Orthogonal Multiple Access Techniques Research Articles

Energy minimization for IRS-and-UAV-assisted mobile edge computing

Intelligent reconfigurable surface (IRS) is an emerging technology for the enhancement of spectrum and energy efficiency. We propose a novel IRS-and-unmanned aerial vehicle (UAV)-Assisted mobile edge computing (MEC) framework, where a MEC server installing on an UAV to facilitate task calculations by mobile users (MUs), and an IRS modulates channels between MUs and the UAV. Non-orthogonal multiple access (NOMA) is employed for further improving system-wide spectral efficiency. There are needs for joint optimization of multiple parameters, e.g., the task partition parameters and the transmit power of all MUs, the reflection coefficient matrix of the IRS and the movement trajectory of the UAV, and such needs raises the challenge of minimizing the long-term total energy consumption of all MUs while satisfying required transmission rate and task completion delay. We divide optimization tasks into two sub-problems and propose specific solutions respectively, i.e., relevant decisions about the UAV and MUs to be solved by deep reinforcement learning (DRL); and the reflection coefficient matrix of the IRS to be solved by block coordinate descent (BCD). A series of experiments have verified the effectiveness of the proposed communication techniques and optimization algorithms. Simulation results demonstrate that (1) NOMA-IRS technique achieves better energy efficacy compared to the cases where random IRS or no IRS is deployed and the conventional orthogonal multiple access (OMA) technique with IRS. (2) our proposed deep deterministic policy gradient (DDPG)-BCD algorithm outperforms other four benchmark algorithms in solving the complex and dynamic optimization problem.

Ergodic analysis of IRS-NOMA with inter-cell interference and Imperfect-CSI and SIC over Nakagami-m faded channel

Future wireless technology requires higher data rates, low latency, and flexibility to provide services to users. To fulfil these demands, various multiple access techniques are proposed. Among these techniques, the non-orthogonal multiple access technique (NOMA) is providing better features compared to orthogonal multiple access (OMA) techniques, such as more number of radio resources with low latency. In NOMA based communication system, if a user is lying on the cell's edge, their performance is poor. Recently, intelligent reflecting surfaces (IRS)-NOMA system is introduced to enhance its performance. To implement IRS-NOMA in a real-time scenario, the impact of inter-cell interference and imperfect-channel state information (CSI) and successive interference cancellation (SIC) is very much required. In this work, we derived analytical expressions to evaluate the Ergodic capacity of the IRS-NOMA over the Nakagami-m faded channel by considering inter-cell interference, imperfect-CSI, and SIC. By considering these factors, this work offers a comprehensive understanding of the system's capabilities and limitations. Here, two user IRS-NOMA is considered and also evaluated the analytical results by varying fading parameter (m), number of interferers (K), error in CSI and SIC, and IRS elements. These results are also supported by simulated results.

Simulation and Analysis of the Code Domain NOMA with UFMC for 5G Wireless Networks

In fifth generation (5G) wireless networks, radio access techniques and multi-carrier waveforms play a vital role in meeting the diversified demands of ultra-low latency, massive connectivity, and higher throughput. Multi-access schemes used conventionally in 4G system was Orthogonal Multiple Access (OMA) technique. The OMA techniques suffer from inefficient spectrum utilization, high latency, and supports a limited number of users. Next-generation networks, Non-Orthogonal Multiple Access (NOMA), has a great potential, in which multiple users are simultaneously served using the same time, frequency, or code resource increasing the throughput. Code domain-NOMA (CD-NOMA) is the key technique implemented in the system design where multiple users are distinguished based on unique user-specific spreading codes. The NOMA system could significantly benefit from Universal Filtered Multi-Carrier (UFMC) modulation waveform in terms of flexibility, spectral efficiency, compatibility with Multiple Input Multiple Output (MIMO) technique, and relaxed synchronization requirements. The novel integrated system proposed in the paper is CD-NOMA-UFMC with convolutional codes. The major outcome of the paper is that the combination of UFMC air interface modulation technique with CD-NOMA access method can be the most effective way to meet the growing demands of 5G.

