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Schilling, D. L.

Publications and source records attributed to Schilling, D. L..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Delta modulation

The overshoot suppression algorithm has been more extensively studied. Computer generated test-pictures show a radical improvement due to the overshoot suppression algorithm. Considering the delta modulator link as a nonlinear digital filter, a formula that relates the minimum rise time that can be handled for given filter parameters and voltage swings has been developed. The settling time has been calculated for the case of overshoot suppression as well as when no suppression is employed. The results indicate a significant decrease in settling time when overshoot suppression is used. An algorithm for correcting channel errors has been developed. It is shown that pulse stuffing PCM words in the DM bit stream results in a significant reduction in error length.

Schilling, D. L.↗
NASA NTRS1973

Optimal space communications techniques

The design, development, and analysis are reported of a digital phase-locked loop (DPLL) for FM demodulation and threshold extension. One of the features of the developed DPLL is its synchronous, real time operation. The sampling frequency is constant and all the required arithmetic and logic operations are performed within one sampling period, generating an output sequence which is converted to analog form and filtered. An equation relating the sampling frequency to the carrier frequency must be satisfied to guarantee proper DPLL operation. The synchronous operation enables a time-shared operation of one DPLL to demodulate several FM signals simultaneously. In order to obtain information about the DPLL performance at low input signal-to-noise ratios, a model of an input noise spike was introduced, and the DPLL equation was solved using a digital computer. The spike model was successful in finding a second order DPLL which yielded a five db threshold extension beyond that of a first order DPLL.

Schilling, D. L.↗
NASA NTRS1973

Overshoot suppression in Adaptive Delta Modulator links for video transmission

An overshoot suppression scheme to improve the performance of the Digital Song Adaptive Delta Modulator for picture transmission is described. The overshoot suppression algorithm has been verified using computer simulation on a PDP-8. It is also shown that the additional hardware required for the actual implementation of the algorithm is simpler than those encountered in the literature, and gives better signal tracking accuracy.

Weiss, L.↗
NASA NTRS1972

Delta modulation

The results are presented of a study dealing with the problems of source encoding using delta modulation. An algorithm is described which was employed in the design of an adaptive delta modulation. The algorithm is extremely inexpensive to implement and features extremely desirable characteristics such as a 40 db dynamic range and a 90 percent non-redundant word intelligibility at a bit rate of 9.6 kb/s. A new concept is presented in delta modulation design, the nth-order delta modulator. The nth order delta modulator increases the maximum SNR of a delta modulator but not its dynamic range. It is shown that a 2nd order delta modulator, which employs two delta modulators in cascade, results in a 15 db output SNR improvement over a linear delta modulator operating at 27 db. Two additional areas of research are discussed. The first area involves decomposition of voice and the second is concerned with the source encoding of video signals.

Schilling, D. L.↗
NASA NTRS1972

Gaussian and click noise in an FM/FM multiplex receiver.

An FM/FM system is one in which the signal information frequency modulates a subcarrier, which, in turn, frequency modulates a main carrier for transmission. The detection process then involves two frequency demodulators in sequence. Using Rice's click model for both FM demodulators, we obtain the average click rate and an approximate output spectrum that include the effect of the impulses generated by the carrier demodulator on the subcarrier demodulation at and below threshold. We then focus on the threshold behavior of these systems and the proportioning of their modulation parameters so as to provide certain desired characteristics. We find that due to the filtering action of the second demodulator, the number of output clicks from carrier generated spikes can be orders of magnitude smaller, yet their contribution to the output noise can be much greater than that produced by the first demodulation.

Stochel, N. H.↗
NASA NTRS1972

Compression of transmission bandwidth requirements for a certain class of band-limited functions.

A study of source-encoding techniques that afford a reduction of data-transmission rates is made with particular emphasis on the compression of transmission bandwidth requirements of band-limited functions. The feasibility of bandwidth compression through analog signal rooting is investigated. It is found that the N-th roots of elements of a certain class of entire functions of exponential type possess contour integrals resembling Fourier transforms, the Cauchy principal values of which are compactly supported on an interval one N-th the size of that of the original function. Exploring this theoretical result, it is found that synthetic roots can be generated, which closely approximate the N-th roots of a certain class of band-limited signals and possess spectra that are essentially confined to a bandwidth one N-th that of the signal subjected to the rooting operation. A source-encoding algorithm based on this principle is developed that allows the compression of data-transmission requirements for a certain class of band-limited signals.

