High bit rate RFID system

• US 7,787,568 B2
• Filed: 06/22/2006
• Issued: 08/31/2010
• 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
• Primary Examiner(s): PUENTE, EVA YI ZHENG
• Application Number:
  US11/472,453
• Publication Number:
  US 20070297534A1
• Time in Patent Office: 1,531 Days
• Field of Search: 375/316, 375/261, 375/340, 375/320, 370/468, 370/343, 370/480
• 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) 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 the 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 determined closest point, 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.

2. The RFID reader of claim 1, wherein the data value has N bits, where M=2^N.

3. The RFID reader of claim 1, 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.

4. The RFID reader of claim 3, wherein the average signal generator is configured generate the averaged corrected in-phase reference signal according to:

5. The RFID reader of claim 1, wherein the average signal generator is configured as a sliding window average generator.

6. The RFID reader of claim 1, 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.

7. The RFID reader of claim 1, 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:

8. The RFID reader of claim 1, wherein M=16, wherein the corrected constellation points generator is configured to generate 16 corrected constellation points (I_c1-I_c16) according to:

9. The RFID reader of claim 1, 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.

10. The RFID reader of claim 1, wherein M=16.

11. 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 the 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 determined closest point, 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.

12. The method of claim 11, 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.

13. The method of claim 12, 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;

14. The method of claim 11, wherein said generating an averaged corrected in-phase reference signal and an averaged corrected quadrature-phase reference signal comprises calculating a sliding window average.

15. The method of claim 11, 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.

16. The method of claim 11, 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;

17. The method of claim 11, 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;

18. The method of claim 11, 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.

19. 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 the 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 determined closest point, 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.