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At least 73 records · Page 4

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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

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 NTRS1984

Demodulator for AM and SSB-SC Signals

Compatible linear demodulator (CLD) detects either amplitude modulation (AM) or single-sideband suppressed-carrier (SSB-SC) modulation. Carrier recovery homodyne product detector designed for voice communication but easily scaled to other frequencies.

Hearn, C. P.↗

NASA NTRS1982

Telemetry system

The means of telemetering digital data from a spacecraft to the Deep Space Network is addressed. Phase shift keying and uncoded quadriphase shift keying modulations are discussed along with demodulation and decoding systems. Telemetry system losses and noisy reference performance for suppressed carrier receivers are also examined.

Yuen, J. H.↗

NASA NTRS1983

Two-way satellite time transfer using low power CW tones

In the search for an economical means of precise time transfer, the NRC Time Laboratory decided to adapt the techniques used by radio astronomers in an experiment to compare the phases of the local oscillators at widely separated VLBI stations. The objective is to design a system which would use commercial satellites, and which would be of reasonable cost for the ground stations and for operations. Two satellite ground stations were installed at NRC about 100 m from the Time Laboratory. For the preliminary experiment, a channel on the Anik Al 6/4 GHz satellite was made available by TELESAT Canada. Two tones were transmitted + or - MHz from the suppressed carrier. The difference frequency of 32 MHz was recorded using narrow band receivers. A low level 1 MHz phase modulation was added to identify the 32 MHz cycle, giving 1 microsec ambiguity in the time transfer. With less than 1/4 W in each tone, the EIRP is 43 dB below that of a normal TV Earth station, and no frequency dispersion is required. The measurements taken each second for the 32 MHz have an rms scatter of 1 ns.

Costain, C. C.↗

NASA NTRS1985

Discriminator Aids Phase-Lock Acquisition

Voltage-controlled oscillator in suppressed-carrier detector acquire carrier frequency and phase quickly with help of frequency-discriminator arrangement. To obtain discriminator function, filter bandwidth in quadrature (Q) leg of detector is widened with respect to bandwidth of filter in inphase (l) leg.

Carson, L. M.↗

NASA NTRS1984

Effects of NRZ-M Modulation on Convolutional Codes Performance

Non-return-to-zero mark (NRZ-M) modulation is often used to resolve data sense in suppressed carrier telemetry systems because such systems are subject to half cycle slips that result in complementing the encoded data stream. The performance of coded telemetry systems with NRZ-M is sensitive to the order in which the various operations are done. A system that demodulates the NRZ-M waveform and then decodes performs differently from a system that does the decoding first. The performance of the NASA standard (7, 1/2) convolutional codes is determined for several systems using NRZ-M. Several different demodulation schemes for NRZ-M are considered. It is shown that, even for the best soft-decision method examined, there is a 2.7 dB loss at a decoded bit error rate of 0.005 if the NRZ-M demodulation occurs before rather than after Viterbi decoding.

Deutsch, L. J.↗

NASA NTRS1982

Galileo probe relay receiver

For the Jovian mission, the data link from the Galileo probe to the orbiter uses suppressed-carrier Manchester encoded BPSK modulation and is protected with R = 1/2, K = 7 convolutional coding. The receiver closes the link by acquiring, tracking, and demodulating the data. It has to operate in a highly stressed environment with severe frequency offset, frequency rate, wind gust, and antenna spin conditions. Salient features are described and breadboard test data presented.

Prouty, D. A.↗

NASA NTRS1982

Communication satellite ground station receiver performance at low data rates

Performance of satellite ground station receivers at low data rates is analyzed for power-limited satellites, when various amounts of frequency dynamics are present. Specifically, the lowest data rates for which the receiver can successfully demodulate suppressed-carrier BPSK data under a wide variety of conditions are determined. Minimum data rates on the order of 100 to 1400 bits per second are achievable with a bit error probability less than 0.00001 and with a mean time to cycle slip on the order of 1/2 hour or more, when Costas loops are employed for carrier extraction.

Riddle, L. P.↗

NASA NTRS1988

The behavior of a Costas loop in the presence of space telemetry signals

The telemetry modulation index, telemetry bit rate, subcarrier waveform, and subcarrier frequency are shown to be the key system parameters that contribute to the performance degradation of a Costas loop in the presence of space telemetry signals. The effects of the Doppler in the loop are also investigated. The results of this study were input to the Consultative Committee for Space Data Systems (CCSDS) for consideration in the future standard suppressed-carrier space telemetry system.

Nguyen, T. M.↗

NASA NTRS1991

Microwave Oscillator Would Have Reduced Phase Noise

Microwave oscillators of proposed new type incorporate suppressed-carrier/negative-feedback feature to reduce phase noise near their carrier frequencies. Concept results in phase noise less than achievable by cryogenically stabilized microwave components or by room-temperature oscillators stabilized by quartz crystals. Implemented in three different versions.

Dick, G. John↗

NASA NTRS1991

Analysis Of Lock Detection In Costas Loops

Report presents analysis of detection of phase lock in Costas loops, used in coherent binary-phase-shift-keying communication systems to track both subcarrier and suppressed carrier signals. Detection of phase lock important part of operation and monitoring of operation of Costas or other tracking loop, provides insight into behavior of loop in real time. Focuses on effects of phase jitter and correlation between samples of phase error in all-digital Costas loop, in which lock detection implemented via algorithm. Applicable to both sinusoidal and square-law carrier signals, incorporates new mathematical models of square-law and absolute-value detectors.

