GSM sistemi ve santral tasarımı
GSM system and exchange design
- Tez No: 66572
- Danışmanlar: DOÇ. DR. CEVDET IŞIK
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Elektronik ve Haberleşme Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 123
Özet
ÖZET Bu tezin konusu GSM sisteminde bir santral tasarımının nasıl yapıldığını ortaya koymaktır. Bunun için önce GSM sistemlerinin genel özellikleri üzerinde durulmaktadır. Sonra santral tasarımına değinilmiştir. Burada verilen santral tasarımı donanım (hardware) ağırlıklıdır. Dolayısı ile her santral tasarımında zorunlu olarak bulunan yazılım (software) ihtiyacı üzerinde bu tez çalışmasında durulmamıştır. Tez çalışması bu yazılım ihtiyacını karşılamak üzere istenildiğinde devam ettirilebilir. Tezin konusu olan santral donanımının tasarımına yönelik yapılmış çalışmalar bölüm sırasına göre aşağıda özetlenmektedir. Giriş bölümünde yapılan santral tasarımının kapsamı verilmiştir. Bölüm 2' de GSM sistemlerinin Türkiye ve dünyadaki tarihçesi belirtilmiştir. Bölüm 3' de, GSM sistemlerinde RF dalgalarının insan sağlığı üzerindeki etkileri ve bu konuda dünyada belirlenmiş standart değerler anlatılmaktadır. Bölüm 4' de GSM sistemlerinde kullanılan teknikler ve iletim problemleri verilmiştir. 5. Bölüm, sisteme genel bir bakışı vermektedir. Bunun için sırası ile coğrafi ağ yapısı, GSM ağ ve trafik durumları üzerinde durulmaktadır. Bölüm 6, santral taşınırımın verildiği bölümdür. Burada Mobil Servisler Anahtarlama Merkezi tasarımı, Ana İstasyon Denetleyicisi tasarımı ve santralin enerji dağılımı verilmiştir. Bölüm 7 sonuç bölümüdür. IX
Özet (Çeviri)
SUMMARY GSM SYSTEM AND EXCHANGE DESIGN The importance of GSM system is increasing in this era of communications. Cellular systems now give more freedom to people who want to talk or simply communicate without preventing them moving as long as they are within the coverage area of the network. Digital technology is the keyword behind all these advantages of mobile communications. Cellular telecommunications is one of the fastest growing and most demanding telecomminications applications ever. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. In many cases, cellular solutions successfully compete with traditional wire networks and cordless telephones. In the long term perspective cellular systems, using a digital technology, will become the universal method of telecommunication. In 1982 the Nordic PTTs sent a proposal to CEPT (Conference Europeenne de Posal et Telecommunications) to specify a common European telecommunication service at 900 MHz. A standardisation group for GSM-Global System for Mobile communication-was established in order to formulate the specifications for this pan-European mobile cellular radio system. During 1982-1985 there were discussions of whether to build an anologue or a digital system but in 1985 it was decided to specify a digital system. The next step was to choose between a narrowband and a broadband solution. In 1986 there was a field test in Paris where different companies, with different solutions, competed. In May 1987 the narrowband TDMA (Time Division Multiple Access) solution was chosen. At the same time, the first 13 countries (in United Kingdom two operators) signed MoU (Memorandum of Understanding) commiting themselves to fulfill the specifications and promised to have a GSM system running by July 1, 1991, thus opening a very large potential market. In addition to international roaming, GSM provides new user services, such as high speed data communication, facsimile and short message service. The GSM technical specifications are designed to work togetherwith other standards, e.g. ISDN (Integrated Services Digital Network). Interworking between the standards is in this way assured. The system specifications for the GSM network are: Frequency band: Uplink: 890 MHz-915 MHz Downlink: 935 MHz-960 MHz Carrier distance: 45 MHz Carrier separation: 200 kHz (the first carrier at 890.2 MHz) Modulation: GMSK (Gaussian Minimum Shift Keying) Air transmission rate: 270 kbit/ s Access method: TDMA (Time Division Multiple Access) In cellular mobile communication systems, communication occurs between the exchange and roaming mobile stations. The geographical area in which the mentioned communication occurs, is called a“cell”. And the Location Area is the name given to a certain area where all these certain group of cells come together. Each cell has a Base Transceiver Station (BTS) operating on a set of radio channels. These are different from the channels used in neighbouring cells to avoid interference. A group of BTSs is controlled by a Base Station Controller (BSC). Each area in the system has a certain identity-Location Area Identity and the system uses this to find the active subscriber. A number of Location Areas is named as an MSC Service Area. Additionally, the system needs certain databases to keep track of subscriber, which the most important of these databases is the Home Location Register (HLR). The Visitor Location Register (VLR) also is another database containing information about all the MSs currently located in the MSC area. AUC, whose function is to provide the HLR with authentication parameters is connected to the HLR. SIM (Subscriber Identity Module) is a small unit containing the subscription and together make up the mobile station with the mobile equipment. If someone in the fixed network (PSTN) wants to make a call to a GSM subscriber, the exchange in the PSTN will connect the call to a gateway, which is often realized in an MSC. The Mobile Station (MS) is the subscriber equipment. It may be in the form of a permanently installed vehicle mobile, a transportable which operates as a full vehicle mobile, which may also be undipped and used independently, or a portable capable of being carried in a pocket or briefcase. Portable may also be fitted to vehicle mounted adaptors. The MS is thus