High bit rate RFID system

• US 20070297534A1
• Filed: 06/22/2006
• Published: 12/27/2007
• Est. Priority Date: 06/22/2006
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Okunev, Yuri
• Granted Patent: US 7,787,568 B2
• Time in Patent Office: Days
• US Class Current: 375/316
• CPC Class Codes: H04L 2027/003 at baseband only
• CPC Class Codes: H04L 2027/0057 quadrature phase
• CPC Class Codes: H04L 27/362 Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated H04L27/366 takes precedence
• CPC Class Codes: H04L 27/365 Modulation using digital generation of the modulated carrier (not including modulation of a digitally generated carrier)
• CPC Class Codes: H04L 27/3854 using a non - coherent carrier, including systems with baseband correction for phase or frequency offset

Abstract

Methods, systems, and apparatuses for quadrature amplitude modulation (QAM) based radio frequency identification (RFID) systems are described. In an aspect, a tag transmitter performs QAM signal mapping and quadrature modulation of a carrier wave (CW), to transmit a QAM response signal. In another aspect, a QAM-enabled reader receiver receives the QAM tag response signal, and performs quasi-coherent signal processing, based on tracking of QAM signal parameters in a decision feedback loop.

Claims

1. A radio frequency identification (RFID) tag for communicating with a RFID reader, comprising:

an antenna configured to receive a radio frequency signal from a reader;

a memory configured to store a first plurality of data bits;

a mapper configured to receive a plurality of N data bits of the first plurality of data bits, and to map the plurality of N data bits into a point of an M-QAM constellation of points, where M=2^N, and where the point is defined by an I coordinate and a Q coordinate; and

a quadrature modulator configured to generate a quadrature modulated radio frequency signal based on the I and Q coordinates and the received radio frequency signal;

wherein the antenna is configured to radiate the quadrature modulated radio frequency signal.

2. The RFID tag of claim 1, wherein the quadrature modulator includes:

an in-phase portion configured to modulate an in-phase component of the received radio frequency signal with the I coordinate,

a quadrature-phase portion configured to modulate a quadrature-phase component of the received radio frequency signal with the Q coordinate, and

a summer configured to sum an output signal of the in-phase portion and an output signal of the quadrature-phase portion to generate a quadrature modulated radio frequency signal.

3. The RFID tag of claim 2, wherein the I coordinate and the Q coordinate each have a sign and a level.

4. The RFID tag of claim 2, wherein N=4 and M=16, wherein the mapper maps the 4 data bits into the point of the 16-QAM constellation of points.

5. The RFID tag of claim 4, wherein the quadrature modulator further includes:

a 4-bit register that stores the 4 data bits;

a first inverter;

a second inverter;

a first attenuator; and

a second attenuator.

6. The RFID tag of claim 5, wherein the first inverter is configured to invert a phase of the quadrature-phase component of the received radio frequency signal if a first data bit of the 4 data bits has a first logical value, and to not invert the phase of the quadrature-phase component of the received radio frequency signal if the first data bit has a second logical value;

wherein the second inverter is configured to invert a phase of the in-phase component of the received radio frequency signal if a second data bit of the 4 data bits has the first logical value, and to not invert the phase of the in-phase component of the received radio frequency signal if the second data bit has the second logical value;

wherein the first attenuator is configured to not attenuate the quadrature-phase component of the received radio frequency signal if a third data bit of the 4 data bits has the first logical value, and to attenuate the quadrature-phase component of the received radio frequency signal if the third data bit has the second logical value; and

wherein the second attenuator is configured to not attenuate the in-phase component of the received radio frequency signal if a fourth data bit of the 4 data bits has the first logical value, and to attenuate the in-phase component of the received radio frequency signal if the fourth data bit has the second logical value.

7. The RFID tag of claim 6, wherein the first and second attenuators are each configured to divide by 3.

8. The RFID tag of claim 2, wherein the quadrature modulator further includes a 90 degree phase shifter that receives the received radio frequency signal and generates the quadrature-phase component of the received radio frequency signal.

9. A method in a radio frequency identification (RFID) tag for communicating with a RFID reader, comprising:

receiving a radio frequency signal from a reader;

storing a first plurality of data bits;

mapping a plurality of N data bits of the first plurality of data bits into a point of an M-QAM constellation of points, where M=2^N, and where the point is defined by an I coordinate and a Q coordinate;

generating a quadrature modulated radio frequency signal based on the I coordinate, the Q coordinate, and the received radio frequency signal; and

radiating the quadrature modulated radio frequency signal.

