LABORATORY MANUAL ON Digital COMMUNICATION TECHNIQUES

LABORATORY MANUAL

ON

Digital COMMUNICATION TECHNIQUES

DEPARTMENT OF ELECTRONICS &TELECOMMUNICATION ENGINEERING

Contents

Sl.no Experiments to be performed Page no

1 Study the functioning of PCM. 2 Study the functioning of Delta modulator

3 Study the functioning of Adaptive Delta Modulator4 Study of Time division multiplexing5 To study the different channel coding and decoding technique. 6 Generation and reception of ASK7 Generation and reception of PSK

8 Generation and reception of FSK.

9 To transmit and receive of signals (audio, video, tone )simultaneously through satellite link.

10 To study PC to PC data transmission through satellite link

11 Study the spectrum of BPSK, QPSK, OQPSK with spectrum analyzer

12 Spreading and dispreading using additive white Gaussian noise generation techniques. (Using MATlab)

13 Transmit different types of signals using a ISDN system

14 Analyze the process of data communication in LAN using LAN trainer and compare the performance different media access techniques

Rules & regulations

(1) Each student must contain a lab record for each laboratory module, recording their individual work & results for each experiment.

(2) For most lab modules you will be assigned to a lab group. Each group typically consisting of five students, who are required to complete each exercise as a team. The detailed organization of work within a group should be agreed by the group members themselves. Every student is required to be familiar with all the aspects of each exercise, to participate actively in carrying it out, and to maintain his/her own individual lab record. Any disagreements over the organization of group work should be referred to a demonstrator.

(3) It is essential to study the lab manual, in detail in advance of each exercise.(4) Students are required to attend the lab sessions. Neither the demonstrator nor

the academic supervisors are responsible for missing a lab session. But missing a single session without explanation will normally mean you that you will be deemed to have extra compensatory lab for that experiment or you will be awarded no marks for that lab session.

(5) Arrive prepared with your lead kits, tools, pens, pencils, scales & calculator.(6) Keep the equipments with care & use those for intended purposes. You are

completely financially responsible for loss or damage to equipments signed out to you.

(7) While performing experiments be aware about the electrical supplies.(8) After the completion of the experiment properly keep the equipments in their

respective positions.(9) Only one compensatory lab class can be arranged for those students who miss an

experiment only on the medical ground.(10) Mobile phones are strictly prohibited inside the laboratory.(11) The student has to come to the lab class with proper dress code offered by the

institution.(12) The student is not allowed to bring his /her shoes, bags inside the lab except lab

record, pens, and pencils etc, which are required for the experiment.(13) Any misconduct by the student, either to the demonstrator or to the supervisor,

will lead to suspension of the student from the lab classes.

LAB PLAN

Total experiments to be held : 10

Full mark of each experiment : 10

No of sub groups in a batch : 10

No of students in each group : 3

Division of mark in each Experiment:

SL.NO CATEGORY MARKS1 Viva voce 32 Experiment 33 Record 24 Attendance 15 Discipline 1

TOTAL MARKS 10

Grades awarded to the Student:

Grade MarksO 90 -100 marksE 80-89 marksA 70-79 marksB 60-69 marksC 50-59 marksD 40-49 marks

Experiment-1

Aim of the Experiment:-

To study the functioning of PCM.

Objective:-

To observe

1.Sampling

2. Quantization

3.Encodeing

Equipments required

Sl. No Equipments Required Specification1 PCM trainer kit VCT07

2 Power Supply 230V AC

3 CRO 50MHz

4 Patch Chords 10:15 Crocodile Chords --------

Theory:-

Pulse code modulation(PCM):

PCM is a digital scheme for transmitting analog data. The signals in PCM are binary;

that is, there are only two possible states, represented by logic 1 (high) and logic0 (low).

This is true no matter how complex the analog waveform happens to be. Using PCM, it is

possible to digitize all forms of analog data, including full-motion video, voices, music,

telemetry, and virtual reality (VR). To obtain PCM from an analog waveform at the source

(transmitter end) of a communications circuit, the analog signal amplitude is sampled

(measured) at regular time intervals. The sampling rate, or number of samples per second,

is several times the maximum frequency of the analog waveform in cycles per second or

hertz. The instantaneous amplitude of the analog signal at each sampling is rounded off to

the nearest of several specific, predetermined levels. This process is called quantization.

