Wireless Networks

1
Wireless Networks

• Team Members
• Charlie ONeal
• Alicia Stevenson
• Richie Crawford
• Jimmy Gibbs
• Kashif Riaz

2
ADVANCED MOBILE PHONE SERVICE

• Since the 1980s the most common mobile telephone
  system in North America has been Advance Mobile
  Phone Service(AMPS).
• This system has three basic types of devices the
  Mobile, Base Transceiver, Mobile Switching
  Center(MSC).
• The mobile communicates with the base
  transceiverthe transceiver communicates with the
  mobiles and with the MSC. The MSC coordinates
  the activities of the base transceiver and also
  connects calls to the public wired telephone
  network.

3
Mobile Units

• Mobile units can be mobile in vehicles or
  portable hand held. Each AMPS mobile unit
  contains a modem that can switch between many
  frequencies.
• The maximum transmission power of vehicle based
  units is usually an order of magnitude larger
  than the maximum power for portable units.

4

• Each Advanced Mobile Phone Service mobile unit
  has three identification numbers
• Electronic Serial Number- a 32-bit hardware
  identifier assigned to the mobile when
  manufactured.
• System Identification Number- a 15-bit code that
  identifies the system operator with which the
  mobile is associated. Allows the system to
  determine roaming.
• Mobile Identification Number-a 34-bit identifier
  representing the 10-digit telephone number of the
  mobile

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Base Transceiver

• Supports full duplex communication with the
  mobile.
• The base transceivers are connected to a
  controlling MSC, usually by microwaves or wire.

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Mobile Switching Center

• Performs the switching functions for the mobile
  network(e.g., Handoffs as the mobile travels from
  cell to cell)
• Coordinates backup
• Collects data collection to support billing
• Tests and monitors the system
• Connects the mobile network to, and sets up calls
  for, the wired public switching network

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GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS
Commonly known as GSM Introduced in 1991 in
Europe To provide a common Second Generation
Technology Based on First Generation Systems
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FEATURES
Subscriber Identity Module (SIM)                 
   Portable device                    Stores
subscriber identification number                 
   Stores the authorized networks                
    Stores the encryption keys Encrypted
Transmission                    A5
chiper                    A3 chiper
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FEATURES (Contd.)
Supports Data and Image Services                 
   Based on the ISDN model                   
Supports rates up to 9.6 kbps
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The GSM Layout
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Home Location Register (HLR) Database            
        stores both permanent and temporary
information Visitor Location Register (VLR)
Database                    stores temporary
information Authentication Center (AuC)
Database                    holds authentication
and encryption keys Equipment Identity Register
(EIR) Database                    keeps track of
equipment
12
The GSM Spectral Allocation
25 MHz for Base transmission (935-960 MHz) 25 MHz
for Mobile transmission (890-915 MHz) The Radio
Frequency carriers                    every 200
kHz                    provides 124 full-duplex
channels                    channels modulated
at 270.833 kbps
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CHANNEL TYPES
Traffic Channels                    Carry
digitalized signal Control Channels              
      Broadcast                    Common
Control                    Dedicated Control
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Four ways to divide spectrum

• Frequency division multiplexing (FDM)
• Time division multiplexing (TDM)
• Space division multiplexing (SDM)
• Code division multiplexing (COM)

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Space Division Multiplexing

• Uses the same spectral band in two physically
  disjoint places.
• The same frequency can be used in two different
  cells as long as the cells a far enough apart so
  that their signals do not interfere.
• Uses highly directional antennas so that the same
  frequency may be used for two communications

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Code Division Multiplexing

• Based on spread spectrum
• Signal can be spread out so longer messages may
  be transmitted.
• Advantage- Able to gain immunity from various
  kinds of noise and multipath distortion.
• Can also be used for hiding and encrypting
  signals.

