Panimalar Engineering College

Transcription

1 PANIMALAR ENGINEERING COLLEGE (A CHRISTIAN MINORITY INSTITUTION) JAISAKTHI EDUCATIONAL TRUST ACCREDITED BY NATIONAL BOARD OF ACCREDITATION (NBA) Bangalore Trunk Road, Varadharajapuram, Nasarathpettai, Poonamallee, Chennai DEPARTMENT OF ELECTRONICS & COMMUNICATION ENGINEERING DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING EC 6512 COMMUNICATION SYSTEM LAB MANUAL V SEMESTER ECE (ODD SEM YEAR )

2 DEPARTMENT OF ECE VISION To emerge as a centre of excellence in providing quality education and produce technically competent Electronics and Communication Engineers to meet the needs of industry and Society. MISSION M1: To provide best facilities, infrastructure and environment to its students, researchers and faculty members to meet the Challenges of Electronics and Communication Engineering field. M2: To provide quality education through effective teaching learning process for their future career, viz placement and higher education. M3: To expose strong insight in the core domains with industry interaction. M4: Prepare graduates adaptable to the changing requirements of the society through life long learning. PROGRAMME EDUCATIONAL OBJECTIVES 1. To prepare graduates to analyze, design and implement electronic circuits and systems using the knowledge acquired from basic science and mathematics. 2. To train students with good scientific and engineering breadth so as to comprehend, analyze, design and create novel products and solutions for real life problems. 3. To introduce the research world to the graduates so that they feel motivated for higher studies and innovation not only in their own domain but multidisciplinary domain. 4. Prepare graduates to exhibit professionalism, ethical attitude, communication skills, teamwork and leadership qualities in their profession and adapt to current trends by engaging in lifelong learning. 5. To practice professionally in a collaborative, team oriented manner that embraces the multicultural environment of today s business world. PROGRAMME OUTCOMES 1. Engineering Knowledge: Able to apply the knowledge of Mathematics, Science, Engineering fundamentals and an Engineering specialization to the solution of complex Engineering problems. 2. Problem Analysis: Able to identify, formulate, review research literature, and analyze complex Engineering problems reaching substantiated conclusions using first principles of Mathematics, Natural sciences, and Engineering sciences. 3. Design / Development of solutions: Able to design solution for complex Engineering problems and design system components or processes that meet the specified needs with appropriate considerations for the public health and safety and the cultural, societal, and environmental considerations.

3 4. Conduct investigations of complex problems: Able to use Research - based knowledge and research methods including design of experiments, analysis and interpretation of data, and synthesis of the information to provide valid conclusions. 5. Modern tool usage: Able to create, select and apply appropriate techniques, resources, and modern Engineering IT tools including prediction and modeling to complex Engineering activities with an understanding of the limitations. 6. The Engineer and society: Able to apply reasoning informed by the contextual knowledge to access societal, health, safety, legal and cultural issues and the consequent responsibilities relevant to the professional Engineering practice. 7. Environment and sustainability: Able to understand the impact of the professional Engineering solutions in societal and environmental context, and demonstrate the knowledge of, and need for sustainable development. 8. Ethics: Able to apply ethical principles and commit to professional ethics and responsibilities and norms of the Engineering practice. 9. Individual and Team work: Able to function effectively as an individual, and as a member or leader in diverse teams, and in multidisciplinary settings. 10. Communication: Able to communicate effectively on complex Engineering activities with the Engineering community and with society at large, such as, being able to comprehend and write effective reports and design documentation, make effective presentations, and give and receive clear instructions. 11. Project Management and Finance: Able to demonstrate knowledge and understanding of the engineering and management principles and apply these to one s own work, as a member and leader in a team, to manage projects and in multidisciplinary environments. 12. Life long learning: Able to recognize the needs for, and have the preparation and ability to engage in independent and life-long learning in the broadest contest of technological change. PROGRAMME SPECIFIC OUTCOMES 1. Graduates should demonstrate an understanding of the basic concepts in the primary area of Electronics and Communication Engineering, including: analysis of circuits containing both active and passive components, electronic systems, control systems, electromagnetic systems, digital systems, computer applications and communications. 2. Graduates should demonstrate the ability to utilize the mathematics and the fundamental knowledge of Electronics and Communication Engineering to design complex systems which may contain both software and hardware components to meet the desired needs. 3. The graduates should be capable of excelling in Electronics and Communication Engineering industry/academic/software companies through professional careers.

4 EC6512 COMMUNICATION SYSTEMS LABORATORY L T P C OBJECTIVES: The student should be made to: To visualize the effects of sampling and TDM To Implement AM & FM modulation and demodulation To implement PCM & DM To implement FSK, PSK and DPSK schemes To implement Equalization algorithms To implement Error control coding schemes LIST OF EXPERIMENTS: 1. Signal Sampling and reconstruction 2. Time Division Multiplexing 3. AM Modulator and Demodulator 4. FM Modulator and Demodulator 5. Pulse Code Modulation and Demodulation 6. Delta Modulation and Demodulation 7. Observation (simulation) of signal constellations of BPSK, QPSK and QAM 8. Line coding schemes 9. FSK, PSK and DPSK schemes (Simulation) 10. Error control coding schemes - Linear Block Codes (Simulation) 11. Communication link simulation 12. Equalization Zero Forcing & LMS algorithms(simulation) TOTAL: 45 PERIODS OUTCOMES: At the end of the course, the student should be able to: CO1:Simulate end-to-end Communication Link CO2:Demonstrate their knowledge in base band signaling schemes through implementation FSK, PSK and DPSK CO3:Apply various channel coding schemes & demonstrate their capabilities towards the improvement of the noise performance of communication system CO4:Simulate & validate the various functional modules of a communication system BRIDGING THE CURRICULUM GAP Course outcomes CO1-CO4 is satisfied by Anna university syllabus. To bridge the gap between Anna University and IIT, experiments like ASK, PWM and PAM are implemented using hardware and Linear delta modulation and OFDM spectrum simulated using Matlab and Experiments like FM radio receiver, ASK, FSK and BPSK using Software defined Radio are included from NIT. - Course Instructors

5 INDEX S.NO LIST OF EXPERIMENTS PAGE NO. 1. AM Modulation and Demodulation 2 2. FM Modulation and Demodulation 8 3. Sampling and Reconstruction Time Division Multiplexing Simulation of Digital Modulation Techniques- ASK,FSK,PSK,QPSK,DPSK 6. Signal Constellation of BPSK, QPSK & QAM Communication Link Simulation using SDR Digital Modulation PSK Digital Modulation QPSK Pulse Code Modulation Delta and Adaptive Delta Modulation Line Coding and Decoding Error Control Coding using MATLAB Simulation of Equalization Techniques Content Beyond Syllabus 82 24

6 LIST OF EXPERIMENTS: CYCLE I 1. AM Modulation and Demodulation 2. FM Modulation and Demodulation 3. Sampling and Reconstruction 4. Time Division Multiplexing 5. CYCLE II Simulation of Digital Modulation Techniques- ASK,FSK,PSK,QPSK,DPSK 6. Signal Constellation of BPSK, QPSK & QAM 7. Communication Link Simulation 8. Digital Modulation PSK 9. Digital Modulation QPSK 10. Pulse Code Modulation, 11. Delta and Adaptive Delta Modulation 12. Line Coding and Decoding 13. Error Control Coding using MATLAB 14. Simulation of Equalization Techniques

7 CIRCUIT DIAGRAM AMPLITUDE MODULATION DEMODULATION 1

8 EXPT.NO.1 AM MODULATION AND DEMODULATION AIM: To construct amplitude modulator and demodulator circuit and plot the waveforms. COMPONENTS REQUIRED: THEORY : S.NO. NAME OF THE EQUIPMENT / COMPONENT RANGE QUANTITY 1 Transistor BC Diode 1N Capacitors 0.1µF, 0.01µF 2,1 4 Resistors 100K,22K,500Ω,20 0K,10Ω 2, 1each 5 Decade Inductance Box 10 mh 1 6 Function Generators 1 MHz 2 7 CRO 20MHz 1 8 Bread board Regulated Power supply 0-30V 1 Modulation can be defined as the process by which the characteristics of carrier wave are varied in accordance with the modulating wave (signal). Modulation is performed in a transmitter by a circuit called a modulator. Need for modulation is as follows: Avoid mixing of signals Reduction in antenna height long distance communication Multiplexing Improve the quality of reception Ease of radiation. Amplitude Modulation is the process of changing the amplitude of a relatively high frequency carrier signal in proportion with the instantaneous value of the modulating signal. The output waveform contains all the frequencies that make up the AM signal and is used to transport the information through the system. Therefore the shape of the modulated wave is called the AM envelope. With no modulating signal the output waveform is simply the carrier signal. Coefficient of modulation is a term used to describe the amount of amplitude change present in an AM waveform. There are three degrees of modulation available based on value of modulation index. 1) Under modulation : m<1, E m < E c 2) Critical modulation: m-1, E m = E c 3) Over modulation: m>1, E m > E c 2

