Introduction To Communication Engineering PDF

Introduction to Communication Engineering Course: History of Engineering Sciences Lecturer: Dr. Mohamed A. El-Shimy Department: Electrical Engineering Department, Affiliation: Alexandria University, Egypt. Academic Term: Fall 2024 1. Introduction Communication is the transfer of information (da...

Introduction to Communication Engineering Course: History of Engineering Sciences Lecturer: Dr. Mohamed A. El-Shimy Department: Electrical Engineering Department, Affiliation: Alexandria University, Egypt. Academic Term: Fall 2024 1. Introduction Communication is the transfer of information (data) from one point (the source) to another (the destination) over a transmission channel. It focuses on the ability to convey information quickly and efficiently, which could be sound (an audio signal), images (a video signal), or data (a digital signal). Information transfer is frequently achieved by modulating the information onto an electromagnetic wave (EMW), which acts as a carrier for the information signal. This EMW can be selected from radio frequencies up to optical range frequencies as shown in the figure. More details can be found in Appendix A. Multiple communication systems are used to convey various information such as: ▪ Telegraph and Telephony System ▪ Cellular Mobile Networks ▪ Wireless Networks ▪ Audio and Video Broadcasting ▪ Satellite Communications & GPS ▪ Optical Communication system 2. General Communication System A block of diagram of a general communication system is shown in the figure. Transmitter Takes the information and converts it to a signal suitable to transmission. Receiver Takes the transmitted signal and converts it back into required information. Transmission channel The physical medium over which the signal is transmitted. 3. Communication Channels It is the physical medium over which the signal is transmitted. Transmitted signal encounters several problems such as attenuation, amplitude and phase distortion, and multipath distortion. The channel problems can be minimized but not avoided due to practical constraint limitations. Such as the power-limit and bandwidth-limit constraints. These limitations result in constraining the amount of data that can be transmitted reliably over any communication channel. The communication channels can be classified into two classes as follows. Channel Wireline Wireless Twisted- Coaxial Optical Radio Microwave Optical Paire Cable Fiber A. Wireline Channels EMWs carrying the information are guided by a bounded medium. The channel is well modeled and assumed to be known at the transceiver. Common types of wireline channels include: Copper Wire It is made of two insulated copper wires pair that are twisted together to reduce crosstalk. It is the oldest and most common type of communication cable. It is used in telephone networks to connect a customer to a central office and in data cables. The first copper telegraph lines were installed in the 1840s and the first copper telephone lines were installed in the 1870s. It is relatively inexpensive and easy to install. However, it has a limited bandwidth of several hundred kilohertz (kHz). Coaxial Cable It consists of a central copper conductor surrounded by a layer of insulation and a bounded copper shield. It was invented in 1929 at AT&T Bell Telephone Laboratories and it was first used commercially in the 1940s to connect telephone exchanges. By the 1950s, it was used to transmit television signals and to connect a receiver and an antenna of the TV together. It has a higher bandwidth than copper wire of several (MHz). However, it is also more expensive and difficult to install. Waveguide A single conductor (hollow metal tube) of rectangular or circular cross section that transmit microwaves. The idea of using a hollow metal tube to guide electromagnetic waves was first proposed in the late 19th century by Lord Rayleigh.  In the 1930s, waveguides began to be developed and used in micrwave communications such as in radar systems and satellite communication systems. It has a very high bandwidth that operates in the GHz (microwave) range. However, it is more expensive and difficult to install. Optical Fiber Cable It is a dielectric waveguide that uses light to transmit data. It is made of a bundle of thin glass or plastic fibers. It is the preferred choice for long distance connections between cities and countries for large transmission of data. The principle of guiding light through refraction dates to the mid-19th century. In the 1970s, Corning Glass Works announced the development of optical fiber. It offers a much higher bandwidth compared to the others with a relatively low signal attenuation. However, it is the most expensive and difficult installing type. Copper Wires Coaxial Cable Waveguide Optical Fiber Bandwidth Limited High Very High Extremely High Cost Low Medium High High Distance Short Medium Short Long Installation Easy Medium Difficult Difficult Cable TV and Radar and high-speed data Telephone and Applications Broadband Satellite and long-range low-speed data internet communication communication B. Wireless Channels They are the medium through which the transmission of information is done wirelessly using EMWs without the use of physical guided cables. The channel is a broadcast medium; hence interference can occur due to simultaneous transmission of different signals from other users of the channel. Wireless channels can be classified based on various factors: Frequency Band o Radio Frequency are relatively lower frequencies used for traditional wireless communication like radio and tv broadcasting, cellular networks, Wi-Fi … etc. o Microwaves are higher frequencies used for satellite communications, point- to-point links, radar … etc. o Optical Frequency are used for short-range communications like remote controls, Li-Fi … etc. Propagation Environment o Indoor within buildings. They are influenced by walls, furniture, and people. o Outdoor are in open space. They are affected by terrain, atmospheric conditions and so on. Indoor Outdoor 4. Message Signal They are the information-carrying signal that contains the data needs to be transmitted. They can be classified based on the type of the data they carry. Analog Messages They are continuous signals, such as an audio or video signals, characterized by data whose values vary over a continuous range and are defined for a continuous range of time. Early communication technologies relied on analog signals. Digital Messages They are discrete signals representing information as discrete values (usually 0s or 1s) such as the output of a teletype machine. They have become the main message form in modern communication systems 5. Carrier Modulations A. Definition It is a process where a message signal modulates a carrier signal. Based on the message signal, the carrier modulation has firstly emerged in the early 20th century with analog modulation techniques. Then in the late 20th century, digital modulation techniques have revolutionized communication. The carrier signal is normally a sinusoidal signal with a general function: 𝑓(𝑡) = 𝐴sin(𝜔𝑡 + 𝜙) where 𝐴 is the amplitude, 𝜔 is the frequency, and 𝜙 is the phase. Through modulation, one of the carrier parameters is varied in proportion to the message signal. B. Types of Modulation Analog Modulation Digital Modulation Analog Signal Digital Signal Carrier Signal Carrier Signal Amplitude Modulation (AM) Amplitude Shift Keying (ASK) Frequency Modulation (FM) Frequency Shift Keying (FSK) Phase Modulation (PM) Phase Shift Keying (PSK) C. Why Modulation? For comparison, the carrier and the message signal can be viewed as a stone and a piece of paper. The paper cannot go far in an open medium by itself; thus, it is wrapped around a stone to be thrown over a longer distance. Some of the important reasons for this are as follows. 