Method of determining inter-symbol interference in transmission systems

Claim 1

A method of determining an inter-symbol interference, ISI, level of a signal received at a location along a communication facility, comprising the steps of: a) for each of a first plurality of received signals having different Signal-to-Noise, S/N, ratios, determining a minimum bit-error rate, BER, value by varying threshold levels of a decision circuit connected to said location, thereby forming a first group of minimum BER values, b) after replacing at least one segment of the communication facility with a non-ISI producing attenuator, for each of a second plurality of received signals having different S/N ratios, determining a second minimum BER value by varying threshold levels of the decision circuit, thereby forming a second group of minimum BER values, and c) determining the ISI level for a predetermined BER value using the first and second groups of minimum BER values obtained in steps a) and b).

Claim 2

A method of determining an inter-symbol interference, ISI, level of a signal received at a location along a communication facility, comprising the steps of: a) for each of a first plurality of received signals having different Signal-to-Noise, S/N, ratios, determining a minimum bit-error rate, BER, value by varying threshold levels of a decision circuit connected to said location, thereby forming a first group of minimum BER values, b) after replacing at least one segment of the communication facility with a non-ISI producing attenuator, for each of a second plurality of received signals having different S/N ratios, determining a second minimum BER value by varying threshold levels of the decision circuit, thereby forming a second group of minimum BER values, and c) determining the ISI level for a predetermined BER value using the first and second groups of minimum BER values obtained in steps a) and b).

Claim 3

A method of determining an inter-symbol interference, ISI, level of a received signal at a location along the communication facility, comprising the steps of: a) for each of a first plurality of received signals having different Signal-to-Noise, S/N, ratios, determining a threshold level of a decision circuit connected to said location at which a minimum bit-error rate, BER, value occurs, and while maintaining the determined threshold level constant at the decision circuit, measuring a minimum, BER, value as a function of the power for each of said first signals, to obtain a first group of minimum BER values, b) after replacing at least one segment of the communication facility with a non-ISI producing attenuator, repeating step a), for each of a second plurality of received signals having different S/N ratios, to obtain a second group of minimum BER values and c) determining the ISI level for a predetermined BER value using the first and second group of minimum BER values obtained in steps a) and b).

Claim 4

A method of determining an inter-symbol interference, ISI, level of a received signal at a location along the communication facility, comprising the steps of: a) for each of a first plurality of received signals having different Signal-to-Noise, S/N, ratios, determining a threshold level of a decision circuit connected to said location at which a minimum bit-error rate, BER, value occurs, and while maintaining the determined threshold level constant at the decision circuit, measuring a minimum, BER, value as a function of the power for each of said first signals, to obtain a first group of minimum BER values, b) after replacing at least one segment of the communication facility with a non-ISI producing attenuator, repeating step a), for each of a second plurality of received signals having different S/N ratios, to obtain a second group of minimum BER values and c) determining the ISI level for a predetermined BER value using the first and second group of minimum BER values obtained in steps a) and b).

Claim 16

A method of determining an inter-symbol interference, ISI, level of a signal received at a location along a communication facility, comprising the steps of: a) for each of a first plurality of received signals having different Signal-to-Noise, S/N, ratios, determining a minimum bit-error rate, BER, value by varying threshold levels of a decision circuit connected to said location, thereby forming a first group of minimum BER values, b) after replacing at least one segment of the communication facility with a non-ISI producing attenuator, for each of a second plurality of received signals having different S/N ratios, determining a second minimum BER value by varying threshold levels of the decision circuit, thereby forming a second group of minimum BER values, and c) determining the ISI level for a Predetermined BER value using the first and second groups of minimum BER values obtained in steps a) and b) and wherein step c) includes the steps of: plotting 1) a first line connecting at least two of the first plurality of minimum BER values and 2) a second line connecting at least two of the second plurality of minimum BER values as a function of their respective associated received signal S/N ratio, for a predetermined BER value, selecting where that predetermined BER value intersects the first and second plotted lines to obtain a first and a second S/N ratio, and subtracting the second S/N ratio from the first S/N ratio to determine an ISI value.

Claim 17

A method of determining an inter-symbol interference, ISI, level of a signal received at a location along a communication facility, comprising the steps of: a) for each of a first plurality of received signals having different Signal-to-Noise, S/N, ratios, determining a minimum bit-error rate, BER, value by varying threshold levels of a decision circuit connected to said location, thereby forming a first group of minimum BER values, b) after replacing at least one segment of the communication facility with a non-ISI producing attenuator, for each of a second plurality of received signals having different S/N ratios, determining a second minimum BER value by varying threshold levels of the decision circuit, thereby forming a second group of minimum BER values, and c) determining the ISI level for a Predetermined BER value using the first and second groups of minimum BER values obtained in steps a) and b) and wherein step c) includes the steps of: plotting 1) a first line connecting at least two of the first plurality of minimum BER values and 2) a second line connecting at least two of the second plurality of minimum BER values as a function of their respective associated received signal S/N ratio, for a predetermined BER value, selecting where that predetermined BER value intersects the first and second plotted lines to obtain a first and a second S/N ratio, and subtracting the second S/N ratio from the first S/N ratio to determine an ISI value.

Claim 19

A method of determining an inter-symbol interference, ISI, level of a digital optical signal received at a location along an optical fiber communication facility, comprising the steps of: a) for each of a first plurality of received signals having different Signal-to-Noise, S/N, ratios, determining a minimum bit-error rate, BER, value by varying threshold levels of a decision circuit connected to said location, thereby forming a first group of minimum BER values, b) after replacing at least one segment of the optical fiber with a non-ISI producing attenuator, for each of a second plurality of received signals having different S/N ratios, determining a second minimum BER value by varying threshold levels of the decision circuit, thereby forming a second group of minimum BER values, and c) determining the ISI level for a predetermined BER value using the first and second groups of minimum BER values obtained in steps a) and b).

Claim 20

A method of determining an inter-symbol interference, ISI, level of a digital optical signal received at a location along an optical fiber communication facility, comprising the steps of: a) for each of a first plurality of received signals having different Signal-to-Noise, S/N, ratios, determining a minimum bit-error rate, BER, value by varying threshold levels of a decision circuit connected to said location, thereby forming a first group of minimum BER values, b) after replacing at least one segment of the optical fiber with a non-ISI producing attenuator, for each of a second plurality of received signals having different S/N ratios, determining a second minimum BER value by varying threshold levels of the decision circuit, thereby forming a second group of minimum BER values, and c) determining the ISI level for a predetermined BER value using the first and second groups of minimum BER values obtained in steps a) and b).