9 MODEL GRAPH: 3

10 Demodulation is the reverse process of modulation and converts the modulated carrier back to the original information. Demodulation is performed in a carrier by a circuit called a demodulator. ADVANTAGES: 1) Relatively inexpensive 2) Low quality form of modulation DISADVANTAGES: 1) Low efficiency 2) Small operating range APPLICATION: 1) Commercial broadcasting of both audio and video signals 2) Two way mobile radio communication such as citizen band (CB) radio. PROCEDURE: 1. Rig up the circuit as per the circuit diagram. 2. Set the carrier signal using function generator and measure the amplitude and time period. 3. Set the modulating signal and measure the amplitude and time period. 4. Vary the amplitude around the carrier voltage. 5. Note down the maximum (E max ) and minimum (E min ) voltages from the CRO. 6. Calculate the modulation index using the formula. 7. Apply the AM signal to the detector circuit. 8. Observe the amplitude demodulated output on the CRO. 9. Compare the demodulated signal with the original modulating signal (Both must be same in all parameters). Plot the observed waveforms. 4

11 TABULATION: INPUT SIGNAL: Signals Amplitude (V) Modulating signal Carrier signal MODULATED SIGNAL: Emax (V) Emin (V) DETECTED SIGNAL: Time period (ms) m = (Emax Emin)/ (Emax + Emin) % Amplitude (V) Time period (ms) Frequency (KHz) Frequency (KHz) Type of modulation 5

12 RESULT: Thus the characteristics of AM Transmitter and Receiver are studied and the waveforms are observed and plotted. Questions 1. Define Amplitude Modulation. A. AM is a process in which the amplitude of the carrier wave is varied in accordance with some characteristics of the modulating signal. 2. What is the need for Modulation? A. a) Difficult in transmitting signals at low frequencies. b) To minimize signal loss. c) To reduce antenna length. 3. What are the applications of AM? A. Amplitude modulation is utilized in many services such as television, standard broadcasting, aids to navigation, telemeter, radar, facsimile etc. 4. What are the different types of AM? A. Single Side Band, Double Side Band and Vestigial Side Band Modulation are the different types of AM. 5. What are the disadvantages of AM? A. Low efficiency, small operating range, noisy reception. 6

13 BLOCK DIAGRAM FM MODULATOR AND DEMODULATOR 7

14 EXPT.NO:2 FM MODULATION AND DEMODULATION AIM: To plot the modulation characteristics of FM modulator and demodulator and also to observe and measure frequency deviation and modulation index of FM. COMPONENTS REQUIRED: S.NO. NAME OF THE EQUIPMENT / COMPONENT RANGE QUANTITY 1 FM Transmitter and receiver kit 1 2 CRO 20 MHz 1 THEORY: Frequency modulation is a type of modulation in which the frequency of the high frequency (carrier) is varied in accordance with the instantaneous value of the modulating signal. FREQUENCY DEVIATION f and MODULATION INDEX m : The frequency deviation signal frequency, over and under the frequency of the carrier. f represents the maximum shift between the modulated f f max f min 2 We define modulation index m f the ratio between f m f f f f and the modulating frequency f. FREQUENCY MODULATION GENERATION: The circuits used to generate a frequency modulation must vary the frequency of a high frequency signal (carrier) as function of the amplitude of a low frequency signal (modulating signal). In practice there are two main methods used to generate FM. 8

15 MODEL GRAPH: 9

16 DIRECT METHOD An oscilloscope is used in which the reactance of one of the elements of the resonant circuit depends on the modulating voltage. The most common device with variable reactance is the Varactor or Varicap, which is a particular diode which capacity varies as function of the reverse bias voltage. The frequency of the carrier is established with AFC circuits (Automated frequency control) or PLL (Phase locked loop). INDIRECT METHOD: The FM is obtained in this case by a phase modulation, after the modulating signal has been integrated. In this phase modulator the carrier can be generated by a quartz oscillator, and so its frequency stabilization is easier. In the circuit used for the exercise, the frequency modulation is generated by a Hartley oscillator, which frequency is determined by a fixed inductance and by capacity (variable) supplied by varicap diodes. ADVANTAGES: 1. Noise reduction 2. Improved system fidelity 3. Efficient use of power DISADVANTAGE: 1. Requires a wider bandwidth 2. Utilizing more complex circuit in both transmitters and receivers. APPLICATION: 1. Television sound transmission 2. Two way mobile radio 3. Cellular Radio 4. Microwave 5. Satellite Communication System 10

17 TABULATION: Signals Amplitude (V) Time period (ms) Frequency(KHz) Modulating signal Carrier signal Modulated signal Demodulated signal T min = f max = T max = f min = 11

18 PROCEDURE: i) Connect the power supply with proper polarity to the kit. While connecting this ensures that the Power supply is OFF. ii) Switch on the power supply and carry out the following presetting as shown in circuit Diagram. iii) In the FM modulator set the level about 2Vpp and frequency knob to the minimum and switch on 1500 KHz. iv) Observe the Fm modulated waveform from the RF/FM output of the FM modulator measure frequency deviation and modulation index of FM. v) For demodulation switch on the demodulator and carry out the following demodulation connection as shown in circuit diagram. vi) Observe the demodulated waveform and plot the graph. RESULT: Thus the modulation characteristics of FM modulator and demodulator are observed and plotted. Questions: 1. What is Frequency Modulation? Frequency modulation (FM) is a technique in which the frequency of the carrier wave is varied in accordance with the amplitude of the message signal. 3. What is the frequency band for FM radio? The frequency band for FM radio is about 88 to 108 MHz. 4. What is the bandwidth of FM signal? Bandwidth of a FM signal may be predicted using: BW = 2 ( + 1 ) f m ; where is the modulation index and f m is the maximum modulating frequency used. 5.What are the disadvantages of FM? Compared to AM, the FM signal has a larger bandwidth 6. What are the disadvantages of FM? High efficiency and better immunity to noise. 12

19 BLOCK DIAGRAM: CIRCUIT DIAGRAM: (USING MOSFET) 13

20 EXPT.NO. 3 SAMPLING AND RECONSTRUCTION AIM: To sample a signal with different sampling frequencies and to reconstruct the same. COMPONENTS REQUIRED: S.NO. NAME OF THE EQUIPMENT / COMPONENT RANGE QUANTITY 1 Sampling trainer kit CRO 20MHz 1 THEORY: The analog signal can be converted to a discrete time signal by a process called sampling. The sampling theorem for a band limited signal of finite energy can be stated as, A band limited signal of finite energy, which has no frequency component higher than W Hz is completely described by specifying the values of the signal at instants of time separated by 1/2W seconds. It can be recovered from knowledge of samples taken at the rate of 2W per second. Sampling is the process of splitting the given analog signal into different samples of equal amplitudes with respect to time. There are two types of sampling namely natural sampling, flat top sampling. Sampling should follow strictly the Nyquist Criterion i.e. the sampling frequency should be twice higher than that of the highest frequency signal. Where, f s 2 f m f s f m Minimum Nyquist Sampling rate (Hz) Maximum analog input frequency (Hz). 14

21 TABULATION: MODULATING SIGNAL: SAMPLED SIGNAL: Amplitude (V) Amplitude (V) Time period (ms) Frequency (KHz) Sampling frequency (KHZ) Duty Cycle (%) No. of Samples Time period (ms) (for each sample) RECONSTRUCTED SIGNAL Amplitude (V) Time period (ms) Frequency (KHz) Total Time period T on T off (ms) Frequency (KHz) Duty cycle calculation: D = T on / (T on + T off ) = % 15

22 ADVANTAGES: It can store retrieve and transmit signals without any loss With higher sampling rate they can relax low pass filter design requirements for ADC and DAC PROCEDURE: 1. Give the connections as per the block diagram. 2. Apply the modulating signal and measure its amplitude and time period. 3. Set the sampling frequency to 80 KHz and note down the amplitude and time period of the sampled signal. 4. Give the sampled signal to the reconstruction circuit and observe the reconstructed signal. 5. Note down the amplitude and time period of the reconstructed signal. 6. Repeat the same procedure for different sampling frequencies. 7. Plot the above waveforms in the graph. 16

23 MODEL GRAPH: 17

24 RESULT: Thus the given signal is sampled with different sampling frequencies and the waveforms are plotted. Questions: 1. What is aliasing effect? A. The original analog waveform can be recovered from the PAM type samples simply by low pass filtering them If fs <f nyquist (2f m ) then overlapping of adjacent spectrum replicates occurs. This is known as aliasing.due to under- sampling (for f s <2f m ) exact analog waveform cannot be recovered, 2. What is the function of Op-amps in this circuit and what is the effect of frequency of sampling signal? A. Op-amps acts as voltage followers, if the f s <2f m, then distorted waveform is Observed, so to recover the exact signal the sampling signal frequency should be maintained greater than or equal to the 2f m. 3. What are the different types of sampling? A. Instantaneous sampling, Natural sampling and Flat top sampling. 4. State Sampling Theorem. A. The sampling theorem for a band limited signal of finite energy can be stated as, A Band limited signal of finite energy, which has no frequency component higher than W Hz is completely described by specifying the values of the signal at instants of time 18

25 BLOCK DIAGRAM: Patch cord 19

26 EXPT.NO.4 TIME DIVISION MULTIPLEXING AIM: To perform four channel Time Division multiplexing and De multiplexing. COMPONENTS REQUIRED: S.NO. NAME OF THE EQUIPMENT / COMPONENT RANGE QUANTITY 1 Time Division Multiplexing kit CRO 20MHz 1 THEORY: In PAM, PPM the pulse is present for a short duration and for most of the time between the two pulses no signal is present. This free space between the pulses can be occupied by pulses from other channels. This is known as Time Division Multiplexing. Thus, time division multiplexing makes maximum utilization of the transmission channel. Each channel to be transmitted is passed through the low pass filter. The outputs of the low pass filters are connected to the rotating sampling switch (or) commutator. It takes the sample from each channel per revolution and rotates at the rate of f s. Thus the sampling frequency becomes f s the single signal composed due to multiplexing of input channels. These channels signals are then passed through low pass reconstruction filters. If the highest signal frequency present in all the channels is f m, then by sampling theorem, the sampling frequency f s must be such that f s 2f m. Therefore, the time space between successive samples from any one input will be T s =1/f s, and T s 1/2f m. 20

