EE 3131 EE 3801 Telecommunications Fundamentals Wei Jin Alan Pak Tao Lau Professor Assistant Professor CF630 CF608 Tel: 27666180 Tel: 34003346 firstname.lastname@example.org email@example.com Department of Electrical Engineering
Assessment Methods Coursework: 40% Assignments (5%): Questions and exercise problems at the end of each chapter Midterm Tests (30%) Lab. (5%): One lab report chosen from any of the three experiments needs to be handed in one week before the exam. Examination: 60% The duration will be 3 hours. All questions will be compulsory. Course notes: ftp.ee.polyu.edu.hk/aptlau/telecom
Laboratory Experiments The experiments will be performed in the Control and Signal Processing Laboratory in EF401. Three experiments need to be done. The experiments will be on: (1) Conventional Amplitude Modulation (Envelope Modulation) (2) Time Division Multiplexing (3) Pulse Code Modulation You will be informed of the schedule of the labs in due course.
About the Instructor Alan P.T. Lau • B.A.Sc. (2003), M.A.Sc.(2004), Electrical and Computer Engineering, University of Toronto, Canada • Ph.D.(2008), Electrical Engineering, Stanford University, USA • Research area: Fiber-optic communication systems Wireless communication systems Office hours: Wed 10-12 am
Some course logistics Potential problems I foresee on my side: Lecture planning Assumption of Background Speed of instruction Background assumed: AMA 201, 202 or 203: linear algebra, matrix, eigenvalue, eigenvector, Laplace transform, Fourier transform
Some expectations For myself • Prepare for lecture, on time, free to talk after class From you • Turn your mobile to silent and don’t disturb others • Most importantly, participate ~
Course Outline • Main Chapters: • Introduction to Telecommunications • Signal and Systems Analysis • Amplitude Modulation (AM) • Angle Modulation • Pulse Modulation • Digital Communications • Optical Fiber Communications
Introduction to Telecommunications • Objectives: • To provide a broad overview of communication systems • To describe the main components of a communication system • To introduce the concept of a signal • To classify different types of communication systems • To introduce the concept of modulation in communications • To introduce the effect of noises in system performance • To describe the key factors to evaluate the performance of a • communication system
Introduction to Telecommunications What does telecommunications mean? Telecommunications consists of “tele” and “communications”. “tele” --- “over a distance” “communications” --- “the process of exchanging information” Thus , telecommunication means exchanging information over a distance. What are some communication systems we used everyday
Typical Communication Systems Copper wire communication: Telephone Modem, DSL, Broadband Wireless Communication: Cellular communication Radio, TV Broadcast, Satellite communication Fiber-Optic Communication Global Long-Haul communication
The importance of communication systems in modern lives Applications resulting from the development of comm. technologies Yahoo (1994), Email (1996), ICQ (1996), Google (1998), MSN(2000), Friendster (2001), Facebook (2004), Youtube (2005) HDTV (2008), cell phone with data transfer (GPRS) (2000), Wi-Fi (2001), video phone (2005) Now, you can: • Buy things online • Do transactions online and through your cell phone (e-banking) • SMS, message people instantly (ICQ,MSN) • Do almost anything ... Even break up with bf/gf online~~~
Components of a communication system Cell phone system Person who talks on a phone (message source) Micro-phone (sound is converted into electrical signal) Sender antenna to base station to receiver antenna (transmission channel) Speaker (electrical signal is converted back into sound) Person who listens (message destination)
Components of a communication system Cable TV Broadcast system Images or actions to be filmed (message source) Video camera (image message is converted into electrical signal) Underground cables (transmission channel) Television at home (electrical signal is received and converted back into image message) Person who watches television (message destination)
Input signal Transmitted signal message Transmitter Transducer Source Channel Noise, distortion Receiver Transducer Destination Output message Output signal Received signal Components of a communication system Block diagram of a communication system: • Channel • a medium for signal transmission (e.g. copper wire, optical fiber, or free space). Introduce noises and distortion. • Receiver • to recover (demodulate) the output signal from the channel. • Output transducer • to convert the message signal back into the original message. (e.g. speaker, TV) • Destination • the unit to which the message is communicated. • Source • generate a message (human voice, TV picture, or data) • Input transducer • convert a message into a signal (message signal). e.g. microphone, video camera, etc. • Transmitter • to modify (modulate) the message signal for transmissioninto channel.
