Orthogonal Multiple Access Scheme Research Articles

BER Analysis of a Backscatter Communication System With Non-Orthogonal Multiple Access

Backscatter communication (BackCom) has been emerging as a prospective candidate in tackling lifetime management problems for massively deployed Internet-of-things (IoT) devices, which suffer from battery related issues, i.e., replacements, charging, and recycling. This passive sensing approach allows a backscatter sensor node (BSN) to transmit information by reflecting the incident signal from a carrier emitter without initiating its transmission. To multiplex multiple BSNs, power-domain non-orthogonal multiple access (NOMA) is fully exploited in this work. In this paper, we present the design and analysis of a NOMA enhanced bistatic BackCom system for a battery-less smart communication paradigm. Specifically, we derive the closed-form bit error rate (BER) expressions for a cluster of two devices in a bistatic BackCom system employing NOMA with imperfect successive interference cancellation under Nakagami- m fading channel. The obtained expressions are utilized to evaluate the reflection coefficients of devices needed for the most favorable system performance along with the performance comparison with orthogonal multiple access-time domain multiple access scheme (OMA-TDMA).

Robust Secure Beamforming Design for Cooperative Cognitive Radio Nonorthogonal Multiple Access Networks

By the integration of cooperative cognitive radio (CR) and nonorthogonal multiple access (NOMA), cooperative CR NOMA networks can improve the spectrum efficiency of wireless networks significantly. Due to the openness and exposure of wireless signals, secure communication is an important issue for cooperative CR NOMA networks. In this paper, we investigate the physical layer security design for cooperative CR NOMA networks. Our objective is to achieve maximum secrecy rate of the secondary user by designing optimal beamformers and artificial noise covariance matrix at the multiantenna secondary transmitter under the quality-of-service at the primary user and the transmit power constraint at the secondary transmitter. We consider the practical case that the channel state information (CSI) of the eavesdropper is imperfect, and we model the imperfect CSI by the worst-case model. We show that the robust secrecy rate maximization problem can be transformed to a series of semidefinite programmings based on S-procedure and rank-one relaxation. We also propose an effective method to recover the optimal rank-one solution. Simulations are provided to show the effectiveness of our proposed robust secure algorithm with comparison to the nonrobust secure design and traditional orthogonal multiple access schemes.

Performance Analysis and Optimization of NOMA With HARQ for Short Packet Communications in Massive IoT

In this article, we consider the massive nonorthogonal multiple access (NOMA) with a hybrid automatic repeat request (HARQ) for short packet communications. To reduce the latency, each user can perform one retransmission provided that the previous packet was not decoded successfully. The system performance is evaluated for both coordinated and uncoordinated transmissions. We first develop a Markov model (MM) to analyze the system dynamics and characterize the packet error rate (PER) and throughput of each user in the coordinated scenario. The power levels are then optimized for two scenarios, including the power constrained and reliability constrained scenarios. A simple yet efficient dynamic cell planning is also designed for the uncoordinated scenario. Numerical results show that both coordinated and uncoordinated NOMA-HARQ with a limited number of retransmissions can achieve the desired level of reliability with the guaranteed latency using a proper power control strategy. The results also show that NOMA-HARQ achieves a higher throughput compared to the orthogonal multiple access scheme with HARQ under the same average received power constraint at the base station.

Cognitive IoT relaying NOMA networks with user clustering and imperfect SIC

To implement machine type communications (MTCs) in next generation mobile networks, Narrowband-Internet of Things (NB-IoT) need be studied. Such NB-IoT has been released by the third generation partnership project (3GPP) as a promising method to exhibit extended coverage and low energy consumption, especially for cheap MTC devices. However, the existing NB-IoT using orthogonal multiple access (OMA) scheme which cannot provide connectivity for a massive MTC devices. In this paper, we consider NB-IoT using non-orthogonal multiple access (NOMA). We find that power allocation factors for devices in clustering users as main enabler to exhibit differences in term of performance of devices. The worse situation of imperfect successive interference cancellation (SIC) is further studied due to main reason regarding degraded system performance. We derive closed-form expressions of outage probability for devices in a cluster to highlight main parameters affecting quality of devices. We verify our mathematical analysis via Monte-Carlo simulations.