10. The method of claim 9, wherein generating the quadrature modulated radio frequency signal includes:

modulating an in-phase component of the received radio frequency signal with the I coordinate,

modulating a quadrature-phase component of the received radio frequency signal with the Q coordinate, and

summing an output signal of the in-phase portion and an output signal of the quadrature-phase portion to generate the quadrature modulated radio frequency signal.

11. The method of claim 10, wherein N=4 and M=16, said mapping comprises:

mapping the 4 data bits into the point of the 16-QAM constellation of points.

12. The method of claim 11, wherein said generating the quadrature modulated radio frequency signal further includes:

inverting a phase of the quadrature-phase component of the received radio frequency signal if the first data bit of the 4 data bits has a first logical value;

inverting a phase of the in-phase component of the received radio frequency signal if the second data bit of the 4 data bits has the first logical value;

attenuating the quadrature-phase component of the received radio frequency signal if the third data bit of the 4 data bits has a second logical value; and

attenuating the in-phase component of the received radio frequency signal if the fourth data bit has the second logical value.

13. The method of claim 10, wherein said generating the quadrature modulated radio frequency signal further includes:

shifting a phase of the received radio frequency signal by 90 degrees to generate the quadrature-phase component of the received radio frequency signal.

14. A system in a radio frequency identification (RFID) tag for communicating with a RFID reader, comprising:

means for receiving a radio frequency signal from a reader;

means for storing a first plurality of data bits;

means for mapping a plurality of N data bits of the first plurality of data bits into a point of an M-QAM constellation of points, where M=2^N, and where the point is defined by an I coordinate and a Q coordinate; and

means for generating a quadrature modulated radio frequency signal based on the I coordinate, the Q coordinate, and the received radio frequency signal.

15. A radio frequency identification (RFID) reader, comprising:

a demodulator configured to demodulate a received quadrature modulated radio frequency signal to an in-phase signal component and a quadrature-phase signal component that contain a current data symbol;

a decision module configured to determine a closest point of M previously generated corrected constellation points to the in-phase signal component and quadrature-phase signal component;

a demapper module configured to demap the determined closest point to a data value for the current data symbol;

a corrected reference signal generator configured to receive the data value for the current data symbol, the in-phase signal component, and the quadrature-phase signal component, and to generate a corrected in-phase reference signal and a corrected quadrature-phase reference signal;

an average signal generator configured to receive corrected in-phase reference signals and corrected quadrature-phase reference signals generated for each of S data symbols including the current data symbol, and to generate an averaged corrected in-phase reference signal and an averaged corrected quadrature-phase reference signal; and

a corrected constellation points generator configured to receive the averaged corrected in-phase reference signal and the averaged corrected quadrature-phase reference signal, and to generate a current corrected constellation having M current corrected constellation points, wherein each of the M current corrected constellation points is defined by an I coordinate and a Q coordinate.

16. The RFID reader of claim 15, wherein the data value has N bits, where M=2^N.

17. The RFID reader of claim 15, wherein the corrected reference signal generator is configured to generate the corrected in-phase reference signal according to:

I_r=A₀(I cos Δ

−

Q sin Δ

)/A;

and the corrected reference signal generator is configured to generate the corrected quadrature-phase reference signal according to;

Q_r=A₀(Q cos Δ

+I sin Δ

)/A;

wherein;

I=the in-phase signal component,

Q=the quadrature-phase signal component,

I_r=the corrected in-phase reference signal for the current data symbol,

Q_r=the corrected quadrature-phase reference signal for the current data symbol,

Δ

=a phase difference between the local reference signal and a vector formed by the determined closest point,

A=an amplitude of the vector, and

A₀=an amplitude of the local reference signal.

18. The RFID reader of claim 17, wherein the average signal generator is configured generate the averaged corrected in-phase reference signal according to:

19. The RFID reader of claim 15, wherein the average signal generator is configured as a sliding window average generator.

20. The RFID reader of claim 15, wherein the average signal generator is configured to generate the averaged corrected in-phase reference signal and the averaged corrected quadrature-phase reference signal for each received block of S data symbols.

21. The RFID reader of claim 15, wherein M=16, wherein the corrected reference signal generator is configured generate the corrected in-phase reference signal (I_ir) and the corrected quadrature-phase reference signal (Q_ir), according to:

22. The RFID reader of claim 15, wherein M=16, wherein the corrected constellation points generator is configured to generate 16 corrected constellation points (I_c1-I_c16) according to:

23. The RFID reader of claim 15, wherein the decision module is configured to calculate M distance values according to:

distance value (n)=[(I−

I_cn)²+(Q−

Q_cn)²]

wherein;

n=1 through M,

I=the in-phase signal component,

Q=the quadrature-phase signal component,

I_cn=an I coordinate of a corrected constellation point n, and

Q_cn=a Q coordinate of a corrected constellation point n;

wherein the closest point of the M corrected constellation points to the current data symbol is a point n having a minimum distance value (n) of the calculated M distance values.