Classification of communication systems • Depending on the transmission media (channel) used: • line communication system • In line communication, transmission is carried out on the transmission line. • e.g. wire, coaxial cable, optical fiber, etc. • wireless communication system. • In wireless communication, signals from various sources are transmitted through a common media – open space. • e.g. radio, microwave, etc.
Classification of communication systems According to the characteristics of transmitted signals, we have analog communication system and digital communication system. At present, only AM,FM radio remain to be analog communication systems.
Classification of communication systems Duplex (2-way) communication • Phone Conversation • Internet Simplex (1-way) communication
Input signal Transmitted signal message Transmitter Transducer Source Channel Noise, distortion Receiver Transducer Destination Output message Output signal Received signal Signals in communication systems Focus of this course In a communication system, a message must be converted into a signal before it can be transmitted in the transmission channel. What is a signal?
Telecommunications A signal is a set of information or data and is usually a function of time. A typical example of a signal is a time varying electric current that contains the message. An example of time domain signal waveform Should we just simply send a signal from a phone directly to the channel?
Modulation for transmission In a communication system, the function of transmitter is to modify the message signal for efficient transmission to the channel, that is, to perform modulation. What is modulation?
Carrier Wave and Modulation What is a carrier wave? In communications, a carrier wave is a sinusoidal wave of high frequency. For example, Carrier Frequency Phase amplitude Modulation is the process of impressing information onto the carrier for transmission by varying a parameter of the carrier in proportion to a signal. This parameter may be the amplitude, the frequency or the phase of the carrier wave. For example, given a signal m(t), amplitude modulation (AM) can be achieved by multiplying m(t) with the carrier: m(t) – original signal (baseband signal) g(t) -- modulated signal (bandpass signal)
Carrier Wave and Modulation Modulation is performed by the use of a modulator. A modulator is a product device, it varies the carrier wave in accordance with the message signal and the resulting modulated signal “carries” the message information. It carries no information It carries m(t)
902 928 Bandwidth of a signal Bandwidth is the portion of electromagnetic spectrum occupied by a signal. Example: A signal frequency range is 902 to 928 MHz. What is the signal bandwidth? f1 = 902 MHz, f2 = 928 MHz, then BW = f2 – f1 = 26 MHz If a signal has too large of a bandwidth for the channel, it will undergo distortion (explain) and affect system performance
Why is modulation necessary? Why not just transmit the signal directly? Several reasons: 1. Efficient transmission: By the use of modulation,message can be transmitted at a desired frequency band. For example, in radio waves transmission, then for efficient radiation of electromagnetic energy, the physical dimension of the radiating antenna should be at least 0.1. Frequency range of a speech signal: 100 to 3000 Hz Since f = c 100 km 3000 km. An impracticably large antenna!!!
= Why is modulation necessary? • 2. Frequency allocation and efficient spectrum utlilzation: • Modulation can shift the frequency spectrum of the signal to the location centered on the carrier frequency. • e.g. different radio broadcast station has different carrier frequency and modulation allows you to choose the one you like. Modulation moves signal spectrum to its assigned frequency range without overlapping and thus realizing Frequency Division Multiplexing (FDM). We will talk more about it on Chapter 3
Noise in communication systems • What is noise? • undesired signal which carries no information • random and unpredictable, produced by the natural processes
Noise in communication systems • If the noise level becomes high, the information cannot be recovered • Even for lower noise levels, the quality of the information reception will be reduced. (think of bad cell phone reception)
Noise in communication systems In a communication system, there are two main types of noises: The electrical noise that is introduced in the transmitting medium is termed external noise. The noise introduced by the components in the transmitter and receiver is known as internal noise.
Noise in communication systems • External Noise • External noise includes two main types: • Man-made noise: • produced by electromagnetic waves generated by things like electric motors, power lines, etc. • Atmospheric noise: • caused by naturally occurring disturbances in the earth’s atmosphere due to, e.g. lightning, etc.