1. Ease of Transmission Transmission channel acts like a bandpass filter centered at a specific frequency. Thus, both the lowest frequency and the highest frequency components are attenuated. Hence, the modulation shifts the frequency of data signal to allow it to be transmitted over the channel. 2. Ease of Radiation For efficient radiation, the antenna size is typically on the order of a fraction of the wavelength of the radiated signal. For many message signals, the wavelengths are too large which lead to an impractically large antenna. For example, the power in a speech signal is concentrated at frequencies in the range of 100 to 3000 Hz with corresponding long wavelength of 100 to 3000 km. Instead, by transmitting a high-frequency carrier that has a much smaller wavelength comparing to the message frequency, a reasonable antenna size can be achieved. 3. Transmission of Multiple Signals With modulation, multiple signals, such as the output of multiple TV stations, can modulate carrier with different frequencies, which allows transmission at the same time in the same geographical area without interference. At the receiver, TV set for example, a tunable bandpass filter can select the desired station. This method is known as frequency division multiplexing (FDM). 6. Analog Communication System Transferred information takes on a continuum of values. It is based on using analog modulation techniques. It is widely using in old system such as terrestrial radio and television broadcasting systems. The transmitter consists of a modulator and the receiver consists of a demodulator. 7. Digital Communication System Information being transferred is represented in digital format, most commonly as binary digits, or bits. A block diagram of a basic elements of a digital communication system is illustrated. The source output may be either an analog message, such as audio or video signal, or a digital message, such as the output of a teletype machine. In a digital communication system, the message produced by an analog source is converted into a sequence of digits, most commonly as binary digits, or bits. The transmitter modifies the signal for efficient transmission over the channel. It may consist of an A/D converter, an encoder, and a modulator. The receiver reverses the signal modifications made at the receiver and removes the distortions made by the channel. It may consist of a demodulator, a decoder, and a D/A converter. A. Source Encoder It is an efficient representation of information in binary digital form. It eliminates unwanted redundancy in the information to be sent. For example, voice can be encoded into a 64 kbps bitstream for conventional wireline telephony. Audio can be encoded at a bit rate of 128 kbps. B. Channel Encoder It introduces redundancy in a controlled fashion that can be used at the receiver in order to combat errors that may arise from channel imperfections and noise. For example, a trivial form of encoding is to repeat each binary digit m times. This is known as a repetition code. A more sophisticated encoding is to map a sequence of k-bit into a unique n-bit sequence, called a code word. The amount of redundancy introduced is measured by n/k, known as code rate. C. Digital Modulator It serves as the interface to the communication channel. It translates the discrete symbols output by the channel code into an analog waveform that can be transmitted over the physical channel. Binary Modulation: Maps each binary digit into a signal waveform. M-ary Modulation: Transmits one of M waveforms for every b-bit sequence. D. Communication Channel It is the physical medium that provides the connection between the transmitter and the receiver. It can be wireline or wireless channel. The channel behaves as filter that attenuates the transmitted signal and distorts its transmitted waveform. E. Digital Demodulator It processes the analog received waveform, which is a distorted and noisy version of the transmitted waveform. Its main goal is to produce tentative decisions on the transmitted symbols to be fed to the channel decoder. F. Channel Decoder Its goal is to produce an estimate of the sequence of information symbols that were the input to the channel encoder. G. Source Decoder It converts the estimated information bits produced by the channel decoder into a format that can be used by the end user. 8. Why the World is Going Digital? Within the past decade, the “digital technology” is replacing the old “analog technology” by using the powerful and inexpensive high-speed digital circuits. A. Noise Immunity of Digital Signals At the receiver, the extraction of the message from a distorted and noisy signal at the channel output is often easier from digital signals than from analog signals because the digital decision must belong to the finite-sized alphabet. Consider a binary case where two symbols are encoded as pulses and transmitted. At the receiver, the only decision is to select between the two possible received pulses, where the fine details of the pulse shape are not an issue. With modest distortion and noise, the data can be recovered with high accuracy. In contrast, in analog message, the waveform carries the needed information, and a slight distortion or interference will show up in the received signal. B. Regenerative Repeaters Repeaters stations are placed along the communication path of a digital system at distances short enough to ensure that noise and distortion remain within a limit. In digital , the incoming pulses are detected, and new pulses are retransmitted. This prevents the accumulation of noise and distortion along the path. For analog systems, repeaters are basically filters plus amplifiers and are not regenerative. Thus, signals and noise within the same bandwidth cannot be separated. Transmitted signal Received distorted signal (without noise) Received distorted signal (with noise) Regenerated signal (delayed) Appendix A. Electromagnetic Communications Spectrum