高樓大廈gsm網(wǎng)絡(luò)信號(hào)的優(yōu)化實(shí)現(xiàn)畢業(yè)設(shè)計(jì)論文-閱讀頁
2024-09-16 19:43本頁面
【正文】 ubscriptions around the world. Currently there are more than 45 million cellular subscribers worldwide, and nearly 50 percent of those subscribers are located in the United States. It is forecasted that cellular systems using a digital technology will bee the universal method of telemunications. By the year 2020, forecasters predict that there will be more than 100 million cellular subscribers worldwide. It has even been estimated that some countries may have more mobile phones than fixed phones The concept of cellular service is the use of lowpower transmitters where frequencies can be reused within a geographic area. The idea of cellbased mobile radio service was formulated in the United States at Bell Labs in the early 1970s. However, the Nordic countries were the first to introduce cellular services for mercial use with the introduction of the Nordic Mobile Telephone (NMT) in 1981. Cellular systems began in the United States with the release of the advanced mobile phone service (AMPS) system in 1983. The AMPS standard was adopted by Asia, Latin America, and Oceanic countries, creating the largest potential market in the world for cellular. In the early 1980s, most mobile telephone systems were analog rather than digital, like today39。t translate well, so the now mon more globally appealing name was adopted. GSM is a published standard by ETSI, and has now enjoys widespread implementation in Europe, Asia, and increasingly America. There are many arguments about the relative merits of analogue versus digital, but for my mind it es down to this: Analogue sounds better and goes further, Digital doesn39。t (or doesn39。 receive, Data calls, and the evolution of cellular telemunications, various systems have been developed without the benefit of standardized specifications. This presented many problems directly related to patibility, especially with the development of digital radio technology. The GSM standard is intended to address these problems. From 1982 to 1985 discussions were held to decide between building an analog or digital system. After multiple field tests, a digital system was adopted for GSM. The next task was to decide between a narrow or broadband solution. In May 1987, the narrowband time division multiple access (TDMA) solution was chosen. 3. The GSM Network GSM provides remendations, not requirements. The GSM specifications define the functions and interface requirements in detail but do not address the hardware . The reason for this is to limit the designers as little as possible but still to make it possible for the operators to buy equipment from different suppliers. The GSM work is divided into three major systems: the switching system (SS), the base station system (BSS), and the operation and support system (OSS). 19 The Switching System The switching system (SS) is responsible for performing call processing and subscriberrelated functions. The switching system includes the following functional units. home location register (HLR)— The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber39。s identity and ensure the confidentiality of each call. The AUC protects work operators from different types of fraud found in today39。s limits。 eight bits are equivalent to one byte frequency— the number of cycles per unit of time。 the abbreviation kbps represents 1,000 bits per second megahertz (MHz)— 1,000,000 hertz (cycles per second) milliseconds (ms)— onethousandth of a second watt (W)— a measure of power of a transmitter Specifications for different personal munication services (PCS) systems vary among the different PCS works. Listed below is a description of the specifications and characteristics for GSM. frequency band— The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station). channel separation— The separation between adjacent carrier frequencies. In GSM, this is 200 kHz. modulation— Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK). transmission rate— GSM is a digital system with an overtheair bit rate of 270 kbps. access method— GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different calls may share the same carrier. speech coder— GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate.. Speech is encoded at 13 kbps.
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