LABORATORY MANUAL ON Digital COMMUNICATION TECHNIQUES

LABORATORY MANUAL ON Digital COMMUNICATION TECHNIQUESDEPARTMENT OF ELECTRONICS &TELECOMMUNICATION ENGINEERING Contents Sl.no 1 2 3 4 5 6 7 8 9 Experiments to be performed Study the functioning of PCM. Study the functioning of Delta modulator Study the functioning of Adaptive Delta Modulator Study of Time division multiplexing To study the different channel coding and decoding technique. Generation and reception of ASK Generation and reception of PSK Generation and reception of FSK. To transmit and receive of signals (audio, video, tone ) simultaneously through satellite link. To study PC to PC data transmission through satellite link Study the spectrum of BPSK, QPSK, OQPSK with spectrum analyzer Spreading and dispreading using additive white Gaussian noise generation techniques. (Using MATlab) Transmit different types of signals using a ISDN system Analyze the process of data communication in LAN using LAN trainer and compare the performance different media access techniques Page no 10 11 12 13 14 It is essential to study the lab manual. (10) Mobile phones are strictly prohibited inside the laboratory. pencils. scales & calculator. properly keep the (3) (4) (5) (6) (7) (8) (9) Only one compensatory lab class can be arranged for those students who miss an experiment only on the medical ground. Every student is required to be familiar with all the aspects of each exercise. pens. Arrive prepared with your lead kits. Keep the equipments with care & use those for intended purposes.Rules & regulations (1) (2) Each student must contain a lab record for each laboratory module. Neither the demonstrator nor the academic supervisors are responsible for missing a lab session. Students are required to attend the lab sessions. Each group typically consisting of five students. and to maintain his/her own individual lab record. tools. 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. . who are required to complete each exercise as a team. For most lab modules you will be assigned to a lab group. to participate actively in carrying it out. Any disagreements over the organization of group work should be referred to a demonstrator. in detail in advance of each exercise. The detailed organization of work within a group should be agreed by the group members themselves. You are completely financially responsible for loss or damage to equipments signed out to you. While performing experiments be aware about the electrical supplies. recording their individual work & results for each experiment. After the completion of the experiment equipments in their respective positions. and pencils etc. pens. (13) Any misconduct by the student. (12) The student is not allowed to bring his /her shoes. will lead to suspension of the student from the lab classes. either to the demonstrator or to the supervisor. LAB PLAN Total experiments to be held Full mark of each experiment No of sub groups in a batch No of students in each group : : : 10 10 : 3 10 Division of mark in each Experiment: SL. which are required for the experiment.NO 1 2 3 4 5 CATEGORY Viva voce Experiment Record Attendance Discipline TOTAL MARKS MARKS 3 3 2 1 1 10 .(11) The student has to come to the lab class with proper dress code offered by the institution. bags inside the lab except lab record. Encodeing Equipments required Sl. Objective:To observe 1.Sampling 2. No 1 2 3 4 5 Theory:Equipments Required PCM trainer kit Power Supply CRO Patch Chords Crocodile Chords Specification VCT07 230V AC 50MHz 10:1 -------- . Quantization 3.Grades awarded to the Student: Grade O E A B C D Marks 90 -100 marks 80-89 marks 70-79 marks 60-69 marks 50-59 marks 40-49 marks Experiment-1 Aim of the Experiment:To study the functioning of PCM. or six binary digits (bits)respectively. the analog signal amplitude is sampled (measured) at regular time intervals. Connect the circuit. predetermined levels. 4.for example. Using PCM. The sampling rate. including full-motion video. or 64. The signals in PCM are binary. The instantaneous amplitude of the analog signal at each sampling is rounded off to the nearest of several specific. 16. voices. 8. Switch off the power supply after the experiment Procedure:1. music. each represented by some power of 2bits. The number of levels is always a power of 2 -. it is possible to digitize all forms of analog data. These pulses are further processed to restore the original analog waveform. These numbers can be represented by three.Pulse code modulation(PCM): PCM is a digital scheme for transmitting analog data. there are only two possible states. is several times the maximum frequency of the analog waveform in cycles per second or hertz. four. or number of samples per second. To obtain PCM from an analog waveform at the source (transmitter end) of a communications circuit. a pulse code demodulator converts the binary numbers back into pulses having the same quantum levels as those in the modulator.At the destination (receiver end) of the communications circuit. . Apply the signals to the kit. 3. This process is called quantization. Don’t touch the uncovered part of patch cord. that is. and virtual reality (VR). five. Observe the waveforms for PCM. telemetry. 