What is the advantage of 11b over 11a?
Is it only the cost of hardware or anything else..??
Advantages of 11a:
1) Too many channels available
2) Less interference in this band (except for radar, military)
3) Higher data rates (No lower data rates below 6)
'b' and 'g' (2.4 GHz band) have better penetration of walls, trees, and other 'soft' obstructions than 5 GHz. That is about the only advantage that leaps to mind.
For Wi-Fi applications, 'b' has the advantage of being more universally present on client devices that 'g' or 'a'.
I pretty much exclusively use the 5 GHz bands for outdoor, clear LoS applications (using Firetide gear).
2.4 GHz (802.11bg) travels farther than 5 GHz and penetrates walls better, although there is an arguement for the higher data rates of 802.11a negating this advantage indoors.
The bigger advantage is the number of devices that support bg.
The biggest advantages of 802.11a is much less crowded spectrum (don't have to deal with baby monitors, cordless phones, wireless video cameras, microwaves, etc.) and the number of non-overlapping channels available.