Medium frequency broadcast of differential GPS data

The broadcast performance of DGPS (differential global positioning systems)/radio beacons is studied. It is found that a combination of receiver limiting and forward error corrections is very effective against the atmospheric noise which characterizes the MF band. This combination significantly reduces the probability of bit error and the average time between differential updates. The authors compute the probability of link outage versus range, and find that forward error correction significantly increases DGPS/radio beacon coverage. It is found that groundwave/skywave interference slightly increases the probability of outage at moderate ranges. An estimate is made of the expected duration of outage for the DGPS/radio beacon signal. All results are based on analytical and experimental results     

Digital Communication Systems in Impulsive Atmospheric Radio Noise

Analyses are presented of the performance of binary and M-ary coherent and noncoherent communication systems operating in the impulsive atmospheric radio noise environment. The receiver is usually a maximum likelihood detector for white Gaussian interference and therefore has the form of a parallel bank of matched filters followed by decision circuitry. By employing a Poisson or generalized Shot noise model for the impulsive noise with a suitable probability density function (pdf), closed-form expressions and bounds of error probabilities for M-ary noncoherent and coherent amplitude-shift keying (ASK), phase-shift keying (PSK), and frequency-shift keying (FSK) systems are obtained and the results discussed.     

M-ary CPSK Detection with Noisy Reference and Interferences

A general expression of the error probability on an M-ary coherent phase-shift-keyed (MCPSK) signal purturbed by a noisy reference carrier, multiple interferences, and additive Gaussian noise is presented taking into account the frequencey divider in the carrier recovery circuit. First, a new expression for the probability density function (pdf) of the phase of a composite wave of signal, multiple interferences, and additive Gaussian noise is derived. Then this result and a pdf of the phase error modified from the Tikhonov distribution are used to obtain the erro probability of an MCPSK detector. In addition, the comparison between the error probabilities with and without the frequency divider is given, and it is found that the estimation is more pessimistic when the frequency divider is included.     

数字闭环光纤陀螺的调制串扰误差

 通过分析数字闭环光纤陀螺的阶梯波调制信号与输出死区、周期噪声干扰及小角速度漂移的关系，提出了调制串扰误差的概念。指出调制信号与探测器输出信号之间的电交叉耦合及调制信号产生的调制误差是产生调制串扰误差的干扰源。将调制串扰通道模型简化为比例环节和部分积分环节，并和光纤陀螺理想模型结合，建立了光纤陀螺调制串扰误差模型，利用该模型推导出了产生死区的条件及周期噪声干扰和小角速度漂移造成的输出偏差表达式，并对周期噪声的幅值、频率与陀螺输出量级、带宽之间的关系进行了定量分析。调制串扰误差的仿真和实验结果与理论分析结果基本一致，验证了调制串扰误差模型的正确性。     

Decision-Directed Detector for Overlapping PCM/NRZ Signals

A decision-directed (DD) technique for the detection of overlapping PCM/NRZ signals in the presence of white Gaussian noise is investigated. The performance of the DD detector is represented by probability of error PE versus input signal-to-noise ratio (SNR). To examine how much improvement in performance can beachieved with this technique, PE's with and without DD feedback are evaluated in parallel. Further, analytical results are compared with those found by Monte Carlo simulations. The results are shown in good agreement.     

Crosstalk Resistant Receiver for M-ary Multiplexed Communications

Attention is directed to the problem of M-ary signal transmission from a multiplicity of synchronized information sources. A receiver processor is derived which suppresses the effect of crosstalk between nonorthogonal signals. The processor is valid for a general zero mean, noise environment. A probability of error bound is derived for the processor. Several examples illustrate the processor.     

