QPSK

FRANCIS XAVIER ENGINEERING COLLEGE TIRUNELVELI

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

EC2307- COMMUNICATION SYSTEMS LAB

LAB MANUAL

PREPARED BY V.KULANDAI SELVAN, M.E, STALIN JACOB.W,M.E, Asst.Professor ECE, FXEC.

1

S.No

TOPIC

1. SYLLABUS 2. EXPERIMENTS AM MODULATION AND DEMODULATION 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

PAGE NO 4 5

FREQUENCY MODULATION AND DEMODULATION

11

PULSE AMPLITUDE MODULATION

17

PULSE WIDTH MODULATION

21

PULSE POSITION MODULATION

25

GENERATION AND DETECTION OF PCM SIGNAL

29

DELTA MODULATION

34

GENERATION AND DETECTION OF ASK

38

GENERATION AND DETECTION OF FSK

42

GENERATION AND DETECTION OF PSK

46

GENERATION AND DETECTION OF QPSK

50

LINE CODING AND DECODING TECHNIQUES

54

SAMPLING AND TIME DIVISION MULTIPLEXING

62

PHASE LOCKED LOOP

68

PRE-EMPHASIS / DE-EMPHASIS

71

FREQUENCY DIVISION MULTIPLEXING

76

ERROR CONTROL CODING USING MATLAB

79

DESIGN OF ASK, PSK, QPSK, FSK USING MATLAB

84

2

SYLLABUS EC2307 –COMMUNICATION SYSTEMLABORATORY

LIST OF EXPERIMENTS

1. Amplitude modulation and Demodulation. 2. Frequency Modulation and Demodulation 3. Pulse Modulation – PAM / PWM / PPM 4. Pulse Code Modulation 5. Delta Modulation, Adaptive Delta Modulation. 6. Digital Modulation & Demodulation – ASK, PSK, QPSK, FSK (Hardware & MATLAB) 7. Designing, Assembling and Testing of Pre-Emphasis / De-emphasis Circuits. 8. PLL and Frequency Synthesizer 9. Line Coding 10. Error Control Coding using MATLAB. 11. Sampling & Time Division Multiplexing. 12. Frequency Division Multiplexing

3

4

Exp-No:1 Date:

AM MODULATION AND DEMODULATION AIM To transmit a modulating signal after amplitude modulation using AM transmitter and receive the signal back after demodulating using AM receiver. APPARATUS REQUIRED: 1. 2. 3. 4.

AM transmitter trainer kit AM receiver trainer kit CRO Patch cards

THEORY: AMPLITUDE MODULATION: Amplitude Modulation is a process by which amplitude of the carrier signal is varied in accordance with the instantaneous value of the modulating signal, but frequency and phase of carrier wave remains constant. The modulating and carrier signal are given by Vm(t) = Vm sinωmt VC(t) = VC sinωCt The modulation index is given by, ma = Vm / VC. Vm = Vmax – Vmin and VC = Vmax + Vmin The amplitude of the modulated signal is given by, VAM(t) = VC (1+ma sinωmt) sinωCt Where Vm = maximum amplitude of modulating signal VC = maximum amplitude of carrier signal Vmax = maximum variation of AM signal Vmin = minimum variation of AM signal

5

PROCEDURE:

1. 2. 3. 4.

The circuit wiring is done as shown in diagram A modulating signal input given to the Amplitude modulator Now increase the amplitude of the modulating signal to the required level. The amplitude and the time duration of the modulating signal are observed using CRO. 5. Finally the amplitude modulated output is observed from the output of amplitude modulator stage and the amplitude and time duration of the AM wave are noted down. 6. Calculate the modulation index by using the formula and verify them. The final demodulated signal is viewed using an CRO at the output of audio power amplifier stage. Also the amplitude and time duration of the demodulated wave are noted down.

6

KIT DIAGRAM AM TRANSMITTER

7

AM RECEIVER

8

TABULATION: Waveform Message

Amplitude (V)

Time Period (msec)

Frequency

Carrier modulated Demodulated

MODEL GRAPH Message signal Vm

time Vc

Carrier signal

time

AM signal Vmc

time

9

VIVA QUESTION 1. 2. 3. 4. 5.

Define modulation index of an AM signal Draw the phasor diagram of AM signal. As related to AM, what is over modulation, under modulation and 100% modulation? What are the types of AM signals? What are the different types of AM generation?

