Abstract: A method and apparatus which realize an RF bandpass filter having a tunable bandwidth and center frequency over a large range of the radio frequency spectrum. The filter is comprised of a cascade of filter elements. Each element is comprised of a signal splitter which simultaneously feeds a signal to a delay line and a phase shifter in a parallel path. The delayed and phase shifted signals are summed. Each filter element exhibits periodic passbands and alternating transmission zeroes. Each successive filter element has a decreased delay by an incremental factor (e.g., typically 1.2), and exhibits an increase in the frequency intervals between stopband zeroes. The bandwidth is controlled by selecting a number of "activated" ones of the successive elements. A center frequency tuning is performed by adjusting a phase shift coefficient of at least one filter element.

Abstract: An image generator system for producing real time imagery from a digital database includes processors performing in sequence: scene data management, geometry processing, and video processing. The scene data management processor selects and organizes the data base objects, modeled with polygons, and distributes polygons to parallel geometry processing modules. Geometry processing modules convert the images from 3-D to 2-D coordinates and divide the polygons into two-pixel-high scanline-aligned "spans". Spans are collected and sorted in a region buffer associated with each channel of a scene. Occlusion is done hierarchically to conserve time and bandwidth, and antialiasing is performed recursively for the same reasons.

Abstract: A method for determining which objects are visible in each pixel of a digitally-generated image is described. The method uses comparison of distances from the viewpoint (Z-sorting) for occlusion. The number of Z comparisons required is minimized by utilizing a hierarchy of regions in the screen area, and thereby, resolving occlusion for areas larger than pixel areas where possible. Use of the area hierarchy increases the efficiency of the occlusion processing. In a preferred implementation, the screen is divided into equal-sized horizontal regions each corresponding to typically four scanlines. Polygons for each image are subdivided into pieces that correspond to the preset hierarchy of regions, and occlusion processing occurs independently in parallel for two or more regions. Each region is subdivided further into smaller regions, each level of the hierarchy having regions half the size of a higher level region.

Abstract: A packet communication system transmits a stream of L data packets with at least one parity packet transmitted as an L+1.sup.th packet. The parity packet comprises at least, N data segments, each ith data segment being the modulo-2 sum of all identically positioned data segments in the stream of L packets. A node includes adaptive packet stream transmission apparatus which comprises a packet queue for holding a series of packets ready for transmission to a destination node. The adaptive packet stream transmission mechanism further includes modulo-2 sum circuitry for deriving a parity packet for each L transmitted data packets. Transmission control circuitry selectively enables transmission of a parity packet after each L data packets have been transmitted. A processor in the node controls the transmission control circuitry to vary the value of L in accordance with a determined network metric.

Abstract: A compressing a voice signal by the steps of (a) digitizing an input signal that includes a voice signal, the input signal including a coherent noise component; and (b) compressing the digitized voice signal with a synchronized overlap add processor (20). So as to prevent the synchronized overlap add processor from locking to the coherent noise component, the step of compressing includes an initial step of applying the digitized input signal to a linear predictor (16), the linear predictor having time constants selected for attenuating the coherent noise component of the input signal. The residual signal output of the linear predictor includes the voice signal, and an uncorrelated noise component if one is present in the input signal. The operation of the synchronized overlap add processor also functions to attenuate the incoherent noise component.

Abstract: A method and apparatus for analyzing a bit stream having an unknown format that is conveyed through a communications network. The method includes the steps of: (a) storing a plurality of sequentially occurring bits received from a communications network; (b) analyzing a plurality of the stored bits to detect periodicities in the bits; and (c) determining if the detected periodicities exhibit characteristics associated with a known type of data communications format, particularly a synchronous time-division-multiplexed (TDM) data communications format or a packetized data communications format. The step of analyzing includes a step of performing a statistical analysis of the stored bits.

Abstract: A manned space vehicle is described whose altitude control is achieved by constant drag compensation through the action of low level thrusters. The space vehicle include a low pressure electrolyzer that generates hydrogen and oxygen from water in a mass ratio of eight parts of oxygen to one part hydrogen. Oxygen and hydrogen from the electrolyzer are fed to the low level thrusters, with the oxygen proportion being reduced to limit thruster degradation. A life support system employs the excess oxygen from the electrolyzer and extracts carbon dioxide from the atmosphere of the vehicle. The extracted carbon dioxide is fed to the low level thrusters. The carbon dioxide enters into the combustion process with the oxygen and hydrogen, providing additional oxygen to the process and serving as a diluent to reduce the combustion temperature.

Abstract: Apparatus and methods of achieving accurate, unambiguous angle information with a minimum number of antenna elements. The present invention resolves the ambiguities inherent in a long baseline phase interferometer by employing a minimum number of antennas to form shorter baselines. The present invention employs roll motion (antenna rotation) to reorient interferometer baselines and a signal processor to measure the roll angle. Taking interferometer phase data with at least two orientations of the interferometer baselines permits resolution of the ambiguities. This also allows the use of long antenna baselines thereby achieving high angular accuracy with angle ambiguities resolved using only two antenna elements per spatial angle. This reduces system complexity and reduces the required clear aperture area, factors of great significance in missile systems. The invention takes phase data at two or more interferometer baseline orientations and forms a set of simultaneous equations involving the phase ambiguities.