2. This is true no matter how complex the analog waveform happens to be. 32. The output of a pulse code modulator is thus a series of binary numbers. Trace the signals. represented by logic 1 (high) and logic0 (low). Precaution:Don’t give the power supply if the connections were properely made. No 1 2 3 4 5 Theory:Equipments Required DM trainer kit CRO Patch Chords Crocodile Chord Power Supply Specification VCT32 50 MHz 10:1 ----------230V AC .Waveform:- Conclusion:- Experiment-2 Aim of the Experiment:To study the functioning of Delta modulator Objective:Demonstrate the process of Delta modulation Equipments required Sl. When m(t)>mq(t) and a different output V(L) when m(t)<mq(t). Connect the circuit. The digital output of the counter is converted into the analog quantized approximation mq(t) by the D/A Converter. Precaution:Don’t give the power supply if the connections were properely made. The comparator simply makes a comparison between the inputs. Trace the signals Waveform:- Conclusion:- . 2. Switch off the power supply after the experiment Procedure:1. 3.When the binary input which is also the transmitted output S0(t) is at the level V(H). Observe the waveforms for DM.The count direction ie incrementing or decrementing is determined by the voltage levels at the “Command direction command” input to the counter. 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 counter counts up and when it is at the level V(L) the counter counts down. Don’t touch the uncovered part of patch cord.Delta modulation transmits only one bit per symbol. The up-down counter increments or decrements its count by 1 at each active edge of the clock waveform.Hence the comparator compares m(t) and mq(t) and has one fixed output V(H). 4. Apply the signals to the kit. Experiment-3 Aim of the Experiment:Study the functioning of Adaptive Delta Modulator Objective:Demonstrate the process of Adaptive Delta modulation Equipments required:Sl.No 1 2 3 4 Equipments Required ADM trainer Kit CRO Patch Chords Power Supply VCT50 50MHz 10:1 230V AC Specification 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. the step size becomes gradually smaller over time.This error can be reduced by using a low pass filter. Precaution:Don’t give the power supply if the connections were properely made. Observe the waveforms for ADM. Waveform:Trace the signals Conclusion:- . 4. Don’t touch the uncovered part of patch cord. Connect the circuit. Apply the signals to the kit.at the expense of increasing quantizing error. Rather. Otherwise. Switch off the power supply after the experiment Procedure:1. the encoder and decoder assume that slope overload is occurring. 3. and the step size becomes progressively larger. 2. ADM reduces slope error. when several consecutive bits have the same direction value. 1 2 3 4 5 Theory:Name of the Equipment TDM kit CRO Patch cords CRO probes Power supply(AC) Specification ST2503 50MHz -------10:1 230V . No.Experiment-4 Aim of the Experiment:Study of TDM Objective:Analyze the process of time division multiplexing and demultiplexing E quipments required Sl. TDM involves sequencing groups of a few bits or bytes from each individual input stream. Time-division multiplexing:-Time-division multiplexing (TDM) is a digital technology. Don’t touch the uncovered part of patch cord. . Connect the circuit as shown in the figure. 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. and in such a way that they can be associated with the appropriate receiver. 2. If done sufficiently and quickly. 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. Diagram:- Modulation Demodulation Precaution:Don’t give the power supply if the connections were properely made. Switch off the power supply after the experiment Procedure:1. one after the other. A device that performs the multiplexing is called a multiplexer (MUX). The aim is to share an expensive resource. and a device that performs the reverse process is called a demultiplexer (DEMUX).Multiplexing: In telecommunications and computer networks. the receiving devices will not detect that some of the circuit time was used to serve another logical communication path. Use the demodulation circuit to obtain m1(t) and m2(t) back Waveform:- Conclusion:- Experiment-5 Aim of the Experiment:To study the different channel coding and decoding technique Objective:Analyze the process of channel coding and decoding Technique Equipments required Sl. No. 1 2 3 Name of the Equipment Channel Coder Kit CRO Patch cords 50MHz -------Specification .3. Observe the waveforms for PAM-TDM. 4. 