My sgs has been dropiing wifi ever since i had it unless i had it plugged into the power supply, strange as it is after trying every other solution i decided to disable my wifi security, it was on WPA2-PSK [AES], since then i have no wifi issues at all and can stream as watch and dload as long as i wish :).

hope this helps others out, its been doing my head in for days now.:p

My router's wifi security is using WPA2-PSK and it has not been dropping at all (using TP-LINK).

What is your setting for the Wi-Fi sleep policy?

my wifi sleep is set to permanently awake

That's odd, im at work now, so I'm going to try and duplicate your problem with wifi sleep set to "Never" and post back later :)