Hücresel mobil haberleşme sistemlerinde tasarım yöntemleri
Başlık çevirisi mevcut değil.
- Tez No: 46282
- Danışmanlar: PROF.DR. GÜNSEL DURUSOY
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 92
Özet
ÖZET Hücresel mobil haberleşme sistemleri, insanların yerden bağımsız olarak birbirleriyle haberleşebilmelerini sağlayan sistemlerdir. Ancak istenen kalitedeki haberleşmenin sağlanabilmesi, sistem tasarımının iyi yapılmasıyla mümkün olabilmektedir. Sistem tasarımının doğru bir şekilde yapılabilmesi ise, mobil haberleşmeyi ilgilendiren problemlerin iyi anlaşılmasıyla mümkündür. Genel olarak hücresel mobil haberleşme sistemlerinde haberleşme kalitesini belirleyen problemler, yol ve gölgeleme kayıpları, sönüm, gürültü, girişim, yankı ve gecikme olarak sınıflandırılabilir. Bir kısmı mobil olmayan haberleşme tiplerinde de görülebilen bu problemlerin etkisiz kılınması veya olumsuz etkilerinin azaltılması tasarımın büyük bir bölümünü oluşturmaktadır. Tasarımın başka önemli bir boyutu da, şebeke mimarisinin oluşturulmasıdır. Şebeke mimarisi, çoklu erişim yöntemleri, hücre yapıları, kanal tahsis yöntemleri, aktarma algoritmaları gibi tasarım parametrelerinin dikkate alınmasını gerektirir. Sistemin performansının değerlendirilmesi aşamasında başvurulacak spektrum verimliliği kriterleri ve teletrafik analizleri, farklı sistemlerin birbirleriyle kıyaslanması sırasında da tasarımcıya yardımcı olmaktadır. Bu çalışmada, hücresel mobil haberleşme sistemlerindeki problemlerin tanıtılmasından sonra, bunların azaltılması veya giderilmesinde kullanılan yöntemler anlatılmış; hücresel bir sistemin şebeke mimarisi tasarımındaki yeniliklere değinilmiştir. Farklı mimarilere sahip şebekelerin kıyaslanabilmesi için kullanılabilecek kriter ve analizlerin mümkün olduğunca modern hücresel şebekelerde geçerli olanları verilmiş; sonuç olarak da geleceğin hücresel mobil haberleşme sistemleri ve bu konuda yapılabilecek diğer çalışmalar hakkında yorumlarda bulunulmuştur. -XI-
Özet (Çeviri)
SUMMARY DESIGN METHODS IN CELLULAR MOBILE TELECOMMUNICATION SYSTEMS The main purpose of telecommunication systems is to serve for communications between people more than the man-machine communications. Location changes due to the needs of daily life, forced communication engineers to review conventional communication methods. Among the appropriate solutions,“smart card”solution is probably the first one that comes to mind. With this card, anyone can access the telecommunications network on a terminal and can use it in the directions of his communication needs. If this terminal is attached to the network by means of a“tether”, then the mobility limitation of people is the case. Full mobile communication has become possible when the terminals that can be carried on people easily have been commercially available. Maybe the best example is mobile telephones. Though analogue mobile telephones are not so easy to be carried with, now modern digital mobile telephones are so small and light that they can be carried in the pockets of daily clothing's easily. The widespread of mobile telecommunication systems, which will be xa part of our daily life in a short time, is closely related with the proper design of the system at the very beginning. The recent growth of mobile communications started with cellular phones. When they were first introduced, cellular systems revolutionized mobile telephony, by allowing the limited number of radio frequencies available to be reused throughout the service area in a regular and systematic way. Cellular technology made mobile phones available to an enormously increased number of people, and it allowed them to use their radio handsets as if they were ordinary phones, dialing ordinary telephone numbers in the way they had always been used to. -xii-From the user's point of view, cellular is a great improvement on what was available before. But it is not perfect. The price is high, capacity is limited and service quality is variable as systems approach the limit of their capacity. In a short time digital technology has permeated just about every area of electronics, and radio communication is no exception. Digitalization has brought a number of advantages. Digital transmission gives much more consistent speech quality throughout the range of the radio link. Digital signaling, which can be interleaved with the speech signal across the link, allows more sophisticated protocols to cope with interference. Data and voice can be combined in many applications. Perhaps most importantly, the continuing advances in digital chip technology can be exploited to deliver better and cheaper systems. Digital radio transmission fits well with the trend to digital in the fixed network, through international initiatives such as ISDN and IBCN. Infact end to end digital services are likely to reach many users through mobile systems some time before they get there through fixed ISDN. Digital technology also increases the capacity of the radio spectrum by carrying more voice links within the same bandwidth. The fundamental of cellular mobile telecommunication systems is“cellular idea”. Cellular idea refuses the conventional“More users can be accessed only by use of more powerful transmitters”tendency. In cellular mobile telecommunication systems, communication occurs between a fixed base station and moving mobile stations. These geographical