Non-invasive digital communications test system

In a digital communication system comprising:

• a first digital transmitter that converts a first stream of digital data to be transmitted to a stream of symbols, and modulates a first carrier signal responsive to said stream of symbols to produce a first modulated carrier signal,
• a communications channel coupled to said first digital transmitter, that distributes said first modulated carrier signal, said communications channel having an associated channel response that distorts said first modulated carrier signal to produce a distorted first modulated carrier signal,
• a demodulator that receives the distorted modulated carrier signal and extracts an estimated modulation signal,
• a symbol decoder that translates a representation of said estimated modulation signal output into estimates of said first stream of digital data,
• a method of transmitting a second modulated carrier signal through said communications channel comprising the steps of:
• using a second digital transmitter coupled to said communications channel to generate said second modulated carrier signal and transmit said second modulated carrier signal, said second modulated carrier signal overlapping the first modulated carrier signal in the frequency domain;
• generating a difference signal between an ideal modulated signal representing said estimates of said first stream of digital data and said estimated modulation signal as an estimate of an error signal;
• and
• monitoring said error signal to obtain said second modulated carrier signal.

In a digital communications system comprising:

• a digital transmitter that converts digital data to be transmitted to a stream of symbols, and modulates a carrier signal responsive to said stream of symbols to produce a modulated carrier signal,
• a communications channel coupled to said digital transmitter, that distributes the modulated carrier signal, said communications channel having an associated channel response that distorts said modulated carrier signal to produce a distorted modulated carrier signal,
• a demodulator that receives the distorted modulated carrier signal and extracts an estimated modulation signal,
• a symbol decoder that translates a representation of said estimated modulation signal output into estimates of said digital data,
• apparatus for identifying error ingress sources in said communications channel comprising:
• means for generating an ideal modulation signal representing said digital data;
• means for generating a difference signal between said ideal modulation signal and said estimated modulation signal as an estimate of an interfering signal;
• and
• receiving said difference signal into a diagnostic processor
• means for intentionally injecting an ingress signal carrying additional information into the communications channel, said difference signal being a representation of said intentionally injected ingress signal.

In a digital communication system comprising:

• a first digital transmitter that converts a first stream of digital data to be transmitted to a stream of symbols, and modulates a first carrier signal responsive to said stream of symbols to produce a first modulated carrier signal,
• a communications channel coupled to said first digital transmitter, that distributes said first modulated carrier signal, said communications channel having an associated channel response that distorts said first modulated carrier signal to produce a distorted first modulated carrier signal,
• a demodulator that receives the distorted modulated carrier signal and extracts an estimated modulation signal,
• a symbol decoder that translates a representation of said estimated modulation signal output into estimates of said first stream of digital data,
• apparatus for transmitting a second modulated carrier signal through said communications channel comprising:
• means for using a second digital transmitter coupled to said communications channel to generate said second modulated carrier signal and transmit said second modulated carrier signal, said second modulated carrier signal overlapping the first modulated carrier signal in the frequency domain;
• means for generating a difference signal between an ideal modulated signal representing said estimates of said first stream of digital data and said estimated modulation signal as an estimate of an error signal;
• and
• means for monitoring said error signal to obtain said second modulated carrier signal.

In a digital receiver system comprising:

• a demodulator that receives a distorted modulated carrier signal carrying digital data and extracts an estimated modulation signal,
• a symbol decoder that translates a representation of said estimated modulation signal output into estimates of said digital data, a method of diagnosing a communication channel to which said distorted modulated carrier signal was subject, said method comprising the steps of:
• generating an ideal modulation signal representing said digital data;
• generating a difference signal between said ideal modulation signal and said estimated modulation signal as an estimate of an interfering signal, said difference signal being resolved into orthogonal components;
• receiving said difference signal into a diagnostic processor;
• and
• calculating statistics of said difference signal using said orthogonal components using said diagnostic processor.

A communication channel diagnosis system comprising:

• a demodulator that receives a distorted modulated carrier signal carrying digital data and extracts an estimated modulation signal;
• a symbol decoder that translates a representation of said estimated modulation signal output into estimates of said digital data;
• an ideal modulation signal generator that generates an ideal modulation signal representing said digital data;
• a difference signal generator that generates an ideal difference signal between said ideal modulation signal and said estimated modulation signal as an estimate of an interfering signal, said difference signal being resolved into orthogonal components;
• and
• a diagnostic processor that receives said difference signal and calculates statistics of said difference signal using said orthogonal components using said diagnostics processor.