Radio frequency tag location system and method
Determination of the location and bearing of an asset having an RF-tag imbedded therein is accomplished through extended radio frequency triangulation. A beacon arrangement determines the direction of an RF tag from a specially designed beacon node. RF-tag localization is further improved by repeating this measurement from multiple spatially displaced beacon nodes. The beacon nodes are equipped with multiple strategically located antennas and transmit frames with each symbol cyclically switched to a different antenna. The symbols traveling different distances result in phase shifts within the frame received by the RF-tag. From the phase shifts and the known arrangements of the antennas the angle at which the RF-tag is RF visible from the specific beacon node can be estimated. Determination of the signal phase shifts are part of the baseband processing hardware, the rest of the location determination procedure may be realized in software.
1. A method for locating a radio frequency tag using spatially separated beacon nodes, said method comprising the steps of:
providing at least one beacon node comprising a plurality of antennas coupled with an antenna switch, a radio frequency device coupled with the antenna switch, and a microcontroller having outputs and at least one input, the microcontroller being coupled with the radio frequency device and with said antenna switch;
transmitting a plurality of beacon symbols from cyclically selected antennas of each of a plurality of beacon nodes, wherein the microcontroller is configured to select an antenna by controlling said antenna switch through its outputs and wherein the radio frequency device provides timing pulses to the at least one input of the microcontroller which trigger the microcontroller to perform an antenna switch at a symbol boundary;
receiving the plurality of beacon symbols at a radio frequency (RF) tag;
determining phase jumps of the plurality of beacon symbols received at the RF tag and the respective selected antennas transmitting each of the plurality of beacon symbols for each of the plurality of beacon nodes;
estimating an angle-of-arrival (AoA) of the plurality of beacon symbols transmitted from each of the plurality of beacon nodes;
estimating an AoA vector for each of the plurality of beacon nodes from the respective AoA estimates; and
estimating a spatial location of the RF tag from the AoA vectors.
2. The method according to claim 1 , wherein each next one of the plurality of beacon symbols is transmitted from a next one of the cyclically selected antennas.
3. The method according to claim 1 , wherein every other next one of the plurality of beacon symbols is transmitted from a next one of the cyclically selected antennas.
4. The method according to claim 1 , wherein the plurality of beacon symbols are payload portions of transmission frames.
5. The method according to claim 1 , wherein the step of estimating the AoA of the plurality of beacon symbols transmitted from each of the plurality of beacon nodes comprises the step of determining the phase jump of each one of the plurality of beacon symbols in relation to a respective one of the cyclically selected antennas transmitting the one of the plurality of beacon symbols.
6. The method according to claim 1 , wherein the step of estimating the AoA of the plurality of beacon symbols transmitted from each of the plurality of beacon nodes comprises the step of determining the phase jump of every other one of the plurality of beacon symbols in relation to a respective one of the cyclically selected antennas transmitting the every other one of the plurality of beacon symbols.
7. The method according to claim 1 , wherein the step of estimating the AoA provides an azimuth angle estimation.
8. The method according to claim 1 , wherein the step of estimating the AoA provides an elevation angle estimation.
9. The method according to claim 1 , further comprising the steps of calibrating position and orientation of each one of the plurality of beacon nodes by
transmitting a plurality of beacon symbols from the cyclically selected antennas of a one of the plurality of beacon nodes; and
receiving the plurality of beacon symbols on another one of the plurality of beacon nodes with a one of the antennas of the another one of the plurality of beacon nodes.
10. The method according to claim 1 , further comprising the steps of calibrating position and orientation of each one of the plurality of beacon nodes by
transmitting a plurality of beacon symbols from a one of the antennas of a one of the plurality of beacon nodes; and
receiving the plurality of beacon symbols on another one of the plurality of beacon nodes with the cyclically selected antennas of the another one of the plurality of beacon nodes.
11. The method according to claim 1 , further comprising the steps of:
providing a central processing node; and
providing a network for coupling the central processing node to the plurality of beacon nodes.
