Showing papers in "Frequenz in 1995"
TL;DR: Methods are derived for using system and correlation functions for the examination of measured channel characteristics and results are given for the time-Variant Impulse Response, the Scattering Function and the Time-Frequency Correlation Function.
Abstract: System and correlation functions of WSSUS channels are commonly accepted means for channel description in mobile communications. After a brief recapitulation of the theory for WSSUS channels, methods are derived for using system and correlation functions for the examination of measured channel characteristics. The derived methods additionally lead to a simple interpretation of the relations between the functions. Finally results are given for the Time-Variant Impulse Response, the Scattering Function and the Time-Frequency Correlation Function calculated from measured data in an indoor environment
13 citations
TL;DR: Detailed investigations aiming to optimize the service area by means of numerical simulation are presented, where realistic transmitter configurations and common wave propagation models exploiting topographic data have been employed.
Abstract: In order to take advantage of the network gain of digital single frequency networks, the set of parameters that characterize the transmitter network have to be chosen properly. Detailed investigations aiming to optimize the service area by means of numerical simulation are presented, where realistic transmitter configurations and common wave propagation models exploiting topographic data have been employed. The system parameters, such as the maximum effective radiated power per transmitter, have been restricted to realistic values which might be realized in digital audio broadcasting networks to be introduced in the near future. Antenna pattern adjustment appears to be less effective in comparison to improving the single frequency network synchronization schedule.
12 citations
TL;DR: Theoretical limitations for matching networks between the photodiode and the electrical amplifier in an optical receiver are calculated in this paper, where it is shown that exact matching is not possible up to infinite bandwidth.
Abstract: Theoretical limitations for matching networks between the photodiode and the electrical amplifier in an optical receiver are calculated. These limitations are due to the fact that exact matching is not possible up to infinite bandwidth. In an optical receiver power matching and noise matching have to be distinguished, but the noise matching problem can also be transformed into a power matching problem. Concerning the matching between a photodiode and an ohmic resistor a constant frequency response can be realized by an arbitrary complex matching network. In the case of the matching between a photodiode and a field effect transistor a ripple in the frequency response is obtained which cannot be reduced by higher-order matching networks
4 citations
TL;DR: In this article, a generalized asymmetric Gaussian distribution that covers a wide range of length of tails and asymmetry is proposed and employed to approximate the distribution of this discrete data.
Abstract: The (symmetric) trimmed mean estimator truncates the same number of samples at both of sides of the probability distribution. For asymmetric distributions the problem is to decide where to truncate the distribution on the left and right side. A generalized asymmetric Gaussian distribution that covers a wide range of length of tails and asymmetry is proposed and employed to approximate the distribution of this discrete data. Using this distribution, truncation points of the discrete distribution on both sides have been obtained. Starting with the trimmed mean estimator that can be used for symmetrically distributed data, an adaptive generalized trimmed mean (AGTM) estimator is developed and employed to estimate the third-order cumulants. Using these truncation parameters the AGTM of the discrete data series are computed and it is seen that the AGTM performs better in estimating third-order comulants than the mean estimator.
3 citations
TL;DR: In this article, closed-form expressions for the generalised transfer functions of first and second order are derived for a class of non-Gaussian stationary input processes, and it is shown that the obtained parameters are optimum in the mean square sense.
Abstract: Some recent results relating to system identification are described and illustrated in this contribution. The system considered is nonlinear and time-invariant, being represented by a Volterra series up to second order. Closed-form expressions for the generalised transfer functions of first and second order are derived for a class of non-Gaussian stationary input processes. It is shown that the obtained parameters are optimum in the mean square sense. Once the system is identified, we derive a closed-form expression for the quadratic coherence that is a measure of the goodness of fit of the quadratic model. It is shown that this expression simplifies to well known results when the system is linear or its input is Gaussian. Furthermore, we develop estimates of the generalised transfer functions and the quadratic coherence from spectral and bispectral estimates, based on averaged periodograms and bi-periodograms of data stretches of the observed input and output of the system. This method is tested and validated by using simulated input-output data of a known quadratically nonlinear system, with known input signal statistic.
2 citations
TL;DR: A measurement system, the nine channel receiver for the HF- and VHF-band, which allows hardware independent the implementation of various direction finding algorithms, is presented and the results show the superiority of the MUSIC algorithm.
