digital communications laboratory

L A B M A N U A L

Digital Communications LABCourse Code: 11-EC 308LIII/IV B.TECH - I SEMESTERECE

DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERINGKL UNIVERSITYVADDESWARAM, GUNTUR 522 502 (A.P.) INDIA2013-14

DIGITAL COMMUNICATIONS LAB EXPERIMENTS AND MINI PROJECTS.

Class: III B.Tech I Sem Course Code: 11-EC 308L

Hardware with Lab View: 1) Design an ASK Modulator Circuit. 2) Design an ASK Detection Circuit.3) Design a FSK Modulator Circuit. 4) Design a FSK Detection Circuit.5) Design a PSK Modulator Circuit.

Software with MATLAB: 1) PCM and Delta modulationusing Mat lab. 2) Comparison of various baseband pulses (a) sinc pulse (b) raised cosine pulse with different roll off factor (). 3) ASK with optimum reception. 4) Signal space analysis based modulation and Maximum likelihood based demodulation of ASK.5) FSK and PSK with modulation and degeneration.

MINI PROJECTS: 1) Design a Baseband Transmission System with optimum reception using sinc pulses. 2) Design a Baseband Transmission System with optimum reception using raised cosine pulses. 3) Construct an Eye diagram with noise and ISI for baseband transmission (using sinc pulses). 4) Design a BPSK Transmission System with optimum reception.(consider the bit rate as 1bps) 5) Design a BFSK Transmission System with optimum reception.(consider the bit rate as 1bps) 6) Design a QPSK Transmission System with optimum reception.(consider the bit rate as 1bps) 7) Design a DPSK Transmission System with optimum reception.(consider the bit rate as 1bps) 8) Signal space analysis based modulation and Maximum likelihood based demodulation of PSK. Observe the constellation diagram of transmitted and received signal 9) Signal space analysis based modulation and Maximum likelihood based demodulation of QPSK. Observe the constellation diagram of transmitted and received signal 10) Plot Pe ( probability of error) of ASK for various Eb/N0(dB) 11) Plot Pe ( probability of error) of BPSK for various Eb/N0(dB) 12) Plot Pe ( probability of error) of BFSK for various Eb/N0(dB) 13) Plot Pe ( probability of error) of QPSK for various Eb/N0(dB) 14) Plot Pe ( probability of error) of DPSK for various Eb/N0(dB)) 15) Design a digital transmission system using ASK for the transmission and reception of text messages. 16) Design a digital transmission system using PSK for the transmission and reception of text messages. 17) Design a digital transmission system using QPSK for the transmission and reception of text messages. 18) Design a digital transmission system using ASK for the transmission and reception of Audio. 19) Design a digital transmission system using PSK for the transmission and reception of Audio. 20) Design a digital transmission system using QPSK for the transmission and reception of Audio.

1 Amplitude Shift keyingAIM: Design a Amplitude Shift Keying Modulator circuit and verify its functioning with Lab View. TOOLS REQUIRED:Software Tools: Lab ViewHardware Components:S.NoItemRangeQty.

1.DACs6351,62111Each

2.Op-AmpIC7411

3.TransistorBC1071

4.DiodeBY1271

5.Resistors1K, 27K,10 K potentiometer1K -3,remainingEach one 1

6.Capacitors1F1

7.Regulated Power Supply(0-30)V/2A1

8.Bread Board1

9.Connecting Wires

CIRCUIT DIAGRAMS:i MODULATION:

PROCEDURE:1. Connect the circuit as shown in the figure.2. Apply the message signal as input voltage m(t) as 780Hz and apply a sine wave carrier as 9 kHz.3. Observe the waveforms for ASKModel Waveforms:Modulation:

RESULTS: An Amplitude Shift Keying Modulator is designed and verified its functioning with Lab View. VIVA QUESTIONS: 1. What are the applications of ASK?2. What are the limitations of ASK?3. Why ASK is inferior?

2. ASK DetectionAIM: Design a Amplitude Shift Keying Detector circuit and verify its functioning with Lab View. TOOLS REQUIRED:Software Tools: Lab ViewHardware Components:S.NoItemRangeQty.

1.PLL5651

2.ComparatorIC7411

3.

4.Resistors100 K,10K potentiometer100k -1,10K

5.Capacitors0.01 F0.01 F-1


7.Bread Board1

8.Connecting Wires

ASK DemodulatorAn ASK signal can be demodulated using an envelope detector. A simple envelope detector circuit is shown in Fig.2.

ASK Demodulation

R=1k C=1F PROCEDURE: 1. Connect the circuit as shown in the circuit diagram. 2. Interface the DACs to the CPU by testing with Lab View 3. Simulate the Function Generator in Lab View and apply the message signal (Square Wave) as input voltage m (t) at 780Hz and a Sine Wave carrier at 9 kHz. 4. Simulate Oscilloscope and observe the ASK waveforms 5. Use the demodulation circuit to obtain m (t) back.

