-
Lithium–sulfur (Li–S) batteries with high energy density and long cycle life are considered to be one of the most promising next-generation energy-storage systems beyond routine lithium-ion batteries. Various approaches have been proposed to break down technical barriers in Li–S battery systems. The use
of nanostructured metal oxides and sulfides for high sulfur utilization and long life span of Li–S batteries is reviewed here. The relationships between the intrinsic properties of metal oxide/sulfide hosts and electrochemical performances of Li–S batteries are discussed. Nanostructured metal oxides/ sulfides hosts used in solid sulfur cathodes, separators/interlayers, lithium- metal-anode protection, and lithium polysulfides batteries are discussed respectively. Prospects for the future developments of Li–S batteries with nanostructured metal oxides/sulfides are also discussed.
標簽：
電池
納米結構
硫化物
金屬氧化物
上傳時間：
2017-11-23
上傳用戶：653357637
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From the transition of analog to digital communication along with seamless mobility and
high computing power of small handheld devices, the wireless communications industry has
seen tremendous changes leading to the integration of several telecommunication networks,
devices and services over last 30 years. The rate of this progress and growth has increased
particularly in the past decade because people no longer use their devices and networks for
voice only, but demand bundle contents such as data download/streaming, HDTV, HD video ,
3D video conferencing with higher efficiency, seamless connectivity, intelligence, reliability
and better user experience. Although the challenges facing service providers and
telecommunication companies differ by product, region, market size, and their areas of
concentration but time to market, efficient utilization of their assets and revenue expansion,
have impacted significantly how to manage and conduct their business while maintaining
sufficient margin.
標簽：
Convergence
Networks
Beyond
4G
of
上傳時間：
2020-05-26
上傳用戶：shancjb
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Mobile communication devices like smart phones or tablet PCs enable us to
consume information at every location and at every time. The rapid development
of new applications and new services and the demand to access data in real time
create an increasing throughput demand. The data have to be transmitted reliably
to ensure the desired quality of service. Furthermore, an improved utilization of
the bandwidth is desired to reduce the cost of transmission.
標簽：
Architectures
Processing
Baseband
Signal
for
上傳時間：
2020-05-26
上傳用戶：shancjb
-
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.
標簽：
Cognitive
Radio
Networks
上傳時間：
2020-05-26
上傳用戶：shancjb
-
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.
標簽：
Cognitive
Wireless
Network
上傳時間：
2020-05-26
上傳用戶：shancjb
-
Rapid growth of wireless communication services in recent decades has created
a huge demand of radio spectrum. Spectrum scarcity and utilization inefficiency
limit the development of wireless networks. Cognitive radio is a promising tech-
nology that allows secondary users to reuse the underutilized licensed spectrum of
primary users. The major challenge for spectrum sharing is to achieve high spectrum
efficiency while making non-intrusive access to the licensed bands. This requires in-
formation of availability and quality of channel resources at secondary transmitters,
however, is difficult to be obtained perfectly in practice.
標簽：
Opportunistic
Spectrum
Sharing
上傳時間：
2020-05-31
上傳用戶：shancjb
-
Radio frequency spectrum is a scarce and critical natural resource that is utilized for
many services including surveillance, navigation, communication, and broadcast-
ing. Recent years have seen tremendous growth in the use of spectrum especially by
commercial cellular operators. Ubiquitous use of smartphones and tablets is one
of the reasons behind an all-time high utilization of spectrum. As a result, cellular
operators are experiencing a shortage of radio spectrum to meet bandwidth
demands of users. On the other hand, spectrum measurements have shown that
much spectrum not held by cellular operators is underutilized even in dense urban
areas. This has motivated shared access to spectrum by secondary systems with no
or minimal impact on incumbent systems. Spectrum sharing is a promising
approach to solve the problem of spectrum congestion as it allows cellular operators
access to more spectrum in order to satisfy the ever-growing bandwidth demands of
commercial users.
標簽：
Spectrum
Sharing
Between
Radars
上傳時間：
2020-06-01
上傳用戶：shancjb
-
For more than three decades, Micro Electro Mechanical Systems (MEMS) have
steadily transitioned out of research labs and into production forming a more than $10 billion
market [1]. MEMS devices such as accelerometers, pressure sensors and microphones, to name
a few, have seen immense utilization, particularly in the consumer electronics market, because
of their compact sizes and minute power consumptions. In addition, these devices benefit from
batch fabrication, which has enabled year-over-year reductions in cost [2]. In recent years,
標簽：
Frequency
Tunable
MEMS
上傳時間：
2020-06-06
上傳用戶：shancjb
-
In this age of science and technology, the global economy has developed so much that our
lifestyles are now extremely modernized and developed. In some ways, modern society
seems to have reached the utmost state of advancement in various areas, including eco-
nomic development, science and technology pursuit, and the utilization of the given nat-
ural environment. However, it is important to consider approaches that may allow human
beings to stay longer on the Earth while enjoying fulfilling and peaceful daily lives.
標簽：
Ecological
Networks
Design
Smart
Home
of
上傳時間：
2020-06-06
上傳用戶：shancjb
-
Resource allocation is an important issue in wireless communication networks. In
recent decades, cognitive radio technology and cognitive radio-based networks have
obtained more and more attention and have been well studied to improve spectrum
utilization and to overcomethe problem of spectrum scarcity in future wireless com-
munication systems. Many new challenges on resource allocation appear in cogni-
tive radio-based networks. In this book, we focus on effective solutions to resource
allocation in several important cognitive radio-based networks, including a cogni-
tive radio-basedopportunisticspectrum access network, a cognitiveradio-basedcen-
tralized network, a cognitive radio-based cellular network, a cognitive radio-based
high-speed vehicle network, and a cognitive radio-based smart grid.
標簽：
Cognitive
Networks
Radio
上傳時間：
2020-06-07
上傳用戶：shancjb
