A Digital Open-Loop Adaptive Processor

A new technique for adaptive processing applications, which is superior to the conventional Applebaum-Howells adaptive loop, is presented. The new technique is based on open-loop digital processing and does not have the limitations of the conventional closedloop analog processor. In contrast with the conventional adaptive loop, the open-loop processor has effectively infinite gain, is unconditionally stable, and does not depend on the power level of the auxiliary signal.     

Digital Control of High Performance Aircraft Using Adaptive Estimation Techniques

Since the early 1960's, a rapid advance in signal processing, including filtering and estimation techniques, has been evident. In contrast, applied feedback control, particularly for aircraft, is currently based on technology available prior to 1960, i. e., primarily either constant gain feedback or at most a standard gain-scheduling. In this paper, an adaptive signal processing algorithm is joined with gain-scheduling to produce an effective scheme for controlling the dynamics of high performance aircraft. A technique is presented for a reduced-order model (the longitudinal dynamics) of a high performance short-takeoff-and-landing (STOL) aircraft. The actual controller views the nonlinear behavior of the aircraft as being equivalent to a randomly switching sequence of linear models taken from a preliminary piecewise-linear fit of the system nonlinearities. The adaptive nature of the estimator is necessary to select the proper sequence of linear models along the flight trajectory. From the analysis of the reduced-order model the nonlinear behavior has been found to be well approximated by assuming an effective switching of the linear models at random times, the durations of which reflect the motion of the aircraft in response to pilot commands.     

The Performance of an LMS Adaptive Array with Frequency Hopped Signals

The performance of an LMS adaptive array with a frequency hopped, spread spectrum desired signal and a CW interference signal is examined. It is shown that frequency hopping has several effects on an adaptive array. It causes the array to modulate both the amplitude and the phase of the received signal. Also, it causes the array output SINR (signal-to-interference-plus-noise ratio) to vary with time and thus increases the bit error probability for the received signal. Typical curves of the desired signal modulation and the time-varying SINR at the array output are presented. It is shown how the array performance depends on hopping frequency, frequency jump size, interference frequency, signal arrival angles, and signal powers.     

Optimal Array Processor Performance Trade-offs under Directional Uncertainty

Detection performance in terms of the receiver operating characteristic (ROC) curve is obtained for three specific problems involving either signal or noise source location uncertainty. The array processors are optimum in the sense that they form the likelihood ratio of the outputs of the individual array elements. Performance trade-offs due to signal uncertainty, signal and noise source location uncertainty, and array size are presented.     

Prediction of Adaptive Array Performance

A direct relationship between the conventional properties of an array and the array performance in an adaptive mode is given. Expressions are provided to obtain the output signal-to-interference-plus-noise ratio (SINR) of an adaptive array in terms of its conventinal pattern and the locations of the desired signal and jammers. These expressions permit one to evaluate the performance of an adaptive array without an exhaustive search for all possible scenarios and parametric values to ascertain that the required performance levels be met. In fact, one can predict the jammer locations for which the array will provide its best and worst performance by observing the conventional pattern. Several examples are provided to demonstrate the relationship between the conventional pattern and the adaptive array performance. The examples include both linear and planar arrays.     

Digital Radiometer Performance

This work investigates the performance of an all-digital, total-power radiometer (TPR), consisting of RF, mixer, and IF stages followed by an analog-to-digital converter (ADC). Square-law detection and smoothing is performed in a digital computer. A figure of merit, the degradation factor, is defined which compares the digital TPR with an ideal analog TPR. Exact results are obtained which include the effects of saturation, finite step size, and finite sampling rate of the ADC. A good approximation is developed which compares favorably with the exact results under certain conditions. The use of a general digital filter for smoothing is considered. A new parameter, the ?equivalent summation number?, is shown to be analogous to the equivalent integration time of an analog TPR.     

Design and Performance of an Adaptive Kalman Receiver for Synchronous Data Transmission

A class of multilevel linear-modulation data-transmission systems, over unknown, slowly time-varying, and bandlimited channels is considered. It is shown how sequence estimation in the presence of Gaussian noise and intersymbol interference can be carried out by means of a discrete Kalman estimator. Moreover, the receiver can be provided with data-aided adaptive loops for performing channel identification, carrier recovery, and timing extraction. A computational method is presented to evaluate the average probability of error of the overall system in the presence of inter-symbol interference, additive noise, and phase-and sampling-synchronization errors. The method is based upon nonclassical one-and two-dimensional quadrature rules, which are outlined in the Appendix. As an example, numerical performance results related to a phase-shift-keying (PSK) system are given. The results are obtained by means of general-purpose and system-oriented computers.     

Performance Analysis of a Dwell-Time Processor for Monopulse Beacon Radars

Performance of a monopulse air traffic control radar beacon system (ATCRBS) target data extractor is analyzed via an analytical approach. Results refer to a statistical analysis of the section of the receiver which associates replies sent by the desired aircraft during the antenna dwell-time. Some numerical results are reported which refer to the ATCRBS section to be devised in the discrete address beacon system (DABS).     

Performance of a Modified Applebaum Adaptive Array

The performance of a modified Applebaum adaptive array is studied. The new array is obtained by removing the desired signal component from the output signal fed back to the correlator of an Applebaum type adaptive array. Various signal scenarios, including single desired signals or multiple simultaneous desired signals are examined. The new array is less sensitive to beam pointing errors and does not cause power inversion of desired signals. In the case of multiple simultaneous desired signals, the new array does not degrade the SNRs of strong desired signals.     