Modeling Queuing Delay of 5G NR With NOMA Under SINR Outage Constraint

In this paper, we present an analytical model to characterize the average queuing delay for non-orthogonal multiple access (NOMA) downlink system by taking the outage event into account such that the user fails either decoding its own signal or performing SIC for the signals of other users at the receiver when the SINR is lower than a predefined outage threshold. The departure process of the queuing model is characterized by obtaining the first and second moment statistics of the service time that depends on the resource allocation strategy, the packet size and channel distributions. The proposed model is utilized to obtain the optimum power allocation that minimizes the maximum of the average queuing delay (MAQD) for a two-user network scenario. The Monte Carlo simulation experiments are performed to numerically validate the model by providing MAQD results for both NOMA and orthogonal multiple access (OMA) schemes. The results demonstrate that the NOMA achieves lower latency for low SINR outage thresholds while its performance is degraded faster than OMA as the SINR outage threshold increases such that OMA outperforms NOMA beyond a certain threshold. Another important result is that the latency performance of NOMA is significantly degraded when the 5G NR frame types having wider bandwidth are utilized. The results provide powerful insights for queuing delay analysis of 5G services.

Enhancing Physical Layer Security With Artificial Noise in Large-Scale NOMA Networks

This paper investigates the secrecy outage performance for a large-scale downlink system with full-duplex (FD) non-orthogonal multiple access (NOMA) transmission aided by artificial noise (AN). In the system, legitimate users (LUs) are randomly distributed according to homogeneous Poisson point processes whereas a passive eavesdropper (Eve) is certainly located. We introduce a secure cooperative communication scheme, in which nearby NOMA users operating in FD mode act as jammers and generate AN to enhance the physical layer security (PLS) of the legitimate transmission. Closed-form expressions in terms of the secrecy outage probability (SOP) for a user pair are acquired. Following the mathematical results, secrecy diversity order analysis is further carried out for two scenarios, i.e., 1) fixed transmit signal-to-noise ratio (SNR) at the Eve, and 2) transmit SNR at the Eve being proportional to that of LUs. Closed-form expressions of asymptotic SOP for the two scenarios are also obtained. Monte Carlo simulations are performed to certify the veracity of the theoretic analysis and illustrate that the proposed scheme employing both AN and FD-NOMA is superior in the secrecy outage to the NOMA scheme without AN and the orthogonal multiple access scheme with AN. Furthermore, the SOP performance enhancement through proper secrecy rate target selection and power allocation optimization is also evidenced by the simulations.

On the spectral efficiency of cell-free large-scale MIMO non-orthogonal multiple access systems

The spectral efficiency (SE) of an uplink cell-free large-scale multi-input multi-output (MIMO) non-orthogonal multiple access (NOMA) system which relies on the superimposed pilot (SP) transmission strategy is investigated. Closed-form expressions of the achievable SE with the maximal ratio combining (MRC) receiver filters are derived and compared against the orthogonal multiple access (OMA) counterparts. Based on the tractable results, we quantitatively explore the impacts of the pilot training strategy, the OMA and NOMA schemes, the number of user equipments (UEs), the power balance factor between pilot and data signals, and the length of the coherent interval (CI) on SE enhancement. Several insightful conclusions are drawn by assuming that the SP interference in the data detection process can or cannot be perfectly eliminated from the data estimates. All the analytical results are verified by numerical simulation experiments.

Joint optimization ofNOMA‐enabled backscatter communications for beyond5G IoTnetworks

This article optimizes the link‐level of NOMA‐enable backscatter communication (BackCom) for beyond fifth‐generation (B5G) Internet‐of‐things (IoT) networks. Specifically, we jointly optimize the transmit‐power (TP) of IoT users and the reflection‐coefficient (RC) of the backscatter tag (BackTag), where the target is to increase the sum capacity (SumCap) of NOMA‐enabled BackCom. The problem of TP and RC is formulated as convex optimization, and we exploit KKT conditions to obtain the optimal solutions. The pure NOMA without BackCom and conventional orthogonal multiple access (OMA) schemes are also presented as the benchmark schemes. Our results significantly outperform the pure NOMA and conventional OMA schemes.