zones witnessing the communication are called“cells”. The shape and dimension of cells varies with the number and speed of mobile stations and also the traffic density in the coverage area. In the analogue cellular mobile telecommunication systems, the radius of macrocells may be between 5-1 0 km, while in today's modern mobile telecommunication systems it's usually between 1-2 km. Also, microcells and picocells of several hundreds of meters are very commonly used. By splitting the cells into smaller cells (cell splitting) and by reusing some channel groups in other cells, the subscriber capacity can be increased. Though it's possible to increase the system capacity with the reuse of channel groups (channel reuse), the number of -XIII-subscribers that can be involved to the system is limited. The demand for the service is growing rapidly, and in the heavily populated areas, the service is reaching its limit, what is known as“the brick wall”. This trend is further enhanced by the increasing penetration of handheld portable units into service, which serve a pedestrian population with a much higher density. The obvious solution for the systems of that vintage is to shrink the cell size and“scale”the cell clustering pattern. This trend has been ongoing in the heavily populated areas. Further shrinking the cell surfaces new challenges: -The smaller cell coverage requires lower antenna heights, getting in the urban areas below the roof levels and changing the propagation regime. The heavy cabling connecting the cell site to the antenna has to be reduced to enable the positioning of the antennas at lamp-post heights in the streets. -The small cells require a much denser wire lines backhaul infrastructure to the cells. The cost of the infrastructure has to decrease substantially to make the microcell network economical. -The real estate for the cell sites are overly expensive in the urban areas and the need arises for a more compact unattended cell site. Microcells are thus identified with the technical solutions proposed to cope with the aforementioned issues. Newly proposed architectures introduce the concept of remoting the antennas from cell site, thus allowing for many microcells to be served by a single attended center. Microcells can be classified as the following: -Hot spots: These service areas with a higher teletraffic density or areas that are poorly covered. A hot spot is typically isolated and embedded in a cluster of larger cells. -Downtown Clustered Microcells: These occur in a dense contiguous area that serves pedestrians and mobiles. They are typically found in an -XIV-“urban maze of street canyons”with antennas located far below building height. -In Building, 3-D Cells: These serve office buildings and pedestrians. This environment is highly clutter dominated, with an extremely high density and relatively slow user motion, and strong concern for the power consumption of the portable units. Hence, the aim of the system designer, is to increase the system capacity without destroying the quality of communication by optimizing the number of users and related problems. An important parameter here, is the ratio of the distance between the cells that use the same channel groups, to the radius of the cells. Another problem that comes with dividing the whole coverage area into cells is the user's leaving his original cell and moving into an adjacent cell. A sequence of processes should be realized in the network in order to prevent the call from unwanted termination. This problem can be overcome by allocation of a free channel to the subscriber in the new cell after determination of the cell which the mobile station moves into. In a good cellular mobile telecommunication system, subscribers are expected to move to any direction they wish. This motion of the subscribers between cells of one system or between cells of different systems is called“roaming”. As a result, cellular mobile communication suffers many problems that the system designer should take into consideration during design process. In this thesis, the genera! common design problems of cellular mobile telecommunication system and the methods in reducing and overcoming these problems are analyzed. In the second chapter, the effects of mobile environment on radio waves and the problems that the system designer faces are introduced in detail; the explanations of design parameters which will be used in later steps and statistical definitions are given. Third chapter deals with the methods which can be used to reduce the faced problems. The prediction of propagation path loss, reducing fades -xv-and interferences, the minimization of echo and delay problems are the common purposes in both analogue and digital systems. Multiple access schemes, efficiency criteria, cell structures, channel allocation schemes and new algorithms for handovers are discussed in the fourth chapter. In this chapter, significant new methods are tried to be given in priority. Fifth chapter, concentrates on the teletraffic models developed specially for cellular systems. The common point for the given models is that they can be applied to modern cellular mobile telecommunication systems. In the last chapter, future mobile communication systems and possible studies that can be carried out are interpreted. -xvi-
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