CPE 493g: Wireless Networking

1
CPE 493gWireless Networking

• Matthew C. Valenti
• Associate Professor
• Electrical Engineering
• West Virginia University
• Lecture Note Set 1
• A Brief History of (Wireless) Telecommunication
• Aug. 24, 2005

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Announcements

• Reading assignments
• Chapter 1 of textbook.
• N. Chandran and M.C. Valenti, Three generations
  of wireless cellular systems, IEEE Potentials,
  vol. 20, no. 1, pp. 32-35, Feb./March 2001.
• Assignment one will be posted soon.

4
How many cellular subscribers are there?

• from The New Yorker, Oct. 16, 2000.

5
The Wireless Revolution
1000
100
Millions of Subscribers
10
1
0.1
1983
1986
1989
1992
1995
1998
2001
2004
2005
Source www.ctia.org
6
Largest Carriers in the US

• Cingular, 49.1 million (GSM)
• Verizon, 43.8 million (CDMA)
• Sprint, 24.8 million (CDMA)
• T-mobile, 17.3 million (GSM)
• Nextel, 16.2 million (iDen)
• In the US, the wireless industry brings in
  100B/yr.

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Wireless Worldwide

• Over 1.7 billion subscribers.
• Penetration Rates for Select Countries
• Taiwan 101
• U.K 100
• Italy 96
• Netherlands 94
• Germany 84
• France 76
• Japan 65
• United States 59
• Russia 50
• India 9
• China 38

Growing Fast
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When was the first wireless network deployed?
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The Optical Telegraph

• 1793, France, Claude Chappe.
• Semaphore flags on hills.
• 566 stations covered all of France.

3 miles
Hill 1
Hill 2
Hill 3
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Optical Telegraph

• 1793
• Arms placed into 96 positions.
• 4 positions were control signals
• 92 signals used for messaging.

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Message Switching

• Network nodes were created where several optical
  telegraph lines met (Paris and other sites)
• Store-and-Forward Operation
• Messages arriving on each line were decoded
• Next-hop in route determined by destination
  address of a message
• Each message was carried by hand to next line,
  and stored until operator became available for
  next transmission

source Leon-Garcia
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Electrical Telegraph

• 1834, Gauss and Weber develop early telegraph
• 1837, First patents
• Cooke and Wheatstone in UK
• Samuel Morse in US
• May 24, 1844 First long-distance transmission.
• Samuel Morse
• Baltimore to Washington.
• What hath God wrought?

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Morse Code
source Leon-Garcia
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Electric Telegraph Networks

• Electric telegraph networks exploded
• Message switching Store-and-Forward operation
• Key elements Addressing, Routing, Forwarding
• Optical telegraph networks disappeared

source Leon-Garcia
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Who InventedWireless Telegraphy?

• June 1897, UK, Marconi.
• Spark-gap transmitter.
• Wireless transmission of Morse-coded signals.

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The Wireless Telegraph

• Wireless (electrical) telegraph (Marconi).
• 1899, Transmission across English channel.
• 1901, 1st transatlantic communication.
• 1907, Commercial ship-to-shore service.

17
AM for Voice Communications

• Up until 1906, wireless could only transmit
  Morse-coded signals.
• Dec. 24, 1906, U.S., Reginald Fessenden.
• First wireless voice transmission.
• Brant Rock, MA, to New York, NY.
• AM Amplitude Modulation.

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Commercial Broadcast Radio

• When was first commercial AM radio broadcast?
  Where?
• Nov. 2, 1920, Pittsburgh.
• KDKA transmitter built by Frank Conrad.

AM radio from 1937
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Frequency Modulation (FM)

• 1933, US, E. Armstrong.
• Paved the way for mobile and portable
  communications.
• Low-power.
• Clear reception.
• Tolerates noise, interference, and fading.
• Two-way FM police car radio, Motorola, 1941.

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Early Advances in Mobile Radio
1921
1935
1950
1983
1965
1983, Cellular in Chicago
1921, Dispatch radio (1-way)
1930, Dispatch radio (2-way)
1940, Handie-Talkie
1946, Radiotelehone
1979, Cellular in Tokyo
1965, Automatic Trunking
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AM Mobile radio

• 1921, Detroit, police car dispatch.
• one way.
• 1930, Bayonne NJ, push-to-talk.
• two way.
• Half-duplex.

