MOBILE COMPUTING (TCS-054)Anurag Malik Associate Professor
Shivanshu Rastogi Assistant Professor
CE & IT Dept. M.I.T Moradabad B.Tech VIII CS / IT UNIT I
Recommended Books:1. 2. 3.
4.
J. Schiller, Mobile Communications, Addison Wesley A. Mehrotra,
GSM System Engineering Asok K. Talukder, Mobile
ComputingTechnology, Applications & Service Creation, TMH Raj
Kamal,Mobile Computing, Oxford University Press1
Mobile Computer A computer which you can take with you all
around. You can do all the things which can be done with a desktop
computer. You should be able to use same software, which you use on
a desktop computer. Mobile computer - How? One possibility is to
have a standalone computer capable of storing large amount of
software and data files, processing power to support the required
applications. Modern day laptop computer are something like this.
Whenever you are static, connect to internet through an access
point and you can do the file transfer, telnet, web browsing etc..
While on the move, connectivity is desired for using software which
require cooperation of at least two machines.2
Mobile Computing
Mobile computing is a generic term describing one's ability to
use technology while moving, as opposed to portable computers,
which are only practical for use while deployed in a stationary
configuration. Using a computing device while in transit. Mobile
computing implies wireless transmission, but wireless transmission
does not necessarily imply mobile computing. Fixed wireless
applications use satellites, radio systems and lasers to transmit
between permanent objects such as buildings and towers.
Mobile computing device Acts as a terminal Have wireless
connectivity to the network Whatever command or application you run
is executed on a remote server. Mobile computing device acts as
remote terminal. Issues in mobile computing networks Nature of
medium Mobility Portability3
Wireless characteristics
Variant Connectivity
Low bandwidth and reliability
Frequent disconnections
predictable or sudden Broadcast medium
Asymmetric Communication Monetarily expensive
Charges per connection or per message/packet
Connectivity is weak, intermittent and expensive4
What is Mobility
Mobility means different things to different people. Some people
are quite happy being able to get around town. Others view the
world in terms of time distance-Obviously, range of motion is an
important aspect of mobility. Another factor in mobility is ease of
access. What might be considered mobile in one context is quite
immobile in another. A more pertinent example of mobility is the
ever decreasing size of cellular telephones. What was once
considered a "mobile phone" had to be transported in a vehicle.
This continuing decrease in size and weight of handsets has greatly
increased the mobility of cellular subscribers. We define mobility
as the ability to send and receive communications anytime anywhere.
Mobility means that both source and destination devices,
applications and people are free of the constraints imposed by
physical location.5
Mobility Characteristics
Location changes location management - cost to locate is added
to communication Heterogeneity in services bandwidth restrictions
and variability Dynamic replication of data data and services
follow users Querying data - location-based responses Security and
authentication System configuration is no longer static6
Two aspects of Mobility
Mobility
User Mobility : a user communicates, anytime, anywhere using any
access technology Device Portability : A device can connect to the
network anytime and anywhere.Wireless X X
Mobile X X
Example Stationary computer Notebook in ahotel Wireless LAN in
buildings Cellular Phone
The demand for mobile communication creates the need for
integration of wireless networks into existing fixed networks:In
the local range: standardization of IEEE 802.11 (Wireless LAN, WLAN
considering existing wired standards like Ethernet) In Wide area
range: e.g. Internetworking of GSM and ISDN IN the Internet
protocols: Mobile IP as enhancement of normal IP7
Portability Characteristics
Resource constraints Mobile computers are resource poor Reduce
program size interpret script languages (Mobile Java?) Computation
and communication load cannot be distributed equally Small screen
sizes Asymmetry between static and mobile computers Battery power
restrictions transmit/receive, disk spinning, display, CPUs, memory
consume power Battery lifetime will see very small increase need
energy efficient hardware (CPUs, memory) and system software
planned disconnections - doze mode Power consumption vs. resource
utilization 8
Mobile Computing Functions
User Mobility: User should be able to move from one physical
location to another location and use the same service. E.g. user
moves from London to New Delhi and uses Internet to access the
corporate application the same way the user uses in home office.
Network Mobility: User should be able to move from one Network to
another network and use the same service. E.g. user moves from
London to New Delhi and uses the same GSM phone to access the
corporate application through WAP. In home Network he uses this
services over GPRS whereas in Delhi he access it over the GSM
Network. Bearer Mobility: User should be able to move from one
bearer to another and use the same service. E.g. user was using a
service though WAP bearer in his home N/W in Bangalore. He moves to
Coimbatore, where WAP is not supported, he switch over to voice or
SMS bearer to access the same application. (switching from BSNL to
Vodafone on roaming)
9
Mobile Computing Functions
Device mobility: User should be able to move from one device to
another and use the same service. E.g. could be sales
representatives using their desktop computer in home office. During
the day while they are on the street they would like to use their
Palmtop to access the application. Session Mobility: A user session
should be able to move from one useragent environment to another.
E..g. could be a user was using his service through a CDMA iX
network. The user entered into the basement to park the car and got
disconnected from the CDMA n/w. User goes to home office and starts
using the desktop. The unfinished session in the CDMA moves from
the mobile device to the desktop computer. Service Mobility: User
should be able to move from one service to another. E.g. a user is
writing a mail. To complete the mail user needs to refer to some
other information. In a desktop PC, user simply opens another
service (browser) and moves between them using the task bar. User
should be able to switch amongst services in small footprint
wireless devices like in the desktop. (In a browser we use HTTP to
open yahoo. COM page and POP3 or SMTP to send & receive mail )
Host Mobility: The user device can be either a client or server.
