Showing papers on "Pulse-position modulation published in 1974"

Adaptive Delta Modulation with Delayed Decision

Abstract: A class of adaptive schemes for delta modulation is considered whereby the decision about step size is a function of the present and the last k symbols. Such schemes are studied by computer simulations using speech-like signals through evaluation of SNR. Occasional large overshoots appear in the reconstructed signal after the integrater, and to avoid such events it is proposed to store a few signal samples and decide on the proper bit stream taking into account the adaptive logic. Two quadratic criteria have been tried, and improvements of a few decibels have been established with six stored signal samples and a sampling rate of 48 and 24 kHz. Results indicate that other criteria functions may achieve still higher values of SNR.

Synchronization Using Pulse Edge Tracking in Optical Pulse-Position Modulated Communication Systems

Abstract: A pulse-position modulated (PPM) optical communication system using narrow pulses of light for data transmission requires accurate time synchronization between transmitter and receiver. The presence of signal energy in the form of optical pulses suggests the use of a pulse edge-tracking method of maintaining the necessary timing. In this report the edge-tracking operation in a binary PPM system is examined, taking into account the quantum nature of the optical transmissions. Consideration is given first to "pure" synchronization using a periodic pulsed intensity, then extended to the case where position modulation is present and auxiliary bit decisioning is needed to aid the tracking operation. Performance analysis is made in terms of timing error and its associated statistics. Timing error variances are shown as a function of system signal-to-noise ratio.

Pulse position and phase modulator

Abstract: An electronic circuit for generating pulse position modulation or phase modulation. Pulse position modulation is generated by applying a composite signal, which is the summation of a radio frequency ramp voltage and a modulating voltage, to the input of a fixed threshold trigger circuit. The output pulses of the trigger circuit are of constant magnitude and duration but vary in time in response to the modulating voltage. Phase modulation is generated by passing the output pulses of the trigger circuit through a filter tuned to some odd harmonic of the frequency of said output pulses to recover a phase modulated sinewave.

A Micropower Pulsewidth-Modulation-Pulse-Position-Modulation Two-Channel Telemetry System for Biomedical Applications

Abstract: A novel micropower, two-channel telemetry system, which has been used to transmit the occurrence of the QRS complex of the heart waveform and temperature information, is described. The system employs pulsewidth-modulation (PWM) and pulse-position-modulation (PPM) methods plus a few unique circuits and system-design techniques so that it has the following desirable features. 1) The transmitting unit consumes extremely low power due to low duty cycle and yet delivers high peak power for better receiving. In addition, the unit is compensated (not regulated) for battery voltage variation. 2) By means of adaptive threshold, pulse-width-discrimination and pulse-rate-discrimination networks, the receiving unit is relatively noise free in signal identification. Information in analog and digital form are available at the output for convenience. A prototype system was designed and fabricated. Test results are presented. Due to the availability of the integrated circuits on the market, medical doctors and biologists will be able to duplicate the system if the system-size problem is not severe. Although the design was not trivial, the implementation is quite straightforward. Hence it is believed that device or integrated-circuit manufacturers would be able to implement it in a much more compact form.

Multi-channel differential pulse code modulation system

Abstract: A multi-channel differential pulse code modulation system providing communication between a plurality of analog signal sources and corresponding signal sinks employing time shared differential pulse code modulation encoders and decoders.

Adaptive Phase and Amplitude Modulation on a Frequency Dispersive Fading Channel

Abstract: Differentially coherent phase shift keying (DPSK) is commonly used to provide data communication on frequency dispersive channels. To obtain higher data rates one can increase the number of phases or employ combined amplitude-phase modulation. In this paper we compare the performance of multilevel DPSK with the performance of Type I amplitude-phase modulation on a frequency dispersive channel with additive noise. For the Type I system differential modulation is used to amplitude encode a single bit, and ordinary DPSK is used to encode up to four phase bits. Curves of bit error probability versus the effective signal-signal-to-noise ratio of the channel are presented for both the amplitude and phase encoded bits. From these curves the appropriate amount of amplitude modulation to be employed in a high rate Type I system can be obtained. Performance comparisons between multilevel DPSK and Type I modulation are then presented under conditions of both equal average and peak transmitter power.

Effects of System Inaccuracies on the Probability of Bit Error for Pulsed Communication Systems

Abstract: Digital communication systems using the narrow pulses generated by a mode-locked laser are extremely efficient in their use of average laser power However, these narrow pulses require precise system timing and decision intervals matched to the pulse width This paper extends previous work by Gagliardi in this area to consider the effects of pulse timing errors and pulse width mismatch on the probability of bit error for on-off keying, binary pulse position modulation, and quarternary pulse position modulation formats The general expressions are derived, and a number of examples are plotted