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İmpulsif gürültünün incelenmesi ve V.32 modemin impulsif gürültülü ortamda hata başarımı

Başlık çevirisi mevcut değil.

  1. Tez No: 55689
  2. Yazar: ERCAN BÜYÜKKARA
  3. Danışmanlar: DOÇ.DR. ÜMİT AYGÖLÜ
  4. Tez Türü: Yüksek Lisans
  5. Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1996
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 112

Özet

ÖZET Bu tez çalışmasında, impulsif gürültünün V.32 modem içeren bir sayısal iletişim sistemi üzerindeki bozucu etkisi araştırılmıştır. Bu nedenle impulsif gürültü incelenerek, kurulan impulsif gürültü modelinin, değişik darbe biçimleri ve darbe süreleri için bilgisayarda üretilmesi yoluna gidilmiştir. Daha sonra kafes kodlamalı modülasyon tekniğini kullanan V.32 modem yapısı araştırılarak, bu modemi içeren ve Gauss İçin optimum standart alıcı yapısını kullanan bir iletişim sisteminin, Gauss ve impulsif gürültülü ideal karakteristikli kanallar için hata başarımları bilgisayar benzetimi yoluyla incelenmiştir. Bilgisayar benzetim modeli oluşturularak elde edilen sonuçlarla, hata başarım eğrileri çizilmiştir. İmpulsif gürültünün, sürekli gürültüye göre, sistem başarımını daha kötüye götürdüğü görülmüş ve impulsif gürültünün darbe biçiminin ve darbe süresinin sistem başarımı üzerine etkileri, elde edilen sonuçlara göre değerlendirilmiştir.

Özet (Çeviri)

