Chapter 1

Wireless Communication and Mobile Computing
IMNW 6121
April – May 2021 G.C.
ESHETE ALIGAZ
School of Informatics, KIoT, Wollo University, Ethiopia.

Chapters / Course Outline
• Wireless and Mobile Technology (Chapter – 1)
• Wireless Communication and Mobile Computing Environments(Chapter – 2)
• Telecommunication Systems (Chapter – 3)/NOT EXAM PART/
• Emerging Wireless and Mobile Networks (Chapter – 4)
• Pervasive Computing (Chapter – 5)
2

Assessment and Grading System
Mobile Application Development Project Report (20%)
Seminar presentation (10%)
Assignment(s) – 20%
Final Written Examination – 50%
3

Chapter – 1
Wireless and Mobile Technology
Contents included in this chapter are:
1.1. Overview of Wireless and Mobile Technologies
1.2. Radio Technologies and Platforms
1.3. Wireless Communication Algorithms
1.3.1. Multiple Input Multiple Output (MIMO)
1.3.2. Cooperative Communications
1.3.3. Dynamic Spectrum Access (DSA)
1.3.4. Network Coding

A big picture which connects mobile
computing and wireless communications

Introduction to Mobile Computing

• Mobile computing systems are computing systems that may be easily
moved physically and whose computing capabilities may be used while
they are being moved.
• Examples are laptops, personal digital assistants (PDAs), and mobile
phones.
• By distinguishing mobile computing systems from other computing
systems we can identify the distinctions in the tasks that they are
designed to perform, the way that they are designed, and the way in
which they are operated.
• There are many things that a mobile computing system can do that a
stationary computing system cannot do; these added functionalities are
the reason for separately characterizing mobile computing systems. 7

• Among the distinguishing aspects of mobile computing systems are
their prevalent wireless network connectivity, their small size, the
mobile nature of their use, their power sources, and their
functionalities that are particularly suited to the mobile user.
• Because of these features, mobile computing applications are inherently
different than applications written for use on stationary computing
systems.
8

A brief history of Mobile computing
• The following figure shows a timeline of mobile computing development.
• One of the very first computing machines, the abacus, which was used as
far back as 500 B.C., was, in effect, a mobile computing system because
of its small size and portability.
• As technology progressed, the abacus evolved into the modern
calculator. Most calculators today are made with an entire slew of
mathematical functions while retaining their small size and portability.
• The abacus and calculators became important parts of technology not
only because of their ability to compute but also because of their ease of
use and portability.
• You can calculate the proceeds of a financial transaction anywhere as
long as you had an abacus in 500 B.C. or have a calculator today. But,
calculating numbers is only one part of computing.
9

10

• Other aspects of computing, namely storage and interchange of
information, do not date as far back as the abacus.
• Though writing has always been a way of storing information, we can
hardly call a notebook a computing storage mechanism.
• The first mobile storage systems can be traced back only as far as the
advent of the age of electronics.
11

• A mobile computing system, as with any other type of computing system, can
be connected to a network. Connectivity to the network, however, is not a
prerequisite for being a mobile computing system. Dating from the late 1960s,
networking allowed computers to talk to each other.
• Networking two or more computers together requires some medium that
allows the signals to be exchanged among them. This was typically achieved
through wired networks.
• Although wired networks remain the predominant method of connecting
computers together, they are somewhat cumbersome for connecting mobile
computing devices. Not only would network ports with always-available
network connectivity have to be pervasive in a variety of physical locations, it
would also not be possible to be connected to the network in real time if the
device were moving.
• Therefore, providing connectivity through a wired system is virtually cost
prohibitive. This is where wireless communication systems come to the rescue
(Refer the following figure).
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13

• By the 1960s, the military had been using various forms of wireless
communications for years. Not only were wireless technologies used in a
variety of voice communication systems, but the aviation and the space
program had created great advances in wireless communication as well.
• First, the military developed wireless communication through line of
sight: If there were no obstacles between point A and point B, you could
send and receive electromagnetic waves.
• Then came techniques that allowed for wireless communication to
encompass larger areas, such as using the atmosphere as a reflective
mechanism. But, there were limitations on how far a signal could reach
and there were many problems with reliability and quality of
transmission and reception.
14

• By the 1970s, communication satellites began to be commercialized.
With the new communication satellites, the quality of service and
reliability improved enormously.
• Still, satellites are expensive to build, launch, and maintain. So the
available bandwidth provided by a series of satellites was limited.
• In the 1980s cellular telephony technologies became commercially viable
and the 1990s were witness to advances in cellular technologies that
made wireless data communication financially feasible in a pervasive
way.
15

• Today, there are a plethora of wireless technologies that allow reliable
communication at relatively high bandwidths.
• Of course, bandwidth, reliability, and all other qualitative and quantitative
aspects of measuring wireless technologies are relative to time and people’s
expectations.
• Though most wireless networks today can transmit data at orders of
magnitude faster speeds than just ten years ago, they are sure to seem
archaically slow soon.
• It should, however, be noted that wired communication systems will almost
certainly always offer us better reliability and higher data transmission
bandwidths as long as electromagnetic communications is the primary means
of data communications.
• The higher frequency sections of the electromagnetic spectrum are difficult to
use for wireless communications because of natural noise, difficulty of
directing the signal (and therefore high losses), and many other physical
limitations.
16

• Because the greatest advances in mobile communications originated in
the military, it is no surprise that one of the first applications of wireless
communication for mobile computing systems was in displaying terrain
maps of the battlefield.
• From this, the global positioning system (GPS) evolved so that soldiers
could know their locations at any given time.
• Portable military computers were provided to provide calculations,
graphics, and other data in the field of battle. In recent years, wireless
telephony has become the major provider of a revenue stream that is
being invested into improving the infrastructure to support higher
bandwidth data communications.
17

Is Wireless Mobile or Is Mobile Wireless?
• In wireless connectivity, mobile computing devices found a great way to
connect with other devices on the network. In fact, this has been a great
source of confusion between wireless communications and mobile
computing.
• Mobile computing devices need not be wireless. Laptop computers,
calculators, electronic watches, and many other devices are all mobile
computing devices. None of them use any sort of wireless
communication means to connect to a network.
• Even some hand-held personal assistants can only be synchronized with
personal computers through a docking port and do not have any means
of wireless connectivity.
18

• So, before we embark on our journey in learning about mobile
computing, it should be clear that wireless communication systems are a
type of communication system. What distinguishes a wireless
communication system from others is that the communication channel is
space itself.
• There are a variety of physical waveguide channels such as fibre optics or
metallic wires. Wireless communication systems do not use a waveguide
to guide along the electromagnetic signal from the sender to the
receiver.
• They rely on the mere fact that electromagnetic waves can travel
through space if there are no obstacles that block them. Wireless
communication systems are often used in mobile computing systems to
facilitate network connectivity, but they are not mobile computing
systems. 19

• Recently, computer networks have evolved by leaps and bounds. These
networks have begun to fundamentally change the way we live. Today, it is
difficult to imagine computing without network connectivity. Networking and
distributed computing are two of the largest segments that are the focus of
current efforts in computing.
• Networks and computing devices are becoming increasingly blended together.
Most mobile computing systems today, through wired or wireless connections,
can connect to the network. Because of the nature of mobile computing
systems, network connectivity of mobile systems is increasingly through
wireless communication systems rather than wired ones.
• And this is quickly becoming somewhat of a nonmandatory distinguishing
element between mobile and stationary systems. Though it is not a
requirement for a mobile system to be wireless, most mobile systems are
wireless.
20

