Recent changes in how people consume multimedia services are causing an explosive increase in mobile traffic. With more and more people using wireless networks, the demand for the ultra-fast wireless communications systems is increasing. To date, this demand has been accommodated with advanced modulation schemes and signal-processing technologies at microwave frequencies. However, without increasing the carrier frequencies for more spectral resources, it may be quite difficult to keep up with the needs of users. Although there are several alternative bands, recent advances in terahertz-wave (THz-wave) technologies have attracted attention due to the huge bandwidth of THz waves and its potential for use in wireless communications. The frequency band of 275 ~ 3000 GHz , which has not been allocated for specific uses yet, is especially of interest for future wireless systems with data rates of 10 Gb/s or higher. Although THz communications is still in a very early stage of development, there have been lots of reports that show its potential. In this review, we will examine the current progress of THz-wave technologies related to communications applications and discuss some issues that need to be considered for the future of THz communications.

Present and Future of Terahertz Communications

An ultrawideband 3.1-10.6-GHz low-noise amplifier employing an input three-section band-pass Chebyshev filter is presented. Fabricated in a 0.18-/spl mu/m CMOS process, the IC prototype achieves a power gain of 9.3 dB with an input match of -10 dB over the band, a minimum noise figure of 4 dB, and an IIP3 of -6.7 dBm while consuming 9 mW.

An ultrawideband CMOS low-noise amplifier for 3.1-10.6-GHz wireless receivers

Wireless sensor networks (WSNs) monitor dynamic environments that change rapidly over time. This dynamic behavior is either caused by external factors or initiated by the system designers themselves. To adapt to such conditions, sensor networks often adopt machine learning techniques to eliminate the need for unnecessary redesign. Machine learning also inspires many practical solutions that maximize resource utilization and prolong the lifespan of the network. In this paper, we present an extensive literature review over the period 2002–2013 of machine learning methods that were used to address common issues in WSNs. The advantages and disadvantages of each proposed algorithm are evaluated against the corresponding problem. We also provide a comparative guide to aid WSN designers in developing suitable machine learning solutions for their specific application challenges.

https://ink.library.smu.edu.sg/cgi/viewcontent.cgi?article=3963&context=sis_research

Machine Learning in Wireless Sensor Networks: Algorithms, Strategies, and Applications

We propose the concept of ultra-broadband terahertz communication, based on directed non-line-of-sight (NLOS) transmissions. Potential applications of such a system supporting multi-gigabit data rates are given, and put into the context of currently emerging WLANs/WPANs. The technology and propagation constraints serve as boundary conditions for the determination of the required antenna gain to support ultra-broadband communication. Resulting high-gain antenna requirements will necessitate highly directed transmissions. We propose the use of omni-directional dielectric mirrors to support directed NLOS paths. Their performance is investigated with ray-tracing simulations of a terahertz propagation channel in a dynamic office environment, which is calibrated with measured building-material and mirror parameters. We demonstrate that a directed NLOS path scheme will make a terahertz communication system robust to shadowing. Furthermore, we show that dielectric mirrors covering only parts of the walls will significantly enhance the signal coverage in a typical indoor scenario.

Short-Range Ultra-Broadband Terahertz Communications: Concepts and Perspectives

An ultra-wideband 3.1-10.6-GHz low-noise amplifier employing a broadband noise-canceling technique is presented. By using the proposed circuit and design methodology, the noise from the matching device is greatly suppressed over the desired UWB band, while the noise from other devices performing noise cancellation is minimized by the systematic approach. Fabricated in a 0.18-mum CMOS process, the IC prototype achieves a power gain of 9.7 dB over a -3 dB bandwidth of 1.2-11.9-GHz and a noise figure of 4.5-5.1 dB in the entire UWB band. It consumes 20 mW from a 1.8-V supply and occupies an area of only 0.59 mm2

A Broadband Noise-Canceling CMOS LNA for 3.1–10.6-GHz UWB Receivers

This article provides an overview of ultra-wideband (UWB) wireless systems. System issues are discussed including modulation schemes, pulse shapes, interference issues, and channel characterization. Several communications- and radar-specific implementation issues are also addressed. Much of the description is provided in the context of pulse-based UWB or impulse radio. Furthermore, a section is dedicated to describing the role of the FCC and how current regulations are shaping UWB. The last section extends this discussion and presents several possible applications, providing examples of each.