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How CDM Works
                                             
Ca
 
Cb
Cc
18

• Su(d) d1xc1d2xc2d3xc3d4xc4d5xc5d6xc6
• A sending a 1 bit
• Sa(1,-1,-1,1,-1,1)
• 1x1(-1)x (-1)(-1)x(-1)1x1(-1)x(-1)1x1 6
• A sending a 0 bit
• Sa(-1,1,1,-1,1,-1)
• -1x11x(-1)1x(-1)(-1)x11x(-1)(-1)x1 -6

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Which access method to use

• FDM- Used in first generation systems, way to
  wasteful of spectrum.
• TDMA- Are less expensive then CDMA and has more
  successful experiences.
• CDMA- Has increased range and other additional
  features.

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Third Generation Wireless Communication

• To provide fairly high speed wireless
  communications
• Support multimedia, data
• Video and voice

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International Mobile Telecommunications for 2000
(IMT-2000)

• Voice quality
• 144 kbps data rate available to users
• 384 kbps available to pedestrians
• Support 2.048 Mbps office use
• Support both packet switched and circuit switched
  data services

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IMT-2000

• Adaptive interface for Internet
• Efficient use of available spectrum
• Support wide mobile equipment
• Flexibility for new technologies

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Wireless Application Protocol (WAP)

• WAP is universal
• Provides mobile wireless phones
• Personal digital assistants (PDAs)
• Telephony and information services
• Works with al wireless networks
• Based on IP, XML, HTML, and HTTP

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WAP Specifications

• WWW programming model
• Wireless Markup Language, XML
• Small browser for wireless terminal
• Lightweight communication protocol
• Framework for wireless telephony applications
  (WTAs)

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Satellite Communication

• Satellites are characterized by orbits
• Most common is geostationary (GEOS)
• GEOS can be at 35,838 km above earth

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Advantages of GEOS

• No frequency changes
• Tracking is simplified
• At 35,838 km above earth, three satellites cover
  most of earth

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Disadvantages of GEOS

• A weak signal
• Polar regions are poorly served
• Delay in sending a signal from the equator

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Low and Medium Earth Orbiting Satellites (LEOS
MEOS)

• The original ATT proposal
• Lightsats orbit 320 to 1100 km above earth
• Many satellites are needed for 24 hour coverage
• Many proposals have been made

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One Proposal

• Little LEOSs
• Frequencies below 1 GHz and no more than 5 MHz
• Aimed at paging, tracking, and low rate messaging
• Orbcom is an example

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A Second Proposal

• Big LEOSs
• Frequencies above 1 GHz
• Offer voice and positioning services
• Globalstar is an example

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LEOS vs. MEOS

• LEOSs can be seen for minutes
• LEOSs are lower than MEOSs
• MEOSs can be seen for hours
• MEOSs are 10,000 km above earth

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Applications

• One-way broadcast, especially video services
• Video Services include
• TV programming
• Point-to-point broadcasting
• Multipoint distribution
• Direct broadcast
• Provide global communication

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Iridium

• 66 small LEOSs
• Motorola proposed the system in 1987
• It is named for the element iridium
• It cost 5 billion
• It is owned by Iridium, Inc. but built and
  operated by Motorola

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Iridium

• Services
• Including voice, paging, and messaging services
• Satellites and Orbits
• 66 satellites operate in nearly polar orbits
• Communications
• 1600 to 1700 MHz used between users and
  satellites
• 18 to 30 GHz between satellites and gateways and
  satellites

35
Richies Question

• What are the three identification numbers each
  Advanced Mobile Phone Service mobile unit has?
  And describe each number.

36
Kashifs Question
How does the GSM system authenticate its
subscriber?
37
Charlies Question

• Using CDM what can be gained from apparent waste
  of spectrum?

38
Jimmys Question

• What is the third generation capabilities
  according to the International Mobile
  Telecommunication in the year 2000?

39
Alicias Question

• List three advantages and three disadvantages of
  geostationary satellites.