24. The RFID reader of claim 15, wherein M=16.

25. A method in a radio frequency identification (RFID) reader of communicating with RFID tags, comprising:

demodulating a received quadrature modulated radio frequency signal to an in-phase signal component and a quadrature-phase signal component that contain a current data symbol;

determining a closest point of M previously generated corrected constellation points to the in-phase and quadrature-phase signal components;

demapping the determined closest point to a data value for the current data symbol;

generating a corrected in-phase reference signal and a corrected quadrature-phase reference signal based on the data value for the current data symbol, the in-phase signal component, and the quadrature-phase signal component;

generating an averaged corrected in-phase reference signal and an averaged corrected quadrature-phase reference signal based on corrected in-phase reference signals and corrected quadrature-phase reference signals generated for S data symbols including the current data symbol; and

generating a corrected constellation having M corrected constellation points based on the averaged corrected in-phase reference signal and the averaged corrected quadrature-phase reference signal, wherein each of the M corrected constellation points is defined by an I coordinate and a Q coordinate.

26. The method of claim 25, wherein said generating a corrected in-phase reference signal and a corrected quadrature-phase reference signal comprises:

generating the corrected in-phase reference signal according to;

I_r=A₀(I cos Δ

−

Q sin Δ

)/A; and

generating the corrected quadrature-phase reference signal according to;

Q_r=A₀(Q cos Δ

+I sin Δ

)/A;

wherein;

I=the in-phase signal component,

Q=the quadrature-phase signal component,

I_r=the corrected in-phase reference signal for the current data symbol,

Q_r=the corrected quadrature-phase reference signal for the current data symbol,

Δ

=a phase difference between the local reference signal and a vector formed by the determined closest point,

A=an amplitude of the vector, and

A₀=an amplitude of the local reference signal.

27. The method of claim 26, wherein said generating an averaged corrected in-phase reference signal and an averaged corrected quadrature-phase reference signal comprises:

generating the averaged corrected in-phase reference signal according to;

28. The method of claim 25, wherein said generating an averaged corrected in-phase reference signal and an averaged corrected quadrature-phase reference signal comprises calculating a sliding window average.

29. The method of claim 25, wherein said generating an averaged corrected in-phase reference signal and an averaged corrected quadrature-phase reference signal generating an average for each received block of S data symbols.

30. The method of claim 25, wherein M=16, wherein generating the corrected in-phase reference signal and the corrected quadrature-phase reference signal comprises:

generating the corrected in-phase reference signal (I_ir) and the corrected quadrature-phase reference signal (Q_ir), according to;

31. The method of claim 25, wherein M=16, wherein said generating a corrected constellation having M corrected constellation points comprises:

generating 16 corrected constellation points (I_c1-I_c16) according to;

32. The method of claim 25, wherein said determining the closest point comprises:

calculating M distance values according to;

distance value (n)=[(I−

I_cn)²+(Q−

Q_cn)²]

wherein;

n=1 through M,

I=the in-phase signal component,

Q=the quadrature-phase signal component,

I_cn=an I coordinate of a corrected constellation point n, and

Q_cn=a Q coordinate of a corrected constellation point n; and

determining the minimum distance value of the calculated M distance values;

wherein the closest point is a point n corresponding to the determined minimum distance value (n) of the calculated M distance values.

33. A system in a radio frequency identification (RFID) reader of communicating with RFID tags, comprising:

means for demodulating a received quadrature modulated radio frequency signal to an in-phase signal component and a quadrature-phase signal component that contain a current data symbol;

means for determining a closest point of M previously generated corrected constellation points to the in-phase and quadrature-phase signal components;

means for demapping the determined closest point to a data value for the current data symbol;

means for generating a corrected in-phase reference signal and a corrected quadrature-phase reference signal based on the data value for the current data symbol, the in-phase signal component, and the quadrature-phase signal component;

means for generating an averaged corrected in-phase reference signal and an averaged corrected quadrature-phase reference signal based on corrected in-phase reference signals and corrected quadrature-phase reference signals generated for S data symbols including the current data symbol; and

means for generating a corrected constellation having M corrected constellation points based on the averaged corrected in-phase reference signal and the averaged corrected quadrature-phase reference signal, wherein each of the M corrected constellation points is defined by an I coordinate and a Q coordinate.