The number of levels is always a power of 2 -- for example, 8, 16, 32, or 64. These numbers

can be represented by three, four, five, or six binary digits (bits)respectively. The output of a

pulse code modulator is thus a series of binary numbers, each represented by some power

of 2bits.At the destination (receiver end) of the communications circuit, a pulse code

demodulator converts the binary numbers back into pulses having the same quantum levels

as those in the modulator. These pulses are further processed to restore the original analog

waveform.

Precaution:-

Don’t give the power supply if the connections were properely made.

Don’t touch the uncovered part of patch cord.

Switch off the power supply after the experiment

Procedure:-

1. Connect the circuit.

2. Apply the signals to the kit.

3. Observe the waveforms for PCM.

4. Trace the signals.

Waveform:-

Conclusion:-

Experiment-2


To study the functioning of Delta modulator

Objective:-

Demonstrate the process of Delta modulation

Equipments required

Sl. No Equipments Required Specification1 DM trainer kit VCT32

2 CRO 50 MHz3 Patch Chords 10:14 Crocodile Chord -----------5 Power Supply 230V AC

Theory:-

Delta modulation transmits only one bit per symbol. The analog signal which is to be encoded into digital data m(t) and its quantized approximation mq(t) are applied to the input of the comparator. The comparator simply makes a comparison between the inputs.Hence the comparator compares m(t) and mq(t) and has one fixed output V(H).When m(t)>mq(t) and a different output V(L) when m(t)<mq(t).

The up-down counter increments or decrements its count by 1 at each active edge of the clock waveform.The count direction ie incrementing or decrementing is determined by the voltage levels at the “Command direction command” input to the counter.When the binary input which is also the transmitted output S0(t) is at the level V(H),the counter counts up and when it is at the level V(L) the counter counts down. The digital output of the counter is converted into the analog quantized approximation mq(t) by the D/A Converter.

Precaution:-




Procedure:-



3. Observe the waveforms for DM.

4. Trace the signals

Waveform:-

Conclusion:-

Experiment-3


Study the functioning of Adaptive Delta Modulator

Objective:-

Demonstrate the process of Adaptive Delta modulation

Equipments required:-

Sl.No Equipments Required Specification

1 ADM trainer Kit VCT50

2 CRO 50MHz

3 Patch Chords 10:1

4 Power Supply 230V AC

Theory:-

Adaptive delta modulation (ADM) or continuously variable slope delta modulation (CVSD) is a modification of DM in which the step size is not fixed. Rather, when several consecutive bits have the same direction value, the encoder and decoder assume that slope overload is occurring, and the step size becomes progressively larger. Otherwise, the step size becomes gradually smaller over time. ADM reduces slope error,at the expense of increasing quantizing error.This error can be reduced by using a low pass filter.

Precaution:-




Procedure:-



http://en.wikipedia.org/wiki/Continuously_variable_slope_delta_modulation

3. Observe the waveforms for ADM.

4. Trace the signals

Waveform:-

Conclusion:-

Experiment-4


Study of TDM

Objective:-

Analyze the process of time division multiplexing and de-multiplexing

E quipments required

Sl. No. Name of the Equipment Specification

1 TDM kit ST2503

2 CRO 50MHz

3 Patch cords --------

4 CRO probes 10:1

5 Power supply(AC) 230V

Theory:-

Multiplexing: In telecommunications and computer networks, multiplexing (also known as mixing) is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. A device that performs the multiplexing is called a multiplexer (MUX), and a device that performs the reverse process is called a demultiplexer (DEMUX).

Time-division multiplexing:-Time-division multiplexing (TDM) is a digital technology. TDM involves sequencing groups of a few bits or bytes from each individual input stream, one after the other, and in such a way that they can be associated with the appropriate receiver. If done sufficiently and quickly, the receiving devices will not detect that some of the circuit time was used to serve another logical communication path.

