Method and apparatus for improving reception of an RFID tag response
A method and apparatus for improving reception of responsive RFID signals is provided. The method includes transmitting a plurality of interrogation signals each having a different polarization to activate one or more RFID tags. Responsive signals from the RFID tags are analyzed for receive symbol quality data to select a transmit polarization subset. These polarizations are then used for transmitting further interrogation signals to the RFID tags. The apparatus includes a dual element orthogonal radiator coupled to a transmitter and receiver. A processor controls the transmitter and receiver to transmit a series of RFID interrogation signals each having a different polarization, and receive a series of responsive signals from one or more RFID tags. The responsive signals are analyzed to select a particular a transmit polarization subset that will improve reception of future responsive signals from the RFID tags.
1. A method comprising:
transmitting a plurality of interrogation signals to activate one or more RFID tags, each of the plurality of interrogation signals being transmitted with a different polarization, and each different polarization at a different polarization step size starting from a beginning polarization to an end polarization;
receiving a plurality of responsive signals from the one or more RFID tags;
analyzing received symbol quality data for each of the plurality of responsive signals using quality parameters to select a transmit polarization subset having received symbol quality data that is above a quality threshold;
transmitting further interrogation signals to the one or more RFID tags using the selected transmit polarization subset.
2. The method of claim 1 , wherein transmitting includes transmitting the plurality of interrogation signals with a different linear slant polarizations.
3. The method of claim 1 , wherein transmitting includes transmitting the plurality of interrogation signals with a different elliptic polarizations.
4. The method of claim 1 , wherein transmitting includes periodically repeating the transmitting the plurality of interrogation signals using coarse or fine step sizes depending on the time of day.
5. The method of claim 1 , which includes repeating the method to update the transmit polarization subset when the received symbol quality data falls below the quality threshold.
6. The method of claim 5 , wherein the quality threshold is based upon one or more of the following group of quality parameters: bit error rate, packet error rate, total data errors, RFID tag read rate or RFID tag capture rate.
7. The method of claim 1 , wherein transmitting the plurality of interrogation signals each having a different polarization further comprises varying at least one of a magnitude and a phase of orthogonally phased quadrature interrogation signal components to produce a transmitted interrogation signal having a selected polarization.
8. The method of claim 1 , wherein the a transmit polarization subset results in the further interrogation signals arriving at the one or more RFID tags at a substantially linear polarization with respect to the one or more RFID tags.
9. A method comprising:
transmitting a plurality of interrogation signals to activate one or more RFID tags, each of the plurality of interrogation signals being transmitted with a different polarization;
receiving a plurality of responsive signals from the one or more RFID tags;
analyzing received symbol quality data for each of the plurality of responsive signals using quality parameters to exclude certain polarizations to provide a selected transmit polarization subset having received symbol quality data that is above a quality threshold;
transmitting further interrogation signals to the one or more RFID tags using the selected transmit polarization subset; and
wherein transmitting the plurality of interrogation signals further comprises determining a beginning polarization, an end polarization and a polarization step size for transmitting a plurality of interrogation signals.
10. The method of claim 9 , wherein transmitting includes transmitting the plurality of interrogation signals through a sweep of different polarizations.
11. The method of claim 9 , wherein transmitting includes periodically repeating the transmitting the plurality of interrogation signals using coarse or fine step sizes depending on the time of day.
12. The method of claim 10 , which includes repeating the method when the received symbol quality data falls below the quality threshold.
13. The method of claim 12 , wherein the quality threshold is based upon one or more of the following group of quality parameters: bit error rate, packet error rate, total data errors, RFID tag read rate or RFID tag capture rate.
14. The method of claim 9 , wherein transmitting the plurality of interrogation signals each having a different polarization further comprises varying at least one of a magnitude and a phase of orthogonally phased quadrature interrogation signal components to produce a transmitted interrogation signal having a selected polarization.
15. A system comprising:
an antenna system having a first antenna element with a first polarization and a second antenna element having a second polarization being orthogonal to the first polarization;
a transmitter coupled to the antenna system;
a receiver coupled to the antenna system;
a processor coupled to the transmitter and receiver and programmed to:
control the transmitter to transmit a series of RFID interrogation signals to one or more RFID tags, each of the series of RFID interrogation signals having a varied transmit polarization;
control the receiver to receive a series of responsive signals from the one or more RFID tags;
analyze received symbol quality data for each of the series of responsive signals using quality parameters to select a transmit polarization subset having received symbol quality data that is above a quality threshold; and
transmit further interrogation signals to the one or more RFID tags using the selected transmit polarization subset; and
wherein the processor is further programmed to periodically re-transmit the series of RFID interrogation signals at different polarization step sizes.
16. The system of claim 15 , wherein the processor is further programmed to periodically re-transmit the series of RFID interrogation signals using coarse or fine step sizes depending on the time of day.
17. The system of claim 15 , wherein the processor is further programmed to analyze received symbol quality data using one or more of the following group of quality parameters for each of the series of responsive signals: bit error rate; packet error rate; total data errors; RFID tag read rate; RFID tag capture rate.
18. The system of claim 15 , wherein the processor is further programmed select the transmit polarization subset such that transmission of the further interrogation signals results in the further interrogation signals arriving at the one or more RFID tags at a substantially linear polarization with respect to the one or more RFID tags.