Non-orthogonal Resource Allocation Research Articles

A Survey of NOMA-Aided Cell-Free Massive MIMO Systems

The Internet of Everything is leading to an increasingly connected intelligent digital world. Envisaged sixth-generation wireless networks require new solutions and technologies due to stringent network requirements. The benefits of cell-free massive MIMO (CF-mMIMO) and non-orthogonal multiple access (NOMA) have brought substantial attention to these approaches as potential technologies for future networks. In CF-mMIMO, numerous distributed access points are linked to a central processing unit, which allocates the same time-frequency resources to a smaller group of users. On the other hand, NOMA can support more users than its orthogonal counterparts by utilizing non-orthogonal resource allocation. This paper provides a comprehensive review and survey of NOMA-aided CF-mMIMO (CF-mMIMO-NOMA). Specifically, we present a comprehensive review of massive MIMO, CF-mMIMO, and NOMA. We then present a state-of-the-art research review of CF-mMIMO-NOMA. Finally, we discuss the challenges and potential of combining CF-mMIMO-NOMA with other enabling technologies to enhance performance.

Cooperative Secrecy Techniques for Improving Physical Layer Security in NOMA-Based PLC Networks

Power Line Communication (PLC) can achieve noticeable savings in infrastructure deployment time and cost, where it uses the existing power lines for data transmission. Non-orthogonal multiple access (NOMA), is a promising technique that can accommodate multiple users via non-orthogonal resource allocation and so, it can notably improve spectral efficiency and reduce the electromagnetic compatibility of PLC networks. Data privacy is of crucial importance in PLC design due to its broadcasting nature. Therefore, this paper presents several cooperative secrecy techniques for improving physical layer security in NOMA-based PLC networks considering two different security constraints, which are signal eavesdroppers and multiple cooperative eavesdroppers. The secrecy performance is measured in terms of two performance metrics: ergodic secrecy capacity (ESC) and secrecy outage probability (SOP). Monte Carlo simulation results validate the accuracy of the analytical model and derivations.

The dynamic power allocation to maximize the achievable sum rate for massive MIMO‐NOMA systems

The demand of mobile networks and quality of service have recently increased to higher Spectral Efficiency (SE) or Energy Efficiency (EE) and massive connectivity for 5G wireless communications. The concept of beamforming Multiple-Input Multiple-Output (MIMO) is capable of significantly reducing the amount of required Radio Frequency Chains (RFCs) used by massive MIMO systems without remarkable performance loss. However, in existing beamformed MIMO, the amount of supported devices cannot be higher than the amount of RFCs using the same time-frequency resources, and it is the basic limit for these systems. To address this issue, non-orthogonal multiple access (NOMA) has been recently recommended, which can accommodate higher covered using via non-orthogonal resource allocation. Nevertheless, power allocation is a core factor of the NOMA scheme. However, maximizing the sum rate problem based on power allocation in Massive MIMO-NOMA scenarios is non-convex and non-linear, which creates a very challenging situation to acquire the closed-form approach. Thus, in this paper, an approach to this difficulty is outlined for Massive MIMO-NOMA systems to maximize the sum rate as a convex and linear problem. Simulation results of the suggested Beamformed MIMO-NOMA (BMN) algorithm show that a higher achievable sum rate is achieved compared with the usual beamformed MIMO.

Machine-type communications in NOMA-based terahertz wireless networks

Terahertz (THz) band is one of the most promising aspects of wireless communication systems because of its potential to meet the growing demands for the envisioned next-generation of cellular communications. THz band connectivity can alleviate bandwidth shortages and transmit power constraints using multiple-input multiple-output (MIMO) systems. To obtain better throughput and enhanced spectral efficiency, non-orthogonal multiple access (NOMA) configuration can be incorporated into MIMO systems, as NOMA uses non-orthogonal resource allocation by assigning the same carrier frequency to multiple devices in the power domain. In this paper, we focus on 2 × 1 MIMO-NOMA and cooperative 2 × 1 MIMO-NOMA systems for THz spectrum in the downlink transmission. In order to evaluate the effectiveness of the proposed system architecture, we derive accurate data rate, transmission latency, and reliability expressions for 2 × 1 MIMO-NOMA system consists of critical and non-critical devices by leveraging finite block length theory. Moreover, we derive the closed-form expressions for power splitting coefficients, data rate, transmission latency, and reliability for the considered cooperative 2 × 1 MIMO-NOMA system. Extensive numerical results are presented to validate the feasibility of the proposed 2 × 1 MIMO-NOMA as well as the cooperative 2 × 1 MIMO-NOMA systems in the THz band.