When it is a server or host, some of the complexities change. In
case of host mobility the mobility of IP needs to be taken care
of.10
WHY WIRELESS NETWORK Advantages Spatial flexibility in radio
reception range Ad hoc networks without former planning No problems
with wiring (e.g. historical buildings, fire protection, esthetics)
Robust against disasters like earthquake, fire and careless users
which remove connectors! Disadvantages Generally very low
transmission rates for higher numbers of users Often proprietary,
more powerful approaches, standards are often restricted
Consideration of lots of national regulations, global regulations
are evolving slowly Restricted frequency range, interferences of
frequencies11
Types of Wireless NetworksCellular Networks Base stations
distributed over the area to be covered Each base station covers a
cell Need of an infrastructure network connecting all base stations
Used for mobile phone networks and data networks like Wireless LAN
Mobile Ad-Hoc Networks (MANETs) Self-configuring network of mobile
nodes Each node serves as client and router No infrastructure (base
stations) necessary, direct connections between any pair of nodes
E.g. Bluetooth Mesh Networks Enhancement of above concepts: Ad-hoc
network with infrastructure Allow a whole mesh of connections
between wireless nodes Increased fault tolerance E.g. used in WiMAX
12
Classification of Wireless Network
13
Wireless Personal Area Network (WPAN)
14
Wireless Local Area Network (WLAN)
15
Wireless Metropolitan Area Network (WMAN)
16
Wireless Wide Area Network (WWAN)
17
Frequencies For Communication
18
19
20
21
22
23
Limitations of Mobile Environmentsy
Limitations of the Wireless Network y heterogeneity of
fragmented networks y frequent disconnections y limited
communication bandwidth Limitations Imposed by Mobility y lack of
mobility awareness by system/applications y route breakages
Limitations of the Mobile Computer y short battery lifetime y
limited capacities24
y
y
Mobile Applications
Vehicles transmission of news, road condition etc ad-hoc network
with near vehicles to prevent accidents Emergencies early
transmission of patient data to the hospital ad-hoc network in case
of earthquakes, cyclones military ... Traveling salesmen direct
access to central customer files consistent databases for all
agents mobile office
25
Mobile Applications
Web access outdoor Internet access intelligent travel guide with
up-to-date location dependent information Location aware services
find services in the local environment, e.g. printer Information
services push: e.g., stock quotes pull: e.g., nearest cash ATM
Disconnected operations mobile agents, e.g., shopping Entertainment
ad-hoc networks for multi user games
26
Mobile Computing ArchitecturePresentation Tier Application Tier
Java Server PagesRMI
Data Tier
Internet ExplorerSOAP
iPlanet Web Server
IBM WebSphere BEA WebLogic JBOSS IIOP iPlanet Jakarta SOAP
Enterprise Java Beans SQL XML Servlets JDBC
XML Data Stores Database
Netscape NavigatorIIOP
Jigsaw
XSLT
Opera
Apache
HTML
LIB WWWXML
Zeus
WML / HDML
Applications & Web Services ZOPE CGI (C. Perl, Python)
Aggregation Service Data Feeds
Java URL ClassHTTP
RPC ZEND PHP
XML
LynxHTTPS
Lotus Domino mail and Documents
JavascriptRoxen XML MS Transaction Server COM Applications
Adapter Pike Equipment MS Exchange MS Commerce Server
WAP Browser
J2MEVoice
Internet Information Server
COM
Legacy Applications
ASP
27
Mobile Computing Architecture
To design a system for mobile computing, we need to keep in mind
that the system will be used through any network, any bearer, any
agent and any device. The three tier architecture is better suited
for an effective networked client/server design It provides
increased performance, flexibility, maintainability, reusability
and scalability while hiding the complexity of distributed
processing from the user. Centralized process logic makes
administration and change management easier by localizing changes
in central place and using it throughout the systems. The
network-centric mobile computing architecture uses a three-tier
architecture. User Interface or Presentation Tier :This layer deals
with user facing device handling and rendering. This tier includes
a user system interface where user services (such as session, text
input, dialog and display management) reside. This is the layer of
agent applications and systems. These applications run on the
client device and offer all the user interfaces. This tier is
responsible for presenting the information to the end user. Humans
generally use visual and audio means to receive the information
from machines (laptop, cell phones, paltops, tablet PC, touch
screen.) The visual presentation will relate to rendering on a
screen which includes Web browsers like Mozila, lynx, Internet
Explorer and Netscape Navigator, WAP browsers.
28
Mobile Computing Architecture Process Management or Application
Tier : This layer is for application programs or process management
where business logic and rules are executed. This layer is capable
of accommodating hundreds of users. In addition to ensure reliable
completion tier controls transactions and asynchrono, queuing to
ensure reliable completion of transactions. It performs the
business logic of processing user input, obtaining data, and making
its presentation decisions. In certain cases, this layer will do
the transcoding of data for appropriate rendering in this layer. It
includes technology like CGIs, Java, JSP, .NET services, PHP or
ColdFusion, deployed in products like Apache, WebSphere, WebLogic,
iPlanet , Pramati, JBOSS or ZEND and database-independent. A few
additional management functions (decisions on rendering, network
management, security, datastore access etc.) need to be performed
which are implemented using different middleware software. A
middleware framework is defined as a layer of software, which sits
in the middle between the OS and the user facing software. The
different types of middleware are: 1. Message-Oriented Middleware
2. Database Middleware 3. Transaction Processing Middleware 4.
Transcoding Middleware 5. Communication Middleware 6. Distributed
Object & components29
Mobile Computing ArchitectureDatabase Management or Data Tier :
This layer is for database access and management. It is used to
store data needed by the application and acts as a repository for
both temporary and permanent data. The data could be stored in any
form of datastore or database (relational, legacy, text). The data
can also be stored in XML format for interoperability with other
system and data sources. JBoss :- A popular open source Java
application server that supports the J2EE 1.3 specifications. Runs
under any J2SE 1.3 or later Java virtual machine. Based on an JMX
core where other pieces of the system are plugged in. Supports
JNDI, Servlet/JSP (Tomcat or Jetty), EJB, JTS/JTA, JCA, JMS. Also
supports Clustering (JavaGroups), Web Services (Axis), and IIOP
integration (JacORB). iPlanet was a product brand that was used
jointly by Sun Microsystems and Netscape Communications Corporation
when delivering software and services as part of a nonexclusive
cross marketing deal. iPlanet Directory Server ,iPlanet Web Server
,iPlanet Web Proxy Server, iPlanet Portal Server , iPlanet Portal
Search,iPlanet Application Server ,iPlanet Messaging Server ,
iPlanet Calendar Server, iPlanet Meta Directory, iPlanet Instant
Messaging Server . The Apache HTTP Server, commonly referred to
simply as Apache a web server notable for playing a key role in the
initial growth of the World Wide Web. Apache was the first viable
alternative to the Netscape Communications Corporation web server
(currently known as Sun Java System Web Server), and has since
evolved to rival other Unix-based web servers in terms of
functionality and performance. The majority of all web servers
using Apache are Linux web servers.