• Nevertheless, let us emphasize that wireless connectivity and mobility
are orthogonal in nature though they may be complementary.
• For example, we can have a PDA that has no wireless network
connectivity; however, most PDAs are evolving into having some sort of
wireless connectivity to the network.
21

• There are four pieces to the mobile problem: the mobile user, the mobile
device, the mobile application, and the mobile network.
• We will distinguish the mobile user from the stationary user by what we
will call the mobile condition: the set of properties that distinguishes the
mobile user from the user of a typical, stationary computing system.
22

• We will wrap the differences between typical devices, applications, and
networks with mobile devices, applications, and networks into a set of
properties that we will call the dimensions of mobility: the set of
properties that distinguishes the mobile computing system from the
stationary computing system.
23

Added dimensions of mobile computing
24

• It should be obvious that any mobile computing system can also be
stationary!
• If we stop moving it, it is stationary. So, we can say that mobile
computing systems are a superset of stationary computing systems.
• Therefore, we need to look at those elements that are outside of the
stationary computing subset.
• These dimensions of mobility are as follows:
25

1. location awareness,
2. network connectivity quality of service (QoS),
3. limited device capabilities (particularly storage and CPU),
4. limited power supply,
5. support for a wide variety of user interfaces.
26

1. Location awareness
• A mobile device is not always at the same place: Its location is constantly
changing.
• The changing location of the mobile device and the mobile application
presents the designers of the device and software applications with
great difficulties.
• However, it also presents us with an opportunity of using the location
and the change in location to enhance the application.
• These challenges and opportunities can be divided into two general
categories: localization and location sensitivity.
27

• Localization is the mere ability of the architecture of the mobile
application to accommodate logic that allows the selection of different
business logic, level of work flow, and interfaces based on a given set of
location information commonly referred to as locales.
• Localization is not exclusive to mobile applications but takes a much
more prominent role in mobile applications. Localization is often
required in stationary applications where users at different geographical
locations access a centralized system.
• For example, some point-of-sale (POS) systems and e-commerce Web
sites are able to take into account the different taxation rules depending
on the locale of the sale and the location of the purchase.
• Whereas localization is something that stationary applications can have,
location sensitivity is something fairly exclusive to mobile applications.
28

• Location sensitivity is the ability of the device and the software
application to first obtain location information while being used and then
to take advantage of this location information in offering features and
functionality.
• Location sensitivity may include more than just the absolute location of
the device. It may also include the location of the device relative to some
starting point or a fixed point, some history of past locations, and a
variety of calculated values that may be found from the location and the
time such as speed and acceleration.
29

• There are a variety of methods for collecting and using the location of
the user and the device.
• The user may simply be prompted for his or her location, but this
wouldn’t make a very user-friendly application.
• Imagine a system that can only give you directions to where you want to
go if you know where you are: It will be useful often, but occasionally,
you won’t know where you are or it would be too difficult to figure out
your location.
• The device may be reset for a relative location if it has the ability to
sense motion and can keep track of the change of location for some
period of time after this reset.
• Most location-sensing technologies use one or more of three categories
of techniques: triangulation, proximity, and scene analysis.
30

• Triangulation (See the figure) relies on age-old geometric methods that
allow calculation of the location of a point that lies in the middle of three
other points whose exact locations are known. If the distance to each
one of the three points is known, we can use geometric techniques to
calculate the exact location of the unknown point.
• Proximity-based methods measure the relative position of the unknown
point to some known point.
• Scene analysis relies on image processing and topographical techniques
to calculate the location of the unknown point based on a view of the
unknown point from a known point.
31

• The most well known location sensing system today is GPS. GPS-enabled
devices can obtain latitude and longitude with accuracy of about 1–5 m.
• GPS has its roots in the military; until recently, the military placed
restrictions on the accuracy of GPS available for public use. Most of
these restrictions have now been lifted.
• GPS devices use triangulation techniques by triangulating data points
from the satellite constellation that covers the entire surface of the
earth.
• If a device does not have GPS capabilities but uses a cellular network for
wireless connectivity, signal strength and triangulation or other methods
can be used to come up with some approximate location information,
depending on the cellular network. 33

• Regardless of how location information is obtained, it is one of the major
differences between mobile and stationary systems.
• Location information can be to mobile applications what depth can be to
two-dimensional pictures; it can give us an entirely new tool to automate
tasks.
• An example of a stand-alone mobile software application that uses
location information could be one that keeps track of the route that a
user drives from home to work every day without the user entering the
route manually; this could then be used to tell the user which route is
the fastest way to get to work on a particular day or which route may
result in the least amount of gas consumed.
34

• An example of a wirelessly networked mobile application taking
advantage of location could be one that shows a field service worker
where to go next, once he or she is finished with a task at one site, based
on the requests for work in the queue and the location of the field
service worker.
• It should be noted that acquiring position information requires
connectivity to some network-based infrastructure.
• Conclusion: Location information promises to be one of the biggest
drivers of mobile applications as it allows for the introduction of new
business models and fundamentally new methods of adding productivity
to business systems. 35

2. Quality of Service
• Whether wired or wireless connectivity is used, mobility means loss of
network connectivity reliability.
• Moving from one physical location to another creates physical barriers
that nearly guarantee some disconnected time from the network. If a
mobile application is used on a wired mobile system, the mobile system
must be disconnected between the times when it is connected to the
wired docking ports to be moved.
• In the case of wireless network connectivity, physical conditions can
significantly affect the quality of service (QoS).
• For example, bad weather, solar flares, and a variety of other climate-
related conditions can negatively affect the (QoS).
36

• This unreliability in network connectivity has given rise to the QoS field
and has led to a slew of accompanying products. QoS tools and products
are typically used to quantify and qualify the reliability, or unreliability, of
the connectivity to the network and are mostly used by network
operators.
• Network operators control the physical layer of the network and provide
the facilities, such as Internet Protocol (IP), for software application
connectivity.
37

• Usually, the QoS tools, run by the network operators, provide information
such as available bandwidth, risk of connectivity loss, and statistical
measurements that allow software applications to make smart computing
decisions.
• The key to designing and implementing mobile applications is that network
connectivity and QoS need to be taken into account with an expanded scope.
Most software applications, take advantage of networking in some way and,
therefore, do have network connectivity features.
• Stationary applications typically need not worry about the quality of network
connectivity as this is handled by lower level layers than the application: the
operating system, the hardware (such as the network card in a personal
computer), the network itself, and all of the other components that make
network computing possible.
• Stationary software applications typically assume some discrete modes of
connectivity mostly limited to connected or disconnected. This works for most
applications because most wired network connectivity is fairly reliable.
38

• However, the effect of QoS in designing mobile applications is much more profound.
• Whereas typical non-mobile applications need to know how to stop operating
“gracefully” when suddenly disconnected from the network, mobile applications
have to know how to continue to operate even after they are disconnected from the
network or while they connect and disconnect from the network intermittently and
frequently.
• For example, let us take the case of a user who is traveling on a train, is using an
application on his PDA connected wirelessly to some network, and is downloading a
work-related report to look over when the train passes through a tunnel and he loses
network connectivity. If the application does not have the ability to stop partway
through the download process and restart when connectivity is restored, the user
may never be able to retrieve the desired file as he passes through one tunnel after
the other and the download process starts over and over again.
• The application, therefore, must know how to deal with lack of reliable connectivity.
39