Signalling overhead diminution in M-MIMO using NOMA transmission

With the increase in demand for mobile and Internet of Things devices, Orthogonal Multiple Access (OMA) cannot manage the maximum number of users. In this technique, the number of radio frequencies must be equivalent to the number of users. It causes to increase in signalling overhead. Therefore, it requires special attention to reduce the signalling overhead to escalate the spectral and energy efficiency. This paper investigates different Non Orthogonal Multiple Access (NOMA) techniques, and the results are compared with OMA techniques. A novel NOMA technique Multi User Shared Access (MUSA) is applied. It adjusts maximum users and has good spectral and energy efficiency compared to OMA techniques. In this proposed technique, maximum complex spreading codes are generated for the users and each user picks that code and transmits its data at the same radio frequency chain. The proposed scheme MUSA-NOMA has 12.8% more energy efficiency and 6.51% spectral efficiency compared to SCMA-NOMA and 32% more energy efficiency and 18.5% spectral efficiency compared to OMA.Article highlightsImagine you're using your phone in a crowded area where many people are also trying to connect, signalling congestion will occur. In traditional setups, it is difficult to manage everyone's signals.Instead of dealing with each person's signal separately, NOMA allows the communication system to treat similar groups together, streamlining the process.It's like having group discussions instead of one-on-one talks, making the whole communication setup more efficient and less complicated. This way, your phone and the network can handle many connections more smoothly, providing a better experience for everyone.

Performance Improvement and Analysis of NOMA in densely populated networks

ABSTRACT Non Orthogonal Multiple Access technique (NOMA) is a potential and promising candidate for 5 G and beyond 5 G due to its better spectral efficiency and low latency. However, it faces implementation challenges in densely populated networks due to its computational complexity. In NOMA, for decoding user information at the receiver end, it needs to perform times perfect Successive Interference Cancellation (SIC) operation. Hence, in a dense network, where the number of users is high, the implementation of NOMA becomes tedious. In order to improve the performance of NOMA implementation, in this work, the concept of Cooperative Modulated-NOMA (CM-NOMA) is applied in the considered densely populated networks model. Performance analysis of the system in terms of outage probability, Symbol-to-Error Rate (SER) and achievable data rate in both one-to-one and cooperative communications scenarios are done. The analytical expressions are also validated using Monte Carlo simulation. The results show that the deployment of CM-NOMA in a densely populated network increases the performance of the system, and also reduces the computational complexity.

Comparative Analysis of NOMA and OMA Schemes: GSVD-based NOMA Systems and the Role of Mobile Edge Computing

This paper presents a comprehensive study that examines the fundamental concept of the non-orthogonal multiple access (NOMA) scheme and provides its detailed comparison with the orthogonal multiple access (OMA) technique. Furthermore, the paper explores the application of the generalized singular value decomposition (GSVD) method in conjunction with NOMA, accompanied by a detailed review of GSVD-based NOMA systems. This study also introduces the concept of mobile edge computing (MEC) and extensively discusses its key parameters. Furthermore, a comprehensive analysis of NOMA MEC is presented, shedding light on its potential advantages and challenges. The aims of this study are to provide a comprehensive understanding of the aforementioned topics and contribute to the advancement of MIMO-NOMA systems.