27 TABULATION 1. TRANSMITTED SIGNALS: 3. RECEIVED SIGNALS: Channel Amplitude (V) Time period (ms) Frequency (KHz) Channel Amplitude (V) Time period (ms) Frequency (KHz) 2. SAMPLED SIGNAL Channel Amplitude (V) MODEL GRAPH: No.of Samples Time period (ms) (for each sample) Ton Toff Total Time period(ms) Frequency (KHz) 21

28 PROCEDURE: 1. Give the connections as per the block diagram. 2. Apply the four input sinusoidal signals of different frequency to four channels and measure the amplitude and time period of each signal. 3. Observe and measure the amplitude and frequency of the sampled signal for each channel individually. 4. Then observe the multiplexed waveform in the CRO. 5. Apply the multiplexed signal to the demultiplexer circuit and observe the original signals transmitted. 6. Measure the amplitude and time period of demultiplexed signal for each channel individually. 7. Plot all the waveforms in the graph. RESULT: Thus the Time division multiplexing and demultiplexing waveforms are obtained. Questions 1. What is multiplexing? A. It is a process in which a single transmission channel is shared by a no. of base band signals. 2. What is TDM? A. In TDM, different time intervals rather than frequencies are allotted to different signals. During these intervals these signals are sampled and transmitted. Thus, this system transmits information intermittently rather than continuously. 3. What are the advantages of TDM? A. a)low cost equipment b) Ease of installation and maintenance c) Low and constant delay d) unsurpassed voice quality and e) standards based. 4. What are the applications of TDM? A. In telecommunications and signal processing applications. 22

29 SIMULATED WAVEFORM 23

30 EXPT.NO.5 SIMULATION OF DIGITAL MODULATION TECHNIQUES 1. Simulation of ASK AIM: To implement ASK using MATLAB. SOFTWARE REQUIRED: PROGRAM: MATLAB clc; t=0:0.0001:0.15; m = square(2*pi*10*t); c = sin(2*pi*60*t); y1=(m.*c); for i = 1:1500 if(m(i)==1) y1(i) = c(i); else y1(i) = 0; end end figure(1) subplot(311); plot(m); subplot(312); plot(c); subplot (313); plot (y1); RESULT: Thus ASK was implemented using MATLAB. 24

31 SIMULATED WAVEFORM 25

32 2. Simulation of FSK AIM: To implement FSK using MATLAB. SOFTWARE REQUIRED: PROGRAM: MATLAB clc; t = 0:0.0001: 0.15; m = square (2*pi*10*t); c1 = sin (2*pi*60*t); c2 = sin (2*pi*120*t); s1 = (m.*c1); for i = 1 : 1500 if(m(i)==1) s1(i)=c2(i); else s1(i)=c1(i); end end figure(2); subplot(411); plot(m); subplot(412); plot(c1); subplot(413); plot(c2); subplot(414); plot(s1); RESULT: Thus FSK was implemented using MATLAB. 26

33 SIMULATED WAVEFORM 27

34 3. Simulation of PSK AIM: To implement PSK using MATLAB. SOFTWARE REQUIRED: PROGRAM: MATLAB clc; c11 = sin(2*pi*60*t); t = 0:0.0001:0.15; m = square (2*pi*10*t); c22 = sin((2*pi*60*t)+ pi); s2 = (m.*c11); for i = 1:1500 if(m(i)==1) s2(i)=c11(i); else s2(i)=c22(i); end end figure(3); subplot(411); plot(m); subplot (412); plot(c11); subplot (413); plot (c22); subplot(414); plot(s2); RESULT: Thus PSK was implemented using MATLAB. 28

35 SIMULATED WAVEFORM 29

36 4. Simulation of QPSK AIM: To implement QPSK using MATLAB. SOFTWARE REQUIRED: MATLAB PROGRAM: clc; clear all; close all; Tb=1; t=0:(tb/100):tb; fc=1; c1=sqrt(2/tb)*cos(2*pi*fc*t); c2=sqrt(2/tb)*cos(2*pi*fc*t); N=8; m=rand(1,n); t1=0; t2=tb; for i=1:2:(n-1) t=[t1:(tb/100):t2]; if m(i)>0.5 m(i)=1; m_s= ones (1,length(t)); else m(i)=0; m_s= -1*ones (1,length(t)); end odd_sig(i,:)=c1.*m_s; if m(i+1)>0.5 m(i+1)=1; m_s=ones(1,length(t)); else m(i+1)=0; m_s=-1*ones(1,length(t)); end even_sig(i,:)=c2.*m_s; qpsk=odd_sig+even_sig; subplot(3,2,4);plot(t,qpsk(i,:)); title('qpsk signal');xlabel('t--->');ylabel('s(t)'); grid on; hold on; t1=t1+(tb+.01); t2=t2+(tb+.01); end hold off ;subplot(3,2,1);stem(m); title('binary data bits'); xlabel('n--->');ylabel('b(n)'); grid on; subplot(3,2,2);plot(t,c1); title('carrier signal-1'); xlabel('t--->');ylabel('c1'); grid on; subplot(3,2,3);plot(t,c2); title('carrier signal-2'); xlabel('t--->');ylabel('c2'); grid on; RESULT: Thus QPSK was implemented using MATLAB. 30

37 SIMULATED OUTPUT: 31

38 5. Simulation of DPSK AIM: To implement DPSK using MATLAB. SOFTWARE REQUIRED: PROGRAM: MATLAB clc; clear all; close all; N=10^4 rand('state',100); rand('state',200); ip=rand(1,n)>0.5,ipd=mod(filter(1,[1-1],ip),2); s=2*ipd-1; n=1/sqrt(2)*[randn(1,n)+j*randn(1,n)]; Eb_N0_db=[-3:10]; for ii=1:length(eb_n0_db) end y=s+10^(-eb_n0_db(ii)/20)*n; ipdhat_coh=real(y)>0; iphat_coh=mod(filter([1-1],1,ipdhat_coh),2); nerr_dbpsk_coh(ii)=size(find([ip-iphat_coh]),2); simber_dbpsk_coh=nerr_dbpsk_coh/n; theoryber_dbpsk_coh=erfc(sqrt(10.^(eb_n0_db/10))).*(1-5*erfc(sqrt(10.^(eb_n0_db/10)))); close all; figure semilogy(eb_n0_db,theoryber_dbpsk_coh,'b.-'); hold on; semilogy(eb_n0_db,simber_dbpsk_coh,'mx-'); aixs([ ^-6 0.5]); grid on; legend('theory','simulation'); xlabel('eb/n0,db');ylabel('bit error rate'); title('bit error probability curve for coherent demodulation of dbpsk'); RESULT: Thus DPSK was implemented using MATLAB. 32

39 Quadrature EC 6512-Communication System Lab OUTPUT: BPSK constellation diagram BPSK Received signal signal constellation In-Phase 33

40 EXPT.NO. 6 SIGNAL CONSTELLATION OF BPSK, QPSK & QAM AIM: To plot the constellation diagram of digital modulation system BPSK, QPSK & QAM using MATLAB. SOFTWARE USED: MATLAB THEORY: A constellation diagram is a representation of a signal modulated by an arbitrary digital modulation scheme. It displays the signal as a two dimensional scatter diagram in the complex plane at symbol sampling instants. It can also be viewed as the possible symbols that may be selected by a given modulation scheme as points in the complex plane. PROGRAM: BPSK clc; clear all; close all; M=2; k=log2(m); n=3*1e5; nsamp=8; X=randint(n,1); xsym = bi2de(reshape(x,k,length(x)/k).','left-msb'); Y_psk= modulate(modem.pskmod(m),xsym); Ytx_psk = Y_psk; EbNo=30; SNR=EbNo+10*log10(k)-10*log10(nsamp); Ynoisy_psk = awgn(ytx_psk,snr,'measured'); Yrx_psk = Ynoisy_psk; h1=scatterplot(yrx_psk(1:nsamp*5e3),nsamp,0,'r.'); hold on; scatterplot(yrx_psk(1:5e3),1,0,'k*',h1); title('constellation diagram BPSK'); legend('received signal','signal constellation'); axis([ ]); hold off; 34

41 Quadrature Quadrature EC 6512-Communication System Lab QPSK QAM constellation diagram 16 PSK Received signal signal constellation In-Phase constellation diagram 16 QAM Received signal signal constellation In-Phase 35

