Tektronix, Inc.

Textronic, Inc.

Xiaofen Chen

Thomas L Kuntz

Linley F Gumm

Kyle L Bernard

Soraya J Matos

Nikhil M Deshpande

Kathryn A Engholm

Thomas C Hill

Donald J Dalebroux

Larry R Lockwood

Dana E Whitlow

Leroy J Willmann

A fault severity check and source identification method for a frequency domain instrument accesses acquired reflection data for a transmission line under test. From the acquired data reflection surfaces are isolated as a function of distance. Each reflection surface is examined to produce a frequency response profile and a worst-case reflection response to determine fault severity. The frequency response profile may also be correlated in a pattern recognition algorithm with known reference source profiles to determine the source identification for the fault.

Fault severity check and source identification

A display of code domain power (CDP) for a code domain multiple access (CDMA) signal having multiple spreading factors is in the form of a three-dimensional graphic having as axes code domain power, code index and spreading factor to provide a visual indication of both power and spreading factor for active codes. Sub-codes of base codes may be identified by any suitable means, such as highlighting. Sub-codes may be suppressed and the power level of the base codes adjusted accordingly to represent the total power of the active codes.

Visualization of active codes, their spreading factors and power levels, in a code domain power display

A modulation analyzer includes a smoothing processor which processes the coordinates of symbol landing points to generate a curve that optimally fits the landing points under a selected criterion.

Enhanced constellation display for VSB television signals

An improved calibration method for a vector network analyzer stores sparse calibration data, interpolates system error data from the sparse calibration data for each measurement by the vector network analyzer, and creates calibrated measurement data from the system error data and uncorrected measurement data at each measurement frequency. The sparse calibration data may be generated by measuring every Nth frequency step over a calibration frequency range greater than a specified measurement frequency range, or by measuring every frequency step over the calibration frequency range and compressing the resulting measurement data. The interpolation may be achieved by using a curve-fit algorithm, such as a parametric polynomial curve fitting algorithm.

Calibration for vector network analyzer

A measurement receiver demodulator has a first processing channel for producing a filtered signal sample output where the signal samples are processed through a transmission system receiver filter and a second processing channel producing an unfiltered signal sample output where the signal samples are not processed through the transmission system receiver filter. The first processing channel down converts digitally modulated IF signal samples and filters the down converted signal samples using a combined transmission system receiver filter and front end hardware compensation filter. A synchronizer produces timing phase and rate offset parameters that are applied to a resampling filter to synchronize the filtered signal samples to symbol instances of the symbol modulation. The filtered, time-aligned signal samples are scaled using a derived scaling factor. A pilot offset level, if present, is estimated and removed. The resultant signal samples are processed through an equalizer to produce filtered, time-aligned, scaled equalized signal samples that are output as filtered signal samples. The second processing channel receives the down converted signal samples and uses compensation and equalization filter coefficients, timing parameters, and the scaling from the first processing channel in compensation, resampling and equalization filters and a scaler to produce compensated, time-aligned, scaled equalized signal samples that are output as unfiltered signal samples.

Measurement receiver demodulator

A method of broadband receiver amplitude/phase normalization uses internal normalization sources&mdash;a thermally compensated noise source and a pseudo random sequence generator. A calibrated signal is applied to the input of the broadband receiver and processed by a digital signal processor to generate a gain versus frequency table. Then the internal noise source is applied to the input of the broadband receiver and process by a digital signal processor to generate a noise level versus frequency table. Finally the internal pseudo random sequence generator applies a pseudo random sequence waveform to the input of the broadband receiver, the pseudo random sequence waveform being process by the digital signal processor to generate equalization filter coefficients for the IF stages.

Broadband receiver amplitude/phase normalization using a broadband temperature compensated noise source and a pseudo random sequence generator

A method of interference cancellation in antenna test measurements is achieved by acquiring an acquisition at a test port of an antenna test instrument in response to an internal signal source, stamping the data acquisition time, and measuring a signal vector that has both a reflection signal component and an interference signal component. Another acquisition at the test port without the internal signal source is obtained with limited data points to detect whether there are interference signals. If there is significant interference power, a complete acquisition is obtained without the internal signal source, the data acquisition time is stamped, and an interference vector that has only the interference signal is measured. Then the interference frequency is measured, an interference phase shift between the two data acquisitions is calculated, an interference vector for the combined reflection/interference vector is predicted using the interference vector and the phase shift, and the predicted interference vector is subtracted from the signal vector to obtain the actual reflection signal for the antenna in the absence of interference.

