Tektronix, Inc.

Textronic, Inc.

Thomas L Kuntz

Xiaofen Chen

Nikhil M Deshpande

Kathryn A Engholm

Linley F Gumm

Kyle L Bernard

Shigetsune Torin

Craig D Bryant

Ian S Dees

Soraya J Matos

David L Suryan

Thomas A Elliot

Jerry L Young

A test and measurement instrument having initial display center frequency and span settings and configured to process an input signal is disclosed. The test and measurement instrument includes a processor configured to digitize the input signal and locate a primary peak and determine a primary peak center frequency of the input signal. The processor is configured to adjust the initial display center frequency setting based on the primary peak center frequency. The processor is configured to perform a bandwidth comparison by comparing a bandwidth of the primary peak at a peak bandwidth test level to a peak bandwidth threshold. The processor is configured adjust the initial span setting based on the bandwidth comparison and generate a processed waveform signal using the adjusted display center frequency and span settings.

Automatic center frequency and span setting in a test and measurement instrument

A two stage adaptive filter for use in a batch receiver includes an equalizer filter having as inputs an acquired signal representing a batch of data points and an equalizer filter value. The filtered signal is batch processed to produce reference and data symbols, which symbols are input to a residual filter to generate iteratively over the batch an error value. The error value is convolved with the equalizer filter value to produce a new equalizer filter value for use by the equalizer filter when a next batch of data points is processed.

Two stage adaptive equalizer for a batch receiver

A system and method is provided enabling identification of different PN offsets values for CDMA signals without access to a GPS signal, such as when making measurements within indoor environments. When a timing reference, such as that provided by a GPS signal, is lost, the frame boundary timestamp of the CDMA signal itself is used. The parameters of the strongest available PN offset are used. The timing error is determined and the new timing reference timestamp is estimated. The strongest PN is used as the time reference and tau is corrected for. In further embodiments, a user may be able to provide identifying information allowing the estimated timing reference timestamp to be determined even when a GPS signal was never established for providing an initial timing reference.

System and method for using CDMA PN offset to maintain instrument timing reference

A time history display of orthogonal code power levels by spreading factor is generated by displaying each data record of code domain power as a line, with each point in the line representing a different code index and the color or brightness of each data point representing the associated base code power level. With the data records displayed as contiguous lines, as each new data record is acquired it is added as a new line of the display while the line representing the oldest data record is deleted from the display. For communications standards where the code spreading factor varies, both bit-reversed and Walsh code graphs are displayed to show the grouping of the sub-codes that make up a base code. In this way the time history display indicates timing and trend information to a user.

Time history display of orthogonal code power levels

A display of code power levels and relationships of multiple spreading factor orthogonal codes in a code division multiple access (CDMA) signal has a first code graph of code domain power (CDP) for all the codes at the largest code spreading factor that includes all codes at all spreading factors plotted in a linear code indexing order and a second graph of CDP where the codes are plotted in bit-reversed order to group together the sub-codes of each code of lower spreading factor. Markers on each graph are tied together such that movement of one marker on one graph to a particular code value causes the other marker on the other graph to move to the corresponding code value. The sub-codes related to a particular code bar in the graphs indicated by the markers may be differentiated by using grey scale or color variations. A base code power level indicator, which may be in the form of a horizontal bar on the bit-reversed order graph spanning the group of sub-codes corresponding to a particular spreading factor, provides a power indication for the base code.

Display of code power levels and relationships of multiple spreading factor orthogonal codes in a CDMA signal

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

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

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

An adaptive equalizer for use in a digital transmission receiver includes Q-channel regeneration. A equalization filter produces complex valued equalized signal samples representative of a digital transmission signal. A slicer produces ideal real component values of the equalized signal samples. A Q-regeneration filter produces ideal imaginary component values of the equalized signal samples from the ideal real component values. The ideal real and imaginary component values are combined with the component values of the equalized signal samples to produce a complex valued error signal. The error signal is fed back to scale update values for updating coefficient values of the equalization filter. Delays in the equalizer provide storage to synchronize various equalizer signal and component values with the Q-regeneration filter output.

Adaptive equalizer with complex signal regeneration and method of operation

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.

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Portland, OR, United States of America

Thomas L Kuntz