Clutter Map CFAR Analysis

An analysis of the probability of target detection for a clutter map CFAR using digital exponential filtering has been performed. General performance equations are derived. The probability of detection versus signal-to-noise ratio is plotted for a false alarm probability of 1.E-06 for several weight values. The CFAR loss is plotted for a detection probability of 0.9 and false alarm probabilities of 1.E-06 and 1.E-08.     

Instantaneous Frequency Estimation Using Adaptive Linear Predictor Weights

A computationally efficient scheme for estimating the digital instantaneous frequencies of narrowband inputs is introduced. The frequency estimates are obtained by searching for minima of the inverse input power spectrum. This spectrum is estimated at each input sample from the weights of an adaptive linear predictor which uses the LMS (least mean square) algorithm to update its weights. The related minima are sought via an iterative search algorithm, referred to as the iterative frequency estimator. This algorithm is computationally more efficient than available methods, and also provides a higher resolution. Simulation results are included; these include tracking of random message sequences in FM signals, and the formant frequency estimation of speech.     

Normalized LMS Algorithm Degradation Due to Estimation Noise

The steady-state weight vector derived by either the least mean square (LMS) or normalized least mean square (NLMS) algorithms has random deviations from the optimum values. These deviations increase the steady-state residue power. A previous paper derived the LMS weight noise effects for a multiple sidelobe canceller (MSLC) application. This paper describes the NLMS weight noise effects. It is shown that for a thermal noise environment, the weight noise effect for the LMS algorithm is insignificant but is quite significant for the NLMS algorithm. Calculations for example noise plus interference environments imply that the NLMS weight noise effects are always larger than that for LMS.     

Design of the HEAO Main Bus Shunt Regulator

The High Energy Astronomy Observatory (HEAO) main bus regulator contains a redundant error amplifier (REA) and a 12-section sequenced shunt transconductance amplifier (STA) in which not more than three and not less than one shunt section are in an active control mode regardless of a failure in any one of the twelve sections. The part of the work concerned with the shaping of the frequency response of the REA and STA minor feedback loops and of the teolator major feedback loop is described. Emphasis is on the application of a general design technique embodying a "design-analyze-measure iteration loop," in which a first-cut design and analysis is corrected ard improved after experimental observation of discrepancies and deficiencies. In particular, an incipient high-frequency oscillation was thereby reliably eliminated. It is demonstrated that analysis techniques involving a minimum of algebra can provide full quantitative information on an efficient and reliable system design.     

Harmonic Radar Systems for Near-Ground In-Foliage Nonlinear Scatterers

The radar transmission equation for a harmonic radar operating over a planar, finite dielectric Earth through foliage is derived for an interesting class of nonlinear scatterers. The received power can typically depend on range to the (-14) power for small objects near the ground. The maximum detection range of a ground-based system is related to all major system parameters: it is most sensitive to polarization, transmit antenna height, and transmit wavelength; moderately sensitive to transmit power and transmit antenna area; and least sensitive to receive antenna area, harmonic scattering cross section, and mode of data processing. For example, there is seen to be a best apportionment of total available aperture area into disjoint transmit and receive apertures which can be well approximated by the equal gain condition. Also, there is seen to be a critical path distance through foliage; at distances less than this, small wavelengths are desirable and, conversely, the upper transmit frequency limit may be set by nonlinear scatterer response. Airborne synthetic aperture radar systems are discussed and quantification of harmonic noise and effects of scatterer fluctuation are made. A useful phenomenological model of a nonlinear scatterer is given that is consistent with some observations and predicts a frequency dependence. Nonlinear scatterer effects on range resolution are discussed.     

A Functionally Redundant Altimeter

A scheme to provide redundant sensor data in an automatic control system using the principle of functional redundancy is described. Normally there are three redundant radar altimeters used in the terminal phase of automatic landing of jet transport airplanes. This scheme replaces one of these altimeters with a data processing scheme based on a Kalman filter. The filter is driven by altitude rate and acceleration signals from the air data computer and vertical accelerometer. A special initialization technique employs the two altimeter signals. The feasibility of this scheme is indicated by tests in which data obtained from these several sensors during flight tests are used to drive the functionally redundant altimeter.     

Limiting Performance of Generalized Sign Test Detector

The limiting performance of the generalized sign test detector as the number M of target returns becomes infinite has been derived by Hansen and Olsen [1]. Simple expressions are derived herein for the limiting performance for finite M as K, the number of noise samples in the reference set, becomes infinite. Curves are presented which indicate how this limiting performance is approached as K is increased for both constant target returns and fluctuating target returns.     

Microprocessor-Controlled Communications in an Advanced Instrument Landing System

The application of 4-bit microprocessors to the communication of the control and status signals found in an advanced aircraft instrument landing system is presented. The advantages as well as some of the peculiarities of such an approach are described. Among the benefits, one must include the possibility of a very convenient and understandable human interface.     

Ultra-reliable real-time control systems-future trends

Today's aircraft use ultra-reliable real-time controls for demanding functions such as Fly-By-Wire (FBW) flight control. Future aircraft, spacecraft and other vehicles will require greater use of these types of controls for functions that currently are allowed to fail, fail to degraded operation, or require human intervention in response to failure. Fully automated and autonomous functions will require ultra-reliable control. But ultra-reliable systems are very expensive to design and require large amounts of on-board equipment. This paper will discuss how the use of low-cost sensors with digital outputs, digitally commanded fault-tolerant actuation devices and interconnecting networks of low-cost data buses offer the promise of more affordable ultra-reliable systems. Specific technologies and concepts to be discussed include low-cost automotive and industrial data buses, “smart” actuation devices with integral fault masking capabilities, management of redundant sensors, and the fault detection and diagnosis of the data network. The advantages of integrating the control and distribution of electrical power with the control system will be illustrated. The design, installation, and upgrade flexibility benefits provided by an all-digital and shared network approach will be presented. The economic benefits of systems that can operate following failure and without immediate repair will be reviewed. The inherent ability of these redundant systems to provide effective built-in test and self-diagnostics capabilities will be described. The challenges associated with developing ultra-reliable software for these systems and the difficulties associated with exhaustive verification testing will be presented as will additional development hurdles that must be overcome