1.
DILLA UNIVERSITY
COLLEGE OF ENGINEERING & TECHNOLOGY
School of Computing & Informatics
M. Sc in Computer Science & Networking
By
Chapter-01
Dr. Ananda Kumar K S M.Tech, Ph.D
Associate Professor, School of Comp & Info
Email: anandgdk@du.edu.et
COET, Dilla University 1
Course Number CN6117
Course Title Mobile Computing

2.
Mobile Computing
CHAPTER-01
1. Mobile Networking
2. Applications of wireless networks and
mobile communications
3. Multiple Access Schemes
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3.
1. Mobile Networking
 Mobile networking refers to technology that
can support voice and/or data network
connectivity using wireless, via a radio
transmission solution. The most familiar
application of mobile networking is the mobile
phone.
 Over the last few decades, mobile radio
communications have become ubiquitous
throughout the world.
 People have become accustomed to the
technology through commercial mobile phones.
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4.
Cont..
 The mobile network infrastructure that
enables communications has become a
normal part of urban environment in which
people live.
 There is also great number of other
mobile radio applications essential in the
modern world that are used in navigation,
transportation, machine-to-machine
communications (M2M), robotics, emergency
and low enforcement services, broadcasting,
space exploration, the military and so on.
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5.
Cont..
 Each application was developed on the basis
of specific needs and, in some aspects, the
mobile radio networks for emergency services
and commercial mobile services are different.
 Nonetheless, the underlying principles in
mobile communications, such as radio link design
given performance constraints, separation of
control and traffic channels, mobility support,
principles of the channel allocation in the cell,
radio network management and so on, have lots
in common in many applications.
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6.
Cont..
 Many people will be mobile – already one of the key
characteristics of today’s society.
 Think, for example, of an aircraft with 800 seats.
Modern aircraft already offer limited network access to
passengers, and aircraft of the next generation will offer
easy Internet access.
 In this scenario, a mobile network moving at high
speed above ground with a wireless link will be the only
means of transporting data to and from passengers.
 Think of cars with Internet access and billions of
embedded processors that have to communicate with, for
instance, cameras, mobile phones, CD-players, headsets,
keyboards, intelligent traffic signs and sensors.
 This plethora of devices and applications show the
great importance of mobile communications today.
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7.
Cont..
 Before presenting more applications, the
terms ‘mobile’ and ‘wireless’ as used
throughout this course should be defined.
 There are two different kinds of mobility:
user mobility and device portability.
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8.
User mobility and Device portability
User mobility
 User mobility refers to a user
who has access to the same or
similar telecommunication
services at different places,
i.e., the user can be mobile,
and the services will follow
him or her.
 Examples for mechanisms
supporting user mobility are
simple call-forwarding
solutions known from the
telephone or computer
desktops supporting roaming
(i.e., the desktop looks the
same no matter which
computer a user uses to log
into the network).
Device portability
• With device portability, the
communication device moves
(with or without a user).
• Many mechanisms in the
network and inside the device
have to make sure that
communication is still
possible while the device is
moving.
• A typical example for systems
supporting device portability is
the mobile phone system,
where the system itself hands
the device from one radio
transmitter (also called a base
station) to the next if the
signal becomes too weak
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9.
A communication device can thus exhibit one of the following
characteristics:
 Fixed and wired: This configuration describes the typical
desktop computer in an office. The devices use fixed networks for
performance reasons.
 Mobile and wired: Many of today’s laptops fall into this
category; users carry the laptop from one place to the next,
reconnecting to the company’s network via the telephone network
and a modem.
 Fixed and wireless: This mode is used for installing networks,
e.g., in historical buildings to avoid damage by installing wires, or at
trade shows to ensure fast network setup.
 Mobile and wireless: This is the most interesting case. No cable
restricts the user, who can roam between different wireless
networks. Most technologies discussed in this course deal with this
type of device and the networks supporting them. Today’s most
successful example for this category is GSM with more than 800
million users.
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10.
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Elements of a wireless network
network
infrastructure
10

11.
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wireless hosts
 laptop, smartphone
 run applications
 may be stationary (non-
mobile) or mobile
 wireless does not always
mean mobility
Elements of a wireless network
network
infrastructure
11

