Wireless Overview

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Mobile Communications
Overview

Lecturer:

Michael O'Grady

Course:

MSc Ubiquitous & Multimedia Systems

Unit:

Context Sensitive Service Delivery

Lecture:

Outline





Introduce some basic wireless
concepts
Describe the evolution of cellular
telecommunications networks
Reflect on the services supportèd by
cellular networks
Consider the issue of standardization
in wireless communications

Recall: PSTN
Public Switched Telephone Network
“Concatenation of the interconnected Networks operated by
the various telephone companies (telcos) and public utility
companies (PTTs) throughout the world”
Originally Later -

human operated (plugboards), analogue
signal
Electromechanical switches

Today -

Automated, digital

But ……

the so-called “last mile problem”

Recall: PLMN
Public Land Mobile Network (PLMN)
Operated by either government agency or
government appointed
company.
 Objective is to deliver services to those
members of the public who are mobile.
 May be considered an extension or an
integral part of the PSTN.
 Uses Wireless technologies.


Advantages of Wireless








Constant connection
Access to up-to-date information
Minimum installation issues
Freedom to roam
Scalability
No cables
Extensibility e.g remote areas with
satellite

Disadvantages of Wireless








Careful planning of network essential
Environment generally hostile
Security
Safety
spectrum licenses
poor data rates
cost (domain dependant)

Some Historical Developments
Origins debatable but ….







1887 - Hertz demonstrates EM waves
1896 - Marconi demonstrates wireless
telegraph apparatus
1901 - First radio signal across the
Atlantic (Cornwall to Newfoundland)
1914 - First wireless voice transmission
1946 - PSTN augmented with wireless
1947 - Cellular Network proposed

Why Cellular?
 Originally proposed by D. H. Ring in an
unpublished paper.
 Why?


Potential for existing systems to expand
was severely limited.

 How?


Reuse frequencies so as to maximize the
use of the available radio spectrum thus
improving scalability.

Note: This issue will be revisited when the GSM architecture is discussed.

Standardization
 Advantages include





accelerates the availability of new equipment and
services
lowers costs through increased competition
ensures reliability of supply
ensures interoperability

 De Jure


defined by industry groups or government agencies

 De Facto


established as the result of a product dominating the
market

1G - Characteristics
 Analogue transmission technology
 Pioneered semiconductor and
microprocessor technology
 Focus on voice
 Data services almost non-existent
 Incompatible standards
 Different frequencies and signaling
 International roaming impossible

 Inefficient use of the radio spectrum

1G - NTT
 Nippon Telephone & Telegraph (NTT)
 Now NTT DoCoMo

 1979
 Tokyo
 World’s first operational cellular
system

1G - NMT-450
Nordic Mobile Telephone 450
1982
Sweden
First wireless communications
standard deployed in Europe
 Pioneered the use of light portable
handsets
 Supported international roaming





1G - AMPS
 Advanced Mobile Phone System
(AMPS)
 1982
 USA
 Mandated (FCC) as the standard to
which all operators in the USA had
to adhere to.

1G - TACS






Total Access Coverage (TACS)
1985
UK
Adaptation of AMPS
Complies with frequency allocation
in Europe

1G - Network Access Technique
 Frequency Division Multiple Access
(FDMA)
 Subdivides the available spectrum
into a number of frequency slots
 Each user is assigned a separate
frequency.

1G - Services
 Standard voice
 No data services
 No supplementary services
 Call barring

The 1G Landscape








A series of incompatible networks
Limited capacity for expansion
Limited support for roaming
Susceptible to interference
Poor security
No support for wireless data
No third party applications

Solution: 2G
 Digital techniques rather than analogue
 Increased flexibility
 error control
 compression

 More efficient use of available
bandwidth
 Increased compatibility with the fixed
component of the PSTN
 Increased quality of service
 Possibility of wireless data services

2G - GSM
 Global System for Mobile
Communication (GSM)
 Conceived in 1982
 Deployed in 1992 in Europe
 European Telecommunications
Standards Institute (ETSI)
 Most successful 2G system
 863 million users in 197 countries

2G - D-AMPS
 Digital Advanced Mobile Phone
Service (DAMPS)
 Also called IS-54 (Interim Standard 54)

 1991
 Dual mode terminals ensuring
backward compatibility
 IS-136 introduced in 1996
 Telecommunications Industry
Association (TIA) TR-45 Committee

2G - IS-95







Interim Standard 95 (IS-95)
Also called cdmaOne
1993
USA
Qualcomm Inc.
Pioneered the use of the network
access technique CDMA

2G - PDC





Personal Digital Cellular (PDC)
1991
Japan
Two modes
 Full-rate
 Half-rate

 12% of global digital subscriptions in
1999.

