ABSF WROTE:PS2 wireless joystick is using infra-red to send data to the main unit. Infra-red would normally not travel very far due to it was designed for that purpose and it would not pass through walls. If you want it to go 20m and beyond, the cheap RF modules if used with matching aerial might be able to go that far. The RC for model car or model planes uses more powerful RF transmitter designs in order to go hunreds of meters. If you can afford, Xbee module would be the better choice.
Allen, actually Wireless PS2 is not using Infrared, at least from what I get. The packaging actually stated it is using 2.4GHz, I open the casing, it is a wireless module which I do not recognize, should be customized wireless module. Yes, it cannot go far as the main purpose is not for distance control, as kl84 said, when you play PS2, normally is in a room, I have try 10 meters before, but not sure about your PS2 because there are many type in the market.
Also as far as I know, SONY does not come out with wireless PS2, all those wireless PS2 in market is not from SONY