Introduction-Communication Systems-Lecture Slides, Slides of Data Communication Systems and Computer Networks

Download Introduction-Communication Systems-Lecture Slides and more Slides Data Communication Systems and Computer Networks in PDF only on Docsity! Introduction Background and History • Marconi patents the wireless telegraph (1895). • Ship‐to‐store radiotelephone service initiated on the east coast of USA (1919). • First mobile radio for the police at Detroit, USA (1921). • First two‐way mobile radio system for police at New Jersey, USA (1933). • Frequency modulation invented by Edwin H. Armstrong (1935). 2 docsity.com • The interconnection of mobile users to the public telephone network (mobile telephone service) in St. Louis, Missouri, USA (1946). • The cellular network concept proposed in Bell Labs (1947). • The first fully automatic (switching) mobile telephone system in Richmond, Indiana, USA (1948). • The bandwidth of FM mobile radiotelephones in USA decrease from the original 120Khz in 1950, and 30Khz at early (1960). 3 docsity.com • DCS 1800 digital cellular system(extension of GSM) began operation at 1800Mhz frequency range in Europe (1983). • Introduction of TDMA digital cellular system in USA during the first half of 1990s. • NMT‐900 analog cellular system was shut down in Nordic countries, Netherlands and Switzerland 2000, to free more bandwidth for the GSM system. • Standardization work for third generation cellular system (IMT‐2000 and UMTS standards) from 1991; the first commercial 3rd generation cellular system has been opened for limited use in Japan in 2001. 6 docsity.com Mobile Wireless networks in comparison to fixed  wireless networks • Higher loss‐rate due to interface ‐emission of, e.g., engines, lightening • Restrictive regulations of frequencies ‐frequency have to be coordinated, useful frequencies are almost all                   occupied • Low transmission rates ‐Local some Mbits/s, regional currently, e.g. 9.6kbits/s with GSM • Higher delay higher jitter ‐connection setup time with GSM in the second range, several  hundred milliseconds for other wireless systems • Lower security, simple active attacking ‐radio interface accessible for everyone, base station can be simulated, thus  attracting calls from mobile phones • Always shared medium  ‐secure access  mechanisms important 7 docsity.com Wireless systems: overview of the development cellular phones satellites cordiess wireless phones LAN 1980: 1981: cto NMT 450 53a se | 1983: Inmarsat-A 7 + 3 4 NMT 900 5 1987: CT1+ 4G — fourth generation? EP & 8 docsity.com The road to IMT-2000 IMT-2000 THE emerging network of the 21st century (ZY e Zone 1: 2Gs: Satellite public mobile & privat residential & networks fixed networks fixed networks 12 docsity.com Overlay Networks-the global goal Wide- area Overlay Networks Regicnal- Area 13 docsity.com The conventional mobile radio reached technically mature level in the early 1970s by utilizing trunking, improved FM technology, direct dialing and automatic switching. However, there was a serious capacity problem in conventional mobile radio due to the network architecture. The traditional approach to mobile radio network architecture was similar to radio or television broadcasting. • A high‐power transmitter on top of the highest peak in the area providing fair to average coverage over an area with radius of 60 to 80 Km. This meant that still a single user reserved a single radio channel over all this area for the entire duration of a call. For example, the New York City in the 1970s this kind of system could provide 12 simultaneous mobile calls for a population of substantially over 10 million people. 16 docsity.com On uplink, even the traditional mobile radio networks utilized relatively densely receiving sites, since mobile stations used low‐power transmitters, so that they could not always get a signal back to the middle of town. However, all these receiving sites were serving the same customer on a particular carrier frequency, and hence the use of multiple receivers did not increase the system capacity. • A large number of low‐power transmitters, each of them designed to serve only a small coverage area (cell) with radius of couple of Kilometers. This makes it possible to reuse the same frequencies in different cells. 17 docsity.com However, due to the interference between adjacent cells the same frequencies can not be used in every cell, but it is necessary to skip several cells before reusing a particular frequency. Even with this restriction the capacity increases from the broadcast‐type mobile radio is impressive. Moreover, since the interference between adjacent cells is determined by the transmitters powers in these cells the frequency reuse pattern can be easily changed by spitting a single cell to several smaller cells with lower transmitter power in the geographical areas, where the traffic load is high. 18 docsity.com International roaming is possible • In a cellular system it must also be possible to make calls from one MS to another MS when both are located in the operator’s service area. It must also be possible for the MS to have access to the fixed telephone network (PSTN, Public switched Telephone Network). • It is considered very important hat ongoing calls are not interrupted regardless of MS mobility. This creates a need to reroute on‐going calls, which means switching the call to another frequency or to another base station (BS). This procedure is call Handover. 21 docsity.com • The second generation of cellular radio, digital cellular radio can provide besides conventional speech technology very wide range of services: circuit and packet switched data, short messages, facsimile etc. It is difficult to accommodate these services into analog networks, and especially it is difficult to multiplex different kinds of services into one radio channel. • The digital radio transmission is also more resistant to noise and interference than analog transmission. Thus, the radio system can be designed for lower signal‐to‐noise ratio or signal‐to‐interference ratio. 22 docsity.com • The bandwidth of digital speech signal is normally higher than the bandwidth of the original analog signal. However, since the digital transmission is more resistant to interference, it is possibly by using advanced digital modulation techniques and low bit rate speech coding methods to achieve higher spectral efficiency in digital than to achieve kin analog transmission. • In addition most advantages of use of digital technology for communication in general also apply for cellular systems. These advantages include:  Use of digital integrated circuits.  Error correction  Equalization  Performance monitor ability  Security  Connectivity to other networks 23 docsity.com The fig on the following page shows a forecast on the number of subscribers in the global telephone network up to year 2010 prepaid in the Bell Labs in 1997. According to this forecast, the global penetration of wireless services (cellular, Personal communication, wireless LANs, etc) will be 21% of the global population of seven billion people in the year 2010. In tis year the penetration of ireless services will exceed the global penetration of wireless services, which is expected to be around 20%. 26 docsity.com Number of Subscribers in Global Telephone Network 2'000 > 1'800 ¥ 1'600 Fixed 1'400 ; —tl— Mobile 1'200 1'000 ¥ 800 A 600} —__-— 400 jaye = 200 0-7 T TT T 1982 84 86 88 90 92 94 96 98 2000 Source: ITU 27 ® docsity.com 02 04 Even this forecast has been found to be too conservative, and some recent estimates predict that the number of cellular subscribers may exceed on Billion (1000 thousand) already during the year 2002. The following fig shows another (more conservative) forecast on the number of subscribers in digital cellular networks network up to year 2003 prepaid by Ericsson in 1998. 28 docsity.com