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Bina içi propagasyonun sisülasyon yardımıyla incelenmesi

Başlık çevirisi mevcut değil.

  1. Tez No: 75126
  2. Yazar: ERDİNÇ TEKBAŞ
  3. Danışmanlar: PROF. DR. ERCAN TOPUZ
  4. Tez Türü: Yüksek Lisans
  5. Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1998
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Elektronik ve Haberleşme Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 104

Özet

ÖZET Bu tezde, binaiçi propagasyonun simülasyon yardımı ile incelemesi yapılmıştır. Tüm dünyada telsiz haberleşme teknolojilerine rağbet giderek artmaktadır. Bu durumda, fabrika, ofis veya ev gibi binaiçi mekanlarda propagasyon modellemesi büyük önem kazanmaktadır. Bir bina içi sistem tasarlanırken, özellikle iki parametre gözönüne alınır: Ağırlaştırılmış grup gecikmeleri farkı(rms delay spread) ve fading. Bu tezde, büyük ölçekli ve küçük ölçekli fading incelemesi yapılarak, belli bir verici-alıcı uzaklığı için ortalama sinyal şiddeti ve çok küçük bir alanda bu sinyal şiddetinin hızlı değişimleri incelenmiştir. Çalışmalarda DECT sistemi örnek alınarak, sayısal hesaplarda çalışma frekansı 1.8 GHz civarında alınmıştır. Boş ve izole bir oda içindeki verici ve alıcı anten ile yapılan simülasyonda, Geometrik Optik yöntemi kullanılmıştır. İmaj yönteminden yararlanılmış, alıcıda katkı yapan tüm ışınlar gözönüne alınarak hassas bir sonuç elde edilmeye çalışılmıştır. Yansıma sayısı arttıkça alıcı noktalarda hesaplanan alan şiddetlerinin belirli değerlere yakınsadığı ve dolayısıyla, ışın serisinde üç yansımaya kadar olan terimlerin alınmasının yeterli olacağı gözlenmiştir. Simülasyonun doğruluğu açısından, verici ve alıcı anten yükseklikleri farklı olduğunda ve birden fazla yansıma gözönüne alındığında ortaya çıkan depolarizasyon etkisi incelenmiş ve tasarımda konulacak marjlar ile bu etkinin ihmal edilebileceği gösterilmiştir. Alıcıdaki alan şiddeti değerlerine smoothing uygulanmış, böylece büyük-ölçekli ve küçük-ölçekli fading' e bakılmıştır. Bulmuş olduğumuz simülasyon sonuçlan, Rappaport-Sandhu'nun [14] ampirik sonuçları ile karşılaştırılmış ve uyum içinde oldukları görülmüştür. Ayrıca, iki komşu odada bulunan verici ve alıcı anten arasındaki iletim de incelenmiştir. İki oda arasındaki duvarın kalınlığının propagasyon üzerindeki etkileri tartışılmış ve duvar kalınlığım gözönüne alarak elde edilen simülasyon sonuçlan, duvar kalınlığının ihmal edilmesi durumundaki sonuçlarla karşılaştırılmıştır. Tasarımda konulacak belli marjlar ile bu etkinin de ihmal edilebileceği gösterilmiştir. İki odalı durum için, üç yansımalıya kadar ışınlar için imaj ağacının nasıl oluşturulduğu gösterilmiştir. İki odalı simülasyonda, ikinci odadaki istenen yüzeylerin herbiri üzerinde Geometrik Optik yöntemi ile alan dağılımını bulmak çok hesap gerektireceğinden hibrit bir yöntem geliştirilmiştir. Verici anten ile alıcı düzlemi arasında yeteri kadar uzaklık olduğunda, alan değişimi tüm düzlem üzerinde global olarak ifade edilmeye çalışılmıştır. Parabolik Denklem-Işın Optik(PERO) yöntemi denilen bu teknikte, ikinci odanın eksenel yöndeki karşılıklı duvarları üzerinde alan dağılımı Işın Optik yöntemi ile bulunmuştur. Bu yüzeylerdeki ışınların oda içine yayılan ışınlar olduğu düşünülmüştür. Bu alanların belli aralıklarla oda içerisinde istenilen yüzeye çekilmesi ve süperpozisyon yapılması ile yeni alan dağılımı bulunmuş ve Geometrik Optik 'yöntemi ile o yüzeyde bulunan simülasyon sonuçları ile karşılaştırılmıştır. Kullanılan Parabolik Denklem algoritması dar açılı bir algoritma olduğundan, yüzeyin orta kısımlarında bulunan sonuçların uyum içinde olduğu gözlenmiştir. X

Özet (Çeviri)

