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At the dawn of the next-generation wireless systems and networks, massive multiple-input multiple-output (MIMO) in combination with leading-edge technologies, methodologies, and architectures are poised to be a cornerstone technology. Capitalizing on its successful integration and scalability within 5G and beyond, massive MIMO has proven its merits and adaptability. Notably, a series of evolutionary advancements and revolutionary trends have begun to materialize in recent years, envisioned to redefine the landscape of future 6G wireless systems and networks. In particular, the capabilities and performance of future massive MIMO systems will be amplified through the incorporation of cutting-edge technologies, structures, and strategies. These include intelligent omni-surfaces (IOSs)/intelligent reflecting surfaces (IRSs), artificial intelligence (AI), Terahertz (THz) communications, and cell-free architectures. In addition, an array of diverse applications built on the foundation of massive MIMO will continue to proliferate and thrive. These encompass wireless localization and sensing, vehicular communications, non-terrestrial communications, remote sensing, and inter-planetary communications, among others. [ABSTRACT FROM AUTHOR]

Summary: Among the several features and capabilities introduced by every new 3GPP release on 5G cellular systems, the latest Release 17 will be remembered as the first that specifies a set of enhancements and adaptations to support mobile broadband services via satellite direct access. Specifically focused on the necessary physical layer mechanism and procedure modifications, this paper will present in detail the 3GPP work about the inclusion of satellite systems in 5G networks. [ABSTRACT FROM AUTHOR]

Mobile communication via high-altitude platforms operating in the stratosphere is an idea that has been on the table for decades. In the past few years, however, with recent advances in technology and parallel progress in standardization and regulatory bodies like the 3rd Generation Partnership Project (3GPP) and International Telecommunications Union (ITU), these ideas have gained considerable momentum. In this article, we present a comprehensive overview of high-altitude platform stations (HAPS) as international mobile telecommunications (IMT) base stations (BS) (HIBS). We lay out possible use cases and summarize the current status of the development from a technological point of view as well as standardization in 3GPP and regarding spectrum aspects. We then present some system-level simulation results to shed light on the performance of HIBS. We conclude by pointing out several directions for future research. [ABSTRACT FROM AUTHOR]

Summary: To acquire phosphorus, cyanobacteria use the typical bacterial ABC‐type phosphate transporter, which is composed of a periplasmic high‐affinity phosphate‐binding protein PstS and a channel formed by two transmembrane proteins PstC and PstA. A putative pstS gene was identified in the genomes of cyanophages that infect the unicellular marine cyanobacteria Prochlorococcus and Synechococcus. However, it has not been determined whether the cyanophage PstS protein is functional during infection to enhance the phosphate uptake rate of host cells. Here we showed that the cyanophage P‐SSM2 PstS protein was abundant in the infected Prochlorococcus NATL2A cells and the host phosphate uptake rate was enhanced after infection. This is consistent with our biochemical and structural analyses showing that the phage PstS protein is indeed a high‐affinity phosphate‐binding protein. We further modelled the complex structure of phage PstS with host PstCA and revealed three putative interfaces that may facilitate the formation of a chimeric ABC transporter. Our results provide insights into the molecular mechanism by which cyanophages enhance the phosphate uptake rate of cyanobacteria. Phosphate acquisition by infected bacteria can increase the phosphorus contents of released cellular debris and virus particles, which together constitute a significant proportion of the marine dissolved organic phosphorus pool. [ABSTRACT FROM AUTHOR]

Summary: Marine intertidal sediments fluctuate in redox conditions and nutrient availability, and they are also known as an important sink of nitrogen mainly through denitrification, yet how denitrifying bacteria adapt to this dynamic habitat remains largely untapped. Here, we investigated novel intertidal benthic ecotypes of the model pelagic marine bacterium Ruegeria pomeroyi DSS‐3 with a population genomic approach. While differing by only 1.3% at the 16S rRNA gene level, members of the intertidal benthic ecotypes are complete denitrifiers whereas the pelagic ecotype representative (DSS‐3) is a partial denitrifier lacking a nitrate reductase. The intertidal benthic ecotypes are further differentiated by using non‐homologous nitrate reductases and a different set of genes that allow alleviating oxidative stress and acquiring organic substrates. In the presence of nitrate, the two ecotypes showed contrasting growth patterns under initial oxygen concentrations at 1 vol% versus 7 vol% and supplemented with different carbon sources abundant in intertidal sediments. Collectively, this combination of evidence indicates that there are cryptic niches in coastal intertidal sediments that support divergent evolution of denitrifying bacteria. This knowledge will in turn help understand how these benthic environments operate to effectively remove nitrogen. [ABSTRACT FROM AUTHOR]