30
Mobile Computing ArchitectureZope is a free and open-source,
object-oriented web application server written in the Python
programming language. Zope stands for "Z Object Publishing
Environment." It can be almost fully managed with a web-based user
interface. Zope publishes on the web Python objects that are
typically persisted in an object database, ZODB. Basic object
types, such as documents, images, and page templates, are available
for the user to create and manage through the web. Specialized
object types, such as wikis, blogs, and photo galleries, are
available as third-party add-ons (called products), and there is a
thriving community of small businesses creating custom web
applications as Zope products. Zend Framework is a simple,
straightforward, open-source software framework for PHP 5 designed
to eliminate the tedious details of coding and let you focus on the
big picture. Its strength is in its highly-modular MVC design,
making your code more reusable and easier to maintain. The Roxen
WebServer, from the Swedish company Roxen Internet Software, is a
viable alternative for those who find Apache inappropriate for
their needs. Although Apache dominates the internet web server
market, it has some weak points: it lacks a built-in SQL database
backend, flexible administration tools and easy SSL certificate
management. All of these features can be found, however, in the
Roxen WebServer. In fact, Roxen includes so many additional
features that it seems more like an application server than an
ordinary web server. PHP is a scripting language originally
designed for producing dynamic web pages. It has evolved to include
a command line interface capability and can be used in standalone
graphical applications. Jakarta Struts is incredibly useful in
helping you create excellent Web applications. When you use Jakarta
Struts, your applications should work more effectively and have
fewer bugs. Just as important (because your time is important),
Struts should save you hours and hours of programming and
debugging.
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Mobile Computing ArchitectureWebLogic server is based on Java 2
Platform, Enterprise Edition (J2EE), the standard platform used to
create Java-based multi-tier enterprise applications. J2EE platform
technologies were developed through the efforts of BEA Systems and
other vendors in collaboration with the main developer, Sun
Microsystems. Because J2EE applications are standardized modules,
WebLogic can automate many system-level tasks that would otherwise
have demanded programming time. Pike is an outliner that's been
custom-fitted to plug into Manila sites. You can create and edit
stories with Pike. You can use it to edit your home page. And you
can also use it to edit the myriad of templates that define how a
Manila site is rendered. It's both a writing and design tool. Pike
is as easy to use as a web browser but has the common features that
web writers and designers need. WebSphere is a set of Java-based
tools from IBM that allows customers to create and manage
sophisticated business Web sites. The central WebSphere tool is the
WebSphere Application Server (WAS), an application server that a
customer can use to connect Web site users with Java applications
or servlets. Servlets are Java programs that run on the server
rather than on the user's computer as Java applets do. Servlets can
be developed to replace traditional common gateway interface (CGI)
scripts.
32
Mobile Computing Architecture
HTTPS (HTTP over SSL or HTTP Secure) is the use of Secure Socket
Layer (SSL) or Transport Layer Security (TLS) as a sublayer under
regular HTTP application layering. HTTPS encrypts and decrypts user
page requests as well as the pages that are returned by the Web
server. The use of HTTPS protects against eavesdropping and
man-in-the-middle attacks. HTTPS was developed by Netscape. HTTPS
and SSL support the use of X.509 digital certificates from the
server so that, if necessary, a user can authenticate the sender.
Unless a different port is specified, HTTPS uses port 443 instead
of HTTP port 80 in its interactions with the lower layer, TCP/IP.
HTTPS encrypts and decrypts the page requests and page information
between the client browser and the web server using a secure Socket
Layer (SSL). IIOP (Internet Inter-ORB Protocol) is a protocol that
makes it possible for distributed programs written in different
programming languages to communicate over the Internet. SOAP
(Simple Object Access Protocol) is a way for a program running in
one kind of operating system (such as Windows 2000) to communicate
with a progam in the same or another kind of an operating system
(such as Linux) by using the World Wide Web's Hypertext Transfer
Protocol (HTTP) and its Extensible Markup Language (XML) as the
mechanisms for information exchange. Since Web protocols are
installed and available for use by all major operating system
platforms, HTTP and XML provide an already at-hand solution to the
problem of how programs running under different operating systems
in a network can communicate with each other. SOAP specifies
exactly how to encode an HTTP header and an XML file so that a
program in one computer can call a program in another computer and
pass it information. It also specifies how the called program can
return a response. The Extensible Markup Language (XML) is a
general-purpose specification for creating custom markup languages.
It is classified as an extensible language, because it allows the
user to define the mark-up elements. XML's purpose is to aid
information systems in sharing structured data, especially via the
Internet ,to encode documents, and to serialize data; in the last
context, it compares with text-based serialization languages such
as JSON and YAML HTTP, short for HyperText Transfer Protocol, is
the protocol for transferring hypertext documents that makes the
World Wide Web possible.
33
Mobile Computing Architecture
Remote Method Invocation (RMI) is the process of activating a
method on a remotely running object. RMI offers location
transparency in the sense that it gives the feel a method is
executed on a locally running object. Java RMI (Remote Mathod
Invocation) provides a mechanism for supporting distributed
computing. remote procedure call, a type of protocol that allows a
program on one computer to execute a program on a server computer.