Upper Limits on the Performance of the Optimum Processor in Mismatched Environment

In most signal detection problems, information about the observations is not precisely known beforehand. The performance of the likelihood ratio processor (LRP), designed according to a preassumed observation vector parameter, is investigated when the actual processed observations have a vector parameter that differs from the preassumed design vector parameter. An upper limit on the performance of the LRP is obtained when the actual and design vector parameters are equal. The possible need for using adaptive processors is determined by this LRP performance investigation.     

Adaptive Forward Error Control for Digital Satellite Systems

Two hybrid schemes of time-frequency resource sharing to increase the rain margin of Ku-and Ka-band satellite systems are proposed. Scheme 1 requires sharing a small pool of bandwidth for adaptive forward error control coding, sharing a small pool of time frame for rate reduction, and sharing a portion of low frequency time-division multiple access (TDMA) back-up frame for downlink transmission to the rain affected stations. Scheme 2 utilizes variable rate modulation and forward error correction, shares a small pool of time frame for rate reduction, and shares a portion of low frequency TDMA back-up frame. Effective usable capacities of the system using these schemes are calculated. Distribution of resources in order to maximize the effective usable capacity is also analyzed. The results obtained are compared with other adaptive schemes. Preliminary analysis shows that the utilized capacity of scheme 1 exceeds 99 percent of the effective usable capacity possible if it never rains for an outage of 0.05 percent and fade margin of 2.5 dB. For scheme 2 similar performance is achievable at a fade margin of 1.5 dB. For higher outage objectives the loss of effective utilized capacity is higher for scheme 2.     

Exact Angular Accuracy of an Amplitude Comparison Sequential-Lobing Processor

Assume E1 and E2 are the squares of two sequential envelopes from the sequential lobing of an antenna in a given plane. Independent thermal noise is generally present in the envelopes. The statistic e = (E2 ? E1)/(E2 + E1) has been used as an estimate of the angle to a target for the significant region of small angles compared to a beamwidth. For a nonfading target, the probability density and characteristic function of e are obtained in closed form. Thence, the exact bias, standard deviation, and rms error in estimating the noise-free value e of e are obtained for all e and signal-to-noise ratios. The same type of statistic as e can be used to estimate time delay in a split range gate tracker.     

航空发动机部件特性自适应计算方法

发展了一种预测发动机部件特性的自适应模型方法,该方法以发动机通用特性为基础,利用单纯型优化方法,将发动机主要性能参数和过程参数的偏差函数最小为优化目标,以部件特性藕合因子为被优参数,此法能较好地预测出不同飞行条件下发动机的风扇、压气机、燃烧室、高、低压涡轮等部件特性.应用于某算例的计算结果表明,发动机主要性能参数和过程参数的计算偏差均在0.5%之内,对发动机各截面总温、总压计算偏差均在1%之内.预测出的部件特性已成功用于发动机故障诊断方程的建立.     

The Power-Inversion Adaptive Array: Concept and Performance

The use of a power-inversion adaptive array to improve the signal-to-interference ratio in a communication system is described. "Power inversion" refers to the ability of an adaptive array to invert the power ratio of two received signals. The power-inversion ion technique is useful because it does not require detailed ledgeknow about desired-signal structure or arrival angle. The perform ance attainable with a power-inversion array is described and typical al design curves are presented.     

The Performance of Adaptive Array in a Dynamic Environment

The performance of adaptive arrays for jamming cancellation isdegraded due to relative angular movements between the arrayelements and the signal sources in space. We consider small angularvariations about the steady state of a linear (power inversion) arraycaused by either 1) a discrete angular jump, or 2) a continuousangular movement with constant angular velocity. Performancedegradation is assessed in terms of the resulting increase in the totaloutput power relative to its steady-state (minimum) value. Theresults reported are independent of the algorithm used to minimizethe output mean square error (MSE) and are supported bycomputer simulations.     

On a Specific Performance Limitation of Partially Adaptive Antennas

An analysis shows the performance degradation of a sidelobe cancellation system as the consequence of a basic property of partially adaptive antennas when neighboring interference directions are weighted differently in sign by the radar antenna sidelobes.     

A Comparison of Binary Delay-Lock Tracking-Loop Implementations

The delay-lock loop is a device for tracking the delay difference between two correlated waveforms. It is used as a synchronizing loop for binary communications and tracking. The delay tracking performance is derived for various radio-frequency implementations of the binary delay-lock loop. Amplitude and biphase modulation by pseudorandom sequences are considered. Three types of receivers are analyzed for each modulation: envelope correlation, phase-coherent correlation, and phase-lock demodulation followed by video correlation.     

Polarization Separation by an Adaptive Filter

The technique of adaptive filtering as applied to the design of a frequency-reuse receiving antenna which can provide optimum isolation from signals of unwanted polarization.     

Effects of Perturbations on the Performance of Optimum/Adaptive Arrays

An investigation of the effects of system and medium perturbations, and the deviations of signal field statistics from usual assumptions, on the performance of adaptive arrays is presented. The emphasis is placed on the determination of the sensitivity of the adaptive processors to perturbations, rather than its overall performance in a representative background. The numerical results are limited to CW signals, and a frequency domain element space adaptive beam-former is modeled for the majority of the results. Representative comparative results including frequency domain beam space, time domain element space, and matched array processors are also given.