Smith, I. R.↗
NASA NTRS1972

Distortion in the frequency demodulator using feedback.

The response of a frequency demodulator using feedback (FMFB) to a frequency modulated signal is analyzed. Canonical equations of operation are obtained. Harmonic distortion is calculated for the case of a sinusoidal modulating signal. Intermodulation distortion is calculated assuming a noise-like modulation. Design curves are presented. The special case of harmonic and intermodulation distortion in a discriminator is also presented. It is shown that the results obtained in this paper by treating the discriminator as a degenerate FMFB compare favorably with those obtained by other authors. However, the results presented here do not require digital computation.

Hoffman, E.↗
NASA NTRS1972

An all digital phase locked loop for FM demodulation.

A phase-locked loop designed with all-digital circuitry which avoids certain problems, and a digital voltage controlled oscillator algorithm are described. The system operates synchronously and performs all required digital calculations within one sampling period, thereby performing as a real-time special-purpose computer. The SNR ratio is computed for frequency offsets and sinusoidal modulation, and experimental results verify the theoretical calculations.

Greco, J.↗
NASA NTRS1971

Delta modulation

The conclusions of the design research of the song adaptive delta modulator are presented for source encoding voice signals. The variation of output SNR vs input signal power/when 8, 9, and 10 bit internal arithmetic is employed. Voice intelligibility tapes to test the 10-bit system are used. An analysis of a delta modulator is also presented designed to minimize the in-band rms error. This is accomplished by frequency shaping the error signal in the modulator prior to hard limiting. The result is a significant increase in the output SNR measured after low pass filtering.

Schilling, D. L.↗
NASA NTRS1971

A variable-step-size robust delta modulator.

Description of an analytically obtained optimum adaptive delta modulator-demodulator configuration. The device utilizes two past samples to obtain a step size which minimizes the mean square error for a Markov-Gaussian source. The optimum system is compared, using computer simulations, with a linear delta modulator and an enhanced Abate delta modulator. In addition, the performance is compared to the rate distortion bound for a Markov source. It is shown that the optimum delta modulator is neither quantization nor slope-overload limited. The highly nonlinear equations obtained for the optimum transmitter and receiver are approximated by piecewise-linear equations in order to obtain system equations which can be transformed into hardware. The derivation of the experimental system is presented.

Song, C. L.↗
NASA NTRS1971

Delta Modulation

An optimum adaptive delta modulator-demodulator configuration is derived. This device utilizes two past samples to obtain a step size which minimizes the mean square error for a Markov Gaussian source. The optimum system is compared using computer simulations with the linear delta modulator and an enhanced Abate delta modulator. In addition the performance is compared to the rate distortion bound for a Markov source. It is shown that the optimum delta modulator is neither quantization nor slope-overload limited. The results show that the output signal-to-noise ratio is independent of the input signal power and is subject only to the limitations of the hardware employed. In addition, voice was recorded using these systems. The demodulated voice indicates negligible degradation is caused by the optimum system and by the enhanced Abate system while the linear delta modulator suffers significant degradation at a sampling frequency of 56 kilobits/sec.

Schilling, D. L.↗
NASA NTRS1971

Robust delta modulation.

A new Robust Delta Modulator configuration is presented. The system is optimum in the sense of minimizing the mean square error. Under certain conditions it is shown that the optimum system reduces to an enhanced Abate scheme. The optimum system, obtained by Song, uses the polarity of the past two samples and the signal estimates, to obtain the appropriate step size. Since the signal statistics are estimated by the system they are not needed a priori. The system has been constructed and tested. Experimental pictures and voice tapes are presented.

Song, C. L.↗
NASA NTRS1971

A design of an all digital FM discriminator.

This paper describes the design of an all digital FM discriminator. The system can be easily constructed using ordinary commercially available, digital IC's. In addition, the output SNR above threshold is computed. It is shown that the output noise consists of two terms: the first being the expected output gaussian noise having a parabolic power spectral density and the second being a quantization noise produced by the finite-level detection process used in the receiver.

Garodnick, J.↗