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20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Wireless Technologies
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Outline
•
Wireless technology overview
•
Cellular communications
•
Satellite systems
•
Wireless LAN
–
802.11, Bluetooth, UWB
•
Mobility support
–
WAP
•
Wireless applications
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Why Wireless?
•
Human freedom
–
Portability v. Mobility
•
Objective: “anything, anytime, anywhere”
•
Mobility
–
Size, weight, power
–
Functionality
–
Content
•
Infrastructure required
•
Cost
–
Capital, operational
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Worldwide Mobile Subscribers
SOURCE: CTIA, iGillottResearch, 2001
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Electromagnetic Spectrum
SOURCE: JSC.MIL
SOUND
LIGHT
RADIO
HARMFUL RADIATION
VHF = VERY HIGH FREQUENCY
UHF = ULTRA HIGH FREQUENCY
SHF = SUPER HIGH FREQUENCY
EHF = EXTRA HIGH FREQUENCY
4G CELLULAR
56-100 GHz
3G CELLULAR
1.5-5.2 GHz
1G, 2G CELLULAR
0.4-1.5GHz
UWB
3.1-10.6 GHz
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
MOBILE
FIXED
MARITIME MOBILE
BROADCAST
AERO
RADIOLOCATION
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Wireless Telephony
SOURCE: IEC.ORG
AIR LINK
PUBLIC SWITCHED
TELEPHONE NETWORK
WIRED
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Cell Clusters
SOURCE: IEC.ORG
ACTUAL COVERAGE
AREA OF CELL 1
ACTUAL COVERAGE
AREA OF CELL 3
CELL 1 OVERLAPS 6 OTHERS
DIFFERENT FREQUENCIES
MUST BE USED IN ADJACENT
CELLS
SEVEN DIFFERENT SETS OF
FREQUENCIES REQUIRED
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Space Division Multiple Access (SDMA)
PATTERN CAN BE
REPLICATED OVER
THE ENTIRE EARTH
200 FREQUENCIES
IN ONE CELL
TOTAL NUM BER OF
FREQUENCIES = 1400
WORLDWIDE
MANY CELLS CAN SHARE
SAME FREQUENCIES IF
SEPARATED IN SPACE
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Cell Handover
SOURCE: R. C. LEVINE, SMU
AS PHONE MOVES FROM CELL “A” TO CELL “B”:
• CELL “A” MUST HAND THE CALL OVER TO “B”
• PHONE MUST CHANGE FREQUENCIES
• CELL “A” MUST STOP TRANSMITTING
Minimum
performance
contour
Handover threshold
contour
A
Bx y
z
ANIMATION
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Cell Sizes
MACROCELL: $1M
MICROCELL: $250K
SLOW-MOVING
SUBSCRIBERS
FAST-MOVING
SUBSCRIBERS
PICOCELLS
GSM:
100m - 50 km
250 km/hr
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Multiple Access
•
Many users sharing a resource at the “same time”
•
Needed because user must share cells
•
FDMA (frequency division)
–
Use different frequencies
•
TDMA (time division)
–
Use same frequency, different times
•
CDMA (code division)
–
Use same frequency, same time, different “codes”
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Frequency Division Multiplexing (FDMA)
Advantages:
•
No dynamic coordination
Disadvantages:
•
Inflexible & inefficient if
channel load is dynamic
and uneven
k
2
k
3
k
4
k
5
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6
k
1
f
t
c
Each channel gets a band (range) of frequencies
Used in traditional radio, TV, 1G cellular
EACH CHANNEL
OCCUPIES SAME
FREQUENCY
AT ALL TIMES
SOURCE: NORMAN SADEH
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
k
2
k
3
k
4
k
5
k
6
k
1
Time Division Multiplexing (TDMA)
Each channel gets entire spectrum for a certain (rotating)
time period
Advantage: Can assign more time to senders with heavier loads
3X capacity of FDMA, 1/3 of power consumption
Disadvantage: Requires precise synchronization
SOURCE: NORMAN SADEH
f
t
c
FREQUENCY BAND
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Combining TDMA and FDMA
f
t
c
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k
3
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5