Model Waveforms: Demodulation:

3. Frequency Shift KeyingAIM: Design a Frequency Shift Keying Modulator Circuit and verify its functioning with Lab View. TOOLS REQUIRED:Software Tools: Lab ViewHardware Components: S.NoItemRangeQty.


2.Op-AmpLF398,IC741Each one 1

3.Resistors10K, 47K,10 K potentiometer10K -3,remainingEach one 1


5.Bread Board1

6.Connecting Wires

Theory: Generation of FSK Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK (BFSK). 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. In binary FSK system, symbol 1 & 0 are distinguished from each other by transmitting one of the two sinusoidal waves that differ in frequency by a fixed amount. Si (t) = 2E/Tb cos 2f1t, 0 t Tb = 0, elsewhere Where i=1, 2 & Eb=Transmitted energy per bit Transmitted freq= i = (nc+i)/Tb, and n = constant (integer), Tb = bit interval Symbol 1 is represented by S1 (t) Symbol 0 is represented by S0 (t)CIRCUIT DIAGRAMS: MODULATION:

PROCEDURE:1. Connect the circuit as shown in the figure.2. Apply the input voltage c1(t) at 50kHz and c2(t) at 100kHz. Apply Binary data at 1kHz.3. Observe the waveforms for FSK.4. Use the demodulation circuit to obtain Binary data back.Model Waveforms:

RESULTS: A Frequency Shift Keying Modulator is designed and verified its functioning with Lab View.

4.FSK DetectionAIM: Design a Frequency Shift Keying Detector circuit and verify its functioning with Lab View. TOOLS REQUIRED:Software Tools: Lab ViewHardware Components:S.NoItemRangeQty.

1.PLL5651

2.ComparatorIC7101

3.Resistors600, 5K,10 K 10k -3,remainingEach one 1

6.Capacitors0.1F,0.05 F,0.2 F,0.02 F,0.01 F0.1F-1,0.05 F-1,0.2 F-1,0.02 F-2,0.01 F-1


8.Bread Board1

9.Connecting Wires

CIRCUIT DIAGRAMS:1 DEMODULATION:

PROCEDURE:PROCEDURE: 1. Connect the circuit as shown in the circuit diagram. 2. Interface the DACs to the CPU by testing with Lab View 3. Simulate the Function Generator in Lab View and apply Sine Wave carrier signals c1 (t) with a voltage 9v at 50 kHz and c2 (t) at 100 kHz. Apply Binary data at 1 kHz. 4. Simulate Oscilloscope and Observe the FSK waveforms 5. Use the demodulation circuit to obtain Binary data back. Model Waveforms:

RESULTS: A Frequency Shift Keying Detector is designed and verified its functioning with Lab View.

5. Binary Phase Shift KeyingAIM: Design a Binary Phase Shift Keying Modulator Circuit and verify its functioning with Lab View. TOOLS REQUIRED:Software Tools: Lab ViewHardware Components: S.NoItemRangeQty.


2.Op-AmpLF398,IC741Each one 1

3.Resistors1K, 10 K,47K, 10 K potentiometer1K -2,10K -2, remaining Each one 1


5.Bread Board1

6Connecting Wires

CIRCUIT DIAGRAMS:i MODULATION:

PROCEDURE:1. Connect the circuit as shown in the figure.2. Apply the input voltage c(t) at 8kHz,3.5V and Apply Binary data at 1kHz.,3.5V3. Observe the waveforms for BPSK.

Model Waveforms:

RESULTS: A Binary Phase Shift Keying Modulator and Demodulator are designed and verified its functioning with Lab View.

VIVA QUESTIONS:1. What are the applications of BPSK?2. What are the merits of BPSK?3. Compare bandwidth requirement of BPSK with other modulation Schemes.

Experiment -1. Date :

PCM and Delta Modulation

Introduction:

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, DVD and Compact Discformats, as well as other uses such as digital telephone systems. A PCM stream is a digital representation of an analog signal, in which the magnitude of the analog signal is sampled regularly at uniform intervals, with each sample being quantized to the nearest value within a range of digital steps. Delta modulation (DM or -modulation) is an analog-to-digital and digital-to-analog signal conversion technique used for transmission of voice information where quality is not of primary importance. DM is the simplest form of differential pulse-code modulation (DPCM) where the difference between successive samples is encoded into 1-bit data streams.

Aim: To implement PCM and Delta Modulation. Student should observe the affect of companding in PCM and the increase of sampling rate, frequency of the input in DM ( slope overload distortion , granular noise)

Software Used:

Matlab.

Algorithm:

1) Generate a sinusoid. 2) Using the inbuilt commands uencode and udecode encode and decode the input using PCM without companding. 3) Using the inbuilt commands uencode, udecode and compand encode and decode the input using PCM with companding. 4) Observe the differences between step 2 and step 3 by plotting the figures. 5) Now generate a sinusoid with a high sampling rate. 6) Determine the step size for DM. 7) Using a for loop encode all the samples to get the Delta Modulation waveform 8) Generate the binary sequence for each sample. 9) Increase the frequency of the input and observe the change in delta to preserve the information when delta modulated.

