Communications Engineering

Course information

Catalog Description:

This course provides the first contact of the students with the field of Telecommunications;therefore, the curriculum to introduce basic concepts and familiarize the students with the wide

object of Telecommunications.

Course objective:

The objective of this course to provide students the basics of telecommunication, then Introduce students to the basic elements of analog and digital communication systems and their functions (transmitter, receiver, channel). Perform signal analysis in time and frequency domain, sampling and conversion between analog and digital signals.

The students will have a good knowledge of analog modulation techniques and basics of digital modulations. give students an overview for how to analysis digital communication systems over noisy channels.

Course Learning Outcomes:

upon successful completion of this course module students possess advanced knowledge, skills and competences in the subject of Telecommunications that enable them to Understand and possess the basic concepts, principles and tools for the description of telecommunication signals and systems.

Students Understand and possess the basic concepts, principles and characteristics/parameters of modulations systems, analog‐to‐digital conversion systems, time/frequency division multiplexing, noise in telecommunication systems.

Finally, students have a good knowledge about baseband modulation such as AM, FM.

Course content Definition of telecommunication:

telecommunications, also known as telecom, is the exchange of information over significant distances by electronic means and refers to all types of voice, data and video transmission. This is a broad term that includes a wide range of information transmitting technologies such as telephones (wired and wireless), microwave communications, fiber optics, satellites, radio and television broadcasting, the internet and telegraphs.

Telecommunications refers to the transfer of data(communications) from a transmitter to a receiver

across a distance, as we show in the following figure

  • Sender is the person who sends a message. It could be a transmitting station from where the signal is transmitted.
  • Channel is the medium through which the message signals travel to reach the destination.
  • Receiver is the person who receives the message. It could be a receiving station where the transmitted signal is being received.

Types of Telecommunication Systems

Telecommunications of one kind or another are not a modern invention. The first successful attempts at telecommunication systems included signal fires which were used since ancient times. The 18th Century saw the invention of optical telegraphy communications systems, also known as semaphore lines while the late 19th Century gave rise to radio technology. Today, we use the Internet and telephones for the vast majority of our telecommunications although there is an even wider variety of telecommunication systems in use today.

  • Optical Telecommunications

Optical telecommunication is the oldest and simplest type. Optical telecommunications systems include everything from signaling flags used on boats to the semaphore optical telegraphy lines of the past. Although fiber optic communication falls into the same category, it is rather different to every other form of optical telecommunication in that it relies on converting data into beams of light. These may be carried over fiber optic cables or by using an infrared connection.

  • Radio Telecommunication Systems

Radio technology allows for wireless communication over large distances. Radio broadcasts are sent out by radio transmitters and then decoded at the other end in real time. Perfected about the turn of the 20th Century, radio remains one of the main forms of communication in the world today. Television is also a form of radio communication.

Analog and digital signal

Definition of Analog Signal

Analog signal is a kind of continuous wave form that changes over time. An analog signal is further classified into simple and composite signals. A simple analog signal is a sine wave that cannot be decomposed further. On the other hand, a composite analog signal can be further decomposed into multiple sine waves. An analog signal is described using amplitude, period or frequency and phase. Amplitude marks the maximum height of the signal. Frequency marks the rate at which signal is changing. Phase marks the position of the wave with respect to time zero.

Definition of Digital Signal

Digital signals also carry information like analog signals but is somewhat is different from analog signals. Digital signal is noncontinuous, discrete time signal. Digital signal carries information or data in the binary form i.e. a digital signal represent information in the form of bits. Digital signal can be further decomposed into simple sine waves that are called harmonics. Each simple wave has different amplitude, frequency and phase. Digital signal is described with bit rate and bit interval. Bit interval describes the time require for sending a single bit. On the other hand, bit rate describes the frequency of bit interval.

Analog signal is converted to a digital signal using a two-step process.

  1. Sampling
  2. Quantization

The device used to do this is called as ADC (Analog to Digital Converter).

