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

1

FSATIE TELECOMMUNICATION FSATIE TELECOMMUNICATION WORKSHOPWORKSHOP

FSATIE TELECOMMUNICATION FSATIE TELECOMMUNICATION WORKSHOPWORKSHOP

Overview of WiFiOverview of WiFi

Presented by David JohnsonPresented by David JohnsonMobile platform technology leaderMobile platform technology leaderIcomtekIcomtekCSIRCSIR

2Author: D L Johnson

Overview of WiFi 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


Overview of WiFi – usage scenariosOverview of WiFi – usage scenarios


Overview of WiFi – usage scenariosOverview of WiFi – usage scenarios

Hotspots inside coffee shops, airports etc.Hotspots inside coffee shops, airports etc. Corporate wirelessly enabled LAN’sCorporate wirelessly enabled LAN’s Point to point links between access points (even Point to point links between access points (even

bluetooth access points)bluetooth access points) Voice over IP links within residential or business Voice over IP links within residential or business

premises boundaries (Operators use VoIP across premises boundaries (Operators use VoIP across boundaries)boundaries)

Video links for telehealth applicationsVideo links for telehealth applications Rural connectivity solutions to connect schools, Rural connectivity solutions to connect schools,

hospitals and clinics to each other and to the internethospitals and clinics to each other and to the internet


Overview of WiFi - historyOverview of WiFi - history

Early 90’s: Many proprietry WLAN systems operating in the 2.4GHz Early 90’s: Many proprietry WLAN systems operating in the 2.4GHz and 900MHz, eg. Lucent WaveLANand 900MHz, eg. Lucent WaveLAN

1990: IEEE802 standards committee formed the 802.11 Wireless LAN 1990: IEEE802 standards committee formed the 802.11 Wireless LAN working groupworking group

Jul 26, 1997: IEEE approved the 802.11 standard which was Jul 26, 1997: IEEE approved the 802.11 standard which was published on 18 November, 1997published on 18 November, 1997

1998: Several manufactures began manufacturing 802.11 compliant 1998: Several manufactures began manufacturing 802.11 compliant wireless cards capable of 1,2 Mbps linkswireless cards capable of 1,2 Mbps links

1999: IEEE approved 802.11 a and 802.11b standard1999: 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 2001, the FCC announced new rules allowing additional modulations

such as OFDM in the 2.4GHzsuch as OFDM in the 2.4GHz 2002: 802.11g released to create 802.11a equivalent in 2.4GHz band2002: 802.11g released to create 802.11a equivalent in 2.4GHz band


Overview of Wifi - contextOverview of Wifi - context

The IEEE 802 groupThe 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


Overview of WiFi – Phycial layer (FHSS)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


Overview of WiFi – Phycial layer (DSSS)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


Overview of WiFi – Phycial layer (OFDM)Overview of WiFi – Phycial layer (OFDM)

Distributes the data over a large number of carriers that are spaced Distributes the data over a large number of carriers that are spaced apart at precise frequenciesapart at precise frequencies

Carriers are orthogonal which means that carriers are placed at the Carriers are orthogonal which means that carriers are placed at the nulls in the modulation spectra of each othernulls in the modulation spectra of each other

Results in high spectral efficiency, resiliency to RF interference, and Results in high spectral efficiency, resiliency to RF interference, and lower multi-path distortionlower multi-path distortion


Overview of WiFi – MAC layerOverview of WiFi – MAC layer

Media Access Control (MAC) layer specification has Media Access Control (MAC) layer specification has similarities to the 802.3 Ethernet wired line standardsimilarities to the 802.3 Ethernet wired line standard

Standardised across 802.11a/b/gStandardised across 802.11a/b/g Uses a protocol scheme known as carrier-sense, multiple Uses a protocol scheme known as carrier-sense, multiple

access, collision avoidance (CSMA/CA)access, collision avoidance (CSMA/CA) Avoids collisions instead of detecting collisions used in Avoids collisions instead of detecting collisions used in

802.3802.3 RF energy is measured at the antenna and if the received RF energy is measured at the antenna and if the received

signal strength is below a specified threshold the channel signal strength is below a specified threshold the channel is declared clearis declared clear

CSMA/CA protocol can use a request to send, clear-to-CSMA/CA protocol can use a request to send, clear-to-send, and acknowledge in sequential fashionsend, and acknowledge in sequential fashion

Communication is established when one of the nodes Communication is established when one of the nodes sends an RTS framesends an RTS frame


Overview of WiFi – MAC layerOverview of WiFi – MAC layer

Hidden nodeHidden 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


Overview of WiFi – summary of standardsOverview of WiFi – summary of standards


Overview of WiFi – Actual throughputOverview of WiFi – Actual throughput

TechnologyTechnology Transactions Transactions per secondper second

Mbps of TCP Mbps of TCP payload payload throughputthroughput

Transactional Transactional speed relative speed relative to 802.11bto 802.11b

11b, 11 Mbps11b, 11 Mbps 479479 5.65.6 1.01.0

11a, 54 Mbps11a, 54 Mbps 23362336 27.327.3 4,94,9

11g, 54 Mbps/no 11g, 54 Mbps/no protectionprotection

23362336 27.327.3 4.94.9

11g, 54 Mbps/CTS-11g, 54 Mbps/CTS-to-self protectionto-self protection

11131113 13.013.0 2.32.3

11g, 54 11g, 54 Mbps/RTS/CTS Mbps/RTS/CTS protectionprotection

750750 8.88.8 1.61.6


Overview of WiFi – rural connectivityOverview of WiFi – rural connectivity





Point-to-Multipoint link configurationPoint-to-Multipoint link configuration

Point-to-Point link configurationPoint-to-Point link configuration


Overview of WiFI – The FutureOverview of WiFI – The Future

Combination of 802.11a/b/g in a single chipCombination of 802.11a/b/g in a single chip Standby power consumption reduced by 10x to enable Standby power consumption reduced by 10x to enable

embedded WiFi solutions depending on batteriesembedded WiFi solutions depending on batteries 802.11i security standard to be implemented in new WiFi 802.11i security standard to be implemented in new WiFi

productsproducts Speeds from 108 Mbps to 300 Mbps proposed for 2005 Speeds from 108 Mbps to 300 Mbps proposed for 2005

and referred attentively as 802.11nand referred attentively as 802.11n Guaranteed QOS for VoIPGuaranteed QOS for VoIP UWB could be competition to 802.11 in the future but UWB could be competition to 802.11 in the future but

probably only in many years to comeprobably only in many years to come

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

Documents