Radio frequency proximity detection and identification system and method

1. An audience measurement system comprising a radio frequency (RF) proximity detection and identification system, comprising:

a plurality of portable people meters (PPM), each comprising an RF transmitter, wherein each of the PPM's receives a control signal, modulates an RF signal to a preset modulation frequency upon receipt of the control signal, and wirelessly transmits the modulated signal via the respective RF transmitter, wherein each of the RF signals are modulated with a respectively different modulation frequency; and

an RF receiver that monitors a proximity of each PPM using the wirelessly transmitted modulated signals actually received from respective PPM's, determining the modulation frequency thereof, and transmitting the modulation frequency to a remote location for processing user identification and audience measurement based on the monitored proximity of each PPM.

2. The RF proximity detection and identification system of claim 1 , wherein a transmission power of each RF transmitter is preset to transmit the modulated signal within a predetermined range.

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

RF transmitters respectively located in each PPM, wherein each RF transmitter is operative for receiving a control signal, modulating an RF signal to a preset modulation frequency in response to the control signal, and wirelessly transmitting the modulated signal, each of the RF transmitters being operative to modulate the RF signal with a respectively different modulation frequency; and

an RF receiver located in the base unit that monitors a proximity of each PPM using the wirelessly transmitted modulated signal actually received by the RF receiver, determining the modulation frequency thereof, and transmitting the modulation frequency to a remote location for processing user identification and audience measurement based on the monitored proximity of each PPM.

4. The system of claim 3 , wherein the transmission power of each RF transmitter is preset to transmit the modulated signal within a predetermined range.

5. The system of claim 4 , wherein each RF transmitter further comprises an RF modulator for receiving the control signal and outputting an RF signal modulated to its respectively different modulation frequency.

6. The system of claim 4 , wherein the RF receiver further comprises an RF demodulator unit for receiving each wirelessly transmitted RF modulated signal, demodulating each received signal, and determining the modulation frequency of the each received signal.

7. 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.

8. The RF proximity detection and identification method of claim 7 , wherein a transmission power of the transmission of the each modulated signal is preset to transmit within a predetermined range.

9. 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.

10. The RF proximity detection and identification system of claim 9 , wherein the modulating frequencies are transmitted to a remote location for further processing.

11. The RF proximity detection and identification system of claim 10 , wherein a transmission power of each the transmitter is preset to transmit the modulated signal within a predetermined range.