustering with continuous phase modulation in NOMA systems

ABSTRACT Power-domain NOMA can enlarge the spectrum efficiency and capacity via serving multiple users in the same time slot. Up to now, there are still some issues to be addressed in the NOMA system with multiple users: how many users the NOMA system can accommodate with limited power, how to mitigate the interference among the users, what’s the achievable bound of capacity with limited power at the base station, and how to tackle with two or more users having similar distances to the base station. In the paper, the approximated CPM capacity in the NOMA system over Rayleigh channel is derived. Then, an adaptive user-clustering is proposed in downlink NOMA system, such that the achievable sum-rate will get high enough. Moreover, the optimal allocation of power for each user in each cluster is derived and evaluated. In the end, the performances such as outage probability, capacity, peak-to-average power ratio (PAPR), and bit error ratio (BER) are simulated as comparison.

Joint Power Control and Phase Shift Design for Future PD-NOMA IRS-Assisted Drone Communications under Imperfect SIC Decoding.

Intelligent reflecting surfaces (IRS) and power-domain non-orthogonal multiple access (PD-NOMA) have recently gained significant attention for enhancing the performance of next-generation wireless communications networks. More specifically, IRS can smartly reconfigure the incident signal of the source towards the destination node, extending the wireless coverage and improving the channel capacity without consuming additional energy. On the other side, PD-NOMA can enhance the number of devices in the network without using extra spectrum resources. This paper proposes a new optimization framework for IRS-enhanced NOMA communications where multiple drones transmit data to the ground Internet of Things (IoT) devices under successive interference cancellation errors. In particular, the power budget of each drone, PD-NOMA power allocation of IoT devices, and the phase shift matrix of IRS are simultaneously optimized to enhance the total spectral efficiency of the system. Given the system model and optimization setup, the formulated problem is coupled with three variables, making it very complex and non-convex. Thus, this work first transforms and decouples the problem into subproblems and then obtains the efficient solution in two steps. In the first step, the closed-form solutions for the power budget and PD-NOMA power allocation subproblem at each drone are obtained through Karush-Kuhn-Tucker (KKT) conditions. In the second step, the subproblem of efficient phase shift design for each IRS is solved using successive convex approximation and DC programming. Numerical results demonstrate the performance of the proposed optimization scheme in comparison to the benchmark schemes.

Performance Analysis of Multi-User NOMA Wireless-Powered mMTC Networks: A Stochastic Geometry Approach

In this paper, we aim to improve the connectivity, scalability, and energy efficiency of machine-type communication (MTC) networks with different types of MTC devices (MTCDs), namely Type-I and Type-II MTCDs, which have different communication purposes. To this end, we propose two transmission schemes called connectivity-oriented machine-type communication (CoM) and quality-oriented machine-type communication (QoM), which take into account the stochastic geometry-based deployment and the random active/inactive status of MTCDs. Specifically, in the proposed schemes, the active Type-I MTCDs operate using a novel Bernoulli random process-based simultaneous wireless information and power transfer (SWIPT) architecture. Next, utilizing multi-user power-domain non-orthogonal multiple access (PD-NOMA), each active Type-I MTCD can simultaneously communicate with another Type-I MTCD and a scalable number of Type-II MTCDs. In the performance analysis of the proposed schemes, we prove that the true distribution of the received power at a Type-II MTCD in the QoM scheme can be approximated by the Singh-Maddala distribution. Exploiting this unique statistical finding, we derive approximate closed-form expressions for the outage probability (OP) and sum-throughput of massive MTC (mMTC) networks. Through numerical results, we show that the proposed schemes provide a considerable sum-throughput gain over conventional mMTC networks.

A new approach of successive interference cancellation decoder in power domain non-orthogonal multiple access transmission

A new approach of successive interference cancellation decoder in power domain non-orthogonal multiple access transmission

Design and performance evaluation of successive interference cancellation based Slotted Aloha MAC protocol

