Conventional Non-orthogonal Multiple Access System Research Articles

Enhancing Reliability and Security of UAV-Enabled NOMA Communications With Power Allocation and Aerial Jamming

In view of the scarce spectrum resources and inconvenient deployment in wireless communications, this work focuses on an unmanned aerial vehicle (UAV) enabled non-orthogonal multiple access (NOMA) system where a UAV deployed as a base station serves two users by NOMA. A joint power allocation and aerial jamming (PAAJ) scheme is proposed to achieve reliable and secure communications for the system in the presence of a malicious eavesdropper. To be specific, dynamic power allocation is adopted to ensure the reliability of the system and another friendly UAV jammer is introduced to improve the security of the system. The closed-form expressions of connection outage probability (COP), secrecy outage probability (SOP), and effective secrecy throughput (EST) are derived to evaluate the performance of the security-required user in the practical condition of probabilistic line-of-sight (LoS) and non-line-of-sight (NLoS) air-to-ground (A2G) channels. Moreover, the asymptotic EST is analyzed to obtain further insights. Numerical results show the validity of theoretical derivations and the superiority of the proposed PAAJ scheme over benchmark schemes. The EST of the UAV-enabled NOMA communication system outperforms the conventional terrestrial NOMA system at the low transmitting power from the UAV base station. There exists an optimal height of the UAV base station to maximize the EST, which provides a useful framework for designing UAV-enabled communication systems with heterogeneous service requirements.

Joint Multi-User Decoding for Polar-Coded Uplink Non-Orthogonal Multiple Access Systems

Polar-coded non-orthogonal multiple access (NOMA) is a competitive candidate for future wireless physical layer access techniques. The conventional NOMA system employs successive interference cancellation (SIC) for signal decoding. The SIC decoding procedure is optimal only when the code length is sufficiently long. Transmissions with long codes may undergo channel fluctuations. Considering the channel fluctuations, we propose a joint multi-user successive cancellation decoding algorithm for the polar-coded uplink NOMA system. It is shown by simulation results that the proposed joint multi-user decoding algorithm is robust to channel fluctuations.

Outage Analysis and Reliability Enhancement of Hybrid VLC-RF Networks Using Cooperative Non-Orthogonal Multiple Access

Visible light communication (VLC) is a promising communication technology that benefits from several advantages over other wireless communication techniques. However, the capacity of VLC systems is limited by the low modulation bandwidth of light-emitting diodes (LEDs) used as transmitters. To circumvent this bottleneck, non-orthogonal multiple access (NOMA) is popularly used in VLC systems. However, due to high inter-user interference at the receivers, NOMA suffers from poor outage performance, especially if the number of users is large. We propose to boost the outage performance of a NOMA-based VLC system by incorporating multi-user cooperative diversity over radio frequency (RF) links, thereby transforming it into a hybrid VLC-RF system. Such a system with cooperative NOMA (CoNOMA) has enhanced reliability compared to a conventional non-cooperative NOMA system. We formulate the expressions for the outage probability of the proposed system and analyze the outage performance for various power allocation schemes used in NOMA. We study the effects of increasing the number of users and the target data rate on the system’s overall outage performance. We also model the reliability of the multi-user CoNOMA system using Markov chains and evaluate the various reliability parameters for each user. We show that the outage performance and reliability of the VLC system are significantly enhanced by employing cooperative diversity using CoNOMA.

Performance analysis of downlink NOMA system with diversity combining schemes over [formula omitted]–[formula omitted] fading channel

A novel downlink multiuser non-orthogonal multiple access (NOMA) system is proposed in which diversity combining techniques are employed at each user. In particular, selection combining (SC), equal gain combining (EGC), and maximum ratio combining (MRC) diversity techniques are adopted by each user to improve the performance of the system. The outage and sum-rate analysis of the proposed system are presented for L branch diversity combiner over η–μ fading channel with imperfect successive interference cancellation (SIC). In addition, an exact closed-form expression for the probability density function (PDF) of signal-to-noise ratio (SNR) at the output of equal gain combiner is derived using Laplace transform approach for η–μ fading channel. The proposed system completely outperforms the conventional NOMA system and among the proposed schemes, NOMA with MRC diversity has the best performance, as expected. The outage performance of the proposed NOMA system is compared with that of orthogonal multiple access (OMA) system. The theoretical results are verified with the simulation results.