Abstract: Radio direction findings is of great significance especially in the field of electronic reconnaissance. There exist many radio direction finding algorithms, but most of them fail in interference fields caused by existence of more than one radiation source or by multipath transmission. High resolution spectral estimation techniques are useful to resolve interference fields with more than one incoming wave. In this paper one of these algorithms, the MUSIC (MUltiple SIgnal Classification) algorithm, is described. A measurement system, the nine channel receiver for the HF- and VHF-band, which allows hardware independent the implementation of various direction finding algorithms, is presented. Furthermore, in simulations and measurements, the MUSIC algorithm is compared with conventional beamforming techniques. The results show the superiority of the MUSIC algorithm
2 citations
TL;DR: In this article, the dispersion properties of the waveguide are taken into account by expanding the electric field in terms of waveguide modes; the modes are transformed by the mirrors.
Abstract: A new mode calculation procedure for unstabel waveguide resonators is presented. The dispersion properties of the waveguide are taken into account by expanding the electric field in terms of waveguide modes; the modes are transformed by the mirrors. This approach allows to determine the eigenvalues of resonators even with very high Fresnel numbers. Our results are close to those calculated with other methods
2 citations
TL;DR: The object of this paper is to do the inventor Steinbuch justice in his lifetime and to cause some reflections in German research administration people, how to avoid wrong decisions in future.
Abstract: In 1961 Karl Steinbuch published a paper on a novel neural system which he called «Lernmatrix». It attracted some attention but fell into oblivion very soon, in particular when supporters of artificial intelligence as e.g. M. Minsky demonstrated «convincingly» that these structural approaches were not worth much. In some respects it held true for the contemporary one layer perceptrons and adalines etc. but not for the multi layer «Lernmatrix». This can be shown by converting the unusual matrix representation into today's diagrams of neural networks. The result is a network which is almost identical with the main structure of present prevailing multi layer perceptrons. It is the object of this paper on the one hand to do the inventor Steinbuch justice in his lifetime and on the other hand to cause some reflections in German research administration people, how to avoid wrong decisions in future
2 citations
TL;DR: The known standard NCO is regarded as a special case of a generalized NCO, and the NCO design problem is reduced to a filter design problem [3], and especially for high requirements new effective structures are derived thereby.
Abstract: A new method to analyze Numerically Controlled Oszillators (NCO) is presented. In contrast to the known methods [1,2], which work with techniques of error calculation, the theory of linear time-variant systems [3,4,5] is used. The known standard NCO is regarded as a special case of a generalized NCO, and the NCO design problem is reduced to a filter design problem [3]. Especially for high requirements new effective structures are derived thereby.
1 citations
TL;DR: Methods for the security of the entire communication process including link management are discussed in Part II, which includes the integration of the system components to achieve a generaI concept in the form of a layered architecture, an appropriate key management and cryptographical protocols.
Abstract: A communication system for train control based on the GSM mobile radio standard was introduced in Part I. Cryptographical and error control mechanisms are required to ensure integrity and authentica-tion and have to be developed in accordance with the transmission standard, communication network and service definition. The message authentication code as the main security component for a single data block was analyzed and dimensioned by means of information theory in Part I. Methods for the security of the entire communication process including link management are discussed in Part II. Topics are the integration of the system components to achieve a generaI concept in the form of a layered architecture, an appropriate key management and cryptographical protocols as well as the adaptation to the GSM system
1 citations
TL;DR: In this article, the authors describe the methods and problems of simulating the electromagnetic field using the Finite Integration Technique (FIT), and the results for different regimes are summarized and presented within the context of accepted current literature.
Abstract: The calculation of the characteristics of car antennas represents a complex electromagnetic field problem because the influence of the car body has to be taken into account as exactly as possible. Numerical simulation can help to give an overview of the optimal position of a car antenna for different frequency ranges. This paper describes the methods and problems of simulating the electromagnetic field using the Finite Integration Technique (FIT). The results for different regimes are summarized and presented within the context of accepted current literature
TL;DR: In this article, a significant increase of the major-lobe peak reflection coefficient at microwave and millimetre wave centre frequencies can be achieved by optimizing the optical excitation wavelength as well as the surface recombination velocity and the carrier lifetime of semiconductor substrate.