JTIDS链路性能分析与仿真

从链路层的角度出发,介绍了美军联合信息分发系统(JTIDS)的技术体制;并对其传输性能进行了分析;在用SPW软件建立的系统的链路仿真平台上,系统在不同条件下,例如高斯白噪声、多网干扰、点频及部分频带干扰以及非理想同步,对误码性能进行了仿真测试;最后,还对JTIDS系统的抗干扰能力进行了评估。     

Noise and Transmission Delays in Mutual Synchronization Systems

This paper considers the effects of noise and transmission delays in a phase-averaging mutual synchronization system. The basic analytical ideas are developed with respect to a two-station system which contains first-or second-order analog phase-lock loops. From the equation describing the phase error dynamics of each system, a generalized Fokker-Planck equation is derived. It is used to obtain a good approximate analytic expression for the phase error probability density function (PDF), which is confirmed by simulation. An important quantity for such mutual synchronization systems, under random disturbances, is the variance of the frequency deviation. This may be obtained directly from a knowledge of the phase error PDF. The above development is then extended to a mutual synchronization system of arbitrary size.     

Monopulse tracking of Rayleigh targets: a simple approach

A simple derivation of the probability distribution of the monopulse ratio is presented. The derivation is based upon a conditional distribution and considers both Rayleigh targets and simple non-Rayleigh cases. The mean is obtained almost without calculation. The variance expression is given completely general noise and glint interpretation. Analytical expressions for angle error mean and spread, including noise, target width, and unresolved targets, are presented as functions of antenna position, in simple and comprehensive diagrams     

Spread-Spectrum Signaling for Distributed Fiber Optic Systems

One of the stringent requirements on the receivers of distributed industrial fiber optic systems is fast and accurate adaptive thresholding and a wide dynamic range. This is due to the existence of variable link lengths and geometry, especially in multipleaccess situations, coupled with unipolar optical signaling. This paper analyzes the application of a simple spread-spectrum system in such fiber-optic data links. It proposes a detector model that yields a tractable expression for the probability of error. The optimum threshold and the probability of error are then related to the received optical power, bit rate, and spectrum-spreading factor. A procedure is indicated by which, based on the minimum expected received power, a spreading facor and a threshold are chosen to insure a given maximum error rate at all the receivers.     

Performance Analysis of Monopulse Receivers for Secondary Surveillance Radar

In modern secondary surveillance radar (SSR) the monopulse technique is currently introduced for the measurement of the azimuth of the targets. The monopulse technique is based on a suitable processing of signals received by a multiple antenna. In SSR the signals are generated by a transponder on the aircraft as replies to interrogations from ground equipment, and consist of trains of pulses. The monopulse measurements can be carried out on the basis of a single pulse from each train, so that it provides a great number of azimuth estimates. Many monopulse measurement devices exist, corresponding to different processing techniques. From the point of view of accuracy and precision, their behaviors differ with respect to the sources of errors, both internal (noise and imperfect calibrations) and external (interference and propagation effects). The four main types of monopulse receivers are analyzed here with respect to the effects of the internal error sources on the resulting measurement accuracy. After an introductory discussion of the performances of the receivers, a detailed analysis is carried out on the basis of a general mathematical model. The results are given in an analytical form and in some comprehensive diagrams.     

On the performance of serial networks in distributed detection

Distributed detection on the serial (or tandem) topology is considered with the probability of error performance criterion. Previously published efforts, while presenting probability of detection versus false alarm results, limited the number of array elements to two or three. For the detection of known, equally likely signals in additive, symmetric noise, the author presents simple recursive expressions for the threshold values and the performance of the system. Examples for known signals in Gaussian and Laplacian noise show the degradation in performance due to the array structure     

ECCM capabilities of an ultrawideband bandlimited random noise imaging radar

Investigated here is high-resolution imaging of targets in noisy or unfriendly radar environments through a simulation analysis of the ultrawideband (UWB) continuous-wave (CW) bandlimited random noise waveform. The linear FM chirp signal was selected as a benchmark radar waveform for comparison purposes. Simulation of the recovery of various types of target reflectivity functions (TRFs) for these waveforms were performed and analyzed. In addition, electronic counter-countermeasure (ECCM) capabilities for both types of systems were investigated. The results are compared using the error between the interference (jamming)-free recovered TRF and the recovered TRF under noisy conditions as a function of the signal-to-interference/jamming ratio (SIR/SJR). Our analysis shows that noise waveforms possess better jamming immunity (of the order of 5-10 dB improvement over the linear FM chirp) due to the unique radar correlation processing in the receiver.     