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

A Novel Downlink IM-NOMA Scheme

In the next generations of communication systems, resources' scarcity devolves to a more critical point as a consequence of the expected massive number of users to be served. Furthermore, the users' contradicting requirements on quality of service forces the network to behave in a dynamic way in terms of the multiple access orchestration and resource assignment between users. Hence, the linear relation between the number of served users and the required (orthogonal or semi-orthogonal) resources in the orthogonal multiple access (OMA) schemes is no longer sufficient. As promising candidates, Non-orthogonal multiple access (NOMA) schemes and index modulation (IM) techniques are emerging to satisfy the ever-increasing connectivity demands and spectral efficiency. In this article, a novel IM-based NOMA downlink scheme, termed as IM-NOMA, is proposed, where the base station (BS) selects a channel or more to serve each user based on the IM concept and the corresponding power level is allocated based on the NOMA concept. At the users' ends, maximum likelihood and successive interference cancellation (SIC) detection methods are considered and their error rate, outage probability and computational complexity are studied. Simulation results confirm the advantage of the proposed IM-NOMA scheme and that it can outperform the conventional NOMA system.

Resource Allocation in Intelligent Reflecting Surface Assisted NOMA Systems

This article investigates the downlink communications of intelligent reflecting surface (IRS) assisted non-orthogonal multiple access (NOMA) systems. To maximize the system throughput, we formulate a joint optimization problem over the channel assignment, decoding order of NOMA users, power allocation, and reflection coefficients. The formulated problem is proved to be NP-hard. To tackle this problem, a three-step novel resource allocation algorithm is proposed. Firstly, the channel assignment problem is solved by a many-to-one matching algorithm. Secondly, by considering the IRS reflection coefficients design, a low-complexity decoding order optimization algorithm is proposed. Thirdly, given a channel assignment and decoding order, a joint optimization algorithm is proposed for solving the joint power allocation and reflection coefficient design problem. Numerical results illustrate that: i) with the aid of IRS, the proposed IRS-NOMA system outperforms the conventional NOMA system without the IRS in terms of system throughput; ii) the proposed IRS-NOMA system achieves higher system throughput than the IRS assisted orthogonal multiple access (IRS-OMA) systems; iii) simulation results show that the performance gains of the IRS-NOMA and the IRS-OMA systems can be enhanced via carefully choosing the location of the IRS.

Capacity Analysis of an AF Relay Cooperative NOMA System Using MRC

Non-orthogonal multiple access (NOMA) is widely studied in both academia and industry due to its high spectral efficiency over orthogonal multiple access (OMA). To effectively improve spectrum efficiency, an amplify-and-forward (AF) cooperative NOMA system is proposed as well as a novel detection scheme is proposed, in which we first perform successive interference cancellation (SIC) twice at U1 for the two signals received from two time slots to remove interference from symbol 2, then two new signals apply max ratio combining (MRC). In addition, a closed-form upper bound approximation for the ergodic capacity of our proposed system is derived. Monte-Carlo simulations and numerical analysis illustrate that our proposed system has better ergodic capacity performance than the conventional cooperative NOMA system with decode-forward (DF) relay, the conventional cooperative NOMA system with AF relay and the proposed AF cooperative NOMA system in [16]. In addition, we can see that ergodic capacity of all NOMA cooperative systems increase with the increase of transmit SNR. Finally, simulations display that power allocation coefficients have little effect on ergodic capacity of all NOMA cooperative systems. This is due to this fact that ergodic capacity of two symbols can be complementary with changing of power allocation coefficients.

