Patent ID: 7574732

Claim:
A networking security system, the networking security system comprising: an RFID reader, the RFID transmitting a signal to an RFID tag, wherein the RFID reader transmits a plurality of transmitted signals to the RFID tag and receives a plurality of backscatter-modulated signals from the RFID tag, at least two of the plurality of transmitted signals having a different fundamental frequency, wherein the at least two of the plurality of transmitted signals having a different fundamental frequency have a randomly selected frequency difference; a distance calculator, the distance calculator determining a distance to the RFID tag from the transmitted signal, wherein the distance calculator determines a phase for each of the plurality of backscatter-modulated signals from the RFID tag, and wherein the distance calculator determines the distance to the RFID tag by determining a rate of change of the phase in the plurality of backscatter-modulated signals with respect to rate of change in the fundamental frequency of the plurality of transmitted signals; and an access controller, the access controller selectively permitting access from a mobile computing device to a wireless networking system based on the determined distance to the RFID tag.