Using RPC, a system developer need not develop specific procedures
for the server. The client program sends a message to the server
with appropriate arguments and the server returns a message
containing the results of the program executed. Microsoft COM
(Component Object Model) technology in the Microsoft Windows-family
of Operating Systems enables software components to communicate.
COM is used by developers to create re-usable software components,
link components together to build applications, and take advantage
of Windows services. The family of COM technologies includes COM+,
Distributed COM (DCOM) and ActiveX Controls. Java database
connectivity (JDBC) is the JavaSoft specification of a standard
application programming interface (API) that allows Java programs
to access database management systems. The JDBC API consists of a
set of interfaces and classes written in the Java programming
language. Using these standard interfaces and classes, programmers
can write applications that connect to databases, send queries
written in structured query language (SQL), and process the
results. SQL (Structured Query Language) is a database computer
language designed for the retrieval and management of data in
relational database management systems (RDBMS), database schema
creation and modification, and database object access control
management. SQL is a programming language for querying and
modifying data and managing databases. SQL was standardized first
by the ANSI and (later) by the ISO
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Typical Application : Road traffic
35
World Wide Web and Mobility
HTTP/ HTML have not been designed for mobile
applications/devices HTTP Characteristicsstateless, connection
oriented overheads big protocol headers, uncompressed content
transfer
HTML Characteristicsdesigned for computers with high
performance, color high-resolution display, mouse, hard disk
typically, web pages optimized for design, not for communication;
ignore endsystem characteristics
Adaptations for Mobile WWWEnhanced browsers and/or servers
Client proxy: pre-fetching, caching, off-line use Network proxy:
adaptive content transformation for connections Client and network
proxy New protocols/languages: WAP/WML
36
Early Wireless Communication
37
History Of Wireless Communication 1896 - Guglielmo Marconi First
demonstration of wireless telegraphy (digital!) Long wave
transmission, high transmission power necessary (>200kw) 1907 -
Commercial transatlantic connections Huge base stations (30 100m
high antennas) 1915 - Wireless voice transmission New York - San
Francisco 1920 - Discovery of short waves by Marconi Reflection at
the ionosphere Smaller sender and receiver, possible due to the
invention of the vacuum tube (1906, Lee DeForest and Robert von
Lieben) 1926 - Train-phone on the line Hamburg - Berlin Wires
parallel to the railroad track
38
History Of Wireless Communication 1928 - Many TV broadcast
trials (across Atlantic, color TV, TV news) 1933 - Frequency
modulation (E. H. Armstrong) 1958 - A-Netz in Germany Analogue,
160MHz, connection setup only from the mobile station, no Handover,
80% coverage, 1971 11000 customers 1972 - B-Netz in Germany
Analogue, 160MHz, connection setup from the fixed network too (but
location of the mobile station has to be known) available also in
Austria, Netherlands and Luxembourg, 1979 13000 customers in
Germany 1979 - NMT at 450MHz (Scandinavian countries) 1982 - Start
of GSM-specification Goal: pan-European digital mobile phone system
with roaming 1983 - Start of the American AMPS (Advanced Mobile
Phone System, analog) 1984 - CT-1 standard (Europe) for cordless
telephones39
History Of Wireless Communication 1986 - C-Netz in Germany
Analog voice transmission, 450MHz, hand-over possible, digital
signaling, automatic location of mobile device Was in use until
2000, services: FAX, modem, X.25, e-mail, 98% coverage 1991 -
Specification of DECT Digital European Cordless Telephone (today:
Digital Enhanced Cordless Telecommunications) 1880-1900MHz,
~100-500m range, 120 duplex channels, 1.2Mbit/s data transmission,
voice encryption, authentication, up to several 10000 user/km2,
used in more than 50 countries 1992 - Start of GSM In Germany as D1
and D2, fully digital, 900MHz, 124 channels Automatic location,
hand-over, cellular Roaming in Europe - now worldwide in more than
170 countries Services: data with 9.6kbit/s, FAX, voice, ...
40
History Of Wireless Communication 1994 - E-Netz in Germany GSM
with 1800MHz, smaller cells As E-plus in Germany (1997 98% coverage
of the population) 1996 - HiperLAN (High Performance Radio Local
Area Network) ETSI, standardization of type 1: 5.15 - 5.30GHz,
23.5Mbit/s Recommendations for type 2 and 3 (both 5GHz) and 4
(17GHz) as wireless ATM-networks (up to 155Mbit/s) 1997 - Wireless
LAN IEEE 802.11 IEEE standard, 2.4GHz and infrared, 2Mbit/s Already
many (proprietary) products available in the beginning 1998 -
Specification of GSM successors UMTS (Universal Mobile
Telecommunication System) as European proposals for IMT-2000
Iridium: 66 satellites (+6 spare), 1.6GHz to the mobile phone41
History Of Wireless Communication1999 - Standardization of
additional wireless LANs IEEE standard 802.11b, 2.4-2.5GHz,
11Mbit/s Bluetooth for piconets, 2.4Ghz, 0 D4.c4 4 d4 D2.c2 2
d2
99
Idea of Communication with Coding TechniqueChip Sequence
C1[+1, +1, +1 , +1]
C2[+1, -1, +1 , -1]
C3[+1, +1, -1 , -1]
C4[+1, -1, -1 , +1]
Bit 0 1 -1[ -1, -1, -1 , -1] [-1, +1, -1 , +1]
Bit 0 2 -1
[ -1 , -1, -3 , +1 ] Communication Channel[0 , 0 , 0 , 0 ] [+1 ,
-1 , -1 , +1]
3 Silent
0
4
+1 Bit 1
Data Representation in CDMA Data Bit 0 -1 Data Bit 1 +1 Silent
-> 0100
CDMA Coding scheme
Each user is associated with a different code, say v. If the
data to be transmitted is a digital zero, then the actual bits
transmitted will be v, and if the data to be transmitted is a
digital one, then the actual bits transmitted will be v. For
example, if v=(1,1), and the data that the user wishes to transmit
is (1, 0, 1, 1) this would correspond to (v, v, v, v) which is then
constructed in binary as ((1,1),(1,1),(1,1),(1,1)). For the
purposes of this article, we call this constructed vector the
transmitted vector. Each sender has a different, unique vector v
chosen from that set, but the construction method of the
transmitted vector is identical. Now, due to physical properties of
interference, if two signals at a point are in phase, they add to
give twice the amplitude of each signal, but if they are out of
phase, they "subtract" and give a signal that is the difference of
the amplitudes. Digitally, this behavior can be modeled by the
addition of the transmission vectors, component by component.
