Showing papers on "Pulse-position modulation published in 1969"

M-ary Poisson Detection and Optical Communications

Abstract: This paper presents an investigation of the problem of maximum likelihood detection of one of M Poisson processes in a background of additive Poisson noise. When the observables correspond to counts of emitted photoelectrons, the problem models a discrete version of a coherent M -ary optical communication system using photon counters in the presence of background radiation. Consideration is given to an average distance and a detection probability criterion. The advantages of an M -ary pulsed intensity set (Poisson intensities wholly concentrated in a single counting interval) are demonstrated. The performance of such intensity sets is exhibited in terms of error probabilities, pulse widths, signal-tonoise ratio, and channel capacity. Behavior as a function of number M of intensities is also discussed. By appropriate conversion these results may be used for determining power requirements in an optical pulse position modulation system.

The Design of a Pulse-Position Modulated Optical Communication System

Abstract: In recent literature the advantages of an idealized narrow-width pulse-position modulated (PPM) optical communication system, using coherent sources and direct photodetection, have been shown. In this paper the practical design of such an operating PPM link is considered. System performance in terms of error probabilities and information rates is derived in terms of key parameters, such as power levels, number of PPM signals, pulse width, and bandwidths. Both background radiation and receiver thermal noise are included. Design procedures utilizing this data are outlined. Whenever possible, optimal design values and parameter tradeoffs, in terms of maximizing information rate or minimizing transmitter power, are shown. The effect on performance of photomultipliers and their inherent statistics is also presented. Although the basic analysis is derived in terms of photon "counts," the necessary system optics equations are introduced to allow for overall optical hardware design. The primary underlying assumption is that synchronization is maintained at all times between the transmitter and receiver.

FREQUENCY PULLING AND PULSE POSITION MODULATION OF PULSING cw GaAs INJECTION LASERS

Abstract: The frequency pulling and locking of intensity pulsations from continuously operating GaAs injection lasers have been studied by varying the frequency of the externally applied locking signal in the vicinity of the self‐induced pulse rate or one of its harmonics. The ability of the laser pulse rate to follow a rapidly varying locking signal has led to the first realization of optical pulse position modulation with microwave repetition rates. Modulation rates attainable with this effect are expected to be as high as one‐half the self‐induced pulse rate.

A PPM/PM Hybrid Modulation System

Abstract: The objective of a pulse-modulation (PM) system is to yield as high as possible an output signal-to-noise ratio (S/N)_{0} for a given channel signal-to-noise ratio (S/N)_{0} and bandwidth expansion factor β. In particular, one would like to design a modulation system in which the (S/N)_{0} approaches that of the Shannon bound (S/N)_{0} \leq [1 + (S/N)_{c}\beta^{-1}]^{\beta} . For a fixed system such as the pulse-position modulation (PPM), the relationship between (S/N)_{0} and (S/N)_{c} , must be linear above threshold. Thus to approach the β-power behavior of the Shannon bound, we must consider a family of PM systems. A class of systems is analyzed in which phase modulation of varying modulation indices is amplitude modulated by a PPM signal of fixed bandwidth. I t i s shown that when (S/N)_{c} , is large, the performance is proportional to the square of the modulation index which can be increased without changing the signal bandwidth. However, as the modulation index is increased, more sidelobes appear in the output of likelihood receiver which lead to large so-called anomolous errors. The effect of the sidelobes can be decreased significantly by redesigning the PPM signal since its autocorrelation function amplitude modulates the sidelobes. A new upper bound on the mean-squared error is derived which takes into account the effects of the noise at these sidelobe peaks. The bound depends functionally on the waveform which is used in the PPM modulator, and this raises the question as to which signal is the best one to use. An optimization problem is formulated using state-space techniques and solved numerically using a known algorithm. It is shown that it is possible to reduce the threshold significantly using optimally designed waveforms. The Barankin bounds are applied to the PPM/PM waveform to give lower bounds on the mean-squared error. It is therefore possible to bracket the actual performance region of the PPM/PM modulation system. The lower bounds lead to upper bounds on (S/N)_{0} and a sequence of bounds, each representing the best performance possible for a given modulation index, is obtained. The envelope of these bounds is then compared with the Shannon bound, and it is shown that although the PPM/PM modulation does not have performance closely approaching the Shannon bound, it does represent a substantial improvement over straight PPM.

Selection of Multichannel Digital Data Systems for Troposcatter Channels

Abstract: This paper presents an exposition of the role of power and bandwidth utilization considerations in the selection of communication techniques for troposcatter channels. The comparative power utilization efficiencies of a large number of techniques are considered both from the point of view of utilizing transmitter prime power and from the point of view of effectively using the actual received power. A data rate packing factor is defined to rate the bandwidth utilization efficiency of various carrier modulation, multiplexing, and information modulation techniques. An examination of the efficiencies of the various techniques leads to an optimum class of TDM modems.