Same channel for both directions
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Portable two-way radio

• 1940, US, Motorola
• Handie-Talkie, AM.
• 1943, US, Dan Noble
• Walkie-Talkie, FM.

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Early Radiotelephone Service

• Radiotelephone.
• 1946, St. Louis, ATT.
• First wireless connection to the PSTN.
• PSTN Public Switched Telephone Network.
• System called MTS
• Mobile Telephone Service.
• FM _at_ 150 MHz
• Initially half-duplex (push-to-talk).
• 120 kHz channels in 1946.
• Only 1-3 channels per city.

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Mobile Telephone Service (MTS)

• MTS
• High power transmitter, at high elevation.

Same Frequecies
Call dropped
Washington
Baltimore
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Improved Mobile Telephone Service (IMTS)

• Improvements to MTS
• Full-duplex signaling, 1965.
• No need for push-to-talk.
• Improved capacity
• 120 kHz channels in 1946.
• 60 kHz channels in 1950 (2x capacity).
• 30 kHz channels in 1965 (4x capacity).
• Automatic trunking, 1965.
• Allows more subscribers.

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Non-trunked Radio System

• Prior to 1965,
• Each mobile unit is permanently assigned one of
  the possible frequencies.
• If someone is using your frequency, you cant
  place a call ---- even if one of the other
  channels is open.
• Not very efficient!

Radio Channel
Radio Channel
Radio Channel
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Trunked Radio System

• After 1965,
• The mobile is dynamically assigned a frequency.
• Any open channel can be used.
• The blocking probability is greatly reduced.
• This translate to an increased number of
  subscribers.

Radio Channel
Radio Channel
Radio Channel
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The Demise of IMTS

• Problems with IMTS
• Poor service.
• 50 probability of blockage.
• No handoff from one region to next.
• Not enough capacity.
• Example New York city, 1976.
• Population of 10,000,000 .
• 12 channels.
• 545 subscribers .
• 3,700 on waiting list.

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The Birth of Cellular

• Problem with IMTS
• Not enough channels for the demand.
• Solution
• Release more bandwidth.
• 1974-1975, FCC released 80 MHz of bandwidth
  previously used by UHF television.
• Break the coverage region into cells
• The cellular concept.

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The Cellular Concept

• Transmit power drops off with distance.
• When you are far-enough away you can re-use the
  channel.
• Similar concept to frequency re-use for radio and
  television stations.

Ch 1
Ch 2
Ch 3
Ch 1
Low power transmitter, Frequency is re-used
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The Cellular Concept
Set 1
Set 2
Set 3
Set 2
Set 3
Ch 1
Set 4
Set 1
Lower power transmitters provide coverage to a
small portion of the service area. Frequency is
reused
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Cell Patterns
Idealized Cells
Idealized Coverage
Footprint
Reality!
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The Cellular Concept
Cluster 1
Cluster 2

• Break the metropolitan area into small areas
• Each area is approximated with a hexagonal cell.
• A base station is located at the center of each
  cell.
• Each cell is assigned only a fraction of the
  total number of channels.
• Cells that are sufficiently far apart can reuse
  the same frequency.
• By Aug. 2005, there were 175,000 base stations in
  the US alone.

A
F
B
A
B
F
G
E
G
C
E
C
D
A
D
F
B
G
E
C
D
Cluster 3
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Frequency Reuse
2
1
2
5
1
5
4
4
7
3
7
3
6
6
2
5
1
4
7
3
N 7
6
36
Cell Pattern N 4
2
3
1
2
2
4
1
3
3
1
4
2
4
3
1
4
37
Hand Off
Ch 2
Ch 1
Mobile must be transferred between cells as it
moves
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Sectorized Antennas

• Further interference reduction by using
  sectorized antennas.

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First Generation Cellular Systems

• Japan, 1979
• NTT Advanced Mobile Telephone (NAMT).
• 400/800 MHz, FM, 25 kHz channels.
• Europe
• 1981
• NMT 450, Sweden.
• 1985
• C-450, Germany.
• E-TACS, UK.
• R2000, France.
• RMTS, Italy
• US
• 1983 (Chicago).
• AMPS Advanced Mobile Phone System.
• Developed by ATT.
• FM _at_ 800MHz, 30 kHz channels.

