I bought an iPhone 3GS, second hand that was on iOS6. The wifi signal on it is terrible, I can be in the room next to the router and have 2 or 1 bars and it will drop connection every now and then. If I'm in my bedroom upstairs I can't get signal on the phone at all with WiFi and I'm less than 15 meters away from the router. This also happens with iOS 4.1 (The only version I can downgrade to). Any ideas?