A Modification to Improve the Inverse Filter of Senmoto and Childers

An inverse filter, contained in a recently published paper by Senmoto and Childers, is improved by the application of a shaping function derived by Turin in an earlier paper.     

Characterization of High-Rate QPSK Channel with Adaptive Equalization

A computer simulation model capable of predicting the performance nce of a high-dta-rate end-to-end communication system with adaptive equalization is described in this paper. The model is used to characterize the behavior of NASA's proposed tracking and data relay satellite system (TDRSS), while accounting for signal distortion effects due to operational conditions and the required hardware are components necessary to fulfill mission objectives. Specifically, the performance of the TDRSS high-dta-rate lik (300 Mbps) is defined, both with and without adaptive equalization.     

Automatic Checkout and Monitoring in the AN TPQ-27 Radar System

This paper describes automatic monitoring equipment built in to a precision tracking radar system to detect and isolate faults. The purpose of the monitoring equipment is to minimize the mean time to repair faults and to exercise the overall system for pre-mission alignment and calibration. In addition, it is used to periodically check for performance degradation in key areas of the system. The paper describes the design approach used to meet the above requirements. Three types of signals are monitored: analog, digital, and switch closure. A list of each type is given and the technique used to monitor each is described. The design approach for pre-mission alignment and calibration is outlined. Tests performed are: RF alignment of the boresight axis, range tracking accuracy, angle servo calibration and accuracy, and receiver figure of merit measurements.     

Optimal Precession Control of Randomly Perturbed Spin-Stabilized Satellite

Dynamics of the satellite angular momenta is modeled by ordinary differential equations with additive white noise. A feedback controller er is desired to maintain tolerable satellite momenta and to economize ze the fuel consumption. The stochastic optimal control problem is transformed into an equivalent deterministic optimization problem involving a parabolic partial differential equation. Necessary optimality y conditions are used to develop a computation algorithm. Results regarding optimal controls, expected costs, and confinement probabilities in different noisy environments are presented.     

The Effect of Weighting upon Signal-to-Noise Ratio in Pulse Bursts

The Doppler sidelobes of a received pulse burst may be partially controlled by varying the amplitudes of the pulses in the burst or sequence upon transmission and/or reception. When there is a peak power limitation, weighting the amplitudes produces a loss in signal-to-noise ratio. A general expression is derived for the loss factor under the peak power limitation, and loss factor formulas are given for the following cases: Case A: Full nominal weights upon reception. Uniform weights on transmission. Case B: Square roots of the nominal weights on both transmission and reception. Case C: Full nominal weights on both transmission and reception. These cases are listed in order of increasing loss. Numerical results are tabulated for regular spacings and for the following nominal weights: 1) Dolph-Tchebycheff, 2) Taylor, 3) Hamming, and 4) Hann.     

Remote sensing of precipitation by a satellite-borne microwave remote sensor

The problem of remote sensing of precipitation by a satellite-borne microwave rain scatterometer is discussed. A downward-looking scanning pencil-beam antenna system is used. The combination of the range-gate method and low side lobe level is used to separate echoes from precipitation layers in the main lobe from ground clutter in the side lobes. Various parameters of the satellite-borne microwave rain scatterometer are calculated and characteristics of systems at 10 and 34.45 GHz are considered. The transmitter peak power needed to observe precipitation with sufficient signal-to noise ratio is calculated by means of the radar equation. The signal (i.e. the received power from the resolution volume of the precipitation) and the received power due to the ground clutter are calculated and the signal-to-clutter ratio is obtained by applying the radar equation. An airborne microwave rain scatterometer is proposed for preliminary experiments.     

Detection Performance of the Cell Averaging LOG/CFAR Receiver

The cell averaging LOG/CFAR receiver is a special implementation of a constant-false-alarm-rate (CFAR) receiver in which the noise level estimate is derived from a set of contiguous time samples of the output of a logarithmic (LOG) detector as obtained from a tapped delay line. This CFAR receiver is capable of operating over a larger dynamic range of noise levels than a conventional cell averaging CFAR receiver, but with somewhat poorer detectability. The performance in stationary Gaussian noise of the cell averaging LOG/CFAR receiver with no post-detection integration is determined in this paper. For a small number of reference noise samples, results were obtained by a Monte Carlo simulation using the technique of importance sampling. For a large number of reference noise samples, a second moment analysis gave the desired results. Both these results can be summarized in the following simple formula, NLOG = 1.65NLIN - 0.65, which relates the number of reference samples required by each of the two receivers for equivalent performance. Thus, for the cell averaging LOG/CFAR receiver to give the same detection performance as the conventional cell averaging CFAR receiver, the number of reference noise samples has to be increased by up to 65 percent.     

Modeling and Estimation for Tracking Maneuvering Targets

A new approach to the three-dimensional airborne maneuvering target tracking problem is presented. The method, which combines the correlated acceleration target model of Singer [3] with the adaptive semi-Markov maneuver model of Gholson and Moose [8], leads to a practical real-time tracking algorithm that can be easily implemented on a modern fire-control computer. Preliminary testing with actual radar measurements indicates both improved tracking accuracy and increased filter stability in response to rapid target accelerations in elevation, bearing, and range.