This is Wireless Communication and Mobile Computing, Lecture notes of Mobile Computing

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IT 408: Mobile Computing

1

Wireless LANs

IT

Application

Transport

Network

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Data Link

Physical

Infrared vs Radio Transmissions

• Basic txn technologies for WLANs
• Infrared
  • Based on txn of infra red light (900 nm wavelength)
  • Uses light(direct or diffused)
  • Simple and extremely cheap– Simple and extremely cheap
  • Infra red data association (IrDA) interface standard
  • Data rates upto 115kbps , 1.15 Mbps
  • No licenses are needed for infra red technology
  • Can get easily shielded – cannot penetrate walls or other obstacles (^) IT408 4

• Radio
  • Can cover larger areas
  • Uses radio txn in GHz range
  • Used with most wide area networks, mobile cellular phones, etcphones, etc
  • Higher txn rates: eg 54 Mbps
  • Most WLANs rely on radio txn
    • IEEE802.11 also standardized infra red

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Wireless Networks

• Wireless Personal Area Networks
  • Bluetooth/Infrared based
• Wireless Local Area Networks
  • 802.11 based Wi-Fi
• Hi-speed wireless LAN
  • HiperLAN
• Wireless Wide Area Networks
  • WiMAX IT408 7

Wireless Personal Area Networks (WPAN)

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WPAN…

• Bluetooth is based on IEEE 802.15 standard
• Operate in the license-free 2.4 GHz ISM band
• Piconet
  • collection of bluetooth devices which are synchronized to the same hopping sequencesynchronized to the same hopping sequence
• Devices in a piconet
  • Master (M)
  • Slave (S)
  • Parked (P)
  • Standby (SB) (^) IT408 10

• Piconet

S P

• Upto 7 slaves
• Master determines thehopping sequence
• Slaves synchronize to that pattern

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S M

SB S

S

P

• Slaves synchronize to that pattern
• Parked devices are participants in the piconet but are inactive known and can be activated withinfew ms
• Standby devices do not participate inthe piconet
• 3-bit addressing mechanism for activemembers

IEEE 802.

• Most famous WLAN specification
  • Many products are based on this specification
• Wireless LAN standard defined in the unlicensed spectrum (2.4 GHz and 5 GHz bands)

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spectrum ( 2. 4 GHz and 5 GHz bands)

802.11 (contd.)

• Uses radio and infrared transmissions
• Standards covers the MAC sublayer and PHY layers
  • MAC support for multiple physical layers with different medium sense, transmission charactersits
  • Support for power management to save battery

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• Support for power management to save battery
• Handling of hidden nodes

• Stations
  • Terminals with access mechanisms to the wireless medium, and radio contact to the AP
• BSS
  • Stations and AP within the same radio coverage
• ESS
  • Network formed by one or more BSSs
  • Has unique ESSID (network name)
• Distribution system
  • Connects several BSSs via the AP to form single ntk
• Portal
  • Connects the wireless networks(via APs) with other (wired) LANs IT408 16

802.11 - Infrastructure

Portal

802.11 LAN 802.x LAN

BSS (^1) AccessPoint

STA (^1)

IT408 (^) Source: Schiller 17

Distribution System AccessPoint

802.11 LAN

BSS (^2)

STA (^2) STA (^3)

ESS

802.11 architecture (contd.)

• The ovals can be thought of as the coverage area within which member stations can directly communicate
• The Independent BSS (IBSS) is the simplest LAN. It

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• The Independent BSS (IBSS) is the simplest LAN. It may consist of as few as two stations
• IBSS is also called the ad hoc mode

802.11 - ad-hoc network

• Direct communication within a limited range - Station (STA): terminal with access mechanisms to the wireless

802.11 LAN

STA (^1) BSS (^1)

STA (^2)

STA (^3)

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mechanisms to the wireless medium

• Basic Service Set (BSS): group of stations using the same radio frequency 802.11 LAN

BSS (^2)

STA (^4)

STA (^5)

Source: Schiller