42 Program for QPSK & QAM: clc; clear all; close all; M=16; k=log2(m); n=3*1e5; nsamp=8; X=randint(n,1); xsym = bi2de(reshape(x,k,length(x)/k).','left-msb'); Y_qam= modulate(modem.qammod(m),xsym); Y_qpsk= modulate(modem.pskmod(m),xsym); Ytx_qam = Y_qam; Ytx_qpsk = Y_qpsk; EbNo=30; SNR=EbNo+10*log10(k)-10*log10(nsamp); Ynoisy_qam = awgn(ytx_qam,snr,'measured'); Ynoisy_qpsk = awgn(ytx_qpsk,snr,'measured'); Yrx_qam = Ynoisy_qam; Yrx_qpsk = Ynoisy_qpsk; h1=scatterplot(yrx_qam(1:nsamp*5e3),nsamp,0,'r.'); hold on; scatterplot(yrx_qam(1:5e3),1,0,'k*',h1); title('constellation diagram 16 QAM'); legend('received signal','signal constellation'); axis([ ]); hold off; h2=scatterplot(yrx_qpsk(1:nsamp*5e3),nsamp,0,'r.'); hold on; scatterplot(yrx_qpsk(1:5e3),1,0,'k*',h2); title('constellation diagram 16 PSK'); legend('received signal','signal constellation'); axis([ ]); hold off; RESULT: Thus the constellation diagrams of digital modulation system BPSK, QPSK & QAM are simulated & plotted in MATLAB. 36

43 INTRODUCTION TO SDR KIT What is Software defined radio (SDR)? Software defined radio is defined as an environment where Hardware and Software are different parts allows user to implement the operating functions of hardware through a modifiable software. Complete design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used. Where SDR can be used? Due to its wide RF range it covers a wide range of applications including high frequency communications, FM and TV broadcast, cellular, Wi-Fi, ISM, and lot more. Starting from simple experiments, it makes you grow in experience and complexity up to being able to deal with competence and master the fundamental elements which makes the Software Based Radio. FEATURES RFCoverage from70mhz 6 GHz RF GNU Radio and open BTS support through the open source USRP Hardware Driver USB 3.0 High speed interface (Compatible with USB 2.0) Flexible rate 12 bit ADC/DAC 1TX, 1 RX, Half or Full Duplex Xilinx Spartan 6 XC6SLX75 FPGA Up to 56 MHz of real-time bandwidth Power DC Input: 6V SOFTWARE DESCRIPTION What is GNU Radio? GNU Radio is a software library, which can be used to develop complete applications for radio engineering and signal processing. Introduction GNU Radio is a free and open-source software development toolkit that provides signal processing blocks to implement software radios. It can be used with readily-available low-cost external RF hardware to create software-defined radios, or without hardware in a simulation-like environment. GNU Radio is licensed under the GNU General Public License (GPL) version 3. All of the code is copyright of the Free Software Foundation. While all the applications are implemented using python language while critical signal processing path is done using C++ language. 37

44 PROCEDURE TO WORK ON GNU Radio Companion: GNU Radio Companion (GRC) is a graphical user interface that allows you to build GNU Radio flow graphs. It is an excellent way to learn the basics of GNU Radio. This is the first in a series of tutorials that will introduce you to the use of GRC. Procedure for Amplitude modulation: STEP 1:Click on GRC. STEP 2: Click on options and name the title and change generate options as WX GUI. 38

45 STEP3: Click variable and change ID and value. STEP 4: Press control+f and search for signal source. 39

46 STEP 5: Place the signal source for message signal as amplitude modulation. STEP 6: Change the properties in signal source as (i) Output Type: Float (ii)waveform: Cosine (iii)frequency: 100 (iv)amplitude: 2 and 40

47 STEP 7: Place another signal source for carrier signal in amplitude modulation. STEP 8: Change properties in signal source as (i) Output type: float (ii) Waveform: Sine (iii) Frequency: 100K (iv) Amplitude: 2 41

48 STEP 9: Press control + F and search Multiply block. STEP 10: Place Multiply for multiply the message signal and carrier signal. 42

49 STEP 11: Change properties in multiply as (i) ID Type: Float (ii)num Inputs: 2 STEP 12: Press Control + F and search for scope sink and Place WX GUI Scope sink. 43

50 STEP 13: Change the properties in Wx GUI scope sink as (i) Type: Float (ii)num input: 2 STEP 14: Connect wires of signal source to multiply and connect to WX GUI scope sink. 44

51 STEP 15: Click Run and stop. OUTPUT WAVEFORM: 45

52 EXPT.NO.7 COMMUNICATION LINK SIMULATION USING SDR AIM: TRAINER KIT. To construct an Amplitude modulator and demodulator and using SDR EQUIPMENTS REQUIRED: SDR Trainer Kit -1 SMA Connector-1 USB device -1 THEORY: AMPLITUDE MODULATION Amplitude modulation is the process of changing the amplitude of a relatively high frequency carrier signal in proportion with the instantaneous value of the modulating signal. BLOCK DIAGRAM: RESULT: Thus the Amplitude modulation was studied using SDR kit. 46

53 BLOCK DIAGRAM: 47

54 EXPT.NO.8 DIGITAL MODULATION PSK AIM: To generate Phase Shift Keying signal and plot the graph. EQUIPMENTS/COMPONENTS REQUIRED: S.NO COMPONENTS / EQUIPMENTS QUANTITY 1. Phase shift keying transmitter kit 2. CRO 3. Function generator Few 4. Patch chords THEORY: To facilitate the transmission of a signal over a communication bandwidth, a simple modulation of digital technique called phase shift keying is adopted, in which the binary signals symbol 0 and symbol 1 are transmitted with a phase shift with respect to each other. At the transmitter side, the message signal which is in analog form is converted to digital type and is modulated through a sinusoidal carrier frequency. The transmitter output will be a signal in which logic 1 and logic 0 are represented by an phase. There are different form of PSK such as BPSK, QPSK etc., At the receiver side using threshold device, the received signal is converted into either logic 1 or logic 0. APPLICATION: Wireless LAN RFID Bluetooth communication 48

55 MODEL GRAPH TABULATION SIGNAL Clock Sin 2 Sin 3 Control Input AMPLITUDE (V) TIMEPERIOD PSK Modulated output PSK Demodulated output (µs) FREQUENCY (KHz) 49

56 PROCEDURE: 1. The connections are made as per the block diagram The message signal is applied to the input and also the carrier from function generator. The PSK waveform is obtained. Tabulate the Amplitude and time period. Plot the Graph. RESULT: Thus the Phase Shift Keying waveform is obtained and plotted. QUESTIONS: 1.What are the advantages of BPSK? BPSK has a bandwidth which is lower than of BFSK is the best of all systems in the presence of noise. It gives the minimum possibility of error and it has very good noise immunity. 2.What are the advantages of differential phase shift keying? i.no need to generate the carrier at the receiver end. This means that complicated circuitry for generation of local carrier is avoided. ii.the bandwidth required for DPSK is less compared to binary PSK. 3. What are the disadvantages of differential phase shift keying? The probability of error is high compared to binary PSK. 4.Why is PSK always preferable over ASK in coherent detection? ASK has amplitude variations, hence noise interference is more,psk method has less noise interference. It is always preferable. 5. What is signal constellation diagram? Signal constellation refers to a set of possible message points. 50

57 BLOCK DIAGRAM 51

58 EXPT.NO.9 DIGITAL MODULATION QPSK AIM: To generate Quadrature Phase Shift Keying signal and plot the graph. EQUIPMENTS/COMPONENTS REQUIRED: S.NO COMPONENTS / EQUIPMENTS QUANTITY 1. QPSK transmitter kit 2. CRO 3. Function generator Few 4. Patch chords THEORY: In pass band digital communication techniques, there are three basic techniques of modulation. They are PSK, ASK, FSK. The basic form of phase shift keying is binary phase shift keying abbreviated as BPSK. The major disadvantages of BPSK are that, it occupies a much large bandwidth and each and every bit is modulated by phase shifts. In order to obtain an efficient usage of channel bandwidth Quadrature phase shift keying techniques is introduced in which there is a phase shift which occurs for a set of bits which is also called as Dibits. Thus, the phase shift occurs for two bits in sequence and the phase shift generally follows the Gray code sequence. The QPSK of two bits is obtained by adding the odd position bits and BPSK of even position bits and producing QPSK. The Dibits are 00,10,11,01. They have a phase shift of π/4, 3π/4, 5π/4, 7π/4 respectively. Thus, the QPSK signal is obtained. The main advantage is that it utilizes efficiently the bandwidth of transmission channel. APPLICATION: It is widely used in satellite broadcasting It is used in streaming SD channels and some HD CHANNELS

59 MODEL GRAPH QPSK-MODULATION QPSK-DEMODULATION 53

60 PROCEDURE: 1. The connections are made as per the block diagram. 2. The modulating inputs and the in phase and Quadrature component carriers are given as input. 3. QPSK wave is obtained. 4. Tabulate the amplitude and time period of QPSK. 5. Plot the graph. 54

61 TABULATION: SIGNAL AMPLITUDE (V) Data in Q bit I bit Sin 1 Sin 2 Sin 3 Sin 4 Modulated output Clock Demodulated output PHASOR DIAGRAM TIMEPERIOD (ms) FREQUENCY (KHz) T ON ms T OFF ms 55