SUMMARY In this study two simulation models are developed and used to investigate several features of radio wave propagation in indoor environments. The aim in propagation modelling is to find impulse response function and coverage. In this thesis, emphasis is given on coverage characteristics and computed results for different indoor environments given. Two techniques are developed to investigate fading characteristics of wireless indoor propagation, namely, an image-based ray tracing algorithm and a hybrid algorithm -called Parabolic Equation-Ray Optics(PERO)~ It is known that, prior to the advance of wireless telephony, about 70 % of the calls did not reach the called party. Wireless communication technologies have therefore found a futile ground of growth. Today wireless communication technologies are widely used in houses, factories, offices etc. In this context, the design of indoor systems has also been gaining importance. In designing an indoor system, there are two important characteristics to be considered : Rms delay spread and fading. In this study, we investigated only the fading characteristics of the channel. We have considered two different environments: an empty,isolated room and two adjacent rooms. Using various typical sets of parameters we have calculated the variation of the signal strength with the aid of the algorithms described above. In this thesis, we propose two methods, each one of which may provide definite advantages with respect to the other for certain problem types. The first approach is an image-based ray tracing model which is a simple algorithm when transmitter and receiver are in the same room and when contributing terms of the ray series is limited to no more than three or four reflections. The second model is a hybrid model which uses both Geometric Optics method and Parabolic Equation method together. This hybrid method has advantages when the room wherein the signal strength has to be determined does not contain the transmitter, and hence the straightforward application of the ray method becomes cumbursome and inefficient. The developed methods are applicable to all indoor wireless systems above 1 GHz. However, due to its more demanding nature in terms of the tolerances in designing parameters and due to its prosperious technological future, the DECT system is used as a reference model in performing numerical calculations. In Chapter 1, an introduction to the subject is given. We begin by outlining, the need of developing wireless communication systems, and present a short historical survey of these systems. The main standarts of cordless and mobile systems, their features and their differences are also given in this chapter. xivRelevant features of the DECT system are introduced in Chapter 2. The layers of DECT system are given and reviewed in some detail. The technical and functional featuresof the DECT system are also explained and the advantages of this system are discussed. Adjacent channel and co-channel interference issues are also addressed and intersymbol interference is defined. In Chapter 3, the mechanisms of multipath interference in mobile radio channels are explained together with the constraints brought by the multipath. The effects of multipath is examined. Impuls response model of a multipath channel is developed and is shown that a mobile radio channel may be modeled as a linear filter with a time varying impulse response. Large-scale and small-scale propagation models predict the mean signal strength for an arbitrary transmitter-receiver (T-R) seperation distance and are useful in estimating the radio coverage area of a transmitter. On the other hand, small scale propagation or fading models characterize the rapid fluctuations of the received signal strength over very short travel distances (a few wavelengths) or short time durations (on the order of seconds). In Chapter 4, the main propagation mechanisms, namely: Reflection, diffraction and scattering are investigated. In the algorithms developed in this thesis we consider only reflection and transmission. These mechanisms can be addressed within the realm of the standard ray (or geometric) optics. Geometric Optics method used in establishing the ray tracing method is briefly introduced. It is well known that, certain boundary value problems can be significantly simplified by casting the original problem into an equivalent one via introducing image sources and removing certain boundaries. This approach is referred to the image theory. Image constructions can easily be adapted to indoor propagation channels which generally involve plane parallel reflecting surfaces. In this thesis, image theory is used in order to trace the rays emanating from the transmitter and arriving the receiver. When a radio wave propagating in a medium impinges upon another medium having different electrical properties, the wave is partially reflected and partially transmitted. The fundamental equations defining reflection and transmission of the rays through the walls are given. The electric field intensity of the reflected and transmitted waves may be related to the incident wave through the Fresnel reflection coefficients. The reflection coefficient is a function of the material properties, and generally depends on the wave polarization, angle of incidence and the frequency of the propagating wave. The reflection coefficients are calculated and the results are given in graphical form for a number of cases, also including some lossy dielectrics as a function of the incidence angle and polarization. Permitivities and conductivities of several materials which are likely to be used in indoor environments are given in tabular form as a function of operating frequency. XVGenerally one only considers horizontal (E-field is perpendicular to the plane of incidence and vertical (E-field is parallel to the plane of incidence) polarizations, since the description of the reflecting phenomena is then significantly simplified. However, in indoor environments the polarization of the ray fields is subject to change upon each reflection. In order to obtain accurate results, one should therefore properly account for the depolarization effects. Depolarization will be an issue, when the transmitter and receiver hights are not equal or when two or more ray reflections are to be considered. An algorithm is developed to trace the polarization changes after each reflection which allows us to investigate the effect of the polarization changes on received