Browse Prior Art Database

AC Cycle Phase Constant Noise Identification and Avoidance Method

IP.com Disclosure Number: IPCOM000115501D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 91K

Publishing Venue

IBM

Related People

Cato, RT: AUTHOR

Abstract

When problems are encountered in communicating over the power lines, it is extremely useful to be able to identify the problem. Frequently interference of some kind is the problem, as opposed to a weak signal.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

AC Cycle Phase Constant Noise Identification and Avoidance Method

      When problems are encountered in communicating over the power
lines, it is extremely useful to be able to identify the problem.
Frequently interference of some kind is the problem, as opposed to a
weak signal.

      Quick identification of the source of the interference is the
key to maintaining a reliable data link and thus a satisfied
customer.  This invention provides the customer or customer engineer
an automatic means of classifying the source of interference which is
a very important step in finding and eliminating the interference.
Put another way, knowing the characteristics of the interference
helps tremendously in identifying it and then eliminating it.

      This method of classifying interference as AC cycle phase
dependent requires that the AC cycle phase be known at the instant of
interference.  A common means of measuring AC cycle phase is relative
to the zero crossing of the AC cycle.  This disclosure holds with the
measurements being made relative to any place in the AC cycle, but
the zero crossing will be assumed to be the reference point.

      It is common for power line communication systems to
synchronize their transmissions with the AC cycle.  This is done in
order to transmit the data packets near the AC cycle zero crossing
and therefore attempt to avoid phase constant interference.  Thus the
AC phase measurement hardware is typically available in power
communication systems.  Thus it would be easy for a competitive power
line communications system to duplicate this invention.

      When a transmitter actually transmits a packet, it "remembers"
to look for an acknowledgement from the receiver that the packet
arrived successfully.  This invention would have the transmitter also
remember the AC cycle phase information associated with each packet.
The phase information could be a byte read from a constantly counting
counter that is reset every time the AC cycle crosses zero volts.

      When an acknowledgement is not received from the addressed
receiver, the transmitter would log this fact as well as the AC cycle
phase information of the lost packet.  After a suitable amount of
lost packet data is collected, the data would be analyzed to see if
an unusual percentage of packets are lost at a particular place in
the AC cycle.  Random interference would be uniformly spread across
all of the AC cycle.  If an unusually high percentage of packets...