FSATIE TELECOMMUNICATION WORKSHOP

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 LANs
• 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 90s 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 dont 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