12. The method according to claim 1 , wherein the beacon symbols are direct sequence spread spectrum (DSSS) symbols, the method further comprises
after receiving a timing pulse at the microcontroller synchronizes a subsequent antenna switch to a transmitted symbol.
13. The method according to claim 12 , wherein the microcontroller comprises a timer for performing said synchronization.
14. The method according to claim 13 , wherein a symbol length is 16 microseconds.
15. A method for locating a radio frequency tag using spatially separated beacon nodes, said method comprising the steps of:
providing at least one beacon node comprising a plurality of antennas coupled with an antenna switch, a radio frequency device coupled with the antenna switch, and a microcontroller having outputs and at least one input, the microcontroller being coupled with the radio frequency device and with said antenna switch;
transmitting a plurality of beacon symbols from an antenna of a radio frequency (RF) tag;
receiving the plurality of beacon symbols on cyclically selected antennas of each of a plurality of beacon nodes, wherein the microcontroller is configured to select an antenna by controlling said antenna switch through its outputs and wherein the radio frequency device provides timing pulses to the at least one input of the microcontroller which trigger the microcontroller to perform an antenna switch at a symbol boundary;
determining phase jumps of the plurality of beacon symbols transmitted from the RF tag and the respective selected antennas receiving each of the plurality of beacon symbols for each of the plurality of beacon nodes;
estimating an angle-of-arrival (AoA) of the plurality of beacon symbols received at each of the plurality of beacon nodes;
estimating AoA vectors of each of the plurality of beacon nodes from the AoA estimates; and
estimating a spatial location of the RF tag from the AoA vectors.
16. The method according to claim 15 , wherein each next one of the plurality of beacon symbols is received at a next one of the cyclically selected antennas.
17. The method according to claim 15 , wherein every other next one of the plurality of beacon symbols is received at a next one of the cyclically selected antennas.
18. The method according to claim 15 , wherein the plurality of beacon symbols are payload portions of transmission frames.
19. The method according to claim 15 , wherein the step of estimating the AoA of the plurality of beacon symbols received at each of the plurality of beacon nodes comprises the step of determining the phase jump of each one of the plurality of beacon symbols in relation to a respective one of the cyclically selected antennas receiving the one of the plurality of beacon symbols from the RF tag.
20. The method according to claim 15 , wherein the step of estimating the AoA of the plurality of beacon symbols received at each of the plurality of beacon nodes comprises the step of determining the phase jump of every other one of the plurality of beacon symbols in relation to a respective one of the cyclically selected antennas receiving the every other one of the plurality of beacon symbols from the RF tag.
21. The method according to claim 15 , wherein the step of estimating the AoA provides an azimuth angle estimation.
22. The method according to claim 15 , wherein the step of estimating the AoA provides an elevation angle estimation.
23. The method according to claim 15 , further comprising the steps of calibrating position and orientation of each of the plurality of beacon nodes by
transmitting a plurality of beacon symbols from the cyclically selected antennas of a one of the plurality of beacon nodes; and
receiving the plurality of beacon symbols on another one of the plurality of beacon nodes with a one of the antennas of the another one of the plurality of beacon nodes.
24. The method according to claim 15 , further comprising the steps of calibrating position and orientation of each one of the plurality of beacon nodes by
transmitting a plurality of beacon symbols from a one of the antennas of a one of the plurality of beacon nodes; and
receiving the plurality of beacon symbols on another one of the plurality of beacon nodes with the cyclically selected antennas of the another one of the plurality of beacon nodes.
25. The method according to claim 15 , further comprising the steps of:
providing a central processing node; and
providing a network for coupled the central processing node to the plurality of beacon nodes.
26. The method according to claim 15 , wherein the beacon symbols are direct sequence spread spectrum (DSSS) symbols and the radio frequency device determines a phase and magnitude information of each received symbol, the method further comprises
after receiving a timing pulse at the microcontroller, reading phase and magnitude information by the microcontroller from the radio frequency device through an interface between the microcontroller and the radio frequency device.
27. The method according to claim 26 , wherein the interface is a serial interface.
28. The method according to claim 26 , wherein a symbol length is 16 microseconds and the microcontroller comprises a timer to synchronize an antenna switch to a symbol.