Abstract: Based on earlier published results from theoretical and experimental investigations on light-induced distributed Bragg reflection waveguide gratings, a significant increase of the major-lobe peak reflection coefficient at microwave and millimetre wave centre frequencies can be achieved by optimizing the optical excitation wavelength as well as the surface recombination velocity and the carrier lifetime of semiconductor substrate. Further improvement of the reflection of the single-crystal full-semiconductor substrate formerly used by a ceramic one with a polycrystalline semiconductor film evaporated
TL;DR: In this paper, a concept and applications of some optimal equalizing antialiasing filters for the use in analog-digital-conversion are presented. But the proposed filters are not optimal with respect either to the (bounded) mean squared-or to the maximum norm.
Abstract: Topics of this paper are a concept and applications of some optimal equalizing antialiasing filters for the use in analog-digital-conversion. The filters are cascade combinations of analogue and nonrecursive digital systems, where benefits of oversampling are used to advantage. Equalizations of magnitude and phase or group delay, respectively, are performed in the passband by the digital filter. The effect of such equalizations in the time domain is investigated with respect to the step response, which is of special interest for measuring technique and signal analysis. The designed filters are optimal with respect either to the (bounded) mean squared- or to the maximum norm. A convex semi-infinite programming technique will be presented as a way of dealing with the proposed design problems. Furthermore, an easy implementable way will we described for one filter in detail.
TL;DR: In this article, the authors examined parametric density estimation of the decision signal for efficient simulation of optical heterodyne systems and proved that the power of the procedure is proved from three typical realized optical heterodynet systems the probability density function and bit error rate are compared.
Abstract: To estimate bit error probability we examine parametric density estimation of the decision signal for efficient simulation of optical heterodyne systems. The parameters are calculated by moment method. From 3 typical realized optical heterodyne systems the power of the procedure is proved. Both, probability density function and bit error rate are compared.
TL;DR: In this paper, a new finite element approach is demonstrated which is able to describe the electric field near the cone in a more effective way and at the same time reduces the necessary amount of computer time and memory by the use of special finite elements.
Abstract: The amount of emission current in vacuum microelectronic devices strongly depends on the electric field near the emitter. Simulation results of dependence of the electric field on different parameters (geometry, space charge) are shown for cone as well as for wedge emitters and important electrical parameters (current-voltage-characterics) are calculated. Finally a new finite element approach is demonstrated which is able to describe the electric field near the cone in a more effective way and at the same time reduces the necessary amount of computer time and memory by the use of special finite elements. The hereto essential field theory is also presented
TL;DR: A new type of signal processing is used for signal acquisition and coherent demodulation, which does not need auxiliary signals like suppressed carrier or residual sideband.
Abstract: In this paper first redundant (m-2)-coding is characterized. Using this code n bit symbols are converted to 1 bit symbols containing only one logical-one state. Next these symbols are parallel-series-AMI converted to a zero-mean pseudo ternary signal. Modulating a sinussoidal carrier with this signal a (m-2)-3APK-coded signal with low average signal power is generated, which can be transmitted by single-sideband transmission systems. Bit-error-probability of (m-2)-3APK-coded signals is calculated. These signals can be demodulated coherently by using carrier recovery circuits or non-coherently by using squaring circuits. For demonstration a (16-2)-3APK-coded SSB system is realized and error probability tests are performed. While using well-known WEAVER method of SSB modulation, a new type of signal processing is used for signal acquisition and coherent demodulation, which does not need auxiliary signals like suppressed carrier or residual sideband.
TL;DR: Simulations of a simple synchronisation circuit show that a word length of ten bit of the A/D-converter at the receive side is sufficient to reach a synchronisation error rate which is more than ten times lower than the symbol error rate of the best known C-8/4-PSK code.
Abstract: In this contribution a method for block synchronisation of time variant trellis coded 8/4-PSK signal sequences without using additional information is presented. The block structure of the coded signal is the result of using the 4- and the 8-PSK modulation alphabets in an alternating way. The different modulation alphabets correspond to different trellis segments which are compounded to the resulting block-trellis diagram. The Viterbi detector needs the correct information to which trellis segment the current receive signal belongs. It is shown that the block synchronisation can be performed by calculating two complex fourth order moments of the receive signal. Simulations of a simple synchronisation circuit show that a word length of ten bit of the A/D-converter at the receive side is sufficient to reach a synchronisation error rate which is more than ten times lower than the symbol error rate of the best known C-8/4-PSK code.
TL;DR: In this article, a Statistik von ungefaehr 500 Radarabtastungen des Olympuspfades zeigt gute Uebereinstimmung with gleichzeitig durchgefuehrten Bakenmessungen.