An HARQ Assisted Cognitive NOMA Scheme for Secure Transmission With Imperfect SIC

This paper employs hybrid automatic repeat request (HARQ) to assist the cognitive non-orthogonal multiple access (NOMA) scheme for secure transmission in Internet of Things networks where the security-required (SR) users with high-security requirements and quality of services (QoS)-sensitive (QS) users with real-time process requirements are paired to perform NOMA for increasing the network connectivity. In addition, the imperfect successive interference cancellation (SIC) is considered at both legitimate users and eavesdropper for providing a realistic analysis. The closed-form expressions for the connection outage probability (COP), the secrecy transmission probability (RSP), and effective secrecy throughput (EST) of the SR user are derived in the proposed lightweight but efficient randomized retransmission scheme (RRS). As benchmarks, the secrecy performances of the fixed retransmission scheme (FRS) and orthogonal multiple access (OMA) scheme are also investigated. Besides, the asymptotic secrecy analysis is given to gain a better insight into secrecy performance. The analytical results developed in the paper demonstrate that HARQ is beneficial to secrecy transmission and the RRS outperforms or equals to the FRS and OMA scheme when the transmit power and secrecy coding redundancy is sufficiently high.

Sub-Channel Scheduling, Task Assignment, and Power Allocation for OMA-Based and NOMA-Based MEC Systems

In this paper, sub-channel scheduling, task assignment and power allocation are investigated for orthogonal multiple access (OMA)-based and non-orthogonal multiple access (NOMA)-based mobile edge computing (MEC) systems. Based on different channel conditions and computational capacities, computational tasks are partially offloaded to the MEC server via OMA or NOMA protocols. In order to minimize the total energy consumption, an optimization problem under the task execution latency constraint is formulated and divided into two sub-problems. By utilizing matching theory, the formulated sub-channel allocation problem is solved by a proposed low-complexity algorithm, where the joint optimization of task assignment and power allocation is performed at each iteration. Based on the delay constraint, some insights are obtained, and the closed-form solutions of task assignment coefficients and transmit power are derived. Furthermore, the offloading strategy in both OMA and NOMA schemes is analyzed, which shows that the optimal task assignment coefficient is decided by the energy consumption efficiency (ECE). Simulation results indicate that: i) the proposed sub-channel allocation algorithm and derived closed-form solutions can significantly improve the MEC system in terms of the energy consumption; ii) the provided offloading strategy can be dynamically and efficiently employed with different channel conditions and computational capacities.

Performance of NOMA-Enabled Cognitive Satellite-Terrestrial Networks With Non-Ideal System Limitations

Satellite-terrestrial networks (STNs) have received significant attention from research and industry due to their capability of providing a stable connection to rural and distant areas, where the allocation of terrestrial infrastructures is uneconomical or difficult. Moreover, the STNs are considered as a promising enabler of fifth-generation communication networks. However, expected massive connectivity in future communication networks will face issues associated with spectrum scarcity. In this regard, the integration of cognitive radio and non-orthogonal multiple access (NOMA) techniques into STNs is considered as a promising remedy. Thereafter, in this article, we investigate NOMA-assisted cognitive STN under practical system conditions, such as transceiver hardware impairments, channel state information mismatch, imperfect successive interference cancellation, and interference noises. Generalized coverage probability formulas for NOMA users in both primary and secondary networks are derived considering the impact of interference temperature constraint and its correctness is verified through Monte Carlo simulation. Furthermore, to achieve performance fairness among the users, power allocation factors based on coverage fairness for primary and secondary NOMA users are provided. Moreover, the numerical results demonstrate superior performance compared to the ones obtained from an orthogonal multiple access scheme and examine the imperfection's impact on the system performance in terms of coverage and throughput.

Performance Analysis of Energy Harvesting-Assisted Overlay Cognitive NOMA Systems With Incremental Relaying

In this paper, we analyze the performance of an energy harvesting (EH)-assisted overlay cognitive non-orthogonal multiple access (NOMA) system. The underlying system consists of a primary transmitter-receiver pair accompanied by an energy-constrained secondary transmitter (ST) with its intended receiver. Accordingly, ST employs a time switching (TS) based receiver architecture to harvest energy from radio-frequency signals of the primary transmissions, and thereby uses this energy to relay the primary information and to transmit its own information simultaneously using the NOMA principle. For this, we propose two cooperative spectrum sharing (CSS) schemes based on incremental relaying (IR) protocol using amplify-and-forward (AF) and decode-and-forward (DF) strategies, viz., CSS-IAF and CSS-IDF, and compare their performance with the competitive fixed relaying based schemes. The proposed IR-based schemes adeptly avail the degrees-of-freedom to boost the system performance. Thereby, considering the realistic assumption of the NOMA-based imperfect successive interference cancellation, we derive the expressions of outage probability for the primary and secondary networks under both CSS-IAF and CSS-IDF schemes subject to the Nakagami-m fading. In addition, we quantify the throughput and energy efficiency for the considered system. The obtained theoretical findings are finally validated through numerous analytical and simulation results to reveal the advantages of the proposed CSS schemes over the baseline direct link transmission and orthogonal multiple access schemes.

