Bell Telephone Laboratories

Peter F Lynn

David L Favin

Paul J Snyder

Accurate and reliable measurements of transmission parameters, e.g., envelope delay distortion or frequency response, of a network or facility (105) are obtained in a test system (FIG. 1) employing digital data acquisition units (121) by utilizing a unique test signal including a plurality of tones. A set of test signals is transmitted over the facility (105), a set of measurements is made of the received version for each test signal, each set of measurements is time averaged, and an ensemble of time-averaged sets of measurements is used to generate the desired measurements of the transmission parameters. System efficiency is enhanced by measuring prescribed transmission impairments, e.g., nonlinear distortion (3OID), signal-to-noise ratio (S/N) and frequency shift (FS) on the facility under evaluation and dynamically determining test system parameters in accordance with predetermined relationships with the measured impairments (FIGS. 5, 6 and 7), namely, the number (D) of test signals in the set of test signals, the maximum number (T) of consecutive measurements to be time-averaged, the required number of measurements (M) and the number of time-averaged measurements to be made in order to obtain a desired measurement accuracy.

Adaptive multitone transmission parameter test arrangement

Accurate and reliable measurement results are obtained in a test system (FIG. 1) employing digital data acquisition units (121) when measuring frequency response or envelope delay distortion of a network or communication facility (105) by employing a unique test signal (21-tone) including a plurality of tones, each tone having amplitude, frequency, phase component values determined and assigned in accordance with prescribed criteria. The phase component values are determined in accordance with a relationship dependent on the number of tones in the test signal, and in one example, are initially assigned on a random, one-to-one basis to the tones. In a specific embodiment, a test signal is utilized having 21 tones. Further problems arising from nonlinearities on the facility under evaluation (105) are minimized by transmitting the 21-tone test signal a plurality of times and by reassigning the phase component values to the tones each time the test signal is transmitted. In a specific example, the phase component values are reassigned to the tones in counterclockwise, circular fashion after each transmission of the test signal until each tone has taken on each phase component value. Once measurements, i.e., data records, of the transmitted test signal have been obtained, they are utilized to obtain a spectrum, and in turn, the frequency components of the spectrum are employed to obtain the desired measurement of frequency response or envelope delay distortion.

Multitone frequency response and envelope delay distortion tests

Errors in test results are minimized in a test system (FIG. 1) employing digital data acquisition units (121) when measuring intermodulation distortion of a voice frequency communication facility (105) by employing a unique 3-tone test signal. To this end, the three tones have predetermined amplitude, frequency and phase relationships to obtain a test signal having a desired optimum probability density function which is substantially Gaussian. Additionally, circuit noise components are eliminated from the test results by obtaining a measure of noise with a single tone test signal and subtracting it out from the three tone test results. In a specific embodiment, a measure of the power spectrum resulting from the three tone signal and the power spectrum of the single tone signal are obtained, combined and utilized to obtain measurements of second and third order intermodulation distortion products compensated for noise.

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Little Silver, NJ, United States of America

Peter F Lynn