Abstract: Jahreshaeufigkeitsverteilungen der 20-GHz-Olympus-Bakendaempfung, Regenrate und Strahlungstemperatur werden verglichen. Aus Radiometer- und Radarmessungen in zwei orthogonalen linearen Polarisationen werden Tropfengroessenverteilungen abgeleitet. Eine Statistik von ungefaehr 500 Radarabtastungen des Olympuspfades zeigt gute Uebereinstimmung mit gleichzeitig durchgefuehrten Bakenmessungen.
TL;DR: In this article, a modification based on weighted Burg technique was proposed to reduce the variance of the frequency estimation, which was proved to be superior to the original coefficient-constrained lattice filter structure.
Abstract: The measurement of physical quantities based on estimating of single-sinusoid frequency is the starting point of this paper. The described method is particular interesting for robust estimating of frequency from shot data records. Potential applications of such a frequency estimator include the estimation of time-varying Doppler frequency shift in radar or Laser-Doppler-Anemometer. The starting point is a computationally efficient method based on coefficient-constrained lattice filterstructures (CLF) that proposed by Hu and Phan [1]. This method yields an unbiased frequency estimate independent of the initial phase, but the variance of the frequency estimation depends strongly on signal-to-noise ratio (SNR). The objective of this paper is to devise a modification based on weighted Burg technique to reduce the variance of the frequency estimation. The superiority of this modification will be proved.
TL;DR: In this article, an offset-4-PSK-system offsetmPSK system was proposed to avoid phase jumps of π for any m. This was shown to reduce the Spectrum-Spreading Effect in m-ary PSK-signals.
Abstract: Nonlinear amplification of heavily frequencyband limited nonconstant envelope m-ary PSK-signals (m = 4, 8, 16,...., 2 n ), (n=2, 3, 4 ;...) leads to the Spectrum-Spreading-Effect which degrades the Bit Error Probability. Strong envelope fluctuations occur especially during phase transitions of π. Starting from the well known Offset-4PSK-system Offset-mPSK-systems are presented in this paper avoiding phase jumps of π for any m. Hence a more constant envelope is obtained. By means of a redundant encoding process which is also presented in the paper phase jumps occurring in m-ary PSK-systems can be minimized to n/m. Through that for any m a constant signal envelope is obtained if modulation is carried out by sequences of rectangular pulses or sequences of weak frequencyband limited rectangular pulses.
TL;DR: It is found that for the implementation of the prime factor FFT algorithm on a modern digital signal processor (DSP), e.g. the ADSP 2100, the shortlength DFT-modules exhibiting the minimum multiply configuration as developed by S. Winograd are not the optimum choice.
Abstract: We found that for the implementation of the prime factor FFT algorithm on a modern digital signal processor (DSP), e.g. the ADSP 2100, the shortlength DFT-modules exhibiting the minimum multiply configuration as developed by S. Winograd are not the optimum choice. New modules which yield an increase of up to 15% in execution speed and a 1 bit increase in accuracy are designed by a novel powerful method
TL;DR: In this article, the blind equalization of non-minimum phase channels driven by correlated signals that are not linear processes is studied and the unknown channel can be identified using the following methods: Dual Mode Maximum Kurtosis Deconvoltion (MKD), Fixed Pole IIR MKD, Decision-Feedback MKD.
Abstract: We address blind equalization of nonminimum phase channels driven by the correlated signals that are not linear processes. First we discuss the channel model for partial response signals (and AMI code), which have nulls in their spectrum. We show that the unknown channel (or equalizer) can be identified using the following methods : Dual Mode Maximum Kurtosis Deconvoltion (MKD), Fixed Pole IIR MKD, Decision-Feedback MKD.
TL;DR: In this article, bistatischer Streufeldberechnungen nach der Integralgleichungsmethode (IEM) and der physikalisch-optischen Hochfrequenznaeherung (PO) with Messergebnissen werden verglichen.
Abstract: Die Ergebnisse bistatischer Streufeldberechnungen nach der Integralgleichungsmethode (IEM) und der physikalisch-optischen Hochfrequenznaeherung (PO) mit Messergebnissen werden verglichen. Die Untersuchungen wurden an drei elektrisch ideal leitfaehigen Testkoerpern mit Ausdehnungen von einigen Wellenlaengen durchgefuehrt. Die Ueberpruefung der Rechnungen erfolgt durch Messungen an den Testkoerpern im Millimeterwellenbereich (94 GHz).
TL;DR: In this paper, the basic principle of the generation of high resolution complex target microwave images from scattered fields is outlined, and the derivation of so-called target characteristic parameters as well as target characteristic polarizations is described.
