Powering RFID tags using multiple synthesized-beam RFID readers
Synthesized-beam RFID readers may be used to manage and provide information about RFID tag populations. In one embodiment, two or more synthesized-beam readers synthesize respective RF beams towards a tag location. The synthesized-beam readers may coordinate their pointing by means of a controller, a peer-to-peer network, or by using a master-slave arrangement. The synthesized-beam readers may coordinate their transmissions to increase the RF energy available to a tag at the pointing location.
1. A method for inventorying a Radio Frequency Identification (RFID) tag comprising:
communicating, from a controller, a target location to a first synthesized-beam RFID reader and to a second synthesized-beam RFID reader;
steering, responsive to the communicated target location, a first beam from the first synthesized-beam reader to the target location and a second beam from the second synthesized-beam reader to the target location;
transmitting, simultaneously, from the first synthesized-beam reader a modulated RF inventory signal and from the second synthesized-beam reader a substantially unmodulated RF signal;
receiving, responsive to the modulated RF inventory signal, a tag reply at one of the first and second synthesized-beam readers; and
transmitting, from one of the first and second synthesized-beam readers, a modulated RF acknowledgment signal responsive to the tag reply, and from the other of the first and second synthesized-beam readers a substantially unmodulated RF signal.
2. The method of claim 1 , wherein the target location includes at least one of:
a beam indicator;
a floor location;
a Cartesian coordinate; and
a polar coordinate.
3. The method of claim 1 , further comprising adjusting at least one of a power and a frequency of the RF signal from at least one of the first and second synthesized-beam readers to increase an inventory range of the RFID tag.
4. The method of claim 3 , wherein the adjusting comprises sweeping over a range of values.
5. The method of claim 3 , wherein the adjusting is adaptive and based on one or more of:
an environmental condition;
a received tag reply;
a tag performance characteristic; and
a tag population size.
6. The method of claim 1 , further comprising steering the second beam to a plurality of locations in a vicinity of the target location.
7. The method of claim 1 , further comprising synthesizing the second beam in response to at least one of:
determining that the first beam is an outer beam;
determining that a number of inventoried tags is less than an expected number; and
determining that the tag is moving toward a periphery of a field-of-view of the first synthesized-beam reader.
8. A method for inventorying a Radio Frequency Identification (RFID) tag comprising:
communicating, from a first synthesized-beam RFID reader, a target location to a second synthesized-beam RFID reader;
steering a first beam from the first synthesized-beam reader to the target location;
steering, responsive to the communicated target location, a second beam from the second synthesized-beam reader to the target location;
transmitting, simultaneously, from one of the first and second synthesized-beam readers a modulated RF inventory signal and from the other of the first and second synthesized-beam readers a substantially unmodulated RF signal;
receiving, responsive to the modulated RF inventory signal, a tag reply at one of the first and second synthesized-beam readers; and
transmitting, from one of the first and second synthesized-beam readers, a modulated RF acknowledgment signal responsive to the tag reply, and from the other of the first and second synthesized-beam readers a substantially unmodulated RF signal.
9. The method of claim 8 , wherein the target location includes at least one of:
a beam indicator;
a floor location;
a Cartesian coordinate; and
a polar coordinate.
10. The method of claim 8 , further comprising adjusting at least one of a power and a frequency of the RF signal from at least one of the first and second synthesized-beam readers to increase an inventory range of the RFID tag.
11. The method of claim 10 , wherein the adjusting comprises sweeping over a range of values.
12. The method of claim 10 , wherein the adjusting is adaptive and based on one or more of:
an environmental condition;
a received tag reply;
a tag performance characteristic; and
a tag population size.
13. The method of claim 8 , further comprising steering the second beam to a plurality of locations in a vicinity of the target location.
14. The method of claim 8 , further comprising synthesizing the second beam in response to at least one of:
determining that the first beam is an outer beam;
determining that a number of inventoried tags is less than an expected number; and
determining that the tag is moving toward a periphery of a field-of-view of the first synthesized-beam reader.
15. A method for inventorying a Radio Frequency Identification (RFID) tag comprising:
storing at least one target location and at least one corresponding target-location time in first and second synthesized-beam RFID readers;
steering, at the target-location time, a first beam from the first synthesized-beam reader to the target location and a second beam from the second synthesized-beam reader to the target location;
transmitting, simultaneously, from one of the first and second synthesized-beam readers a modulated RF inventory signal and from the other of the first and second synthesized-beam readers a substantially unmodulated RF signal;
receiving, responsive to the modulated RF inventory signal, a tag reply at one of the first and second synthesized-beam readers; and
transmitting, from one of the first and second synthesized-beam readers, a modulated RF acknowledgment signal responsive to the tag reply, and from the other of the first and second synthesized-beam readers a substantially unmodulated RF signal.
16. The method of claim 15 , wherein the target location includes at least one of:
a beam indicator;
a floor location;
a Cartesian coordinate; and
a polar coordinate.
17. The method of claim 15 , further comprising adjusting at least one of a power and a frequency of the RF signal from at least one of the first and second synthesized-beam readers to increase an inventory range of the RFID tag.
18. The method of claim 17 , wherein the adjusting comprises at least one of:
sweeping over a range of values; and
adaptive adjustment based on one or more of an environmental condition, a received tag reply, a tag performance characteristic, and a tag population size.
19. The method of claim 15 , further comprising coordinating the target-location time between the first and second synthesized-beam readers by at least one of:
a timer;
a trigger signal; and
a communication from one of the first and second synthesized-beam readers to the other of the first and second synthesized-beam readers.
20. The method of claim 15 , further comprising steering the second beam to a plurality of locations in a vicinity of the target location at the target-location time.