2G - Network Access Technique
 Time Division Multiple Access (TDMA)


Users share a frequency band by multiplexing
their transmissions in time

 In practice ..




Available spectrum is divided into frequency
channels (recall FDMA!)
Each frequency channel is further subdivided
into cyclic timeslots (1,2,3,1,2,3,1,2,3 …)
A call is assigned a time slot

2G - Services
 Depends on
 Network standard
 Operator policies

 Improved standard telephony
(speech)
 Basic wireless data
 Additional services
 Call barring

Example: GSM Services
 Teleservices
 Speech
 Emergency calls
 Short Message Service (SMS)

 Bearer Services
 Telefax
 Basic data (9.6kb/s)

 Supplementary Services
 Call forwarding
 Call barring

2G - 3G Transition Driver?

 Higher data bandwidth requirement
 anticipated subscriber demand for





audio/Video streaming
other multimedia services
collaborative services
location services

 Possibility of third party applications
being developed

Recall: Circuit v Packet
Switching
 Circuit Switched ..


A dedicated channel is established for
the duration of a call

 Packet Switched …


A message is subdivided into packets
which are sent individually and may
follow different routes to their
destination. The packets are then used
to reassemble the original message.

3G - Migration Strategies
 Migrate straight to 3G


This approach is being take by some operators
in Japan (PDC) and the USA (IS-95)

 Migrate incrementally to 3G





Operators progressively and incrementally
incorporate a number of technologies into
their networks
This approach is taken by operators in both
Europe and the USA
This strategy is sometimes referred to as 2.5G

2.5G - HSCSD (GSM)
 High Speed Circuit Switched Data
(HSCSD)
 Uses existing GSM infrastructure and
interface
 Data rates of up to 57.6 kb/s (4
channels @ 14.4 kb/s)
 Inefficient for certain types of
application

2.5G - GPRS (GSM)





General Packet Radio Service (GPRS)
Introduces packet switching to GSM
“Always-on”
Uses multiple timeslots (channels)
 14.4 kb/s per channel
 Maximum of 115.2 kb/s

 Dynamic resource allocation
 Supports IP
 Billing per KB, NOT per sec.

2.5G - EDGE (GSM)
 Enhanced Data rates for GSM Evolution
(EDGE)
 Maximum 384 kb/s
 8 Phase Shift Keying (8PSK)
 Send more bits down the line
 3 fold increase over GSM

 Two classes of handset:
 Class A (EDGE only on downlink)
 Class B ( EDGE on uplink and downlink)

2.5G - D-AMPS (IS-136+)
 Two phase migration path


IS-136+





Integrate GPRS
Note: packet switching already supported by
Cellular Digital Packet Data (CDPD)!

IS-136 High Speed Outdoor


Integrate EDGE

 Subscribers can roam between IS-136HS
and GSM networks supporting EDGE

2.5G - IS-95B (IS-95)
 Enhanced version of IS-95
 Already supports packet switching
(CDPD)
 Maximum of 115.2 (8 channels @
14.4kb/s)
 Realistically …
 28.8 kb/s to 57.6 kb/s on downlink
 14.4 kb/s on uplink

2.5G - Services
 Standard services that can use
packet switching:
 WWW browsing
 email
 file downloading e.g. mp3
 Multimedia Messaging Service (MMS)

3G - The IMT2000 Initiative
 Conceived in 1986
 Sought to define a single world-wide
standard for accessing the global
telecommunications infrastructure from
both terrestrial and satellite mobile
systems
 Problem: backward compatibility
 So five standards approved for the air
interface!

3G - Air Interface Standards I







IMT-DS (Direct Spread), also known as
Wideband CDMA Frequency Division
Duplex (W-CDMA-FDD).
IMT-TC (Time Code) or W-CDMA Time
Division Duplex (W-CDMA-TDD).
IMT-MC (Multi-Carrier) or CDMA2000.
IMT-SC (Single Carrier), also known as
EDGE or UWC-136.
IMT-FT (Frequency
sytems e.g. DECT

Time),

for

cordless

3G - Interface Standards II
Radio-Interface Standard

Cellular Network

Standards Organisation

IMT-DS

GSM, PDC

3GPP

IMT-TC

D-AMPS

3GPP

IMT-MC

IS-95, PDC

3GPP2

IMT-SC

Any TDMA Network

UWCC

Table 1: 3G interface standards for the predominant 2G networks.

3G - Principal Requirements - I
 Support for voice quality comparable
with fixed line networks;
 Support for both circuit-switched and
packet-switched data services;
 Support for roaming between
different IMT-2000 operators;
 Support for greater capacity and
improved spectrum efficiency;

3G - Principal Requirements - II
 A data rate of 144 kb/s for users
moving quickly e.g. moving vehicles;
 A data rate of 384 kb/s for pedestrians;
 A data rate of 2 Mb/s in a low mobility
or office environment.
 Note how a network using GPRS and
EDGE meets most of these criteria!

