@swimmer thanx for your quick answer,
I just like to share with you this portion of a reading material and just visit here
http://www.terena.org/events/archive/tnnc/1B/1B3/1B3.html for complete details.
"The benefits of the system are: 5.7GHz is a new and unused frequency which will not interfere with 2.4GHz, our test show that half-duplex bandwidth for UDP packets of 1500 bytes is approximately 9Mbps for up to 13km, and the equipment cost is a little more than a wireless client using Aironet equipment. The difficulties are: 5.7GHz does not have the same range as 2.4GHz (increasing frequency means greater signal attenuation over distance), a parabolic antenna is required for distances of more than 2km, and cable length is very limited because of high signal loss with coaxial cabling at 5.7GHz. "