RESULT Thus the AM signal was transmitted using AM trainer kit and the AM signal detected using AM detector kit. Exp-No: 02 10

Date:

FREQUENCY MODULATION AND DEMODULATION AIM To transmit a modulating signal after frequency modulation using FM transmitter and receive the signal back after demodulating using FM receiver. APPARATUS REQUIRED: 1. 2. 3. 4.

FM transmitter trainer kit FM receiver trainer kit CRO Patch cards

THEORY: Frequency modulation (FM) is a form of modulation that represents information as variations in the instantaneous frequency of a carrier wave. (Contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant.) In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal. Shifting the carrier frequency among a set of discrete values can represent digital data, a technique known as frequency-shift keying. FM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech (see FM broadcasting). Normal (analog) TV sound is also broadcast using FM. A narrowband form is used for voice communications in commercial and amateur radio settings. The type of FM used in broadcast is generally called wide-FM, or W-FM. In two-way radio, narrowband narrow-fm (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into space. FM is also used at intermediate frequencies by most analog VCR systems, including VHS, to record the luminance (black and white) portion of the video signal. FM is the only feasible method of recording video to and retrieving video from magnetic tape without extreme distortion, as video signals have a very large range of frequency components — from a few hertz to several megahertz, too wide for equalizers to work with due to electronic noise below -60 dB. FM also keeps the tape at saturation level, and therefore acts as a form of noise reduction, and a simple limiter can mask variations in the playback output, and the FM capture effect removes print-through and pre-echo. A continuous pilot-tone, if added to the signal — as was done on V2000 and many Hi-band formats — can keep mechanical jitter under control and assist time base correction.

11

PROCEDURE:

1. 2. 3. 4.

The circuit wiring is done as shown in diagram A modulating signal input given to the Frequency modulator Now increase the modulated signal to the required level. The amplitude and the time duration of the modulating signal are observed using CRO. 5. Finally the frequency modulated output is observed from the output of frequency modulator stage and the amplitude and time duration of the FM wave are noted down.

12

KIT DIAGRAM: FM TRANSMITTER

FM RECEIVER 13

14

MODEL GRAPH

TABULATION: Waveform

Amplitude (V)

Time Period (msec)

Frequency

Message Carrier modulated Demodulated

15

VIVA QUESTION 1. 2. 3. 4. 5.

Define frequency deviation in FM? Draw the phasor diagram of FM signal. What are the different types of FM generation? What do you mean by narrowband and wideband FM? What are the advantages of FM.?

RESULT Thus the FM signal was transmitted using FM trainer kit and the FM signal detected using FM detector kit.

16

Exp-No: 3 Date:

PULSE AMPLITUDE MODULATION AIM To generate Pulse Amplitude signal using PAM modulator. APPARATUS REQUIRED: 1. PAM trainer kit 2. CRO 3. Patch cards THEORY This type of modulation is used as the first step in converting an analog signal to a discrete signal or in cases where it may be difficult to change the frequency or phase of the carrier. In this case the carrier is a pulse train rather than a sine wave and the spectrum of the carrier consists of several components at 2np/T where T is the time between pulses. The applet below shows a PAM signal and how it varies with modulating signal amplitude and frequency. The spectrum of the PAM signal is shown at the top in black. In this case each component of the carrier's spectrum has become an AM spectrum. Notice that the spectrum contains a component at the modulating frequency, which makes the PAM signal relatively easy to demodulate. Pulseamplitude modulation, acronym PAM, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. Pulse-amplitude modulation is now rarely used, having been largely superseded by pulse-code modulation and, more recently, by pulse-position modulation.

PROCEDURE 1. The circuit wiring is done as shown in diagram 2. A modulating signal input and clock signal is given to the PAM modulator 3. The amplitude and the time duration of the modulating signal are observed using CRO. 4. Finally the PAM output is observed from the output of PAM modulator stage and the amplitude and time duration of the PAM wave are noted down. 5. PAM signal is applied to the filter circuit for demodulation process. 6. After demodulation the original signal is recovered.

17

KIT DIAGRAM

18

MODEL GRAPH

TABULAR COLUMN

S.No

Name of the signal

1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

Amplitude in V

Time period in Sec

Frequency in Hz

19

VIVA QUESTIONS: 1. 2. 3. 4. 5.

What is PAM? Differentate with PAM and PCM. Write the application of PAM. Draw the PAM signal. Write the time period equation of PAM

RESULT Thus the PAM signal was generated using PAM modulator.