As a result of densification, the performance of the wireless networks has become highly interference-limited and energy inefficient. To overcome this problem, interference mitigation techniques such as Successive Interference Cancellation (SIC) can be used to decode multiple packets simultaneously at the receiver. In this context, we analyze a SIC-based Slotted Aloha (SIC-SA) Medium Access Control (MAC) protocol for wireless networks. We derive expressions for packets decoding probability and optimal transmission probability of the nodes of the SIC-SA MAC protocol. Our derivation is based on the order statistics of Independent and Identical/non-Identical exponentially distributed received-signal-powers from the nodes under the Rayleigh channel condition. Throughput, delay, and energy efficiency of the SIC-SA MAC protocol have been derived and validated against simulation. The effect of path loss exponent, SINR threshold, and the number of nodes on the performance of SIC-SA have been studied. The performance of SIC-SA in a network of nodes distributed randomly according to the Poisson Point Process has been analyzed. Extension of our analysis to Power Domain Non-Orthogonal Multiple Access (NOMA) has been demonstrated. We also analyzed the impact of imperfect estimation of channel state information and imperfect SIC at the receiver. Results show an improvement in performance metrics of SIC-SA over the traditional Slotted Aloha.

NOMA Joint Channel Estimation and Signal Detection Using Rotational Invariant Codes and GMM-Based Clustering

This letter studies the joint channel estimation and signal detection for the uplink power-domain non-orthogonal multiple access. The proposed technique performs both detection and estimation without the need of pilot symbols by using a clustering technique. We apply rotational-invariant coding to assist signal detection at the receiver without sending pilot symbols. We utilize Gaussian mixture model (GMM) to automatically cluster the received signals without supervision and optimize decision boundaries to improve the bit error rate (BER) performance. Simulation results show that the proposed scheme without using any pilot symbol achieves almost the same BER performance as that for the conventional maximum likelihood receiver with full channel state information.

Design of Power Location Coefficient System for 6G Downlink Cooperative NOMA Network

Cooperative non-orthogonal multiple access (NOMA) is a technology that addresses many challenges in future wireless generation networks by delivering a large amount of connectivity and huge system capacity. The aim of this paper is to design the varied distances and power location coefficients for far users. In addition, this paper aims to evaluate the outage probability (OP) performance against a signal-to-noise ratio (SNR) for a 6G downlink (DL) NOMA power domain (PD) and DL cooperative NOMA PD networks. We combine a DL cooperative NOMA with a 16 × 16, a 32 × 23, and a 64 × 64 multiple-input multiple-output (MIMO) and a 128 × 128, a 256 × 256, and a 512 × 512 massive MIMO in an innovative method to enhance OP performance rate and mitigate the power location coefficient’s effect for remote users. The results were obtained from Rayleigh fading channels using the MATLAB simulation software program. According to the outcomes, increasing the power location coefficients for the far user from 0.6 to 0.8 reduces the OP rate because increasing the power location coefficient for the far user decreases the power location coefficient for the near user, which results in less interference between them. In terms of the OP performance rate, the DL cooperative NOMA outperforms the NOMA. According to the findings, the DL cooperative NOMA OP rate outperforms the DL NOMA by a rate of 10−0.5. Whereas the 16 × 16 MIMO enhances the OP for the far user by 78.0 × 10−4, the 32 × 32 MIMO increases the OP for the far user by 19.0 × 10−4, and the 64 × 64 MIMO decreases the OP rate for the far user by 5.0 × 10−5. At a SNR of 10 dB, the 128 × 128 massive MIMO improves the OP for the far user by 1.0 × 10−5. The 256 × 256 massive MIMO decreases the OP for the far user by 43.0 × 10−5, and the 512 × 512 massive MIMO enhances the OP for the far user by 8.0 × 10−6. The MIMO techniques improve the OP performance, while the massive MIMO technology enhances the OP performance dramatically.

POTENTIAL SOLUTIONS, CHALLENGES AND IMPLEMENTATION ISSUES FOR NOMA IN 5G COMMUNICATIONS

Non-Orthogonal Multiple Access (NOMA), a promising radio access technology for 5G and beyond networks, has recently attracted a lot of interest because of its higher spectral efficiency and capacity to serve multiple users simultaneously while maintaining the same time and frequency resources. 5G mobile networks will be able to accommodate at least 100 billion connections between devices, a 1000-fold growth in system capacity, improved coverage, high data rates, and ultra-low energy consumption. A base station (BS) can serve numerous users at the same time, frequency, and code resource thanks to NOMA, which implements multiple access (MA) by utilizing a new dimension - the power domain. One of the fundamental NOMA methods that performs successive interference cancellation (SIC) at the receiver and superposition coding (SC) at the transmitter is the power domain NOMA

