Non-orthogonal Multiple Access Scheme Research Articles

Dynamic Power Allocation for Uplink NOMA With Statistical Delay QoS Guarantee

Most existing optimization objectives considered in non-orthogonal multiple access (NOMA) power allocation schemes are non-delay-sensitive metrics. In order to apply NOMA to various Internet of Things scenarios, the delay must be considered. The effective capacity of users, which characterizes the capacity under specific expiration probabilities, can potentially be a performance metric of statistical delay quality of service (QoS). In this paper, we propose two novel dynamic power allocation schemes with statistical delay QoS guarantee in the uplink NOMA system with paired users. One of the schemes maximizes the sum effective capacity (SEC) of the strong and weak users, which is a non-convex nonlinear optimization problem and is solved by Lagrangian dual decomposition and successive convex approximation (SCA). The other one maximizes the effective energy efficiency (EEE) of uplink NOMA, which is a fractional optimization problem and is solved by integrating the Dinkelbach method, SCA, and Lagrangian dual decomposition. Numerical results show that the SEC and EEE can be significantly improved by the proposed schemes, compared to the existing NOMA and orthogonal multiple access power allocation schemes.

Cooperative Non-Orthogonal Multiple Access Scheme for Cellular Two-Way Relay Networks

Cooperative Non-Orthogonal Multiple Access Scheme for Cellular Two-Way Relay Networks

Jointly Adaptive Distributed Beamforming and Resource Allocation for Buffer-Aided Multiple-Relay NOMA Networks

In this paper, a novel jointly adaptive transmission strategy for buffer-aided multiple-relay non-orthogonal multiple access (NOMA) networks is proposed. By leveraging time diversity brought by the data storage buffer, and multiple relays’ beamforming gains, the source node broadcasts data in the first hop and all relays perform distributed beamforming to transmit information to users with NOMA in the second hop. Our focus is on maximizing the average network throughput (ANT) by jointly optimizing the mode selection, power and rate allocation at the source node, as well as the rate allocation and distributed beamforming coefficients at the relays along the time. As a solution to this complex problem, we propose an online scheduling scheme, which first adopts the Lyapunov optimization methodology to convert the ANT maximization problem into the drift-plus-penalty function minimization problem at each time slot. Secondly, focusing on the non-convexity of the transformed problem at each time slot, a novel two-loop algorithm is proposed as an effective solution. Extensive performance evaluation results have revealed the superiority of the proposed scheme as compared to other benchmark access schemes, namely, buffer-aided single relay NOMA, maximum ratio transmission based NOMA and buffer-aided time division multiple access schemes.

A weighted-beam-superposition method for mmWave massive MIMO-NOMA systems

Millimeter wave (mmWave) massive multiple input multiple output (MIMO) and non-orthogonal multiple access (NOMA) are recognized as key technologies in the forthcoming beyond the fifth-generation (B5G) and the sixth-generation (6G) wireless networks. In this paper, we propose a multi-beam MIMO NOMA scheme where each beam is augmented by weighted beam superposition to focus the beam in a manner targeted at each user. This method exploits the full array of antennas within each beam to maximize the gain of each beam. To guarantee fairness for the weak user (lower channel gain) in each group, we use a method of power allocation, which satisfies the weak user with a minimum demanded for the quality of service (QoS). To improve further the sum rate when the QoS of the weak users is satisfied, the coefficient of strong users are set to the largest value. In system simulations, we compare the performance of differnet multi beam schemes, together with a single beam scheme, and a Time Division Multiple Access (TDMA) scheme at different levels of the signal noise ratio (SNR). Based on the simulation results, the proposed method significantly increases system sum rate.

Quality ensured non‐orthogonal multiple access based downlink scalable video coding multicasting over cognitive radio network

AbstractThe combination of the cognitive radio network (CRN) and non‐orthogonal multiple access (NOMA) technologies for scalable video coding (SVC) can be considered as a promising approach for quality‐driven video transmission over a fifth‐generation (5G) network. Advanced techniques such as efficient channel allocation, advanced sensing strategy, and optimum power allocation can combinedly improve the overall system performance. In this context, we propose an intergroup content‐aware proportionate channel allocation policy, sensing time optimization strategy and quality of service (QoS) ensured intragroup power allocation scheme for downlink SVC multicasting over CRN using NOMA technology to enhance the quality of experience (QoE) of secondary users (SUs). We propose an optimum power allocation strategy for different NOMA layers to maximize the weighted sum rate of different SVC groups ensuring the individual QoS requirements. Although the power allocation problem seems to be nonconvex, however, it can be transformed into a convex function under some specific conditions which are discussed in this article. Extensive simulation reveals that our proposed power allocation scheme for NOMA with QoS constraint outperforms the other two conventional schemes, that is, NOMA fixed power allocation and NOMA without QoS constraint in terms of average weighted sum rate and average QoE of SUs.