Dual-Polarized Massive MIMO-RSMA Networks: Tackling Imperfect SIC

The polarization domain provides an extra degree of freedom (DoF) for improving the performance of multiple-input multiple-output (MIMO) systems. This paper takes advantage of this additional DoF to alleviate practical issues of successive interference cancellation (SIC) in rate-splitting multiple access (RSMA) schemes. Specifically, we propose three dual-polarized downlink transmission approaches for a massive MIMO-RSMA network under the effects of polarization interference and residual errors of imperfect SIC. The first approach implements polarization multiplexing for transmitting the users' data messages, which removes the need to execute SIC in the reception. The second approach transmits replicas of users' messages in the two polarizations, which enables users to exploit diversity through the polarization domain. The third approach, in its turn, employs the original SIC-based RSMA technique per polarization, and this allows the BS to transmit two independent superimposed data streams simultaneously. An in-depth theoretical analysis is carried out, in which we derive tight closed-form approximations for the outage probabilities of the three proposed approaches. Accurate approximations for the ergodic sum-rates of the two first schemes are also derived. Simulation results validate the theoretical analysis and confirm the effectiveness of the proposed schemes. For instance, under low to moderate cross-polar interference, the results show that, even under high levels of residual SIC error, our dual-polarized MIMO-RSMA strategies outperform the conventional single-polarized MIMO-RSMA counterpart. It is also shown that the performance of all RSMA schemes is impressively higher than that of single and dual-polarized massive MIMO systems employing non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA) techniques.

Multigateway precoded NOMA in multibeam satellite multicast systems

In this paper, we consider multigateway-based multibeam satellite non-orthogonal multiple access (NOMA) multicast systems. We investigate the improvement in spectral efficiency and accessibility by superimposing multiple signals on each beam at the same frequency and time resource employing NOMA, where multiple gateways transmit precoded signals to alleviate inter-beam interference caused by full frequency reuse. We formulate an optimization problem of maximizing the sum rate while satisfying the gateways and satellite transmission power constraints, where the precoding vector and power allocation for superposition coding as well as the decoding order for successive interference cancellation are optimized. This optimization problem is challenging to solve due to its non-convex mixed-integer nonlinear programming. However, a suboptimal solution can be obtained using a block coordinate descent algorithm. The simulation results of the proposed NOMA technique are compared with those of the orthogonal multiple access (OMA) technique. The proposed technique outperforms the OMA technique. We also investigate the impact of channel imperfection and decoding capability of the proposed algorithm through some selected simulation results.

Low-complexity selective mapping technique for PAPR reduction in downlink power domain OFDM-NOMA

To support ultra-massive connectivity, non-orthogonal multiple access (NOMA) techniques are expected to be used in 6G instead of conventional orthogonal multiple access (OMA) techniques. Furthermore, given that orthogonal frequency division multiplexing (OFDM) was used by 4G and 5G, NOMA is expected to be combined with OFDM to mitigate frequency selectivity in multipath channels. However, after passing through nonlinear high power amplifiers (HPAs), OFDM-NOMA has reportedly suffered from nonlinear distortion due to the high peak-to-average power ratio (PAPR) problem, thus reducing users’ achievable data rates, sum rate capacity, and users’ bit error rate after going through nonlinear HPAs. Many PAPR reduction techniques have been introduced in the literature; however, high PAPR reduction gain comes at the expense of computational complexity. In this paper, a novel selective mapping (SLM) scheme for PAPR reduction in OFDM-NOMA systems is proposed. By utilizing the structure of the OFDM-NOMA transmitter, the proposed SLM scheme achieves the same performance as that of the conventional SLM scheme while requiring less computational complexity.

Distinctive analysis of power and frequency allocation for Device to Device (D2D) communication

Wireless communication makes an impeccable advancement from 1 G to 5 G and beyond. Simultaneously, modern technologies like Internet of Things (IoT) and Vehicular Communications also emerged. Improved connectivity between many different devices is provided by 5 G, which maximises data throughput and reduces interference. Non-Orthogonal Multiple Access (NOMA) schemes or Orthogonal Multiple Access techniques (OMA) suit 5 G. It is a NOMA-based device-to-device communication by correlating it with the Orthogonal Frequency Division Multiple Access (OFDMA). NOMA is also utilized to propose an optimal power allocation scheme and duly evaluated. The aim of such a scheme is to achieve a minimized outage and a maximized sum rate. A NOMA based Greedy Interference Algorithm is proposed for interference management by exquisite frequency allocation. The results generated from a comprehensive evaluation justify the algorithm utilization. Simulation results infer that the algorithms proposed improves system throughput and enhance energy efficiency.