Interference cancellation in antenna test

Reference frequency spur cancellation in a synthesized measurement receiver is achieved by determining for any given frequency to which the receiver is tuned a list of integer multipliers of the reference frequency that produce spurious signals in the receiver's passband. For those values the amplitude and phase for each spurious signal is determined in the digital domain and subtracted from the digital signal from the receiver. The reference frequency is then offset slightly and the measurement repeated. The maximum values between each measurement are combined to produce a measurement for the input signal without spurious signals.

Reference frequency spur cancellation in synthesized measurement receivers

A method of estimating pilot signal phase embedded in a wideband digital signal modulating a RF signal that is down converted to an intermediate frequency and digitized includes the steps of summing a block of the signal samples for removing the modulation data and generating data values representative of vector locations of the pilot signal with each data value representing an angular rotation of the pilot signal vector, and calculating the phase of the pilot signal by determining the arc tangent of the data values. The method produces a computationally efficient narrow band filter generated at the pilot signal frequency by simple addition of the digital data values. The method is usable in a software based 8-VSB digital television demodulation system.

Method of estimating pilot signal phase in a digitally modulated RF signal

A method of estimating symbol timing phase and rate offsets of a sampled digitally modulated signal having repetitive symbol sync sequences includes the steps of estimating symbol sync sequence locations in a block of signal samples using a cross-correlation with a reference pattern of ideal symbol sync sequences. Signal samples within subranges defining the symbol sync sequences in the block of signal samples are filtered for removing intersymbol interference. An iterative process of cross-correlation of the filtered signal samples within the subranges using the reference pattern of ideal symbol sync sequences and an ideal symbol sync correction pattern generates timing phase and rate offset values that are used to derive filter coefficients for resampling the filtered signal samples within the subranges using an interpolating filter. The rate offset value is derived using a linear model and performing an optimal estimation. The iterative cross-correlation and resampling process continues until the rate of change of timing phase and rate offset values are minimized. The timing phase and rate offset values are provided to a resampling FIR filter for generating properly synchronized signal samples that are time aligned to symbol-spaced boundaries.

Method of estimating timing phase and rate offsets in digital data

A system for in-service nonlinearity measurements measures such nonlinearities by way of comparing received linear error-corrected unfiltered signal samples with re-generated reference signal samples to calculate magnitude and phase nonlinear error values. Linear distortion is removed from the received signal samples in order to truly characterize nonlinear behavior of the transmitter. The linear error-corrected received signal samples are generated without applying the receiver shaping filtering. Reference signal samples are re-generated from estimated transmitted symbols from the unfiltered linear error-corrected received signal samples. The transmitted symbols are estimated using a multi-region slicer which dynamically estimates constellation decision levels from the unfiltered signal samples. A weighted, least-square based polynomial regression is performed on magnitude and phase nonlinear error values to estimate magnitude and phase nonlinear error functions while suppressing the impact of other non-systematic distortions.

In-service measurement of transmitter nonlinearities

A system and method for in-service transmitter phase noise measurements determines phase nonlinearity by way of comparing unfiltered signal samples and regenerated reference signal samples to calculate phase nonlinearity error. Linear distortion is removed from the received signal samples in order to truly characterize nonlinear behavior of the transmitter. The unfiltered signal samples are generated without applying the receiver shaping filtering. Reference signal samples are regenerated from estimated transmitted symbols derived from the unfiltered signal samples. The transmitted symbols are estimated using a segmented slicer which dynamically estimates constellation decision levels from the unfiltered signal samples. A weighted, least-square based polynomial regression is performed on phase error samples of the unfiltered signal samples to estimate a phase nonlinear error function while suppressing the impact of other non-systematic distortions. The nonlinear phase error is removed from the phase error to produce phase noise containing carrier phase jitter and additive noise. A threshold is determined for replacing phase error values outside the threshold with random values having a distribution equivalent to the carrier phase jitter. The carrier phase jitter may be displayed as a power spectrum of the phase noise.

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West Linn, OR, United States of America

Xiaofen Chen