US 2007/0177694 A1Published application

Method and apparatus for signal processing in RFID receivers

AssigneeSymbol Technologies, Inc.

InventorsYuri Okunev, Kevin Powell

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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. Correlation coefficients for the in-phase and quadrature components of the received signal are calculated over a shifted bit interval. Performing a correlation over a shifted bit interval relative to the real bit interval allows the base-band receiver to involve a two-bit interval in making a decision about each transmitted bit. In contrast, in a conventional decoding algorithm, a single bit interval is involved in the decision-making process. Thus, the current method provides a 3 dB energy gain compared to the conventional method. A single zero-mean reference signal is used to compute correlation coefficients, eliminating constant components of the received signal, and simplifying digital implementation of the base-band receiver. A value of the output data is determined based on the combined correlation coefficients.

Claims20

Dependent claims

A method for decoding an encoded data signal, comprising:

(a) receiving the encoded data signal including a plurality of data symbols, wherein a time period T is a length of a data symbol of the encoded data signal, wherein a current data symbol begins at time t and ends at time (t+T);
(b) correlating an in-phase component of the received signal with a reference signal over a period t−T/2 to t+T/2 to generate a first in-phase correlation coefficient for the current data symbol;
(c) correlating an in-phase component of the received signal with a reference signal over a period t+T/2 to t+3T/2 to generate a second in-phase correlation coefficient for the current data symbol;
(d) correlating a quadrature component of the received signal with the reference signal over a period t−T/2 to t+T/2 to generate a first quadrature correlation coefficient for the current data symbol;
(e) correlating a quadrature component of the received signal with the reference signal over a period t+T/2 to t+3T/2 to generate a second quadrature correlation coefficient for the current data symbol;
(f) multiplying the first in-phase correlation coefficient with the second in-phase correlation coefficient to produce an in-phase cross-correlation value;
(g) multiplying the first quadrature correlation coefficient with the second quadrature correlation coefficient to produce a quadrature cross-correlation value;
(h) adding the in-phase cross-correlation value and the quadrature cross-correlation value to produce an integral cross correlation value;
and
(i) determining a decoded value for the current data symbol based on the integral cross-correlation value.

7 more elements

A base-band digital receiver that decodes an encoded data signal, the encoded data signal including a plurality of data symbols, wherein a time period T is a length of a data symbol of the encoded data signal, wherein a current data symbol begins at time t, the receiver comprising:

an in-phase correlator that correlates an in-phase component of the encoded data signal with a reference signal over a period t+T/2 to t+3T/2 to generate an in-phase correlation coefficient for the current data symbol;
a quadrature correlator that correlates a quadrature component of the received signal with the reference signal over the period t+T/2 to t+3T/2 to generate a quadrature correlation coefficient for the current data symbol;
a first delay module that receives the in-phase correlation coefficient associated with the time period t+T/2 to t+3T/2 while outputting a delayed in-phase correlation coefficient associated with a prior time period t−T/2 to t+T/2;
a second delay module that receives the quadrature correlation coefficient associated with the time period t+T/2 to t+3T/2 while outputting a delayed quadrature correlation coefficient associated with the prior time period t−T/2 to t+T/2;
a first multiplier that multiplies the in-phase correlation coefficient with the delayed in-phase correlation coefficient to produce an in-phase cross-correlation value;
a second multiplier that multiplies the quadrature correlation coefficient with the delayed quadrature correlation coefficient to produce a quadrature cross-correlation value;
and
a decision module that adds the in-phase cross-correlation value and the quadrature cross-correlation value to produce an integral cross-correlation value, and determines a decoded value for the current data symbol based on the integral cross-correlation value.

5 more elements

Dependencies are inferred from the claim text.