Diagram:-

http://en.wikipedia.org/wiki/Time-division_multiplexing

http://en.wikipedia.org/wiki/Demultiplexer

http://en.wikipedia.org/wiki/Multiplexer

http://en.wikipedia.org/wiki/Process_(engineering)

http://en.wikipedia.org/wiki/Computer_networks

http://en.wikipedia.org/wiki/Telecommunications

Modulation Demodulation

Precaution:-




Procedure:-

1. Connect the circuit as shown in the figure.

2. Apply the input voltage m1(t) as 2v at 1kHz and m2(t) as 3v at 10kHz. Apply carrier square pulse

as 4v at 3kHz.

3. Observe the waveforms for PAM-TDM.

4. Use the demodulation circuit to obtain m1(t) and m2(t) back

Waveform:-

http://en.wikipedia.org/wiki/File:Telephony_multiplexer_system.gif

Conclusion:-

Experiment-5


To study the different channel coding and decoding technique

Objective:-

Analyze the process of channel coding and decoding Technique

Equipments required


1 Channel Coder Kit

2 CRO 50MHz


4 CRO probes 10:1


Theory:-

Precaution:-




Procedure:-

Tabulation:-

Waveform:-

Conclusion:-

Experiment-6


Study of ASK

Objective:-

Analyze the Generation and reception of ASK



1 ASK Trainer Kit VCT17

2 CRO 50MHz


4 CRO probes 10:1


Theory:-

Amplitude-shift keying (ASK) is a form of modulation that represents digital data as variations in the amplitude of a carrier wave. The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and phase constant. The level of amplitude can be used to represent binary logic 0s and 1s. We can think of a carrier signal as an ON or OFF switch. In the modulated signal, logic 0 is represented by the absence of a carrier, thus giving OFF/ON keying operation and hence the name given. Like AM, ASK is also linear and sensitive to atmospheric noise, distortions, propagation conditions on different routes in PSTN, etc. Both ASK modulation and demodulation processes are relatively inexpensive. The ASK technique is also commonly used to transmit digital data over optical fiber. For LED transmitters, binary 1 is represented by a short pulse of light and binary 0 by the absence of light. Laser transmitters normally have a fixed "bias" current that causes the device to emit a low light level. This low level represents binary 0, while a higher-amplitude light wave represents binary 1.

Precaution:-




Diagram:-

(Modulation) (Demodulation)

Procedure:-


2. Apply the input voltage m (t) as 500Hz. Apply carrier square pulse as 1kHz.

3. Observe the waveforms for ASK

4. Use the demodulation circuit to obtain m(t) back.

Waveform:-

Conclusion:-

Experiment-7


Study of PSK

Objective:-

Analyze the Generation and reception of PSK



1 PSK Trainer Kit VCT21

2 CRO 50MHz


4 CRO probes 10:1


Theory:-

Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave).Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data. This requires the receiver to be able to compare the phase of the received signal to a reference signal — such a system is termed coherent (and referred to as CPSK).Alternatively, instead of using the bit patterns to set the phase of the wave, it can instead be used to change it by a specified amount. The demodulator then determines the changes in the phase of the received signal rather than the phase itself. Since this scheme depends on the difference between successive phases, it is termed differential phase-shift keying (DPSK). DPSK can be significantly simpler to implement than ordinary PSK since there is no need for the demodulator to have a copy of the reference signal to determine the exact phase of the received signal (it is a non-coherent scheme). In exchange, it produces more erroneous demodulations. The exact requirements of the particular scenario under consideration determine which scheme is used.

Precaution:-

Don’t give the power supply if the connections were properely made.Don’t touch the uncovered part of patch cord.


Procedure:-

1. Connect the circuit as shown in the figure.2. Apply the input voltage m (t) as 500Hz. Apply carrier square pulse as 1kHz.3. Observe the waveforms for PSK4. Use the demodulation circuit to obtain m(t) back.Diagram:-

(Modulation of PSK Signal)

(Demodulation of PSK Signal)

Waveform:-

Conclusion:-

Experiment-8


Study of FSK.

Objective:-

Analyze the Generation and reception of FSK.



1 FSK Trainer Kit VCT18

2 CRO 50MHz


4 CRO probes 10:1


Theory:-

frequency shift keying (FSK) is a method for representing digital data with analog signals by using a change in the frequency of the carrier to represent information. It is thus a type of modulation. FSK with two frequencies, corresponding to the digital values 0 and 1 (see diagram) is the primary method used by low-speed modems.FSK is a low performance type of digital modulation. Binary FSK is a form of constant amplitude angle modulation, BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s) information. With this scheme, the "1" is called the mark frequency and the "0" is called the space frequency

Precaution:-



Procedure:-

1.Connect the circuit as shown in the figure.2. Apply the input voltage m (t) as 500Hz. Apply carrier square pulse as 1kHz.3. Observe the waveforms for FSK4. Use the demodulation circuit to obtain m(t) back.