Abstract: The basic principle of the generation of high resolution complex target microwave images from scattered fields is outlined, and the derivation of so-called target characteristic parameters as well as target characteristic polarizations is described. Special emphasis is given to the analysis of localized scattering centres. A fast procedure for the generation of two-dimensional microwave images under real-time conditions is explained in detail. Finally, two methods for stuying bistatic scattering effects on a monostatic measurement range are introduced.
TL;DR: In this paper a method is presented to replace the succeeding transforms in a transform coding system that contain several transforms in succession by a single general transform.
Abstract: In this paper a method is presented to replace the succeeding transforms in a transform coding system that contain several transforms in succession by a single general transform. The replaced transform can be those which use multiple overlapping blocks and the principle of Time Domain Aliasing Cancellation (TDAC). So it is possible to describe with this method a hybrid system containing a subband filter and a TDAC-transform in succession. Such a hybrid system is used in the ISO/IEC Standard 11172-3 Layer 3.
TL;DR: A communication system for train control based on the GSM mobile radio standard is introduced as an example of a safety-related application, but data transmission is exposed to stochastic errors as well as intelligent cryptographical attacks.
Abstract: A communication system for train control based on the GSM mobile radio standard is introduced as an example of a safety-related application. However, data transmission is exposed to stochastic errors as well as intelligent cryptographical attacks. In order to prevent or detect such falsifications, methods of cryptography and error control coding are required, the message authentication code (MAC) beeing the most important component. Part I deals with the analysis of the MAC by means of information theory. Topics are its interpretation as an error detection code and its design and dimensioning in accordance with the constraints of security and reliability. Part II [1] presents the general concept for the safety-related application in the form of a layered architecture and the adaptation to the GSM system
TL;DR: This paper shows, that a combination of QPSK and FSK has power advantages in comparison with n-PSK or n-QAM of the same order.
Abstract: The combination of phase- and frequency modulation allows to realize modulation schemes with a high power efficiency. This paper shows, that a combination of QPSK and FSK has power advantages in comparison with n-PSK or n-QAM of the same order. Without pulse shaping, the four dimensional combined phase- and frequency modulation requires no greater 99 % bandwidth than a two dimensional modulation of the same order. Furthermore, it is possible to reduce the bandwidth by pulse shaping. The proposed modulation schemes are used in such cases, where the power efficiency is of great interest.
TL;DR: In this paper, the problems of blind equalization and system identification are discussed, i.e., adaptive algorithms which do not use any training sequence, and the main result is a closed-form eigenvector solution to blind equalisation.
Abstract: In this paper the problems of blind equalization and system identification are discussed, i. e. adaptive algorithms which do not use any training sequence. The main result is a closed-form eigenvector solution to blind equalization. This relationship leads directly to a closed-form solution to blind system identification which is an eigenvector problem, too. On the basis of these results iterative algorithms can be developed which show very fast convergence speeds compared with alternative methods known so far and, furthermore, are very robust with respect to a system order overfit and the influence of additive gaussian noise.
TL;DR: In this paper, it is shown that the power spectral density of the equivalent photocurrent noise can be reduced significantly by a simple series inductance, and a lower frequency bound for the use of transmission lines in matching networks is given.
Abstract: There is a theoretical limitation for the noise matching in an optical receiver between a field effect transistor in the input stage and the photodiode. This theoretical limitation is compared with values of realizable matching networks. It is shown that the power spectral density of the equivalent photocurrent noise can be reduced significantly by a simple series inductance. The use of more complex matching networks yields only a small improvement. Furthermore, a lower frequency bound for the use of transmission lines in matching networks is given
TL;DR: The second-order polyspectrum as mentioned in this paper is defined as the Fourier transform of the second order cumulant function and is defined without requiring stationarity, which is the generalization of the power spectrum to the analysis of nonstationary processes.
Abstract: The second-order polyspectrum is the Fourier transform of the second-order cumulant function and is defined without requiring stationarity. It is the generalization of the power spectrum to the analysis of nonstationary processes. The second-order polyspectrum is capable of measuring, identifying, and characterizing the potential information concerning the second-order time-dependencies of a nonstationary process. In this paper, we apply the second-order polyspectrum. We use the second-order polyspectrum as a diagnosis and classification tool for simulated data, biological data, and sonar data. Finally, we investigate a beamforming procedure for nonstationary seismic data.