L o v e l y P r o f e s s i o n a l U n i v e r s i t y

N H - 1 , L u d h i a n a -J a l a n d h a r H i g h w a y , N r .

C h e h a r u R a i l w a y B r i d g e , P h a g w a r a

0 1 8 2 4 - 5 1 0 2 7 70 1 8 2 4 - 5 1 0 1 0 4

3 / 3 0 / 2 0 1 0

Diwakar BajajThis document is part of Data Communication and Networks; it consists of assignment based on following topics:

Analog to Digital Signal ConversionsBaud RateBit RateASKFSKPSKMultiplexersMedia TransmissionError DetectingError CorrectingRedundancy

Homework # 2

Submitted By:

Diwakar Bajaj

R-A1801-B28

10805455

Submitted By:

Diwakar Bajaj

R-A1801-B28

10805455Submitted To:

Mr. Ramandeep Singh

Computer Science

CSE356

datya

D

Submitted To:

Mr. Ramandeep Singh

Computer Science

CSE356

datya

D

Ques1. Compare the various digital to Analog signals conversion mechanisms. Also discuss

which technique is better?

Solution:

Digital-to-analog conversion is the process of changing one of the characteristics of an

analog signal based on the information in digital data. Digital information is modulated on the

carrier signal by modifying one or more of its characteristics (amplitude,frequency,phase).This

kind of modification is called Modulation (or shift Keying)

There are different types of digital to analog conversion:

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Amplitude Shift Key:

The amplitude (or height) of the sine wave varies to transmit the

ones and zeros. ASK transmission is highly susceptible to noise interference. The term

noise refers to voltages introduced onto a line by various things such as heat or

electromagnetic induction created by other sources.

Frequency Shift Key:

The frequency of carried signal is varied to represent binary 1 or 0. FSK

avoids most of the noise problems of

ASK, because the receiving device is looking for specific frequency

changes over a given number of periods, it can ignore voltage spikes.

Phase Shift Key:

The phase of carrier is varied to represent binary 1 or 0. Both amplitude

and frequency remain constant as the phase changes. For example, if we

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start with a phase of 0 degrees to represent binary 0, then we can change

phase to 180 degree to send binary 1.

Quadrature Amplitude Modulation:

Quadrature amplitude modulation means

combining ASK and PSK. Modulation technique used in the cable/video networking world.

Instead of a single signal change representing only 1 bps – multiple bits can be represented by a

single signal change. Combination of phase shifting and amplitude shifting (8 phases, 2

amplitudes)

QAM is the better technique for Digital to Analog Conversion as compared to ASK, FSK and

PSK.

Ques2. A periodic signal has a bandwidth of 35 Hz . The highest frequency is 75 Hz. What is the

lowest frequency? Draw the spectrum if the signal contains all frequency of same amplitude.

Solution:

Bandwidth of Periodic Signal B : 35Hz

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Highest Frequency of Periodic Signal fh : 75Hz

Lowest Frequency of Periodic Signal fl : x

Bandwidth = fh – fl

35 = 75 – x

35 – 75 = -x

Lowest Frequency of Periodic Signal fl = 40Hz

Ques3. A non-periodic composite signal has a bandwidth of 250 kHz with the middle frequency

of 175 kHz and peak amplitude of 15 volts. Two extreme frequencies have amplitude of 0. Draw

the frequency domain of the signal with explanation.

Solution:

Let fh be the Highest Frequency and fl be the Lowest Frequency

Fh – Fl = B (Bandwidth)

Fh – Fl =250 ……….. (i)

(Fh+Fl)/2 = 175

Fh + Fl =350 ………..(ii)

From (i) and (ii)

We get,

The lowest frequency (fl) must be at 50 kHz and the highest frequency (fh) at 300 kHz.

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Ques4. Calculate the baud rate for the given bit rate and type of modulation?

a) 400bps,FSK

Solution:

S = N / r

Where N is Bit Rate, N = 400bps

In this case, r = 1

Baud Rate S = N / r = 400 / 1 = 400 baud

b) 6000bps,ASK

Solution:

S = N / r

Where N is Bit Rate, N = 6000bps

In this case, r = 1

Baud Rate S = N / r = 6000 / 1 = 6000 baud

c) 8000bps,QPSK

Solution:

S = N / r

Where N is Bit Rate, N = 6000bps

In this case, r = 2

Baud Rate S = N / r = 6000 / 2 = 3000 baud

d) 72000bps,64QAM

Solution:

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S = N / r

Where N is Bit Rate, N = 72000bps

In this case, r = 1

Baud Rate S = N / r = 72000 / 1 = 72000 baud

Ques5. Draw the constellation diagram for the following

a) ASK with peak amplitude values of 2 and 4

Solution:

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b) Binary PSK with a peak amplitude value of 3

c) 8-QAM with two different peak amplitude values of 1 and 3, and 4 different phases

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Ques6. Give the various multiplexing techniques?

Solution:

Multiplexing is the set of techniques that allows the simultaneous transmission of

multiple signals across a single data link. As data and telecommunications use

increases, so does traffic.

Multiplexing can be divided into three categories:

Frequency Division Multiplexing:

In this we have three channels both attached to MUX

(Input) and DEMUX (Output). It’s in Analog.

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FDM is an analog multiplexing technique that combines analog signals.

Demultipexing :

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Hierarchy of Analog:

Wavelength Division Multiplexing:

WDM is an analog multiplexing technique to combine

optical signals.

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Time Division Multiplexing:

TDM is a digital multiplexing technique for combining several

low-rate channels into one high-rate one.

Two types: Synchronous and Asynchronous

Synchronous has different meaning from that used n other areas of telecommunication. Here

Synchronous means multiplexer allocates exactly the same time slot to each device at all times.

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Synchronous TDM is not always efficient.

Asynchronous:

It is designed to avoid waste. Total speed of input lines can be greater than the capacity of the

path. The number of time slots in an asynchronous TDM frame is based on a statistical analysis

of the number of input lines that are likely to be transmitting at any given time.

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Ques7. What are the various transmission media?

Solution:

Transmission Media is done through Physical Layer, which converts the data into

bits.

Classes of Transmission Media:

Guided Media:

Guided media, which are those that provide a conduit from one device to another,

include twisted-pair cable, coaxial cable, and fiber-optic cable.

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Twisted Pair Cable

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UTP Connector

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UTP Performance

Coaxial Cable:

Used for cable television, LANs, etc

Conductors share a common center axial, hence the term “co-axial”

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Categories of Coaxial Cable:

Performance of Coaxial Cable

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Optical Fibre:

Performance of Optical Fibre

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Unguided Media:

It is also known as Wireless Media. Unguided media transport

electromagnetic waves without using a physical conductor. This type of communication is often

referred to as wireless communication.

Propagation Methods in Unguided Media:

Wireless Transmission Media can be of three types:

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o Radio waves are used for multicast communications, such as AM, FM, maritime radio,

cordless phones, television, and paging systems. Ranged from 3kHz – 1GHz

o Microwaves are used for unicast communication such as cellular telephones, satellite

networks, and wireless LANs. Ranged from 1-300GHz

o Infrared signals can be used for short-range communication in a closed area using line-

of-sight propagation. Ranged from 300 GHz to 400 THz. cannot penetrate walls:

prevents interference between two systems. Useless for long-range communication

o

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Ques8. Discuss in detail the concept of redundancy in error detection and correction?

Soluion:

Redundancy is a process in which detecting and correcting of error is done.

In this, Sender sends extra bits, which are also known as redundant bits along with data to

receiver.

The receiver checks the data and keeps the required data and discards the unused data.

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