Waveform:-

Conclusion:-

Experiment-9


To transmit and receive of signals (audio, video, tone )simultaneously through satellite link.

Objective:-

Analysis of transmission of Audio,Video and Tone signals


i) Satellite Transponder ii) Data for Transmission

Theory:-

Satellite communications are comprised of 2 main components:

The Satellite

The satellite itself is also known as the space segment, and is composed of three separate units, namely the fuel system, the satellite and telemetry controls, and the transponder. The transponder includes the receiving antenna to pick-up signals from the ground station, a broad band receiver, an input multiplexer, and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink. The primary role of a satellite is to reflect electronic signals. In the case of a telecom satellite, the primary task is to receive signals from a ground station and send them down to another ground station located a considerable distance away from the first. This relay action can be two-way, as in the case of a long distance phone call. Another use of the satellite is when, as is the case with television broadcasts, the ground station's uplink is then downlinked over a wide region, so that it may be received by many different customers possessing compatible equipment. Still another use for satellites is observation, wherein the satellite is equipped with cameras or various sensors, and it merely downlinks any information it picks up from its vantage point.

The Ground Station

This is the earth segment. The ground station's job is two-fold. In the case of an uplink, or transmitting station, terrestrial data in the form of base band signals, is passed through a base band processor, an up converter, a high powered amplifier, and through a parabolic dish antenna up to an orbiting satellite. In the case of a downlink, or receiving station, works in the reverse fashion as the uplink, ultimately converting signals received through the parabolic antenna to base band signal.

Transmitted Data

A typical satellite link involves the transmission or uplinking of a signal from an Earth station to a satellite. The satellite then receives and amplifies the signal and retransmits it back to Earth, where it is received and reamplified by Earth stations and terminals. Satellite receivers on the ground

include direct-to-home (DTH) satellite equipment, mobile reception equipment in aircraft, satellite telephones, and handheld devices.

Block Diagram:-

(SATELLITE TRANSMITTER & RECEIVER)

Precaution:-


Switch off the power supply after the experimentProcedure:-


2. Setup the kit as shown in the diagram and transmit the data.

3. Observe the data for transmitted and received signalsConclusion:-

Experiment-10


To study PC to PC data transmission through satellite link

Objective:-

Equipments required

i) Satellite Transponderii) PC for Data Transmission

Theory:-

Satellite communications are comprised of 2 main components:

The Satellite

The satellite itself is also known as the space segment, and is composed of three separate units, namely the fuel system, the satellite and telemetry controls, and the transponder. The transponder includes the receiving antenna to pick-up signals from the ground station, a broad band receiver, an input multiplexer, and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink. The primary role of a satellite is to reflect electronic signals. In the case of a telecom satellite, the primary task is to receive signals from a ground station and send them down to another ground station located a considerable distance away from the first. This relay action can be two-way, as in the case of a long distance phone call. Another use of the satellite is when, as is the case with television broadcasts, the ground station's uplink is then downlinked over a wide region, so that it may be received by many different customers possessing compatible equipment. Still another use for satellites is observation, wherein the satellite is equipped with cameras or various sensors, and it merely downlinks any information it picks up from its vantage point.

The Ground Station

This is the earth segment. The ground station's job is two-fold. In the case of an uplink, or transmitting station, terrestrial data in the form of base band signals, is passed through a base band processor, an up converter, a high powered amplifier, and through a parabolic dish antenna up to an orbiting satellite. In the case of a downlink, or receiving station, works in the reverse fashion as the uplink, ultimately converting signals received through the parabolic antenna to base band signal.

Transmitted Data

A typical satellite link involves the transmission or uplinking of a signal from an Earth station to a satellite. The satellite then receives and amplifies the signal and retransmits it back to Earth, where it is received and reamplified by Earth stations and terminals.

Satellite receivers on the ground include direct-to-home (DTH) satellite equipment, mobile reception equipment in aircraft, satellite telephones, and handheld devices.