1 2 3 Name of the Equipment ASK Trainer Kit CRO Patch cords Specification VCT17 50MHz -------- .4 5 CRO probes Power supply(AC) 10:1 230V Theory:- Precaution:Don’t give the power supply if the connections were properely made. No. Switch off the power supply after the experiment Procedure:- Tabulation:Waveform:Conclusion:- Experiment-6 Aim of the Experiment:Study of ASK Objective:Analyze the Generation and reception of ASK Equipments required:Sl. Don’t touch the uncovered part of patch cord. Laser transmitters normally have a fixed "bias" current that causes the device to emit a low light level. Like AM. In the modulated signal. 2. Don’t touch the uncovered part of patch cord. while a higher-amplitude light wave represents binary 1. ASK is also linear and sensitive to atmospheric noise. thus giving OFF/ON keying operation and hence the name given. Apply carrier square pulse as 1kHz. Precaution:Don’t give the power supply if the connections were properely made. keeping frequency and phase constant. . logic 0 is represented by the absence of a carrier. Apply the input voltage m (t) as 500Hz. propagation conditions on different routes in PSTN.4 5 CRO probes Power supply(AC) 10:1 230V Theory:Amplitude-shift keying (ASK) is a form of modulation that represents digital data as variations in the amplitude of a carrier wave. Both ASK modulation and demodulation processes are relatively inexpensive. This low level represents binary 0. distortions. For LED transmitters. etc. The level of amplitude can be used to represent binary logic 0s and 1s. Connect the circuit as shown in the figure. The ASK technique is also commonly used to transmit digital data over optical fiber. Switch off the power supply after the experiment Diagram:- (Modulation) (Demodulation) Procedure:1. We can think of a carrier signal as an ON or OFF switch. binary 1 is represented by a short pulse of light and binary 0 by the absence of light. The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal). Waveform:- Conclusion:- Experiment-7 Aim of the Experiment:Study of PSK Objective:Analyze the Generation and reception of PSK Equipments required:Sl. No.3. Use the demodulation circuit to obtain m(t) back. Observe the waveforms for ASK 4. 1 2 3 4 Name of the Equipment PSK Trainer Kit CRO Patch cords CRO probes Specification VCT21 50MHz -------10:1 . Precaution:Don’t give the power supply if the connections were properely made. Use the demodulation circuit to obtain m(t) back. Connect the circuit as shown in the figure. Switch off the power supply after the experiment Procedure:1. Don’t touch the uncovered part of patch cord. In exchange. 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. 3.Alternatively.5 Theory:- Power supply(AC) 230V Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing. instead of using the bit patterns to set the phase of the wave. 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). each assigned a unique pattern of binary digits. Usually. determines the phase of the received signal and maps it back to the symbol it represents. the phase of a reference signal (the carrier wave). each phase encodes an equal number of bits. PSK uses a finite number of phases. Each pattern of bits forms the symbol that is represented by the particular phase. thus recovering the original data. it produces more erroneous demodulations. The exact requirements of the particular scenario under consideration determine which scheme is used. 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). Observe the waveforms for PSK 4. Since this scheme depends on the difference between successive phases. The demodulator.Any digital modulation scheme uses a finite number of distinct signals to represent digital data. Apply carrier square pulse as 1kHz. Diagram:- . 2. Apply the input voltage m (t) as 500Hz. or modulating. which is designed specifically for the symbol-set used by the modulator. it is termed differential phase-shift keying (DPSK). Objective:- .(Modulation of PSK Signal) (Demodulation of PSK Signal) Waveform:- Conclusion:- Experiment-8 Aim of the Experiment:Study of FSK. No. Apply carrier square pulse as 1kHz. 2. FSK with two frequencies. Waveform:- . 3.FSK is a low performance type of digital modulation. With this scheme. Don’t touch the uncovered part of patch cord. the "1" is called the mark frequency and the "0" is called the space frequency Precaution:Don’t give the power supply if the connections were properely made. corresponding to the digital values 0 and 1 (see diagram) is the primary method used by low-speed modems. BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s) information. Binary FSK is a form of constant amplitude angle modulation.Analyze the Generation and reception of FSK. Use the demodulation circuit to obtain m(t) back. Switch off the power supply after the experiment Procedure:1. Equipments required:Sl. It is thus a type of modulation. Apply the input voltage m (t) as 500Hz.Connect the circuit as shown in the figure. Observe the waveforms for FSK 4. 