A PPM/PM Hybrid Modulation System

Abstract: The objective of a pulse-modulation (PM) system is to yield as high as possible an output signal-to-noise ratio (S/N), for a given channel signal-to-noise ratio (S/N), and bandwidth expansion factor p. In particular, one would like to design a modu- lation system in which the (SIN), approaches that of the Shannon bound For a fixed system such as the pulse-position modulation (PPM), the relationship between and (SIN), must be linear above threshold. Thus to approach the p-power behavior of the Shannon bound, we must consider a family of PM systems. A class of sys- tems is analyzed in which phase modulation of varying modu- lation indices is amplitude modulated by a PPM signal of fixed bandwidth. It is shown that when (SIN), is large, the performance is proportional to the square of the modulation index which can be increased without changing the signal bandwidth. However, as the modulation index is increased, more sidelobes appear in the output of likelihood receiver which lead to large so-called anomolous errors. The effect of the sidelobes can be decreased significantly by redesigning the PPM signal since its autocorrelation function amplitude modulates the sidelobes. A new upper bound on the mean-squared error is derived which takes into account the effects of the noise at these sidelobe peaks. The bound depends func- tionally on the waveform which is used in the PPM modulator, and this raises the question as to which signal is the best one to use. An optimization problem is formulated using state-space tech- niques and solved numerically using a known algorithm. It is shown that it is possible to reduce the threshold significantly using opti- mally designed waveforms. The Barankin bounds are applied to the PPM/PM waveform to give lower bounds on the mean-squared error. It is therefore possible to bracket the actual performance region of the PPM/PM modulation system. The lower bounds lead to upper bounds on and a sequence of bounds, each representing the best performance possible for a given modulation index, is obtained. The envelope of these bounds is then compared with the Shannon bound, and it is shown that although the PPM/PM modulation does not have performance closely approaching the Shannon bound, it does represent a substantial improvement over straight PPM.

Photon detection for an optical pulse code modulation system (Corresp.)

Abstract: A mathematical model is formulated for an optical PCM system. Using the signal-to-noise ratio at the decision circuit as the performance criterion, the optimization of a nonlinear detector is carried out. Closed-form expressions for the jointly optimum electrical filtering and biasing, and for the maximum signal-to-noise ratio are obtained.

A Class of Signals for Analog Telemetry over a Coherent Channel

Abstract: This paper proposes and studies a class of signals which generalize frequency position modulation (FPM) and pulse position modulation (PPM). The generalization adds a degree of freedom analogous to a duty factor. Varying this quantity has an effect similar to that of varying the time-bandwidth occupancy in an FPM or PPM system, but it does not significantly increase the channel occupancy. The mean-square error is studied under large signal-to-noise ratio conditions and in the threshold region. We find that the additional degree of freedom allows us to trade between performance in these two ranges of signal-to-noise ratio. The nature of the signals, and their error behavior make them well suited to adaptive telemetry over a coherent channel. Small degrees of channel incoherence are considered and shown to produce only a small degradation in performance.

An Experimental Pulse Code Modulation Encoder for 24 Speech Channels

Abstract: An encoder is described which features nonuniform qnantizing by combining the processes of encoding and compression. The encoder utilizes the feedback weighing principle and achieves compression in accordance with a 13-segment characteristic. A distinguishing feature of the encoder is that it uses a certain redundancy in circuit elements instead of employing elements with close tolerances.

On delta modulation.

Abstract: The purpose of this thesis is to introduce Delta Modulation as an alternative to the more conventional carrier and pulse modulations, Chapter I briefly discusses the carrier and pulse modulations from the standpoint of signal - to - noise ratio, bandwidth occupancy and threshold effects. In this way, the merits of each is brought to the fore and the superiority of FM and PCM can he seen. Chapter II introduces Delta Modulation, a pulse code modulation, giving an extensive review of much of the more prominent literature on the subject. Aspects such as channel capacity, power, spectral densities, overloading, signal - to - noise ratio and bandwidth, are discussed. In Chapter III an experimental Delta-Sigma Modulation System is described in detail, from design to performance. Observations are made which correspond to some made in theory. The system transmits static signals and AC signals up to 20 HZ. The accuracy is good and the circuits simple. In Chapter IV suggestions are made to improve the systemis performance by simple means. Also mentioned are more elaborate means (Continuous Delta Modulation) which enhance the performance considerably but detract from the simplicity. Much of the literature quoted in the bibliography shows and discusses how delta modulation is simple in circuitry yet has all the advantages of PCM. It is upon this theme that the prototype Delta-Sigma Modulator is designed and built. All the circuits are kept as simple as possible. With integrated circuits, delta modulation is fast becoming an economical proposition. Delta modulation, though simple to implement, requires greater bandwidth than the conventional carrier modulations and PCM (for the same performance). At times this would make Delta Modulation uneconomical. However, there is a place for Delta Modulation alongside FM and PCM for some particular applications.