Wireless USB is based on Ultra_Wide_Band(UWB) technology. It operates like digital Morse code, one specific short pulse represents "1" while another specific pulse represents "0", no carrier frequency is needed to convey the information. So someone calls it "digital" radio. Due to its short pulse, its signal spectrum may cover several GHz range to interference other communication device like GPS, WLAN , GSM .... . So its transmit power must be very very low to prevent this interference, and this limitation will limit its usage range within few meters.