Multiple Access in Cognitive Radio Networks: From Orthogonal and Non-Orthogonal to Rate-Splitting

Due to the increasingly complicated communication scenarios and network architectures as well as growing traffic demands for high speed connectivity, dynamic spectrum allocation in fifth generation (5G) networks becomes insufficient to guarantee the satisfaction of main network requirements in terms of spectrum efficiency (SE), scalability, delay, and energy efficiency (EE). Enormous multiple access schemes and cognitive radio (CR) network scenarios come to fulfill these requirements and enhance network functionalities. With multiple access schemes, users are able to transmit their data streams simultaneously under maximum capacity constraints. On the other hand, vacant spectrum holes are exploited in an opportunistic manner via CR and software defined radio. In order to exploit these spectrum holes as well as meeting different network requirements, several multiple access techniques have been presented that have been initiated through the adoption of orthogonal multiple access (OMA) scheme. Additionally, non-orthogonal multiple access (NOMA) and space division multiple access (SDMA) are presented to achieve a promising multiplexing gain as well as to address the inefficient spectrum utilization incurred with OMA schemes. However, such multiplexing gain is limited as it depend on the channel conditions. Accordingly, a generalized multiple access scheme has been presented recently, namely rate splitting multiple access (RSMA), to further enhance the SE. In this paper, we provide a comprehensive study regarding the key multiple access schemes presented for CRNs to further enhance the use of spectral resources, and additionally highlights the key implementation challenges and the enabling techniques addressed to overcome it. We have given a special attention to the enhances provided by RSMA as compared with OMA, SDMA, and NOMA techniques. Finally, some open issues are spotted to shed lights on the need for further studies and future research efforts.

Outage performance analysis of full-duplex assisted non-orthogonal multiple access with bidirectional relaying mode

The fifth-generation (5G) wireless network needs massive connectivity to allow large number of users access to network in the same time. Non-orthogonal multiple access (NOMA) and full-duplex (FD) are two promising techniques recommended for the 5G wireless network. This work combines these approaches to improve system outage performance in the situation of bidirectional cooperative relaying. The main metric to evaluate system performance relying on outage probability. Notably, the outage expression for such a system under the Nakagami-m fading environment is derived for exact and approximate computation. The simulation results demonstrated the effectiveness of NOMA and FD in low transmit power compared to conventional half-duplex (HD) and orthogonal multiple access (OMA) schemes.

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.

Max Completion Time Optimization for Internet of Things in LEO Satellite-Terrestrial Integrated Networks

In this article, we investigate max completion time optimization for Internet of Things (IoT) in LEO satellite-terrestrial integrated networks (STINs), in which IoT devices use non-orthogonal multiple access (NOMA) scheme to transmit data to central earth stations (CESs), and orthogonal multiple access (OMA) scheme is used for data transmission from CESs to LEO satellite. We decouple this problem into two subproblems: 1) max completion time optimization in terrestrial networks and 2) max completion time optimization among satellite beams. Different from the existing works about NOMA data transmission in terrestrial networks, we propose a cooperative NOMA scheme, and derive the closed expressions of the optimal cooperative data and the optimal transmit power of IoT devices. Based on the closed-form expressions, a joint subcarrier assignment and cooperative NOMA pairing (JSACNP) approach is proposed to minimize the max completion time in terrestrial networks by utilizing matching theory. Then, to minimize the max completion time among satellite beams, the optimal linear receiver expression is derived with fixed transmit power. Convex optimization is utilized to solve transmit power optimization, we propose an algorithm to solve it by CVX tool. An iterative algorithm is proposed for improved performance. Finally, numerical results are provided to evaluate our proposed algorithms, compared with some other proposed approaches or algorithms.