LED non-linearity mitigation in a NOMA-OFDM VLC system using a union of precoder and companding

The power domain non-orthogonal multiple access (NOMA) has been considered as an outstanding candidate for 5G visible light communication networks. Due to the various salient features like robustness to multi-path fading, low latency, high compatibility with multiple input multiple output systems, etc. orthogonal frequency division multiplexing access (OFDM) is foreseen to exist in 5G systems. NOMA-based optical OFDM (O-OFDM) is expected to be a promising candidate for supporting high rate internet connectivity, especially for green indoor mobile networks. The OFDM waveform suffers from high PAPR issue. The high PAPR degrades the BER and also enhances the non-linearity in an O-OFDM system. In this paper, a hybrid technique using a blend of precoder with compander is implemented to reduce the PAPR of NOMA based DC-biased O-OFDM (DCO-OFDM) system. The proposed NOMA DCO-OFDM system exhibits a low PAPR of only 4.3 dB. Also, for a reference bit error rate of 10\(^{-4}\), the proposed technique displays an error vector magnitude of 13.2 dB.

Multi-dimensional disturbance secure communication system with dynamic key hiding transmission based on power-domain non-orthogonal multiple access

Data security is becoming more critical in networks as high-speed and large-capacity optical transmission becomes more common. Cryptographic protocols at the MAC layer and higher tiers of the protocol stack are under threat as a result of quantum computer developments. Optical physical layer encryption has great advantages in optical communication security transmission, which can be compatible with a variety of networks, and achieve an efficient and secured ultra-high high-speed data transmission. In this work, we propose a physical layer encryption scheme based on orthogonal frequency division multiplexing power-domain non-orthogonal multiple access (OFDM-PD-NOMA) technique for the dynamic key hiding transmission and multi-dimensional disturbance. The encryption scheme realizes multi-point mutual-coupling key transmission and multi-dimensional disturbance encryption by a 3D discrete chaotic model. The encrypted data and the dynamic key are transmitted together by multichannel signals in PD-NOMA, then, the chaotic signal generated by chaotic generator is used to mask the dynamic key. 3D chaotic sequences generated by the dynamic key are used to encrypt bits, symbols and carriers of the original signal. The initial key, the dynamic key and the chaotic signal realize multi-point mutual-coupling. We conduct a 74.6 Gb/s encrypted quadrature phase shift keying (QPSK)-OFDM-PD-NOMA signal transmission over 2 km 7 core fiber. The key space of encrypted scheme can reach 10462. Finally, experimental results show that the original data can be recovered accurately, and the bit error rate (BER) of the dynamic key is close to zero. The security and reliability of the system have been verified, and this scheme has an important application prospect in the future optical communication system.

Guaranteeing QoS for NOMA-Enabled URLLC Based on κ-μ Shadowed Fading Model.

Sixth-generation (6G) wireless communication scenarios are complex and diverse. Small-scale fading is a key part of wireless channels and its impact on performance in scenarios with time sensitivity and 6G ultrareliable and low latency communications (URLLC) quality-of-service requirements cannot be ignored. Therefore, it is necessary to accurately characterize small-scale fading when designing wireless communication systems. In this paper, we derive approximate closed form expressions for the probability density function, cumulative distribution function and moment-generating function of the postprocessing signal-to-noise ratio following the zero-forcing detector in a cell-free massive multiple-input multiple-output (CF mMIMO) system. CF mMIMO system is a nonorthogonal multiple access (NOMA) system that enables users to share all channel uses and can ensure the fairness of the communication quality experienced by different users. Our key contributions include the extension of the – shadowed fading model to a CF mMIMO system and the proposal of theoretical tools (the derived closed-form expression) to improve its mathematical tractability. By exploiting the statistical characterizations of the arrival and service processes, another important contribution is the exploitation of the upper bound of the queuing delay violation probability (UB-QDVP) over the Mellin transforms of the arrival and service processes in the proposed CF mMIMO system under the – shadowed fading model. Corroborated by extensive simulations, our analyses validate that the CF mMIMO system outperforms the orthogonal multiple access and power-domain NOMA systems and reveal the relationships among different small-scale fading types, energy efficiency, delay and the UB-QDVP, as well as the accuracy and effectiveness of the proposed theoretical tools based on the – shadowed fading model.