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Frequency Allocations

• It is 1981 and you are the chairman of the FCC.
  How do you allocate frequencies?
• Give the license to just one company, creating a
  monopoly like the power and phone companies.
• Let two companies have licenses to balance
  trunking efficiency and competition.
• Let any company that wants to offer service have
  a license to encourage maximum competition.
• Frequency allocations
• 1981, FCC allocates 40 MHz of BW
• Dualopoly 2 providers _at_ 20MHz ea)
• 666 channels in each of 734 markets
• 1986, another 10 MHz allocated
• 832 channels

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Cellular System Block Diagram
Mobile Switching Center
MS
BS
HLR/VLR Databases
Voice
Data
Data
Voice
BS
MS
Processing Center
PSTN
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Common Air Interface
Forward
Reverse

• Control Channels Call setup, access to traffic
  channels.
• Traffic Channels Voice calls and messages.
• Signaling Channels Networking signals during a
  call.

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Roaming and IS-41

• Prior to 1991, true roaming was not possible.
• Roaming ability to use your cell phone outside
  your home service area.
• Temporary fixes
• Clearing house data base.
• Follow-me call forwarding.
• In 1991, the IS-41 standard was created.
• Makes it possible for roamers to originate and
  receive phone calls.
• Enables hand-off across system boundaries.

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Enhanced 911 and Geolocation

• Oct. 1996, FCC ruling.
• Basic 911, October 1997.
• All cellular and PCS systems must have basic
  ability to process 911 call without user
  validation.
• Even cell-phones with expired service are able to
  make 911 calls.
• Enhanced 911 (E-911).
• Phase I, April 1, 1998.
• Ability to locate the cell that the call
  originated from.
• Can make 911 call from any analog phone.
• Even if subscription is expired.
• Phase II, October 2001
• Handset-based geolocation
• Position location within 50 m (150 m) 67 (95)
  of the time.
• Network-based geolocation
• Position location within 100 m (300 m) 67 (95)
  of the time.
• All carriers missed the deadline.
• Full implementation delayed until Dec. 31, 2005

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Limitations of 1-G Systems

• Despite having 832 available channels, large
  metropolitan areas became saturated.
• The analog nature of AMPS does not allow
  efficient data transmission.
• 30 kHz per user is spectrally inefficient.
• Newer technology could increase number of
  subscribers per Hz.
• AMPS requires up to 4 W transmit power.
• The poor power efficiency results in short
  battery life.
• Biological concerns due to high power
  transmissions.

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Second Generation Systems

• By the mid-1990s reduced IC costs made digital
  transmission more cost effective than analog.
• Benefits of digital
• Source coding
• Compression and vocoding.
• Can reduce the amount of bandwidth required for
  voice and video.
• Channel coding
• Error correction/detection
• Reduces the amount of required transmit power.
• Improves performance in fading and interference.

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Multiple-access for Digital Communication Systems

• The frequency spectrum must be shared by all the
  users in the system.
• Three method for sharing spectrum
• FDMA
• Frequency-division multiple-access.
• TDMA
• Time-division multiple-access.
• CDMA
• Code-division multiple-access.
• Most modern systems use combinations
• TDMA/FDMA
• CDMA/FDMA

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FDMA

• Frequency-division multiple-access.
• Each user is assigned one frequency

Channel 1
2
3
4
frequency
guard band
30 kHz
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TDMA

• Time-division multiple-access
• All users transmit at same frequency.
• Each user transmits at a different time.

User 1
User 1
20 msec time slot
time
User 2
User 2
guard time
User 3
User 3
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GSM

• Global System for Mobile communications.
• Europe, 1992.
• Now available in 200 countries.
• 1.442 billion users in Aug. 2005.
• Actually a hybrid of TDMA and FDMA
• 125 FDMA channels at 200 kHz each.
• 8 TDMA time-slots per frequency.
• 1,000 total TDMA/FDMA channels.
• High data rate capabilities (2.5G)
• GPRS Up to 171.2 kbps (but 48k more typical)
• EDGE 384 kbps

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CDMA

• Code-division multiple-access
• All users transmit at the same time and in the
  same frequency band.
• Users are distinguished by transmitting different
  signals.
• The signals have a wide-bandwidth
• Spread-Spectrum.
• The signals are chosen for low co-channel
  interference.
• Frequency-Hopping Spread-Spectrum.
• Direct-Sequence Spread-Spectrum.
• 270 Million subscribers worldwide by Aug. 2005
• 100 million in North America

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Frequency-Hopping Spread-Spectrum (FH/SS)

• The channel is divided into several
  frequency-slots
• At each instant of time, the transmitter sends a
  signal in one of the frequency-slots.
• After a short period of time, a new
  frequency-slot is used.
• Several users share the same channel.
• Occasionally there will be collisions.
• However, the collisions are infrequent.

