Hi Naseef
When clients drop connections, very rarely is it down to an infrastructure problem, there are only a few instances when an AP will initiate or force the disconnection of a client device. I would start by looking at the client devices themselves. First task is always check the wireless adapter device drivers and make sure they are on the latest version. 9 times out of 10 this will get rid of connectivity issues.
If you still have problems, then take a look and make sure that your RF environment meets with the requirements of the device (i.e. primary RSSI, secondary RSSI and SNR). You may also want to do some spectrum analysis of the environment to ensure that you do not have any sources of non 802.11 RF that could be disrupting communication.
Regards
Simon