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Simon, M. K.

Publications and source records attributed to Simon, M. K..

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Effects of data asymmetry on Shuttle Ku-band communications link performance

This paper systematically analyzes the signal-to-noise ratio degradations which can potentially occur due to data asymmetry in digital transmission systems. Suitable asymmetry models are developed and error probability performance for various types of data detectors (integrate-and-dump filter, filter-sample detector, and gated-integrate-and-dump filter) is derived. Although this work was done to resolve problems being encountered in the Shuttle Ku-band return link design, specifically for the 50 Mbit/s convolutionally encoded channel (NRZ format), generalizations are made which provide results for other cases of interest (other Ku-band return link channels, or other systems entirely). This paper therefore considers Manchester data formats (in addition to NRZ) and uncoded transmission (in addition to convolutionally coded transmission). The effects of bandlimiting are also considered.

Simon, M. K.↗
NASA NTRS1978

Error probability performance of unbalanced QPSK receivers

A simple technique for calculating the error probability performance and associated noisy reference loss of practical unbalanced QPSK receivers is presented. The approach is based on expanding the error probability conditioned on the loop phase error in a power series in the loop phase error and then, keeping only the first few terms of this series, averaging this conditional error probability over the probability density function of the loop phase error. Doing so results in an expression for the average error probability which is in the form of a leading term representing the ideal (perfect synchronization references) performance plus a term proportional to the mean-squared crosstalk. Thus, the additional error probability due to noisy synchronization references occurs as an additive term proportional to the mean-squared phase jitter directly associated with the receiver's tracking loop. Similar arguments are advanced to give closed-form results for the noisy reference loss itself.

Simon, M. K.↗
NASA NTRS1978

Tracking performance of unbalanced QPSK demodulators. I - Biphase Costas loop with passive arm filters

Unbalanced quadriphase-shift-keying (QPSK) is an attractive means for transmitting two digital data streams which in general have different average powers, data rates, and data formats. Previous analyses of the tracking performance of Costas loop demodulators of unbalanced QPSK have accounted only for the filtering effect produced by the loop's two arm filters on the equivalent additive noise perturbing the loop. When the bandwidth of these filters is selected on the basis of the order of the data rate, as is typical of optimum Costas loop design, the filtering degradations of the data modulations themselves and the cross-modulation noise produced by their multiplication in the loop often cannot be neglected. The purpose of this paper is to incorporate these additional filtering effects into the analysis. Many of the results obtained herein are in the form of closed-form expressions which can easily be evaluated numerically for design and performance prediction purposes.

Simon, M. K.↗
NASA NTRS1978

Tracking performance of unbalanced QPSK demodulators. II - Biphase Costas loop with active arm filters

In a Costas loop study for biphase modulation conducted by Simon and Lindsey (1977), it was demonstrated that considerable improvement in tracking performance could be obtained by employing active arm filters of the integrate-and-dump type as opposed to passive arm filters. An investigation is conducted concerning the possibility to obtain a similar performance improvement for an unbalanced quadriphase-shift-keying (QPSK) modulation. It is found that the biphase Costas loop can be used as an efficient demodulator of QPSK in cases in which the ratio of data rates is of the same order of magnitude as the inverse of the power ratio. These cases involve approximately equal signal energies in the two channels.

Simon, M. K.↗
NASA NTRS1978

Optimum receiver structures for phase-multiplexed modulations

A MAP (maximum a posteriori) estimation loop is derived for a QPSK signal and, by suitable approximation to the nonlinearity which arises as a consequence of the MAP theory, is reconfigured with practical realizations that are valid for high and low SNRs. In particular, it is shown that by approximating the hyperbolic tangent nonlinearity in the MAP estimation loop by the first two terms in its power series, an interesting practical realization of this loop results which applies at low SNRs. The error signal in this loop is formed by multiplying the error signal and lock detector output signal of a conventional biphase Costas loop. A generalized linear in-phase channel configuration is proposed which allows carrier reconstruction from an unbalanced QPSK signal at all ratios of data rates and powers in the two channels, even in the limit as these ratios simultaneously approach unity, i.e., balanced quadriphase.

