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802.11a, or 802.11b

The Dual Dilemma - 802.11a, or 802.11b - Which is best, where?
No question about it, today, the most widely used wireless LAN's comply with the 802.11b standard.  Recent ready availability of the 802.11a access points and radio cards has brought up what is rapidly becoming another widely used wireless LAN solution.  In light of this variety, the question is raised: Which to use, 802.11a, or 802.11b?
Each type defines their own physical layer; 802.11a radios send data up to 54 Mbps using OFDM (Orthogonal Frequency Division Multiplexing) and transmit at 5 GHz, while 802.11b send data at up to 11 Mbps using direct sequence spread spectrum modulation and transmit at 2.4 GHz.
Ultimately, the performance of 802.11a gives excellent support for bandwidth thirsty applications, but the higher operating frequency often results in a relatively shorter range.  There have been demonstrations of 802.11a radios handling 54 Mbps with distances of around 60 feet, which is far less than the 300 feet or so that you will find with 802.11b units.  In comparison with 802.11b, you'll need a considerably larger number of 802.11a access points to blanket a facility - particularly large ones.
The differences in radio frequency and modulation type of 802.11a and 802.11b unfortunately cause them to not operate well together.  Thus, an end-user with an 802.11a radio card will NOT be able to connect to an 802.11b access point.  The 802.11 standard offers no real interoperability between their unique physical layers.

PERFORMANCE CHOICE GUIDELINES

802.11a:
  • Will give you a much higher performance than b.  If you need to support higher end applications such as voice, video, and transmission of large files and images, 802.11b most likely will have trouble keeping up.

  • If there is a dense concentration of end-users (such as in convention centers, airports, and computer labs).  When there are many competing for the same access point, 802.11a will offer greater total throughput.

  • Should be used if there is strong RF interference within the 2.4 GHz band.  Bluetooth devices and wireless phones could overpopulate the radio spectrum in your facility and cause a significant decrease in 802.11b performance.  Using 802.11a operating in the 5 GHz band will avoid this interference completely.
802.11b:
  • If you already have a significant investment in 802.11b units.  There is a proportionately higher cost associated with moving from a grander-scale 802.11b system to 802.11a, and it will not be an easy sell to the financial decision-makers in your company.

  • If range requirements are important. If you operate in a large facility such as a department store or warehouse, 802.11b will be less costly because you will need fewer access points.

  • Should be considered if the end-users are sparsely distributed.  802.11b will be the best to handle your performance requirements if there are less end-users competing for each access point's throughput.  Unless you have strong needs for extremely high performance per end-user, 802.11b will be the best solution.
BOTH???
  • Interoperability between 802.11a and 802.11b will improve significantly within the next year or so.  There are companies that are developing a dual 802.11a/b chipset that will enable product developers to deliver wireless LAN devices that talk BOTH 802.11a AND 802.11b.  This will result in access points being able to deploy the dual a/b solution, as well as the radio within an end-user device being able to automatically sense whether the access point is a or b and respond accordingly.  In the future, the inability to communicate between the two platforms will diminish, giving forward-thinking communications professionals a chance to use BOTH 802.11a and 802.11b to their fullest potential - even in the most difficult of circumstances.



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