Why does my IPhone light up?

Around every 10-30 seconds my IPhone 4 automatically lights up (when in lock mode). I believe it is doing it whenever my 3G service (AT&T) changes its signal… I.e. Goes from 4 bars to 3. But i'm not sure if that's the problem. It is really killing my battery horrifically and i would really like help. Is there a setting to stop this or does anyone know how to solve it?

Its natural