SYSTEMS AND METHODS FOR JOINT BEAMFORMING AND PREAMBLE DETECTION

• US 20120188058A1
• Filed: 11/30/2011
• Published: 07/26/2012
• Est. Priority Date: 11/30/2010
• Status: Active Grant

• Current Assignee: Mojix Inc
• Original Assignee: Mojix Inc
• Inventors: Jones, Christopher R., Lee, Dong-U
• Granted Patent: US 8,929,494 B2
• Time in Patent Office: Days
• US Class Current: 340/10.1
• CPC Class Codes: G06K 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas

Abstract

Systems and methods for reading RFID tags using joint beamforming and preamble detection in accordance with embodiments of the invention are disclosed. One embodiment includes an antenna array comprising a plurality of antenna elements, a joint beamformer and preamble detector configured to receive inputs from each of the antenna elements, and a decoder configured to receive a resampled signal from the joint beamformer and preamble detector and to decode data using the resampled signal. In addition, the joint beamformer and preamble detector is configured to correlate the inputs from the antenna elements against a correlation sequence at a plurality of starting sample positions and predetermined rates, use the correlations to select a starting sample position and rate for decoding the received signal, use the correlations to determine beamforming coefficients for combining the inputs, and resample the combined inputs based upon the selected starting sample position and rate.

Claims

1. An RFID reader system, comprising:

an antenna array comprising a plurality of antenna elements;

a joint beamformer and preamble detector configured to receive inputs from each of the plurality of antenna elements, where the joint beamformer and preamble detector is configured to;

correlate the inputs from the plurality of antenna elements against a correlation sequence at a plurality of starting sample positions and a plurality of predetermined rates;

use the correlations to select a starting sample position and rate for decoding the received signal;

use the correlations to determine beamforming coefficients for combining the inputs from each of the plurality of antenna elements; and

resample the combined inputs from each of the plurality of antenna elements based upon the selected starting sample position and rate;

a decoder configured to receive the resampled signal from the joint beamformer and preamble detector and to decode data using the resampled signal.

2. The RFID reader system of claim 1, wherein the RFID reader system comprises a plurality of exciters and an RFID receiver system including the antenna array, the joint beamformer and preamble detector and the decoder.

3. The RFID reader system of claim 1, wherein the joint former and preamble detector comprises a skipping based correlator configured to correlate the inputs from the plurality of antenna elements against a correlation sequence at a plurality of starting sample positions and plurality of predetermined rates.

4. The RFID reader system of claim 3, wherein:

the skipping based correlator comprises a symbol accumulator circuit and a tapped delay line; and

correlations for different starting sample positions and rates can be determined using the outputs of different taps from the tapped delay line.

5. The RFID reader system of claim 1, wherein the inputs from each of the plurality of antenna elements comprises samples of the in-phase and quadrature channels of each antenna element.

6. The RFID reader system of claim 5, wherein the joint beamformer and preamble detector is configured to use the complex correlations of each of the antenna elements at the selected starting sample and rate to determine the beamforming coefficients.

7. The RFID reader system of claim 6, wherein the joint beamformer and preamble detector is configured to determine the complex beamforming coefficient (b_i) of an antenna element i in an array of n antenna elements can be generated as follows:

8. The RFID reader system of claim 1, wherein the RFID reader system is configured to request data from an RFID tag encoded using FM0 modulation (TRext=1).

9. The RFID reader system of claim 8, wherein the correlation sequence includes 12 pilot symbols and 6 preamble symbols of an FM0 modulated pilot and preamble (TRext=1) in accordance with the EPCglobal Gen2 specification.

10. The RFID reader system of claim 1, wherein the RFID reader system is configured to request data from an RFID tag encoded using Miller-2 modulation (TRext=0).

11. The RFID reader system of claim 10, wherein the correlation sequence corresponds to the latter 20 FM0 symbols of a Miller-2 modulated pilot and preamble (TRext=0) in accordance with the EPCglobal Gen2 specification.

12. The RFID reader system of claim 1, wherein the RFID reader system is configured to request data from an RFID tag encoded using Miller-4 modulation (TRext=0).

13. The RFID reader system of claim 12, wherein the correlation sequence corresponds to the latter 40 FM0 symbols of a Miller-4 modulated pilot and preamble (TRext=0) in accordance with the EPCglobal Gen2 specification.

14. The RFID reader system of claim 1, wherein the RFID reader system is configured to request data from an RFID tag encoded using Miller-8 modulation (TRext=0).

15. The RFID reader system of claim 14, wherein the correlation sequence corresponds to the latter 48 FM0 symbols of a Miller-8 modulated pilot and preamble (TRext=0) in accordance with the EPCglobal Gen2 specification.

16. A method of detecting data transmitted by an RFID tag using an RFID receiver comprising an antenna array and a joint beamformer and preamble detector, comprising:

receiving sampled streams from each antenna element in the antenna array using the RFID receiver;

correlating each stream against a predetermined correlation sequence for each of a plurality of possible starting samples and at each of a plurality of predetermined rates using the joint beamformer and preamble detector;

summing the magnitude of the correlation value of each sample position and rate across each of the antenna streams using the joint beamformer and preamble detector;

selecting the sample position and rate having the highest sum of correlation value magnitudes using the joint beamformer and preamble detector;

determining beamforming coefficients based on the correlations of each stream at the selected sample position using the joint beamformer and preamble detector;

combining the antenna outputs based upon the beamforming coefficients using the joint beamformer and preamble detector;

resampling the combined antenna outputs based upon the selected starting sample and rate using the joint beamformer and preamble detector to produce a resampled signal; and

decoding the transmitted data based upon the resampled signal using the RFID receiver.