12.
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infrastructure mode
 base station connects
mobiles into wired
network
 handoff: mobile changes
base station providing
connection into wired
network
Elements of a wireless network
network
infrastructure
12

13.
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Characteristics of selected wireless links
Indoor
10-30m
Outdoor
50-200m
Mid-range
outdoor
200m – 4 Km
Long-range
outdoor
5Km – 20 Km
.056
.384
1
4
5-11
54
2G: IS-95, CDMA, GSM
2.5G: UMTS/WCDMA, CDMA2000
802.15
802.11b
802.11a,g
3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO
4G: LTWE WIMAX
802.11a,g point-to-point
200 802.11n
Data
rate
(Mbps)
13

14.
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infrastructure mode
 base station connects
mobiles into wired
network
 handoff: mobile changes
base station providing
connection into wired
network
Elements of a wireless network
network
infrastructure
14

15.
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ad hoc mode
 no base stations
 nodes can only
transmit to other
nodes within link
coverage
 nodes organize
themselves into a
network: route
among themselves
Elements of a wireless network
15

16.
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Wireless network taxonomy
single hop multiple hops
infrastructure
(e.g.,APs)
no
infrastructure
host connects to
base station (WiFi,
WiMAX, cellular)
which connects to
larger Internet
no base station, no
connection to larger
Internet (Bluetooth,
ad hoc nets)
host may have to
relay through several
wireless nodes to
connect to larger
Internet: mesh net
no base station, no
connection to larger
Internet. May have to
relay to reach other
a given wireless node
MANET,VANET
16

