I- Introduction to Telecommunication Techniques Introduction to Telecommunications 11/17/2018 I- Introduction to Telecommunication Techniques I-1 What Is Telecommunications? Telecommunications has been defined as a technology concerned with communicating from a distance, and we can categorize it in various ways. Figure Below shows one possible view of the different sections of telecommunications. It includes mechanical communication and electrical communication because telecommunications has evolved from a mechanical to an electrical form using increasingly more sophisticated electrical systems.

Introduction to Telecommunication Techniques I-2 Significance of Telecommunications We look at telecommunications from different points of view in order to understand what a complicated system we are dealing with and how dependent we are on it. Telecommunications networks make up the most complicated equipment in the world. Let us think only of the telephone network, which includes more than 2 billion fixed and cellular telephones with universal access. In addition, many other networks are interconnected with the telephone network. No other system in the world exceeds the complexity of telecommunications networks. Telecommunications services have an essential impact on the development of a community. In the developing, countries the fixed telephone density, that is, the teledensity, is fewer than 10 telephones per 1,000 inhabitants; in developed countries in, North America and Europe, there are around 500 to 600 fixed telephones per 1,000 inhabitants. The economic development of developing countries depends on (in addition to many other things) the availability of efficient telecommunications services. The operations of a modern community are highly dependent on telecommunications. We can hardly imagine our working environment without telecommunications services. The local area network (LAN) to which our computer is connected is interconnected with the LANs of other sites throughout our company.

Introduction to Telecommunication Techniques Telecommunications plays an essential role on many areas of everyday living. Everyday life is dependent on telecommunications. • Banking, automatic teller machines, telebanking; • Aviation, booking of tickets; • Sales, wholesale and order handling; • Credit card payments; • Booking of hotel rooms by travel agencies; • Material purchasing by industry; • Government operations, such as taxation. I-3 Development of telecommunications systems and services. The development and expansion of some telecommunications services is also illustrated in the following Figure.

Introduction to Telecommunication Techniques 1990–1997 The first digital cellular system, Global System for Mobile Communications (GSM), is put into commercial use and its breakthrough is felt worldwide. 2001–2005 Digital TV starts to replace analog broadcast TV; 2005– Digital TV will replace analog service and start to provide interactive services in addition to broadcast service; third generation cellular systems and WLAN technologies will provide enhanced data services for mobile user

Introduction to Telecommunication Techniques I-4 Electronic communications involves the study of how information is transferred from one place to another over electronic channels. Information in the form of sound or visual images is processed into electrical signals by transducers. A microphone is the transducer for converting energy in the form of sound pressure waves into electrical energy: A television camera is the transducer for conversion of visual images into electrical video signals. Further electronic processing can convert these signals into a digital format. Once the information is processed into suitable electrical signal, we must determine how these signals can be transmitted over long distances to be made available for one or millions of users. This figure illustrates, in a block—diagram form. information gathered. transformed into electrical signals, and processed for transmission. Typical transmission media are Transmission lines or optical ( light ) cable, and space from antenna to antenna, the distances and broadcast coverage involved usually result in vast energy loss thus requiring very sensitive receiving and processing systems before the signals can be reproduced into the desired form for the user

Introduction to Telecommunication Techniques Introduction to Telecommunications 11/17/2018 Introduction to Telecommunication Techniques I-5 Analog Transmitter In simplest terms, an RF transmitter accepts an electrical signal from some information source and transmits a high-power analog RF carrier signal modulated with the information. Another input to the transmitter is also required—a power supply. The function of transmitter circuits is to convert power from the power supply into the modulated output signal as efficiently as possible.

Introduction to Telecommunication Techniques I-6 Analog Receiver High-frequency receiver uses the heterodyne technique to down-convert the received signal to an intermediate frequency (IF) signal, fIF = fLO — fRF is selected while the other signals fLO, fRF, and fLo + fRF are rejected by filtering. Such a receiver is referred to as a superheterodyne, or superhet, receiver, The circuit most used in modem radios for frequency conversion is called a mixer. The mixer allows the oscillator circuit to function separately from the nonlinear mixing process. The block diagram shown below illustrates a superheterodyne receiver with a mixer and separate local oscillator (LO). The filter shown is tuned to the difference (IF) frequency and is followed by IF amplification ahead of the demodulator. As indicated, the superheterodyne principle is used in AM, FM, and PM receivers.

The standard AM broadcast band in North America extends from 535 to 1605 kHz, with transmitted carrier frequencies every 10 kHz from 540 to 1600 kHz (± 20 Hz tolerance). The 10 kHz of separation between AM stations allows for a maximum modulation frequency of 5 kHz, since the modulation process produces sidebands above and below the carrier. Another standard used for commercial broadcast AM radio is a receiver IF fixed at 455 kHz. The 455 kHz is chosen because it is below the lowest transmitted signal frequency yet high enough to avoid radio frequency interference (RFI) from signals called the image. The most important reason for using the heterodyne (mixing) technique in a multichannel receiver is to allow for a fixed-tuned IF system. Thus most of the gain and sensitivity of the superhet receiver is provided by a factory-tuned IF section. Then, selecting different stations is a matter of retuning the RF input to the new station frequency and consequently retuning the Local Oscillator frequency in order to achieve the IF=fLO-fRF = 455KHz

Introduction to Telecommunication Techniques I-7 Digital Transmitter The following block diagram represent multiplexed PCM transmitter system.

Introduction to Telecommunication Techniques I-8 Digital Transmitter/Receiver The following block diagram represent Codec ( Coding and Decoding System) (SAR = Successive Approximation Register) it is used as Analog to Digital Converter (ADC) The Digital to Analog Converter (DAC) is Part of ADC