Signal decoding method and apparatus with dynamic noise threshold

• US 7,609,784 B1
• Filed: 06/12/2007
• Issued: 10/27/2009
• Est. Priority Date: 04/26/2004
• Status: Active Grant

• Current Assignee: DGI Creations, LLC
• Original Assignee: DGI Creations, LLC
• Inventors: Heistermann, Fritz
• Primary Examiner(s): Torres; Juan A
• Application Number:
  US11/811,891
• Time in Patent Office: 868 Days
• Field of Search: 375/329, 329/304, 329/306
• US Class Current: 375/329
• CPC Class Codes: H04B 2203/542 using zero crossing information
• CPC Class Codes: H04B 2203/5466 using three phases conductors
• CPC Class Codes: H04B 3/54 Systems for transmission via power distribution lines
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end

Abstract

An apparatus and method for use by a receiver in decoding information sent by phase-shift keying over a carrier frequency for use with power line carrier (PLC) applications as it is adapted to appropriately position the sampling window based on a zero crossing of one of the phases of the power line. The method allows for receipt and processing of information on more than one carrier frequency and from transmitters operating on a phase of the power line that is different than the phase used by alternating current at the power grid frequency on the receiver to detect the zero crossings of the power line. Optionally, a threshold parameter may be dynamically adjusted in reaction to the underlying level of noise so as to reduce the number of bursts carrying actual data that are discarded as having only noise. A number of alternative embodiments are included.

Claims

1. A method of decoding a phase shift keying signal carried on a carrier frequency over a power line operating at a power grid frequency, the method comprising the steps of:

using a zero crossing detector to detect a zero crossing of the alternating current on a first phase of the power line operated at the power grid frequency;

using a receiver to receive a burst of received analog signal carried on a carrier frequency over a power line;

converting at least a portion of the burst of received analog signal carried on the carrier frequency to a set of digital samples, the portion corresponding to the analog signal during a burst sampling window between zero crossings established in relation to the detected zero crossing on the first phase of the power line;

creating a set of digital values of an ideal cosine wave with a frequency substantially equal to the carrier frequency;

creating a set of digital values of an ideal sine wave with frequency substantially equal to the carrier frequency;

multiplying a subset of digital samples from the burst with a subset of corresponding created digital values for the ideal cosine wave and storing the sum of the products as the In-Phase Component of the set of digital samples;

multiplying the subset of digital samples from the burst with a subset of corresponding created digital values for the ideal sine wave and storing the sum of the products as the Quadrature component of the set of digital samples;

discarding the In-Phase component and the Quadrature component if an energy level in the received analog signal does not exceed a threshold value;

when the energy level in the received analog signal exceeds a threshold value, obtaining a phase offset for the received analog signal from an ideal cosine wave by obtaining the Arctangent of the quotient of the Quadrature component divided by the In-Phase component;

using pairs of obtained phase offsets from adjacent bursts to decode the binary information conveyed by phase shift keying in the received analog signal; and

dynamically adjusting the threshold value based on measurements of the energy level in the received analog signal.

2. The method of claim 1 wherein the energy level in the received analog signal compared to the threshold value is based upon a maximum absolute value of either the In-Phase Component or the Quadrature Component.

3. The method of claim 2 wherein the energy level is the most significant bit of the maximum absolute value of either the In-Phase Component or the Quadrature Component.

4. The method of claim 1 wherein the dynamic adjustment of the threshold value based on the energy level in the received analog signal captures the maximum energy level is a series of bursts in a batch.

5. The method of claim 4 wherein the number of bursts in the series is close to the number of bursts in the average message.

6. The method of claim 4 wherein the number of bursts in the series is in the range of half to double the number of bursts in the average message.

7. The method of claim 4 wherein a series of energy levels for the maximum energy level in a series of bursts are evaluated as a block to see a net value on a comparison of the number of batches with a maximum energy level in excess of the current threshold versus batches with a maximum energy level below the current threshold and the net value is compared with set points to determine if the threshold should be adjusted.