3. Limited Device Storage and CPU
• No one wants to carry around a large device, so most useful mobile
devices are small.
• This physical size limitation imposes boundaries on volatile storage, non-
volatile storage, and CPU on mobile devices.
• Though solid-state engineers are working on putting more and more
processing power and storage into smaller and smaller physical volumes,
nevertheless, as most mobile applications today are very rudimentary.
40

• Today’s mobile applications are resource-starved.
• So, although the designers of modern applications designed to run on
personal computers (PCs) and servers continue to care less and less
about system resources such as memory and processing power, it is a
sure bet that memory limitations will be around for a long time for
mobile applications because when it comes to mobile systems and
devices, smaller is nearly always better.
41

• Smaller devices are easier to carry and, consequently, may become more pervasive.
• This pervasiveness also largely depends on the price of the devices. Making
electronic devices very small normally increases the cost, as the research and
development that go into making devices smaller are very expensive.
• But, once a technology matures and the manufacturing processes for making it
becomes mostly automated, prices begin to decline. At the point when the device is
more and more of a commodity, smaller also means less expensive.
• This is why a PDA is much less expensive than a PC and yet it is much smaller.
• So, there is not a simple proportional relationship between size of device and cost
of device.
• Our general rule stands that when it comes to mobile systems and devices, smaller
is nearly always better. The small size serves the mobile purpose of the device the
best.
42

• Limitations of storage and CPU of mobile devices put yet another constraint
on how we develop mobile applications.
• For example, a mobile calendaring application may store some of its data on
another node on the network (a PC, server, etc.). The contacts stored on the
device may be available at any time. However, the contact information that
exists only on the network is not available while the device is disconnected
from the network.
• But, because the amount of data that can be stored on each type of device
varies depending on the device type, it is not possible to allocate this storage
space statically.
• Mobile applications must be designed to optimize the use of data storage and
processing power of the device in terms of the application use by the user.
43

4. Limited Power Supply
• Batteries are improving every day and it is tough to find environments where
suitable AC power is not available. Yet, often the user is constantly moving
and devices are consuming more and more power with processors that have
more and more transistors packed into them.
• The desirability of using batteries instead of an AC power source combined
with the size constraints creates yet another constraint, namely a limited
power supply.
• This constraint must be balanced with the processing power, storage, and size
constraints; the battery is typically the largest single source of weight in the
mobile device. 44

4. Limited Power Supply
• The power supply has a direct or an indirect effect on everything in a mobile
device. For example, the brighter the display, the more battery power is used,
so the user interface is indirectly coupled to the power supply.
• Most power management functionality is built into the operating system of
the mobile device. Therefore, when it comes to device power management,
the design focus is more on making the right choice in selecting the proper
platform (device, operating system, etc.) and configuring the platform
properly.
• In a typical stationary application, this would suffice. But, in mobile
applications, we need to look everywhere we can to save power. 45

5. Varying User Interfaces
• Stationary users use non-mobile applications while working on a PC or a
similar device. The keyboard, mouse, and monitor have proved to be fairly
efficient user interfaces for such applications.
• This is not at all true for mobile applications.
• Examples of some alternative interfaces are voice user interfaces, smaller
displays, stylus and other pointing devices, touch-screen displays, and
miniature keyboards.
• Using a combination of interface types is common.
46

• For example, drivers who want to get some directions to their destination
may use a data-enabled cellular phone, navigate through a simple graphical
user interface (GUI) menu to a driving directions application, and then
retrieve the desired directions through a voice user interface by saying the
address of the source and destination and listening to the directions.
• However, entering text on the small display of a cellular phone and through
the numeric keys of a phone is very cumbersome.
47

User interfaces are difficult to design and implement for the following reasons:
1. Designers have difficulties learning the user’s tasks.
2. A balance must be achieved among the many different design aspects, such as
standards, graphic design, technical writing, internationalization, and
performance.
3. The existing theories and guidelines are not sufficient.
4. Iterative design is difficult.
5. It is difficult to test user interface software.
6. Today’s languages do not provide support for user interfaces.
7. Programmers report an added difficulty of modularization of user interface
software.
48

Introduction to wireless communications
49

• Marconi invented the wireless telegraph in 1896. By encoding alphanumeric
characters in analog signals, he sent telegraphic signals across the Atlantic
Ocean.
• This led to a great many developments in wireless communication networks
that support radio, television, mobile telephone, and satellite systems that have
changed our lives.
• The wireless networks themselves have improved tremendously with notable
advances in cellular networks, satellite communications, and wireless local area
networks.
• More recently, many mobile computing applications (computing applications
that run partially or completely on mobile devices) have emerged that fully
exploit the capabilities of wireless networks and mobile devices. The end result
is numerous developments with far-reaching impact on business, education,
entertainment, and daily lifestyles.
50

• Mobile computing and wireless communications have created several
opportunities because of the appeal of wireless communications – typified by
the overused slogan of “communications anytime and anywhere.”
• However, these developments have also raised several technical and business
issues and have introduced a tremendous amount of new terms (see the
upcoming figure).
51

52

• Before proceeding, let us clarify the difference between mobile computing and
wireless communication networks. As shown in the following table, mobile
computing devices may or may not be connected to wireless networks.
• For example, you can have desktop computers – typically stationary devices –
interconnected through a wireless network in an office building that is not wired
for networking. This may happen in older buildings or houses being used for
offices.
• In these situations, it is quicker to set up a wireless LAN than to wait for the
facility to be wired. Similarly, you can have a mobile computer connected to a
wired network. This is quite typical nowadays.
53

54

Several highlights
• Mobile computing and wireless systems can be discussed in terms of:
• Wireless networks that transport the messages
• Middleware that hides the networking issues
• Applications that are used to support mobile users
• Many mobile computing applications have been developed and are being
developed at present. Examples include:
• Mobile business (m-business) applications such as mobile commerce, mobile portals, and
mobile supply chain management systems.
• Mobile government applications that provide wireless access to health, education,
transportation, and welfare services.
• Mobile life applications such as multi-media message services between friends, and
movie, restaurant, and route finders on mobile devices.
55

Strengths and Weakness of Wireless Communications
56

Strengths of Wireless Communications
• The strengths of wireless systems that are driving their growth are:
• Social and cultural factors. Wireless systems conform to our inherently mobile lifestyles.
In our personal and business lives, our employees, partners, customers, relatives and
friends are always moving around. Wireless systems fit well in this increasingly mobile
environment with the need for information/transactions anytime and anywhere.
• Advances in wireless networks. A particular appeal of wireless systems, in addition to
their flexibility, is the steady increase in wireless data rates. Higher data rates are
achievable with broadband wireless technology for applications such as graphics, video,
and audio. Broadband wireless networks give higher data rates that compete with wired
networks, plus they enjoy convenience and reduced cost.
57

• Niche applications. In some cases, wireless is the only option. For example, wired
communications over very long distances (between Ethiopia and South Africa, for
example) are virtually impossible, and wireless is the only choice for space explorations. In
addition, many law enforcement and battlefield applications can only work with wireless
communications. For example, it is difficult to lay cables in a battlefield, or to carry a
wired device when chasing a criminal.
• Special situations. Wireless communications make more sense in several situations. For
example, satellite communication is a good choice to connect far-flung and hard-to-reach
areas. In addition, it may be difficult to lay cables in hostile environments. In the war-torn
country of Syria or Yemen, for example, it was hazardous for the workers to lay cables
along roads between major cities; so wireless links were used instead.
58

