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

2 Author: D L Johnson Overview of WiFi IEEE 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 Author: D L Johnson Overview of WiFi – usage scenarios

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

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

6 Author: D L Johnson Overview of Wifi - context u The IEEE 802 group +IEEE 802.1™ Bridging & Management Bridging & Management +IEEE 802.2™: Logical Link ControlLogical Link Control +IEEE 802.3™: CSMA/CD Access MethodCSMA/CD Access Method +IEEE 802.4™: Token-Passing Bus Access Method Token-Passing Bus Access Method +IEEE 802.5™: Token Ring Access MethodToken Ring Access Method +IEEE 802.6™: DQDB Access MethodDQDB Access Method +IEEE 802.7™: Broadband LANBroadband LAN +IEEE ™: SecuritySecurity +IEEE ™: WirelessWireless +IEEE ™: Demand Priority AccessDemand Priority Access +IEEE ™: Wireless Personal Area Networksireless Personal Area Networks +IEEE ™: Broadband Wireless Metropolitan Area NetworksBroadband Wireless Metropolitan Area Networks

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

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

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

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

11 Author: D L Johnson Overview of WiFi – MAC layer u 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 Author: D L Johnson Overview of WiFi – summary of standards

13 Author: D L Johnson Overview of WiFi – Actual throughput Technology Transactions per second Mbps of TCP payload throughput Transactional speed relative to b 11b, 11 Mbps a, 54 Mbps ,9 11g, 54 Mbps/no protection g, 54 Mbps/CTS- to-self protection g, 54 Mbps/RTS/CTS protection

14 Author: D L Johnson Overview of WiFi – rural connectivity

15 Author: D L Johnson Overview of WiFi – rural connectivity

16 Author: D L Johnson Overview of WiFi – rural connectivity u Point-to-Multipoint link configuration u Point-to-Point link configuration

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