17.
2. APPLICATIONS OF WIRELESS NETWORKS AND MOBILE
COMMUNICATIONS
a) Vehicles
b) Emergencies
c) Business
d) Replacement of wired networks
e) Infotainment and more
f) Location dependent services
g) Mobile and wireless devices
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18.
a. Vehicles
 Today’s cars already comprise some, but
tomorrow’s cars will comprise many wireless
communication systems and mobility aware
applications.
 Music, news, road conditions, weather
reports, and other broadcast information are
received via digital audio broadcasting (DAB)
with 1.5 Mbit/s.
 For remote areas, satellite communication
can be used, while the current position of the
car is determined via the global positioning
system (GPS).
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19.
b. Emergencies
 Just imagine the possibilities of an ambulance
with a high-quality wireless connection to a
hospital.
 Vital information about injured persons can
be sent to the hospital from the scene of the
accident.
 All the necessary steps for this particular type
of accident can be prepared and specialists can
be consulted for an early diagnosis.
 Wireless networks are the only means of
communication in the case of natural disasters
such as hurricanes or earthquakes.
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20.
c. Business
 A travelling salesman today needs instant
access to the company’s database: to ensure that
files on his or her laptop reflect the current
situation, to enable the company to keep track of
all activities of their travelling employees, to keep
databases consistent etc.
With wireless access, the laptop can be turned
into a true mobile office, but efficient and
powerful synchronization mechanisms are
needed to ensure data consistency.
 Gas stations may offer WLAN hot spots as
well as gas.
 Trains already offer support for wireless
connectivity.
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21.
d. Replacement of wired networks
 In some cases, wireless networks can also be
used to replace wired networks, e.g., remote
sensors, for tradeshows, or in historic buildings.
 Due to economic reasons, it is often
impossible to wire remote sensors for weather
forecasts, earthquake detection, or to provide
environmental information. wireless
connections, e.g., via satellite, can help in this
situation.
 Tradeshows need a highly dynamic
infrastructure, but cabling takes a long time and
frequently proves to be too inflexible.
 Wireless access points in a corner of the
room can represent a solution.
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22.
e. Infotainment and more
 Static information might be loaded via CD-
ROM, DVD, or even at home via the Internet. But
wireless networks can provide up-to-date
information at any appropriate location.
 The travel guide might tell you something
about the history of a building (knowing via GPS,
contact to a local base station, or triangulation
where you are) downloading information about a
concert in the building at the same evening via a
local wireless network.
 Another growing field of wireless network
applications lies in entertainment and games to
enable, e.g., ad-hoc gaming networks as soon as
people meet to play together.
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23.
f. Location dependent services
Several services that might depend on the
actual location can be distinguished:
• Follow-on services
• Location aware services
• Privacy
• Information services
• Support services
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24.
g. Mobile and wireless devices
The following list gives some examples of mobile
and wireless devices graded by increasing
performance (CPU, memory, display, input
devices etc.).
Sensor
Embedded controllers
Pager
Mobile phones
Personal digital assistant
Pocket computer
Notebook/laptop
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25.
3. TYPES OF MOBILE NETWORK BY MULTIPLE-ACCESS SCHEME
 Mobile radio networks can be distinguished
by operation modes, services and applications
and multiple-access schemes.
 A major influence on the development of
commercial radio communication systems is the
scarcity of radio spectrum available for
utilization.
 An apparent objective is to assign the
maximum number of users to an available radio
frequency segment.
 This objective is achieved by using various
multiple-access schemes.
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26.
Cont..
Here, we list the four most common technologies:
a) 1) Frequency division multiple access (FDMA)
b) 2) Time-division multiple access (TDMA)
c) 3) Code division multiple access (CDMA)
d) 4) space division multiple access (SDMA).
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27.
Multiple Access
• Access coordination may be carried out in different domains:
– frequency domain
– time domain
– code domain
– space domain.
• Four main multiple access technologies are used by the
wireless networks:
– frequency division multiple access (FDMA)
– time division multiple access (TDMA)
– code division multiple access (CDMA)
– space division multiple access (SDMA).
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28.
A. Frequency Division Multiple Access
 FDMA is certainly the most conventional method
of multiple access and was the first technique to be
employed in modern wireless application.
 The channel bandwidth is a function of the
services to be provided and of the available
technology and is identified by its center frequency,
known as a carrier.
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29.
Frequency Division Multiple Access (FDMA)
User 1
User 2
User n
…
Time
Frequency
• Separate (unique) carrier frequency per user
• All 1G (first-generation) systems use FDMA
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Basic Structure of a FDMA System
- 1 BS and n MSs - fi’ and fi – for MS #i
MS #1
MS #2
MS #n
BS
f1’
f2’
fn’
f1
f2
fn
…
…
…
Reverse channels
(Uplink)
Forward channels
(Downlink)
30
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31.
FDMA Channel Structure
1 2 3 … n
Frequency
Total bandwidth W = N * Wc
(for reverse channels or for forward channels)