Integration of Cognitive Radio Technology in NOMA-Based B5G Networks: State of the Art, Challenges, and Enabling Technologies

The integration of cognitive radio (CR) technology and non-orthogonal multiple access (NOMA) techniques, referred to as CR-based NOMA system, has been recently configured as a promising solution to meet the requirements of beyond fifth generation (B5G) networks, especially those related to Internet-of-Things (IoT) applications. With such integration, power domain NOMA allows multiple users to share the same orthogonal resource blocks, while CR technology enables opportunistic bandwidth utilization by permitting secondary users (SUs) to access the licensed spectrum frequency without interrupting the primary users’ (PUs) activities. To support the massive connectivity requirements of IoT-based networks, several multiple-access techniques have been recently combined with CR-based NOMA systems, including orthogonal multiple access (OMA) and multiple-antenna techniques. For example, in CR-based OMA-NOMA systems, the licensed frequency band is split into several channels, and a set of SUs is served on each channel using the NOMA technique. This paper provides an overview and analysis of the state-of-the-art CR-based NOMA network architecture. It summarizes the main design challenges related to the practical implementation of such systems. Furthermore, this paper presents the advances of combining CR-based NOMA with recent multiple-access techniques, where the potential capabilities and the design challenges of such integrated systems are also investigated and discussed. On the other hand, this paper demonstrates the potential capabilities of deploying recent technologies in CR-based NOMA networks. The technologies include intelligent reflecting surfaces, terahertz communications, machine learning, unmanned aerial vehicles, and hybrid NOMA systems. Finally, future research directions and open issues are provided and discussed.

Outage Probability analysis of Power Domain MISO-NOMA in Rayleigh Fading Channel

The multiple access technique of the current wireless communication system depends on the orthogonal multiple access (OMA) technique. The availability of orthogonal resources is limited in OMA and cannot support the increasing demand for a large number of users and efficient use of the spectrum in the coming years. The Non-orthogonal multiple access (NOMA) is considered in the future release of 5G and beyond 5G. In NOMA, multiple users can be dealt with in the same resource block at the same time, which allows NOMA to provide large connectivity, low latency, and high spectral efficiency. In this paper, the outage probability expression for the MISO-NOMA downlink system is derived by employing an indefinite quadratic form (IQF) approach. Analytical results are compared with the Monte Carlo simulations which validate our theoretical derivations. Further, the performance of the MISO-NOMA system is assessed with different numbers of users in the system and different SNR values.

Improved Dynamic Power Allocation Scheme for Massive Connectivity in NOMA System

In a wireless network, the radio resources are allocated to the users based on the Orthogonal Multiple Access (OMA) technique. The performance of the network can be improved by introducing non-Orthogonal multiple access (NOMA) whenever the number of users increases tremendously. There is much scope in improving the outage probability, bit error rate (BER), high spectral efficiency and latency. To improve this, Non-Orthogonal Multiple Access (NOMA) technique has been discussed in this paper with fair power allocation technique. The effect of fixed power and dynamic power allocation has been discussed and compared, the Bit error rate (BER) and achievable rate have been analyzed and compared. The NOMA uses Successive interference cancellation (SIC) at the receiver for decoding the individual user’s data which is a complex process. The effect of imperfect SIC has also been evaluated and analyzed. In dynamic Power allocation technique higher power is devoted to the far users due to which the near user goes into outage. A new technique has been proposed to reduce the outage power while taking the target rate and SNR of each user into consideration. The results show an improvement in outage probability in comparison with the state of art technique.