101
CDMA Coding scheme
If sender0 has code (1,1) and data (1,0,1,1), and sender1 has
code (1,1) and data (0,0,1,1), and both senders transmit
simultaneously, then this table describes the coding steps: Step
Encode sender0 Encode sender1 encode0=vector0.data0
encode0=(1,-1).(1,-1,1,1) encode0=((1,-1),(-1,1),(1,-1),(1,-1))
signal0=(1,-1,-1,1,1,-1,1,-1) encode1=vector1.data1
encode1=(1,1).(-1,-1,1,1) encode1=((-1,-1),(-1,-1),(1,1),(1,1))
signal1=(-1,-1,-1,-1,1,1,1,1)
0 vector0=(1,-1),data0=(1,0,1,1)=(1,-1,1,1)
vector1=(1,1),data1=(0,0,1,1)=(-1,-1,1,1)
1 2 3 4
Because signal0 and signal1 are transmitted at the same time
into the air, they add to produce the raw signal:
(1,-1,-1,1,1,-1,1,-1) + (-1,-1,-1,-1,1,1,1,1) =
(0,-2,-2,0,2,0,2,0)
102
CDMA Coding scheme
This raw signal((0,-2,-2,0,2,0,2,0)) is called an interference
pattern. The receiver then extracts an intelligible signal for any
known sender by combining the sender's code with the interference
pattern, the receiver combines it with the codes of the senders.
The following table explains how this works and shows that the
signals do not interfere with one another: Step Decode sender0
Decode sender1
0 1 2 3 4
vector0=(1,-1), pattern=(0,-2,-2,0,2,0,2,0) vector1=(1,1),
pattern=(0,-2,-2,0,2,0,2,0) decode0=pattern.vector0
decode1=pattern.vector1 decode0=((0,-2),(-2,0),(2,0),(2,0)).(1,-1)
decode1=((0,-2),(-2,0),(2,0),(2,0)).(1,1)
decode0=((0+2),(-2+0),(2+0),(2+0))
decode1=((0-2),(-2+0),(2+0),(2+0)) data0=(2,-2,2,2)=(1,0,1,1)
data1=(-2,-2,2,2)=(0,0,1,1)
Further, after decoding, all values greater than 0 are
interpreted as 1 while all values less than zero are interpreted as
0. For example, after decoding, data0 is (2,-2,2,2), but the
receiver interprets this as (1,0,1,1).103
CDMA Coding scheme
We can also consider what would happen if a receiver tries to
decode a signal when the user has not sent any information. Assume
signal0=(1,-1,-1,1,1,-1,1,-1) is transmitted alone. The following
table shows the decode at the receiver:
Step Decode sender0 Decode sender1 0 vector0=(1,-1),
pattern=(1,-1,-1,1,1,-1,1,-1) vector1=(1,1),
pattern=(1,-1,-1,1,1,-1,1,-1) 1 decode0=pattern.vector0
decode1=pattern.vector1 2
decode0=((1,-1),(-1,1),(1,-1),(1,-1)).(1,-1))
decode1=((1,-1),(-1,1),(1,-1),(1,-1)).(1,1) 3
decode0=((1+1),(-1-1),(1+1),(1+1))
decode1=((1-1),(-1+1),(1-1),(1-1)) 4 data0=(2,-2,2,2)=(1,0,1,1)
data1=(0,0,0,0)
When the receiver attempts to decode the signal using sender1s
code, the data is all zeros, therefore the cross correlation is
equal to zero and it is clear that sender1 did not transmit any
data.104
Synchronous CDMA They use orthogonal codes. completely reject
arbitrarily strong signals using different codes, due to the
orthogonality of these systems It cant use the spectrum more
efficiently in mobile telephony applications. No such flexibility
in allocation of resources. There are a fixed number of orthogonal
codes, timeslots or frequency bands that can be allocated for CDM,
Synchronous CDMA is ideally not suited to a mobile network where
large numbers of transmitters each generate a relatively small
amount of traffic at irregular intervals
Asynchronous CDMA It use unique "pseudo-random" or
"pseudo-noise" (PN) sequences. This is not true for Asynchronous
CDMA; rejection of unwanted signals is only partial. It can use the
spectrum more efficiently in mobile telephony applications. offers
a key advantage in the flexible allocation of resources There is no
strict limit to the number of users that can be supported in an
Asynchronous CDMA system Asynchronous CDMA is ideally suited to a
mobile network where large numbers of transmitters each generate a
relatively small amount of traffic at irregular intervals
105
Advantages
Can share a common bandwidth without interfering each other.
Flexible network planning (planning is no longer needed) Greater
coverage (larger area for a given amount of power ) High capacity
(greater coverage capacity) Cost (larger profit for providers due
to increased capacity, less infrastructure) Clarity Customer
satisfaction (privacy, better call quality longer battery life
dueto less power consumption, prevent cross talks)
Compatibility (dual mode analog and digital)106
Disadvantages
Poor Synchronization Difficulty to satisfy synchronization
requirements. Self jamming Self jamming is a steep deterioration of
performance as a result of poor synchronization. Poor
synchronization causes partial-correlation with the codes of other
users and the result will be a vast increase of the interference.