Step 1: Sampling converts a continuous time continuous amplitude (real valued) signal to discrete time continuous amplitude (still real valued) signal. Remember only time axis is discretized and not the amplitude axis.

The sampling rate fs is the number of samples per second. The time interval between samples is called the sampling interval Ts=1/fs

Nyquist Sampling Rate: A signal should be sampled at a rate greater than twice its maximum frequency.

The Nyquist-Shannon sampling theorem states that the sampling rate for exact recovery of a signal composed of a sum of sinusoids is larger than twice the maximum frequency of the signal. This rate is called the Nyquist sampling rate fNyquist.

Fs > fNyquist =2fmax

Step 2: Quantization converts the discrete time continuous amplitude signal to discrete time and discrete valued (from a set of finite values, so that it can be represented by finite bits and can be stored on a computer).

We have two categories of communication system

  • Analog communication system
  • Digital communication system

Analog Communication:

The elements of basic analog communication system are input signal or information, input transducer, transmitter, channel, Noise, Receiver, Output transducer.

1.Information or Input signal:

The information is transmitted from one place to another. This information can be in the form of a sound signal like speech, or it can be in the form of pictures or it can be in the form of data information.

2.Input transducer:

The information in the form of sound, picture or data signals cannot be transmitted as it is. First it has to be converted into a suitable electrical signal. The input transducer block does this job. The input transducer commonly used are microphones, TV etc.

3.Transmitter:

The function of the transmitter is to convert the electrical equivalent of the information to a suitable form so that it can transfer over long distance. Basic block in transmitter are: Amplifier, Oscillator, Mixer.

4.Channel:

The communication channel is the medium used for transmission of electrical signal from one place to other. The communication medium can be conducting wires, cables, optical fibers or free space. Depending on the type of communication medium, two types of communication system exists, the first Line communication: the first is the line communication as optical fibers, Telephone, Cable TV. The second is Radio communication, the radio communication systems use the free space as their communication medium. The transmitted signal is in the form of electromagnetic waves. E.g. Mobile communication, satellite communication.

5.Noise:

Noise is an unwanted electrical signal which gets added to the transmitted signal when it is travelling towards the receiver. Due to noise quality of information gets degrade. Once added the noise cannot be separated out from the information.

6.Receiver:

The receiver always converts the modulated signal into original signal which consist of Amplifier, Oscillator, Mixer.

7.Output transducer:

Output transducer converts electrical signal into the original form i.e. sound or TV pictures etc.

Advantages of Analog communication

  1. Transmitters and receivers are simple
  2. Low bandwidth requirement
  3. FDM (Frequency division multiplexing) can be used

Disadvantages of Analog Communication

  1. Noise affects the signal quality
  2. It is not possible to separate noise and signal
  3. Repeaters cannot be used between transmitter and receiver
  4. Coding is not possible
  5. It is not suitable for the transmission of secret information

Digital Communication

  1. Input Transducer

This is a transducer which takes a physical input and converts it to an electrical signal (Example: microphone). This block also consists of an analog to digital converter where a digital signal is needed for further processes. A digital signal is generally represented by a binary sequence

  1. Source Encoder

The source encoder compresses the data into minimum number of bits. This process helps in effective utilization of the bandwidth. It removes the redundant bits (unnecessary excess bits, i.e., zeroes).

  1. Channel Encoder

The channel encoder, does the coding for error correction. During the transmission of the signal, due to the noise in the channel, the signal may get altered and hence to avoid this, the channel encoder adds some redundant bits to the transmitted data. These are the error correcting bits.

For the other block it’s like analog communication.

