My Iphone 4s Keeps On Losing Wifi Connection?

Me and my wife bills this month double. We are not on unlimited data plan. But still with our last iphone 3G, its wifi connectivity is very good that we rarely go beyond our data plan. With the 4S iphone, I noticed that it goes out of wifi connectivity even at home. I mostly used it for music but then would be surprised after few minutes of listening that it already is out of wifi connectivity and is using our carrier signal. Is there a way to improve or prevent it from happening?