Near-far problem power control is necessary for mitigating the
Near-far problem. There are some factors for imperfect power
control such as: feedback delays, imperfect power estimates,
traffic conditions, errors in the feedback channel. Network
complexity Complex network support is needed for implementing soft
handoff, and also for countering multipath and fading effects.
Throughput Low throughput efficiency for large number of
users.107
CDMA ApplicationsA p p lic a t io n s :G P S O n e P o s it io n
L o c a t io n T e c h n o lo g y P o s itio n lo c a tio n c o n c
e p t a p p lic a tio n s . 1. 2. 3. 4. G e t d ir e c tio n s o n
th e m o v e L o c a te a lo s t p e t P r o v id e tr a ff ic a n
d n a v ig a tio n s e r v ic e s L o c a te V e h ic le s a n d A
s s e ts c o n c e p ts a p p lic a tio n s
h t t p ://w w w .s n a p t r a c k .c o m /im p a c t /in d e x
.js p
Q t v S t r e a m in g V id e o a n d A u d io S u p e r io r p
la y b a c k r a te s in a f u lly in te g r a te d s o f tw a r e
s o lu tio n
2 D a n d 3 D G a m in g E n g in e L if e - lik e a n im a tio
n in 2 D a n d 3 D e n v ir o n m e n ts .
h t t p ://w w w .c d m a t e c h .c o m /s o lu t io n s /m u
lt im e d ia .js p
108
GSM Vs. CDMAGSM is a widely spread standard GSM provided by
BSNL, AIRTEL, ESCOTEL etc GSM users are almost 8 times in number
than CDMA users worldwide GSM is far better than CDMA in voice
quality GSM base stations consumes more power than CDMA and also
covers a less distance cell size in GSM is small compared to GSM.
CDMA is a patented technology CDMA provided by Reliance CDMA users
are almost 8 times less in number than GSM users worldwide CDMA is
poor than GSM in voice quality CDMA base stations consumes less
power than GSM and also covers a large distance cell size in CDMA
is larger compared to GSM.
109
GSM Vs. CDMAIt covers a large area of more than 25 user cannot
go beyond a short Kms. distance charging area (SDCA) which is
roughly a radius of 25 km. GSM offers slower data download CDMA
offers faster data download
On a GSM phone your account On a CDMA phone, your account
information along with your contact information is programmed into
your list and other personal data are stored cellular phone on a
SIM card (Subscriber Identity Module) Maximum 384kbps practice).
download speed (around 140kbps of Maximum download speed of about
in 2mb/s (about 700kbps in practice)
Europe, South Africa, Australia, and CDMA is mostly used in
America and many Middle and Far East countries some parts of Asia
have chosen to adopt GSM110
GSM Vs. CDMAIt uses TDMA. It is 2nd generation Its year of first
use was 1991 Roaming is worldwide Battery life is very good due to
simple protocol, good coverage and mature, power efficient chipsets
Hard Handoff It uses CDMA It is 3rd generation Its year of first
use was 2000 Roaming is limited Battery life lower due to high
demands of CDMA power control and young chipsets Soft Handoff
111
GPRS
General Packet Radio Service (GPRS) is a Mobile Data Service
available to users of Global System for Mobile Communications (GSM)
and IS-136 mobile phones. It provides data rates from 56 up to 114
Kbps. GPRS data transfer is typically charged per kilobyte of
transferred data, while data communication via traditional circuit
switching is billed per minute of connection time, independent of
whether the user has actually transferred data or has been in an
idle state. GPRS can be used for services such as Wireless
Application Protocol (WAP) access, Short Message Service (SMS),
Multimedia Messaging Service (MMS), and for Internet communication
services such as email and World Wide Web access. 2G cellular
systems combined with GPRS is often described as "2.5G", that is, a
technology between the second (2G) and third (3G) generations of
mobile telephony. It provides moderate speed data transfer, by
using unused Time division multiple access (TDMA) channels in, GPRS
is integrated into GSM Release 97 and newer releases. It was
originally standardized by European Telecommunications Standards
Institute (ETSI), but now by the 3rd Generation Partnership Project
(3GPP). The General Packet Radio Service (GPRS) is a new nonvoice
value added service that allows information to be sent and received
across a mobile telephone network. It supplements today's Circuit
Switched Data and Short Message Service. GPRS is NOT related to GPS
(the Global Positioning System), a similar acronym that is often
used in mobile contexts.
112
GPRSGPRS Handset Classes: There are three different classes of
devices. 1. Class A handsets can do both voice and data at the same
time (simultaneously). If you were to receive a voice call will
using the Internet, say, the connection would be placed on busy
while you answer the call, rather than have it disconnected. 2.
Class B handsets are voice and packet data capable, but not at the
same time. It can only support either a voice or data service at a
time. But like in Class A above, a voice call would put the data
call on hold, and vice versa. 3. Class C handsets can handle only
non-simultaneous data and voice calls. The user must manually
select the service they wish to connect to. (SMS is also optional
for Class C terminals).
113
GPRS
1.
2.
3.
4.
Classes of GPRS Services: Mobile devices can request different
types of traffic to be prioritized in a attempt to give the user
their desired level of connectivity. There are 4 types of classes.
Precedence Class: An application can be assigned precedence classes
1,2, or 3. If an application has higher precedence (1) than
another(3) then its traffic will be given a higher priority. Delay
classes: Applications can request predictive delay classes which
guarantee an average and 95% delay. Reliability class: application
can request differing levels of reliability for its data depending
on its tolerance of data loss. Throughput class: Applications can
choose different profiles for throughput.
