Radio frequency proximity detection and identification system and method

A radio frequency (RF) proximity detection and identification method for use in an audience measurement system comprising the steps of:

• in each of a plurality of portable people meters, modulating an RF signal to a preset modulation frequency upon receipt of a control signal to produce a respective modulated signal, the preset modulation frequency being different for each of the plurality of portable people meters;
• wirelessly transmitting each respective modulated signal from a transmitter of a corresponding portable people meter;
• monitoring the proximity of each portable people meter to an RF receiver based on each wirelessly transmitted modulated signal actually received in the RF receiver;
• determining the modulation frequency of each received signal;
• and
• transmitting each determined modulation frequency to a remote location for processing user identification and audience measurement based on the monitored proximity of each portable people meter.

An audience measurement system having a plurality of portable people meters (PPM's), the system containing a radio frequency (RF) proximity detection and identification system, the RF proximity detection and identification system comprising:

• an RF transmitter unit contained in each of the plurality of PPM's, the RF transmitter unit comprising an RF modulation unit for receiving a control signal and modulating an RF signal to a preset modulation frequency to produce a respective modulated signal, the preset modulation frequency being different for each of the PPM's, wherein the RF transmitter transmits the respective modulated signal as an RF modulated signal;
• a receiver for monitoring respective proximities of each of the plurality of PPM's based on each the transmitted respective modulated signal actually received in the receiver;
• and
• an RF demodulator unit for demodulating each received modulated signal, and determining the modulating frequency of each the signal, wherein the receiver transmits each determined modulation frequency to a remote location for processing user identification and audience measurement based on the monitored proximity of each PPM.