CS176 Spring 2006 Introduction to Wireless Networks

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CS176 Spring 2006Introduction to Wireless
Networks

• Administrivia
• Homework 2 posted online
• Note new due date
• Project proposal due before HW 2!!
• See lecture schedule page
• Today
• 180o turn in topics
• P2P ? Wireless Networking
• This week
• Intro to wireless
• Media Access Protocols
• Today slides courtesy of Prof. Heather Zheng and
  Prof. Elizabeth Belding-Royer

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Wireless is VERY Important!
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History of Wireless
Italian inventor Guglielmo Marconi's 1901
transmission of a wireless signal from Ireland to
Canada.
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From Wired to Wireless
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Wired vs. Wireless

• Wired Networks
• high bandwidth
• low bandwidth variability
• low error rates (10-6)
• symmetric connectivity
• can listen on wire
• high power machines
• high resource machines
• need physical access (security)
• low delay
• connected operation

• Wireless Networks
• low bandwidth
• high bandwidth variability
• high error rates (10-3)
• possible asymmetric connectivity
• hidden terminal problem
• low power machines
• low resource machines
• need proximity
• higher delay
• disconnected operation

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Why Go Wireless

• Mobile wireless networks
• Enable anywhere/anytime connectivity
• Bring computer communications to areas without
  pre-existing infrastructure
• Faster network setup (ad hoc -gt instant!)
• Enable mobility
• Enable new applications

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Types of Wireless Devices

• Laptops
• Palmtops
• PDAs
• Cellphones
• Pagers
• Sensors

resources
Portability
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Wireless Communication

• Infrared (IR)
• cable replacement technology, point to point
• advantages
• simple and very cheap
• no interference from electrical devices
• no licenses needed
• disadvantages
• low bandwidth (about 115 kbps)
• quite easily shielded
• line of sight needed

• Radio (RF)
• used by most wireless systems
• advantages
• covers larger areas
• better penetration
• higher data rates
• (11Mbps 802.11b, 54Mbps 802.11a and g)
• disadvantages
• higher interference among signals
• only permitted at certain frequency bands

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What is different
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Why?

• Radio wave propagation (sort of like your voice)
• Decreasing signal strength
• Radio waves lose energy due to absorption or
  scattering
• Multi-path fading reflections from multiple
  objects time varying due to mobility
• Interference
• Your signal is noise to others in the same
  frequency band
• Broadcast nature
• Network dynamics
• Moving objects, weather
• Node mobility

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Challenges

• Wireless channels are a difficult and
  capacity-limited broadcast communications medium
• Traffic patterns, user locations, and network
  conditions are constantly changing
• Energy and delay constraints change design
  principles across all layers of the protocol
  stack
• Fundamental problems well look at
• Media Access Control (MAC) protocolsWho gets to
  talk and when?
• Routing protocolshow do you deliver your message
  to destination X?

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Existing Wireless Networks

• Wireless Metropolitan Area Network (WMAN)
• Cellular/Wireless Wide Area Network (WWAN)
• Local Area Network (WLAN)
• Personal Area Network (WPAN)
• Ad hoc networks
• Sensor networks
• Emerging networks (variations of ad hoc
  networks)
• Info-stations
• Vehicular networks

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Network Architectures
Cellular Networks (hierarchical systems) ? QoS
mobility ? , lack of innovations

• WLAN / Mesh networks
• Simple, cheap ? Poor management

Ad hoc networks ? no infrastructure cost ? no
guarantee

• Sensor networks
• ? Energy limited, low processing power

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Wireless Info-station

• General Idea
• Local wireless coverage (radius 50
  meters)Automatic exchange of information with
  wireless gadgets in range
• Applications
• Location-dependent information
• non-urgent information
• Distribute course material to students
• Info-stations for retail environments
• Design issues
• Scheduling and allocation
• Prolong battery life
• Reliable data transfer

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Inter-Vehicular Communication

• Providing information to drivers

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Cellular Phone Networks
Bob _at_ Santa Barbara
Internet
David _at_ New York City
PSTN
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Cellular Systems

• Geographic region divided into cells
• Frequencies/timeslots/codes reused at
  spatially-separated locations (shown as different
  colors)
• Base stations/radio network controllers
  coordinate handoff and control
• Base stations assign transmission schedule to
  users
• Radio network controllers coordinate among base
  station

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Wireless Local Area Networks (WLANs)

• WLANs connect local computers (100m range)
• Infrastructure mode everyone connected to the AP
• Ad hoc mode peer-to-peer
• Breaks data into packets
• Channel access is shared (random access)
• Backbone Internet provides best-effort service
• Poor performance in some apps (e.g. video)

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Wireless LAN Standards

• 802.11b (Current Generation)
• Standard for 2.4GHz band (80 MHz)
• Frequency hopped spread spectrum
• 1.6-10 Mbps, 500 ft range
• 802.11g (New Standard)
• Standard in 2.4 GHz and 5 GHz bands
• OFDM
• Speeds up to 54 Mbps
• 802.11a (Emerging Generation)
• Standard for 5GHz band (300 MHz)
• OFDM with time division
• 20-70 Mbps, variable range
• Similar to HiperLAN in Europe

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WiMAX - Wireless Metropolitan Area Networks
(802.16)

• WiMax (Worldwide Interoperability for Microwave
  Access)
• Mainly for broadband last mile in unwired
  areas, and on back-haul for WiFi hotspots
• Inexpensive alternative to cable, DSL
• Also expected to support mobile wireless
• Compete with cellular networks (OFDM vs. CDMA)
• Range (31miles, 45km), Data rate 75Mbps,
  Frequency (2-11GHz)
• Lack of spectrum to deploy WiMAX ?
• Bill Gates and other leaders from Intel, Dell,
  Cisco Systems urged lawmakers to speed the
  transition to digital television in order to free
  up radio spectrum for wireless broadband services

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Personal Area Networks (PAN) - Bluetooth

• Cable replacement RF technology (low cost)
• Short range (10m, extendable to 100m)
• 2.4 GHz band (crowded)
• 1 Data (700 Kbps) and 3 voice channels
• Widely supported by telecommunications, PC, and
  consumer electronics companies

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Ultra-Wide-Band (UWB)

• UWB is an impulse radio sends pulses of tens of
  picoseconds to nanoseconds
• Uses a lot of bandwidth (GHz)
• Spectrum allocation overlays existing users, but
  its allowed power level is very low to minimize
  interference
• 7.5 GHz of free spectrum in the U.S.
• Good things about UWB
• Low Power CMOS transmitters
• 100 times lower power than Bluetooth for same
  range / data rate
• Very high data rates possible
• 500 Mbps at 10 feet under current regulations

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IEEE 802.15.4 / ZigBee Radios

• Low power, low rate WPAN
• Supports data transmission rates of up to 250
  Kbps at a range of up to 30 meters.
• Data rates of 250 kbps (_at_2.4 GHz), 40 kbps (_at_ 915
  MHz), and 20 kbps (_at_868 MHz)
• slower than 802.11b (11 Mbps) and Bluetooth (1
  Mbps) 
• CSMA-CA channel access
• Low power (battery life multi-month to years)
• Low-range, low data-rate, low cost ? ideal for
  RFID tags

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Thats It for Today

• On Thursday
• Media Access Control