Offering space-based Internet services with mega-constellations of low Earth orbit (LEO) satellites is a promising solution to connecting the unconnected. It can complement the coverage of terrestrial networks to help bridge the digital divide. However, there are challenges from operational obstacles to technical hurdles facing the development of LEO satellite access. This article provides an overview of the state of the art in LEO satellite access, including the evolution of LEO satellite constellations and capabilities, critical technical challenges and solutions, standardization aspects from 5G evolution to 6G, and business considerations. We also identify several areas for future exploration to realize tight integration of LEO satellite access with terrestrial networks in 6G. [ABSTRACT FROM AUTHOR]

The large-scale and ever-growing use of unmanned aerial vehicles (UAVs) in a wide range of applications is foreseen to be a major part of beyond 5G and 6G wireless networks in the next decade. The effective support of such massive deployment of UAVs requires offering reliable, secure, and cost-effective wireless connectivity. Cellular networks play essential roles in serving UAVs acting as flying user equipments. While the cellular networks provide promising connectivity solutions for UAVs, enabling robust UAV operations faces several challenges. In this article, an overview of key barriers and design considerations of widespread commercial use of flying UAVs are presented along with their potential solutions. In addition, we discuss how cellular networks can support UAVs by relying on their advanced features, network intelligence, key enabling technologies for beyond 5G and 6G, and exploiting new tools from machine learning. Finally, we shed light on offering wireless services to high altitudes and the integration of non-terrestrial networks with terrestrial networks toward limitless connectivity in 6G. [ABSTRACT FROM AUTHOR]

A drop of seawater contains numerous microspatial niches at the scale relevant to microbial activities. Examples are abiotic niches such as detrital particles that show different sizes and organic contents, and biotic niches resulting from bacteria–phage and bacteria–phytoplankton interactions. A common practice to investigate the impact of microenvironments on bacterial evolution is to separate the microenvironments physically and compare the bacterial inhabitants from each. It remains poorly understood, however, which microenvironment primarily drives bacterioplankton evolution in the pelagic ocean. By applying a dilution cultivation approach to an undisturbed coastal water sample, we isolate a bacterial population affiliated with the globally dominant Roseobacter group. Although varying at just a few thousand nucleotide sites across the whole genomes, members of this clonal population are diverging into two genetically separated subspecies. Genes underlying speciation are not unique to subspecies but instead clustered at the shared regions that represent ~6% of the genomic DNA. They are primarily involved in vitamin synthesis, motility, oxidative defense, carbohydrate, and amino acid utilization, consistent with the known strategies that roseobacters take to interact with phytoplankton and particles. Physiological assays corroborate that one subspecies outcompetes the other in these traits. Our results indicate that the microenvironments in the pelagic ocean represented by phytoplankton and organic particles are likely important niches that drive the cryptic speciation of the Roseobacter population, though microhabitats contributed by other less abundant pelagic hosts cannot be ruled out. [ABSTRACT FROM AUTHOR]

Drones are increasingly used in a wide variety of industries and services and are delivering profound socioeconomic benefits. Technology needs to be in place to ensure the safe operation and management of this growing fleet of drones. In the past decades, mobile networks have connected tens of billions of devices on the ground and are now ready to connect drones flying in the sky. In this article, we share some of our findings concerning cellular connectivity for low-altitude drones. We first present and analyze field measurement data collected during drone flights in a commercial LTE network. We then present simulation results to shed light on the performance of a network when it is serving many drones simultaneously over a wide area. The results, analysis, and design insights presented here help enhance understanding of the applicability of and performance concerns related to providing mobile connectivity for lowaltitude drones. [ABSTRACT FROM AUTHOR]

