6G System Research Articles

Licensed Countrywide Full-Spectrum Allocation: A New Paradigm for Millimeter-Wave Mobile Systems in 5G/6G Era

The traditional static allocation of a portion of the licensed spectrum specified for a country to a mobile network operator (MNO) is no longer sufficient to address the required spectrum demand, as well as efficient to utilize the allocated spectrum. To overcome these constraints, i.e. to increase the spectrum availability and utilization, in this paper, we present a new paradigm for the spectrum allocation called licensed countrywide full-spectrum allocation (LCFSA) to allocate the licensed countrywide full 28 GHz millimeter-wave (mmWave) spectrum to each MNO of a country to operate its small cells per building subject to avoiding co-channel interference (CCI). Since most data is generated indoors, the countrywide full mmWave spectrum allocated to an MNO is considered reusing further to its in-building small cells. CCI avoidance in both the time-domain and frequency-domain is presented along with deducing the conditions for optimality. We derive average capacity, spectral efficiency (SE), energy efficiency (EE), and cost efficiency (CE) for LCFSA, and perform extensive numerical and simulation results and analyses for a country consisting of four MNOs. It is shown that LCFSA with both the time-domain and frequency-domain CCI avoidance schemes provide similar performance improvement in average capacity, SE, EE, and CE by about 296%, 164%, 75%, and 60% respectively for no interfering user equipments (UEs), whereas by about 59.2%, 6.1%, 37.2%, and 0.45% respectively for all interfering UEs with the frequency-domain CCI scheme. Moreover, it is found that the improvement in the above metrics does not change with the spectrum reuse factor (RF) and the number of buildings of small cells per macrocell L, and the impact of interfering UEs can be compensated by adjusting RF. Finally, we show that LCFSA can satisfy the SE and EE requirements for sixth-generation (6G) systems by adjusting either RF or L, or both.

Towards 6G in-X Subnetworks With Sub-Millisecond Communication Cycles and Extreme Reliability

The continuous proliferation of applications requiring wireless connectivity will eventually result in latency and reliability requirements beyond what is achievable with current technologies. Such applications can for example include industrial control at the sensor-actuator level, intra-vehicle communication, fast closed loop control in intra-body networks and intra-avionics communication. In this article, we present the design of short range Wireless Isochronous Real Time (WIRT) in-X subnetworks aimed at life-critical applications with communication cycles shorter than 0.1 ms and outage probability below 10 -6 . Such targets are clearly beyond what is supported by the 5th Generation (5G) radio technology, and position WIRT as a possible 6th Generation (6G) system. WIRT subnetworks are envisioned to be deployed for instance in industrial production modules, robots, or inside vehicles. We identify technology components as well as spectrum bands for WIRT subnetworks and present major design aspects including frame structure and transmission techniques. The performance evaluation considering a dense scenario with up to 2 devices per m 2 reveal that a multi-GHz spectrum may be required for ensuring high spatial service availability. The possibility of running WIRT as an ultra-wideband underlay system in the centimeter-wave spectrum region is also discussed. Aspects related to design of techniques for the control plane as well as enhancements to the presented design is the focus of our ongoing research.

6G Wireless Communication Systems: Applications, Requirements, Technologies, Challenges, and Research Directions

The demand for wireless connectivity has grown exponentially over the last few decades. Fifth-generation (5G) communications, with far more features than fourth-generation communications, will soon be deployed worldwide. A new paradigm of wireless communication, the sixth-generation (6G) system, with the full support of artificial intelligence, is expected to be implemented between 2027 and 2030. Beyond 5G, some fundamental issues that need to be addressed are higher system capacity, higher data rate, lower latency, higher security, and improved quality of service (QoS) compared to the 5G system. This paper presents the vision of future 6G wireless communication and its network architecture. This article describes emerging technologies such as artificial intelligence, terahertz communications, wireless optical technology, free-space optical network, blockchain, three-dimensional networking, quantum communications, unmanned aerial vehicles, cell-free communications, integration of wireless information and energy transfer, integrated sensing and communication, integrated access-backhaul networks, dynamic network slicing, holographic beamforming, backscatter communication, intelligent reflecting surface, proactive caching, and big data analytics that can assist the 6G architecture development in guaranteeing the QoS. Besides, expected applications with 6G communication requirements and possible technologies are presented. We also describe potential challenges and research directions for achieving this goal.