Secure PD-NOMA with Multi-User Cooperation and User Clustering in Both Uplink and Downlink PD-NOMA

The power domain non-orthogonal multiple access (PD-NOMA) scheme has gained tremendous interest with the multiple access behavior for fifth-generation (5G) wireless communication. Although the overall performance is improved through accurate power distribution among users’ signals, it depends on the user clustering strategy. Moreover, the PD-NOMA communication is not completely secured due to its broadcast nature, which is still a major problem. This paper presents a novel low-complexity short code-based technique utilized by the registered users and the 5G base station (gNodeB) for communication. By doing so, the PD-NOMA scheme is made secure from unregistered users or eavesdroppers. We proposed a three-step user clustering strategy that selects the best cluster among all the possible clusters to improve the overall performance. The proposed clustering strategy achieves a low outage probability in PD-NOMA systems. Moreover, it uses a multi-user decode and forward cooperative relaying scheme with PD-NOMA (Cop-PD-NOMA) to increase the coverage range of the gNodeB. In the multi-user Cop-PD-NOMA, the strong users (near users) are used as relay stations to aid the weak users (far users) by the decode and forward (D&F) technique. The proposed work provides a secure PD-NOMA network and the most effective user clustering approach during validation. The bit-error-rate (BER) comparisons demonstrate that multi-user cooperation outperforms single-user cooperation in Cop-PD-NOMA communication.

ML-based reconfigurable symbol decoder: An alternative for next-generation communication systems

Modern Machine Learning (ML) techniques offer numerous opportunities to enable intelligent communication designs while addressing a wide range of problems in communication systems. A wide majority of communication systems ubiquitously employ the Maximum Likelihood (MLH) decoder in the symbol decoding process with QPSK modulation, thereby providing a non-reconfigurable solution. This work addresses the application of an ML-based reconfigurable solution for such systems. The proposed decoder can be considered a strong candidate for future communication systems, owing to its upgradable functionality, lower complexity, faster response, and reconfigurability. First, a novel low-complexity dataset for model training/testing is generated, that uses only the received symbols. Subsequently, three predictors are extracted from each of the received noisy symbols for model training/testing. The model is then trained/tested using nineteen standard ML-based classifiers, and the computations of various performance metrics indicate the suitability of Naïve Bayes (NB), and Ensemble Bagged Decision Tree (EBDT) classifiers for the model. The simulation results show that the model respectively delivers significant decoding accuracies and error rates of about 93% and 7% during testing, even for a low SNR of 5 dB. Moreover, the statistical analysis of simulation results shows the marginal superiority of the Gaussian Naïve Bayes (GNB) classifier. Further, the model reconfiguration is validated using a BPSK modulated dataset. Finally, a user-separation scheme that eliminates Successive Interference Cancellation (SIC) in the next-generation Power-Domain (PD) Non-Orthogonal Multiple Access (NOMA) networks is suggested by employing the proposed decoder.

On the Performance of the Unified NOMA Framework for Satellite-Terrestrial Networks with Hardware Impairments

A unified nonorthogonal multiple access (NOMA) framework for satellite-terrestrial network is investigated over Shadowed-Rician fading channels, which can be applied to both power domain NOMA (PD-NOMA) and code domain NOMA (CD-NOMA). Under the realistic assumption of hardware impairments (HIs) and imperfect successive interference cancellation (SIC), the achievable outage probability of the paired users is analyzed first, and the closed-form expressions of exact and asymptotic outage probability are derived. Next, the ergodic sum rate is investigated in different levels of HIs and residual interference. In addition, the energy efficiency in the delay-tolerant transmission mode is studied to characterize the performance of the satellite-terrestrial network. Finally, the Monte Carlo simulation results demonstrate the accuracy of theoretical derivation and showcase the effects of a wide range of satellite channel parameters and the realistic assumption on outage probability, ergodic rate, and energy efficiency.

