The Telecommunications industry has seen a rapid boost within the last decade. New realities
and visions of functionalities in various Telecommunications networks have brought forward the
concept of next-generation networks (NGNs). The competitions among operators for support-
ing various services, lowering of the cost of having mobile and cellular phones and smartphones,
increasing demand for general mobility, explosion of digital traffic, and advent of convergence
network technologies added more dynamism in the idea of NGNs. In fact, facilitating con-
vergence of networks and convergence of various types of services is a significant objective of
NGNs.
Performance analysis belongs to the domain of applied mathematics. The
major domain of application in this book concerns Telecommunications sys-
tems and networks. We will mainly use stochastic analysis and probability
theory to address problems in the performance evaluation of telecommuni-
cations systems and networks. The first chapter will provide a motivation
and a statement of several problems.
Recent decades have shown a tremendous expansion of the Internet. The number of
connected terminals has increased by orders of magnitude, traffic has grown exponen-
tially, coverage has become ubiquitous and worldwide, and today’s sophisticated Web
2.0 applications are increasingly providing services which hitherto have been the realm
of Telecommunications, such as Skype and video conferencing. This has even led to the
thought that access to the Internet might one day be a universal right of every citizen.
This evolution will accelerate in the coming decades.
Soon after Samuel Morse’s telegraphing device led to a deployed electri-
cal Telecommunications system in 1843, waiting lines began to form by those
wanting to use the system. At this writing queueing is still a significant factor in
designing and operating communications services, whether they are provided
over the Internet or by other means, such as circuit switched networks.
This book provides the essential design techniques for radio systems that
operate at frequencies of 3 MHz to 100 GHz and which will be employed in
the telecommunication service. We may also call these wireless systems,
wireless being synonymous with radio, Telecommunications is a vibrant indus-
try, particularly on the ‘‘radio side of the house.’’ The major supporter of this
upsurge in radio has been the IEEE and its 802 committees. We now devote
? . an entire chapter to wireless LANs WLANs detailed in IEEE 802.11. We
also now have subsections on IEEE 802.15, 802.16, 802.20 and the wireless
? . ? metropolitan area network WMAN . WiFi, WiMax,, and UWB ultra wide-
. band are described where these comparatively new radio specialties are
demonstrating spectacular growth.
We are currently witnessing an increase in Telecommunications norms and
standards given the recent advances in this domain. The increasing number of
normalized standards paves the way for an increase in the range of offers and
services available for each consumer. Moreover, the majority of available radio
frequencies have already been allocated.
Wireless communications and networking technology are advancing at a very rapid
pace. Newer technologies and standards are evolving to serve the ever-increasing num-
ber of users demanding different types of mobile applications and services. Research
and development activities on wireless technology constitute one of the most impor-
tant segments of research and development in the Telecommunications area today.
Commoditization is a serious threat to the Telecommunications industry. Most CSPs offer
similar services at rates designed to win what has become a price war. As a result, many
face decreasing margins and difficulty sustaining differentiation based on prices or
products alone. On top of commoditization, CSPs also face competition from OTT
providers and an increasingly knowledgeable and demanding customer base. With
access to growing amounts of data from an ever-increasing number of sources and
devices, today’s empowered, savvy consumers know what they want and expect to get it.
This paper presents a Hidden Markov Model (HMM)-based speech
enhancement method, aiming at reducing non-stationary noise from speech
signals. The system is based on the assumption that the speech and the noise
are additive and uncorrelated. Cepstral features are used to extract statistical
information from both the speech and the noise. A-priori statistical
information is collected from long training sequences into ergodic hidden
Markov models. Given the ergodic models for the speech and the noise, a
compensated speech-noise model is created by means of parallel model
combination, using a log-normal approximation. During the compensation, the
mean of every mixture in the speech and noise model is stored. The stored
means are then used in the enhancement process to create the most likely
speech and noise power spectral distributions using the forward algorithm
combined with mixture probability. The distributions are used to generate a
Wiener filter for every observation. The paper includes a performance
evaluation of the speech enhancer for stationary as well as non-stationary
noise environment.
The first edition of this book was published in 1992. Nine years later it had become
clear that a second edition was required because of the rapidly changing nature of
telecommunication. In 1992, the Internet was in existence but it was not the
household word that it is in the year 2001. Cellular telephones were also in use
but they had not yet achieved the popularity that they enjoy today. In the current
edition, Chapter 1 has been revised to include a section on the Internet. Chapter 10 is
new and it covers the facsimile machine; I had overlooked this important tele-
communication device in the first edition. Chapter 11 is also new and it describes the
pager, the cordless telephone and the cellular telephone system. These are examples
of a growing trend in Telecommunications to go ‘‘wireless’’.
