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unpublished paper.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
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
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)
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
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)
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?