20

Exp-No: 04 Date:

PULSE WIDTH MODULATION AIM To generate Pulse Width Modulation signal using PWM modulator. APPARATUS REQUIRED: 1. PWM trainer kit 2. CRO 3. Patch cards

THEORY Pulse width modulation is defined as an analog modulation technique in which the width of each pulse is made proportional to the instantaneous amplitude of the signal at the sampling instant. Pulse Width modulator circuit shown is basically a monostable multivibrator with a modulating input signal applied at pin-5. By the application of continuous trigger at pin-2, a series of output pulses are obtained, the duration of which depends on the modulating input at pin-5. The modulating signal applied at pin-5 gets superimposed upon the already existing voltage (2/3) Vcc at the inverting input terminal of UC. This in turn changes the threshold level of the UC and the output pulse width modulation takes place. The modulating signal and the output waveform are drawn in fig. It may be noted from the output waveform that the pulse duration, that is, the duty cycle only varies, keeping the frequency same as that of the continuous input pulse train trigger. PROCEDURE 1. The circuit wiring is done as shown in diagram 2. A modulating signal is given to the PWM modulator 3. The amplitude and the time duration of the modulating signal are observed using CRO. 4. Finally the PWM output is observed from the output of PWM modulator stage and the amplitude and time duration of the PWM wave are noted down. 5. PWM signal is applied to the filter circuit for demodulation process. 6. After demodulation the original signal is recovered.

KIT DIAGRAM 21

22

MODEL GRAPH

TABULAR COLUMN S.No

Name of the signal

1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

Amplitude in V

Time period in Sec

Frequency in Hz

23

VIVA QUESTION 1. 2. 3. 4. 5.

What is PWM? How is the carrier generated in the above circuit? What is the mode of operation in the above circuit? Mention the power flow in PWM circuit. Differentiate PWM and PPM.

RESULT Thus the Pulse Width Modulation signal was generated using PWM modulator. 24

Exp-No: 05 Date:

PULSE POSITION MODULATION AIM To generate Pulse Position Modulation signal using PPM modulator. APPARATUS REQUIRED: 1. PPM trainer kit 2. CRO 3. Patch cards THEORY Pulse position modulation is defined as an analog modulation technique in which the signal is sampled at regular intervals such that the shift in position of each sample is proportional to the instantaneous value of the signal at the sampling instant. The Pulse-position modulation can be constructed by applying a modulating signal to pin 5 of a 555 timer connected for astable operation as shown in fig. The output pulse position varies with the modulating signal, since the threshold voltage and hence the time delay is varied. It may be noted from the output waveform that the frequency is varying leading to pulse position modulation. PROCEDURE 1. The circuit wiring is done as shown in diagram 2. A modulating signal is given to the PPM modulator 3. The amplitude and the time duration of the modulating signal are observed using CRO. 4. Finally the PPM output is observed from the output of PPM modulator stage and the amplitude and time duration of the PPM wave are noted down. 5. PPM signal is applied to the filter circuit for demodulation process. 6. After demodulation the original signal is recovered.

25

KIT DIAGRAM

26

MODEL GRAPH

TABULAR COLUMN S.No Name of the signal 1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

Amplitude in V

Time period in Sec

Frequency in Hz

27

VIVA QUESTION 1. 2. 3. 4. 5.

What is PPM? How is the carrier generated in the above circuit? What is the mode of operation in the above circuit? Mention the power flow in PPM circuit. Differentiate PAM and PPM.

RESULT Thus the Pulse Position Modulation signal was generated using PPM modulator.

28

Exp-No: 06 Date:

GENERATION AND DETECTION OF PCM SIGNAL AIM To generate a PCM signal using PCM modulator and detect the message signal from PCM signal by using PCM demodulator.

APPARATUS REQUIRED PCM kit, CRO and connecting probes THEORY Pulse code modulation is a process of converting an analog signal into digital. The voice or any data input is first sampled using a sampler (which is a simple switch) and then quantized. Quantization is the process of converting a given signal amplitude to an equivalent binary number with fixed number of bits. This quantization can be either midtread or mid-raise and it can be uniform or non-uniform based on the requirements. For example in speech signals, the higher amplitudes will be less frequent than the low amplitudes. So higher amplitudes are given less step size than the lower amplitudes and thus quantization is performed non-uniformly. After quantization the signal is digital and the bits are passed through a parallel to serial converter and then launched into the channel serially. At the demodulator the received bits are first converted into parallel frames and each frame is de-quantized to an equivalent analog value. This analog value is thus equivalent to a sampler output. This is the demodulated signal. In the kit this is implemented differently. The analog signal is passed trough a ADC (Analog to Digital Converter) and then the digital codeword is passed through a parallel to serial converter block. This is modulated PCM. This is taken by the Serial to Parallel converter and then through a DAC to get the demodulated signal. The clock is given to all these blocks for synchronization. The input signal can be either DC or AC according to the kit. The waveforms can be observed on a CRO for DC without problem. AC also can be observed but with poor resolution.

29

PROCEDURE 1. Power on the PCM kit. 2. Measure the frequency of sampling clock. 3. Apply the DC voltage as modulating signal. 4. Connect the DC input to the ADC and measure the voltage. 5. Connect the clock to the timing and control circuit. 6. Note the binary work from LED display. The serial data through the channel can be observed in the CRO. 7. Also observe the binary word at the receiver end. 8. Now apply the AC modulating signal at the input. 9. Observe the waveform at the output of DAC. 10. Note the amplitude of the input voltage and the codeword. Also note the value of the output voltage. Show the codeword graphically for a DC input.

30

KIT DIADRAM

MODEL GRAPH 31

TABULAR COLUMN

S.No

Name of the signal

1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

4

Demodulated

Amplitude in V

Time period in Sec

Frequency in Hz

Signal

32

VIVA QUESTIONS: 1. What is the expression for transmission bandwidth in a PCM system? 2. What is the expression for quantization noise /error in PCM system? 3. What are the applications of PCM? 4. What are the advantages of the PCM? 5. What are the disadvantages of PCM?

RESULT Thus the PCM signal was generated using PCM modulator and the message signal was detected from PCM signal by using PCM demodulator. 33

Exp-No: 07 Date:

DELTA MODULATION AIM To transmit an analog message signal in its digital form and again reconstruct back the original analog message signal at receiver by using Delta modulator. APPARATUS REQUIRED DM kit, CRO and connecting probes THEORY Delta modulation is the DPCM technique of converting an analog message signal to a digital sequence. The difference signal between two successive samples is encoded into a single bit code. The block and kit diagrams show the circuitry details of the modulation technique. A present sample of the analog signal m(t) is compared with a previous sample and the difference output is level shifted, i.e. a positive level (corresponding to bit 1) is given if difference is positive and negative level (corresponding to bit 0) if it is negative. The comparison of samples is accomplished by converting the digital to analog form and then comparing with the present sample. This is done using an Up counter and DAC as shown in block diagram. The delta modulated signal is given to up counter and then a DAC and the analog input is given to OPAMP and a LPF to obtain the demodulated output. PROCEDURE 1. Switch on the kit. Connect the clock signal and the modulating input signal to the modulator block. Observe the modulated signal in the CRO. 2. Connect the DM output to the demodulator circuit. Observe the demodulator output on the CRO. 3. Also observe the DAC output on the CRO. 4. Change the amplitude of the modulating signal and observe the DAC output. Notice the slope overload distortion. Keep the tuning knob so that the distortion is gone. Note this value of the amplitude. This is the minimum required value of the amplitude to overcome slope overload distortion. 5. Calculate the sampling frequency required for no slope overload distortion. Compare the calculated and measured values of the sampling frequency.

KIT DIAGRAM 34

35

MODEL GRAPH

TABULAR COLUMN S.No Name of the signal 1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

4

Demodulated

Amplitude in V

Time period in Sec

Frequency in Hz

Signal

36

VIVA QUESTIONS: 1. What are the advantages of Delta modulator? 2. What are the disadvantages of delta modulator? 3. How to overcome slope overload distortion? 4. How to overcome Granular or ideal noise? 5. What are the differences between PCM & DM? 6. Define about slope over load distortion? 7. What is the other name of Granular noise? 8. What is meant by staircase approximation? 9. What are the disadvantages of Delta modulator? 10. Write the equation for error at present sample?

RESULT Thus the analog message signal in its digital form was transmitted and again the original analog message signal was reconstructed at receiver by using Delta modulator and Demodulator. 37

Exp-No: 8 Date:

GENERATION AND DETECTION OF ASK AIM To construct and generate Amplitude Shift Keying signal and detect the message signal. APPARATUS REQUIRED ASK kit, CRO and connecting probes

THEORY ASK or ON-OFF key is the simplest digital modulation technique. In this method there is only one unit energy carrier it is switched ON/OFF depending upon the input binary sequence to transmit symbol 0 & 1. No pulse is transmitted output contains some complete no of cycle of carrier frequency. The disadvantage of ASK is the modulated carrier signal is not continuously transmitted. The peak power requirement is also high. The bit error probability rate is also not required in this technique.

PROCEDURE 1. Make connections as shown in the diagram. 2. Set the input signal and carrier signal. 3. Obtain ASK signal 4. Measure the amplitude and frequency 5. Obtain the demodulated output.

38

KIT DIAGRAM

39

MODEL GRAPHH

TABULAR COLUMN S.No Name of the signal 1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

4

Demodulated

Amplitude in V

Time period in Sec

Frequency in Hz

Signal

40

VIVA QUESTIONS: 1. What is the difference between PSK&ASK? 2. What is the band width requirement of a ASK? 3. Explain the operation of ASK detection? 4. What are the advantages of APSK? 5. What is meant by ASK?

RESULT Thus the Amplitude Shift Keying signal was generated and the message signal was reconstructed

41

Exp-No: 9 Date:

GENERATION AND DETECTION OF FSK AIM To generate a Frequency Shift Keying signal using FSK modulator and detect the message signal from FSK signal using FSK detector. APPARATUS REQUIRED FSK kit, CRO and connecting probes THEORY Frequency Shift Keying is the process generating a modulated signal from a digital data input. If the incoming bit is 1, a signal with frequency f1 is sent for the duration of the bit. If the bit is 0, a signal with frequency f2 is sent for the duration of this bit. This is the basic principle behind FSK modulation. Basically a 555 timer is used as an Astable multivibrator, which generates a clock pulse of frequency determined by the values of R and C in this circuit. This is divided by 2, 4, 8 and 16 using 74163 IC, and two of these outputs are used in a NAND logic gates circuit, to generate a FSK modulated wave. To this NAND gates circuit a binary data sequence is also supplied. The circuit operation causes a frequency f1 for bit 1, and f2 for bit 0. In the demodulator circuit, the FSK modulated signal is applied to a high Q tuned filter. This filter is tuned to the frequency of either 0 or 1. This filter passes the selected frequency and rejects the other. The output is then passed through a FWR (Full Wave Rectifier) circuit and the output is now above zero volts only. It is then passed through a comparator; if the input to the comparator is greater than threshold value, the output is 1, else it is 0. This digital output of the comparator is the demodulated FSK output. PROCEDURE: 1. Make connections as shown in the circuit diagram. 2. Set the input signal and carrier signal. 3. Obtain FSK signal 4. Tabulate the output data and draw the graph. 5. Justify the obtained output with theoretical calculation.

42

MODEL GRAPH

TABULAR COLUMN S.No Name of the signal 1

Modulating Signal

2

Carrier Signal 1

3

Carrier Signal 2

4

Modulated Signal

5

Demodulated

Amplitude in V

Time period in Sec

Frequency in Hz

Signal

43

VIVA QUESTIONS: 1. Define Binary FSK signal? 2. What is meant by carrier swing? 3. Define Frequency deviation of FSK signal? 4. What are the advantages of this FSK signal? 5. Give the differences between FSK & FM?

RESULT

Thus the Frequency Shift Keying signal wag generated using FSK modulator and the message signal was detected from FSK signal using FSK detector.

44

Exp-No: 10 Date:

GENERATION AND DETECTION OF PSK AIM To generate a Phase Shift Keying signal using PSK modulator and detect the message signal from PSK signal using PSK detector. APPARATUS REQUIRED PSK kit, CRO and connecting probes THEORY PSK is a digital modulation scheme which is analogues to phase modulation. In binary phase shift keying two output phases are possible for a single carrier frequency one out of phase represent logic 1 and logic 0. As the input digital binary signal change state the phase of output carrier shift two angles that are 180o out of phase. In a PSK modulator the carrier input signal is multiplied by the digital data. The input carrier is multiplied by either a positives or negatives consequently the output signal is either +1sinwct or - 1sinwct. The first represent a signal that is phase with the reference oscillator the latter a signal that is 180o out of phase with the reference oscillator. Each time a change in input logic condition will change the output phase consequently for PSK the output rate of change equal to the input rate range and widest output bandwidth occurs when the input binary data are alternating 1/0 sequence. The fundamental frequency of an alternate 1/0 bit sequence is equal to one half of the bit rate.

PROCEDURE 1. Make connections as shown in the diagram. 2. Set the input signal and carrier signal. 3. Obtain PSK signal 4. Measure the output data and draw the graph. 5. Obtain the demodulated output.

45

KIT DIAGRAM

46

MODEL GRAPH

TABULAR COLUMN

S.No

Name of the signal

1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

4

Demodulated

Amplitude in V

Time period in Sec

Frequency in Hz

Signal

47

VIVA QUESTIONS: 1. What is the bandwidth requirement of BPSK? 2. What is the expression for error probability of BPSK reception using coherent matched filter detection? 3. What are the draw backs of BPSK? 4. Draw the Power spectral density of BPSK? 5. What are the major differences between DPSK&BPSK? 6. What are the advantages of BPSK over a PSK signal?

RESULT Thus the Phase Shift Keying signal wag generated using PSK modulator and the message signal was detected from PSK signal using PSK detector.

48

Exp-No: 11 Date:

GENERATION AND DETECTION OF QPSK AIM To generate a Quadrature Phase Shift Keying signal using QPSK modulator and detect the message signal from QPSK signal using QPSK detector. APPARATUS REQUIRED QPSK kit, CRO and connecting probes THEORY QPSK is another form of angle-modulated, constant-amplitude digital modulation. It is an M-ary encoding technique where M=4. with QPSK four output phases are possible for a single carrier frequency. Two bits (a dibit) are clocked into the bit splitter. After both bits have been serially inputted, they are simultaneously parallel outputted. One bit is directed to the I channel and the other to the Q channel. The I bit modulates a carrier that is in phase with the reference oscillator and the Q bit modulates a carrier that is 900 out of phase with the reference carrier. QPSK modulator is two BPSK modulators combined in parallel. The input QPSK signal is given to the I and Q product detectors and the carrier recovery circuit. The carrier recovery circuit produces the original transmit carrier oscillator signal. The recovered carrier must be frequency and phase coherent with the transmit reference carrier. The QPSK signal is demodulated in the I and Q product detectors, which generate the original I and Q data bits. The output of the product detectors are fed to the bit combining circuit, where they are converted from parallel I and Q data channels to a single binary output data stream. PROCEDURE: 1. Connect the binary input data to I-channel. 2. Connect the binary input data to Q-channel. 3. Connect the sine wave input to balanced modulator (I channel) as a carrier signal and to sine wave input to balanced modulator (Q channel) as a carroer signal. 4. Switch on the power supply. 5. Display binary input data on CRO. Adjust pot1 and pot3 to get bipolar data. 6. Adjust gain control pot to set equal amplitude in I and Q channel. 7. Obtain QPSK signal. 8. Connect the QPSK to input of QPSK demodulator. 9. Obtain the demodulated QPSK signal.

KIT DIAGRAM 49

\

50

MODEL GRAPH

TABULAR COLUMN

S.No

Name of the signal

1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

4

Demodulated

Amplitude in V

Time period in Sec

Frequency in Hz

Signal

51

VIVA QUESTIONS: 1. What is the difference between PSK&QPSK? 2. What is the band width requirement of a QPSK? 3. Explain the operation of QPSK detection? 4. What are the advantages of QPSK? 5. What is meant by differential encoding?

RESULT Thus the Quadrature Phase Shift Keying signal wag generated using QPSK modulator and the message signal was detected from QPSK signal using QPSK detector.

52

Exp-No: 12 Date:

LINE CODING AND DECODING TECHNIQUES AIM : To study different line coding techniques. APPARATUS REQUIRED: 1. Communication trainer kit 2. Multi Output Power Supply. 3. Patch cords. 4. DSO/CRO THEORY: We need to represent PCM binary digits by electrical pulses in order to transmit them through a base band channel. The most commonly used PCM popular data formats are being realized here. Line coding refers to the process of representing the bit stream (1‟s and 0‟s) in the form of voltage or current variations optimally tuned for the specific properties of the physical channel being used. The selection of a proper line code can help in so many ways: One possibility is to aid in clock recovery at the receiver. A clock signal is recovered by observing transitions in the received bit sequence, and if enough transitions exist, a good recovery of the clock is guaranteed, and the signal is said to be self-clocking. Another advantage is to get rid of DC shifts. The DC component in a line code is called the bias or the DC coefficient. Unfortunately, most long-distance communication channels cannot transport a DC component. This is why most line codes try to eliminate the DC component before being transmitted on the channel.Such codes are called DC balanced, zero-DC, zero-bias, or DC equalized.Some common types of line encoding in common-use nowadays are unipolar, polar, bipolar, Manchester, MLT-3 and Duobinary encoding. These codes are explained here: 1. Unipolar (Unipolar NRZ and Unipolar RZ): Unipolar is the simplest line coding scheme possible. It has the advantage of being compatible with TTL logic. Unipolar coding uses a positive rectangular pulse p(t) to represent binary 1, and the absence of a pulse (i.e., zero voltage) to represent a binary 0. Two possibilities for the pulse p(t) exist3: Non-Return-to-Zero (NRZ) rectangular pulse and Return-to-Zero (RZ) rectangular pulse. The difference between Unipolar NRZ and Unipolar RZ codes is that the rectangular pulse in NRZ stays at a positive value (e.g., +5V) for the full duration of the logic 1 bit, while the pule in RZ drops from +5V to 0V in the middle of the bit time. 53

A drawback of unipolar (RZ and NRZ) is that its average value is not zero, which means it creates a significant DC-component at the receiver (see the impulse at zero frequency in the corresponding power spectral density (PSD) of this line code

UNIPOLAR NRZ CODE

The disadvantage of unipolar RZ compared to unipolar NRZ is that each rectangular pulse in RZ is only half the length of NRZ pulse. This means that unipolar RZ requires twice the bandwidth of the NRZ code. Polar (Polar NRZ and Polar RZ): In Polar NRZ line coding binary 1‟s are represented by a pulse p(t) and binary 0‟s are represented by the negative of this pulse -p(t) (e.g., -5V). Polar (NRZ and RZ) signals .Using the assumption that in a regular bit stream a logic 0 is just as likely as a logic 1,polar signals (whether RZ or NRZ) have the advantage that the resulting Dccomponent is very close to zero.

54

The rms value of polar signals is bigger than unipolar signals, which means that polar signals have more power than unipolar signals, and hence have better SNR at the receiver. Actually, polar NRZ signals have more power compared to polar RZ signals. The drawback of polar NRZ, however, is that it lacks clock information especially when a long sequence of 0‟s or 1‟s is transmitted. Non-Return-to-Zero, Inverted (NRZI): NRZI is a variant of Polar NRZ. In NRZI there are two possible pulses, p(t) and –p(t). A transition from one pulse to the other happens if the bit being transmitted is a logic 1, and no transition happens if the bit being transmitted is a logic 0.

This is the code used on compact discs (CD), USB ports, and on fiber-based Fast Ethernet at 100-Mbit/s .

55

MANCHESTER ENCODING: In Manchester code each bit of data is signified by at least one transition. Manchester encoding is therefore considered to be self-clocking, which means that accurate clock recovery from a data stream is possible. In addition, the DC component of the encoded signal is zero. Although transitions allow the signal to be self-clocking, it carries significant overhead as there is a need for essentially twice the bandwidth of a simple NRZ or NRZI encoding

POWER SPECTRA OF LINE CODES:


Unipolar most of signal power is centered around origin and there is waste of power due to DC component that is present.
Polar format most of signal power is centered around origin and they are simple to implement.
Bipolar format does not have DC component and does not demand more bandwidth, but power requirement is double than other formats.
Manchester format does not have DC component but provides proper clocking.

56

PROCEDURE 1. Connect the PRBS (test point P5) to various line coding formats. Obtain the coded output as per the requirement. 2. Connect coded signal test point to corresponding decoding test point as inputs. 3. Set the SW1 as per the requirement. 4. Set the potentiometer P1 in minimum position. 5. Switch ON the power supply. Press the switch SW2 once. 6. Display the encoded signal on one channel of CRO and decoded signal on second channel of CRO.

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KIT DIAGRAM

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MODEL GRAPH

TABULAR COLUMN

S.No

Name of the signal

1

Modulating Signal

2

Carrier Signal

3

Modulated Signal

4

Demodulated

Amplitude in V

Time period in Sec

Frequency in Hz

Signal

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VIVA QUESTION 1. 2. 3. 4. 5.

State NRZ unipolar format State NRZ polar format. State NRZ bipolar format. Define data Signalling Rate. Define modulation rate.

RESULT Thus the different line coding techniques was studied.