• Wireless for older buildings. In many cases, wireless is chosen because the buildings are
too old for installing cables.
• Developments in mobile devices. The new breed of wireless handsets have many
attractive features such as digital cameras, and pictures. The availability of new mobile
devices such as powerful laptop computers, PDAs, and cellular telephones with Internet
and wireless data access capabilities is also driving the growth.
• Increased revenue and productivity possibilities. The revenue opportunities created via
location-based services and m-commerce have lured several companies and investors into
this area. In addition, the productivity improvements to be gained via wireless extensions
to enterprise applications and processes are tremendous. For example, mobile customer
relationship management systems can capture customer information in real time and
allow marketing reps to be more productive.
59

• Industrial and regulatory factors. The convergence of telecommunications and software
industries coincides with the adoption of wireless standards such as WAP and Bluetooth,
along with the cultural and regulatory drivers in various countries.
60

Weakness and Issues of Wireless Communications
• Wireless is convenient and less expensive but some business, political and
technical difficulties inhibit wireless technologies.
• A major limitation is security of wireless systems because wireless
communications are technically easier to eavesdrop and intrude. There are also
some additional limitations. These include lack of industry-wide standards, data
rate limitations as compared to wired networks (despite progress), and device
limitations.
• These weaknesses can be discussed in terms of social, business, and technology
issues.
61

Social Issues
• Wireless systems, despite their popularity, have raised some social issues. Privacy and
security are among the top.
• Consider, for example, the privacy issue raised by location-based services (LBSs).
Wireless networks have to keep track of the user location to direct the messages to
the users as they move around. For example, cellular networks keep a Visitor Location
Register (VLR) – a database – that records the location of a user as he moves from one
cell to another.
• Suppose you take a train from Addis to Mekkelle and turn on your cellular phone
when you get on the train. Then the VLR will indicate that now you are in Addis. As the
train travels through several cities, you will change several cells along the way (each
cell is between 10 to 15 miles) and the VLR will be updated accordingly.
• Thus the VLR log will show when you were in Addis and what path you took on your
way to Mekkelle. This information traces your movement and could be considered
private, but the cellular providers can sell or give this information to others – a
potential privacy issue.
62

Social Issues
• The general concern about wireless security is that wireless networks are easier
to tap into. Within this broad area, users are concerned with several privacy and
security issues. For example, the call setup information that includes the user ID
and other information should be protected, and the speech and data
transmitted during a wireless session should be kept private and confidential.
• Some possible health issues have been raised due to the increased use of
cellular phones and other wireless equipment. In particular, some media
attention has focused on a possible link between cellular (cell) phone use and
brain cancer, originally because of a lawsuit that alleged such a link. The
American Cancer Society studied this issue and found no consistent association
between cellular phone use and brain cancer.
63

Social Issues
• The bottom line is that cellular telephones are a relatively new technology, and
we do not yet have full information on possible health effects. There is no
evidence at present that they cause brain cancer, but other studies are looking
at other potential health hazards. Stay tuned.
• Irritation and public nuisance are also a concern. With the increased use of
cellular phones, for example, it is virtually impossible to find a quiet moment.
Cellular phones ring everywhere at any moment – classrooms, meetings, quiet
dinners, weddings, and funerals.
• Due to the increased number of accidents caused by drivers who were talking
on their cellular phones, use of cellular phones while driving has been
prohibited in many countries. 64

Business Issues
• From a business point of view, the major hurdle is a good business case for m-
business. There have to be compelling business reasons for adopting mobile
communications at the enterprise level. The two important questions are:
• What can the customer do that could not be done before?
• What can a business do that it could not do before?
• These two questions go to the heart of the matter. Of course, other questions
need to be asked for developing a good business case: can a business make
money by using this model; who are the customers and how will they benefit
from this product or service; what exactly is the problem that is being solved;
and can the end-users adopt and use this service? Variants of these questions
need to be asked for new initiatives. 65

Technology Issues
• Wireless systems, although improving steadily, encounter several technical
barriers that deter the adoption of wireless technologies. For example, lack of
security solutions at the enterprise level is a major concern.
• In addition, there are diverse standards for mobile computing applications,
mobile computing platforms, and wireless networks that hinder adoption.
• The multitude of mobile devices with different form factors and capabilities, and
slow and error prone networks also do not help the cause of rapid adoption. In
particular, it is difficult for wireless networks to compete with the data rates of
fiber optic networks, especially if two sites can be connected easily with a fiber
cable.
66

Mobile Business, Mobile Government and Mobile Life:
An Evolution
67

m-Business: An Evolution
• A great deal of activity in mobile computing and wireless communications at
present falls under the umbrella of m-business.
• Simply stated, m-business (mobile business) is conducting business by exploiting
the mobile devices and wireless networking. m-Business goes beyond e-
business to take advantage of the wide range of mobile, in many cases
handheld, devices that are connected through wireless networks. Thus:
m-Business = e-Business + Wireless Networks + Mobile Devices
• The following figure shows one view that casts e-business evolution into four
broad stages – the final stage is m-business.
68

• Stages of Evolution
• Stage 1: Basic Websites. This stage became popular in the mid 1990s and is still
the foundation of many corporate websites. The basic idea is to use the
websites to display/advertise company products. All other company operations
are largely unaffected. For example, the customers have to separately order the
products that they select by browsing through company websites.
70

• Stage 2: Basic e-Commerce. In this stage, the consumers could select the
products through the Internet and then also buy them from a seller. This stage
mainly concentrates on C2B (consumer-to-business) operations where the
service is not only advertised but can also be purchased over the Internet by the
consumers.
71

• Stage 3: e-Business. This stage goes beyond the basic e-commerce sites by
running the entire business through Internet technologies. In this stage, Internet
and Web technologies take a central role in gluing services across multiple
organizational units spanning different organizations. It adds B2B (business-to-
business) interactions to C2B as encountered in the previous two stages. The
B2B interactions, although hidden from the users, take place directly between
business partners. This stage, popular at the turn of the 21st century, is at the
core of contemporary e-business activities like online shopping, trading
between business partners, and integration of business processes across
organizational boundaries (e.g., workflows across organizations through IT).
• An example is Amazon.com – when you order a book from Amazon.com, many
other suppliers may be involved in this transaction.
72

• Stage 4: Next-Generation Enterprises (Mobile Businesses). This stage goes
beyond stage 3 to add mobility, intermediaries (trading hubs, emarkets) and
real-time business monitoring and control.
• In next-generation enterprises (NGEs), also known as “real-time enterprises,”
the interactions between business activities within an enterprise are conducted,
monitored, and controlled electronically and through mobile devices.
• The Internet-based IT infrastructure becomes the primary source of company
business in this model. In fact, NGEs rely almost exclusively on the Internet-
based IT infrastructure to conduct business, and often result in restructuring
and transformation of the industry.
73