Guard Band Wg
4
Frequency
Protecting
bandwidth
…
f1’ f2’ fn’
…
f1 f2 fn
Reverse channels Forward channels
Subband Wc
31
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32.
b. Time Division Multiple Access
 TDMA is another widely known multiple-
access technique and succeeded FDMA in
modern wireless applications.
 In TDMA, the entire bandwidth is made
available to all signals but on a time-sharing
basis.
 Transmission then occurs within a time
interval known as a (time) slot.
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33.
Time Division Multiple Access (TDMA)
User
1
User
2
User
n
…
Time
Frequency
• Separate (unique) time slot per user
• The same carrier (frequency) split into time slots
• Each frequency efficiently utilized by multiple users
• Most of 2G systems use TDMA
33
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34.
Basic Structure of TDMA
MS #1
MS #2
MS #n
BS
…
…
Reverse channels
(Uplink)
Forward channels
(Downlink)
t
Frequency f ’
#1
…
#1
…
Frame
Slot
…
#1
…
#1
Frame
…
t
Frequency f
Frame Frame
…
t
#2
…
#2
…
…
t
#n
… #n
…
…
#2
…
#2
…
t
…
#n
…
#n
…
t
Slot
34
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35.
TDMA Frame Structure
…
Time
Frequency
#1
#2
#n
#1
#2
#n
… …
#1
#2
#n
Frame Frame
Frame
Head Data
Guard
time
Time slot
Notice Guard time between
Time slots
- Minimize interference due to
propagation delays
35
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36.
c. Code Division Multiple Access
 CDMA is a nonconventional multiple-access technique that
immediately found wide application in modern wireless systems.
 In CDMA, the entire bandwidth is made available
simultaneously to all signals.
 In theory, very little dynamic coordination is required, as
opposed to FDMA and TDMA in which frequency and time
management have a direct impact on performance.
 To accomplish CDMA systems, spread-spectrum techniques are
used.
 In CDMA, signals are discriminated by means of code sequences
or signature sequences.
 Each pair of transmitter-receivers is allotted one code sequence
with which a communication is established.
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37.
Code Division Multiple Access (CDMA)
• Separate (unique) code per user
• Code sequences are orthogonal
=> different users can use same frequency simultaneously (see Fig above)
• Some 2G systems use CDMA / Most of 3G systems use CDMA
User
1
Time
Frequency
User
2
User
n
Code
.
.
.
37
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38.
Structure of a CDMA System (with FDD)
Notes:
1) FDD (frequency division duplexing) since f for all forward channels, and f’ for
all reverse channels
2) Ci = i-the code
3) Ci’ x Cj’ = 0, i.e., Ci’ and Cj’ are orthogonal codes on f’
Ci x Cj = 0, i.e., Ci and Cj are orthogonal codes on f
MS #1
MS #2
MS #n
BS
C1’
C2’
Cn’
C1
C2
Cn
…
…
…
Reverse channels
(Uplink)
Forward channels
(Downlink)
Frequency f ’ Frequency f
38
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39.
d. Space Division Multiple Access
 SDMA is a nonconventional multiple-access technique
that finds application in modern wireless systems mainly in
combination with other multiple-access techniques.
 In SDMA, the entire bandwidth is made available
simultaneously to all signals.
 Signals are discriminated spatially, and the
communication trajectory constitutes the physical
channels.
 The implementation of an SDMA architecture is based
strongly on antennas technology coupled with advanced
digital signal processing.
 The antenna beams must be electronically and
adaptively directed to the user so that.
 The location alone is enough to discriminate the user.
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40.
Space Division Multiple Access (SDMA)
The concept
of SDMA
Beam n Beam 1
Beam 2
Beam 3
Beam i
s(f,t,c) s(f,t,c)
s(f,t,c)
s(f,t,c)
s(f,t,c)
Space divided into spatially separate sectors
Omni-directional
transmission
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41.
Transmission in SDMA
The basic structure of a SDMA system
MS1
MS2
MS3
BS
Beam 1 Beam 2 Beam 3
 Noise and
interference for
each MS and BS is
minimized
 Enhance the quality
of communication
link and increase
overall system
capacity
 Intra-cell channel
reuse can be easily
exploited
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42.
Multiple Access Techniques in use
Multiple Access
Technique
Advanced Mobile Phone System (AMPS) FDMA/FDD
Global System for Mobile (GSM) TDMA/FDD
US Digital Cellular (USDC) TDMA/FDD
Digital European Cordless Telephone (DECT) FDMA/TDD
US Narrowband Spread Spectrum (IS-95) CDMA/FDD
Cellular System
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43.
Comparison of Various Multiple Division Techniques
43
Technique FDMA TDMA CDMA SDMA
Concept
Divide the frequency
band into disjoint
sub-bands
Divide the time into
non-overlapping
time slots
Spread the signal
with orthogonal
codes
Divide the space in to
sectors
Active terminals
All terminals active
on their specified
frequencies
Terminals are active
in their specified
slot on same
frequency
All terminals active
on same frequency
Number of terminals
per beam depends on
FDMA/
TDMA/CDMA
Signal
separation
Filtering in
frequency
Synchronization in
time
Code separation Spatial separation
using smart antennas
Handoff Hard handoff Hard handoff Soft handoff Hard and soft
handoffs
Advantages Simple and robust Flexible Flexible Very simple, increases
system capacity
Disadvantages
Inflexible, available
frequencies are fixed,
requires guard
bands
Requires guard
space,
synchronization
problem
Complex receivers,
requires power
control to avoid
near-far problem
Inflexible, requires
network monitoring to
avoid intra cell
handoffs
Current
applications
Radio, TV and
analog cellular
GSM and PDC 2.5G and 3G Satellite systems, LTE
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44.
References
Reference Text Books:
• J. Schiller, Mobile Communications, Addison
Wesley, 2003.
• Alexander Kukushkin, Introduction to Mobile
Network engineering GSM,3G-WCDMA, LTE
and the Road to 5G, Wiley
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45.
THANK YOU
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