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Results for “Pulse-position modulation”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
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NASA NTRS1988

Modulation techniques for deep-space pulse-position modulation (PPM) optical communication

The extremely energy-efficient pulse-position modulation (PPM) format is being actively developed as a basis for optical communications with deep-space probes. Attention is presently given to different modulation schemes for the efficient production of laser pulses over a broad range of repetition rates. Both Q-switching and cavity dumping modulation methods are available for the envisioned diode-pumped Nd:YAG laser source. Numerical calculation results are presented for cavity-dumping.

Rayman, Marc D.↗
NASA NTRS1987

Error control coding for satellite and space communications

The optical direct detection channel is discussed. It is shown how simple trellis coded modulation can be used to improve performance or increase throughput (in bits per second) without a bandwidth expansion and no performance loss. In fact, a modest performance gain can be achieved. The concentration is on signals derived from the pulse-position modulation format by allowing overlap.

Georghiades, Costas N.↗
NASA NTRS1972

The effect of timing errors in optical digital systems.

The use of digital transmission with narrow light pulses appears attractive for data communications, but carries with it a stringent requirement on system bit timing. The effects of imperfect timing in direct-detection (noncoherent) optical binary systems are investigated using both pulse-position modulation and on-off keying for bit transmission. Particular emphasis is placed on specification of timing accuracy and an examination of system degradation when this accuracy is not attained. Bit error probabilities are shown as a function of timing errors from which average error probabilities can be computed for specific synchronization methods. Of significance is the presence of a residual or irreducible error probability in both systems, due entirely to the timing system, which cannot be overcome by the data channel.

Gagliardi, R. M.↗
NASA NTRS1980

Optical-communication systems for deep-space applications

The feasibility of using optical communication systems for data telemetry from deep space vehicles to Earth based receivers is evaluated. Performance analysis shows that practical, photon counting optical systems can transmit data reliably at 30 to 40 dB high rates than existing RF systems, or can be used to extend the communication range by 15 to 20 dB. The advantages of pulse-position modulation (PPM) formats are discussed, and photon counting receiver structures designed for PPM decoding are described. The effects of background interference and weather on receiver performance are evaluated. Some consideration is given to tracking and beam pointing operations, since system performance ultimately depends on the accuracy to which these operations can be carried out. An example of a tracking and pointing system utilizing an optical uplink beacon is presented, and it is shown that microradian beam pointing is within the capabilities of state-of-the-art technology. Recommendations for future theoretical studies and component development programs are presented.

Vilnrotter, V. A.↗
NASA NTRS1981

Practical codes for photon communication

It is shown that even assuming a noiseless model for photon communication for which capacity (measured in nats/photon) is infinite, it is unlikely that a signaling efficiency of even 10 nats/photon could be achieved in practice. Pulse-position modulation plus Reed-Solomon coding is shown to yield practical results in the range of 2 to 3 nats/photon. In addition, a channel model appropriate for the study of noiseless photon communication, referred to as a photon channel, is presented. The use of q-ary pulse position modulation (q-PPM) on the photon channel is investigated. It is shown that q-PPM channel capacity is log q nats/photon, and performance curves (error probability versus signaling efficiency) are given for coded and uncoded q-PPM.

Mceliece, R. J.↗
NASA NTRS1981

Capacity, cutoff rate, and coding for a direct-detection optical channel

It is shown that when Pierce's pulse-position modulation scheme with 2 to the L power positions (where L is some positive integer) is used on a self-noise-limited direct-detection optical communication channel, there results a (2 to the L power)-ary erasure channel that is equivalent to the parallel combination of L completely correlated binary erasure channels. The capacity of the full channel is the sum of the capacities of the component channels, but the cutoff rate of the full channel is shown to be much smaller than the sum of the cutoff rates. An interpretation of the cutoff rate is given that suggests a complexity advantage in coding separately on the component channels. It is shown that if short-constraint length convolutional codes with Viterbi decoders are used on the component channels, then the performance and complexity compare favorably with the Reed-Solomon coding system proposed by McEliece (1979) for the full channel. The reasons for this unexpectedly fine performance by the convolutional code system are explored in detail, as are various facets of the channel structure.

Massey, J. L.↗
NASA NTRS1984

Efficient Coding for Optical Communication

Possibility of using photon counting, rather than conventional linear amplification, for optical communications discussed. Study suggests combination of pulse-position modulation and Reed-Solomon coding gives signaling efficiency of 3 to 4 bits/photon.

Mceliece, R. J.↗
NASA NTRS1985

Direct-Photon-Detection Communications

Optical communications system based on direct detection of photons rather than heterodyning of carrier with local oscillator. Direct-detection system uses single laser source, pulse-position modulation, and Reed-Solomon coding to protect against burst errors. Conventional photomultiplier tube is receiver. Technology applicable to terrestrial communications.