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6
k
1
Each channel gets a certain frequency band for a certain
amount of time. Example: GSM
Advantages:
•
More robust against frequency-
selective interference
•
Much greater capacity with
time compression
•
Inherent tapping protection
Disadvantages
•
Frequency
changes must
be coordinated
SOURCE: NORMAN SADEH
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Time-Division Multiple Access
SOURCE: QUALCOMM
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Code Division Multiplexing (CDMA)
•
Each channel has unique
“code”
•
All channels use same spectrum
at same time but orthogonal codes
•
Advantages:
–
bandwidth efficient – code space is huge
–
no coordination or synchronization
between different channels
–
resists interference and tapping
–
3X capacity of TDMA, 1/25 power consumption
•
Disadvantages:
–
more complex signal regeneration
•
Implemented using spread spectrum
k
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3
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5
k
6
k
1
f
t
c
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Cellular Generations
•
First
–
Analog, circuit-switched (AMPS)
•
Second
–
Digital, circuit-switched (GSM, Palm) 10 Kbps
•
Advanced second
–
Digital, circuit switched, Internet-enabled (WAP)
10 Kbps
•
2.5
–
Digital, packet-switched, TDMA (GPRS, EDGE)
40-400 Kbps
•
Third
–
Digital, packet-switched, wideband CDMA (UMTS)
0.4 – 2 Mbps
•
Fourth
–
Data rate 100 Mbps; achieves “telepresence”
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
GSM Architecture
SOURCE: UWC
LIST OF
ROAMING
VISITORS
LIST OF SUBSCRIBERS
IN THIS AREA
STOLEN, BROKEN
CELLPHONE LIST
ENCRYPTION,
AUTHENTICATION
INTERFACE TO LAND
TELEPHONE NETWORKS
HIERARCHY
OF CELLS
CELL TRANSMITTER
& RECEIVER
PHONE
SIM:
IDENTIFIES A
SUBSCRIBER
DATA RATE: 9.6 Kbps
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
SMS – Short Message Service
•
Integral part of GSM standard
–
Added to other standards as well
•
Uses control channel of phone
–
Send/Receive short text messages
–
Sender pays (if from mobile phone)
•
Phone has "email" address
–
SMTP Interface
•
Only in the US, not the rest of the world
•
Allows messages to be sent for free!
–
•
1 BILLION SMS/day worldwide
Technology Message
Length
2
way?
GSM 160 bytes Yes
TDMA/PDC 160 bytes No
CDMA 256 bytes Yes
iDEN 140 bytes Yes
SOURCE: GEMBROOK SYSTEMS
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
SMS in Banking
Credit card used
Joe’s HiFi
$1245
Bank
Back-end
Systems
Internet
Bank Web Site
Message from YourBank: Credit card
purchase of $1245 at Joe’s HiFi.
Message appears within seconds
on the customer’s phone
SMS
Monitoring
Application
Customer
Alert me to all credit
card transactions
greater than $100.
Cell Tower
Air
Wireless
Carrier
SMS
Carrier
SOURCE: GEMBROOK SYSTEMS
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Satellite Systems
SOURCE: WASHINGTON UNIV.
GEO
M EO
LEO
GEO (22,300 mi., equatorial)
high bandwidth, power, latency
MEO
high bandwidth, power, latency
LEO (400 mi.)
low power, latency
more satellites
small footprint
V-SAT (Very Small Aperture)
private WAN
SATELLITE MAP
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
Geostationary Orbit
SOURCE: BILL LUTHER, FCC
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
GPS Satellite Constellation
•
Global Positioning
System
•
Operated by USAF
•
28 satellites
•
6 orbital planes at a
height of 20,200 km
•
Positioned so a
minimum of 5 satellites
are visible at all times
•
Receiver measures
distance to satellite
SOURCE: NAVSTAR
20-751 ECOMMERCE
TECHNOLOGY
FALL 2003
COPYRIGHT © 2003
MICHAEL I. SHAMOS
GPS Trilateration
DISTANCE MEASUREMENTS
MUST BE VERY PRECISE
LIGHT TRAVELS 1018 FEET
EACH MICROSECOND
SOURCE: PETER DANA