A Survey on Successive Interference Cancellation Schemes in Non-Orthogonal Multiple Access for Future Radio Access

The fifth generation (5G) of wireless communication accompanied by the advancement of mobile internet and the Internet of Things (IoT) will create stormy data traffic. The 5G challenges like higher spectral efficiency, massive connectivity, and low latency are addressed by the Non-Orthogonal Multiple Access (NOMA) in recent years. NOMA is proven to be a promising technique from its capability to accommodate a larger number of users in contrast to the conventional orthogonal multiple access (OMA) schemes. NOMA comprises two distinct techniques such as Power-Domain NOMA and Code-Domain NOMA. The non-orthogonal resource allocation in Power-Domain NOMA is practically realized by the Superposition Coding (SC) at the Base Station (BS) and an advanced Successive Interference Cancellation at the User Equipment (UE). In this manuscript, the basic concepts of NOMA, on comparing its channel gain with OMA are discussed first. Specifically, a comprehensive survey of various SIC techniques applied under perfect and imperfect Channel State Information (CSI) uncertainties are summarized in terms of outage probability, ergodic capacity, and system performance. In addition, the sophisticated SIC techniques, when NOMA is integrated with modern wireless communication technologies such as multiple-input multiple-output (MIMO-NOMA) and Cooperative (C-NOMA) communications are investigated. Furthermore, the challenges to be solved with their corresponding opportunities and future research directions of NOMA are explored.

A novel mathematical teletraffic method to evaluate the interoperation of different standards with NOMA systems using order statistics

SummaryBasically, nonorthogonal multiple access (NOMA) allows controllable interferences by nonorthogonal resource allocation with a tolerable increase in receiver complexity, using successive interference cancellation (SIC). In this paper, authors show a novel mathematical model of teletraffic for users accessing, simultaneously, to Wi‐Fi and LTE services by using NOMA, calculating the birth–death process by order statistics. This methodology has not been previously used. The mathematical model is represented by a two‐dimensional Markovian process where the users can born or die in one system or another, independently, and results are validated through simulations. The outcomes demonstrate an increment of the sum‐rate gain for a system where users are ordered in the power domain using order statistics, according to the signal interference plus noise ratio (SINR), compared to a system where these statistics are not employed. By using the proposed mathematical model, the sum‐rate gain increases around 15%, and it is also demonstrated that this algorithm foresees a steady behavior of the sum rate, even when the number of channels is augmented, contrary when no order statistics are employed, in which the sum rate decreases considerably. On the other hand, the blocking probability is also demonstrated based on the chance of moving from one technology to another.

Performance analysis at far and near user in NOMA based system in presence of SIC error

Non-orthogonal multiple access (NOMA) scheme is an emerging 5G technology to improve upon the spectral efficiency. It can support more users than the number of available frequency-,time-, and code-domain resources. The innovation behind NOMA technology is to exploit non-orthogonal resource allocation at the cost of receiver complexity to mitigate the inter-user interference arising due to non-orthogonal signals. In this paper, we present performance analysis of downlink NOMA (DL-NOMA) system in presence of successive interference cancellation (SIC) error over Rayleigh fading channels. In particular, we derive the exact closed-form expressions of bit error rate (BER) at near-user (U1) and far-user (U2) for the considered DL-NOMA system. Besides, we also present the achievable rate analysis of the considered NOMA system and it is observed that its achievable rate is higher as compared to conventional orthogonal multiple access (OMA) schemes. Further, we also determine the optimized power allocation coefficient for the NOMA system. The analytical results are corroborated with the Monte-Carlo simulations. The simulation results are presented for different modulation schemes and for different NOMA scenarios. A close argument between the analytical and simulation results validate our analysis.

RESEARCH ON TECHNICAL CRITERIA OF 5G MOBILE COMMUNICATION SYSTEM AND NON-ORTHOGONAL MULTIPLE ACCESS

Today, with the need of connecting information anytime, anywhere, especially mobile Internet and Internet of Things (IoT), this has set three important requirements:solving the number of connections, increasing the speed of access and higher security than current networks. The ITU-R team has developed contents that related to the technical specifications of the 5th generation (5G) mobile communication system called IMT-2020. In order to address one of the three major requirements of network operators, which is high availability connectivity, non-orthogonal multiple access technologies (NOMA) have been used to solve the problem. In contrast to orthogonal multi-access technology, NOMA serves a large number of users due to the non-orthogonal resource allocation. This article will introduce NOMA techniques and standards for peak data rates, user experience, bandwidth, reliability, latency, transmission capacity. . .