Simon, M. K.↗
NASA NTRS1978

Tracking performance of Costas loops with hard-limited in-phase channel

The paper examines the tracking performance of the Costas loop used in a suppressed carrier receiver with a hard limiter of the in-phase channel arm filter output. Attention is given to assessing the penalty, if indeed it is a penalty rather than an improvement, in this performance relative to a conventional Costas loop without the hard limiter and with an analog third multiplier. In particular, for the case of single-pole Butterworth (RC) arm filters and NRZ data, the squaring loss (tracking jitter penalty relative to a linear loop) is evaluated and illustrated as a function of the ratio of arm filter bandwidth to data rate and data SNR. Also considered is the tracking performance of a hard-limited modified Costas loop wherein the quadrature arm is removed. Corresponding results for the modified Costas loop without the hard limiter are given.

Simon, M. K.↗
NASA NTRS1978

Integrated source and channel encoded digital communication system design study

The particular Ku-band carrier, PN despreading, and symbol synchronization strategies, which were selected for implementation in the Ku-band transponder aboard the orbiter, were assessed and evaluated from a systems performance viewpoint, verifying that system specifications were met. A study was performed of the design and implementation of tracking techniques which are suitable for incorporation into the Orbiter Ku-band communication system. Emphasis was placed on maximizing tracking accuracy and communication system flexibility while minimizing cost, weight, and system complexity of Orbiter and ground systems hardware. The payload communication study assessed the design and performance of the forward link and return link bent-pipe relay modes for attached and detached payloads. As part of this study, a design for a forward link bent-pipe was proposed which employs a residual carrier but which is tracked by the existing Costas loop.

Alem, W. K.↗
NASA NTRS1978

The false lock performance of Costas loops with hard-limited in-phase channel

The ability of a Costas loop to false lock on a data sideband is a problem which must be dealt with in the design of suppressed-carrier receivers which employ such loops for carrier reconstruction. For conventional Costas loops wherein the error signal is formed from the product of two analog signals, the false lock problem has recently been investigated by the author and others and is now well understood. For implementation reasons associated with the reduction of dc offsets, it is often desirable to hard-limit the output of the in-phase channel and replace the analog multiplier which forms the above product with a chopper-type device. The false lock behavior of such a Costas loop with hard-limited in-phase channel is quite different from that of the conventional Costas loop and is the subject of investigation in this paper. Results are also presented for a modified version of the Costas loop wherein the quadrature arm filter is removed.

Simon, M. K.↗
NASA NTRS1978

On the calculation of squaring loss in Costas loops with arbitrary arm filters

Specific numerical results for the squaring loss in Costas loop tracking are discussed for cases when the input data were biphase-L, and the Costas loop arm filters were of the n-pole Butterworth type. It is pointed out that a simple scientific calculator may be used for the computations, provided the transfer function of the arm filter has simple poles. The technique can also be used to compute the squaring loss in other modulation forms, such as unbalanced quadriphase-shift-keying (QPSK).

Simon, M. K.↗
NASA NTRS1978

Phase-locked loops and their application

A collection of papers is presented on the characteristics and capabilities of phase-locked loops (PLLs), along with some applications of interest. The discussion covers basic theory (linear and nonlinear); acquisition; threshold; stability; frequency demodulation and detection; tracking; cycle slipping and loss of lock; phase-locked oscillators; operation and performance in the presence of noise; AGC, AFC, and APC circuits and systems; digital PLL; and applications and miscellaneous. With the rapid development of IC technology, PLLs are expected to be used widely in consumer electronics.

Lindsey, W. C.↗
NASA NTRS1977

Study to investigate and evaluate means of optimizing the Ku-band combined radar/communication functions for the space shuttle

The Ku band radar system on the shuttle orbiter operates in both a search and a tracking mode, and its transmitter and antennas share time with the communication mode in the integrated system. The power allocation properties and the Costa subloop subcarrier tracking performance associated with the baseline digital phase shift implementation of the three channel orbiter Ku band modulator are discussed.