3G - Network Access Technique
 Code Division Multiple Access (CDMA)
Signal is modulated with high bandwidth
spreading waveforms called signature
waveforms or codes. Subscribers may
submit at the same frequency and time but
signal separation is facilitated via the
signature waveform
 In contrast with TDMA
 More robust
 Less susceptible to fading & interference


3G Networks

2G Network
GSM
PDC
IS-95
DAMPS

3G Successor
UMTS
CDMA2000
CDMA2000
IS-136HS or UMTS

Example: 3G Services (UMTS)
 Universal Mobile Telephone System
(UMTS)
 Four QoS classes of services
 Conversational Class
• Voice, video telephony,video gaming

 Streaming Class
• multimedia, video on demand, webcast

 Interactive Class
• WWW browsing, database access, online gaming

 Background Class
• email, SMS, file downloading

Quality of Service (QoS)
“the collective effect of service performances which
determine the degree of satisfaction of a user of a
service”… ITU G1000 specification
 Telecommunications World
 QoS encapsulates all aspects of a service that determine
the degree of satisfaction with that service.

 IP World
 QoS implies guaranteed bandwidth
Pronunciation check: QoS == kwoz

QoS: Network v Customer
 Network performance
 Packet loss, transmission delay, bit
error rates, call set-up times, etc

 But customer interpretation?
 Thus Q.800 suggests:
• Focus on effects as perceived by customer
• No assumptions about network design
• All aspects of the service considered (from
customer perspective)
• Network independent terms used
• Can be assured to a user by a service provider

3.5G
 UMTS
 High Speed Downlink Packet Access (HSDPA)





14 Mbps (but 1 Mbps per subscriber!)
Incremental upgrade
More functionality in Node B
Backward compatible with W-CDMA

 High Speed Uplink Packet Access (HSUPA)
 Other Technologies
 OFDN, WiMAX, etc, etc

4G- Some Speculations





Global Mobility
Increased data rates..100Mbps?
All IP network
When?

Standardisation - ITU
 Founded in 1865 in Paris by 20
European countries





interconnection issues
equipment standardization
uniform instructions for operating equipment
accounting procedures and rules

 Today, affiliated with the UN
 500 new or revised recommendations
every year!

Structure of the ITU
 Telecommunications Standardization
(ITU-T)
 specifications for systems networks and services

 Radiocommunications (ITU-R)
 specifies technical characteristics of terrestrial
and space based wireless services and systems

 Telecommunications Development (ITUD)
 reports, guidelines and recommendations for
developing countries

Wireless Standardization
 Recall IMT2000 vision
 Two global partnerships comprising a
number of traditional standardization
bodies
 Third Generation Partnership Project (3GPP)
 Concerned with EDGE & UMTS advancement

 Third Generation Partnership Project 2 (3GPP2)
 Concerned with CDMA advancement

 Note that membership not mutually
exclusive!

3GPP - Organizational Partners
Organisation
Association of Radio Industries and

Region

URL

Japan

http://www.arib.or.jp

China

http://www.cwts.org

Europe

http://www.etsi.org

Committee T1 (T1)

USA

http://www.t1.org

Telecommunications Technology Association

Korea

http://www.tta.or.kr

Japan

http://www.ttc.or.jp

Businesses (ARIB)
China Wireless Telecommunications
Standard Group (CWTS)
European Telecommunications Standards
Institute (ETSI)

(TTA)
Telecommunications Technology Committee
(TTC)

3GPP2 - Organizational Partners

Organisation

Region

URL

Association of Radio Industries and

Japan

http://www.arib.or.jp

China

http://www.cwts.org

USA

http://www.tiaonline.org

Korea

http://www.tta.or.kr

Japan

http://www.ttc.or.jp

Businesses (ARIB)
China Wireless Telecommunications
Standard Group (CWTS)
Telecommunications Industry Association
(TIA)
Telecommunications Technology Association
(TTA)
Telecommunications Technology Committee
(TTC)

Summary
 Introduced wireless communications
 Described the evolution of the various
generations of cellular networks
 Described the services supported by
the various networks and the issues
effecting their deployment
 Briefly introduced the issue of
standardization

Review Questions
 Compare and contrast the three
generations of mobile networks.
 Trace the evolution of services from 1G
to 3G.
 Identify the advantages and
disadvantages of circuit switched and
packet switched data services from both
an operator and subscriber perspective.
 What benefits do standardization bring
to network operators? Subscribers?

The End

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