Wireless LAN Standards

The WLAN Standards

Lets quickly review the IEEE Wireless LAN standards time line and the protocols.

Year   IEEE     Frequency      Typ Rate Max Rate

1997    802.11    ISM                     1 Mbps 2 Mbps

1999    802.11a  UNII                   25 Mbps 54Mbps (reduced interference with OFDM, faster)

1999    802.11b   ISM                    6.5 Mbps 11Mbps (popular for low cost)

2003    802.11g   ISM                   25 Mbps 54 Mbps

2009    802.11n    ISM or UNII 200Mbps 600Mbps

The legacy 802.11 uses Direct Sequence Spread Spectrum (DSSS) and Frequency-Hopping Spread Spectrum (FHSS) at the physical layer.
DSSS segments the data and sends it over different frequencies at the same time.   FHSS hops between frequency 1 and 2 to send data (i.e  1 101010101 2 101010101010 1 1010101101 2 10101010).

802.11b was approved in 1999, providing 11-Mbps data rate.  It provides speeds of 11, 5.5 and 2 Mbps, and uses 11 channels o fthe Industrial, Scientific and Medical (ISM) frequencies.  802.11b uses DSSS and is backward compatible with other DSSS systems.

802.11a was approved later in 1999.  This standard provides a maximum 54Mbps data rate but is incompatible with 802.11b.  It uses 13 channels of the Unlicensed Unational Information Infrastructure (UNII) frequencies and is incompatible with 802.11b and 802.11g.  It is also known as Wifi5.

IEEE 802.11g was approved in 2003.  The edge over 802.11a is backwards compatibility with 802.11b

802.11n came to us in a timely fashion, when WLAN/WIFI popularity was on a steep rise.   This standard added multiple-input multiple-output (MIMO) antennas and set the new maximum rate at 600Mbps using 4 spatial streams, each with a 40 MHz width.  In addition to DSSS, it uses orthogonal frequency-division multiplexing (OFDM) as a digital carrier modulation method.  it uses both the 2.4 Ghz(ISM) and 5Ghz(UNII) bands.

ISM and UNII

The ISM frequencies are defined by ITU-R radio regulations 5.138 and 5.150.  In the US, the FCC(15.247) specifies the ISM bands for unlicensed use.  ISM bands are specified in the following ranges:

  • 900 MHz to 928 MHz
  • 2.4 GHz to 2.5 GHz (802.1b and 802.1g)
  • 5.75 GHz to 5.875 GHz
There are 11 overlapping channels available, each is 22 MHz wide.
Image from wizwireless(wizbiz.co.nz)
Channels 1, 6 & 11 are used together frequently because they don’t overlap.
*Microwave ovens also operate at 2.45Ghz… which is why you may notice IP packets in your popcorn… or disruptions to your wireless connection. Actually the 2.4Ghz range is pretty popular with many cellphones, bluetooth devices, and other wireless gear operating in the 2.4 GHz range.
UNII radio bands were specified for 802.11a wireless.  UNII operates over these ranges:
  • UNII 1:  5.15 GHz to 5.25 GHz and 5.25GHz to 5.35GHz.
  • UNII 2:  5.47 GHz to 5.725GHz (HiperLAN in Europe)
  • UNII 3:  5.725 GHz to 5.875 GHz (Overlaps with ISM)
 Provides 12 non-overlapping channels for 802.11a.

RESOURCES:

More detailed information about the IEEE 802.11 WLAN Standards can be downloaded directly from IEEE here.

Checkout inSSIDer2 for Windows .
– Inspect your Wi-Fi and surrounding networks
– Scan and filter hundreds of nearby access points
– Troubleshoot competing access points and clogged Wi-Fi channels
– Highlight access points for areas with high Wi-Fi concentration
– Track the strength of received signals in dBm over time
– Sort results by MAC Address, SSID, Channel, RSSI, Time Last Seen
– Export Wi-Fi and GPS data to a KML file in Google Earth

There is also Chanalyzer for Mac.  (Only works if you purchase their Wi-Spy spectrum analyzer) but if you’re doing any sort of work in Wireless – you’d want to be well equipped.

That’s all for today peeps.

~

Gabe@networkdojo.net

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