Source Code:Expected Figures:

Pulse code Modulation.

Delta modulation:

Result: PCM and Delta Modulation are implemented. The effect of companding is observed in PCM. By changing the amplitude and frequency of the input slope overload distortion and granular noise are observed in Delta Modulation. Experiment -2. Date : Comparison of various baseband pulses (a) sinc pulse (b) raised cosine pulse with different roll off factor (). Introduction: In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency (a maximum bandwidth or highest signal frequency). pulse shaping is the process of changing the waveform of transmitted pulses. Its purpose is to make the transmitted signal better suited to its purpose or the communication channel, typically by limiting the effective bandwidth of the transmission. By filtering the transmitted pulses this way, the intersymbol interference caused by the channel can be kept in control. Aim: To understand the concept of pulse shaping. To understand the merits and demerits of sinc pulse and raised cosine pulse by observing the pulses in time domain and frequency domain. Software Used: Matlab. Algorithm: 1) Determine the sampling frequency. 2) Set bit-rate rb to 1. 3) Compute bandwidth w= rb/2. 4) Generate a sinc pulse . 5) Generate a raised cosine pulse with a specified alpha. 6) Observe the two signals . 7) Set rb to 100 and observe the spectrum of the two pulses.

Source Code:Expected Figures: Transmission Pulses in Time domain.

Transmission Pulses in frequency domain:

Result: The sinc and raised cosine pulses are observed in time and frequency domain and their merits and demerits are discussed.


AMPLITUDE SHIFT KEYING WITH OPTIMUM RECEPTION. Introduction:

Amplitude-shift keying (ASK) is a form of modulation that represents digital data as variations in the amplitude of a carrier wave. Any digital modulation scheme uses a finite number of distinct signals to represent digital data. ASK uses a finite number of amplitudes, each assigned a unique pattern of binary digits. Usually, each amplitude encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular amplitude.

Aim: To understand the concept of Amplitude Shift Keying. To understand the process of optimum detection

Software Used: Matlab.

Algorithm:

1) Generate the binary message waveform 2) Multiply the message waveform with the carrier. 3) Take a reference of the carrier for one bit duration. 4) Using the Matched filter detect the received signal. 5) Reconstruct the received signal.

Source Code:

Expected Figures:

ASK Modulated waveform.

Noise corrupted Modulated waveform

Output of the matched filter

Demodulated output:

Result: ASK waveform is generated. Optimum detection process is understood.


Signal space analysis based modulation and Maximum likelihood based demodulation of Real and Complex Modulation schemes

Introduction:

Signal space analysis provides a mathematically elegant and highly insightful tool for the study of digital signal transmission. Signal space analysis permits a general geometric framework for the interpretation of digital signaling that includes both baseband and bandpass signaling schemes. The set of signal waveforms {s1(t), s2 (t), ,sM (t)} can be plotted as a set of N-dimensional vectors with coordinates (ai1, ai2, ,aiN) within the signal space spanned by {1(t), 2(t),, N(t)}. In each time slot of duration T seconds, one of M possible signals s1(t), s2(t),,sM(t) is transmitted. Each of the signals si(t) may be represented by a point in Euclidean space of dimension N M spanned by a set of N orthonormal basis functions. These points are referred to as transmitted signal points or message points. The set of message points corresponding to the set of transmitted signals {s1(t), s2(t),,sM(t)} is called a signal constellation. In a digital receiver, the received signal r(t) is applied to a bank of N correlators whose outputs zj(T) define an observation vector Z(T) = {z1(T), z2(T), , zN(T)}. The observation vector Z(T) represents the received signal r(t) in the same N-dimensional space used to represent the transmitted signals, this is known as the received signal point. The process of deciding which of the signal vectors does the observation vector most closely resemble is equivalent to determining which of the message points is the received signal vector closest to. The detection process can be thought of as a distance measurement (Euclidian distance). Choose the transmitted signal si such that the distance d (r,si) = ||r si|| is minimized

Aim: To understand the concept of signal space analysis. To understand the concept of complex signals and maximum likelihood detection.

Software Used: Matlab.

Algorithm:

1) Generate a binary data with 1 for bit 1 and -1 for bit zero. This is a real modulation scheme. 2) Observe its constellation using the command scatterplot. 3) Add random noise to it. 4) Observe its constellation. 5) Demodulate the noise corrupted signal using maximum likelihood detection.(Euclidean distance between the received and the reference). 6) Generate a binary data with 1+1i for bit 1 and -1-1i for bit 0. This is a complex modulation scheme. 7) Observe its constellation using the command scatterplot. 8) Add random noise to it. 9) Observe its constellation. 10) Demodulate the noise corrupted signal using maximum likelihood detection.(Euclidean distance between the received and the reference). Source Code: Expected Figures:

Constellation diagram for real modulation scheme.

Constellation diagram for complex modulation scheme.

Constellation diagram for Noise corrupted complex Modulation scheme:

Result: Signal space analysis based modulation and Maximum likelihood based demodulation of real and complex modulation schemes are done.

digital communications laboratory

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