62 RESULT: Thus the QPSK wave is obtained and the waveform is plotted. QUESTIONS: 1.What are the advantages of QPSK as compared to BPSK? For the same bit error, the bandwidth required by QPSK is reduced to half as compared to BPSK. 2.List the advantages of Passband transmission. a. Long distance. b. Analog channels can be used for transmission. c. Multiplexing techniques can be used for bandwidth conservation. d. Transmission can be done by using wireless channel also. 3.List the requirements of Passband transmission. i.maximum data transmission rate. ii.minimum probability of symbol error. iii.minimum transmitted power. 4. Highlight the major difference between a QPSK signal and a MSK signal. i. QPSK is a phase modulation ii. iii. MSK is frequency modulation Band width of QPSK is Fb where as MSK is 1.5 Fb 5.Define QPSK In QPSK (Quadriphase Shift Keying), the phase of the carrier takes on one of the four equally spaced values such as S (t) i 2E cos(2 f ct (2i 1) T ,, and t T. 0 elsewhere. 1 as given by 56

63 BLOCK DIAGRAM: ANALOG TO DIGITAL CONVERTER PCM OUTPUT Analog Input SAMPLER QUANTIZED PAM MODEL GRAPH: QUANTIZER ENCODER DIGITALLY ENCODED SIGNAL DE -QUANTIZER DECODER FILTER Demodulated output 57

64 EXPT.NO.10 PULSE CODE MODULATION AIM: To obtain Pulse Code Modulated and demodulated signals using PCM trainer kit. COMPONENTS REQUIRED: NAME OF THE EQUIPMENT / S.NO. RANGE QUANTITY COMPONENT 1 PCM trainer kit CRO 10 MHz 1 THEORY: Pulse code modulation is known as digital pulse modulation technique. It is the process in which the message signal is sampled and the amplitude of each sample is rounded off to the nearest one of the finite set of allowable values. It consists of three main parts transmitter, transmitter path and receiver. The essential operation in the transmitter of a PCM system are sampling, Quantizing and encoding. The band pass filter limits the frequency of the analog input signal. The sample and hold circuit periodically samples the analog input signal and converts those to a multi level PAM signal. The ADC converts PAM samples to parallel PCM codes which are converted to serial binary data in parallel to serial converter and then outputted on the transmission line as serial digital pulse. The transmission line repeaters are placed at prescribed distance to regenerate the digital pulse. In the receiver serial to parallel converter converts serial pulse received from the transmission line to parallel PCM codes. The DAC converts the parallel PCM codes to multi level PAM signals. The hold circuit is basically a Low Pass Filter that converts the PAM signal back to its original analog form. ADVANTAGES: 1. Secrecy 2. Noise resistant and hence free from channel interference 58

65 TABULATION: TRANSMITTED SIGNAL: Amplitude (V) Time period (ms) Frequency (KHz) SAMPLED SIGNAL: No. of Time period (ms) Total Time Channel Amplitude(V) samples (for each sample) Period RECEIVED SIGNAL: Amplitude (V) Time period (ms) Frequency (KHz) PCM OUTPUT: DC Voltage (V) T on Encoded values (ms) T off D6 D5 D4 D3 D2 D1 D0 Frequency (KHz)

66 DISADVANTAGES: 1. Requires more bandwidth APPLICATION: 1. Compact DISC for storage 2. Military Applications. PROCEDURE: RESULT: Questions: 1. Give the connections as per the block diagram. 2. Measure the amplitude and time period of the input signal. 3. Measure the amplitude and time period of the sampled signal. 4. Apply the input signal to the PCM kit and observe and measure the PCM output. 5. Plot the waveforms in the graph. Thus the Pulse Code Modulated signals are obtained and the waveforms are plotted. 1. What is the need of parallel to serial converter? A. To transmit all the bits in one channel. 2. What is the use of Companding? A. Companding is used to overcome quantizing noise in PCM. 3. What are the applications of PCM? A. Because of high immune to noise it can be used for storage systems in CD recording. 4. What should be the minimum B.W. required to transmit a PCM channel? A. B T = vw where v = no. of bits used to represent one pulse, W = Maximum signal frequency. 60

67 BLOCK DIAGRAM BLOCK DIAGRAM FOR DELTA MODULATION AND DEMODULATION 61

68 EXPT. NO. 11 DELTA AND ADAPTIVE DELTA MODULATION AIM: To obtain Delta Modulated and Adaptive Delta modulated waveforms. COMPONENTS REQUIRED: S.NO. 1 NAME OF THE EQUIPMENT / COMPONENT Delta Modulation & Adaptive Delta modulationtrainer kit RANGE QUANTITY CRO 10 MHz 1 3 Patch cords Power Supply (0-30) V 1 THEORY: Delta modulation uses a single bit PCM code to achieve digital transmission of analog signal. With conventional PCM, each code is a binary representative of both the sign and magnitude of a particular sample. The algorithm of delta modulation is simple if the current sample is smaller than the previous sample a logic0 is transmitted. If the current sample is larger than the previous sample a logic 1 is transmitted. ADVANTAGES: Simple system/circuitry Cheap Single bit encoding allows us to increase the sampling rate or to transmit more information at some sampling rate for the given system BW. DISADVANTAGE : Noise and distortion. Major drawback is that it is unable to pass DC information. APPLICATION: Digital voice storage Voice transmission Radio communication devices such TV remotes. 62

69 MODEL GRAPH: TABULATION: DELTA MODULATION Input Signal Integrator 1 output AMPLITUDE (V) TIME PERIOD (ms) FREQUENCY (HZ) Sampler output Integrator 3 output Filter output Demodulated output 63

70 THEORY: Adaptive delta modulation is delta modulation system where the step size of DAC is automatically varied, depending on the amplitude characteristics of the analog input signal. A common algorithm for an adaptive delta modulator is when three consecutive 1s or 0s occur, the step size of the DAC is increased or decreased by a factor of 1.5 APPLICATION: Audio communication system 64

71 MODEL GRAPH: TABULATION: ADAPTIVE DELTA MODULATION TYPE OF SIGNAL AMPLITUDE (V) TIME PERIOD (ms) FREQUENCY (HZ) Input Signal Integrator 2 output Sampler output Integrator 3 output Filter output Demodulated output 65

72 PROCEDURE: 1. Connections are to be given as per the block diagram. 2. Observe the modulated waveforms. 3. Measure the amplitude and time period of both the waveforms. 4. Plot the graph. 5. Repeat the above procedure for adaptive delta modulation also. RESULT: Questions Thus Delta Modulated and Adaptive Delta Modulated waveforms are obtained. 1. What is Delta Modulation? A. Delta modulation is a system of digital modulation developed after pulse modulation. In this system, at each sampling time, say the K th sampling time, the difference between the sample value at sampling time K and the sample value at the previous sampling time (K-1) is encoded into just a single bit. 2. What are the drawbacks of Delta Modulation? A. Slope overload distortion and Granular noise effect are the drawbacks of Delta Modulation. 3. What are the advantages of Delta Modulation? A. The advantages of Delta Modulation are simple system/circuitry; cheap, single bit encoding allows us to increase the sampling rate or to transmit more information at some sampling rate for the given system BW. 4. Can DC information be passed using Delta Modulation? A. No, DC information cannot be passed using Delta Modulation. 66

73 BLOCK DIAGRAM 67

74 EXPT. NO. 12 LINE CODING AND DECODING AIM: To analyze line coding and decoding techniques. COMPONENTS REQUIRED: S.NO. NAME OF THE EQUIPMENT / COMPONENT RANGE QUANTITY 1 Line coding & decoding kit Connecting plugs CRO 10 MHz 1 THEORY: NON-RETURN TO ZERO signal are the easiest formats that can be generated. These signals do not return to zero with the clock. The frequency component associated with these signals are half that of the clock frequency. The following data formats come under this category. Non-return to zero encoding is commonly used in slow speed communications interfaces for both synchronous and asynchronous transmission. Using NRZ, logic 1 bit is sent as a high value and a logic 0 bit is sent as a low value. a) NON-RETURN TO ZERO-LEVEL (NRZ-L) This is the most extensively used waveform in digital logics. All ones are represented by high and all zeros by low. The data format is directly available at the output of all digital data generation logics and hence very easy to generate. Here all the transitions take place at the rising edge of the clock. b) NON-RETURN TO ZERO-MARK (NRZ-M) These waveforms are extensively used in tape recording. All ones are marked by change in levels and all zeros by no transitions, and the transitions take place at the rising edge of the clock. 68

75 LINE CODING WAVE FORM: 69

76 c) NON-RETURN TO ZERO-SPACE (NRZ-S) This type of waveform is marked by change in levels for zeros and no transition for ones and the transitions take place at the rising edge of the clock. This format is also used in magnetic tape recording. d) UNIPOLAR AND BIPOLAR Unipolar signals are those signals, which have transition between 0 to +VCC. Bipolar signals are those signals, which have transition between +VCC to VCC. e) BIPHASE LINE CODING(BIPHASE -L): With the Biphase L one is represented by a half bit wide pulse positioned during the first half of the bit interval and a zero is represented by a half bit wide pulse positioned during the second half of the bit interval. f) BIPHASE MARK CODING(BIPHASE-M): With the Biphase-M, a transition occurs at the beginning of every bit interval. A one is represented by a second transition, half bit later, whereas a zero has no second transition. g) BIPHASE SPACE CODING(BIPHASE-S): With a Biphase-S, a transition occurs at the beginning of every bit interval. A zero is marked by a second transition, one half bit later; one has no second transition. h) RETURN TO ZERO SIGNALS: These signals are called Return to Zero signals since they return to zero with the clock. In this category, only one data format, i.e, the unipolar return to zero(urz); With the URZ a one is represented by a half bit wide pulse and a zero is represented by the absence of pulse. i) MULTILEVEL SIGNALS: Multilevel signals use three or more levels of voltages to represent the binary digits, one and zero instead of normal highs and lows Return to zero alternative mark inversion (RZ - AMI) is the most commonly used multilevel signal. This coding scheme is most often used in telemetry systems. In this scheme, one are represented by equal amplitude of alternative pulses, which alternate between a +5 and -5. These alternating pulses return to 0 volt, after every half bit interval. The Zeros are marked by absence of pulses. 70