Many use cases of UAVs require beyond visual LOS communications. Mobile networks offer wide-area, high-speed, and secure wireless connectivity, which can enhance control and safety of UAV operations and enable beyond visual LOS use cases. In this article, we share some of our experience in LTE connectivity for low-altitude small UAVs. We first identify the typical airborne connectivity requirements and characteristics, highlight the different propagation conditions for UAVs and mobiles on the ground with measurement and ray tracing results, and present simulation results to shed light on the feasibility of providing LTE connectivity for UAVs. We also present several ideas on potential enhancements for improving LTE connectivity performance and identify fruitful avenues for future research. [ABSTRACT FROM AUTHOR]

Many use cases in the Internet of Things (IoT) will require or benefit from location information, making positioning a vital dimension of the IoT. The 3GPP has dedicated a significant effort during its Release 14 to enhance positioning support for its IoT technologies to further improve the 3GPPbased IoT eco-system. In this article, we identify the design challenges of positioning support in LTE-M and NB-IoT, and overview the 3GPP's work in enhancing the positioning support for LTE-M and NB-IoT. We focus on OTDOA, which is a downlink based positioning method. We provide an overview of the OTDOA architecture and protocols, summarize the designs of OTDOA positioning reference signals, and present simulation results to illustrate the positioning performance. [ABSTRACT FROM PUBLISHER]

In 3GPP LTE Release 13, Narrowband Internet of Things (NB-IoT) was standardized for providing wide-area connectivity for massive machine-type communications for IoT. In LTE Release 14, NB-IoT was further developed to deliver enhanced user experience in selected areas through the addition of features such as increased positioning accuracy, increased peak data rates, the introduction of a lower device power class, improved non-anchor carrier operation, multicast, and authorization of coverage enhancements. In this article, we provide an overview of these features introduced for NB-IoT in LTE Release 14. An analysis is given on the applicability of these features and their benefits to enhance the NB-IoT radio access technology. [ABSTRACT FROM AUTHOR]

Narrowband Internet of Things (NB-IoT) is a new cellular technology introduced in 3GPP Release 13 for providing wide-area coverage for IoT. This article provides an overview of the air interface of NB-IoT. We describe how NB-IoT addresses key IoT requirements such as deployment flexibility, low device complexity, long battery lifetime, support of massive numbers of devices in a cell, and significant coverage extension beyond existing cellular technologies. We also share the various design rationales during the standardization of NB-IoT in Release 13 and point out several open areas for future evolution of NB-IoT. [ABSTRACT FROM PUBLISHER]

Millimeter-wave (mmWave) cellular systems are power limited and susceptible to blockages. One promising approach to increasing mmWave connectivity and range is to use relays. Device-to-device (D2D) communications open the door to the vast opportunities of D2D relaying for mmWave cellular systems. In this paper, we study how to select a good relay for a given source–destination pair in a two-hop mmWave cellular system, where the mmWave links are subject to random Bernoulli blockages. In such a system, probing more relays could potentially lead to the discovery of a better relay but at the cost of more overhead. We find that the throughput-optimal relay probing strategy is a pure threshold policy: The system can stop relay probing once the achievable spectral efficiency of the currently probed two-hop link exceeds an optimized threshold. We further characterize the optimal spectral efficiency threshold via a fixed-point equation. [ABSTRACT FROM PUBLISHER]

Dynamic spectrum leasing (DSL) is a promising method to improve the spectrum efficiency. A lot of work has been done about spectrum sharing issues with static models. In this paper, we want to study the behavior of the primary users (PUs) under uncertainty. For this objective, we propose a model with time-varying parameters. The model captures both technical and economic features. We study the long-term behavior of the PUs in the model with stochastic Cournot game theory and variational inequality theory. We show that the PUs can maximize their long-term utilities with a static supply of spectrum. In addition, we also propose two algorithms based on stochastic approximation theory. The convergence and performance of the algorithms are demonstrated theoretically and numerically. The proposed model and analytical framework can be used to study and predict the behaviors of PUs given a DSL system and provide design insights for the DSL system. [ABSTRACT FROM AUTHOR]