Advantages of Digital Communication

  1. Due to the digital nature of the transmitted signal, the interference of additive noise does not introduce many errors. Hence, digital communication has a better noise immunity.
  2. Due to the channel coding techniques used in digital communication, it is possible to detect and correct the errors introduced during the data transmission.
  3. Repeaters can be used between transmitter and receiver to regenerate the digital signal. This improves the noise immunity further.
  4. Due to the digital nature of the signal, it is possible to use the advanced data processing techniques such as digital signal processing, image processing, data compression etc.
  5. TDM (Time Division Multiplexing) technique can be used to transmit many voice channels over a single common transmission channel.
  6. Digital communication is useful in military applications where only a few permitted receivers can receive the transmitted signal.
  7. Digital communication is becoming simpler and cheaper as compared to the analog communication due to the invention of high-speed computers and integrated circuits (ICs)

Disadvantages of Digital Communication

  1. The bit rates of digital systems are high. Therefore, they require a larger channel bandwidth as compared to analog system.
  2. Digital modulation needs synchronization in case of synchronous modulation.

Modulation definition

For a signal to be transmitted to a distance, without the effect of any external interferences or noise addition and without getting faded away, it has to undergo a process called as Modulation. It improves the strength of the signal without disturbing the parameters of the original signal.

Modulation is a process through which audio, video, image or text information is added to an electrical or optical carrier signal to be transmitted over a telecommunication or electronic medium. Modulation enables the transfer of information on an electrical signal to a receiving device that demodulates the signal to extract the blended information.

  • Advantages of Modulation

1.Allows multiplexing
2. Allows adjustments in bandwidth
3. Avoids mixing of signals
4. Improve quality of reception and SNR
5. Reduce height of the antenna
6. Increase the range of communication

The Common modulation methods include the following:

  • Amplitude modulation (AM), in which the height (i.e., the strength or intensity) of the signal carrier is varied to represent the data being added to the signal.
  • Frequency modulation (FM), in which the frequency of the carrier waveform is varied to reflect the frequency of the data.
  • Phase modulation (PM), in which the frequency of the carrier waveform is varied to reflect changes in the frequency of the data (similar but not the same as FM).
  • Polarization modulation, in which the angle of rotation of an optical carrier signal is varied to reflect transmitted data.
  • Pulse-code modulation, in which an analog signal is sampled to derive a data stream that is used to modulate a digital carrier signal.

  1. Some useful Definition in Digital Communication

Bandwidth: is the range of frequencies — the difference between the highest-frequency signal component and the lowest-frequency signal component — an electronic signal uses on a given transmission medium. Like the frequency of a signal, bandwidth is measured in hertz (cycles per second).

Signal-to-Noise Ratio (SNR): A signal-to-noise ratio compares a level of signal power to a level of noise power. It is most often expressed as a measurement of decibels (dB). Higher numbers generally mean a better specification, since there is more useful information (the signal) than there is unwanted data (the noise).

Channel capacity: is the tight upper bound on the rate at which information can be reliably transmitted over a communication channel.

Bit Rate: is the number of bits that are conveyed or processed per unit of time.

Summary

Before the emergence of the Internet and other data networks, telecommunications had a clear meaning: the telephone was an application of technology that allowed people to communicate at a distance by voice. Now, many years later after several technology changes in telecommunications the definition has changed to: Telecommunications is the suite of technologies, devices, equipment, facilities, networks, and applications that support communication at a distance.

The technologies used have changed greatly over the last 50 years. Empowered by research into semiconductors and digital electronics in the telecommunications industry, analog representations of voice, images, and video have been supplanted by digital representations. All types of media can be represented in the same basic form and therefore handled uniformly within a common infrastructure (most commonly as Internet Protocol, or IP, data streams).

Telecommunications are a big part of our society and we wouldn’t be able to live without it anymore.

References

[1] Roger L. Freeman, Fundamentals of Telecommunications, Second Edition, John Wiley & Sons, Inc.2005.

[2] JohnG.Proakis, MasoudSalehi, Communication SYSTEMS Engineering, 2ndEd.Prentic-Hall, INC.2002.

[3] Upamanyu.Madhow, Fundamentals of Digital Communication, Cambridge University Press,2008.

 

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