Method and apparatus for data signal processing in wireless RFID systems

• US 20070025475A1
• Filed: 07/28/2005
• Published: 02/01/2007
• Est. Priority Date: 07/28/2005
• Status: Abandoned Application

• Current Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Okunev, Yuri
• Application Number:
  US11/190,844
• Publication Number:
  US 20070025475A1
• Time in Patent Office: Days
• US Class Current: 375/343
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H04L 25/4904 using self-synchronising codes, e.g. split-phase codes

Abstract

The present invention provides methods and apparatuses for demodulation and decoding of backscattered RFID tag signals, represented by their in-phase and quadrature components at the output of the demodulator in the receiver portion of a reader interrogator. Autocorrelation coefficients for the in-phase and quadrature components of the received signal are calculated. The in-phase and quadrature coefficients are combined. The sign of output data is determined. Embodiments of the present invention are applicable to Gen 2 RFID systems as well as any wireless telecommunications system with the corresponding data modulation and/or encoding technique.

Claims

1. A method for decoding an encoded data signal, comprising:

(a) receiving the encoded data signal having an in-phase signal component I(t) and a quadrature-phase signal component Q(t);

(b) computing an autocorrelation coefficient A_I for the in-phase signal component I(t), wherein the autocorrelation coefficient A_I is determined by

$A_I={\int <br><br>}_{T/2}^T<br><br>I<br><br>\left(t\right)<br><br>I<br><br>\left(t-T/2\right)<br><br>d<br><br>t,$

where

t=time, and

 

a data symbol of the encoded data signal begins at t=0 and ends at t=T;

(c) computing an autocorrelation coefficient AQ for the quadrature-phase signal component Q(t), wherein the autocorrelation coefficient A_Q is determined by

$A_Q={\int <br><br>}_{T/2}^T<br><br>Q<br><br>\left(t\right)<br><br>Q<br><br>\left(t-T/2\right)<br><br>d<br><br>t;<br><br>$

(d) combining autocorrelation coefficients A_I and A_Q to generate a combined signal A that includes a decoded data symbol,

where

A=A_I+A_Q; and

(e) determining a sign for the decoded data symbol.

2. The method of claim 1, wherein the encoded data signal comprises data from a backscattered signal received from a radio frequency identification (RFID) tag.

3. The method of claim 1, wherein the encoded data signal comprises FM0 encoded data, wherein step (e) comprises:

determining a binary data symbol to be corresponding to the sign of combined signal A, wherein the data symbol equals 0 if the sign is negative, and the data symbol equals 1 if the sign is positive.

4. The method of claim 1, wherein the encoded data signal comprises Miller encoded data, wherein step (e) comprises:

determining a binary data symbol to be corresponding to opposite to the sign of combined signal A, wherein the data symbol equals 1 if the determined sign is negative, and the data symbol equals 0 if the determined sign is positive.

5. A base-band receiver, comprising:

a first delay module that receives an in-phase signal component I(t) of an encoded data signal, and delays the in-phase signal component I(t) by T/2, where

t=time, and

a data symbol of the encoded signal begins at t=0 and ends at t=T;

a second delay module that receives a quadrature-phase signal component Q(t) of the encoded data signal, and delays the quadrature-phase signal component Q(t) by T/2;

a first multiplier that multiplies the in-phase signal component I(t) and the delayed in-phase signal component to generate I(t)I(t−

T/2);

a second multiplier that multiplies the quadrature-phase signal component Q(t) and the delayed quadrature-phase signal component to generate Q(t)Q(t−

T/2);

an integrator that integrates I(t)I(t−

T/2) to generate an in-phase autocorrelation coefficient A_I, according to

$A_I={\int <br><br>}_{T/2}^T<br><br>I<br><br>\left(t\right)<br><br>I<br><br>\left(t-T/2\right)<br><br>d<br><br>t,$

wherein the integrator integrates Q(t)Q(t−

T/2) to generate a quadrature-phase autocorrelation coefficient AQ, according to

$A_Q={\int <br><br>}_{T/2}^T<br><br>Q<br><br>\left(t\right)<br><br>Q<br><br>\left(t-T/2\right)<br><br>d<br><br>t,$

wherein the integrator combines A_I and A_Q to generate a combined signal A that includes a decoded data symbol, according to

A=A_I+A_Q; and

a decision module that determines a sign for the decoded data symbol.

6. The receiver of claim 5, wherein the receiver is included in a radio frequency identification (RFID) reader interrogator device.

7. The receiver of claim 5, wherein each of the first and second delay modules comprises a memory unit configured to delay the received signal component by T2.

8. The receiver of claim 5, wherein the integrator accumulates I(t)I(t−

T/2) and Q(t)Q(t−

T/2) during t=T/2 to t=T.

9. The receiver of claim 5, further comprising a synchronization module that generates a symbol synchronization signal, wherein the integrator receives the symbol synchronization signal.

10. The receiver of claim 5, wherein the received encoded data signal comprises FM0 encoded data, wherein the decision module determines a binary data symbol to be corresponding to the sign of combined signal A, wherein the data symbol equals 0 if the sign is negative, and the data symbol equals 1 if the sign is positive.

