Wifi networking is almost a black art. There's so many manufacturers implementing the 'standards' that it's pretty tough to make everything interoperate perfectly. All it takes is one device to cut a corner in one direction and the other in the other direction and you get problems (remember, manufacturers are always out to cut their costs!).
If you're lucky all it'll take is a setting or firmware upgrade (*) to fix the issue, if you're unlucky it's a hardware limitation and short of replacing your router you're out of luck.
Someone -may- be able to assist if you give details of your wireless router (make, model, revision, firmware, settings) but I doubt it. Your best bet may be to raise this with Sony technical support (with all the details I already mentioned) as it's in their interest to ensure their products work on as wide a range of routers as possible. If it's a well-known and widely-used model router they'll want to investigate and fix this.
(*) Check whether or not your router has the latest firmware installed. Newer firmwares often fix glitches like this.