This paper develops a novel analytical framework for asynchronous wireless networks deploying multicarrier transmission over flat-fading channels. Nodes in the network have different notions of timing; therefore, from the viewpoint of a typical receiver, the received signals from different transmitters are asynchronous, leading to a loss of orthogonality between subcarriers. We first develop a detailed link-level analysis based on OFDM, based on which we propose a tractable system-level signal-to-interference-plus-noise ratio (SINR) model for asynchronous OFDM networks. The proposed model is used to analytically characterize several important statistics in asynchronous networks with spatially distributed transmitters, including: (i) the number of decodable transmitters; (ii) the decoding probability of the nearest transmitter; and (iii) the system throughput. The system-level loss from lack of synchronization is quantified, and to mitigate the loss, we compare and discuss four possible solutions including extended cyclic prefix, advanced receiver timing, dynamic receiver timing positioning, and semi-static receiver timing positioning with multiple timing hypotheses. The model and results are general, and apply to ad hoc networks, cellular systems, and neighbor discovery in device-to-device (D2D) networks. [ABSTRACT FROM PUBLISHER]

In a device-to-device (D2D) underlaid cellular network, the uplink spectrum is reused by the D2D transmissions, causing mutual interference with the ongoing cellular transmissions. Massive MIMO is appealing in such a context as the base station's (BS's) large antenna array can nearly null the D2D-to-BS interference. The multi-user transmission in massive MIMO, however, may lead to increased cellular-to-D2D interference. This paper studies the interplay between massive MIMO and underlaid D2D networking in a multi-cell setting. We investigate cellular and D2D spectral efficiencies under both perfect and imperfect channel state information (CSI) at the receivers that employ partial zero-forcing. Compared to the case without D2D, there is a loss in cellular spectral efficiency due to D2D underlay. With perfect CSI, the loss can be completely overcome if the number of canceled D2D interfering signals is scaled with the number of BS antennas at an arbitrarily slow rate. With imperfect CSI, in addition to pilot contamination, a new asymptotic effect termed underlay contamination arises. In the non-asymptotic regime, simple analytical lower bounds are derived for both the cellular and D2D spectral efficiencies. [ABSTRACT FROM PUBLISHER]

This paper addresses two fundamental and interrelated issues in device-to-device (D2D) enhanced cellular networks. The first issue is how D2D users should access spectrum, and we consider two choices: overlay (orthogonal spectrum between D2D and cellular UEs) and underlay (non-orthogonal). The second issue is how D2D users should choose between communicating directly or via the base station, a choice that depends on distance between the potential D2D transmitter and receiver. We propose a tractable hybrid network model where the positions of mobiles are modeled by random spatial Poisson point process, with which we present a general analytical approach that allows a unified performance evaluation for these questions. Then, we derive analytical rate expressions and apply them to optimize the two D2D spectrum sharing scenarios under a weighted proportional fair utility function. We find that as the proportion of potential D2D mobiles increases, the optimal spectrum partition in the overlay is almost invariant (when D2D mode selection threshold is large) while the optimal spectrum access factor in the underlay decreases. Further, from a coverage perspective, we reveal a tradeoff between the spectrum access factor and the D2D mode selection threshold in the underlay: as more D2D links are allowed (due to a more relaxed mode selection threshold), the network should actually make less spectrum available to them to limit their interference. [ABSTRACT FROM PUBLISHER]

Multicast device-to-device (D2D) transmission is important for applications like local file transfer in commercial networks and is also a required feature in public safety networks. In this paper we propose a tractable baseline multicast D2D model, and use it to analyze important multicast metrics like the coverage probability, mean number of covered receivers and throughput. In addition, we examine how the multicast performance would be affected by certain factors like dynamics (due to e.g., mobility) and network assistance. Take the mean number of covered receivers as an example. We find that simple repetitive transmissions help but the gain quickly diminishes as the number of repetitions increases. Meanwhile, dynamics and network assistance (i.e., allowing the network to relay the multicast signals) can help cover more receivers. We also explore how to optimize multicasting, e.g. by choosing the optimal multicast rate and the optimal number of retransmission times. [ABSTRACT FROM PUBLISHER]