Sum Secrecy Rate Maximization in NOMA-Based Cognitive Satellite-Terrestrial Network

In this letter, we present a joint beamforming design for non-orthogonal multiple access (NOMA)-based cognitive satellite-terrestrial network (CSTN), where satellite network applies orthogonal multiple access (OMA) technology and NOMA scheme is utilized by the terrestrial network. The scheme key is to maximize sum secrecy rate of satellite users under the imperfect channel state information, while meeting the rate requirements of terrestrial users and transmit power constraints of the CSTN. Since the formulated optimization problem is non convex and intractable, we convert the original non convex maximization problem to a corresponding tractable convex one by successive convex approximation (SCA) and semidefinite relaxation (SDR), and then propose an SCA-based iterative beamforming algorithm to get the secure beamforming vectors. Finally, numerical simulation results are provided to verify the effectiveness and superiority of the proposed joint beamforming design.

Power Minimization Precoder Design for Uplink MIMO Systems With Multi-Group NOMA Scheme

This paper presents a non-orthogonal multiple access (NOMA) scheme with group detection for uplink multiple-input multiple-output (MIMO) systems, for which an effective precoder design is developed. In the scheme, users are divided into groups in accordance with their locations for detection at the base station. The inter- and intra-group interferences are mitigated by successive interference cancellation (SIC) and transceivers, respectively. Based on a derived approximate signal-to-interference-plus-noise ratio (SINR) for using zero-forcing detection, an iterative power and beamforming update procedure is developed for obtaining the user precoders. The precoder design effectively mitigates the intra-group-inter-user correlation making the adopted approximate SINR represent the original SINR accurately. The proposed multi-group MIMO-NOMA scheme can work under more practical transmit-receive antenna configurations and is shown to outperform upon existing cluster-based MIMO-NOMA schemes in terms of total transmit power for various system configurations. The impact of SIC residuals on the multi-group MIMO-NOMA scheme is investigated. Feasibility conditions for the design under imperfect SIC based on the fractional cancellation error model are developed.

Performance Analysis of Hybrid Cellular and Bidirectional Device-to-Device Cooperative NOMA Communication Systems

In this paper, we consider a coexisting network of cellular transmission and device-to-device (D2D) communication, in which two users need to receive downlink signals from base station (BS), meanwhile, they want to exchange information with each other. For such a network, a hybrid cellular and bidirectional D2D cooperative non-orthogonal multiple access (HCBD-CNOMA) scheme is proposed. To characterize the performance of our proposed scheme, we derive the closed-form ergodic rate and outage probability by considering both perfect and imperfect successive interference cancellation (SIC). To acquire more insights, their corresponding asymptotic expressions are obtained as well. Moreover, considering the fact that the nodes in Internet of Things (IoT) network are usually powered by battery and thus their power is limited, we further consider the scenario that two users are energy-constraint. In this scenario, users first need to harvest energy from the transmission of BS based on time splitting (TS) or power splitting (PS) energy harvesting (EH) protocol and then use these energy to accomplish subsequent communications. Similarly, the exact ergodic rate and outage probability as well as their asymptotic expressions for this scenario are analyzed. Simulation results validate the accuracy of analytical results, and reveal the performance gain of our schemes over the benchmark schemes.

Achievable Rate Volume of Three-User CIS NOMA

Non-orthogonal multiple access (NOMA) enables 5G mobile networks to transmit correlated information sources (CISs) simultaneously, in contrast to orthogonal multiple access. Recently, the achievable data rates were derived for NOMA with CIS. However, only the achievable rate region was investigated for two-user CIS NOMA. Therefore, in this study, we address the achievable rate volume of three-user CIS NOMA. First, the closed-form expression for the achievable rate volume of three-user CIS NOMA is derived. Second, the exact power allocation ranges of the rate volume of three-user independent information source (IIS) NOMA to be achieved by three-user CIS NOMA are derived. Then, it is shown that only a portion of the rate volume of the three-user IIS NOMA scheme can be achieved by the three-user CIS NOMA scheme.