77 TABULATION: ONE ZERO Clock Data Input NRZ-L NRZ-M NRZ-S BIO-L BIO-M BIO-S URZ T ON (ms) T OFF (ms) T ON (ms) T OFF (ms) 71

78 PROCEDURE: 1. Connect power supply in proper polarity to the kits DCL-05 and DCL-06 and switch it on. 2. Connect CLOCK and DATA generated on DCL-05 to CODING CLOCK IN and DATA INPUT respectively by means of the patch-chords provided. 3. Connect the coded data NRZ-L on DCL-05 to the corresponding DATA INPUT NRZ-L, of the decoding logic on DCL Keep the switch SW2 for NRZ-L to ON position for decoding logic as shown in the block diagram. 5. Observe the coded and decoded signal on the oscilloscope. 6. Connect the coded data NRZ-M on DCL-05 to the corresponding DATA INPUT NRZ-M, of the decoding logic on DCL Keep the switch SW2 for NRZ M to ON position for decoding logic as shown in the block diagram. 8. Observe the coded and decoded signal on the oscilloscope. 9. Connect the code data NRZ-S on DCL-05 to the corresponding DATA INPUT NRZ-S, of the decoding logic on DCL Keep the switch SW2 for NRZ-S to ON position for decoding logic as shown in the block diagram. 11. Observe the coded and decoded signal on the oscilloscope. 12. Use RESET switch for clear data observation if necessary. 13. Unipolar to Bipolar/Bipolar to Unipolar: a. connect NRZ-L signal from DCL-05 to the input post IN Unipolar to Bipolar and Observe the Bipolar output at the post OUT. b. Then connect bipolar output signal to the input post IN of Bipolar to Unipolar and observe Unipolar out at post OUT. RESULT: Thus the line coding and decoding techniques were analyzed and observed and the graph is plotted. Questions 1. What is a digital signal? A. A digital signal is a discontinuous signal that changes from one state to another in discrete steps. A popular form of digital modulation is binary, or two levels, digital modulation. 2. What is Line Coding? A. Line coding is the process of arranging symbols that represent binary data in a particular pattern for transmission. 3. What are the common types of line coding used in communication? A. The most common types of line coding used in fiber optic communications include nonreturn-to-zero (NRZ), return-to-zero (RZ), and biphase, or Manchester. 4. In NRZ code, does the presence of a high-light level in the bit duration represent a binary 1 or a binary 0? A. The presence of a high-light level in the bit duration represents a binary 1, while a lowlight level represents a binary How can the loss of timing occur in NRZ line coding? A. loss of timing may result if long strings of 1s and 0s are present causing a lack of level Transitions. 72

79 OUTPUT: COMPUTATION OF CODE VECTORS FOR A CYCLIC CODE Msg= Code = SYNDROME DECODING Recd= Syndrome=7(decimal), 1 1 1(binary) Parmat= Corrvect= Correctedcode=

80 EXPT.NO. 13 ERROR CONTROL CODING USING MATLAB AIM: a. To generate parity check matrix & generator matrix for a (7,4) Hamming code. b. To generate parity check matrix given generator polynomial g(x) = 1+x+x 3. c. To determine the code vectors. d. To perform syndrome decoding PROGRAM: Generation of parity check matrix and generator matrix for a (7,4) Hamming code. [h,g,n,k] = hammgen(3); Generation of parity check matrix for the generator polynomial g(x) = 1+x+x 3. h1 = hammgen(3,[1011]); Computation of code vectors for a cyclic code clc; close all; n=7; k=4; msg=[ ; ; ]; code = encode(msg,n,k,'cyclic'); msg code Syndrome decoding clc; close all; q=3; n=2^q-1; k=n-q; parmat = hammgen(q); % produce parity-check matrix trt = syndtable(parmat); % produce decoding table recd = [ ] %received vector syndrome = rem(recd * parmat',2); syndrome_de = bi2de(syndrome, 'left-msb'); %convert to decimal disp(['syndrome = ',num2str(syndrome_de),... ' (decimal), ',num2str(syndrome),' (binary) ']); corrvect = trt(1+syndrome_de, :);%correction vector correctedcode= rem(corrvect+recd,2); parmat corrvect correctedcode RESULT: Thus encoding and decoding of block codes are performed using MATLAB. 74

81 Quadrature EC 6512-Communication System Lab SIMULATED OUTPUT: Symbol error rate with equalizer: 0 Symbol error rate without equalizer: Scatter plot fitered signal equalized signal ideal signal constellation In-Phase 75

82 EXPT.NO. 14 SIMULATION OF EQUALIZATION TECHNIQUES 1. Simulation of Zero Forcing Equalizer. AIM: To simulate the Zero Forcing Equalizer using MATLAB. SOFTWARE USED: MATLAB THEORY: Equalizer can be employed to mitigate the ISI for a smooth recovery of transmitted symbols and to improve the receiver performance Zero forcing (or) linear equalizer which processes the incoming signal with a linear filter. It is classified into two (a) Symbol spaced equalizer (b) Fractionally spaced equalizer Symbol spaced equalizer: A symbol spaced linear equalizer consist of a tapped delay line that stores samples from the input signal. Here the sample rates of both input & output signals are equal to 1/T. Fractionally spaced equalizer: A Fractionally spaced linear equalizer is similar to a symbol spaced equalizer,but the former receives K input samples before it produces one output sample & updates the weights, where K is an integer. Here the output sample rates is 1/T,while that of input sample is K/T. PROGRAM clc;clear all;close all; M=4; msg=randint(1500,1,m); modmsg=pskmod(msg,m); sigconst=pskmod([0:m-1],m); trainlen=500; chan=[.986;.845;.237; i]; filtmsg=filter(chan,1,modmsg); eqobj =lineareq(8,lms(0.01),sigconst,1); [symbolest,yd]=equalize(eqobj,filtmsg,modmsg(1:trainlen)); h=scatterplot(filtmsg,1,trainlen,'bx');hold on; scatterplot(symbolest,1,trainlen,'r.',h); scatterplot(sigconst,1,0,'k*',h); legend('fitered signal','equalized signal','ideal signal constellation'); hold off; demodmsg_noeq=pskdemod(filtmsg,m); demodmsg =pskdemod(yd,m); [nnoeq,rnoeq]=symerr(demodmsg_noeq(trainlen+1:end),msg(trainlen+1:end)); [neq,req] = symerr(demodmsg(trainlen+1:end),msg(trainlen+1:end)); disp('symbol error rate with equalizer:'); disp(req); disp('symbol error rate without equalizer:'); disp(rnoeq) RESULT: Thus the Zero Forcing Equalizer is simulated in MATLAB. 76

83 true and estimated output EC 6512-Communication System Lab SIMULATED OUTPUT: Enter the system order,n=5 Enter the number of iterations,m= system output desired output error number of iterations 77

84 2. Equalization using LMS Algorithm AIM: To simulate Least Mean Square (LMS) algorithm to adaptively adjust the coefficients of an FIR filter. SOFTWARE USED: MATLAB THEORY: The LMS recursive algorithm used for adjusting the filter coefficients adaptively so as to minimize the sum of squared error is described below. Let x[n] be the input sequence and y[n] be the output sequence of an FIR filter. Then,the output is given by the expression Y[n]= h[k]x[n-k], n=0,1, M Where h[n] is the adjustable coefficients of FIR filter. Let the desired sequence be d[n].then, the error sequence e[n] is given by e[n] = d[n] y[n], n=0,1, M The LMS algorithm starts with any arbitrary choice of h[k],say h 0 [k].for example, we may begin with h 0 [k]=0,0 k N-1.After that each new sample x[n] enters the adaptive filter,we compute the corresponding output, say y[n], form the error signal e[n]=d[n]-y[n],and update the filter coefficients according to the equation h n [k] = h n-1 [k] +µ.e[n].x[n-k], 0 k N-1,n=0,1..where µ is called step size parameter, x[n-k] is the sample of input signal located at the kth tap of the filter at time n and e[n]x[n-k] is an approximation(estimate) of the negative of the gradient for the kth filter coefficients. The step size parameter µ controls the rate of convergence. Large value of µ leads to rapid convergence and smaller value leads to slower convergence. If µ is made too large,the algorithm becomes unstable. In order to ensure convergence and good tracking capabilities in slowly varying channels, the step size parameters is given by µ=1/5np x where N is the length of the adaptive FIR filter and P x is the average power in the input signal which is approximated by P x 1 1 M M n 0 2 x ( n). 78