Device-to-device communication is likely to be added to LTE in 3GPP Release 12. In principle, exploiting direct communication between nearby mobile devices will improve spectrum utilization, overall throughput, and energy consumption, while enabling new peer-to-peer and location-based applications and services. D2D-enabled LTE devices can also become competitive for fallback public safety networks, which must function when cellular networks are not available or fail. Introducing D2D poses many challenges and risks to the long-standing cellular architecture, which is centered around the base station. We provide an overview of D2D standardization activities in 3GPP, identify outstanding technical challenges, draw lessons from initial evaluation studies, and summarize "best practices" in the design of a D2D-enabled air interface for LTE-based cellular networks [ABSTRACT FROM PUBLISHER]

Matching the demand for resources (?load?) with the supply of resources (?capacity?) is a basic problem occurring across many fields of engineering, logistics, and economics, and has been considered extensively in both the Internet and wireless networks. The ongoing evolution of cellular communication networks into dense, organic, and irregular heterogeneous networks (HetNets) has elevated load awareness to a central problem, and introduces many new subtleties. This article explains how several long-standing assumptions about cellular networks need to be rethought in the context of a load-balanced HetNet: we highlight these as three deeply entrenched myths that we then dispel. We survey and compare the primary technical approaches to HetNet load balancing: (centralized) optimization, game theory, Markov decision processes, and the newly popular cell range expansion (a.k.a. biasing), and draw design lessons for OFDMA-based cellular systems. We also identify several open areas for future exploration. [ABSTRACT FROM PUBLISHER]

The explosive growth in data traffic is resulting in a spectrum crunch forcing many wireless network operators to look towards refarming their 2G spectrum and deploy more spectrally efficient Long Term Evolution (LTE) technology. However, mobile network operators face a challenge when it comes to spectrum refarming because 2G technologies such as Global System for Mobile (GSM) is still widely used for low bandwidth machine-to-machine (M2M) devices. M2M devices typically have long life cycles, e.g. smart meters, and it is expensive to migrate these devices to newer technology since a truck roll will typically be required to the site where a device is deployed. Furthermore, with cost of 2G modules several times less than that of LTE, even newly deployed M2M devices tend to adopt 2G technology. Nevertheless, operators are keen to either force their 2G M2M customers to migrate so that they can refarm the spectrum or set aside a portion of the 2G spectrum for continuing operating 2G and only refarm the rest for LTE. In this paper we propose a novel solution to provide GSM connectivity within an LTE carrier through an efficient overlay by reserving a few physical resource blocks for GSM. With this approach, operators can refarm their 2G spectrum to LTE efficiently while still providing some GSM connectivity to their low data rate M2M customers. Furthermore, spectrum can be dynamically shared between LTE and GSM. An approach similar to that proposed in this paper can also be applied for other narrow band technology overlays over LTE. [ABSTRACT FROM PUBLISHER]

Carrier aggregation (CA) and small cells are two distinct features of next-generation cellular networks. Cellular networks with different types of small cells are often referred to as HetNets. In this paper, we introduce a load-aware model for CA-enabled multi-band HetNets. Under this model, the impact of biasing can be more appropriately characterized; for example, it is observed that with large enough biasing, the spectral efficiency of small cells may increase while its counterpart in a fully-loaded model always decreases. Further, our analysis reveals that the peak data rate does not depend on the base station density and transmit powers; this strongly motivates other approaches e.g. CA to increase the peak data rate. Last but not least, different band deployment configurations are studied and compared. We find that with large enough small cell density, spatial reuse with small cells outperforms adding more spectrum for increasing user rate. More generally, universal cochannel deployment typically yields the largest rate; and thus a capacity loss exists in orthogonal deployment. This performance gap can be reduced by appropriately tuning the HetNet coverage distribution (e.g. by optimizing biasing factors). [ABSTRACT FROM AUTHOR]

Despite the central role of mobility in wireless networks, analytical study on its impact on network performance is notoriously difficult. This paper aims to address this gap by proposing a random waypoint (RWP) mobility model defined on the entire plane and applying it to analyze two key cellular network parameters: handover rate and sojourn time. We first analyze the stochastic properties of the proposed model and compare it to two other models: the classical RWP mobility model and a synthetic truncated Levy walk model which is constructed from real mobility trajectories. The comparison shows that the proposed RWP mobility model is more appropriate for the mobility simulation in emerging cellular networks, which have ever-smaller cells. Then we apply the proposed model to cellular networks under both deterministic (hexagonal) and random (Poisson) base station (BS) models. We present analytic expressions for both handover rate and sojourn time, which have the expected property that the handover rate is proportional to the square root of BS density. Compared to an actual BS distribution, we find that the Poisson-Voronoi model is about as accurate in terms of mobility evaluation as hexagonal model, though being more pessimistic in that it predicts a higher handover rate and lower sojourn time. [ABSTRACT FROM PUBLISHER]