Enabling transmission status detection in grant‐free power domain non‐orthogonal multiple access for massive Internet of Things

AbstractGrant‐free access has been identified as a potential solution to support massive machine‐type communications by avoiding the high signaling overhead and latency issues of existing grant‐based channel access mechanisms. Motivated by this, the work in this article proposes a simple, yet efficient, strategy to enable power domain non‐orthogonal multiple access (PD‐NOMA) aided grant‐free communication, where devices can transmit their data in an arrive‐and‐go manner by using randomly chosen power levels. The focus here is on collision detection, which is of prime importance in grant‐free systems. In the considered grant‐free PD‐NOMA scheme, collisions occur when multiple users randomly choose the same resource block and power level for data transmission, which makes it difficult for the base station (BS) to distinguish between their data. Accordingly, the proposed technique aims at early collision detection by introducing special activity indicator symbols (AIS), which are transmitted by each active device before, or at the start of, the actual data packet. The BS then exploits these known AIS to identify successful transmissions and collisions before processing actual data, which avoids unnecessary data transmission by users and/or receiver processing in case of collisions, and prepares the receiver for appropriate data recovery otherwise. It is demonstrated that the proposed technique provides a low complexity and high performance solution to enable transmission status detection in grant‐free PD‐NOMA.

Multiplexing Capacity of Hybrid PD-SCMA Heterogeneous Networks

Hybrid multiple access schemes are considered potential technologies towards achieving optimal spectrum sharing for future heterogeneous networks. Multiple users are multiplexed on a single resource unit in the code domain for sparse code multiple access (SCMA) or power domain for power domain non-orthogonal multiple access (PD-NOMA) and in both domains for the hybrid power domain sparse code non-orthogonal multiple access (PD-SCMA). This allows for effective spectrum usage but comes at a cost of increased detection complexity resulting in loss of performance in terms of outages. It is therefore imperative to determine the user multiplexing capacity for effective performance. This work investigates codebook capacity bounds in small cells, pairing and power capacity bounds for the number of small cell user equipment’s (SUEs) and macro cell user equipment’s (MUEs) that can be multiplexed on a codebook for the developed PD-SCMA technology. Closed-form solutions for codebook, pairing and power multiplexing capacity bounds are derived. The performance of the system results into low outage when the system’s point of operation is within the multiplexing bounds. To alleviate the resource allocation (RA) challenges of such a system at the transmitter, dual parameter ranking (DPR) and alternate search method (ASM) based RA schemes are proposed. The results show significant capacity gain with DPR-RA in comparison with conventional schemes.

Resource allocation for IRS‐assisted MC MISO‐NOMA system

In this paper, a downlink multi-user communication of an intelligent reflecting surface (IRS)-assisted multiple-input single-output (MISO) power-domain non-orthogonal multiple access (NOMA) system is investigated. Considering multi-carrier (MC) transmission and to enhance user fairness, two users are assigned to the same subcarrier. For such a system, the authors optimize active beamforming at the base station (BS), subcarrier allocation policy, and phase shifts at the IRS to maximize the system throughput. A semi-definite relaxation (SDR) is applied to tackle the non-convex optimization problem, and an alternating optimization (AO) algorithm is proposed to obtain a suboptimal solution. Numerical results illustrate the higher throughput of the proposed MC multi-user IRS-aided MISO-NOMA system as compared to the conventional IRS-assisted orthogonal multiple access (OMA) system.

Optimal Rotated QPSK Constellation for a Reliable SOMA Powerline Communication System in Nakagami-m Noise Environment

An <inline-formula> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula>-branch receive diversity powerline communication (PLC) system with two users and the transmitter employing a power-domain non-orthogonal multiple access (PD-NOMA) along with a rotated quadrature phase-shift keying (QPSK) modulation scheme, generally known as semi-orthogonal multiple access (SOMA) for data transmission is considered in this paper. The rotation of the data constellation and a proposed pre-processing at the receiver end for each user eliminate the usage of the additional successive-interference cancellation (SIC) hardware generally used in PD-NOMA PLC systems. Furthermore, optimal receiver structures are proposed using which closed-form expressions of the symbol error probability (SEP) are derived for the users using a characteristic function (c.f.) approach. The optimal rotation of the QPSK constellation minimizing the obtained SEP of the system is also derived. The diversity order of the system and the optimal angle of rotation at high average signal-to-noise ratio (SNR) values are found to be dependent only on the number of diversity branches. Moreover, the general dependence of the optimal rotation angle on various system parameters is corroborated by numerical results which provide various insights into the design of a reliable and energy-efficient PD-SOMA PLC system without the use of SIC hardware. The optimal rotation angle of the QPSK constellation also leads to novel optimal constellations for the users which are different than the conventional constellation utilized for data transmission in digital communication systems.