SYSTEM AND METHOD FOR MEASUREMENT OF DISTANCE TO A TAG BY A MODULATED BACKSCATTER RFID READER
First Claim
1. A system for measuring the distance between a first and second radio, the system comprising:
- a first radio comprising;
a first radio transmitter anda phase sensitive receiver; and
a second radiowherein said first radio transmitter transmits first and second signals at first and second frequencies;
said second radio modulates said first and second signals to create modulated backscattered first and second signals having first and second phase relationships to said first and second signals;
said phase sensitive receiver produces first and second outputs representative of said first and second phase relationships andwherein the distance between the first and second radio is calculated as a function of said first and second outputs.
4 Assignments
0 Petitions
Accused Products
Abstract
Distance to a modulated backscatter tag is measured with a RFID reader that measures changes in phase with frequency of modulated backscattered RF signals. Measured distances are linked to a specific tag. The effects of other sources of reflected and interfering signals are mitigated. The techniques eliminate the need for high RF bandwidth used in time-of-flight methods, and may be used with linear, limiting or other types of amplifiers in the reader receiver. Unambiguous distance to a tag may be found using the derivative of phase with RF frequency of the modulated signal backscattered by a tag. The distance to a tag can be measured with an accuracy on the order of a centimeter. The techniques utilize the characteristics of cooperative backscatter tags (transponders, labels, etc.). New readers implement the techniques which may use unmodified tags.
187 Citations
27 Claims
-
1. A system for measuring the distance between a first and second radio, the system comprising:
-
a first radio comprising; a first radio transmitter and a phase sensitive receiver; and a second radio wherein said first radio transmitter transmits first and second signals at first and second frequencies; said second radio modulates said first and second signals to create modulated backscattered first and second signals having first and second phase relationships to said first and second signals; said phase sensitive receiver produces first and second outputs representative of said first and second phase relationships and wherein the distance between the first and second radio is calculated as a function of said first and second outputs. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
-
-
22. A system for measuring the distance between a first and second radio, the system comprising:
-
a first radio comprising; first and second RF signal generators; a radio receiver comprising first and second in phase (I) and quadrature (Q) mixers; a signal combiner; and a second radio; wherein said first and second RF signal generators transmit simultaneous first and second signals at first and second frequencies through said signal combiner; said second radio modulates said first and second signals to create backscattered first and second signals having first and second phase relationships to said first and second signals; said first I/Q mixer produces a first output representative of said first phase relationship; said second I/Q mixer produces a second output representative of said second phase relationship; and wherein the distance between the first and second radio is calculated as a function of said first and second outputs.
-
-
23. A system for measuring the distance between a first and second radio, the system comprising:
-
a first radio comprising; an RF signal generator; a radio receiver comprising an in phase (I) and quadrature (Q) mixer with limiting amplifiers on the outputs of said mixers; a variable phase shifter for shifting the output of said RF signal generator relative to a reference signal used by said I/Q mixer; and a second radio; wherein said RF signal generator transmits first and second signals at first and second frequencies; said second radio modulates said first and second signals to create modulated backscattered first and second signals having first and second phase relationships to said first and second signals; wherein said variable phase shifter is adjusted to produce a quadrature null at said I/Q mixer for each of said first and second signals; wherein the amount of adjustment of said phase shifter necessary to achieve said quadrature null is representative of said first and second phase relationships; and wherein the distance between the first and second radio is calculated as a function of said first and second phase relationships.
-
-
24. A system for measuring the distance between a first and second radio, the system comprising:
-
a first radio comprising; an RF signal generator; a radio receiver comprising an in phase (I) and quadrature (Q) mixers having I and Q outputs; and an XNOR logic element to combine said I and Q outputs to produce an S signal representative of the polarity of said I and Q outputs; and a second radio; wherein said RF signal generator transmits a swept frequency signal; said second radio modulates said swept frequency signal to create a modulated backscattered swept frequency signal; and wherein RF frequencies corresponding to transitions of said S signal are recorded and used to calculate the distance between the first and second radios.
-
-
25. A system for measuring the distance between a first and second radio, the system comprising:
-
a first radio comprising; an RF signal generator; a radio receiver comprising an in phase (I) and quadrature (Q) mixers having I and Q outputs; a variable phase shifter for varying the phase of the reference signal for the in phase (I) and quadrature (Q) mixers; and an XNOR logic element to combine said I and Q outputs to produce an S signal representative of the polarity of said I and Q outputs; and a second radio; wherein said RF signal generator transmits first and second signals at first and second frequencies; said second radio modulates said first and second signals to create modulated backscattered first and second signals having first and second phase relationships to said first and second signals; and wherein RF frequencies corresponding to transitions of said S signal at said first and second frequencies are recorded and used to calculate the distance between the first and second radios.
-
-
26. A system for measuring the distance between a first and second radio, the system comprising:
-
a first radio comprising; first and second RF signal generators; a radio receiver comprising first and second in phase (I) and quadrature(Q) mixers having I and Q outputs; a first and second XNOR logic elements to combine said first and second I and Q outputs to produce first and second S signals representative of the polarities of said first and second I and Q outputs; and a second radio in motion with respect to the first radio; wherein said first and second RF signal generators transmit simultaneous first and second signals at first and second frequencies; said second radio modulates said first and second signals to create backscattered first and second signals having first and second phase relationships to said first and second signals; said first I/Q mixer and XNOR logic circuit produce first outputs representative of said first phase relationships; said second I/Q mixer and XNOR logic circuit produce second outputs representative of said second phase relationship; and wherein the distance between the first and second radio is calculated as a function of said first and second outputs.
-
-
27. A method for measuring the distance between a first and second radio comprising:
-
transmitting by the first radio first signals at a plurality of frequencies; modulating said first signals by the second radio to create a plurality of backscattered signals having a plurality of phase relationships to said first signals; receiving at the first radio said backscattered signals; producing phase relationship signals at the first radio that are representative of said phase relationships; and calculating the distance between the first and second radio as a function of said phase relationship signals.
-
Specification