85 SIMULATED OUTPUT: comparison of actual weights and estimated weights actual weights estimated weights

86 PROGRAM: clc;clear all;close all; N=input('enter the system order,n='); M=input('enter the number of iterations,m='); if((n>=2)&&(m>=2)) x=rand(m,1); b=fir1(n-1,0.5); n=0.1*randn(m,1); d=filter(b,1,x)+n; h=zeros(n,1); Px=(1/length(x))*sum(x.^2); mu=1/(5*n*px); for n=n:m u=x(n:-1:n-n+1); y(n)=h'*u; e(n)=d(n)-y(n); h=h+mu*u*e(n); end hold on;plot(d,'g'); plot(y(),'r'); semilogy((abs(e())),'m'); title('system output'); xlabel('number of iterations'); ylabel('true and estimated output'); legend('desired','output','error'); hold off; figure,plot(b','k+'); hold on,plot(h,'r*'); legend('actual weights','estimated weights'); hold off; title('comparison of actual weights and estimated weights'); else('system order and number of iterations should be greater than 1'); end RESULT: Thus the Least Mean Square (LMS) algorithm is simulated in MATLAB. 80

87 CIRCUIT DIAGRAM: DEMODULATOR 81

88 CONTENT BEYOND SYLLABUS EXPT.NO.1 AM MODULATION AND DEMODULATION USING IC2206 AIM: To construct amplitude modulator and demodulator circuit and plot the waveforms. COMPONENTS REQUIRED: S.NO. 1 NAME OF THE EQUIPMENT / COMPONENT RANGE IC QUANTITY 2 Resistors 47K,1K,10K, 220Ω 3,1,1,1 3. Capacitors 0.01µF,0.1µF 1,2 THEORY: MODULATOR: An amplitude modulated signal is composed of both low frequency and high frequency components. The amplitude of the high frequency (Carrier) of the signal is controlled by the low frequency (modulating) signal. The envelope of the signal is created by the low frequency signal. If the modulating signal is sinusoidal, then the envelope of the modulated radio frequency (RF) signal will also be sinusoidal. The circuit for generating an AM modulated waveform must produce the product the of the carrier and the modulating signal. 82

89 TABULATION: MODULATING SIGNAL Signals Amplitude (V) Modulating signal Carrier signal MODULATED SIGNAL Time period Frequency (KHz) (ms) Emax (V) Emin (V) m = (Emax Emin) / (Emax + Emin) % DETECTED SIGNAL (V) Amplitude Frequency (KHz) Time period (ms) 83

90 DEMODULATOR: A single diode can be used to detect the AM signal and is called PN diode detector or envelope detector. The diode acts as a rectifier in removing half the envelope resulting in the base band signal with a Dc offset. The offset is removed with a series capacitor, producing the output. Envelope detectors are not perfect. All diodes are nonlinear, and will distort the envelope when it is near the zero voltage level. This effect can be minimized by using a diode with a low forward voltage drop and a strong signal(several 100mV) at the detector. PROCEDURE: 1. Rig up the circuit as per the circuit diagram. 2. Set the carrier signal to 8V, 10 KHz using function generator and measure the amplitude and time period. 3. Set the modulating signal 4V,1 KHz and measure the amplitude and time period. 4. Vary the amplitude around the carrier voltage. 5. Note down the maximum (E max ) and minimum (E min ) voltages from the CRO. 6. Calculate the modulation index using the formula. 7. Apply the AM signal to the detector circuit. 8. Observe the amplitude demodulated output on the CRO. 9. Compare the demodulated signal with the original modulating signal (Both must be same in all parameters). Plot the observed waveforms. 84

91 MODEL GRAPH: 85

92 RESULT: Thus the characteristics of AM Transmitter and Receiver are studied and the waveforms are observed and plotted. 86

93 CIRCUIT DIAGRAM: FREQUENCY MODULATION: FREQUENCY DEMODULATOR: 87

94 EX.NO. 2 FM MODULATOR AND DEMODULATOR USING IC 2206 AIM: To perform frequency modulation and demodulation. COMPONENTS REQUIRED: S.NO. NAME OF THE EQUIPMENT / COMPONENT RANGE QUANTITY 1 IC Resistors 10K,3.3K,150Ω, 47K,10K(POT), 560Ω, 4.7K 1,1,1,1,1, 2,2 3 Capacitors 10µF,1µF,0.01µF,470pF 2,1,3,1 4 Function Generators 1 MHz 2 5 CRO 20MHz 1 6 Bread board Regulated Power supply 0-30V 2 THEORY : Frequency modulation(fm) conveys information over a carrier wave by varying its instantaneous frequency (contrast this with amplitude modulation,in which the amplitude of the carrier is varied while its frequency remains constant).frequency modulation is defined as the process in which the instantaneous frequency of the carrier varies in accordance with the instantaneous values of the modulating signal. Frequency modulation can be regarded as phase modulation where the carrier phase modulation is the time integral of the FM modulating signal Frequency demodulation is the process of retrieving the original modulating signal from the modulating signal. A common method for recovering the information signal is through a Fosterseeley discriminator. The various application of FM modulator and demodulator are Broadcasting, magnetic tape storage, sound, radio. 88

95 TABULATION: signal MODEL GRAPH Signals Amplitude (V) Modulating signal Carrier signal Modulated signal Demodulated Time period (ms) T min = f max = T max = f min = Frequency(KHz) 89

96 PROCEDURE: 1.The circuit connection are made according to the circuit diagram. 2.The power supply and ground connections are made. 3.The modulating input signal and carrier signal is given using function generator. 4.The frequency modulated wave is seen on the CRO 5.The modulated signal is sent as input to a demodulator circuit and demodulated signal is observed on the CRO. RESULT: The modulating signal was frequency modulated and demodulated. 90

97 CIRCUIT DIAGRAM: MODEL GRAPH 91

98 EXPT.NO.3 DIGITAL MODULATION ASK 1. Using hardware AIM: To generate Amplitude Shift Keying signal using operation amplifier 741. COMPONENTS REQUIRED: THEORY: S.NO. NAME OF THE EQUIPMENT / COMPONENT RANGE QUANTITY 1 IC Resistors 1K 3 3 Capacitors 0.01µF 2 4 Decade Resistance Box 2 to 3K 1 5 Function Generator 1 MHz 1 6 CRO 10 MHz 1 7 Bread board Dual Power supply 0-15V 1 In digital modulation technique, binary 1 or 0 is transmitted by changing the amplitude of the carrier signal and is called Amplitude Shift Keying. A sinusoidal signal is used as the carrier signal. The carrier signal is allowed to pass through to transmit binary 1 and is switched off to transmit binary 0. The carrier signal is generated using OP-amp. A square wave is used as the binary signal to be transmitted. DESIGN: Assume f 0 = 16KHz Let C= 0.01 μf f 0 = 1 2 RC ;R= Let R 1 = 1KΩ A = 1+ R f R f 0 c = *16*10 ; A = 3 ; Rf = 2KΩ 1 *0.01*10 1KΩ 92

99 PIN CONFIGURATION: TABULATION: MODULATING SIGNAL: V m (V) T on (ms) T off (ms) Frequency(KHz) CARRIER SIGNAL: Vc(V) Time period (µs) Frequency(KHz) ASK OUTPUT: No. of Time period of Total Time period(ms) Amplitude Frequency cycles each cycle (µs) T on (ms) T off (ms) (V) (KHz) 93

100 PROCEDURE: 1. Connections are given as per the circuit diagram. 2. Measure the amplitude and time period of the square wave input signal. 3. Remove the square wave input and ground that terminal. Now the circuit is a wein bridge oscillator. 4. Verify whether the sinusoidal carrier signal is generated or not. Note down the amplitude and time period of the carrier signal. 5. Apply the square wave input signal and note down the amplitude and time period of the ASK output signal. RESULT: Thus the Amplitude Shift Keying signal is generated and the waveforms are observed 94

101 CIRCUIT DIAGRAM: MODEL GRAPH: 95

102 EXPT.NO. 4 PULSE AMPLITUDE MODULATION AIM: To construct Pulse Amplitude Modulator and Demodulator circuits and observe the waveforms. COMPONENTS REQUIRED: DESIGN: S.NO. THEORY: NAME OF THE EQUIPMENT / COMPONENT 96 RANGE QUANTITY 1 OP-AMP µa Transistor BC Capacitors 0.1µF 2 4 Resistors 1K,10K,22K,1.5K 2,1,1,3 5 Function Generators 1 MHz 2 6 CRO 10MHz 1 7 Bread board Regulated Power supply 0-15V 1 9 Dual Power supply 0-15V 1 Low pass filter design: Let f 1KHz. ; Let C 0.1 F ; 1 R = 2 f C. Substituting we get, R = 1.5 K In Pulse Amplitude Modulation the carrier is a periodic train of pulses. It is discontinuous, discrete process i.e. the pulses are present only at certain distinct intervals of time hence it is most suited for messages that are discrete in nature. However with the help of sampling techniques continuously varying signals can be transmitted on pulsed carriers. Generally pulse modulation and coding go hand in hand as in telegraphy and teletype. The pulse modulated signal, despite the term modulation is base band signals. The base band coding schemes are the actual coding schemes for base band transmission.