available in various forms to suit the user, and will provide him/ her with voice and/ or data facilities. XIThe Base Transceiver Station (BTS) provides the radio path equipment between the MS and the fixed network. It contains radio transmitters and receivers together with channel coding functions to maintain the integrity of the transmitted data. Speech and control information are both carried in digital form in GSM. The Base Station Controller (BSC) is responsible for the use of the radio links resource provided by a group of BTS' s. The BSC thus provides the management of the mobility aspects of calls. For example it is responsible for determining when it is necessary to handover a call in progress from one BTS to another, either within its own group of BTS' s or to one controlled by another BSC. If handover is to another of its own BTS' s it may complete this handover internally. If handover is to a BTS connected to another BSC, the requirements and recommendations are passed to the MSC. The Base Station System (BSS) describes the BSC and its associated BTS' s. The capacities of the BTS and BSC are not defined in GSM. Network operators can choose from the various configurations offered by manifacturers. The requirements of urban and rural environments may be best satisfied by different architectures. The Mobile Services Switching Centre (MSC) provides the call routing functions of a fixed telephone network. Just as the BSC connects to a number of BTS' s, so the MSC connects to a number of BSS' s. Again this number is not defined and can be determined by the switching and call processing capability of the digital switch, together with the capacity of the BSS systems themselves. MSC connects calls to other telephone networks, both fixed Public Switched Telephone Networks (PSTN) and Public Land Mobile Networks (PLMN), as well as to other MSC s in its own network. Thus the MSC provides the central node of the network. For networks to route calls to and from mobile stations and allows users access only to those services to which they subscribe, as mentioned above, a number of databases are used. The Home Location Register (HLR) contains individual subscriber data which includes details of the services subscribed to and the MSC area where the user is currently located. This latter information is used to route calls to the mobile to the appropriate area. A subscriber number indicates which HLR contains his data. The Visitor Location Register (VLR) is normally associated with an MSC and contains some of the HLR data when a mobile is in the area covered by that MSC. This data is again used in call routing. XllThe Equipment Identity Register (EIR) contains list of equipment types of specific equipment serial numbers which an operator wishes to check. This database is independent to control: - access by unapproved equipment; - MSs that have subsequently found to create problems; - stolen individual equipments. The network operator can choose to allow, or bar use, or simply record the use of such an item of equipment. An Authentication Centre (AUC) is used to provide the keys for security of subscriber identity and encrypting of information across both the network and radio air interfaces. It also provides safeguards againts fraud for the network operator and the subscriber. The equpment described above provides the ability to route calls, but to operate it as a telecommunications network requires further layers of manegement control. These layers are jointly described as a Telecommunications Management Network (TMN). The lower of these two -the Operations and Maintenance Centre (OMS), provides the machanism to define the operating configurations of individual nodes (Msc, BSC, BTS and databases) and the equipment within them, and monitor their performance. It allows equipment to be brought in and out of service and handles fault reports. OMC staff typically arrange fault and routine maintenance activities. The Network Management Centre (NMC) determines the overall strategy of the network by providing the facilities to monitor activity within the network. It is a tool to determine the efficiency of network operation by providing a management via of the utilization of resources. Every cellular network needs cell planning, in order to ensure coverage and avoid interference. The cell planning process consists of many different tasks, all together making it possible to achieve a well working network. The cell planning process starts with some sort of traffic and covarage analysis which should produce information about the geographical area of interest and the expected capacity. The traffic demand-that is, how many subscribers will join the system and how much traffic will they generate-will provide the basis for all the cellular network planning. In this study, a GSM exchange of 8000 subscribers was planned. This planned exchange has a similar configuration with the other GSM exchanges which are currently in use in Turkcell network. Our exchange is capable of handling a possible future growth in traffic capacity. For security reasons and for keeping things more understandable, I did not go down to furter details more than the board level while explaining the exchange. XlllNo matter how many precautions have been taken in industry use, high frequency systems still posses harmful effects on living organisms. However, there are some institutions which set standarts on daily use of high frequency and develop ways to prevent its harmful effects on human body. Finally, it can be said that, GSM is an improving technology. Everyday new features are being introduced to the system, therefore making life more comfortable, attrackting more costumers and easing life through telecomminications. When will the devolopment of GSM hit the wall? Sorry, but we can not see that far ahead. XIV
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