A Study on Improved Sum Rate of Cross-Correlated SC NOMA toward 6G URLLC

Since recently only an auto-correlated superposition coding (SC) scheme for non-orthogonal multiple access(NOMA) has been investigated, this paper proposes a cross-correlated SC scheme for NOMA. First, we derive the closed-form expression of the sum rate of the proposed cross-correlated SC scheme. Then, numerical analyses demonstrate that the sum rate of the proposed cross-correlated SC scheme is larger than that of the conventional auto-correlated SC scheme. We also show that for the stronger channel gain user, the signal-to-noise ratio (SNR) gain of the proposed cross-correlated SC scheme is about 15, compared with the conventional auto-correlated SC scheme. As a result, the proposed cross-correlated SC scheme could be a promising technology for 6G ultra-reliable low-latency communications (URLLC).

Correlated Superposition Coding: Lossless Two-User NOMA Implementation Without SIC Under User-Fairness

Non-orthogonal multiple access (NOMA) has a larger achievable sum rate than orthogonal multiple access (OMA). This superiority is achieved via superposition coding (SC) and successive interference cancellation (SIC). In this letter, the authors propose a lossless NOMA implementation without SIC. This implementation is achieved via correlated SC (CSC), in contrast to conventional independent SC (ISC). In addition, correlated non-SIC decoding is performed, in contrast to conventional SIC decoding. Using the random channel coding theorem, we prove that the conditional achievable sum rate given channel gain realizations in the conventional ISC/SIC NOMA scheme can be achieved without SIC, without loss, over the power allocation range of user-fairness.

Rate Splitting Multiple Access in C-RAN: A Scalable and Robust Design

Cloud radio access networks (C-RAN) enable a network platform for beyond the fifth generation of communication networks (B5G), which incorporates the advances in cloud computing technologies to modern radio access networks. Recently, rate splitting multiple access (RSMA), relying on multi-antenna rate splitting (RS) at the transmitter and successive interference cancellation (SIC) at the receivers, has been shown to manage the interference in multi-antenna communication networks efficiently. This paper considers applying RSMA in C-RAN. We address the practical challenge of a transmitter that only knows the statistical channel state information (CSI) of the users. To this end, the paper investigates the problem of stochastic coordinated beamforming (SCB) optimization to maximize the ergodic sum-rate (ESR) in the network. Furthermore, we propose a scalable and robust RS scheme where the number of the common streams to be decoded at each user scales linearly with the number of users, and the common stream selection only depends on the statistical CSI. The setup leads to a challenging stochastic and non-convex optimization problem. A sample average approximation (SAA) and weighted minimum mean square error (WMMSE) based algorithm is adopted to tackle the intractable stochastic non-convex optimization and guarantee convergence to a stationary point asymptotically. The numerical simulations demonstrate the efficiency of the proposed RS strategy and show a gain up to 27% in the achievable ESR compared with state-of-the-art schemes, namely treating interference as noise (TIN) and non-orthogonal multiple access (NOMA) schemes.

Rate-Splitting Multiple Access for Intelligent Reflecting Surface Aided Multi-User Communications

Intelligent reflecting surface (IRS) has recently emerged as a promising technology for 6 G wireless systems, due to its capability to reconfigure the wireless propagation environment. In this paper, we investigate a Rate-Splitting Multiple Access (RSMA) for IRS-assisted downlink system, where the base station (BS) communicates with single-antenna users with the help of an IRS. RSMA relies on rate-splitting (RS) at the BS and successive interference cancellation (SIC) at the users and provides a generalized multiple access framework. We derive a new architecture called IRS-RS that leverages the interplay between RS and IRS. For performance analysis, we utilize an on-off control technique to control the passive beamforming vector of the IRS-RS and derive the closed-form expressions for outage probability of cell-edge users and near users. Moreover, we also analyze the outage behavior of cell-edge users for a sufficiently large number of reflecting elements. Additionally, we also analyze the outage performance of cooperative RS based decode-and-forward (DF)-assisted framework called DF-RS. Through simulation results, it is shown that the proposed framework outperforms the corresponding DF-RS, RS without IRS and IRS-assisted conventional non-orthogonal multiple access (NOMA) schemes. Furthermore, the impact of various system's parameters such as the number of IRS reflecting elements and the number of users on the system performance is revealed.

