Hi,
Is NLOS achievable with 802.11a/b/g. If yes then which 802.11
thanks

Would you care to give us a bit more information, what is blocking your LOS?

it could be building or trees. On point to multipoint LOS is practically not achievable here.
thanks

I have installed about 2 links using 802.11b NLOS, the 1 link is about 1KM through about 50 trees and the other is about 4KM through about 2 trees. 802.11b is the best when you have obstacles as the transmit power on most cards increases when set to 802.11b. I have not managed to get 802.11a working NLOS though. But at the end of the day there are many factors that might affect connectivity with NLOS wifi equiment. There is however unlicenses NLOS equipment available have a look at the Alverion kit.

HI,
The secret of NLOS is based on antenna and on protocol of transmission.
Into the city you need circolar polarization and OFDM protocol. You can use with crcolar antenna all, vertical or horizontal polarizations.