114
GPRS Network System Architechture
A GSM network mainly consists of four components. Mobile Station
(MS) carried by the subscriber . Base Station Subsystem (BSS)
controls radio link with mobile station . Mobile Switching Center
(MSC) is the central component of the NSS. Operates all switching
functions for the mobiles within its jurisdiction. Interface
between mobile and other (including fixed) network. Network
Databases : Home Location Register and Visitor Location Register
together with MSC provides the call routing and roaming
capabilities of GSM. In order to integrate GPRS into the existing
GSM network, two major new core network elements are introduced:
the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support
node (GGSN). Serving GPRS Support Node (SGSN): An SGSN is
responsible for the delivery of data packets from and to the mobile
stations within its service area. SGSNs send queries to Home
Location Registers (HLRs) to obtain profile data of GPRS
subscribers. SGSNs detect new GPRS mobile stations in a given
service area; and, finally, SGSNs process registration of new
mobile subscribers and keep a record of their location inside a
given service area.115
GPRS Network System Architechture
Gateway GPRS Support Node (GGSN) : GGSNs are used as interfaces
between the GPRS backbone network and the external Public Packet
Data Networks. GGSNs maintain routing information that is necessary
to tunnel the Protocol Data Units (e.g IP) to the SGSNs that
service particular mobile stations. Other functions include network
and subscriber screening and address mapping. One or more GGSNs may
support multiple SGSNs. In addition to the new GPRS components,
following existing GSM network elements must also be enhanced in
order to support GPRS. Base Station System (BSS): must be enhanced
to recognize and send user data to the SGSN that is serving the
area. Home Location Register (HLR): must be enhanced to register
GPRS user profiles and respond to queries originating from SGSNs
regarding these profiles.116
GPRS Network System Architecture
As can be seen, there are a number of new standardized network
interfaces introduced: Gb Frame relay connection between the SGSN
and the PCU within the BSS. This transports both user data and
signaling messages to/from the SGSN. (SNDCP,LLC,BSSGP,NS) Gn The
GPRS backbone network, implemented using IP LAN/WAN technology.
Used to provide virtual connections between the SGSN and GGSN. Gi
The point of connection between GPRS and the external networks,
each referenced by the Access Point Name. This will normally be
implemented using IP WAN technology. Gr Interface between the HLR
and SGSN that allows access to customer subscription information.
This has been implemented using enhancements to the existing GSM C7
MAP interface.117
To use GPRS, users specifically need:
A mobile phone or terminal that supports GPRS (existing GSM
phones do NOT support GPRS) A subscription to a mobile telephone
network that supports GPRS; Use of GPRS must be enabled for that
user. Automatic access to the GPRS may be allowed by some mobile
network operators, others will require a specific opt-in; Knowledge
of how to send and/or receive GPRS information using their specific
model of mobile phone, including software and hardware
configuration (this creates a customer service requirement); A
destination to send or receive information through GPRS. Whereas
with SMS this was often another mobile phone, in the case of GPRS,
it is likely to be an Internet address, since GPRS is designed to
make the Internet fully available to mobile users for the first
time. From day one, GPRS users can access any web page or other
Internet applications- providing an immediate critical mass of
uses.118
GPRS Services
Multimedia Messaging Service (MMS) Push to talk over Cellular
PoC / PTT Instant Messaging and Presence -- Wireless Village
Internet Applications for Smart Devices through Wireless
Application Protocol (WAP) Point-to-point (PTP) service:
internetworking with the Internet (IP protocols) Short Message
Service (SMS) Future enhancements: flexible to add new functions,
such as more capacity, more users, new accesses, new protocols, new
radio networks. USB GPRS modem:USB GPRS modems use a terminal-like
interface USB 2.0 and later, data formats V.42bis, and RFC 1144 and
external antennas. Modems can be add in cards (for laptop) or
external USB devices which are similar in shape and size to a
computer mouse. GPRS can be used as the bearer of SMS. If SMS over
GPRS is used, an SMS transmission speed of about 30 SMS messages
per minute may be achieved. This is much faster than using the
ordinary SMS over GSM, whose SMS transmission speed is about 6 to
10 SMS messages per minute
119
Limitations Of GPRS
GPRS does impact a network's existing cell capacity. Only
limited resources. Use for one purpose precludes simultaneous use
for another. Maximum speed of 171.2 kbps only theoretically. Single
user would need all 8 time slots. Network operator would never
allow that. Bandwidth limited. Limited cell capacity for all users
Speeds much lower in reality
120
Features of GPRS
Faster data transfer rates GPRS currently supports an average
data rate of 115 Kbps, but this speed is only achieved by
dedicating all eight time slots to GPRS. Instead, carriers and
terminal devices will typically be configured to handle a specific
number of time slots for upstream and downstream data. The
aggregate cell site bandwidth is shared by voice and data traffic.
GPRS operators will vary in how they allocate the bandwidth.
Typically, they will configure the networks to give precedence to
voice traffic; some may dedicate time slots to data traffic to
ensure a minimum level of service during busy voice traffic
periods. Unused voice capacity may be dynamically reallocated to
data traffic. Always-on connection An always-on connection
eliminates the lengthy delays required to reconnect to the network
to send and receive data. Information can also be pushed to the end
user in real time.
Robust connectivity GPRS improves data transmission integrity
with a number of mechanisms. First, user data is encoded with
redundancies that improve its resistance to adverse radio
conditions. The amount of coding redundancy can be varied,
depending on radio conditions. GPRS has defined four coding schemes
CS1 through CS4. Initially, only CS1 and CS2 will be supported,
which allows approximately 9 and 13 Kbps in each time slot.If an
error is detected in a frame received in the BSS, the frame may be
repeatedly retransmitted until properly received before passing it
on to the GPRS core network.121
Features of GPRS
Broad application support Like the Internet, GPRS is based on
packet-switched data. This means that all native IP applications,
such as email, Web access, instant messaging, and file transfers
can run over GPRS. In addition, its faster data transfer rates
enable GPRS to accommodate higher-bandwidth applications (such as
multimedia Web content) not suited to slower GSM dial-up
connections. GPRS is particularly well suited for applications
based on the Wireless Application Protocol (WAP). Security support
GPRS builds on the proven authentication and security model used by
GSM. At session initiation, a user is authenticated using secret
information contained on a smart card called a Subscriber Identity
Module (SIM). Authentication data is exchanged and validated with
records stored in the HLR network node. GPRS enables additional
authentication using protocols such as RADIUS before the subscriber
is allowed access to the Internet or corporate data networks.