Deep transfer reinforcement learning for resource allocation in hybrid multiple access systems

This paper proposes a resource allocation scheme for hybrid multiple access involving both orthogonal multiple access and non-orthogonal multiple access (NOMA) techniques. The proposed resource allocation scheme employs multi-agent deep reinforcement learning (MA-DRL) to maximize the sum-rate for all users. More specifically, the MA-DRL-based scheme jointly allocates subcarrier and power resources for users by utilizing deep Q networks and multi-agent deep deterministic policy gradient networks. Meanwhile, an adaptive learning determiner mechanism is introduced into our allocation scheme to achieve better sum-rate performance. However, the above deep reinforcement learning adopted by our scheme cannot optimize parameters quickly in the new communication model. In order to better adapt to the new environment and make the resource allocation strategy more robust, we propose a transfer learning scheme based on deep reinforcement learning (T-DRL). The T-DRL-based scheme allows us to transfer the subcarrier allocation network and the power allocation network collectively or independently. Simulation results show that the proposed MA-DRL-based resource allocation scheme can achieve better sum-rate performance. Furthermore, the T-DRL-based scheme can effectively improve the convergence speed of the deep resource allocation network.

Improved Spectral Efficiency and Connectivity in RSMA based 5G V2X Systems

Vehicle to everything (V2X) faces several challenges including high data rate, low latency and stable connectivity requirements. Due to increased number of connected vehicles, Interference too appears to be a serious issue in V2X systems. Consequently, careful selection of multiple access techniques can lead to improved interference mitigation together with higher spectral efficiency and data rate. Vehicle mobility with growing traffic density is a demanding task that affects probability of vehicle connectivity, thereby resulting into requirement of sustained vehicle linkage for ongoing traffic safety. In this regard, our paper employs Rate Splitting Multiple Access (RSMA) technique, which considers change of both channel strength and direction for improved interference mitigation leading towards enhanced spectral efficiency. RSMA is optimized for weighted sum rate, further; it is integrated with mobility management to demonstrate sustained connectivity in the presence of increased traffic density. Presented results have been found promising, both in terms of spectral efficiency and stable connectivity. RSMA 5G V2X outperformed at higher Signal to noise ratio (SNR) values and on average achieved 25% better spectral efficiency compared to Non Orthogonal Multiple Access (NOMA) technique.

Cooperative Scheduler to Enhance Massive Connectivity in 5G and Beyond by Minimizing Interference in OMA and NOMA

The fifth-generation (5G) and beyond 5G (B5G) wireless networks introduced massive machine-type communications (mMTC) to cope with the growing demand of massive Internet of Things (IoT) applications. However, the heterogeneous characteristics of massive IoT and diverse quality of service (QoS) requirements may lead to severe interference that could degrade the expected QoS of the cellular ecosystem. Therefore, this article studies the impact of interference caused by mMTC connections. We theoretically model the intercell interference (ICI) minimization problem for the existing orthogonal multiple access (OMA) technique and propose its corresponding solution. Furthermore, we jointly solve the ICI and the cochannel interference minimization problem for the IoT users when the nonorthogonal multiple access (NOMA) technique is used. For the proposed OMA and NOMA schemes, we design a cooperative scheduler to reduce the impact of such interference. The results show that our proposed schemes provide up to 58%, 75%, and 100% more improvements in terms of user’s data rates, energy consumption, and connection density, respectively.

A Novel User Grouping Algorithm for Downlink NOMA

Non-orthogonal multiple access (NOMA) is one of the promising radio access techniques for resource allocation improvement in the (5th) generation of cellular networks. Compared to orthogonal multiple access techniques, NOMA offers extra benefits, including greater spectrum efficiency which is provided through multiplexing users in the transmission power domain while using the same spectrum resources non-orthogonally. Even though NOMA uses Successive Interference Cancellation to repeal the interference among users, user grouping has shown to have a substantial impact on its performance. This performance improvement can appear in different parameters such as system capacity, data rate, or power consumption. In this paper, we propose a novel user grouping scheme for sum-rate maximization which increases the sum rate by approximately 12–25% in comparison with random user grouping and two other authenticated recent works. In addition to being matrix-based and having a polynomial time complexity, the proposed method is also able to cope with users experiencing different channel gains and powers in different sub-bands. Moreover, the proposed scheme is scalable and can be used for any number of users and sub-bands.