Analysis of Wireless Backhaul Networks Based on Aerial Platform Technology for 6G Systems

Analysis of Wireless Backhaul Networks Based on Aerial Platform Technology for 6G Systems

6G Wireless Systems: A Vision, Architectural Elements, and Future Directions

Internet of everything (IoE)-based smart services are expected to gain immense popularity in the future, which raises the need for next-generation wireless networks. Although fifth-generation (5G) networks can support various IoE services, they might not be able to completely fulfill the requirements of novel applications. Sixth-generation (6G) wireless systems are envisioned to overcome 5G network limitations. In this article, we explore recent advances made toward enabling 6G systems. We devise a taxonomy based on key enabling technologies, use cases, emerging machine learning schemes, communication technologies, networking technologies, and computing technologies. Furthermore, we identify and discuss open research challenges, such as artificial-intelligence-based adaptive transceivers, intelligent wireless energy harvesting, decentralized and secure business models, intelligent cell-less architecture, and distributed security models. We propose practical guidelines including deep Q-learning and federated learning-based transceivers, blockchain-based secure business models, homomorphic encryption, and distributed-ledger-based authentication schemes to cope with these challenges. Finally, we outline and recommend several future directions.

Communications in the 6G Era

The focus of wireless research is increasingly shifting toward 6G as 5G deployments get underway. At this juncture, it is essential to establish a vision of future communications to provide guidance for that research. In this paper, we attempt to paint a broad picture of communication needs and technologies in the timeframe of 6G. The future of connectivity is in the creation of digital twin worlds that are a true representation of the physical and biological worlds at every spatial and time instant, unifying our experience across these physical, biological and digital worlds. New themes are likely to emerge that will shape 6G system requirements and technologies, such as: (i) new man-machine interfaces created by a collection of multiple local devices acting in unison; (ii) ubiquitous universal computing distributed among multiple local devices and the cloud; (iii) multi-sensory data fusion to create multi-verse maps and new mixed-reality experiences; and (iv) precision sensing and actuation to control the physical world. With rapid advances in artificial intelligence, it has the potential to become the foundation for the 6G air interface and network, making data, compute and energy the new resources to be exploited for achieving superior performance. In addition, in this paper we discuss the other major technology transformations that are likely to define 6G: (i) cognitive spectrum sharing methods and new spectrum bands; (ii) the integration of localization and sensing capabilities into the system definition, (iii) the achievement of extreme performance requirements on latency and reliability; (iv) new network architecture paradigms involving sub-networks and RAN-Core convergence; and (v) new security and privacy schemes.

Intelligent Surfaces for 6G Wireless Networks: A Survey of Optimization and Performance Analysis Techniques

This paper surveys the optimization frameworks and performance analysis methods for large intelligent surfaces (LIS), which have been emerging as strong candidates to support the sixth-generation wireless physical platforms (6G). Due to their ability to adjust the behavior of interacting electromagnetic (EM) waves through intelligent manipulations of the reflections phase shifts, LIS have shown promising merits at improving the spectral efficiency of wireless networks. In this context, researchers have been recently exploring LIS technology in depth as a means to achieve programmable, virtualized, and distributed wireless network infrastructures. From a system level perspective, LIS have also been proven to be a low-cost, green, sustainable, and energy-efficient solution for 6G systems. This paper provides a unique blend that surveys the principles of operation of LIS, together with their optimization and performance analysis frameworks. The paper first introduces the LIS technology and its physical working principle. Then, it presents various optimization frameworks that aim to optimize specific objectives, namely, maximizing energy efficiency, sum-rate, secrecy-rate, and coverage. The paper afterwards discusses various relevant performance analysis works including capacity analysis, the impact of hardware impairments on capacity, uplink/downlink data rate analysis, and outage probability. The paper further presents the impact of adopting the LIS technology for positioning applications. Finally, we identify numerous exciting open challenges for LIS-aided 6G wireless networks, including resource allocation problems, hybrid radio frequency/visible light communication (RF-VLC) systems, health considerations, and localization.

