Wireless penetration has witnessed explosive growth over the last two decades.
Accordingly, wireless devices have become much denser per unit area, resulting
in an overcrowded usage of wireless resources. To avoid radio interferences and
packet collisions, wireless stations have to exchange control messages to coordinate
well. The existing wisdoms of conveying control messages could be classified into
three categories: explicit, implicit, or hybrid.
According to the statistics of the Federal Communications Commission
(FCC), temporal and geographical variations in the utilization of the as-
signed spectrum range from 15% to 85%. The limited available radio spec-
trum and the inefficiency in spectrum usage necessitate a new commu-
nication paradigm to exploit the existing spectrum dynamically.
Cognitive radio has emerged as a promising technology for maximizing the utiliza-
tion of the limited radio bandwidth while accommodating the increasing amount of
services and applications in wireless networks. A cognitive radio (CR) transceiver
is able to adapt to the dynamic radio environment and the network parameters to
maximize the utilization of the limited radio resources while providing flexibility in
wireless access. The key features of a CR transceiver are awareness of the radio envi-
ronment (in terms of spectrum usage, power spectral density of transmitted/received
signals, wireless protocol signaling) and intelligence.
Currently, the information and communications technology (ICT) industry sector
accounts for about 2–6% of the energy consumption worldwide, and a significant por-
tion of this is contributed by the wireless and mobile communications industry. With
the proliferation of wireless data applications, wireless technology continues to increase
worldwide at an unprecedented growth rate. This has resulted in an increased number
of installed base stations and higher demand on power grids and device power usage,
causing an increased carbon footprint worldwide.
Thisbookfocusesontheemergingresearchtopic‘green(energy-efficient)wirelessnetworks’
that has drawn huge attention recently from both academia and industry. This topic is highly
motivated due to important environmental, financial and quality-of-experience (QoE) consid-
erations.Duetosuchconcerns,varioussolutionshavebeenproposedtoenableefficientenergy
usage in wireless networks, and these approaches are referred to as green wireless communi-
cations and networking. The term ‘green’ emphasizes the environmental dimension of the
proposed solutions. Hence, it is not sufficient to present a cost-effective solution unless it is
eco-friendly.
Quality of Service ( QoS ) has always been in a world of its own, but as the technology
has been refi ned and has evolved in recent years, QOS usage has increased to the point
where it is now considered a necessary part of network design and operation. As with
most technologies, large - scale deployments have led to the technology becoming more
mature, and QOS is no exception.
In the present era, low observability is one of the critical requirements in aerospace
sector, especially related to defense. The stealth technology essentially relates to
shaping and usage of radar absorbing materials (RAM) or radar absorbing struc-
tures (RAS). The performance of such radar cross section (RCS) reduction tech-
niques is limited by the bandwidth constraints, payload requirements, and other
structural issues. Moreover, with advancement of materials science, the structure
geometry no longer remains key decisive factor toward stealth.
Battery systems for energy storage are among the most relevant technologies of the
21 st century. They – in particular modern lithium-ion batteries (LIB) – are enablers
for the market success of electric vehicles (EV) as well as for stationary energy
storage solutions for balancing fluctuations in electricity grids resulting from the
integrationofrenewableenergysourceswithvolatilesupply 1 .BothEVandstationary
storage solutions are important because they foster the transition from the usage
of fossil energy carriers towards cleaner renewable energy sources. Furthermore,
EV cause less local air pollution and noise emissions compared to conventional
combustion engine vehicles resulting in better air quality especially in urban areas.
Unfortunately, to this day, various technological and economic challenges impede a
broad application of batteries for EV as well as for large scale energy storage and
load leveling in electricity grids.