Block Diagram:-

(Satellite transmitter and receiver for PC)

Precaution:-

Procedure:-


2. Transmit the data from PC to the transponder.

3. Observe the data for transmitted and received signals

Conclusion:-

Experiment-11


Study the spectrum of BPSK, QPSK with spectrum analyzer

Objective:-

Analysis of the spectrum of BPSK,QPSK Signals

Equipments required


1 BPSK Trainer Kit VCT18

2 QPSK Trainer Kit VCT29

3 CRO 50MHz


5 CRO probes 10:1


Theory:-

In binary phase shift keying (BPSK)the transmitted signal is a sinusoid of fixed amplitude .it has one fixed phase when the data is at one level and when the data is at the other level the phase is different by.

If the sinusoid is of amplitude A it has a power ps=(1/2)a2 so that a=

The term ‘quadrature ‘implies that there are four possible phases (4-PSK)wchich the carrier can have at a given time ,as sahown at right on the characterstics constellation for this modulation type.the four phase are labeled {A,B,C,D}corresponding to one {0.90,180,270}degree.

Precaution:-

Procedure:-

Waveform:-

Conclusion:-

Experiment-12

Aim of the Experiment:- Spreading and dispreading using additive white Gaussian noise generation techniques. (Using MATlab)

Objective:-

Equipments required

i)Spread spectrum trainer kit

Theory:-

The term "spread spectrum" refers to the expansion of signal bandwidth, by several orders of magnitude , which occurs when a key is attached to the communication channel.i.e an RF communications system in which the baseband signal bandwidth is intentionally spread over a larger bandwidth by injecting a higher frequency signal.

As a direct consequence, energy used in transmitting the signal is spread over a wider bandwidth, and appears as noise. The ratio (in dB) between the spread baseband and the original signal is called processing gain. Typical spread-spectrum processing gains run from 10dB to 60dB.

To apply a spread-spectrum technique, simply inject the corresponding spread-spectrum code somewhere in the transmitting chain before the antenna (receiver). (That injection is called the spreading operation.) The effect is to diffuse the information in a larger bandwidth. Conversely, you can remove the spread-spectrum code (called a despreading operation) at a point in the receive chain before data retrieval. A despreading operation

reconstitutes the information into its original bandwidth. Obviously, the same code must be known in advance at both ends of the transmission channel. (In some circumstances, the code should be known only by those two parties.)

Diagram:-

(Spread Spectrum communication System)

(Spread spectrum dispreading techniques)

Precaution:-

Procedure:-



3. Observe the waveforms for Spreading and De-Spreading.

4.Trace the waveforms.

Conclusion:-

Experiment-13


Transmit different types of signals using a ISDN system

Objective:-

Equipments required

i) ISDN trainer kit

Theory:-

Integrated Services Digital Network ( ISDN)

(ISDN) is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network. It was first defined in 1988 in the CCITT red book. Prior to ISDN, the phone system was viewed as a way to transport voice, with some special services available for data. The key feature of ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system. There are several kinds of access interfaces to ISDN defined as Basic Rate Interface (BRI), Primary Rate Interface (PRI) and Broadband ISDN (B-ISDN).

ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in potentially better voice quality than an analog phone can provide. It offers circuit-switched connections (for either voice or data), and packet-switched connections (for data), in increments of 64 kilobit/s. A major market application for ISDN in some countries is Internet access, where ISDN typically provides a maximum of 128 kbit/s in both upstream and downstream directions. Channel bonding can achieve a greater data rate; typically the ISDN B-channels of 3 or 4 BRIs (6 to 8 64 kbit/s channels) are bonded.Integrated services refers to ISDN's ability to deliver at minimum two simultaneous connections, in any combination of data, voice, video, and fax, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of most people's complete communications needs.

Diagram:-

Precaution:-

Procedure:-



3. Observe the waveforms for ISDN Communication

Conclusion:-

Experiment-14


Analyze the process of data communication in LAN using LAN trainer and compare the performance different media access techniques

Objective:-

Equipments required

Theory:-

Precaution:-

Procedure:-

Tabulation:-

Waveform:-

Conclusion:-

LABORATORY MANUAL ON Digital COMMUNICATION TECHNIQUES

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