11. The receiver of claim 5, wherein the received encoded data signal comprises Miller encoded data, wherein the decision module determines a binary data symbol to be corresponding to opposite to the sign of combined signal A, wherein the data symbol equals 1 if the sign is negative, and the data symbol equals 0 if the sign is positive.

12. A method for digitally decoding an encoded data signal, comprising:

(a) receiving the encoded data signal having an in-phase signal component I(kΔ

t), and a quadrature-phase signal component Q(kΔ

t);

(b) computing an autocorrelation coefficient A_I,d for the in-phase signal component I(kΔ

t), wherein the autocorrelation coefficient A_I,d is determined by

A_I,d=Σ

I(kΔ

t)*I[(k−

MK₀/2)Δ

t]

where summation is performed over samples from k=(MK₀/2+1) to k=MK₀, where

t=time,

K₀=a number of samples within a subcarrier cycle,

T=duration of a data symbol of the encoded data signal,

M=a number of cycles within T,

MK₀=an even number of samples within T,

Δ

t=T/MK₀,

k=1,2, . . . , MK₀;

(c) computing an autocorrelation coefficient A_Q,d for the quadrature-phase signal component Q(kΔ

t), wherein the autocorrelation coefficient A_Q,d is determined by

A_Q,d=Σ

Q(kΔ

t)*Q[(k−

MK₀/2)Δ

t]

where summation is performed over samples from k=(MK₀/2+1) to k=MK₀;

(d) combining autocorrelation coefficients A_I,d and A_Q,d to generate a combined signal A_d that includes a decoded data symbol, where

A_d=A_I,d+A_Q,d; and

(e) determining a sign for the decoded data symbol.

13. The method of claim 12, wherein the encoded data signal comprises FM0 encoded data, wherein M is equal to 1, wherein step (e) comprises:

determining a binary data symbol to be corresponding to the sign of combined signal A_d, wherein the data symbol equals 0 if the sign is negative, and the data symbol equals 1 if the sign is positive.

14. The method of claim 12, wherein the encoded data signal comprises Miller encoded data, wherein M is equal to 2, 4, or 8, wherein step (e) comprises:

determining a binary data symbol to be corresponding to opposite to the sign of combined signal A_d, wherein the data symbol equals 1 if the sign is negative, and the data symbol equals 0 if the sign is positive.

15. A digital receiver, comprising:

a first delay module that receives an in-phase signal component I(kΔ

t) of an encoded data signal, and delays the in-phase signal component I(kΔ

t) by MK₀/2, where

t=time,

K₀=a number of samples within a subcarrier cycle,

T=duration of a data symbol of the encoded data signal,

M=a number of cycles within T,

MK₀=an even number of samples within T,

Δ

t=T/MK₀, and

k=1,2, . . . , MK₀;

a second delay module that receives a quadrature-phase signal component Q(kΔ

t) of the encoded data signal, and delays the quadrature-phase signal component Q(kΔ

t) by MK₀/2;

a first digital multiplier that multiplies the in-phase signal component I(kΔ

t) and an output of the first delay module to generate

I(kΔ

t)*I[(k−

MK₀/2)Δ

t];

a second digital multiplier that multiplies the in-phase signal component Q(kΔ

t) and an output of the second delay module to generate

Q(kΔ

t)*Q[(k−

MK₀/2)Δ

t];

an adder-accumulator that receives and accumulates signal 1(kΔ

t)* I[(k−

MK₀/2)Δ

t], to generate an in-phase autocorrelation coefficient A_I,d according to

A_I,d=Σ

I(kΔ

t)*I[k−

MK₀/2)Δ

t],

where summation is performed over samples from k=(MK₀/2+1) to k=MK₀;

wherein the adder-accumulator receives and accumulates Q(kΔ

t)* Q[(k−

MK₀/2)Δ

t] to generate a quadrature-phase autocorrelation coefficient A_Q,d according to

A_Q,d=Σ

Q(kΔ

t)*Q[(k−

MK₀/2)Δ

t],

where summation is performed over samples from k=(MK₀/2+1) to k=MK₀;

wherein the adder-accumulator combines A_I,d and A_Q,d to generate a combined signal A_d that includes a decoded data symbol, where

A_d=A_I,d+A_Q,d; and

a decision module that determines a sign for the decoded data symbol.

16. The digital receiver of claim 15, wherein the encoded data signal comprises FM0 encoded data, wherein M is equal to 1, wherein the decision module determines a binary data symbol to be corresponding to the sign of combined signal A_d, wherein the data symbol equals 0 if the sign is negative, and the data symbol equals 1 if the sign is positive.

17. The digital receiver of claim 15, wherein the encoded data signal comprises Miller encoded data, wherein M is equal to 2, 4, or 8, wherein the decision module determines a binary data symbol to be corresponding to opposite to the sign of combined signal A_d, wherein the data symbol equals 1 if the sign is negative, and the data symbol equals 0 if the sign is positive.

18. The digital receiver of claim 15, wherein the encoded data signal comprises data from a backscattered signal received from a radio frequency identification (RFID) tag.

19. The digital receiver of claim 18, wherein the receiver is included in a radio frequency identification (RFID) reader interrogator device.