ISSN:1124-318X    

DOI:10.1002/ett.4460050302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:1124-318X    

DOI:10.1002/ett.4460050303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

ISSN:1124-318X    

DOI:10.1002/ett.4460050304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe performance of coherent receivers in optical communication systems is impaired by polarization mismatchings between the received optical signal and the local laser field. One of the most effective techniques to cope with such a phenomenon is the use of polarization‐diversity receivers which, at the cost of a higher complexity in the optical front‐end and a small performance degradation, guarantee insensitivity to changes in the state of polarization of the received signal. The goal of this paper is twofold: firstly, we present here an exact theoretical analysis of balanced polarization‐diversity receivers for ASK, FSK or DPSK modulation schemes in the shot‐noise‐limited regime, deriving closed‐form expressions for the receiver Bit Error Rate (BER) of each of the cited modulations. Secondly, we assess the sensitivity of the same receivers to a slowly‐varying frequency detuning of the heterodyne laser, in order to allow for a well‐aimed design of the Automatic Frequency Control (AFC) circuit of the local laser. This work was performed in the Framework of the “Telecommunications” project funded by the Italian National Res

ISSN:1124-318X    

DOI:10.1002/ett.4460050305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe phase error statistics of a first‐order phase‐locked loop in the presence of multiple cochannel CW interference and additive noise is derived. An accurate numerical solution based on the nonlinear theory is outlined. Approximate analytical formulae are obtained from the linear theory for low interference‐to‐signal ratios. The linear analysis shows that the phase error statistics in the linear approximation depends only on the interference‐to‐signal ratio independent of the number of interferers and the interference power distribution. Errors appeared in some of the numerical results reported by Yoon and Lindsey [1] in the single interferer case are identified and corrected. Numerical examples forN= 2, 3, and 6 interferers of equal power are given. The effect of the interference power distribution is i

ISSN:1124-318X    

DOI:10.1002/ett.4460050306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractSite diversity is a classical countermeasure to rain attenuation in satellite communications systems at frequencies above 10 GHz. The paper has extended the Two‐Layer Rain Model to predict site diversity performance. Simple physical and statistical hypotheses have been assumed from which the formulae to calculate the bivariate probability distribution of the diversity link have been derived (it is not a best fit model) by standard calculations. The model has been then tested against a large experimental data set of direct (beacon+radiometer) and indirect (radar) experiments, with frequencies up to 30 GHz and distances from 2 km to 48 km. Defining the error ϵ =gpre. –gmea, whereg=G/Ais the ratio between the diversity gain and the single link attenuation (at a given probability), we have obtained= 0.037 and √= 0.129. The model is thus not biased. Similar results have been obtained when ϵ is conditioned to frequency or site separation. The predictions have been then compared to those obtained from Hodge's well‐known formula. The two methods give about the same statistical errors: this means that the simple physical and statistical hypotheses of the Two‐Layer Rain Model hold on average. As the present model needs only a meteorological quantity (i.e. the rain‐rate distribution) and gives a complete “picture” of the statistical process of attenuation, its applicability is more general t

ISSN:1124-318X    

DOI:10.1002/ett.4460050307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA decision feedback equalization scheme comprising of a generalized adaptive infinite impulse response delay filter in the feedback path is proposed and used for equalization of high‐rate digital subscriber loops including severe intersymbol interference and near‐end crosstalk colored noise. The feedback filter compensates the long postcursor intersymbol interference due to the high sampling rate and is composed of parallel sections having one, two or four coefficients and a delay element. The structures of the sections are determined adaptively and in a step‐by‐step procedure. Because of the parallel and, at most, two‐pole sections of the generalized adaptive infinite impulse response delay filter, the stability monitoring requires essentially no computations. To reduce the noise enhancement effect of the prefilter, an adaptive noise predictor is also used. Computer simulation results demonstrate the performance of the proposed structure compared to the conventional decision feedback equalizer with a finite impulse response feedback filter. The main advantage of the proposed system is the significant reduction in the number of coefficients and consequently the adapta

ISSN:1124-318X    

DOI:10.1002/ett.4460050308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractPseudonoise (PN) code tracking loops are essential in various direct‐sequence spread‐spectrum (DSSS) systems for both, communication and navigation applications. This paper shows how to optimize the so‐called modified code tracking loop (MCTL) of first‐ and second‐order by using the mean time to lose lock (MTLL) as a performance criterion. The state equation of the first‐order MCTL is related to the Smoluchowski ‐ Kramers approximation of a second‐order system described by the Langevin equation of motion. For such a specific system, the MTLL is known by the work of Kramers. In case of the second‐order type II loop (having two perfect integrators), which cannot be described by the Langevin equation, the computation of the MTLL is based on the singular perturbation method. Optimal parameters maximizing the MTLL under the constraint of Doppler effects and the channel noise are derived for both type of loops, resulting in very simple expressions that can be used immediately for a practical loop design. Measurements performed for the first‐order MCTL verify the theoretical optimal loop parameters and indicate that the time to lose lock is exponentially distributed. Monte Carlo simulations confirm also very well the theoretical results in case of a second‐order loop and hence, show that the application of the singular perturbation method yields an excellent appr

ISSN:1124-318X    

DOI:10.1002/ett.4460050309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe detection list of sequential detection algorithms like the Generalized‐Stack‐Algorithm normally includes paths with different search lengths. Therefore, a special metric, the socalled Fano metric, has to be used to allow a comparison between the path metrics. A drawback of the Fano metric is its great computational effort in the case of a time‐variant channel impulse response which occurs typically at data transmission over frequency‐selective mobile radio channels. In this paper the most expensive part of the metric is replaced by a bias depending on the instantaneous signal‐to‐noise ratio and the phase characteristic of the channel. Simulation results obtained for the GSM system show the good performance of this method in view of bit error rate and computational complexity relative to the optimum Viterb

ISSN:1124-318X    

DOI:10.1002/ett.4460050310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractAn improved method is presented to describe handwritten characters in terms of Generalized Fourier Descriptors (GFDs). There are two important problems in describing handwritten characters, namely straight line fitting and circle matching problems. The appropriate methods for obtaining the solutions of these two problems are presented. These results were applied on handwritten characters in oeder to have a simple character description in which characters are approximated by straight line pieces and circle segments. Using these results, calculations were then performed on the characters to obtain their GFDs. These calculations can be useful in the fields of character recognition and signature validation. Moreover, since this description is based on simple curves, it will have rfficient coding when data tranamission is concerned.

ISSN:1124-318X    

DOI:10.1002/ett.4460050311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY