I have a WiFi 801.11n/g network from the ADSL box of my provider (Freebox V6, should someone be from France). While streaming video to mobiles (iPhone 4S, iOS 6.0.1 or Galaxy S3/Note 2, Android 4.0.1) I notice that after some time (say, 20 minutes) the synchronization speed drops to about 19 Mbps (from an initial 54 Mbps). This happens both for n and g mode, fairly regularly (though this is not a rule) - I notice the drop when the video stops being fluid. My laptop does not have this issue.
I can clear this off by disconnecting the WiFi and then reconnecting. Rebooting the box also helps. I had exactly the same issue with the previous box (older generation - Freebox V5, a completely different box). There is no particular traffic when the sync speed drops, I am the only one using it at that time. The neighbouring WiFi traffic is quite dense (about 20 AP discovered) but it is stable.
I mostly would like to understand if this is a "normal" behaviour of mobiles (from experience of by design) or if there is a problem somewhere.