Coded Tandem Spreading Multiple Access for Massive Machine-Type Communications

Future IoT applications provoke the connectivity and reliability requirements of machine-type communications, which yield mMTC and URLLC, respectively. In mMTC, grant-free NOMA is adopted to serve massive machine-type devices with low signaling overhead. The challenge of grantfree NOMA for mMTC is the collision induced by non-orthogonal resource allocation. Various grantfree NOMA techniques have been proposed to address this challenge, aiming at high connectivity. In this article, we introduce a novel grant-free NOMA approach, namely coded tandem spreading multiple access (CTSMA). The basic idea is that the data packet of each user is divided into segments, and redundancy segments are generated by coding through the data segments, and multiple orthogonal spreading codes are utilized to tandemly spread the data symbols of different segments from one user. Thereby, collision only occurs on the segments using identical spreading codes, which can be resolved by the redundancy segments to achieve reliable access. In addition to the transmitter and receiver designs, a closedform expression of the collision resolution capability is derived in this article to reveal the trade-off among the connectivity, the reliability, and the user data rate when using CTSMA. Theoretical analysis shows that CTSMA achieves both high connectivity and ultra-reliability at the expense of user data rate.

A Survey of Non-Orthogonal Multiple Access for 5G

In the fifth generation (5G) of wireless communication systems, hitherto unprecedented requirements are expected to be satisfied. As one of the promising techniques of addressing these challenges, non-orthogonal multiple access (NOMA) has been actively investigated in recent years. In contrast to the family of conventional orthogonal multiple access (OMA) schemes, the key distinguishing feature of NOMA is to support a higher number of users than the number of orthogonal resource slots with the aid of non-orthogonal resource allocation. This may be realized by the sophisticated inter-user interference cancellation at the cost of an increased receiver complexity. In this paper, we provide a comprehensive survey of the original birth, the most recent development, and the future research directions of NOMA. Specifically, the basic principle of NOMA will be introduced at first, with the comparison between NOMA and OMA especially from the perspective of information theory. Then, the prominent NOMA schemes are discussed by dividing them into two categories, namely, power-domain and code-domain NOMA. Their design principles and key features will be discussed in detail, and a systematic comparison of these NOMA schemes will be summarized in terms of their spectral efficiency, system performance, receiver complexity, etc. Finally, we will highlight a range of challenging open problems that should be solved for NOMA, along with corresponding opportunities and future research trends to address these challenges.

A Non-Orthogonal Resource Allocation Scheme in Spatial Group Based Random Access for Cellular M2M Communications

Cellular machine-to-machine (M2M) communication can be one of the major candidate technologies to develop an Internet of Things (IoT) platform. A massive number of machine nodes access the cellular networks and typically send/receive small-sized data. In this situation, severe random access (RA) overload and radio resource shortage problems may occur if there is no evolution in the conventional cellular system. Focusing on RA, we need a larger number of preambles, as well as a more efficient resource allocation scheme in order to accommodate a significantly large number of RA requests from machine nodes. In this paper, we propose a non-orthogonal resource allocation (NORA) scheme, combined with our spatial group based RA (SGRA) mechanism, in order to provide a sufficiently large number of preambles at the first step of the RA procedure and non-orthogonally allocate physical uplink shared channel resources at the second step of the RA procedure. As a result, the proposed SGRA-NORA scheme can significantly increase the RA success probability, compared with that of the conventional RA scheme.

Non-orthogonal multiple access for 5G: solutions, challenges, opportunities, and future research trends

The increasing demand of mobile Internet and the Internet of Things poses challenging requirements for 5G wireless communications, such as high spectral efficiency and massive connectivity. In this article, a promising technology, non-orthogonal multiple access (NOMA), is discussed, which can address some of these challenges for 5G. Different from conventional orthogonal multiple access technologies, NOMA can accommodate much more users via nonorthogonal resource allocation. We divide existing dominant NOMA schemes into two categories: power-domain multiplexing and code-domain multiplexing, and the corresponding schemes include power-domain NOMA, multiple access with low-density spreading, sparse code multiple access, multi-user shared access, pattern division multiple access, and so on. We discuss their principles, key features, and pros/cons, and then provide a comprehensive comparison of these solutions from the perspective of spectral efficiency, system performance, receiver complexity, and so on. In addition, challenges, opportunities, and future research trends for NOMA design are highlighted to provide some insight on the potential future work for researchers in this field. Finally, to leverage different multiple access schemes including both conventional OMA and new NOMA, we propose the concept of software defined multiple access (SoDeMA), which enables adaptive configuration of available multiple access schemes to support diverse services and applications in future 5G networks.