A Vision of 6G Wireless Systems: Applications, Trends, Technologies, and Open Research Problems

The ongoing deployment of 5G cellular systems is continuously exposing the inherent limitations of this system, compared to its original premise as an enabler for Internet of Everything applications. These 5G drawbacks are currently spurring worldwide activities focused on defining the next-generation 6G wireless system that can truly integrate far-reaching applications ranging from autonomous systems to extended reality and haptics. Despite recent 6G initiatives1, the fundamental architectural and performance components of the system remain largely undefined. In this paper, we present a holistic, forward-looking vision that defines the tenets of a 6G system. We opine that 6G will not be a mere exploration of more spectrum at high-frequency bands, but it will rather be a convergence of upcoming technological trends driven by exciting, underlying services. In this regard, we first identify the primary drivers of 6G systems, in terms of applications and accompanying technological trends. Then, we propose a new set of service classes and expose their target 6G performance requirements. We then identify the enabling technologies for the introduced 6G services and outline a comprehensive research agenda that leverages those technologies. We conclude by providing concrete recommendations for the roadmap toward 6G. Ultimately, the intent of this article is to serve as a basis for stimulating more out-of-the-box research around 6G.

Expedited Neighbor Discovery in Directional Terahertz Communication Networks Enhanced by Antenna Side-Lobe Information

Terahertz (THz)-band (0.1-10 THz) communication is envisioned as a key wireless technology of the next decade, able to support wireless Terabit-per-second links in 6G systems. THz communication exhibits an extremely large bandwidth (tens to hundreds of GHz) at the cost of a very high path loss (>100 dB for distances beyond a few meters). Therefore, highly directional antennas (DAs) are needed simultaneously in transmission and reception at all times to establish reliable communication links. The application of highly DAs introduces new challenges in the neighbor discovery process. In this paper, a time-efficient neighbor discovery protocol for THz-band communication networks is proposed. The protocol expedites the neighbor discovery process by leveraging the full antenna radiation pattern to detect a series of effective signals and map them to the universal signal patterns, which indicate the potential direction of the signal source. A mathematical framework is developed to compare the neighbor discovery protocols with and without the antenna side-lobes information in free space. The X60 testbed is utilized to validate the proposed neighbor discovery protocol. Furthermore, a feasibility analysis of the proposed protocol inside a bounded space (e.g., a square room) is conducted. Numerical results are presented to illustrate the performance improvements achieved by the proposed protocol when compared to the traditional neighbor discovery protocols with only main-lobe information.

TeraSim: An ns-3 extension to simulate Terahertz-band communication networks

Terahertz (THz)-band (0.1–10 THz) communication is envisioned as a key wireless technology of the next decade, able to support up to multi-Terabit-per-second wireless links in 6G systems. Parallel with the design of THz devices, simulation tools are needed to expedite the development of communication protocols tailored to THz paradigm. In this paper, TeraSim, an extension for ns-3 to simulate THz communication networks, is presented. TeraSim defines and implements separate modules for the THz channel and the physical and link layers. It enables the design and testing of higher layers of the protocol stack without delving with the lower layers technologies.

Millimeter-Wave Communications With Non-Orthogonal Multiple Access for B5G/6G

In order to further improve the system capacity, we explore the integration of non-orthogonal multiple access (NOMA) in millimeter-wave communications (mmWave-NOMA) for future B5G and 6G systems. Compared with the conventional NOMA, the distinguishing feature of mmWave-NOMA is that, it is usually characterized by transmit/receive beamforming with large phased arrays. In this paper, we focus on the design challenges of mmWave-NOMA due to beamforming. Firstly, we study how beamforming affects the sum-rate performance of mmWave-NOMA, and find that with conventional single-beam forming, the performance may be offset by the relative angle between NOMA users. Then, we consider multi-beam forming for mmWave-NOMA, which is shown to be able to achieve promising performance enhancement as well as robustness. Next, we investigate the challenging joint design of the intertwined power allocation and user pairing for mmWave-NOMA. Relevant challenges are discussed and some potential solutions are proposed in detail. We further consider hybrid spatial division multiple access (SDMA) and NOMA in mmWave communications, where some possible system configurations and the corresponding solutions are discussed to address the multi-user issues including multi-user precoding and multi-user interference mitigation. Finally, we present future directions in mmWave-NOMA and summarize the paper.