103 PIN DIAGRAM TABULATION: MODULATING SIGNAL: Vm (V) CARRIER SIGNAL: PAM OUTPUT: Vc (V) Vmax (V) Ton (µs) Vmin (V) Time period Toff (µs) (ms) No.of cycles Total Time period (µs) Frequency f m (KHz) Time period T on (ms) T off (ms) Frequency f c (KHz) Frequency (KHz) Vout (V) Time period (ms) Frequency(KHz) 97

104 PROCEDURE: 1. Rig up the circuit as shown in the figure. 2. Using a function generator generate the carrier signal which is of pulse type with amplitude V c and frequency fc. 3. Using another function generator generate the modulating signal which is analog with amplitude V m and frequency fm. 4. Select the frequency of the carrier signal in such a way that it satisfies sampling theorem. 5. Set the above arrangement and switch on the power supply. 6. Observe the corresponding waveforms with the help of CRO and plot them on the graph. 7. Apply the Pulse Amplitude Modulated signal to the input of the demodulator circuit and note down the demodulated signal and plot in on the graph. RESULT: Thus the Pulse Amplitude Modulator and demodulator circuits are constructed and the waveforms are observed and plotted. 98

105 CIRCUIT DIAGRAM: TRIGGER CIRCUIT 99

106 EXPT.NO.5 PULSE WIDTH MODULATION AIM: To generate the Pulse Width Modulated signal using 555 timer. COMPONENTS REQUIRED: S.NO. NAME OF THE EQUIPMENT / COMPONENT RANGE QUANTITY 1 IC Diode 1N Capacitors 0.1µF, 0.01µF 3,2 4 Resistors 6.8K,10K,1.8K 2,1,1 5 Function Generator 1 MHz 1 6 CRO 20 MHz 1 7 Bread board Regulated Power supply 0-15V 1 DESIGN: Assume carrier frequency f 0 = 750 Hz. The operating frequency of IC 555 timer is given by 1.45 f 0 ( R 2R C THEORY: Let C = 0.1 f,let R A B A B ) A 6. 4 A 6. 8 R,Substituting we get,r k ;R k Pulse Time Modulation is also known as Pulse Width Modulation or Pulse Length Modulation. In PWM, the samples of the message signal are used to vary the duration of the individual pulses. Width may be varied by varying the time of occurrence of leading edge, the trailing edge or both edges of the pulse in accordance with modulating wave. It is also called Pulse Duration Modulation. Pulse width modulation is a one in which each pulse has fixed amplitude but width of the pulses is made proportional to amplitude of the modulating signal at that instant. 100

107 MODEL GRAPH: TABULATION: MODULATING SIGNAL: V m (V) Time period (ms) Frequency(Hz) PWM OUTPUT: Amplitude (V) Time period of each pulse (ms) T on T off T on T off T on T off T on 101

108 Pulse width increase when signal amplitude increases in positive direction and decreases when signal amplitude increases in negative direction. Pulses of PWM is of varying pulse width and hence of varying power component. So transmitter should be powerful enough to handle the power of maximum pulse width. But average power transmitted is only half is peak powerthe main advantage of PWM is system will work even if the synchronization between the transmitter and receiver fails. The emitter coupled monostable multivibrator is an excellent voltage to time converter. Since its capacitor charges if the voltage is varied in accordance with the signal voltage, a series of rectangular pulses will be obtained with varying width as required. PROCEDURE: 1. Rig up the circuit as shown in the circuit diagram. 2. Note down the amplitude (V m ) and time period of the modulating signal. 3. Observe the output at A (carrier signal) and measure the amplitude (V c ) and time period. 4. Observe the spike output at B and measure the amplitude and time period. 5. Apply the modulating signal input and trigger input and observe the PWM output. 6. Note down the amplitude and time period of all the signals and plot them on the graph. RESULT: Thus the Pulse Width Modulated signal is generated using IC 555 timer and its Waveforms are plotted. 102

109 SIMULATION OUTPUT: 103

110 EXPT.NO.6 SIMULATION OF LINEAR DELTA MODULATION AIM: To simulate the linear delta modulation using MATLAB. SOFTWARE USED: MATLAB PROGRAM: clc; clear all close all fs=100; t=0:1/fs:2; m=sin(2*pi*t); plot(m); hold all; AM=1; FM=1; d=2*pi*fm*am/fs; for n=1:length(m); if n==1; e(n)=m(n); eq(n)=d*sign(e(n)); mq(n)=eq(n); else e(n)=m(n)-mq(n-1); eq(n)=d*sign(e(n)); mq(n)=mq(n-1)+eq(n); end end stairs(mq) RESULT: Thus the MATLAB code for linear delta modulation was written & output is verified. 104

111 SIMULATED OUTPUT: 105

112 EX.NO.7 OFDM SPECTRUM AIM: To write and simulate the MATLAB codes for OFDM spectrum (Guard interval insertion). THEORY: Orthogonal frequency-division multiplexing (OFDM), essentially identical to coded OFDM (COFDM) and discrete multi-tone modulation (DMT), is a frequency-division multiplexing (FDM) scheme used as a digital multi-carrier modulation method. A large number of closelyspaced orthogonal sub-carriers are used to carry data. The data is divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth. OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, wireless networking and broadband internet access. The primary advantage of OFDM over single-carrier schemes is its ability to cope with severe channel conditions, without complex equalization filters. Channel equalization is simplified because OFDM may be viewed as using many slowly-modulated narrowband signals rather than one rapidly-modulated wideband signal. 106

113 SIMULATED OUTPUT: 107

114 PROGRAM: clear all; Fd=1; % symbol rate (1Hz) Fs=1*Fd; % number of sample per symbol M=4; % kind(range) of symbol (0,1,2,3) Ndata=1024; % all transmitted data symbol Sdata=64; % 64 data symbol per frame to ifft Slen=128; % 128 length symbol for IFFT Nsym=Ndata/Sdata; % number of frame -> Nsym frame GIlen=144; % symbol with GI insertion GI=16; % guard interval length vector initialization X=zeros(Ndata,1); Y1=zeros(Ndata,1); Y2=zeros(Ndata,1); Y3=zeros(Slen,1); z0=zeros(slen,1);z1=zeros(ndata/sdata*slen,1); g=zeros(gilen,1); z2=zeros(gilen*nsym,1);z3=zeros(gilen*nsym,1); random integer generation by M kinds X = randint(ndata, 1, M); digital symbol mapped as analog symbol Y1 = modmap(x, Fd, Fs, 'qask', M); covert to complex number Y2=amodce(Y1,1,'qam'); for j=1:nsym; for i=1:sdata; Y3(i+Slen/2-Sdata/2,1)=Y2(i+(j-1)*Sdata,1); end z0=ifft(y3); for i=1:slen; z1(((j-1)*slen)+i)=z0(i,1); end for i=1:slen; g(i+16)=z0(i,1); end for i=1:gi; g(i)=z0(i+slen-gi,1); end for i=1:gilen; z2(((j-1)*gilen)+i)=g(i,1); end end graph on time domain figure(1); f = linspace(-sdata,sdata,length(z1)); plot(f,abs(z1)); Y4 = fft(z1); if Y4 is under 0.01 Y4=0.001 for j=1:ndata/sdata*slen; if abs(y4(j)) < 0.01 Y4(j)=0.01; end end Y4 = 10*log10(abs(Y4));graph on frequency domain figure(2); f = linspace(-sdata,sdata,length(y4)); plot(f,y4);axis([-slen/2 Slen/ ]); RESULT: Thus the MATLAB code for OFDM Spectrum was written & output is verified. 108

115 OUTPUT WAVEFORM: 109

116 EX.NO: 8 PULSE POSITION MODULATION AIM: To write and simulate in the MATLAB codes for Pulse position modulation. THEORY: PROGRAM: clc; clear all; close all; fc=1000; fs=10000; fm=200; t=0:1/fs:(2/fm-1/fs); mt=0.4*sin(2*pi*fm*t)+0.5; st=modulate(mt,fc,fs,'ppm'); dt=demod(st,fc,fs,'ppm'); figure subplot(3,1,1); plot(mt); title('message signal'); xlabel('time period'); ylabel('amplitude'); axis([ ]) subplot(3,1,2); plot(st); title('modulated signal'); xlabel('time period'); ylabel('amplitude'); axis([ ]) subplot(3,1,3); plot(dt); title('demodulated signal'); xlabel('time period'); ylabel('amplitude'); axis([ ]) RESULT: Thus the MATLAB code for PPM was written & output is verified. 110

117 EXPT.NO. 9 COMMUNICATION LINK SIMULATION USING SDR AIM: To study all digital modulation techniques using SDR TRAINER KIT. EQUIPMENTS REQUIRED: THEORY: SDR Trainer Kit -1 SMA Connector-1 USB device -1 FREQUENCY MODULATION It is a type of modulation in which the frequency of the high frequency (Carrier) is varied in accordance with the instantaneous value of the modulating signal. The FM modulator is used to combine the carrier wave and the information signal in much the same way as in the AM transmitter. The only difference in this case is that the generation of the carrier wave and the modulation process is carried out in the same block. BLOCK DIAGRAM: 111

118 OUTPUT WAVEFORM: AMPLITUDE PHASE SHIFT KEYING ASK is the simplest modulation technique, where a binary information signal directly modulates the amplitude of an analog carrier. ASK is similar to standard amplitude modulation except there are 2 output amplitudes possible. It is also referred as on-off keying. BLOCK DIAGRAM: 112

119 OUTPUT WAVEFORM: FREQUENCY SHIFT KEYING In FSK, modulating signal is a binary signal that varies between two discrete voltage levels rather than a continuously changing analog waveform. BLOCK DIAGRAM: 113

120 OUTPUT WAVEFORM: BINARY PHASE SHIFT KEYING The simplest form of PSK is binary phase shift keying( N=1 and M=2). 2 phases are possible for the carrier. One phase represents logic 1 & other phase represents logic 0. As the input signal changes state, the phase of the output carrier shifts between two angles that are separated by 180 BPSK is a form of square wave modulation of a continuous wave (CW) signal. BLOCK DIAGRAM 114