1 2 3 4 5 Name of the Equipment FSK Trainer Kit CRO Patch cords CRO probes Power supply(AC) Specification VCT18 50MHz -------10:1 230V 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. Conclusion:- Experiment-9 Aim of the Experiment:To transmit and receive of signals (audio. . video. tone ) simultaneously through satellite link. an up converter. and through a parabolic dish antenna up to an orbiting satellite. . where it is received and reamplified by Earth stations and terminals. and it merely downlinks any information it picks up from its vantage point. The satellite then receives and amplifies the signal and retransmits it back to Earth. and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink. satellite telephones. works in the reverse fashion as the uplink. The transponder includes the receiving antenna to pick-up signals from the ground station. 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. Transmitted Data A typical satellite link involves the transmission or uplinking of a signal from an Earth station to a satellite. Still another use for satellites is observation. is passed through a base band processor. In the case of an uplink. a high powered amplifier. a broad band receiver. namely the fuel system. as is the case with television broadcasts. The primary role of a satellite is to reflect electronic signals. terrestrial data in the form of base band signals. ultimately converting signals received through the parabolic antenna to base band signal. or receiving station. The Ground Station This is the earth segment.Objective:Analysis of transmission of Audio. and the transponder. In the case of a downlink. so that it may be received by many different customers possessing compatible equipment. or transmitting station. In the case of a telecom satellite. an input multiplexer. The ground station's job is two-fold. the satellite and telemetry controls. mobile reception equipment in aircraft. and is composed of three separate units. wherein the satellite is equipped with cameras or various sensors. Satellite receivers on the ground include direct-to-home (DTH) satellite equipment. Another use of the satellite is when.Video and Tone signals Equipments required: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 handheld devices. the ground station's uplink is then downlinked over a wide region. Switch off the power supply after the experiment Procedure:1. Connect the circuit as shown in the figure. Setup the kit as shown in the diagram and transmit the data.Block Diagram:- (SATELLITE TRANSMITTER & RECEIVER) Precaution:Don’t give the power supply if the connections were properely made. Don’t touch the uncovered part of patch cord. 3. Observe the data for transmitted and received signals Conclusion:- Experiment-10 Aim of the Experiment:- To study PC to PC data transmission through satellite link Objective:Equipments required i) Satellite Transponder ii) PC for Data Transmission Theory:- Satellite communications are comprised of 2 main components: . 2. a high powered amplifier. an up converter. and is composed of three separate units. the satellite and telemetry controls. as in the case of a long distance phone call. In the case of a downlink. Another use of the satellite is when. or receiving station. is passed through a base band processor. In the case of an uplink. terrestrial data in the form of base band signals. and it merely downlinks any information it picks up from its vantage point. wherein the satellite is equipped with cameras or various sensors. or transmitting station. In the case of a telecom satellite. The transponder includes the receiving antenna to pick-up signals from the ground station. and the transponder. The primary role of a satellite is to reflect electronic signals. Transmitted Data . and a frequency converter which is used to reroute the received signals through a high powered amplifier for downlink. ultimately converting signals received through the parabolic antenna to base band signal. Still another use for satellites is observation. and through a parabolic dish antenna up to an orbiting satellite. an input multiplexer. 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. the ground station's uplink is then downlinked over a wide region. namely the fuel system. works in the reverse fashion as the uplink. The Ground Station This is the earth segment. as is the case with television broadcasts. a broad band receiver. The ground station's job is two-fold. so that it may be received by many different customers possessing compatible equipment. This relay action can be two-way.The Satellite The satellite itself is also known as the space segment. Transmit the data from PC to the transponder. where it is received and reamplified by Earth stations and terminals. satellite telephones. 