Outage Performance Analysis of Full-Duplex Assisted Non-Orthogonal Multiple Access with Bidirectional Relaying Mode

The fifth-generation (5G) wireless network needs massive connectivity to allow large number of users access to network in the same time. Non-orthogonal multiple access (NOMA) and full-duplex (FD) are two promising techniques recommended for the 5G wireless network. This work combines these approaches to improve system outage performance in the situation of bidirectional cooperative relaying. The main metric to evaluate system performance relying on outage probability. Notably, the outage expression for such a system under the Nakagami-m fading environment is derived for exact and approximate computation. The simulation results demonstrated the effectiveness of NOMA and FD in low transmit power compared to conventional half-duplex (HD) and orthogonal multiple access (OMA) schemes.

HST-NNC: A Novel Hybrid Satellite-Terrestrial Communication With NOMA and Network Coding Systems

Hybrid satellite-terrestrial networks (HSTNs) are considered to be a promising solution in dealing with coverage and mobility challenges encountered in $5^{\mathrm{ th}}$ generation (5G) networks that employ novel multiple access and connectivity schemes. In this respect, non-orthogonal multiple access (NOMA) as well as network coding (NC) schemes have attracted significant attention due to their performance gains which not only improve the quality of wireless transmission but also effectively exploit the available spectrum. In this paper, a combined NOMA-NC (NNC) scheme is presented and integrated into an HSTN consisting of a low earth orbit (LEO) satellite belonging to an LEO constellation, a terrestrial base station (BS), and multiple terrestrial mobile terminals (MTs). The proposed scheme, termed HST-NNC (Hybrid satellite terrestrial-NNC), allows pairs of users to be simultaneously served through NOMA via the terrestrial BS link and the satellite link. Furthermore, the satellite employs random linear network coding (RLNC), within the general framework of systematic network coding (SNC), to improve the reception of the MTs when errors occur. The proposed HST-NNC, as compared to standalone NOMA, does not require additional channel state information (CSI) overheads because the satellite needs only the indices of user pairs to perform RLNC. Performance comparisons of HST-NNC with conventional orthogonal multiple access (OMA) and NOMA optimal user pairing schemes have shown that significant sum rate and BER gains can be obtained under various operating system parameters, such as varying number of MTs and different channel conditions.

Sparse Code Multiple Access: Potentials and Challenges

The massive connectivity is among other unprecedented requirements which are expected to be satisfied in order to follow the perpetual increase of connected devices in the era of Internet of Things. In contrast to the family of conventional orthogonal multiple access schemes, the key distinguishing feature of non-orthogonal multiple access (NOMA) is its capacity to support the massive connectivity. Sparse code multiple access (SCMA) is one of the powerful schemes of code-domain NOMA (CD-NOMA) and is among the promising candidates of multiple access techniques to be employed in future generations of wireless communication systems thanks to the sparsity pattern of its codebooks. This technique has been actively investigated in recent years. In this paper, we provide a comprehensive survey of the state-of-the-art of SCMA. First, we will pinpoint SCMA place in the NOMA landscape including power-domain NOMA and CD-NOMA with the aim of justifying why SCMA is prominent. Then, its system architecture is highlighted and its basic principles are presented, afterwards a review of exiting codebook designs and available SCMA detectors is provided, before showing how resources are expected to be assigned, and how SCMA can be combined with other existing and emerging technologies. Finally, we present a range of future research trends and challenging open issues that should be addressed to optimize SCMA performance.

Survey and Performance Evaluation of Multiple Access Schemes for Next-Generation Wireless Communication Systems

Mobile communication systems are always in continuous evolution due to the demands of the end-users using this technology. Therefore, before the possible launch of 5G, some technologies have opened the way to the new mobile communication system. The need for technologies that provide more comfort to users has led to the construction of complex communication systems that were only science fiction decades ago. The information society in which we are now immersed has been the result of constant progress over time. In this paper, a survey of multiple access schemes for next-generation wireless communication systems is presented. Multiple access schemes are reviewed for possible use in next-generation wireless communication systems such as orthogonal multiple access (OMA), non-orthogonal multiple access (NOMA), and delta-orthogonal multiple access (D-OMA), etc. General comparisons of 1G to 6G are presented. Different types of OMA are explained, and then orthogonal frequency division multiple access (OFDMA) is chosen as an example of the OMA scheme to compare with NOMA and D-OMA. There are two types of NOMA: power-domain and code-domain, which are discussed and compared. Simulation results are presented, and a comparison among different access schemes is provided.