B E V I ( 2 0 1 1 - 2 0 1 5 )

S P R I N G 2 0 1 3

EE344 Communication Systems

D R . S A D I A M U R A W W A T

L E C T U R E 1

Contact Hours2

� Theory Cr Hrs :3, Lab Cr Hrs :1

� Tuesday: 9-11am(A-section)

� Wednesday: 10am-12am (B-section)� Wednesday: 10am-12am (B-section)

� Fri: 10-11(A-section)

� Fri: 11-12(B-section)

� Tutorial : Mon-Fri: 10am-3pm

� 3 quizzes and assignments before and after mid term.(5+5)

Time Line3

Feb Mar April May

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25 28 25 28 20 23

1-11 April-MID

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Academic Honesty:4

� Arrive on time to attend the class. Unexcused absences will affect your grade.

� Turn off cell phones, earphones and other distracting devices.� Be responsible for materials covered in every class.� Hand in your assignments on time at the beginning of the � Hand in your assignments on time at the beginning of the

class. No late submissions are expected.� Speak up whenever you have suggestions or questions.� Work hard to get high score and Give special attention to

lectures and material provided.

You are responsible to behave ethically & honestly. Copying, cheating,forgery, and other unethical or dishonest actions are not tolerated.

Course Outline5

� Basic definitions� Modulation and de-modulation techniques: amplitude,

angle, pulse modulation, digital modulation techniques� Information theory� Error detection and correction� Multiplexing techniques� Multiplexing techniques� Noise and its effects on signal transmission� BER performance of various modulation techniques

under noisy environment.� Overview of other communication Systems(PSTN, Radio

&TV, Cellular, Satellite, Fiber and Cable transmission)� Revision and Problem Discussion

Course Contents6

� Amplitude Modulation Systems: Frequency translation, recovery of base signal, amplitude modulation, maximum allowable modulation, square law demodulator, spectrum of AM signal modulators, balanced modulator, single sideband, vestigial sideband and compatible single sideband system, multiplexing.

� Frequency Modulation Systems: Angle modulation, phase and frequency modulation, relationship between phase and frequency modulation, spectrum of FM signal effect of modulation index on bandwidth. EF generation and detection methods, limiters, frequency multiplication.

� Pulse Modulation Systems: Sampling theorem, low pass signals, pulse amplitude pulse width and pulse position modulation, bandwidth requirements, spectra, cross talk. methods of generation and pulse position modulation, bandwidth requirements, spectra, cross talk. methods of generation and detection of PAM, PVVM signals, pulse code modulation, quantization and commanding. PCM systems, equalization, synchronous and asynchronous PCM systems, delta modulation, phase shift keying, differential phase shift keying, frequency shift keying.

� Noise: Mathematical representation, effect of filtering, response of narrow band filter to noise, superposition of noise, probability density, noise in am, FM system noise calculations, shot noise, thermal noise, noise temperature, noise bandwidth, noise figure, noise figure and equivalent noise in cascaded system, signal to noise ratio.

� Information Theory and Coding: Discrete messages, concept of amount of information, average information, entropy information rate, Shannon’s theorem, channel capacity, relation between band width and S/N ration. Coding: Parity check coding, error correction elementary system.

� Digital Modulation: ASK< PSK< FASK< OOK etc

HEC Recommended Books7

� B. P. Lathi, “Modern Digital and Analog Communication Systems.

� Leon W. Couch, “Digital and Analog Communication Systems.

� John G. Proakis and Masoud Salehi, “Communication Systems.

� Principles of Communication Systems, Taub Schilling McGraw Hill, Latest edition.

� Communication Systems by Bruce Carlson, Latest edition.� Communication Systems by Bruce Carlson, Latest edition.

� Analog and Digital Communication, Simon Haykin, Latest edition.