Mileant, Alexander↗

NASA NTRS1992

Effect Of Phase Unbalance In Product Modulator

Paper presents theoretical study of effect of phase unbalance in product modulator of phase-modulation transmitter in deep-space telemetry system upon performance of system. Mathematical model of product modulator used to derive equations for relative strengths of desired suppressed-carrier component and undesired residual-carrier component of transmitted signal. Also addresses effects of unsuppressed-carrier component on carrier-tracking phase-locked loop and bit detector in receiver.

Nguyen, Tien M.↗

NASA NTRS1993

The MRIS feasibility study

The Microwave Reflectometer Ionization Sensor (MRIS) is an instrument being developed for use in detecting and ranging of electron density layers in the reentry plasma of a space transfer vehicle. The rationale for the selection of the Double Sideband Suppressed Carrier (DSBSC) system used in the feasibility study for the MRIS is presented. A 25 GHz single-oscillator system and a 220 GHz double-oscillator system are described. The 25 GHz system was constructed and tested in the laboratory and test results are presented. As developed, the system employs a sideband spacing of 160 MHz. Based on an estimated electromagnetic wave velocity in the plasma, a round-trip phase shift measurement accuracy of +/- 7.6 degrees was required for the desired +/- 1/2 cm distance measurement accuracy. The interaction of parallel ground and reflecting planes produces interference that prevents the basic DSBSC system from meeting the accuracy goal so a frequency modulation was added to the system to allow averaging of the measured phase deviation. With an FM deviation of +/- 1 GHz, laboratory measurements were made for distances from 5 to 61 cm tip free space. Accounting for the plasma velocity factor, 82 percent of the data were equal to or better than the desired accuracy. Based on this measured result a sideband spacing to 250 MHz could be expected to yield data approximately 96 percent within the accuracy goal.

Neece, Robert T.↗

NASA NTRS1994

A complex symbol signal-to-noise ratio estimator and its performance

This article presents an algorithm for estimating the signal-to-noise ratio (SNR) of signals that contain data on a downconverted suppressed carrier or the first harmonic of a square-wave subcarrier. This algorithm can be used to determine the performance of the full-spectrum combiner for the Galileo S-band (2.2- to 2.3-GHz) mission by measuring the input and output symbol SNR. A performance analysis of the algorithm shows that the estimator can estimate the complex symbol SNR using 10,000 symbols at a true symbol SNR of -5 dB with a mean of -4.9985 dB and a standard deviation of 0.2454 dB, and these analytical results are checked by simulations of 100 runs with a mean of -5.06 dB and a standard deviation of 0.2506 dB.

Feria, Y.↗

NASA NTRS1994

The Block V Receiver fast acquisition algorithm for the Galileo S-band mission

A fast acquisition algorithm for the Galileo suppressed carrier, subcarrier, and data symbol signals under low data rate, signal-to-noise ratio (SNR) and high carrier phase-noise conditions has been developed. The algorithm employs a two-arm fast Fourier transform (FFT) method utilizing both the in-phase and quadrature-phase channels of the carrier. The use of both channels results in an improved SNR in the FFT acquisition, enabling the use of a shorter FFT period over which the carrier instability is expected to be less significant. The use of a two-arm FFT also enables subcarrier and symbol acquisition before carrier acquisition. With the subcarrier and symbol loops locked first, the carrier can be acquired from an even shorter FFT period. Two-arm tracking loops are employed to lock the subcarrier and symbol loops parameter modification to achieve the final (high) loop SNR in the shortest time possible. The fast acquisition algorithm is implemented in the Block V Receiver (BVR). This article describes the complete algorithm design, the extensive computer simulation work done for verification of the design and the analysis, implementation issues in the BVR, and the acquisition times of the algorithm. In the expected case of the Galileo spacecraft at Jupiter orbit insertion PD/No equals 14.6 dB-Hz, R(sym) equals 16 symbols per sec, and the predicted acquisition time of the algorithm (to attain a 0.2-dB degradation from each loop to the output symbol SNR) is 38 sec.

Aung, M.↗

NASA NTRS1994

Tracking the Galileo spacecraft with the DSCC Galileo Telemetry prototype

On day of the year 062, 1994, a prototype of the Deep Space Communications Complex Galileo Telemetry subsystem successfully tracked and processed signals from the Galileo spacecraft, under fully suppressed-carrier modulation. The demonstration took place at Goldstone, employing the 70-m antenna and the 34-m high-efficiency antenna. This article presents the findings from that demonstration. Specific issues are the system performance in terms of signal-to-noise (SNR) degradation and the arraying gain. Validation of the test results is via symbol-error-rate measurement and the standard symbol SNR. The analysis is also extended to include characterization of the signal received from Galileo.

Pham, T. T.↗

NASA NTRS1996

Automated Operations for Galileo Communications

Following the deployment failure of Galileo's high gain antenna, the downlink had to be redesigned so as to effectively use the low gain antenna. The downlink was redesigned to maximize the data return and increase the reliability which required the reconfiguration of the onboard software and the deep space network. The revised downlink features: data compression; antenna arraying; the recoding and reprocessing of telemetry; suppressed carrier tracking, and error-correction coding. The deep space network Galileo telemetry (DGT) subsystem was developed and deployed at three sites in Australia, Spain and the U.S. The DGT was designed as an automated system that continuously monitors and adjusts its parameters and environment in response to either pre-loaded sequences or changes in the internal status.

Statman, Joseph I.↗