In this paper, we extend the distributed power control problem for one-to-one transmissions in Gaussian interference channels to one-to-many transmission scenarios. We assume a user-centric wireless network where the end users play the roles of decision makers. We formulate the power control problem as a noncooperative game. New challenges arise due to the coupling issues among power strategy spaces of distributed end users, which make standard Nash equilibrium based noncooperative game approach inapplicable. Indeed, our problem turns out to be a generalized Nash equilibrium problem (GNEP). Resorting to variational inequality theory, we show several fundamental properties of the GNEP. Then we propose a penalty-based distributed algorithm IP^2JA, which possesses favorable properties for practical implementation. Numerical results are provided to verify our arguments and proposed algorithm. [ABSTRACT FROM AUTHOR]

Over the past few years, unmanned aerial vehicles (UAVs) and other aerial platforms have become central to several aspects of business and daily life. From remote delivery to acquiring landscape information to providing connectivity in emergency scenarios, drone features are proving to be highly beneficial in places where humans cannot reach or are unable to perform in a timely, efficient, or secure manner, thus paving the way for several disruptive new applications. [ABSTRACT FROM AUTHOR]

Phytoplankton contribute almost half of the world's total primary production. The exudates and viral lysates of phytoplankton are two important forms of dissolved organic matter (DOM) in aquatic environments and fuel heterotrophic prokaryotic metabolism. However, the effect of viral infection on the composition and biological availability of phytoplankton-released DOM is poorly understood. Here, we investigated the optical characteristics and microbial utilization of the exudates and viral lysates of the ecologically important unicellular picophytoplankton Prochlorococcus Our results showed that Prochlorococcus DOM produced by viral lysis (Pro-vDOM) with phages of three different morphotypes (myovirus P-HM2, siphovirus P-HS2, and podovirus P-SSP7) had higher humic-like fluorescence intensities, lower absorption coefficients, and higher spectral slopes than DOM exuded by Prochlorococcus (Pro-exudate). The results indicate that viral infection altered the composition of Prochlorococcus -derived DOM and might contribute to the pool of oceanic humic-like DOM. Incubation with Pro-vDOM resulted in a greater dissolved organic carbon (DOC) degradation rate and lower absorption spectral slope and heterotrophic bacterial growth rate than incubation with Pro-exudate, suggesting that Pro-vDOM was more bioavailable than Pro-exudate. In addition, the stimulated microbial community succession trajectories were significantly different between the Pro-exudate and Pro-vDOM treatments, indicating that viral lysates play an important role in shaping the heterotrophic bacterial community. Our study demonstrated that viral lysis altered the chemical composition and biological availability of DOM derived from Prochlorococcus , which is the numerically dominant phytoplankton in the oligotrophic ocean. IMPORTANCE The unicellular picocyanobacterium Prochlorococcus is the numerically dominant phytoplankton in the oligotrophic ocean, contributing to the vast majority of marine primary production. Prochlorococcus releases a significant fraction of fixed organic matter into the surrounding environment and supports a vital portion of heterotrophic bacterial activity. Viral lysis is an important biomass loss process of Prochlorococcus However, little is known about whether and how viral lysis affects Prochlorococcus -released dissolved organic matter (DOM). Our paper shows that viral infection alters the optical properties (such as the absorption coefficients, spectral slopes, and fluorescence intensities) of released DOM and might contribute to a humic-like DOM pool and carbon sequestration in the ocean. Meanwhile, viral lysis also releases various intracellular labile DOM, including amino acids, protein-like DOM, and lower-molecular-weight DOM, increases the bioavailability of DOM, and shapes the successive trajectory of the heterotrophic bacterial community. Our study highlights the importance of viruses in impacting the DOM quality in the ocean., (Copyright © 2021 American Society for Microbiology.)