Outline: Lecture 18

� Communication Systems its fundamentals and components � Base band and modulated signal� Analog and digital transmission. � Signal, Effectiveness of signal, Information, Data, Sender, Receiver, Noise,

Guided and Unguided medium� Unidirectional and Bi-directional communication � Overview of system types: point-point, point-multipoint, broadcast systems; � Overview of system types: point-point, point-multipoint, broadcast systems; � Modes of transmitting Information� Simplex, half & full duplex, baseband & pass band� Multiplexing� Modulation

� Mathematical modeling of signals, time and frequency domain concepts, spectral density, signal to Noise Ratio, Channel Capacity

� Need for modulation Fourier Series and Transforms Review.

9

� Let’s START…

Basic Qs.10

� What is information?

And

� ‘How information flows from one point to another at the most basic level?’

information11

� Information Types: voice, text, images, video, music, digital data.

� Communication Systems: radio/TV broadcasting, PSTN, cellular phones, computer networks, satellite systems, Bluetooth.

� Communication systems send information electronically over communication channels.

� Many different types of systems which convey many different types of information.

� Design challenges include hardware, system and network issues.

� Goal of the communication system is to recreate original information at the receiver with the highest possible fidelity.

Information Representation12

� Communication systems convert information into a format appropriate for the communications channel, typically an electromagnetic wave.

� Analog communication systems convert (modulate) analog information signals into modulated signals, which are also analog.analog.

� Digital communication systems convert information in the form of bits into digital signals.

� Computers and digital devices generate information as bits. Analog information signals can be converted to bits by quantizing and digitizing.

Type of Information13

� Analog signals: voice, music, temperature readings, etc.

� Analog or digital signals: video and images

� Bits: text, computer data, etc.

� Analog signals can be converted into bits by sampling and quantizing.

Basic Communication System14

� Transmitter

� Channel

� Receiver

Block Diagram15

Detailed Communication System16

Block Diagram17

� Source encoder: converts the source or input message into an analog signal or bits called the message signal.

• Transmitter: converts the message signal into a modulated signal in a format suitable for transmission over the channel.

� Channel: Introduces distortion and random noise. Linear channels have output y(t) =x(t) h(t)+n(t), where x(t) is the transmitted (modulated) output y(t) =x(t) h(t)+n(t), where x(t) is the transmitted (modulated) signal, n(t) is the random noise, h(t) is the channel impulse response, and * denotes convolution.

� Receiver: Receiver extracts the original message signal or bits from the channel output signal.

� Source Decoder: Converts the message signal or bits back into the format of the original message.

(contd.)18

Source, Transducer, baseband signal19

Noise Addition20

21

Signal to Noise Ratio22

Transmitting Station23

1. Generates a RF carrier2. Combines it with the baseband signal into a RF signal

through modulation3. Performs additional operations» E.g. analog-to-digital conversion, formatting, coding,spreading, adding additional messages/ characteristicsspreading, adding additional messages/ characteristicssuch as error-control, authentication, or location

information4. Radiates the resultant signal in the form of a modulated

radio wave� Shortly - it maps the original message into the radio-

wave signal launched at the transmitting antenna

Propagation process24

• Transforms, or maps, the radio-wave signal

launched by the transmitter into the incident

radio wave at the receiver antenna

• The propagation mapping involves extra variables • The propagation mapping involves extra variables (e.g. distance, latency), additional radio waves (e.g. reflected wave, waves originated in the environment), random uncertainty (e.g. noise, fading) and distortions

Receiver25

Filters the incident signals : rejects unwanted signals and extract the wanted signal

– The receiver’s response defines a solid “window” in the signal hyperspace

2. Recovers the original message 2. Recovers the original message through reversing the transmitter operations (demodulation, decoding, de-spreading, etc.),

• compensating propagation transformations, and correcting transmission distortions

• Shortly: Maps the incident signals into the recovered message

Analog and Digital Signals26

• Analog signals: varies over a continuous range. Most signals occurring in nature are analog.

• Digital signals: value takes on only a finite set of values (staircase functions).values (staircase functions).

