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WiFi: A Comprehensive Overview

This workshop provides an overview of WiFi, its usage scenarios, history, physical layer technologies (FHSS, DSSS, OFDM), MAC layer protocols, standards, and future developments. Presented by David Johnson, a mobile platform technology leader at Icomtek CSIR.

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WiFi: A Comprehensive Overview

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  1. FSATIE TELECOMMUNICATION WORKSHOP Overview of WiFi Presented by David Johnson Mobile platform technology leader Icomtek CSIR

  2. Overview of WiFi IEEE 802.11 is extension of Ethernet standard (IEEE 802.3) into wireless communications Allows roaming computers to talk to other devices(peer-to-peer) or connect to wired network

  3. Overview of WiFi – usage scenarios

  4. Overview of WiFi – usage scenarios • Hotspots inside coffee shops, airports etc. • Corporate wirelessly enabled LAN’s • Point to point links between access points (even bluetooth access points) • Voice over IP links within residential or business premises boundaries (Operators use VoIP across boundaries) • Video links for telehealth applications • Rural connectivity solutions to connect schools, hospitals and clinics to each other and to the internet

  5. Overview of WiFi - history • Early 90’s: Many proprietry WLAN systems operating in the 2.4GHz and 900MHz, eg. Lucent WaveLAN • 1990: IEEE802 standards committee formed the 802.11 Wireless LAN working group • Jul 26, 1997: IEEE approved the 802.11 standard which was published on 18 November, 1997 • 1998: Several manufactures began manufacturing 802.11 compliant wireless cards capable of 1,2 Mbps links • 1999: IEEE approved 802.11 a and 802.11b standard • 802.11b extended datarate to 11 Mbps using DSSS • 802.11a extended datarate to 54 Mbps using OFDM in 5GHz band • 2001, the FCC announced new rules allowing additional modulations such as OFDM in the 2.4GHz • 2002: 802.11g released to create 802.11a equivalent in 2.4GHz band

  6. Overview of Wifi - context • The IEEE 802 group • IEEE 802.1™ Bridging & Management • IEEE 802.2™: Logical Link Control • IEEE 802.3™: CSMA/CD Access Method • IEEE 802.4™: Token-Passing Bus Access Method • IEEE 802.5™: Token Ring Access Method • IEEE 802.6™: DQDB Access Method • IEEE 802.7™: Broadband LAN • IEEE 802.10™: Security • IEEE 802.11™: Wireless • IEEE 802.12™: Demand Priority Access • IEEE 802.15™: Wireless Personal Area Networks • IEEE 802.16™: Broadband Wireless Metropolitan Area Networks

  7. Overview of WiFi – Phycial layer (FHSS) • Uses 79 separate 1 MHz channels from 2.402-2.480 GHz • Hops about every 0.1 sec (22 hop pattern, 2.5 hop/sec minimum in US) • Immune to single frequency noise, has trouble with wideband noise • Many networks can be located in the same area • Uses less power to transmit & less expensive to build than DSSS

  8. Overview of WiFi – Phycial layer (DSSS) • Signal modulated with a spreading code (11-bit Barker Sequence) • Uses BPSK for 1Mbps, QPSK for 2Mbps • All 802.11b compliant products use the same spreading code • Higher data rates because of “fatter pipe” (about 11 MHz) • Allows for some single frequency noise & higher wideband noise • Only allows for 3 networks in same area • Uses higher power to transmit & more expensive to build than FHSS

  9. Overview of WiFi – Phycial layer (OFDM) • Distributes the data over a large number of carriers that are spaced apart at precise frequencies • Carriers are orthogonal which means that carriers are placed at the nulls in the modulation spectra of each other • Results in high spectral efficiency, resiliency to RF interference, and lower multi-path distortion

  10. Overview of WiFi – MAC layer • Media Access Control (MAC) layer specification has similarities to the 802.3 Ethernet wired line standard • Standardised across 802.11a/b/g • Uses a protocol scheme known as carrier-sense, multiple access, collision avoidance (CSMA/CA) • Avoids collisions instead of detecting collisions used in 802.3 • RF energy is measured at the antenna and if the received signal strength is below a specified threshold the channel is declared clear • CSMA/CA protocol can use a request to send, clear-to-send, and acknowledge in sequential fashion • Communication is established when one of the nodes sends an RTS frame

  11. Overview of WiFi – MAC layer • Hidden node • Due to the lack of arbitration between devices communicating with an access point – collisions can occur • RTS/CTS mechanism can be used but most manufactures don’t implemented this in the firmware

  12. Overview of WiFi – summary of standards

  13. Overview of WiFi – Actual throughput

  14. Overview of WiFi – rural connectivity

  15. Overview of WiFi – rural connectivity

  16. Overview of WiFi – rural connectivity Point-to-Multipoint link configuration Point-to-Point link configuration

  17. Overview of WiFI – The Future • Combination of 802.11a/b/g in a single chip • Standby power consumption reduced by 10x to enable embedded WiFi solutions depending on batteries • 802.11i security standard to be implemented in new WiFi products • Speeds from 108 Mbps to 300 Mbps proposed for 2005 and referred attentively as 802.11n • Guaranteed QOS for VoIP • UWB could be competition to 802.11 in the future but probably only in many years to come

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