Digital Synthesis Method Research Articles

Development of the F/A-18A automatic carrier landing system

The F/A-18A Automatic Carrier Landing System integrates the aircraft flight control system, throttle control system, inertial navigation sensors, and shipboard SPN-42 tracking radar and computer system to achieve fully automatic approach control to the carrier deck in all weather conditions. Accurate touchdown position and sink rate must be achieved under varying conditions of visibility, deck motion, air turbulence, and ship air wake downdraft. Design analysis of this integrated digital control system is described, including digital synthesis methods used and projected performance under wind and deck motion conditions, two shipboard trials have verified the high touchdown accuracy potential of the system, resulting in along-deck touchdown dispersion of only 19 ft for 91 automatic landings.

A simple method for MSK modulation and demodulation

In this letter, a simple method for modulation and demodulation of minimum shift keying (MSK) is proposed. It has a serial structure, and is easier to implement than the conventional parallel type. The MSK signal is generated by a digital synthesis method and the demodulation process is done by a simple sampling scheme.

Synthesis of geophysical data with space-acquired imagery: A review

Geophysical data obtained from ground and airborne platforms have been used in the development of regional geologic models for many years. Space-acquired data and imagery have a shorter but similar history of applications. All these data may be synthesized either manually or digitally. Manual synthesis methods consist of overlaying and comparing maps, whereas digital synthesis methods consist of computer storage and analysis of registered digital data sets. A data base may include topographic, geologic, soils, aeromagnetic, gravity, radiometric, electromagnetic and geochemical data, and Landsat, Seasat, and Heat Capacity Mapping Mission (HCMM) images, all of which can be evaluated individually or compared in multiple layers (overlays). Stereographic models, useful in the correlation and interpretation of geophysical data, have been created from Landsat images by using aeromagnetic, gravity, geochemical, or topographic values to offset Landsat pixels, thus introducing parallax and permitting stereoscopic viewing. Statistical correlation has been used to determine the applicability of specific data sets to the development of geologic or exploration models. Various arithmetic functions have proven useful in developing models from such data sets.

Synthesis of efficient digital beamformers

Digital interpolation beamforming [R. Pridham and R. Mucci, J. Acoust. Soc. Am. 63, 425–433 (1978)] permits a reduction in A/D conversion rate, telemetry bandwidth, and memory throughput, relative to nearest‐sample‐selection beamforming, at the expense of an increase in arithmetic operations. However, conventional synthesis techniques for the up/down sampling interpolator filters used in such a beamformer are typically based on specifications which are not directly related to the beamformer response; thus an excessive computational rate may result. This paper describes an alternative approach to the synthesis of arithmetic digital beamformers, involving the design of the individual digital filters which perform delay interpolation on the hydrophone signals for a given steering direction. It is shown how to set specifications on the amplitude and phase frequency responses of these filters based on beam pattern tolerances. Optimal digital interpolator synthesis methods then yield computationally efficient beamformer solutions. Examples are presented for several array geometries.

A method of digital filter synthesis in the frequency domain

In this letter, a new method of digital filter synthesis is presented. The transfer function of the resulting digital filter closely approximates the corresponding continuous transfer function of the correcting filter with steep transition regions.

H.F. communication receiver performance requirements and realization

Discusses h.f. communication problems and the stringent and often conflicting requirements placed on the performance of any h.f. communication receiver. The H2900 receiver has been designed with these requirements in mind. The receiver uses a novel method of digital frequency synthesis allowing for small frequency increments of 1 Hz.

Transform Method of Fast Digital Synthesis of Unvoiced Speech Sounds

Digital speech synthesis is often carried out by direct convolution of a sequence of unit samples with a sampled impulse response. In the case of unvoiced sounds, this method can lead to the need for an excessively large number of additions per output sample of the synthesized waveform. This is because of the requirement that the synthesized output be essentially Gaussian and possess the correct spectral energy distribution in order to achieve natural-sounding unvoiced sounds. This paper describes a transform method based upon the Cramer-Kolmogarov representation for a stationary process that reduces the required number of additions per output sample by a factor of at least 10, and which has been found experimentally to produce high-quality synthetic speech. The performance of the method is demonstrated by playing a tape recording of the output of an all-digital vocoder that uses this method of synthesis. [Work supported by Air Force Avionics Laboratory, Wright-Patterson Air Force Base, Ohio.]