• Binary signals: value takes on just two values (corresponding to “0”s and “1”s of bits).

• A bit time T is the amount of time required to send one bit. Data rate R = 1/T bits per second (bps).

Signal Power27

Performance Metrics28

� Performance metric for analog systems is fidelity: want m(t) = ˆm(t).

� Performance metric for digital systems is data rate (R bps) and probability of bit error (Pb )(R bps) and probability of bit error (Pb )

Data Rate Tradeoff29

� The data rate in digital communications defines the number of bits per second that are transmitted.

� For a probability of bit error (Pb) of 50%, the data rate can be infinite.

� For channels without distortion or noise, the data rate can be infinite with Pb = 0.

� For a fixed data rate, Pb depends on signal and noise power and the channel characteristics.

� For a given system, increasing data rate typically increases Pb.

Shannon Capacity30

� Defines the maximum data rate at which information can be transferred over a channel without errors.

� For a channel with received signal power S, additive white noise with received noise power N, and bandwidth B:

� C = B log2(1 + S/N) bps.

� Shannon theory does not tell you how to design real communication systems.

� Shannon theory predicted a maximum modem speed of 32 Kbps in 1949. Today we have 56 Kbps modems. (Problem was accuracy of mathematical models, not the theory itself.)

Classification and representation of signals,31

� Frequency Domain

� Time Domain

Contd.

� Simplex

� Half & full duplex

� Baseband

� Pass band� Pass band

Simplex

� Simplex communication is permanent unidirectional communication.Some of the very first serial connections between computers weresimplex connections. For example, mainframes sent data to a printerand never checked to see if the printer was available or if the documentprinted properly since that was a human job.

� Simplex links are built so that the transmitter (the one talking) sends asignal and it's up to the receiving device (the listener) to figure out whatwas sent and to correctly do what it was told. No traffic is possible inthe other direction across the same connection.

Half Duplex

A half duplex link can communicate in only one direction, at a time.

Two way communication is possible, but not simultaneously. Walkie-talkies and CB radios sort of mimic this behavior in that you cannothear the other person if you are talking.

Half-duplex connections are more common over electrical links. SinceHalf-duplex connections are more common over electrical links. Sinceelectricity won't flow unless you have a complete loop of wire, you needtwo pieces of wire between the two systems to form the loop. The firstwire is used to transmit, the second wire is referred to as a commonground. Thus, the flow of electricity can be reversed over thetransmitting wire, thereby reversing the path of communication.Electricity cannot flow in both directions simultaneously, so the link ishalf-duplex.

Full Duplex

Full duplex communication is two-way communication achieved over aphysical link that has the ability to communicate in both directionssimultaneously. With most electrical, fiber optic, two-way radio andsatellite links, this is usually achieved with more than one physicalconnection. Your telephone line contains two wires, one for transmit,the other for receive. This means you and your friend can both talk andlisten at the same time.listen at the same time.

Baseband

The baseband is defined as a transmission signal that contains morethan just a single frequency from 0 Hz to the highest frequencycomponent.

In essence, the baseband is the original signal that is intended to betransmitted. However, this baseband frequency, when transmittedtransmitted. However, this baseband frequency, when transmittedtowards its target, can easily be slowed down or can pick up noise anddistortion, which is why the original baseband signal must betransmitted into radio frequency. Radio frequency, however, also is atrisk for transmission problems, creating the need for a band-pass filter.

Passband

The passband is the output of a band-pass filter. It is a signalthat corresponds to the settings of the band-pass filter. Whilebaseband is the original signal, passband is the filtered signal.

Passband is more technically defined as the portion of thePassband is more technically defined as the portion of thespectrum between limiting frequencies with minimum relativeloss or maximum relative gain. Given the earlier example, aradio tuner set at 107.5 MHz will allow only 107.5 MHz to passthrough. Anything below or above 107.5 MHz will be blockedby the filter.