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Example of FH/SS
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Direct-Sequence Spread-Spectrum (DS/SS)

• Each user is assigned a unique signature
  sequence of N chips.
• N is called the processing gain.
• It is the amount of bandwidth increase.
• Each data bit is modulated using the signature
  sequence.
• The receiver is designed to detect only the
  signature sequence of the desired user.
• However a small amount of energy from the other
  users will leak in due to signal
  cross-correlation.

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DS/SS CDMA
1
0
Spread data 4X the raw data rate
Data
Digital Modulator
x
User 1
Signature waveform
Data
Digital Modulator
User 2
x
Signature waveform
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CDMA and the International Cocktail Party

• Imagine a cocktail party, where each conversation
  is in a different language.
• Because there are many people, there is a lot of
  background noise.
• Despite the background noise, two people can
  converse successfully.
• The ear is trained to hear their native-tongue.

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Multiple-Access
Code

• Three ways to separate signals.
• Frequency
• Time
• Code

Frequency
Time
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FDMA

• Frequency-Division Multiple-Access
• Examples
• AMPS

Frequency
Time
Code
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TDMA

• Time-Division Multiple-Access
• Examples
• USDC/IS-136

Frequency
Time
Code
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CDMA

• Code-Division Multiple-Access
• Examples
• IS-95
• Direct-sequence
• Bluetooth
• Frequency-Hopping

Frequency
Time
Code
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Benefits of Spread Spectrumand CDMA

• Universal frequency resuse.
• Can tolerate interference
• Difficult to jam.
• Produces low interference
• Can be used in uncoordinated systems.
• Example WLANs in unlicensed ISM band.
• Privacy.
• Difficult to intercept.
• Improved performance in multi-path fading
  channels.
• Can combine reflected signals.
• Graceful degradation.
• Can always add just one more user in the system.

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IS-95

• IS-95/cdmaONE, Qualcomm, 1996.
• The only 2-G standard that uses CDMA.
• Uses Direct-Sequence Spread-Spectrum.
• Spreading gain N128.
• Operates in the same band as AMPS
• 800-900 MHz.
• Dual-mode (AMPS/CDMA) operation.
• Gradual transition from AMPS to IS-95
• Each IS-95 channel is 1.23 MHz
• Uses 41 AMPS channels
• 85 million subscribers worldwide in Aug. 2005.

64
Features of IS-95

• IS-95 offers several innovative features
• Voice activity monitoring
• Soft-capacity
• Soft-handoff
• These features translate to a 8-10x capacity
  improvement over AMPS and 4-5x improvement over
  GSM.
• More subscribers using the same frequency band.

65
Voice Activity Monitoring

• With CDMA, multiple data rates are possible.
• 1.2, 2.4, 4.8, or 9.6 kbps.
• The transmitter contains a voice-activity
  monitor.
• During pauses in speech, the low data-rate is
  used.
• 1.2 kbps.
• During normal speech, the high-data rate is used.
• 9.6 kbps.
• Sometimes the middle rates are used.
• This translates to an increase in capacity versus
  TDMA.
• With TDMA there is no way to dynamically change
  the data-rate in the middle of a conversation.

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Soft-Capacity

• The performance of CDMA depends on the number of
  simultaneous users.
• Each additional user reduces the quality for
  everyone by a small amount.
• CDMA offers soft-capacity
• No hard limit on number of users.
• Improved trunking-efficiency.
• Lower blockage capacity.

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Soft-Handoff

• CDMA offers soft-handoff
• Mobile can be connected to 2 base stations at the
  same time.
• Greatly improves performance at cell boundaries.

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Third Generation Systems

• 2-G systems designed for digitized voice
  (circuit-switched).
• New systems are required to support high speed
  data.
• Up to 2 Mbps packet-switched.
• There are too many 2-G standards
• Global roaming is impossible.
• Would like a single 3-G standard.
• Two 3-G standards
• WCDMA (also called UMTS)
• Europe Evolved from GSM (handoff supported)
• Proposed by ETSI supported by Ericsson, Nokia.
• 3GPP The Third Generation Partnership Project.
• cdma-2000
• North America Evolved from IS-95 (backward
  compatible)
• Proposed by TIA supported by Qualcomm.
• Also called 3GPP2.
• 185 million subscribers in Aug. 2005.