Intelligent reflected surfaces assisted code domain non-orthogonal multiple access scheme

Abstract The propagation medium plays a crucial role in any wireless communication networks, the channel between the transmitter and the receiver, deteriorate the quality of the received signal due to the uncontrollable interactions such as scattering, reflection, and refraction in the channel with the surrounding objects. To overcome this challenge, the recent advent of recongurable intelligent surfaces can be helpful, in which the network operators can control the radio waves, eg, the phase, amplitude, frequency, and even polarization, of the impinging signals without the need of complex decoding, encoding, and radio frequency processing operations. On the other hand, few research papers reported an efficient code domain non orthogonal multiple access (NOMA) such as Interleave division multiple access (IDMA) system for wireless information transfer. Persuaded by the capability of this arising RIS technology, the present article is aimed to provide the modified framework of IDMA (code-domain NOMA) communication system based on RIS technology. Simulation results demonstrate that the proposed system achieves better SNR performance than the conventional IDMA framework.

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

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

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

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

Research on Sparse Code Multiple Access Technology

As an important port technology in mobile communication, multiple access can effectively improve the number of user access in the communication system. However, the Orthogonal Multiple Access (OMA) technology has been unable to meet the higher requirements of spectrum efficiency and system capacity in the future, so it is of great practical significance to study and design a new multiple access technology. Sparse Code Multiple Access (SCMA), as a new non-orthogonal multiple Access (NOMA) scheme, improves the number of user access and spectrum utilization by superposition of multi-user information on the same time-frequency resource. And it can well adapt to all kinds of new application scenarios in 5G. This paper introduces SCMA technology from four aspects: basic principle, system model, key technology and its combination with other systems.

Aging and Delay Analysis Based on Lyapunov Optimization and Martingale Theory

The age of information (AoI) is a key performance metric for data freshness in real-time systems, measuring the time elapsed between status updates received at a remote destination. This paper addresses the analysis of both the AoI and the delay for a system demanding timely status updates, consisting of an internet of things (IoT) community, and a multi-core edge computing node (EN). The IoT devices perform channel contention according to a slotted aloha non-orthogonal multiple access scheme with two transmission power levels to access the EN. The objective of the paper is the dynamic selection of both the EN computation capabilities and the suitable access probability for the two power levels, aiming at maximizing the time-average system utility, while guaranteeing the queues stability. The device end-to-end delay is analyzed by resorting to the martingale theoretical approximation under the condition that the Lyapunov optimization framework is performed on a time slot basis, hence leading to a novel instantaneous mixed integer problem formulation. Furthermore, the generalized benders decomposition method is employed to provide a suboptimal solution for the formulated problem. Finally, the accuracy of the proposed framework is validated by comparing the obtained analytical predictions with simulation results.

Secure beamforming with nonorthogonal multiple access transmission in cooperative CR networks for Internet of Things

In this paper, secure beamforming design in cooperative cognitive radio networks for Internet of Things (IoT) is investigated, where we maximize the secrecy sum rate for the IoT devices (IoDs) to protect their communication and employ the nonorthogonal multiple access scheme at the cognitive access point (AP) to serve the cognitive users. The formulated secure beamforming optimization problem is a non-convex problem and its global optimal solution is very hard to find. To overcome this difficulty, we propose an iterative algorithm based on semidefinite programming and monotonic optimization method to obtain the global optimal solution, which has high computational complexity and is suitable for the case that the cognitive AP has a powerful computing ability. For some application scenarios in which the cognitive AP has a lower computing ability, we propose suboptimal solutions based on zero-forcing scheme, which have much lower computational complexity. Furthermore, we derive the limit value of the secrecy sum rate for the IoDs when the transmit power of the cognitive AP goes to infinity, which can serve as an upper bound for our proposed solutions. Numerical results are also provided to verify the effectiveness of our proposed solutions.

Improving Physical Layer Security of Cooperative NOMA System with Wireless-Powered Full-Duplex Relaying

Non-orthogonal multiple access (NOMA) and wireless energy harvesting are two promising technologies for improving spectral efficiency and energy efficiency, respectively. In this paper, we study the physical layer security of a wireless-powered full-duplex (FD) relay-aided cooperative NOMA system. In particular, the source is wiretapped by an eavesdropper, and the FD relay assists the transmission from the source to a near user and a far user with self-energy recycling. To enhance the security performance of the system, we propose an artificial noise (AN)-aided cooperative transmission scheme, in which the relay emits a jamming signal to confuse the eavesdropper while receiving the signal from the source. For the proposed scheme, the ergodic secrecy sum rate (ESSR) is derived to characterize the secrecy performance and a lower bound of ESSR is obtained. Finally, numerical results verify the accuracy of the theoretical analysis of the proposed AN-aided secure transmission scheme. The superiority of the proposed scheme is also demonstrated since this scheme can achieve better secrecy performance, compared to the conventional cooperative NOMA scheme.