do the 4 channel rc helicopter transmitter use interrupt driven program for the controls for sampling the analog signal or it samples the analog signal from the controls after a particular intervals of time, periodically, and sends it to transmitter ?

I think you may get the answer in the links given in the thread
http://www.rcindia.org/radios-and-receivers/simplest-tx-rx-diy-anyone-interested/

In addition to link posted by Kalyan, you might want to search up "PPM" and "RC frame" on google. In short, sampling and transmission is done at about 50 times a second with values inter-positioned in the 20ms time period.

thanks. this link helped me a lot