power level. In general the room containing the receiver cannot be considered as an isolated room and ray interactions with neighbouring rooms have to be considered. In order to investigate these interactions we took a simplified model environment consisting of two adjacent rooms, which interact solely by the common wall between them. We have then investigated the cases when transmitter and receiver are in the same room and when they are in different rooms. The effect of the electrical parameters and thickness of the common wall on the received power is examined. The incident wave is partly reflected and partly transmitted at each boundary. Each reflected wave will itself again be partly reflected and transmitted and this process will continue, leading to an infinite ray series. However, for moderately thick walls these ray interactions can be dealt with collectively. When observed over a time interval which is large in comparison to the relevant ray arrival times, these waves will give rise to resultant reflected and transmitted waves which can be calculated by summing the corresponding“infinite”series. This approach has been followed in the thesis, which corresponds to a“thin wall”assumption. Another factor which has to be considered is that, the path of the transmitted ray is parallel to the path of the incident ray, however it is shifted by an amount which depends on the parameters of both the ray and the wall. These shifts are calculated and the ray fields are corrected accordingly whenever necessary. As noted above, in this thesis image theory is used to obtain the ray paths. An algorithm is developed to calculate ray reflection points and to trace the rays in three dimensions by use of the image tree of the source. Construction of the image tree also helps to perform a more efficient ray tracing, since all derivative branches of the images which do not reach to receiver point can be discarded. Because of the complexity of the problem and excessive computation time requirements, we implemented 3D ray tracing model including only ray fields with up to three reflections. When the number of reflections and transmissions increases, ray field amplitudes decrease so that the ray series may be truncated beyond an upper limit. Thus there is always a trade off between accuracy and computational efficiency. The image trees are given both for an empty and isolated room and also for two adjacent XVIrooms. It is shown that when all rays with up to five reflections are considered, the element of the ray series increases to reach 9000 for the two room problem. Which clearly demonstrates that optimal ray tracing methods should be developed when higher numbers of reflections are to be considered. In Chapter 5, a new method is developed, called Parabolic Equation-Ray Optics(PERO). If there are two adjacent rooms, Geometric Optics may be used to find the power level at a number of potential receiver locations in either room. However, this will be not an efficient way of attacking the problem when it is desired to find it at a large number of receiver locations. In particular, if one is interested in calculating the power level everywhere in the second room, new approaches have to be introduced. We have shown that, when the transmitter and the receiver are in different rooms and well-seperated, and the propagation to receiver locations of interest is predominantly paraxial, then the variation of the fields may be formulated globally. Such a global description is provided by the Split-Step Parabolic Equation(SSPE) type solutions. SSPE provides a framework which serves to advance the given initial field distribution on the reference surfaces. In this method, ray optics will be used in constructing the required initial field distribution on the reference surfaces. Therefore, the proposed method will be referred to the hybrid Parabolic Equation-Ray Optics method(PERO) PERO algorithm can be outlined in two steps: 1) The calculation of the electrical field component corresponding to waves propagating in +z direction on the cross sectional surface at, say z=d (See Fig.5.2) and corresponding to waves propagating in -z direction on z=l. 2) The use of PE to propagate these field distributions from each one of the walls to surfaces parallel to the chosen wall, taking always the surface normal direction(inward directed) as the axial direction of PE. The initial fields are advanced in steps of Az in both directions and the field distribution is found as a superposition of forward and backward propagating paraxial spectra. In Chapter 6, the algorithms developed in the thesis are applied to test problems and numeric solutions are obtained. A few examples of these tests will be described below: In the first example, an empty and isolated room is considered. The images of the transmitter are found and the ray paths connecting the transmitter to the receiver are created. Rays up to the three reflections are considered. Analysis are made for direct+l.,direct+l.+2. and direct+l.+2.+3. reflections. Small-scale fading may be seen clearly. It is shown that the relative received power level converges everywhere as the reflection number increases. By applying smoothing technique, large-scale propagation model is obtained. The variation of the relative power versus range is shown in Figure 1 for different numbers. The parameters used in calculations are listed in the main text (See page 60) xviiI Direkt' 1. in smooth ingl i durumu I Direkl+1+2. in smoothing! i durumu |Direkt+l.+2.+3. ün smoothingli durumu Direkt ışın durumu 10 Uzattım) Figure 1 The variation of relative received power with range In the second example, depolarization effects are considered. When antenna heights of the transmitter and the receiver are equal, and when only single reflections are considered, depolarization effect does not occur. However, when antenna heights are different and three reflections are considered depolarization effects become discernible. This is demonstrated in Figure 2 for the case when up to three reflections are considered and antenna heights are different. The parameters used in the calculations are listed in the main text (See page 71). Since depolarization effects are generally small, they may be ignored provided that some extra margin is allowed in designing the system. WillDcpolarizayon etkisi gözönüne almmanııstır. Depolarizasyon etkisi gözönüne alınmıştır. Direkt ışın durumu 5 10 15 20 lfcakH

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