Performance analysis of discrete wavelet transform for downlink non‐orthogonal multiple access in 5G networks

Non-orthogonal multiple access (NOMA) has been considered a key technology to address the increasing traffic demands for fifth-generation (5G) cellular wireless communication networks and internet of things. The NOMA technique offers efficient bandwidth utilisation, low latency, and support for the massive connectivity of devices in 5G networks. In the conventional NOMA system, orthogonal frequency division multiplexing (OFDM) is used as a pulse-shaping technique that causes high peak to average power ratio (PAPR) due to the superposition of signals of multiple users after passing through inverse fast Fourier transform and spectral inefficiency due to the cyclic prefix insertion. Therefore, an alternate methodology using wavelet OFDM is proposed in this research work, as a pulse-shaping technique for NOMA-based communication systems to improve spectral efficiency and system capacity The main contribution of this study is the analysis of the bit error rate (BER) performance and the effect of carrier frequency offset on system performance of wavelet NOMA (W-NOMA) technique in 5G networks. The simulation results demonstrate that W-NOMA outperforms the conventional NOMA with reference to PAPR and BER.

NOMA-based downlink relaying with media-based modulation

In recent years, non-orthogonal multiple access (NOMA) has attracted considerable attention as a promising multi-access technique for next generation wireless communication systems. Media-based modulation (MBM), which is an emerging index modulation concept, is another technique that can be considered for next generation wireless communication systems due to its high spectral and energy efficiency. In this paper, we propose a NOMA-based decode-and-forward relaying system, where MBM is applied at the source to improve error performance at the relay. We consider a topology consisting of a single source with a single transmit antenna equipped with multiple radio frequency (RF) mirrors, one relay equipped with a single transmit and multiple receive antennas, and multiple users equipped with multiple receive antennas. Pairwise error probability expression for NOMA with multiple receive antennas is derived and the union bound on bit error rate (BER) for the overall system with imperfect successive interference cancellation (SIC) is obtained in closed-form. Analytical results are in agreement with the Monte Carlo simulation results. Moreover, two power allocation optimization problems are formulated in terms of user fairness and quality of service requirements of the users. BER performance of the proposed system is also investigated using the optimum coefficients according to the formulated problems. It is shown that the proposed system outperforms the conventional cooperative NOMA system in terms of error performance as the data rate increases.

Performance Analysis of Cooperative NOMA Systems with Incremental Relaying

In this paper, we investigate the performance of the non-orthogonal multiple access (NOMA) system with incremental relaying, where the relay is employed with amplify-and-forward (AF) or decode-and-forward (DF) protocols. To characterize the outage behaviors of the incremental cooperative NOMA (ICN) system, new closed-form expressions of both exact and asymptotic outage probability for two users are derived. In addition, the performance of the conventional cooperative NOMA (CCN) system is analyzed as a benchmark for the the purpose of comparison. We confirm that the outage performance of the distant user is enhanced when ICN system is employed. Numerical results are presented to demonstrate that (1) the near user of the ICN system achieves better outage behavior than that of the CCN system in the low signal-to-noise ratio (SNR) region; (2) the outage performance of distant user for the DF-based ICN system is superior to that of the AF-based ICN system when the system works in cooperative NOMA transmission mode; and (3) in the low SNR, the throughput of the ICN system is higher than that of the CCN system.

