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Wireless LANs

Comparison of Wireless LAN Standards - 802.11a versus 802.11b 

  IEEE 802.11b IEEE 802.11a
Time Table  Standard in 1997, Products in 2000 Standard in 2001, products in 2002
Frequency Band and bandwidth Transmit at 2.4 GHz -  IEEE 802.11g standard increases speed of 802.11b to 22 Mbps in the same 2.4 GHz band 5 GHz 
Speed 11 Mbps (Effective speed - half of rated speed) 54 Mbps (Effective speed - 50% rated speed)
Modulation Technique Spread Spectrum OFDM (Orthogonal Frequency Division Multiplexing
Distance Coverage Up to 300 feet 60 feet - speed goes down with increased distance
Number of access points required Every 200 feet in each direction Every 50 feet; 
Maturity More matured products Less matured but progressing fast
Market Penetration Quite widespread  Just starting in 2002
Interference with other devices  Band is more polluted - significant interference here  Less interference because of few devices in this band
Interoperability  Current problems  expected to be resolved in future Problems now but expect resolution soon
Cost Cheaper - $300 for access point and $75 for adapter More expensive $ (500 in 01/2002 - will come down
Vendors Major vendors in both camps   

MobileInfo Advisory Notes and Comments

  • Different radio frequency and modulation types of 802.11a and 802.11b causes interoperability problems - though access points with dual radios and roaming have started appearing. Without these type of access points, a device with 802.11b card will not be able to use 802.11a access point.
  • Because of distance limitation issue with IEEE 802.11a standard, you may need as many as 16 times the number of access points as with 802.11b  - wiring the access points could be complex. For large areas like warehouse or a factory, IEEE 802.11b deployment would be more cost effective than one based on IEEE 802.11a unless there is need for bandwidth-hungry applications.
  • IEEE 802.11a standard is suitable for large number of users in fairly close proximity accessing applications that require high bandwidth - video streaming, transmission of large files. Also because of signal penetration characteristics in the two bands, IEEE 802.11a standard based equipment would be more suitable in relatively open offices rather than in enclosed offices with thick walls.
  • You can increase distance coverage by a higher power of access points and antennas. This is an area where you must do more thorough investigation and ultimately do tests in your specific environment.
  • Synad, a UK company has developed 802.11a/b chip set that will allow the device to sense which access point is present. 


Related Resources:
802.11 LANs versus Bluetooth
Wireless Wide Area Networks
Bluetooth Topics
> HomeRF Site
> Broadband Topics - Connecting Fixed Wire LANs through Wireless Links


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