Keywords:

Ultra-wideband;
UWB;
applications;
modulation;
channel modeling

Ultra-Wideband Wireless Systems

Although using geolocation databases is a practical approach for enabling spectrum sharing, it poses a potentially serious privacy problem. Secondary users (queriers), through seemingly innocuous queries to the database, can determine the types and locations of incumbent systems operating in a given region of interest, and thus compromise the incumbents' operational privacy. When the incumbent systems (primary users) are commercial systems, this is typically not a critical issue. However, if the incumbents are federal government systems, including military systems, then the information revealed by the databases can lead to a serious breach of operational privacy. In this paper, we propose privacy-preserving mechanisms and techniques for an obfuscated geolocation database that can enable the coexistence of primary and secondary users while preserving the operational privacy of the primary users.

Protecting the primary users' operational privacy in spectrum sharing

In spectrum sharing, a spatial separation region is defined around primary users (PUs) to protect them from secondary user (SU)-induced interference. This protection region — referred to by a number of names, such as an exclusion zone (EZ) or a protection zone (PZ) — has a static boundary, and this boundary is determined very conservatively to provide an additional margin of protection for the PUs. This legacy notion of interference protection is overly rigid, and often results in poor spectrum utilization efficiency. In this paper, we propose a novel framework for prescribing interference protection for the PUs that addresses some of the limitations of legacy EZs. Specifically, we introduce the concept of Multi-tiered Incumbent Protection Zones (MIPZ), and show that it can be used to dynamically adjust the PU's protection boundary based on the radio environment, network conditions, and the PU interference protection requirement. MIPZ can serve as an analytical framework for quantitatively analyzing a given PZ to gain insights on and determine the tradeoffs between interference protection and spectrum utilization efficiency. It allows a number of SUs, say N, to operate closer to the PU, and improves the overall spectrum utilization efficiency while ensuring a probabilistic guarantee of interference protection to the PU. We leverage the combined power of database-driven spectrum sharing and stochastic optimization theory for dynamically computing the zone boundary and the value of N. Using extensive simulation results, we demonstrate that the proposed framework improves spectrum utilization efficiency by adapting to the changing interference environment through dynamic adjustments of the zone boundary.

Defining incumbent protection zones on the fly: Dynamic boundaries for spectrum sharing

Reducing the size of exclusion zones (EZs) in spectrum sharing is vital for efficient utilization of fallow spectrum as well as for the economic viability of spectrum sharing itself In this paper, we explore two approaches for reducing the size of EZs We show that multi-tiered EZs can be used to improve spectrum utilization efficiency by implementing the concept of differential spectrum access hierarchy Also, we provide quantitative results that show the impact of using a point-to-point mode terrain profile in calculating an EZ's contour Such a terrain profile captures the effects of propagation losses due to area-specific topography, which are not considered by the F-curves, a common method of calculating an EZ's boundary Our results indicate that the use of such a terrain profile results in a noticeable decrease in the size of an EZ

Multi-tier exclusion zones for dynamic spectrum sharing

The exponential growth of wireless systems makes their carbon footprint hard to ignore. This chapter presents statistics related to the energy consumption of cellular networks’ infrastructure in order to motivate the need for more efficient and environmentally friendly communications. A definition of the term “Green Communications” is provided along with different metrics that can be used to quantify energy efficiency for the various aspects of wireless infrastructure. In addition to topics related to cellular infrastructure, the chapter presents a brief review of key techniques that can be potentially used for improving energy efficiency. Furthermore, since improving energy efficiency is not by itself sufficient for low-carbon systems, possible ways of using and managing energy harvested from renewable sources such as solar and ambient RF signals are discussed. Moreover, the concept of Wireless Distributed Computing is introduced to illustrate how a group of wireless devices can share their resources for achieving a set of common goals. Finally, resource allocation is examined for managing the trade-offs involved when simultaneously minimizing the carbon footprint and performing the necessary communication and computation tasks in mobile devices. Haris I. Volos Virginia Tech, USA Dinesh Datla Virginia Tech, USA Xuetao Chen Virginia Tech, USA An He Virginia Tech, USA Ashwin Amanna Virginia Tech, USA Timothy R. Newman University of Maryland, USA S. M. Shajedul Hasan Virginia Tech, USA Jeffery H. Reed Virginia Tech, USA Tamal Bose Virginia Tech, USA

Jeffery H. Reed

Papers

Ultra-Wideband Wireless Systems

Protecting the primary users' operational privacy in spectrum sharing

Defining incumbent protection zones on the fly: Dynamic boundaries for spectrum sharing

Multi-tier exclusion zones for dynamic spectrum sharing

Green Communications: Realizing Environmentally Friendly, Cost Effective, and Energy Efficient Wirel