Weber, C. L.↗
NASA NTRS1977

Optimum design and performance of Costas receivers containing soft bandpass limiters

This paper investigates several key questions concerning the mechanization and design of a Costas receiver for reconstruction of a carrier from a suppressed carrier signal. For baseband NRZ encoded data symbols and a soft bandpass limiter preceding the loop, several design issues which are considered herein and which affect acquisition and tracking performance are: (1) The choice of an IF bandwidth. (2) The optimum choice of the Costas arm filter bandwidths as well as the spectral roll-off characteristics. (3) The optimum choice of loop bandwidth to data rate ratio for a given signal-to-noise ratio. (4) The signal suppression factor and the combined limiter-squaring loss. (5) The variations in loop bandwidth and damping with signal level. (6) The choice of the limiter transfer characteristic. (7) Performance degradation due to the presence of a limiter. Various new results in system design are presented and typical numerical results are given and graphically demonstrated in SNR regions of practical interest. The theory is applicable to the design of carrier reconstruction loops required in the implementation of spread spectrum communication receivers.

Lindsey, W. C.↗
NASA NTRS1977

Tracking performance of symbol synchronizers for Manchester coded data

The implementation and tracking performance of symbol synchronizers for Manchester coded data is presented with motivation provided by maximum a posteriori (MAP) estimation theory. Certain physically relizable closed-loop structures, readily implemented in practice, are suggested by the theory for uncoded data symbols with arbitrary data transition probabilities. The tracking performance of these loops is optimized and comparisons are made among the various configurations over a wide range of system parameters. Although not the major intent of the paper, the acquisition problem is briefly addressed.

Simon, M. K.↗
NASA NTRS1977

Noncoherent pseudonoise code tracking performance of spread spectrum receivers

The optimum design and performance of two noncoherent PN tracking loop configurations, namely, the delay-locked loop and tau-dither loop, are described. In particular, the bandlimiting effects of the bandpass arm filters are considered by demonstrating that for a fixed data rate and data signal-to-noise ratio, there exists an optimum filter bandwidth in the sense of minimizing the loop's tracking jitter. Both the linear and nonlinear loop analyses are presented, and the region of validity of the former relative to the latter is indicated. In addition, numerical results are given for several filter types. For example, assuming ideal bandpass arm filters, it is shown that the tau-dither loop requires approximately 1 dB more signal-to-noise ratio than the delay-locked loop for equal rms tracking jitters.

Simon, M. K.↗
NASA NTRS1977

Optimum performance of suppressed carrier receivers with Costas loop tracking

The performance of suppressed carrier receivers with Costas loop tracking is optimized by proper choice of loop arm filter bandwidth. In particular, it is shown that for a variety of passive arm filter types, there exists, for a given data rate and data signal-to-noise ratio, an optimum filter bandwidth in the sense of minimizing the loop's squaring loss. For the linear theory case, this is equivalent to minimizing the loop's tracking jitter. When symbol synchronization is known, it is shown that by replacing the passive arm filters with active filters, i.e., integrate-and-dump circuits, one can achieve an improvement in carrier-to-noise ratio of as much as 4 to 6 dB depending on the passive arm filter type used for comparison and the value of data signal-to-noise ratio.

Simon, M. K.↗
NASA NTRS1977

On the false lock behavior of polarity-type Costas loops with Manchester coded input

A modification of a Costas loop is described, and the false lock behavior of this system is studied. The modified Costas loop hard limits the output of the in-phase channel, replaces the analog multiplier with a chopper-type device, and is equipped with single-pole arm filters in the loop. The false lock behavior associated with the use of Manchester coded data is investigated; the results can be applied to the assessment of the false lock margin on the Ku-band uplink to the Space Shuttle Orbiter through the TURSS.

Simon, M. K.↗