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A new interpretation of unfiltered Feher-patented quadrature-phase-shift keying (FQPSK) is presented that readily identifies a means for spectral enhancement of the transmitted waveform as well as an improved method of reception. The key to these successes is the replacement of the half-symbol-by-half-symbol mapping originally used to describe FQPSK by a(More)
M-ary pulse-position modulation (PPM) has received considerable attention for direct-detection photon communications over unguided channels. The analysis generally assumes that the signaling set is orthogonal. However, the orthogonality of the signaling set will be destroyed by the finite area and bandwidth of optical detectors, resulting in severe(More)
Using the amplitude-modulation pulse (AMP) representation of continuousphase modulation (CPM) introduced more than a decade ago by Laurent, the power spectral density (PSD) of minimum-shift-keying (MSK)-type modulations (modulation index equal to one-half) is computed in the presence of data imbalance. The advantage of this technique is that closed-form(More)
This article describes a general architecture for fault modeling, diagnosis, and isolation of the DSN antenna array based on computationally intelligent techniques (neural networks and fuzzy logic). It encompasses a suite of intelligent test and diagnosis algorithms in software. By continuously monitoring the health of the highly complex and nonlinear array(More)
This article investigates the performance of the heterodyne detection scheme for optical pulse-position modulation (PPM) communications channels when nonideal laser transmitters are employed. Two aspects of this channel will be considered. First, the limitations of unguided, turbulent channels in accommodating coherent laser communications are addressed.(More)
Advanced Radio Interferometry Between Space and Earth (ARISE) is a space very long baseline interferometry (VLBI) mission with a nominal launch date of 2008. It consists of an inflatable 25-m radio telescope circulating in a highly elliptical Earth orbit with a perigee of 5,000 km and an apogee of 40,000 km. The objective is to observe in conjunction with(More)
The novel network testbed simulators are described: the request protocol simulator and the link protocol simulator. These testbeds are useful for evaluating delay-throughput performances of demand-assisted multiple-access (DAMA) protocols in mobile fading environments. The request protocol testbed simulates the multiple-access scheme for making connection(More)
A generalized maximum a posteriori (MAP) symbol synchronizer for arbitrary nonoverlapping pulse shape and data-transition density is derived, and a simplified realization is presented. Acquisition performance at low to very low symbol signalto-noise ratios (SNRs) is investigated and compared against the conventional datatransition tracking loop (DTTL).(More)
Free-space laser communication is a promising technology to meet the demand for cost-effective wideband support for future NASA missions. JPL has begun construction at the Table Mountain Facility in California of a 1-meter telescope system, known as the Optical Communication Telescope Laboratory (OCTL) and capable of tracking spacecraft from low Earth orbit(More)
Over the past years, NASA and JPL have continuously sought to reduce spacecraft size and mass while increasing its information return capability. Laser communications provide a way of achieving this goal. The highly collimated beam allows for significant reductions in the size and mass of the communications terminal along with reduced power requirements.(More)