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WAP

• from The New Yorker, May 21, 2001.

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Wireless Networking Hierarchy
71
Standardization of Wireless Networks

• Wireless networks are standardized by IEEE.
• Under 802 LAN MAN standards committee.

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Ad Hoc vs.Infrastructure Based Networks
73
IEEE 802.11 Wireless LANs

• Key features of MAC
• Infrastructure or ad-hoc network.
• Coordinated (PCF) or distributed (DCF) operation.
• DCF uses CSMA/CA.
• PHY defines data rate and operating band
• Infrared at 1 or 2 Mbps.
• RF at 1 or 2 Mbps in using FH or DS 2.4 GHZ ISM
  band.
• 802.11b amendment
• 5.5 or 11 Mbps using DS and CCK in 2.4 GHz band.
• 802.11a amendment
• 6-54 Mbps using COFDM in 5-6 GHz U-NII band.
• 802.11g
• 6-54 Mbps using COFDM in 2.4 GHz ISM band.
• 802.11n
• In development. gt 108 Mbps
• IEEE 802.11 can also be used for wireless ISP.

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OFDM
75
the Hidden Terminal Problem in 802.11
76
IEEE 802.16 / WiMAX

• Air interface for fixed broadband wireless
  access systems
• Wireless MAN
• 893 page standard
• Wi-MAX forum/profiles

Base Station
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IEEE 802.16 Wireless MAN
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802.16e

• Ratified July 2005 to be published in Oct.
• Support for 120-150 kmph mobility.
• Asymmetrical link structure.
• Handheld units.

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802.20

• Mobile Broadband Wireless Access (MBWA)
• Dates
• Formed Dec. 11, 2002
• Approval anticipated in Dec. 2006
• Licensed bands lt 3.5 GHz
• Peak data rates gt 1 Mbps
• Mobility up to 250 kmph
• Range gt 15 km

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Bluetooth

• Bluetooth SIG formed in 1998 by Ericsson, Nokia,
  IBM, Toshiba, and Intel.
• Design goals
• Inexpensive 5 single chip solution.
• Short range 10 m or less.
• Low data rate lt 720 kbps.
• Peer-to-peer and ad-hoc networking.
• Data (ACL) and voice (SCO) support.
• Technology
• 2.4 GHz ISM band.
• 79 channels of 1 MHz each.
• Frequency Hopping at 1600 hops/sec.
• Nonorthogonal binary GFSK modulation.

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Throughput of Bluetooth
800
DH5
700
DH3
600
DM5
500
Data Rate in kbps
DM3
400
300
200
DH1
DM1
100
0
5
10
15
20
Es/No in dB
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Bluetooth Profiles

• Hands-free headset.
• Cordless telephone.
• Synchronization of PDA, cell phone, computer.
• Serial port emulation.
• Wearable computing.
• Wireless LAN access.
• Ad-hoc network.
• Peripherals Printer, scanner, fax machine.

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Piconets and Scatternets
84
IEEE 802.15 Wireless PAN

• Standardization began in 1997 under the Ad Hoc
  Wearables Standards Committee.
• Same goals and constraints as Bluetooth
• 2.4 GHz band, 10 m. range, inexpensive.
• Task 1
• Standard almost identical to Bluetooth.
• Task 2
• Coexistence of wireless LANs and PANs.
• Task 3
• 20 Mbps High-rate PAN similar to Bluetooth 2.
• Task 4
• Low rate 2-200 kbps PAN with extremely low power
  consumption for perpetual sensors.

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Other Multihop Networks

• Custom air interface
• MeshNetworks
• 802.11 based
• PacketHop
• LocustWorld
• Tropos (wireless backhaul)
• MeshDynamics
• Open source software
• Mitre
• CUWin
• Standardization
• 802.11s

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Free Space Optical

• Benefits
• 155 Mbps to 1.25 Gbps
• Range limited only by LOS.
• 4 km current state-of-the-art.
• Secure.
• Disadvantages
• Weather, smoke.
• Electro-mechanical pointing
• Acquisition, tracking.

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