Lesh, J. R.↗
NASA NTRS1986

A synchronization technique for optical PPM signals

A technique for maintaining synchronization between optical PPM (pulse-position modulation) pulses and a receiver clock by means of a delay-tracking loop is described and analyzed. The tracking loop is driven by a doubly stochastic Poisson process that contains information about the location of the desired slot boundaries. The slot boundaries are subject to slowly varying random delays that are ultimately tracked by the loop. The concept of fractional rms delay error is introduced to quantify the effects of signal and background induced shot noise on the performance of the delay-tracking loop.

Vilnrotter, V. A.↗
NASA NTRS1987

Phase error statistics of a phase-locked loop synchronized direct detection optical PPM communication system

Receiver timing synchronization of an optical Pulse-Position Modulation (PPM) communication system can be achieved using a phased-locked loop (PLL), provided the photodetector output is suitably processed. The magnitude of the PLL phase error is a good indicator of the timing error at the receiver decoder. The statistics of the phase error are investigated while varying several key system parameters such as PPM order, signal and background strengths, and PPL bandwidth. A practical optical communication system utilizing a laser diode transmitter and an avalanche photodiode in the receiver is described, and the sampled phase error data are presented. A linear regression analysis is applied to the data to obtain estimates of the relational constants involving the phase error variance and incident signal power.

Natarajan, Suresh↗
NASA NTRS1986

A synchronization technique for optical PPM signals

A technique for maintaining synchronization between optical PPM (pulse-position modulation) pulses and a receiver clock by means of a delay-tracking loop is described and analyzed. The tracking loop is driven by a doubly stochastic Poisson process that contains information about the location of the desired slot boundaries. The slot boundaries are subject to slowly varying random delays that are ultimately tracked by the loop. The concept of fractional rms delay error is introduced to quantify the effects of signal and background induced shot noise on the performance of the delay-tracking loop.

Vilnrotter, V. A.↗
NASA NTRS1988

Synchronization Scheme For PPM Communication

Synchronization achieved under difficult, low-signal conditions. Synchronization scheme for pulse-position modulation (PPM) matches pulse, word, and frame timeslots of receiver to received signals to ensure proper identification of received pulses. Involves brief sequence of synchronizing pulses within each transmitted frame and relies on periodic repetition of synchronizing pulses for verification. Use of verification reduces number of synchronizing pulses required but increases time required to achieve synchronization.

Marshall, William K.↗
NASA NTRS1988

Optical communications for future deep-space missions

The development of key technologies for an optical communications system for deep-space probes is discussed. Aspects of the technology include the pulse-position modulation technique for data transmission, a solid-state laser with a Nd:YAG crystal end, nondiffraction-limited receivers, and the application of avalanche photodiodes to improve photon detection. Mission benefits and flight opportunities and applications are discussed. Experiments to test optical communication systems are being planned for the Space Shuttle and the Mars Rover Sample Return misson. Future missions which will probably use the system include Cassini and the Mariner Mark II.

Rayman, Marc D.↗
NASA NTRS1988

Calculations of laser cavity dumping for optical communications

For deep-space pulse-position modulation (PPM) optical communication links using Nd:YAG lasers, two types of laser transmitter modulation techniques are available for efficiently producing laser pulses over a broad range of repetition rates: Q-switching and cavity dumping. The desired modulation scheme is dependent on the required pulse repetition frequency and link parameters. These two techniques are discussed, theoretical and numerical calculations of the internal energy of the laser cavity in cavity dumping are described, and an example of cavity dumping is applied to a link for a proposed experiment package on Cassini.

Robinson, D. L.↗
NASA NTRS1988

Gaussian approximation versus nearly exact performance analysis of optical communication systems with PPM signaling and APD receivers

A 25-Mb/s direct-detection optical communication system that used Q = 4 PPM (pulse-position modulation) signaling was constructed and its performance measured under laboratory conditions. The system used a single-mode AlGaAs laser diode (lambda = 834 nm) and low-noise silicon avalanche photodiode (APD). A procedure for numerically computing system performance is given that uses the nearly exact Webb approximation of the true Conradi distribution for the APD output and does not require excessive amounts of computer time. Comparison revealed that modeling the APD ouptut as a Gaussian process under conditions of negligible background radiation and low (less than 10 to the -12 A) APD bulk leakage currents leads to substantial underestimates of optimal APD gain and overestimates of system bit error probability. Examples illustrate the breakdown of the Gaussian approximation in assessing system performance. The measured performance was in excellent agreement with that predicted by the computational procedure. The system achieved a bit error probability of 10 to the -6 at a received signal energy, corresponding to an average of 60 absorbed photons/bit and optimal APD gain of 700.

Davidson, Frederic M.↗