Returning Passband back to Baseband

After filtering, once the passband signal 107.5 MHz is received, thecircuitry of the radio demodulates and demultiplexes it so that a radiolistener receives, in some manner, the original or intended basebandsignal. While baseband is the original signal, passband is the filteredsignal that is eventually converted back to baseband.

Some short-distance systems do not have to modulate baseband tohigher frequencies before transmission. This is more common in linesthat do not require any form of modulation such as Ethernet. Withoutthe risk of interference or distortion, such systems do not needbaseband to be modulated and filtered to passband before reverting tobaseband.

Multiplexing40

Multiplexing is the process of combining multiple signalsinto one, in such a manner that each individual signal canbe retrieved at the destination.

why?

Since multiple signals are occupying the channel, they needSince multiple signals are occupying the channel, they needto share the resource in some manner.

Types� FDM

� TDM (Synchronous, Asynchronous)

� WDM

FDM41

� Frequency-division multiplexing (FDM) is a form of signal multiplexing where multiplebaseband signals are modulated on different frequency carrier waves and added together tocreate a composite signalIn many communication systems, a single, large frequency band is assigned to the system and isshared among a group of users.

Examples of this type of system include:

1. A microwave transmission line connecting two sites over a long distance.2. AM or FM radio broadcast bands, which are divided among many channels or stations.The stations are selected with the radio dial.The stations are selected with the radio dial.

The deriving of two or more simultaneous, continuous channels from a transmission mediumby assigning a separate portion of the available frequency spectrum to each of the individualchannels. (188)

The simultaneous transmission of multiple separate signals through a shared medium at thetransmitter, the separate signals into separable frequency bands, and adding those resultslinearly either before transmission or within the medium. All the signals may be amplified,conducted, translated in frequency and routed toward a destination as a single signal, resultingin economies which are the motivation for multiplexing.

TDM42

Time-Division Multiplexing

Time-Division Multiplexing (TDM) is a type of digital or analog multiplexing in whichtwo or more signals or bit streams are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel.The time domain is divided into several recurrent timeslots of fixed length, one for each

sub-channel.

Time-division multiplexing (TDM) is a method of putting multiple data streams in asingle signal by separating the signal into many segments, each having a very shortsingle signal by separating the signal into many segments, each having a very shortduration. Each individual data stream is reassembled at the receiving end based on the

timing.

Time division multiplexing (TDM) and has many applications, including wirelinetelephone systems and some cellular telephone systems. The main reason to use TDM isto take advantage of existing transmission lines.

TIME DIVISION MULTIPLEXING (TDM) allows multiple conversations to take place bythe sharing of medium or channel in time. A channel is allocated a the whole of the linebandwidth for a specific period of time. This means that each subscriber is allocated atime slot.

FDM and TDM43

WDM44

In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e. colours) of laser light. This wavelengths (i.e. colours) of laser light. This technique enables bidirectional communications over one strand of fiber, as well as multiplication of capacity.

Modulation45

Carrier

46

Types of Modulation47

� Modulation: Signal is transferred to high frequency for efficient transmission.

e=A sin(ɷt +ɸ)e= instant valueA= maximum amplitudeɷ=angular velocity=2*pi*ft=timeɸ= phase angle

� Three types of Modulation� AM� FM� PM

� (FM+PM)= Angle Modulation

Note: Two basic types of Modulation i.e. Amplitude and Angle.

Modulation48

Main Points49

� There are two main formats of signals, analog and digital. Digital signals are more robust to noise and interference.

� Analog signals can be converted into bits by sampling/quantizing.

� Communication systems modulate analog signals or bits for transmission over a communications channel.transmission over a communications channel.

� The building blocks of a communication system are meant to convert information into an electronic format for transmission, then convert it back to its original format after reception.

� Design goals of transmitter (modulator) and receiver (demodulator) are to mitigate impairments introduced by channel.

Question of Lecture50

� What are different types of Communication System that are existing nowadays?

� What is meant by channel capacity?

� What is the difference between FDM and TDM