Mobile Government (m-Government)
• m-Government, a subset of e-government, is the use of mobile computing and
wireless communication technologies (ICTs) to improve the activities of public
sector organizations.
• The goal of m-government is to make public information and government
services available “anytime, anywhere” to citizens and officials.
• m-Government is not a fundamentally new idea because wireless technology
has always been an important part of law enforcement. The difference is that
today the law enforcement officers can use a laptop wirelessly connected to the
Internet instead of the old two-way radios.
74

• m-Government activities also allow health and safety inspectors to file their
reports from the field in real time using a Pocket PC or handheld terminals.
• An area of considerable growth is to offer several government services to
citizens through the Internet and government networks via mobile devices.
Users can either “pull” the information through the mobile devices by issuing
queries, or have some information sent (“pushed”) to their mobile devices.
• Examples of m-government services are listed below:
75

• C2G (Citizen-to-Government) and G2C m-communications. Governments
recognize that the public has access to mobile devices. Thus these devices are
being used to improve the communications between the government and the
general public.
• For example, once a time, the Hong Kong government sent a text message to 6
million mobile phones to warn against rumours and explain government plans.
The citizens can also send messages to government officials.
76

• m-Transactions: Mobile devices can also be used to make payments (e.g., taxes,
fines) and other transactional services.
• For example, Norway has introduced a mobile tax collecting system. Taxpayers
who have no changes to make to the tax form they receive, can now simply
send a text message with a code word, their identity number and a pin code
instead of returning the form by mail.
77

• m-Voting and m-Administration. Although somewhat controversial, several
experiments in UK have explored voting via mobile phones to get the public
more involved in political decision-making.
• m-Administration is concerned with improving the operations and
communications between the government units (G2G).
• Many law enforcement agencies, for example, use wireless networks to
communicate with other agencies on a regular basis. Another potential area is
government-to-employee (G2E) information, where government employees can
be notified or access information via a mobile device.
78

Mobile life
• This includes social contacts, entertainment, health, sports, etc. Mobile devices
and wireless networks are playing an important role in these areas.
• For example, the current handsets can go beyond the now-familiar web access
and email exchange applications. These devices can take and send/receive
pictures, play audio/video clips, participate in chats, support voice dial (you
speak, the device dials), forward calls, and offer conference calls between 4 to 5
people.
• These capabilities can be used in different aspects of our life – the mobile life.
79

Overview of Wireless Networks
80

The unique features of the wireless networks are:
• The bandwidths, and consequently data rates, of communication channels are
restricted by government regulations. The government policies allow only a few
frequency ranges for wireless communications.
• The communication channel between senders/receivers is often impaired by
noise, interference and weather fluctuations.
• The senders and receivers of information are not physically connected to a
network. Thus the location of a sender/receiver is unknown prior to start of
communication and can change during the conversation.
81

A Classification of Wireless Networks
• Wireless LANs (WLANs)
• Wireless metropolitan area networks (WMANs)
• Wireless WANs (WWANs)
82

A Classification of Wireless Networks
83

Overview of Wireless Networks - WLANs
Wireless LANs: IEEE802.11
• Wireless LANs allow workstations in a building to communicate with each other
without having to be connected to physical cables. This is a major benefit
because LAN wiring can be the most expensive component of a LAN.
• At the time of this writing, wireless LANs have several limitations such as short
distances, lack of wireless adapter cards for PCs and workstations, limited
connectivity to other LANs, and relatively low speeds.
84

• Currently available wireless LANs use one of three signal types to transmit data:
• infrared
• spread spectrum
• narrowband microwave.
85

• Infrared signals behave like ordinary light (they cannot penetrate sold objects).
Thus infrared wireless LANs are limited to data transmission to line of sight.
• Infrared technology is simple and well proven (it is used commonly in remote
controls for VCRs and TVs).
• In addition, infrared signals are not regulated by the Federal Communications
Commission (FCC).
86

• Spread spectrum is most widely used in wireless LANs. These LANs transmit in
the industrial, scientific, and medical bands designated by the FCC.
• Fcc: federal communication committee
• These bands are not licensed but are regulated by the FCC to prevent
interference.
• This technology was developed for military and intelligence operations.
87

• Wireless LANs based on narrowband microwave technology use the 18.82-to-
18.87 GHz and 19.6-to-19.21 GHz frequency ranges.
• These frequency ranges are licensed by the FCC, which means that a vendor
must be approved by the agency to use these frequency ranges. Many wireless
LAN vendors consider this to be a restriction.
• A sample configuration is given in the next slide.
88

89

Wireless LANs: Wireless Personal Area Networks (WPANs), Bluetooth and UWB
• Wireless Personal Area Networks (WPANs) are short-range (10 meter or less)
radio networks for personal, home, and other special uses.
• Within the WPAN family, several specifications such as Bluetooth, wireless
sensor networks, and UWB (Ultra Wideband) have emerged.
90

• Bluetooth is a wireless cable replacement standard that provides a 1 Mbps data
rate over 10 meters or less.
• It typically consists of a group of linked devices, such as a computer wirelessly
• connecting to a set of peripherals, known as a “piconet.”
• Multiple piconets can be formed to provide wider coverage. Due to its relatively
low data rates and very short distances, Bluetooth is being used in home
appliances, “Bluetooth-enabled” cars, and other such applications. A sample
configuration is given in the next slide. 91

92

• UWB (Ultra Wideband) is a relatively new technology and is stronger than the
other short-range wireless systems (such as Bluetooth) because of its simpler
device designs, lower power consumption and higher data rates.
• Another player in the short-range radios is the wireless sensor networks
(WSNs) that are formed between small, low-powered sensor devices mainly for
monitoring and data collection purposes.
• Yet another player in short-range wireless was primarily aimed at the needs of
the small office and home office (SOHO) networks.
93

Overview of Wireless Networks - WMANs
Wireless Metropolitan Area Networks (WMANs) - The Wireless Local Loop(WLL)
• Wireless metropolitan area networks (WMANs) are the wireless local loops
(WLLs) that are gaining popularity with long distance telephone companies.
WLLs allow long distance carriers to bypass the existing wired local loops owned
by local phone carriers.
• The following figure shows a sample configuration in which a local wired loop
has been replaced with a wireless local loop.
94

95

• WLLs are quick and cost-effective for quick setup of local phone services.
Imagine laying millions of miles of copper cables to set up a local wired loop.
• Several technologies exist for WLLs. Examples are wireless ATM and LMDS (Local
Multipoint Distribution Systems).
• WLLs are examples of wireless metropolitan area networks and offer broadband
wireless data rates between 10 to 50 Mbps.
96

• A relatively new entrant in the WLL market is Free Space Optics (FSO), which
uses laser beams to deliver extremely high data rates (around 1 Gbps) over a
few kilometers.
• FSO is gaining popularity because of its high security – it is difficult to intercept
laser beams.
• In the last mile, wireless local loop technologies are providing strong
competition to the wired local loops based on copper or fiber optic networks.
• Wireless solutions have the advantage that they can be installed quickly and less
expensively.
97

The Wireless Wide Area Networks – Cellular Networks
• Cellular telephones were introduced in the mid 1980s. These technologies are
enjoying widespread public approval with a rapidly increasing demand.
• To meet this demand, mobile communications technologies are emerging with
digital speech transmission and the ability to integrate cordless systems into
other networks.
• In the meantime, researchers are developing the next generation of
technologies for the next century.
98