On Combinatorial Models of Generations of Wireless Communication Systems

In this paper, the following issues are considered: (i) a brief review of wireless mobile technologies including their evolution (1G, 2G, 3G, 4G, 5G, and 6G system generations), (ii) the use of hierarchical combinatorial models for the description of wireless communication system generations, and (iii) the use of a twostage modular method for improving (predicting) the version of the 5G wireless system generation (based on the block pack problem). The presented examples illustrate the proposed approaches to modeling and improvemen of wireless communication systems.

Chemiluminescence determination of cefotaxime sodium with flow-injection analysis of cerium (IV)–rhodamine 6G system and its application to the binding study of cefotaxime sodium to protein with on-line microdialysis sampling

A simple, sensitive and rapid flow-injection chemiluminescence (CL) method has been developed for the determination of cefotaxime sodium based on the chemiluminescence reaction of cefotaxime sodium with ceric sulfate and rhodamine 6G in nitric acid solution. The concentration of cefotaxime sodium was proportional with the CL intensity in the range of 4 × 10 −8 – 8 × 10 −6 mol L −1. The detection limit (signal-to-noise ratio = 3) was 1 × 10 −8 mol L −1. Coupled to the technique of on-line microdialysis sampling, this method was successfully applied to study cefotaxime sodium–protein interaction. The drug and protein were mixed in different molar ratios in Ringer's solution, pH 7.4, and incubated at 37 °C in a water bath. The microdialysis probe was utilized to sample the mixed solution at a perfusion rate of 5 μL min −1 and the recovery of cefotaxime sodium under experimental condition was 16.2%. The data obtained by the present Microdialysis-Flow Injection Analysis-CL method was analyzed with the Scatchard analysis and Klotz plot. The estimated association constant ( K) and the number of the binding sites ( n) on one of BSA molecule were 5.94 × 10 4 M −1 and 1.29 (Klotz equation), respectively.

A new sensitive flow‐injection chemiluminescence method for the determination of H2‐receptor antagonists

Based on the chemiluminescence (CL) intensity generated from the potassium ferricyanide [K(3)Fe(CN)(6)]-rhodamine 6G system in sodium hydroxide (NaOH) medium, a new sensitive flow-injection chemiluminescence (FI-CL) method has been developed, validated and applied for the determination of three kinds of H(2)-receptor antagonists: cimetidine (CIMT), ranitidine (RANT) hydrochloride and famotidine (FAMT). Under the optimum conditions, the linear range for the determination was 1.0 x 10(-9)-7.0 x 10(-5) g/ml for CIMT, 1.0 x 10(-9)-5.0 x 10(-5) g/mL for RANT hydrochloride and 5.0 x 10(-9)-7.0 x 10(-5) g/mL for FAMT. During 11 repeated measurements of 1.0 x 10(-6) g/mL sample solutions, the relative standard deviations (RSDs) were all <5%. The detection limit was 8.56 x 10(-10) g/mL for CIMT, 8.69 x 10(-10) g/mL for RANT hydrochloride and 2.35 x 10(-9) g/mL for FAMT (S:N = 3). This method has been successfully implemented for the analysis of H(2)-receptor antagonists in pharmaceuticals.

Energy transfer between unlike fluorophores in uniaxially oriented polymer films monitored by time-resolved and steady-state emission anisotropy

Excitation energy transfer is studied for 3,3′-diethylthiacyanine iodide (DTTHCI, donor) and rhodamine 6G (R6G, acceptor) (system I) and 3,3′-diethyloxacarbocyanine iodide (DTCI, acceptor) (system II) in uniaxially stretched and unstretched polyvinyl alcohol films (PVA). Both systems differ strongly in the orientation degree of acceptor transition moments in the stretched polymeric matrix. As a result of weak orientation of R6G in PVA stretched matrix, strong acceptor depolarization of fluorescence upon donor excitation was observed for system I despite ordering the PVA matrix. However, for system II the transition moments of both DTTHCI and DTCI are correlated and orientate strongly along the direction of stretching resulting in the preservation of acceptor emission anisotropy upon steady-state and pulse excitation.