SUMMARY ANALYSIS OF IMPULSIVE NOISE AND THE V.32 MODEM PERFORMANCE IN IMPULSIVE NOISE Nowadays, the trend in the communication world is form analogue to digital. Consequently a major effect has been oriented towards the design, development and study of digital systems. The performance of digital communication systems is affected by the presence of noise. The noise can cause a very severe degradation in the performance of a digital system. The exact degree of degradation depends upon the type of noise. However, most of the studies on noise effects have been confined to system evaluation in additive continuous type of noise. On the other hand, when the noise is impulsive, serious problems arise and the performance degradation due to the impulsive form of noise is more severe than due to the continuous form in digital communication systems. Thus, for certain applications it becomes important to analyse the effect of additive impulsive noise. For example, the recent increase in data communication over telephone lines has forced designers to account for switching noise. Further, several investigators have evaluated the degrading effect of the non-Gaussian noise on various types of digital signals. A variety of naturally occurring and man-made phenomena exhibit“impulsive”noise behavior. Channels operating in the ELF (extremely low frequencies) and VLF (very low frequencies) bands experience atmospheric discharge; the radiofrequency range comprising HF, VHF, and UHF is plagued by man-made noise in metropolitan areas, and generally contaminated by galactic and solar noise. Wire communications is subject to lightning and switching noise. This various phenomena induce“impulsive”- Vll -noise in communication systems. Impulsive noise also occurs naturally within some communication systems, for example in optical receivers. While the term impulsive is suggestive, there is not a standard or unique definition [1]. However, the most important distinguishing property of impulsive noise from the other noise types is that this type of noise is noncontinuous, consisting of irregular pulses or noise spikes of short duration and of relatively high amplitude. The noise occurs over a wide range of frequencies and may be predominantly impulsive or continuous depending upon the frequency, bandwidth, geophysical location, time of the day and season. In tropics which are the world centries of thunderstorm activity, the noise may, quite often, be impulsive. Extensive studies have been made on the amplitude and time characteristics of this type of noise. The amplitude probability distribution is known to be non-Gaussian [2]. In simulation studies, as impulsive noise sources are modeled; as a pratical matter, it is desirable to have a single general model which can represent the behaviour of a variety of sources simply by changing a small number of parameters. Such a model is presented here. In this thesis, after an extensive literature investigation of the impulsive noise, impulsive noise is modeled, and generated for various pulse shapes and various pulse durations in computer. Then V.32 modem structure using trellis coded modulation technique is investigated, and the performance of digital communication system using a V.32 modem and standard receiver (optimum for Gaussian) is analysed by a computer simulation for channels with Gaussian and impulsive noise. In this examination, the channel's disturbing effects due to its transfer function characteristics have not been considered. Stock, B.W. and Kleiner, B. [3] presented the results of a statistical analysis of impulsive noise on some telephone lines. The analysis consists of two stages: data analysis stage, where the data are characterized through various nonparametric statistics and a model building stage, where the data are matched to models. According to data analysis, telephone noise consists of a deterministic component and a stochastic component. It was assumed that these components can be added. The data analyzed here suggest that the stochastic component is stationary over short periods of time and distinctly nongaussian. Two simple models have been proposed for the nongaussian noise, one based on stable distributions, the other on a mixture of a gaussian process and a nongaussian-filtered Poisson process. Based on the data analyzed here, both models agree intuitively with the physical processes generating telephone noise. But, a - viamore general class of models was never investigated that includes the gaussian-plus- filtered-Poisson process as a special case. Modestino, J.W. and Sankur, B. [4] developed a model for ELF/VLF noise and described its statistical properties. The model consists of the linear combination of a impulsive noise and white Gaussian noise. This model is intuitively satisfying and takes into consideration the underlying physics of the noise phonema. Furthermore, it is analytically tractable as n'th order statistics can be evaluated. The model can be characterized by a few significant parameters and these can calibrated in the light of measured data. The ELF/VLF noise model can easily be generalized to represent noise phonema in a variety of frequency bands and physical environments. On the other hand, the performance of linear and a class of nonlinear receivers in impulsive noise has been analyzed as an application of this model. The degrading effects of the impulsive noise on various types of digital signals are also investigated. For example, Huynh, H. and Lecours, M. [5] analysed the performance of noncoherent M-ary ASK, PSK, and FSK systems in nongaussian noise, more particularly in impulsive noise modeled as an unfiltered generalized stationary Poisson process. In the same way Ziemer, R.E. [6] concerned with the calculation of the probability of symbol error and comparison of coherent, M-ary, digital communication systems operating in impulsive noise environments. Experimental measurements of the error probability are presented and compared with theory. Comparisons of various modulation systems are made under the constraints of equal rate and equal bandwidth. Jain, V.K. and Gupta, S.N. [7] analyzed the performance of a binary baseband system in the presence of mixture of continuous and impulsive noise plus intersymbol interference. The results obtained are very general and the system performance in special cases like purely continuous noise or purely impulsive noise with or without intersymbol interference can be easily derived from the general results. Here also, degradation due to the impulsive form of noise has been shown to be generally more severe than that due to the continuous form. These three investigators also, have analysed the digital modulation/demodulation systems in impulsive noise taking the receiver (optimum for continuous Gaussian noise) to be a matched filter. In Section 2, impulsive noise is described. Models of impulsive noise developed by Stock, B.W. and Kleiner, B. [3] and Modestino, J.W. and Sankur, B. [4] are examined. However, an atmosferic noise model developed by Omura, J.K. and Shaft, P.D. [8] for analyzing the performance of modulation/demodulation systems operating at VLF (very low frequencies) frequencies is also examined. Also in section 2, some IX -methods are explained to counteract the impulsive noise, these methods affecting an amplitude-based or time-based modification to an existing receiver. Further, for optimum detection of binary signals in impulsive noise, optimum and locally optimum receivers (weak signal), consists of nonlinear device followed by a linear filter, considered by Jain, V.K. and Gupta, S.N. [2], are examined. In [8] the performance of modulators and demodulators at very low frequencies (VLF) are also considered for comparison. In Section 3, Trellis coded modulation (TCM) technique involved by Ungerboeck, G. [9], [10], [11], is presented and the basic principles are determined. The differences of this technique from the classical error correction coding are explained. The design of PSK signals based on TCM techniques are shown. Although 3-4 dB coding gains with TCM technique can be obtained, phase ambiguities in the extraction of the carrier reference in receiver cause received signal elements be rotated according to transmitted ones. Lee-Fang Wei [12], [13]; by using differential coding technique and matching binary sequences to the real and rotated channel signals has shown that those phase ambiguities can be eliminated. However, the design procedure for eight-state rotationally invariant convolutional code with 32-CR expanded signal space is explained for CCITT V.32 modem structure. In Section 4, impulsive noise model, for simulation studies of the communication system using V.32 modem, is described. First, the impulsive noise is modeled based on [1], [3] and [4]. Then, according to this model, the impulsive noise is generated in computer, for several values of the model parameters. In Section 5, in order to study the error performance of V.32 modem a simulation model using optimum receiver structure for continuous Gaussian noise is constructed. By using this model, the bit error performances of channels with Gaussian noise and impulsive noise are examined for various phase shapes and pulse durations of the impulsive noise. As a result, we can see that the impulsive noise severely degrades the system performance when the bit error performances are examined. This degradation due to the impulsive noise is more severe than due to the continuous Gaussian noise. The exact degree of degradation depends upon the pulse durations and pulse shapes of the impulsive noise. If the degradation is analysed to the pulse durations of the impulsive noise; a smaller bit error probability can be obtained by decreasing the average number of occurrences of the impulsive noise spikes over one noise pulse. Similarly, a smaller bit error probability can be obtained by decreasing the skewness parameter Vd. On the other hand, if the degradation is analysed to the pulse shapes of impulsive noise, h(t) = A. e"at pulse shape for impulsive noise x -severely degrades the system performance compared to the two other pulse shapes. On the other hand, the bit error performance is improved with increasing oscillation frequency of the impulse envelopes w. However, the exact degree of degradation due to the impulsive noise also depends upon the signal-to-Gaussian noise ratio. When the signal-to-Gaussian noise ratio increases, the bit error probability Pb decreases. All of these interpretations, can be deduced from the simulation curves given in Section 5. XI

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