Wifi shuts down when phone is locked

Greetings: I'm sorry if something like this was posted previously, but I have searched for topics of this nature before posting, and haven't found anything that describes my particular problem. I have an interesting issue that I have noticed lately on my phone. Whenever I have the phone locked, after a while, the WiFi turns off. I know this because when I look at my status bar on my lock screen, it says nothing. it doesn't give me any indication that it's receiving a signal. Also, none of my notifications work like they should. However, when I unlock the phone completely, everything comes right back on line again. This seems also to be an issue when my phone is in Airplane mode, since I put it in this mode while I'm at work, but turning on the WiFi only of course. Also, it seems to have started up in the past couple of weeks. Now, if I'm streaming music and the phone is locked, it doesn't seem to be an issue. In short, if the phone is in airplane mode, but I'm using the WiFi, I have to keep the phone unlocked in order to continue receiving a signal. Has anyone else experienced this little bug, or is this some sort of new power saving feature in iOS7? I have an iPhone 4S, running the latest iOS7 software. Thanks.