99

• The cellular network is comprised of many “cells” that typically cover 10 to 25
miles in area. The users communicate within a cell through wireless
communications.
• A base transceiver station (BTS) is used by the mobile units in each cell by using
wireless communication. One BTS is assigned to each cell.
• Regular cable communication channels are used to connect the BTSs to the
mobile telephone switching office (MTSO). The MTSO determines the
destination of the call received from a BTS and routes it to a proper destination,
either by sending it to another BTS or to a regular telephone network.
• Keep in mind that the communications is wireless within a cell only. The bulk of
cell-to-cell communication is carried through regular telephone lines.
100

• Two issues are of fundamental importance in this conceptual model:
• Cell sizes. The sizes of the cells can be small or large. In some cases, such as
cordless networks, the cell sizes are only a few feet. But in cellular networks, the
cell sizes can be many miles.
• Location (“Roaming”) support. In some cases, the user is only covered for his
“home cell”; in others, the user can roam between cells and still be covered
adequately.
101

• It is good at this point to differentiate between cordless and cellular phones.
• In a cordless network, such as the cordless phone in your home, each telephone
handset is the base station. You cannot go far from the handset (perhaps not more
than 100 feet) if you are using the cordless phone. Cordless networks have smaller cell
sizes and have no roaming support.
• Cordless communication basically operates on the same principle as the cellular
systems; however, cordless systems operate at lower power (suitable for light
telephone devices), so the cell sizes are smaller (usually within a building as compared
to several miles).
• Basically, a cordless system has many more cells that can be accessed by weaker
cellular devices and does not support roaming services. Due to their general use, we
will concentrate more on the cellular networks.
102

• The common features of the cellular and cordless PCS networks are:
• The senders and receivers of information are not physically connected to a
network. Thus the location of a sender/receiver is unknown prior to start of
communication and can change during the conversation.
• The communication channel between senders/receivers is often impaired by
noise, interference and weather fluctuations.
• The bandwidths, and consequently data rates, of communication channels are
restricted by government regulations. The government policies allow only a few
frequency ranges for wireless communications.
103

Evolution of Cellular Networks – The 5G Networks
• 1G: First-generation wireless cellular: These systems, introduced in the early
1980s, use analog transmission, and are primarily intended for speech. It
doesn’t provide roaming support.
• 2G: Second-generation wireless cellular: Introduced in the late 1980s, these
systems use digital transmission and are also intended primarily for speech.
However, they do support low bit-rate data transmissions. The high-tier 2G
systems (2.xG) use GSM & GPRS, and the low tier systems are intended for low-
cost, low-power, low-mobility. These systems, most prevalent at present,
operate at 9.6 Kbps.
104

• 2.5G: Systems are essentially 2G systems that have evolved to medium-rate
(around 100 Kbps) data. As part of the 2.5G initiative, GSM is being extended by
the General Packet Radio Service (GPRS) to support data rates of 112 kilobits
per second.
• 3G: systems are based on packet-switching systems instead of the older circuit-
switching systems used in 2G. The users only pay for the amount of data that
they retrieve. The most popular radio technology in 3G is Wideband CDMA
(collision detect multiple access). This is similar to local area network
technologies such as Ethernet.
105

• 4G: In 2009 and 2010, the term “4G” became associated with mobile
broadband technologies deployed at the time, such as HSPA+ and WiMAX
(Worldwide Interoperability for Microwave Access). Today, 4G usually refers to
HSPA+ or LTE. The vision of 4G is “any-time, any-where and any-content”
• NB: Although the industry is preparing for 5G, LTE capabilities will continue to
improve in LTE-Advanced through the rest of the decade. Many of these
enhancements will come through incremental network investments. Many of
the features planned for 5G may in fact be implemented as LTE-Advanced
extensions prior to full 5G availability.
106

• 5G: 5G groups researching next-generation wireless architecture and
requirements include, among others, the International Telecommunication
Union (ITU), and the 5G Infrastructure Public-Private-Partnership (5G PPP), the
METIS Consortium (Mobile and wireless communications Enablers for the
Twenty-twenty Information Society), and Next Generation Mobile Networks
(NGMN). Wireless technology has progressed to the extent that significant new
capabilities are inevitable, making 5G a possible alternative to wireline
broadband for many subscribers.
107

Evolution of Cellular Networks – From 1G to 5G Networks
108

Satellite Communication Systems
• A satellite is essentially a micro-wave repeater in the sky which receives signals
from transmitting stations on earth and relays these signals back to the
receiving stations on the earth (see the following figure).
• A satellite system consists of the following components:
• Earth Stations – antenna systems on or near the earth
• Uplink – transmission from an earth station to a satellite
• Downlink – transmission from a satellite to an earth station (different from
uplink, typically faster, can be broad)
• Transponder – electronics in the satellite that convert/amplify uplink signals to
downlink signals. There are typically 16 to 20 transponders per satellite, each
with 36-50 MHz BW (bandwidth).
109

110

• A satellite covers a certain area – the higher the satellite, the more area it can
cover. The coverage area of a satellite is called the satellite’s footprint. Only
receiving stations within this footprint can receive the satellite’s signals.
• The oldest example of satellites is the Geosynchronous (GEO) satellites that are
in wide use providing international and long distance telephone services (to
stationary users) and broadcasting services. GEO satellites are placed in the
earth orbit at 22,300 miles – an area called the Clark Belt, after the famous
science-fiction writer who first envisioned satellites in 1945.
111

• Once placed in the Clark Belt, the satellite rotates at the same speed as the
earth’s rotations so the satellite does not appear to move (this is called
geosynchronization).
• Thus the sending and receiving dishes can stay pointed to the satellite without
any readjustments. GEO satellites can provide high communications capacity
and can support several thousand voice channels. However, each satellite
message encounters a 0.25-second delay because of the distance a message has
to travel between a sender and a receiver.
112

• In a satellite communication system, the transmission cost is independent of the
distance between the sender and receiver (two stations 100 miles apart or 1000
miles apart still have to travel thousands of miles to and from the satellite).
• Because of this, satellite communication systems are used to broadcast (i.e.,
send) a message to several receivers simultaneously.
113

Wireless Communication Algorithms
114

• Wireless networks pose many algorithmic challenges:
1. Wireless signal propagation and interference models are very complex.
• Hard to use in rigorous algorithmic research
• Further complicated by emerging technologies like MIMO.
• Models for the dynamics and mobility induces new challenges.
• Mobility models cannot be easily defined in mathematics and yet not well-understood.
• Standard complexity measurements like time and space are not sufficient for wireless
communication algorithms.
• Energy efficiency and consumption is critical in wireless networks and cannot be neglected.
115

• Fortunately, many wireless communication algorithms are proposed by various
research communities. But, most of them have only been studied and analyzed
using simulations(OPNET, NS2, NS3 etc.) or by simple models (Random walk,
Random Wake-up etc.).
• We cannot use many of these algorithms in practice. Because simulation results
may not be same as real-time results.
116

Multiple-Input Multiple-Output (MIMO) Technology
• Multiple-Input Multiple-Output (MIMO) technology is a wireless technology
that uses multiple transmitters and receivers to transfer more data at the same
time.
• MIMO technology takes advantage of a radio-wave phenomenon called
multipath where transmitted information bounces off walls, ceilings, and other
objects, reaching the receiving antenna multiple times via different angles and
at slightly different times.
• MIMO technology leverages multipath behavior by using multiple, “smart”
transmitters and receivers with an added “spatial” dimension to dramatically
increase performance and range. MIMO allows multiple antennas to send and
receive multiple spatial streams at the same time. 117