2. Block Diagram:- (Satellite transmitter and receiver for PC) Precaution:Procedure:1.A typical satellite link involves the transmission or uplinking of a signal from an Earth station to a satellite. Observe the data for transmitted and received signals Conclusion:- Experiment-11 Aim of the Experiment:- Study the spectrum of BPSK. QPSK with spectrum analyzer Objective:- . Connect the circuit as shown in the figure. and handheld devices. The satellite then receives and amplifies the signal and retransmits it back to Earth. mobile reception equipment in aircraft. Satellite receivers on the ground include direct-to-home (DTH) satellite equipment. 3. Precaution:Procedure:Waveform:Conclusion:- .270}degree. 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 (4PSK)wchich the carrier can have at a given time .as sahown at right on the characterstics constellation for this modulation type. 1 2 3 4 5 6 Name of the Equipment BPSK Trainer Kit QPSK Trainer Kit CRO Patch cords CRO probes Power supply(AC) Specification VCT18 VCT29 50MHz -------10:1 230V 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.B.D}corresponding to one {0.C.Analysis of the spectrum of BPSK.QPSK Signals Equipments required Sl.180.90.the four phase are labeled {A. No. the same code must be known in advance at both ends of the transmission channel. energy used in transmitting the signal is spread over a wider bandwidth. (That injection is called the spreading operation.) The effect is to diffuse the information in a larger bandwidth.e an RF communications system in which the baseband signal bandwidth is intentionally spread over a larger bandwidth by injecting a higher frequency signal. (Using MATlab) Objective:Equipments required i)Spread spectrum trainer kit Theory:The term "spread spectrum" refers to the expansion of signal bandwidth. simply inject the corresponding spreadspectrum code somewhere in the transmitting chain before the antenna (receiver). by several orders of magnitude . and appears as noise. you can remove the spreadspectrum code (called a despreading operation) at a point in the receive chain before data retrieval. Obviously. (In some circumstances. The ratio (in dB) between the spread baseband and the original signal is called processing gain.Experiment-12 Aim of the Experiment:Spreading and dispreading using additive white Gaussian noise generation techniques. A despreading operation reconstitutes the information into its original bandwidth. As a direct consequence. the code should be known only by those two parties.) Diagram:- .i. Typical spread-spectrum processing gains run from 10dB to 60dB. which occurs when a key is attached to the communication channel. Conversely. To apply a spread-spectrum technique. Connect the circuit as shown in the figure. 2. 4. Apply the input voltage m (t) as 500Hz.Trace the waveforms. Conclusion:- Experiment-13 Aim of the Experiment:- Transmit different types of signals using a ISDN system Objective:- . Observe the waveforms for Spreading and De-Spreading. Apply carrier square pulse as 1kHz. 3.(Spread Spectrum communication System) (Spread spectrum dispreading techniques) Precaution:Procedure:1. Multiple devices can be attached to the line. There are several kinds of access interfaces to ISDN defined as Basic Rate Interface (BRI). where ISDN typically provides a maximum of 128 kbit/s in both upstream and downstream directions. A major market application for ISDN in some countries is Internet access. The key feature of ISDN is that it integrates speech and data on the same lines. with some special services available for data. typically the ISDN B-channels of 3 or 4 BRIs (6 to 8 64 kbit/s channels) are bonded. That means an ISDN line can take care of most people's complete communications needs. the phone system was viewed as a way to transport voice. which also provides access to packet switched networks. Prior to ISDN. and packet-switched connections (for data). Diagram:- Precaution:- . and used as needed. video. adding features that were not available in the classic telephone system. voice. ISDN is a circuit-switched telephone network system.Integrated services refers to ISDN's ability to deliver at minimum two simultaneous connections. in increments of 64 kilobit/s. and other network services over the traditional circuits of the public switched telephone network. Primary Rate Interface (PRI) and Broadband ISDN (B-ISDN). It offers circuit-switched connections (for either voice or data). video. It was first defined in 1988 in the CCITT red book. data. resulting in potentially better voice quality than an analog phone can provide. Channel bonding can achieve a greater data rate.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. in any combination of data. and fax. designed to allow digital transmission of voice and data over ordinary telephone copper wires. over a single line. Procedure:1. Apply the input voltage m (t) as 500Hz. Apply carrier square pulse as 1kHz. Observe the waveforms for ISDN Communication Conclusion:- Experiment-14 Aim of the Experiment:- 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:- . 2. 3. Connect the circuit as shown in the figure. 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