Enhanced NOMA System Using Adaptive Coding and Modulation Based on LSTM Neural Network Channel Estimation

Non-orthogonal multiple access (NOMA) is the technique proposed for multiple access in the fifth generation (5G) cellular network. In NOMA, different users are allocated different power levels and are served using the same time/frequency resource blocks (RBs). The main challenges in existing NOMA systems are the limited channel feedback and the difficulty of merging it with advanced adaptive coding and modulation schemes. Unlike formerly proposed solutions, in this paper, we propose an effective channel estimation (CE) algorithm based on the long-short term memory (LSTM) neural network. The LSTM has the advantage of adapting dynamically to the behavior of the fluctuating channel state. On average, the use of LSTM results in a 10% lower outage probability and a 37% increase in the user sum rate as well as a maximal reduction in the bit error rate (BER) of 50% in comparison to the conventional NOMA system. Furthermore, we propose a novel power coefficient allocation algorithm based on binomial distribution and Pascal’s triangle. This algorithm is used to divide power among N users according to each user’s channel condition. In addition, we introduce adaptive code rates and rotated constellations with cyclic Q-delay in the quadri-phase shift keying (QPSK) and quadrature amplitude modulation (QAM) modulators. This modified modulation scheme overcomes channel fading effects and helps to restore the transmitted sequences with fewer errors. In addition to the initial LSTM stage, the added adaptive coding and modulation stages result in a 73% improvement in the BER in comparison to the conventional NOMA system.

Performance Improvement of NOMA Scheme Based on Gain of Narrow and Wide Beams

In this paper, we propose a non orthogonal multiple access (NOMA) system using coexisting narrow and wide beams to increase total capacity. In our proposed system, a base station considers the state of user mobility and supports users with either a narrow or a wide beam according to the mobility state. The proposed NOMA system uses the beam gain between a narrow and a wide beam, as well as the power gain from the pathloss difference in NOMA scheme. The system is thus less influenced by user mobility at the point of NOMA pairing. In the proposed system, we consider two power allocation schemes, namely the max and fair power allocation methods, and propose a pairing algorithm to maximize the capacity by minimizing the interference between narrow and wide beam user. The result verifies that the proposed system improves sum throughput, compared with the OMA and conventional NOMA system.

Divide‐and‐allocate: An uplink successive bandwidth division NOMA system

AbstractThis paper investigates a new spectrum‐sharing strategy using non‐orthogonal multiple access (NOMA), a technique that is expected to lead toward the fifth generation of wireless networks. The proposed scheme, namely, successive bandwidth division (SBD), NOMA, is a hybrid approach exploiting the characteristics of both the conventional NOMA system and the orthogonal multiple access (OMA) system. Power allocation is being performed in successive bandwidth division NOMA to maximize the sum rate using a divide‐and‐allocate approach such that all users are allocated with optimal transmission power. Under Rayleigh fading, the probability density function (PDF) of the received signal‐to‐interference‐plus‐noise ratio (SINR) is derived, and closed‐form expressions for the outage probability are presented when channel state information (CSI) is available at the base station. The performance evaluation is carried out in terms of receiver complexity, average sum rate, and outage probability. Simulations results are provided to access and compare the performance of the proposed scheme with other contemporary approaches.

Non-Orthogonal Multiple Access (NOMA) to Enhance Capacity in 5G

Non-orthogonal multiple access (NOMA) where all users share the entire time and frequency resource has paid attention as one of the key technologies to enhance the spectral efficiency and the total throughput. Nevertheless, as the number of users and SIC error increase, the inter-user interference and the residual interference due to the SIC error also increase, resulting in performance degradation. In order to mitigate the performance degradation, we propose grouping-based NOMA system. In the proposed scheme, all users are divided into two groups based on the distance between the BS and each user, where one utilizes the first half of the bandwidth and the other utilizes the rest in the orthogonal manner. On the other hand, users in each group share the spectrum in the non-orthogonal manner. Grouping users can reduce both the inter-user interference and residual interference due to the SIC error, so it can outperform conventional NOMA system, especially in case that the number of users and the SIC error increase. Based on that, we also present the hybrid operation of the conventional and the proposed NOMA systems. In numerical results, the total throughput of the proposed NOMA systems is compared with that of the conventional NOMA systems with regard to the number of users and SIC error. It is confirmed that the proposed NOMA system outperforms the conventional NOMA system as the number of users and the SIC error increase.