Sensitive determination of phenolic compounds using high-performance liquid chromatography with cerium(IV)-rhodamine 6G-phenolic compound chemiluminescence detection

A simple, selective and sensitive determination method of 20 phenolic compounds has been developed using high-performance liquid chromatography (HPLC) with chemiluminescence detection. The method is based on the chemiluminescent enhancement by phenolic compound of the cerium(IV)-rhodamine 6G system in sulfuric acid medium. Twenty phenolic compounds were separated on a XDB-C 8 column with a gradient elution using a mixture of methanol and 1.0% acetic acid as a mobile phase. Under the optimized conditions, a linear working range extends 2 orders of magnitude with the relative standard deviations of intra- and inter-day precision below 4.0%, and the detection limits (S/N = 3) were in the range of 1.5–82.1 ng/ml. The chemiluminescence reaction was compatible with the mobile phase of high-performance liquid chromatography. The proposed method has been successfully applied to the assay of phenolic compounds in red wine without any pretreatment.

Simultaneous determination of quercetin, kaempferol, and isorhamnetin in phytopharma-ceuticals ofHippophae rhamnoides L. by high-performance liquid chromatography with chemiluminescence detection

A novel method based on reversed-phase high-performance liquid chromatography with chemiluminescence detection has been developed for the simultaneous determination of three flavonols including quercetin, kaempferol, and isorhamnetin. The procedure was based on the chemiluminescent enhancement by flavonols of the cerium(IV)-rhodamine 6G system in sulfuric acid medium. The effects of several parameters on the HPLC resolution and CL emission were studied systematically. Good separation was achieved with isocratic elution using a mixture of methanol and aqueous 1.0% acetic acid (37:63, v/v) within 25 min. Under optimized conditions, the linear working range covers 3 orders of magnitude with relative standard deviations below 4.5% for 11 replicate injected flavonol samples, and detection limits (S/N= 3) were 1.6 x 10(-8), 3.5 x 10(-9), and 6.5 x 10(-9) g mL(-1) for quercetin, kaempferol, and isorhamnetin, respectively. The chemiluminescence reaction was compatible with the mobile phase of high-performance liquid chromatography. The proposed method has been successfully applied to the determination of three active flavonols in phytopharmaceuticals of Hippophae rhamnoides L. After a simple extraction procedure, the repeatability and recovery were satisfactory.

High-performance liquid chromatographic assay of parabens in wash-off cosmetic products and foods using chemiluminescence detection

A new method for the simultaneous determination of parabens including methylparaben, ethylparaben, propylparaben, and butylparaben by high-performance liquid chromatography (HPLC) coupled with chemiluminescence detection was developed. The procedure was based on the chemiluminescent enhancement by parabens of the cerium(IV)–rhodamine 6G system in the strong sulfuric acid medium. The good separation of parabens was carried out with an isocratic elution using a mixture of methanol and water (60:40, v/v) within 8.5 min. Under the optimized conditions, a linear working range extends three orders of magnitude with the relative standard deviations of intra- and inter-day precision below 4.5%, and the detection limits were 1.9 × 10 −9, 2.7 × 10 −9, 3.9 × 10 −9, and 5.3 × 10 −9 g ml −1 for methylparaben, ethylparaben, propylparaben, and butylparaben, respectively. The chemiluminescence reaction was well compatible with the mobile phase of high-performance liquid chromatography. The proposed method has been successfully applied to the assay of parabens in wash-off cosmetic products and foods with the minimal sample preparation.

Energy transfer between collagen-dye molecules as a probe of higher-lying electronic states following multiquantum excitation

Under high-intensity nanosecond 1064 nm irradiation of a collagen-rhodamine 6G (R6G) system, multiquantum excitation of the R6G molecules to their S2 state was facilitated. The observation of this effect was achieved through associated energy transfer to the resonant collagen excited state band. Analogous cascaded energy transfer phenomena, resulting from the S2 electronic state of R6G, were observed in an R6G-collagen-coumarin system.

Flow injection kinetic spectrophotometric determination of ascorbic acid based on an inhibiting effect

A rapid and sensitive flow-injection kinetic spectrophotometric method is proposed for the determination of ascorbic acid. The procedure is based on the inhibiting effect of ascorbic acid on the enhancing effect of oxalate on the potassium dichromate-potassium iodide/rhodamine 6G system. The detection limit and linear ranges are 0.08 and 0.10–4.00 μg/ml, respectively. The relative standard deviation of 11 replicate measurements is less than 2.0%. This method has been successfully used to determine ascorbic acid in pharmaceuticals, tomatoes and oranges.