Self-Tuning Multisensor Weighted Measurement Fusion Kalman Filter

For the multisensor systems with unknown noise variances, based on the solution of the matrix equations for the correlation function, the on-line estimators of the noise variance matrices are obtained, whose consistency is proved using the ergodicity of sampled correlation function. Further, two self-tuning weighted measurement fusion Kalman filters are presented for the multisensor systems with identical and different measurement matrices, respectively. Based on the stability of the dynamic error system, a new convergence analysis tool is presented for a self-tuning fuser, which is called the dynamic error system analysis (DESA) method. A new concept of convergence in a realization is presented, which is weaker than the convergence with probability one. It is rigorously proved that the proposed self-tuning Kalman fusers converge to the steady-state optimal Kalman fusers in a realization or with probability one, so that they have asymptotic global optimality. A simulation example for a target tracking system with 3 sensors shows their effectiveness.     

时域内振动与噪声传递路径系统的路径传递度探索

  振动和噪声通过多重和/或多维路径传递，振源、传递路径、受体及其动态交互作用的影响至今没有很好地解决，因此对于后续采用的被动控制或者结构修改以降低振动和噪声水平的技术来说，识别出主要的传递路径是至关重要的。本文基于一般概率摄动有限元法和结构可靠性理论，解决了时域内振动与噪声传递路径系统的路径传递概率的度量问题，提出了时域内振动与噪声传递路径系统的路径传递度的新概念和方法，在考虑工程中的不确定因素以后，在时域内清晰地描述了振动与噪声传递路径系统的路径传递率。     

Envelope Threshold Detection in a Class of Non-Gaussian Interference

This paper considers the detection of a sinusoidal or chirp signal imbedded in wideband FM interference (as might be generated by some types of active jamming), such that after pulse compression or other integration, the interference can be approximated by a sum of sinusoids of independent phase. The detection probability in such non-Gaussian noise is compared to that for Gaussian noise, with the Gaussian result approached, as required, in the limit that the number of sinusoids in the sum increases without bound. For detection using a comparison of the envelope with a threshold which yields a given false-alarm probability (CFAR detection), the detection probability is improved over the case of Gaussian noise, so that the usual approach basing the design on Gaussian noise would be conservative. Using a threshold determined from the envelope mean, the FM interference yields a lower false-alarm probability than for Gaussian noise, with detection probability only slightly degraded.     

Error Probability for Fading CPSK Signals in Gaussian and Impulsive Atmospheric Noise Environments

Recently the performance of digital communication systems in the presence of impulsive atmospheric noise has been evaluated assuming a noise model which is in excellent agreement with experimental results. We evaluate the bit error probability for coherent phase-shift keying (CPSK) signaling assuming the same atmospheric noise model but considering a more reasonable representation of the communication channel which accounts for the simultaneous presence of Gaussian (always present) atmospheric noise and signal fading.     

A Useful Approximation to Binary FSK Probability of Error

A technique for calculating a simple approximation to the probability of error for binary frequency-shift keying (FSK) systems when the predetection bandwidth-bit duration product is large enough so that the signal portion of the detector output is relatively undistorted is described. The results are mathematically simple and avoid the calculation of the density function of the nonclick noise part of the output phase noise.     

Accuracy of Star Occultation Measurements for Satellite Navigation

To determine the orbital parameters of a satellite using star occultations, it is necessary to measure the intensity of stars as they occult. The accuracy of the intensity measurements is reduced by interfering sources of light and internal noise, and is expressed in terms of the magnitude of various sources of interference. Subsequently, a specific system is analyzed in detail. Moonlit cloud tops introduce the largest systematic error. Photon noise from the star radiation, airglow, and moonlit cloud tops are the largest sources of random errors.     

Recursive Methods for Computing Detection Probabilities

Recursive methods are drived for computing detection probabilities for general fluctuating targets in Gaussian noise. For the generalized chi-square family of fluctuating targets, very simple and convenient recursive algrithms result. The methods are also extended to cell-averaging CFAR. Although the detection probability is expressed iw: terms of an infinite series, a convenient expression is derived for the resulting error when the series is truncated. Cell-averaging CFAR results are computed for nonfluctuating, Swering case I, and Swerling case II fluctuating targets.