122
INTERWORKING WITH THE EXTERNAL INTERNET
Before a GPRS mobile station can use GPRS services it must
obtain an address used in the packet data network (a PDP address)
and create a PDP context. The context describes the characteristics
of the connection to the packet data network (PDP type, PDP
address, service precedence, reliability, delay, throughput and
GGSN). With an active PDP context, packets from mobile station will
be sent to its current SGSN first, then this SGSN encapsulates the
IP packets, examines the PDP context, and routes them to
appropriate GGSN. The GGSN decapsulates the packets and sends them
out on the IP network. Similarly packets from the external packet
data network will be routed to the GGSN first, which then queries
the HLR and obtains the information where the MS is currently
located in. It encapsulates the incoming packets and tunnels them
to the current SGSN of the mobile user. The SGSN decapculates the
packets and delivers them to MS. Each GGSN has an IP address and
each mobile station has been assigned an IP address by its GGSN.
Thus the MS's IP address has the same network prefix as the IP
address of its GGSN. In GPRS network, user's current locations are
managed in two levels: Micro mobility management tracks the current
routing area or cell of the mobile station. It is performed by the
SGSN. Macro mobility management keeps track of the mobile station's
current SGSN and stores it in the HLR, VLR, and GGSN.
123
GPRS Transmission Plane Protocol Reference Model
124
GPRS Transmission Plane Protocol Reference Model
All data within the GPRS backbone, i.e. between the GSNs
(SGSNGGSN), is transferred using the GTP (GPRS tunnelling
protocol). GTP can use two different transport protocol, either
reliable TCP for X.25 packets or the non-reliable UDP used for IP
packets. To adapt to the different characteristics of the
underlying networks, the Subnetwork Dependent Convergence Protocol
(SNDCP) is used between an SGSN and the MS On top of SNDCP and GTP
user packet data is tunneled from the MS to the GGSN and vice
versa. To achieve high reliability of packet transfer between SGSN
and MS, a special LLC is used, which comprises ARQ and FEC
mechanisms. A Base Station Subsystem GPRS Protocol (BSSGP) is used
to convey routing and QoS -related information between the BSS and
SGSN. BSSGP doesnt perform error correction and works on top of
Frame relay (FR) network.
125
GPRS Transmission Plane Protocol Reference Model
Radio link dependent protocols are needed to transfer data over
the Um interface. The Radio Link Protocol (RLC) provides a reliable
link. The MAC controls access with signaling procedures for the
radio channel and their maping of LLC frames onto the GSM physical
channels. The radio interface at Um needed for GPRS doesnt require
fundamental changes compared to standard GSM.
126
GPRS: air interfaceRadio Link Control (RLC) Segmentation of the
LLC-Frames in RLC blocks Block size dependent on short-term channel
conditions Backward error correction and data flow control by
Automatic Repeat Request (ARQ) protocol repeating not repairable
RLC blocks selectively Medium Access Control ( MAC) Channel
reservation contains: - one/several time slots (Packet Data
Channels PDCH) of one frequency one uplink status flag (USF) per
Packet Data Channel (PDCH), channel partition of up to 8 ms
127
GPRS: air interface
Medium Access Control ( MAC) Reservation in the uplink (MS to
BSS): MS sends reservation request on a Random Access Channel
(Slotted ALOHA) BTS allocates a (split) channel and sends packet
assignment MS sends data depending on the current priority (USF
flag) Reservation in the Downlink (BSS to MS): BTS displays
transmitting request and informs about the reserved channel MS
supervises the reserved channel and receives
128
GPRS: air interface
Physical Link Control adaptive forward error correction (FEC)
dependent on shortterm channel conditions temporal scrambling
(Interleaving) of the bursts and Mapping on reserved PDCH (Packet
Data Channel) procedure to recognize overbooking situations on the
physical channelSc R t SSSS/ / / l S Pr c SF T il its its Punctur
its t r t (k it/s) . . . .
GPRS Channel Encoding
129
GPRS Applications
Chat Textual and visual information Still & moving images
Web browsing Document sharing/Collaborate working Audio Email, File
Transfer
130
GSM Vs. GPRSIt is circuit switched. It is not Always-on. It is
packet switched. It is Always-on. Youre charged for the time the
channel - Youre charged for the amount of data is reserved. thats
being transported, not for the time that the unit is online. The
System uses the same TDMA (Time The GPRS connection in the t610 can
Division Multiple Access) link with one use as many as 4+1 time
slots. out of seven time slots. Circuit switching provides the
customer with a dedicated channel all the way to the destination.
The customer has exclusive use of the circuit for the duration of
the call, With packet switching, the operator assigns one or more
dedicated channels specifically for shared use. These channels are
up and running 24 hours a day, and when you need to transfer data,
you access a channel and transmit your data.
The standard data rate of a GSM It provides data rates from 56
up to 114 channel is 22.8 kbps Kbps.
131
HSCSD Vs. GPRSIt is circuit switched. It is not Always-on. It is
packet switched. It is Always-on.supports guaranteed quality of
service , Doesnt supports guaranteed quality of service better
protocol for timing-sensitive ,so not a better protocol for
timing-sensitive applications such as image or video transfer.
applications such as image or video transfer is less bandwidth
efficient with expensive is more bandwidth efficient wireless links
expensive wireless links HSCSD is not as widespread as GPRS with
less
GPRS is not as widespread as HSCSD
CSD is just your normal dial up where you GPRS on the other hand
is the internet dial a number to connect to an internet connection
provided by the mobile phone service provider and is limited to
9.6kbps on operator most networks
HSCSD utilizes up to four 9.6Kb or 14.4Kb It provides data rates
from 56 up to 114 time slots, for a total bandwidth of 38.4Kb or
Kbps. 57.6Kb.132
133