Lecturer:Michael O'Grady

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Mobile Communications Overview

• Lecturer Michael O'Grady
• Course MSc Ubiquitous Multimedia Systems
• Unit Context Sensitive Service Delivery
• Lecture

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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

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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 - human
operated (plugboards), analogue signal Later
- Electromechanical switches Today
- Automated, digital But the so-called
last mile problem
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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.

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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

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Disadvantages of Wireless

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

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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

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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  unpublished paper.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.

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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

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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

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1G - NTT

• Nippon Telephone Telegraph (NTT)
• Now NTT DoCoMo
• 1979
• Tokyo
• Worlds first operational cellular system

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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

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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.

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1G - TACS

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

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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.

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1G - Services

• Standard voice
• No data services
• No supplementary services
• Call barring

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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

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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

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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

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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

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2G - IS-95

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

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2G - PDC

• Personal Digital Cellular (PDC)
• 1991
• Japan
• Two modes
• Full-rate
• Half-rate
• 12 of global digital subscriptions in 1999.

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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

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2G - Services

• Depends on
• Network standard
• Operator policies
• Improved standard telephony (speech)
• Basic wireless data
• Additional services
• Call barring

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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

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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

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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.

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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

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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 _at_ 14.4
  kb/s)
• Inefficient for certain types of application

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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.

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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)

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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

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2.5G - IS-95B (IS-95)

• Enhanced version of IS-95
• Already supports packet switching (CDPD)
• Maximum of 115.2 (8 channels _at_ 14.4kb/s)
• Realistically
• 28.8 kb/s to 57.6 kb/s on downlink
• 14.4 kb/s on uplink

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2.5G - Services

• Standard services that can use packet switching
• WWW browsing
• email
• file downloading e.g. mp3
• Multimedia Messaging Service (MMS)

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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!

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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 Time), for cordless sytems e.g.
  DECT

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3G - Interface Standards II
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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

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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!

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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

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3G Networks
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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

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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

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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

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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

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4G- Some Speculations

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

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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!

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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 (ITU-D)
• reports, guidelines and recommendations for
  developing countries

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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!

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3GPP - Organizational Partners
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3GPP2 - Organizational Partners
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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

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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?

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The End