MIMO Technology - Basics
• As a result of the use of multiple antennas, MIMO wireless technology is able to
considerably increase the capacity of a given channel. By increasing the number
of receive and transmit antennas it is possible to linearly increase the
throughput of the channel with every pair of antennas added to the system.
• This makes MIMO wireless technology one of the most important wireless
techniques to be employed in recent years. As spectral bandwidth is becoming
an ever more valuable commodity for radio communications systems,
techniques are needed to use the available bandwidth more effectively. MIMO
wireless technology is one of these techniques.
118

MIMO Technology - SISO
• The simplest form of radio link can be defined in MIMO terms as SISO – Single
Input Single Output. This is effectively a standard radio channel – this
transmitter operates with one antenna as does the receiver. There is no
diversity and no additional processing required.
119

MIMO Technology - SISO
• The advantage of a SISO system is its simplicity. SISO requires no processing in
terms of the various forms of diversity that may be used.
• However the SISO channel is limited in its performance as interference and
fading will impact the system more than a MIMO system using some form of
diversity.
120

MIMO Technology - SIMO
• The SIMO or Single Input Multiple Output version of MIMO occurs where the
transmitter has a single antenna and the receiver has multiple antennas. This is
also known as receive diversity.
• It is often used to enable a receiver system that receives signals from a number
of independent sources to combat the effects of fading. It has been used for
many years with short wave listening / receiving stations to combat the effects
of fading and interference.
121

• SIMO has the advantage that it is relatively easy to implement although it does
have some disadvantages in that the processing is required in the receiver.
• The use of SIMO may be quite acceptable in many applications, but where the
receiver is located in a mobile device such as a cell phone handset, the levels of
processing may be limited by size, cost and battery drain.
• There are two forms of SIMO that can be used:
• Switched diversity SIMO: This form of SIMO looks for the strongest signal and
switches to that antenna.
• Maximum ratio combining SIMO: This form of SIMO takes both signals and sums
them to give the a combination. In this way, the signals from both antennas
contribute to the overall signal.
122

• Switched diversity SIMO: This form of SIMO looks for the strongest signal and
switches to that antenna.
123

124

• Maximum ratio combining SIMO: This form of SIMO takes both signals and sums
them to give the a combination. In this way, the signals from both antennas
contribute to the overall signal.
125

MIMO Technology - MISO
• Multiple Input Single Output (MISO) is also termed transmit diversity. In this
case, the same data is transmitted redundantly from the multiple transmitter
antennas. The receiver is then able to receive the optimum signal which it can
then use to receive extract the required data.
126

MIMO Technology - MISO
• The advantage of using MISO is that the multiple antennas and the redundancy
coding / processing is moved from the receiver to the transmitter. In instances
such as cellphone, this can be a significant advantage in terms of space for the
antennas and reducing the level of processing required in the receiver for the
redundancy coding. This has a positive impact on size, cost and battery life as
the lower level of processing requires less battery consumption.
127

MIMO Technology - MIMO
• MIMO is effectively a radio antenna technology as it uses multiple antennas at
the transmitter and receiver to enable a variety of signal paths to carry the data,
choosing separate paths for each antenna to enable multiple signal paths to be
used.
128

• One of the core ideas behind MIMO wireless systems space-time signal
processing in which time is complemented with the spatial dimension inherent
in the use of multiple spatially distributed antennas, i.e. the use of multiple
antennas located at different points.
• Accordingly MIMO wireless systems can be viewed as a logical extension to the
smart antennas that have been used for many years to improve wireless.
• It is found between a transmitter and a receiver, the signal can take many paths.
• Additionally by moving the antennas even a small distance the paths used will
change. By using MIMO, these additional paths can be used to advantage. They
can be used to provide additional robustness to the radio link by improving the
signal to noise ratio, or by increasing the link data capacity.
129

• The two main formats for MIMO are given below:
• Spatial diversity: Spatial diversity used in this narrower sense often refers to
transmit and receive diversity. These two methodologies are used to provide
improvements in the signal to noise ratio and they are characterised by
improving the reliability of the system with respect to the various forms of
fading.
130

• The two main formats for MIMO are given below:
• Spatial multiplexing : This form of MIMO is used to provide additional data
capacity by utilising the different paths to carry additional traffic, i.e. increasing
the data throughput capability.
131

Benefits of MIMO Technology
• Multiple antenna configurations can be used to overcome the detrimental
effects of multi-path and fading when trying to achieve high data throughput in
limited-bandwidth channels.
• Multiple-input, multiple-output (MIMO) antenna systems are used in modern
wireless standards, including in IEEE 802.11n, and mobile WiMAX systems. The
technique supports enhanced data throughput even under conditions of
interference, multi-path and fading. The demand for higher data rates over
longer distances has been one of the primary motivations behind the
development of MIMO orthogonal- frequency-division-multiplexing (OFDM)
communications systems.
133

Benefits of MIMO Technology
• Superior Data Rates, Range and Reliability
• Systems with multiple antennas at the transmitter and receiver – also referred
to as Multiple Input Multiple Output (MIMO) systems – offer superior data
rates, range and reliability without requiring additional bandwidth or transmit
power. By using several antennas at both the transmitter and receiver, MIMO
systems create multiple independent channels for sending multiple data
streams.
134

COOPERATIVE COMMUNICATION TECHNIQUES IN
WIRELESS NETWORKS
135

Cooperative Communications
• Wireless communications is currently a highly demanded communication
technology that is most functional in terms of mobile access. Since its inception,
it has gone through lots of developmental phases to meet the ever increasing
needs of its wide range of applications.
• The multipath fading, and path loss effects of wireless channels are the biggest
challenges in the history of wireless communications which has induced
considerable research for possible solutions.
• These effects cause random variations of channel quality in time, frequency, and
space that make conventional wireline communication techniques too difficult
to employ in the wireless environment.
136

• Cooperative Communication is a technique which could be employed to
mitigate the effects of channel fading by exploiting diversity gain achieved via
cooperation between nodes and relays. To achieve transmit diversity, a node
would generally require more than one transmitting antenna which is not too
common due to the limits in size and complexity of wireless mobile devices.
• However by sharing antennas with other single-antenna nodes in a multi-user
environment, a virtual multi-antenna array is formed and transmit-diversity is
accomplished. Subsequently, radio coverage is extended without the need to
implement multiple antennas on nodes and increased transmission reliability is
achieved.
137

• The inception of cooperative communication could be attributed to the pioneer
article on the relay channel by Thomas M. Cover and Abbas A. El Gamal back in
1979.
• They modelled a relay channel to include a source node, a relay node and a
destination node, as shown in the following figure.
• Their work was based on the analysis of the capacity of a three-node network
consisting of a source, a relay, and a receiver. The assumption was that all nodes
operate in the same band, therefore the system could be decomposed into a
broadcast channel with respect to the source and a multiple access channel
with respect to the destination.
138

139

Phases of Cooperative Transmissions
• Phase I: A coordination phase
• This is the phase where users exchange their own source data and control messages with
each other and/or the destination.
• Phase II: A cooperation phase
• In this phase, the users cooperatively retransmit their messages to the destination.
140