Outage probability and throughput of cooperative non‐orthogonal multiple access with moving relay in heterogeneous network

AbstractThe demand of high data rate, high quality of service (QoS), and seamless connectivity are growing continuously for vehicular communication over the last few years. Moving relay (MR) is one of the promising techniques to achieve these demands. In the past, heterogeneous network (HetNet) models with one MR on the top of the train have been proposed for high‐speed railway (HSR) using the orthogonal multiple access (OMA) technique. Cooperative non‐orthogonal multiple access (NOMA) is a promising multiple access technique for next‐generation wireless networks. This paper proposes one MR‐based HetNet model using the NOMA over Rayleigh fading channels for downlink communication. Here, half‐duplex (HD) type amplify and forward (AF) relay is used as MR for investigation. We derive the outage probability of a train‐user using the successive interference cancellation (SIC) technique and the outage probability of a cell‐edge‐user by using both direct and indirect signals via MR. The system throughput of the proposed NOMA system is also simulated by considering the effects of perfect and imperfect SIC. The simulation results show that cooperative NOMA provides lower outage performance in comparison with cooperative OMA and outage of vehicular user decreases with lower value of residual interference (RI). Also, the system throughput of the NOMA system decreases with higher values of residual interference. We use Monte Carlo simulation to verify the derived analytical results.

NOMA VLC Systems and Neural Network Approach for Imperfect SIC

Non Orthogonal Multiple Access (NOMA) technique in Visible Light Communications (VLC) enhances the performances like spectral efficiency, achievable data rate, fairness, outage probability, etc. NOMA uses superposition in power domain at the transmitter and Successive Interference Cancellation (SIC) at the receiver. SIC operation is expected to perform perfect cancellation to avoid errors in the received signal. In this paper, Neural Network (NN) methods are used to overcome imperfect SIC in a NOMA VLC system. The Signal to Noise Ratio (SNR), Bit Error Rate (BER), and bitrate performance of the NOMA VLC systems are analyzed using Convolution Neural Network (CNN), long short term memory (LSTM), and Deep Neural Network (DNN) algorithms. Simulation results shows that the NN methods outperforms the conventional NOMA VLC system to a perfect SIC. Considering SNR for the BER 10−4, CNN outperforms SIC by 5 dB, DNN by 2 dB and LSTM by 1.5 dB. Further, CNN also outperforms SIC, DNN, and LSTM based NOMA VLC systems for BER performance as a function of bitrate. Thus, NN-based receiver will be a better alternative for imperfect SIC.

Power allocation with QoS satisfaction in mmWave beamspace MIMO‐NOMA

In this paper, a non-orthogonal multiple access (NOMA) scheme is considered for downlink millimeter-wave (mmWave) transmissions over beamspace massive multiple-input multiple-output (MIMO) channels. To improve the NOMA detection and reduce its complexity, it is assumed that users are grouped in clusters. The major benefit of the NOMA depends on the power allocation (PA) among users. In this context, to ensure the quality of service (QoS) of users, a threshold rate for each user is defined. The aim of this work is to propose a new PA strategy that takes into account the pre-defined threshold rates and maximizes the achievable sum rate. Thereafter, considering the Karush-Kuhn-Tucker (KKT) conditions, a closed-form solution for the PA issue under perfect and imperfect channel state information (CSI) assumptions is derived. Through simulation results, it is shown that the proposed scheme outperforms the conventional orthogonal multiple access techniques in terms of spectral efficiency (SE) and energy efficiency (EE). In addition, the proposed robust PA scheme for the imperfect CSI case reduces the performance loss due to the channel uncertainty.