Noise in communication systems Internal Noise Internal noise is produced by electronic circuits. There are two types of internal noise: thermal noise and shot noise.
Noise in communication systems Thermal Noise Thermal noise is generated in a resistive component due to the rapid and random motion of electrons and atoms inside the component. This motion increases with increasing temperature (hence, “thermal”). This random motion of electrons produces an unpredictable component in a current passing through a resistor (hence, “noise”). It is sometimes referred to as Johnson noise, after its discoverer.
Noise in communication systems • Shot Noise • Shot noise exists in all active devices, especially in transistors. • It is caused by random variations in the arrival rate of electrons or holes at the output of the device.
Noise modeling Shot noise and thermal noise are additive. Noise is one of the factors that limit communication system performance it needs to be measured. How to measure the amount of noise? Noise
Signal-to-Noise Ratio Signal-to-Noise Ratio (SNR or S/N) provides a comparison of noise and signal powers at the same point. It is defined as and in decibel form (which is usually convenient) as
Limits of communication systems Noise imposes a limit on the rate of information transmissionNoise is unavoidable. • Why is noise unavoidable? • At any temperature above absolute zero, thermal energy causes microscopic particles to exhibit random motion. The random motion of charged particles such as electrons generates random currents or voltages called thermal noise. • Thermal noise exists in every communication system.
Limits of communication systems Due to various reasons, every communication system supports transmission at certain limited frequency bands only. Bandwidth and noise limit the communication system performance. Usable Bandwidth
Communication System Performance How to evaluate the performance of a communication system? 1. Efficiency -- To determine the capacity of transmission channel per given bandwidth; 2. Reliability --To determine the signal quality. In an analog communication system, Efficiency is measured by transmission channel bandwidth, B. Reliability is measured by system output signal-to-noise ratio (S/N).
Communication System Performance • Example • A conventional amplitude modulation telephone system requires 8 kHz bandwidth while a new modulation format requires 4 kHz bandwidth . Therefore, • the new system has a higher efficiency than the conventional system. • A telephone system requires a S/N at least 20 dB and a TV picture needs its S/N above 40 dB.
Communication System Performance In a digital communication system, efficiency is measured by bit rate, R, and reliability is measured by bit error rate, Pb. Bit rate: R = n/T (bits/sec) where n is the number of bits sent in T seconds Bit error rate: Pb = number of error bits / total number of bits sent e.g. a digital telephone system requires Pb < 10-3 10-6 and data communication requires Pb < 10-9.
Questions: • Draw a block diagram of a basic communication system. • What is a transducer? What is a signal? What is carrier? • What are main types of internal noise? • Why is modulation important in a communication system? • How to evaluate a communication system? • What are the factors limiting the performance of a communication system? • Find the SNR in dB if the ratio of signal power to noise power is:(a)10 ?(b) 100 ? • Assuming constant noise power, if signal power is increased by 3dB, by what factor is the SNR increased?
Some math revisions: • Trig. identities • Calculus • Taylor series • Probability
Questions 1. Can you increase the SNR by amplifying the signal before the receiver? Why or why not? 2. What type of noise does a transistor has? 3. Find the SNR in dB if the ratio of signal power to noise power is:(a) 10 ?(b) 100 ?
Telecommunications Modulation can be performed by multiplying the message signal, m(t), by a carrier wave (sinusoidal signal), cosct. e.g. g(t) = m(t) cos(ct) where m(t) is the message signal (baseband signal,modulating signal -- signal before modulation), cos(ct) is the carrier wave, and g(t) is the modulated signal (bandpass signal, signal after modulation).
Telecommunications Notice that after modulation the signal transmission takes place at the high frequency carrier which has been modified to carry the lower-frequency message signal. How to perform modulation?
Telecommunications • 3. Efficient spectrum utilization: • The channel bandwidth may be much larger than the signal bandwidth. It would be wasteful if only one signal is transmitted over the channel. • Modulation moves signal spectrum to its assigned frequency range without overlapping and thus realizing Frequency Division Multiplexing (FDM). • Multiplexingisthe process of combining several signals for simultaneous transmission on one channel.