Engineering topics

Sumida, Joe T.

Publications and source records attributed to Sumida, Joe T..

4 records

NASA NTRS1989

Method and system for providing precise multi-function modulation

A method and system is disclosed which provides precise multi-function digitally implementable modulation for a communication system. The invention provides a modulation signal for a communication system in response to an input signal from a data source. A digitized time response is generated from samples of a time domain representation of a spectrum profile of a selected modulation scheme. The invention generates and stores coefficients for each input symbol in accordance with the selected modulation scheme. The output signal is provided by a plurality of samples, each sample being generated by summing the products of a predetermined number of the coefficients and a predetermined number of the samples of the digitized time response. In a specific illustrative implementation, the samples of the output signals are converted to analog signals, filtered and used to modulate a carrier in a conventional manner. The invention is versatile in that it allows for the storage of the digitized time responses and corresponding coefficient lookup table of a number of modulation schemes, any of which may then be selected for use in accordance with the teachings of the invention.

Davarian, Faramaz↗

NASA NTRS1989

DMSK Receiver For Mobile/Satellite Service

Receiver for 2.4-kbit/s differential minimum-shift keying (DMSK) and Gaussian minimum-shift keying(GMSK) suitable for communication between land-mobile stations via geostationary satellites. Operating on phase-shifted signal in 800-MHz band, in presence of fading and Doppler frequency shifts, receiver compact, makes efficient use of frequency spectrum, and wastes little power. Receiver design implemented in very-large-scale-integrated circuits. Basic DMSK receiver design relies on baseband rather than intermediate-frequency processing of in-phase and quadrature signal components because phase errors due to differential delays smaller at baseband.

Davarian, Faramaz↗

NASA NTRS1989

Automatic Frequency Control For DMSK Receiver

Report discusses performance of automatic frequency-control (AFC) subsystem of differential minimum-shift-keying receiver described in "DMSK Receiver for Moblile/Satellite Service," NPO-16659. Describes efforts to quantify behavior of system during acquisition of carrier signal; including theoretical analysis leading to numerical simulation, and measurements of performance of receiving equipment.

Davarian, Faramaz↗

NASA NTRS1989

A multipurpose digital modulator

The theoretical basis and hardware implementation of a versatile device which uses digital signal-processing methods to achieve signal modulation are reported. The carrier-modulation process is formulated as a simple quadrature equation; a generalized description of the signal constellation to be processed is derived; the pulse-shaping scheme is explained; and the system architecture is described in detail and illustrated with diagrams. Experimental results obtained with a breadboard transmitter based on this modulation technique are presented in extensive graphs. The power spectra and eye diagrams generated for different QPSK, 8PSK, and MSK modulation schemes are shown to be in good agreement with theoretical predictions. It is suggested that this modulator could be readily implemented in VLSI and mass produced.

Davarian, Faramaz↗