• A basic cooperation system consists of two users transmitting to a common
destination, as illustrated in the following figure.
• One user acts as the source while the other user serves as the relay and the two
users may interchange their roles as source and relay at different instants in
time.
• In Phase I, the source user broadcasts its data to both the relay and the
destination and in Phase II, the relay forwards the source’s data either by itself
or by cooperating with the source to enhance reception at the destination.
141

142

• The two user cooperation described so far can be readily extended to a large
network by having one user serve as the source and the remaining users serve
as relays at each time instant, as shown in the following figure.
• The relays together form distributed antenna arrays, i.e., arrays whose elements
are not collocated but carried by independent relaying terminals that are able to
achieve spatial diversity and multiplexing gains.
143

• Phase II: A cooperation phase (Single Source, Multiple Relays)
144

• Phase II: A cooperation phase (Multiple Source, Multiple Relays)
145

Application of Cooperative Communications
• The key idea in user-cooperation is that of resource-sharing among multiple
nodes in a network. The reason behind the exploration of user-cooperation is
that the willingness to share power and computation with neighbouring nodes
can lead to savings of overall network resources. The two novel applications are:
1. Wireless Ad-hoc Network
2. Wireless Sensor Networks (WSN)
146

Wireless Ad-hoc Network:
• This is self organizing and autonomous network without any pre-established
infrastructure or centralized controller.
• In this network randomly distributed nodes form a temporarily functional
network that supports seamless leaving or joining of nodes.
• Such networks have been successfully deployed for military communications
and potential civilian applications include commercial and educational use,
disaster management, road vehicle network, etc.
147

Wireless Ad-hoc Network:
148

Wireless Sensor Network:
• Wireless sensor networks (WSNs) have gained worldwide attention in recent
years. The network consist of spatially distributed autonomous sensors to
cooperatively monitor physical or environmental conditions such as
temperature, sound, vibration, pressure, motion or pollutants.
• These sensors are small, with limited CPU processing, computing resources,
memory and power. To combat these limitations, these sensors are equipped
with wireless interfaces which they could use in communicating with one
another and also to form an ad-hoc network cooperatively to send their data to
the base station.
149

Wireless Sensor Network:
150

Communication Model of Cooperative Communications
• Channel Coder: encodes the received packets and forwards them.
• Interleaver: assists in overcoming correlated channel noise such as burst error
or fading. Interleaving helps the correlated noise introduced in the transmission
channel to be statistically independent at the receiver and thus allows better
error correction.
• Modulator: modulates the coded packet symbols.
• Channel: represents the medium, between sender and receiver, through which
the signals are transmitted.
• Demodulator: demodulates the incoming packets and sends them to the
deinterleaver.
• De-interleaver: arranges data back into the original sequence.
• Decoder: decodes the received signal and forwards to the final destination.
151

Communication Model of Cooperative Communications
152

Routing without Network Coding techniques
• An efficient way to address packet loss in wireless networks without network
coding is to use opportunistic routing approaches.
• When a node broadcasts a packet, it is probable that the next-hop does not
receive the packet.
• However, because of the broadcast nature of the wireless medium, and the
diversity among the links, a neighbor of the sender can receive and forward the
packet as the next-hop with high probability.
• In opportunistic routing, there is no specific path from the source to the
destination, and any node that overhears the packet can relay it.
154

• Take the following figure as an example, in which node s wants to send 4
packets to the destination d. The delivery rate of the links are shown beside the
links.
• Assume that each relay node received the packets shown beside the nodes. If
we use traditional shortest path routing, the route from s to d will be fixed.
• Assuming that the chosen route is s→r1 →d, the source node needs to
retransmit the packets p3 and p4.
• On the other hand, if we allow the other nodes that received the packets p3 and
p4 to forward them, the source node will not need to retransmit any packet.
155

156

• The main challenge in opportunistic routing is coordinating the intermediate
nodes. To prevent redundant transmissions, the intermediate nodes need to
send feedback or listen to the other nodes’ transmissions to find out if there is a
neighbor that has received the transmitted packet.
• For this purpose, the intermediate nodes need to be able to overhear each
other, which might not be possible, as shown in the above figure. Network
coding can solve this problem.
157

Network Coding
• Network coding is a technique where relay nodes mix packets using
mathematical operations, which reduces the number of transmitted packets.
• Network coding was first proposed for wired networks to solve the bottleneck
problem and to increase the throughput.
• However, the broadcast nature of wireless networks and the diversity of the
links make network coding more attractive in wireless networks.
• Network coding can be classified as either inter or intra-session.
• Inter-session network coding allows the packets from different sources to be
mixed to solve the bottleneck problem.
• In contrast, intra-session network coding, which can be used to address the
packet loss problem, uses the diversity of the wireless links and mixes packets
from the same sources. 158

Network Coding
• Inter-Session Network Coding.
• The broadcast nature of wireless networks is considered a challenge, as it
creates interference between the links and produces unnecessary multiple
copies of the same packet.
• However, if we allow the intermediate wireless nodes to code the packets, the
broadcast nature becomes an opportunity.
• Consider the example in the figure, where nodes s1 and s2 want to exchange
their own packets, p1 and p2, respectively.
159

Network Coding
• Inter-Session Network Coding.
• Assuming that these nodes are out of range of each other, this communication
incurs four transmissions; two transmissions for sending the packets to the relay
node, and two transmissions for relaying the packets.
• However, the relay node can simply XOR the packets and send the coded packet
p1ꚛp2, which is shown in the figure. The nodes s1 and s2 can retrieve each
others’ packets by XOR-ing p1ꚛp2 with their own packets, p1 and p2, respectively.
• As a result, the number of transmissions has been reduced to three by using
binary network coding.
160

Network Coding – What is XOR operation?
161

Network Coding
• Benefit of Inter-Session Network Coding.
• Inter-session network coding solves the bottleneck problem and reduces the
number of transmissions, by allowing packets from different sessions (sources)
to be coded together.
• By reducing the number of required transmissions, network coding increases
the throughput and decreases the interference between the links in wireless
networks.
162

Network Coding
• Intra-Session Network Coding.
• Another important application of network coding is to provide reliability in
wireless networks. The traditional way to provide reliability for both wired and
wireless networks is to use feedback messages to report the received (or lost)
packets.
• By using feedback messages, the sender node will know which packets need to
be sent again. However, these feedback messages consume bandwidth.
163

Application of network coding
• allowing packets to coded together.
• By reducing the number of required transmissions
• provide reliability in wireless networks.
• feedback messages, the sender node will know which packets need to
be sent again.
164

Network Coding
• Consider the example in the figure; the source node wants to deliver packets p1
and p2 to the node d. consider the reliability is 2/3.
• In intra-session network coding, the source node sends three coded packets,
p1+ p2, p1+ 2p2, and 2p1+ p2, on average, the destination node will receive two
of the three coded packets.
165

Network Coding
• Therefore, the destination nodes will be able to retrieve the packets p1 and p2.
• However, without network coding, we need to use a feedback mechanism or
else the source node needs to transmit each packet twice. As a result,
communication schemes with network coding can provide reliability with a
fewer transmissions than schemes without network coding.
166

Network Coding
• Coding the packets from the same session (source) is called intra-session
network coding, which exploits the diversity of the links.
• In intra-session network coding, the packets from the same source are coded
together (usually linearly), which makes the importance of the packets the
same.
• Therefore, when k packets are coded together, a relay node does not need to
know exactly which packets are received by the destination node; it is thereby
enough to successfully deliver k coded packets out of the transmitted coded
packets.
167

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