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Exp-No:13 Date: SAMPLING AND TIME DIVISION MULTIPLEXING

AIM: To study the process of sampling and time division multiplexing of four signals using pulse amplitude modulation and De-modulation and to reconstruct the signals at the receiver using filters. APPARATUS REQUIRED: 1. Sampling and TDM Communication trainer kit: 2. Multi Output Power Supply. 3. Patch cords. 4. CRO (60MHz) THEORY The Sample and Hold circuit uses two buffers to keep a voltage level stored in a capacitor. Sample will charge the capacitor to the present signal level, while the input buffer ensures the signal won't be changed by the charging process. From there, the output buffer will make sure that the voltage level across the storage cap won't decrease over time. Sclear will short out the storage cap, discharging it and setting the output to 0V.In actual practice, the switches used are various forms of transistor switch, which provides cleaner switching and also allows another circuit to control the sample and clearing operations. Excellent Sample and Hold circuits like the LF398 are available on a single chip for cheap and easy use. Sample and Hold circuits are used internally in Analog to Digital conversion. We might also use them to hold a given signal value from any particular sensor on a robot, for analysis and later use. In TDM, by interleaving samples of several source waveforms in time, it is possible to transmit enough information to a receiver, via only one channel to recover all message waveforms. The conceptual implementation of the time multiplexing of N similar messages fn(t) where n= 1,2,3,…..N is illustrated in fig 1. the time allocated to one sample of one message is called time slot. The time intervals over which all message signals are sampled atleast once is called a Frame. The portion of the time slot not used by the system may be allocated to other functions like signaling, monitoring, synchronization, etc. 61

The four channels CH0, CH1, CH2, and CH3 are multiplexed on a single line TXD with the aid of a electronic switch CD 4016. The CD 4016 latches one of the four inputs I0-I3 depending on the control inputs C0, C1, C2, C3 which are generated by a 2: 4 line decoder. The decoder, depending on the A0 and A1, which start from 00 to 11, generates 0000 to 0011 on the output lines Y0, Y1, Y2 and Y3. On receiving the control signals, the CD4016 latches the first information signal I0 on the first count 0000. In the next clock, the control inputs change their state to 0001 and the input II is latched to the output on the same line. Similarly, all the information signals are multiplexed without any interference on the line PROCEDURE: The sample and hold circuit is assembled with the desired components. The input signal is given to the circuit from the function generator. The amplitude of the input signal should not exceed 10 volts. The frequency of the input signal is set to 600 Hz. The frequency of the sample signal is set to 5600 Hz. The next sample available is zero order holding device, integrate the signal between consequence sampling inputs.

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KIT DIAGRAM SAMPLING

63

TDM

64

MODEL GRAPH FOR SAMPLING

MODEL GRAPH FOR TDM

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VIVA QUESTIONS: 1. What is meant by multiplexing technique and what are the different types of Multiplexers? 2. Briefly explain about TDM&FDM? 3. What is the transmission band width of a PAM/TDM signal? 4. Define crosstalk effect in PAM/TDM system? 5. What are the advantages of TDM system? 6. What are major differences between TDM&FDM? 7. Give the value of Ts in TDM system? 8. What are the applications of TDM system and give some example? 9. What is meant by signal overlapping? 10. Which type of modulation technique will be used in TDM?

RESULT Thus the sampling process was studied and the different types of signals are multiplexed using TDM Technique.

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Exp-No:14 Date:

PHASE LOCKED LOOP AIM: To study the characteristics of Phase Locked Loop . APPARATUS REQUIRED: IC 565 Capacitors Resistors CRO THEORY: If an input signal Vs of frequency fs is applied to the PLL, the phase detector compares the phase and frequency of the incoming signal to that of the output Vo of the VCO. It the two signals differ in frequency and /or phase, an error voltage Ve is generated. The phase detector is basically a multiplier and produces the sum (fs+fo) and difference (fs-fo) components at its output. The high frequency component (fs+fo) is removed by the low pass filter and the difference frequency component is amplified and then applied as control voltage Vc to VCO. The signal Vc shifts the VCO frequency in a direction to reduce the frequency difference between fs and fo. The VCO continues to change frequency till its output frequency is exactly the same as the input signal frequency. The circuit is then said to be locked. PROCEDURE: 1. Make the circuit connection as shown in Fig 2. Measure the practical free running frequency of VCO for zero input. 3. Set the input square wave of 1Vp-p at 1KHz. 4. Increase the input frequency till PLL is locked. This frequency f1 gives the lower end of the capture range. Go on increasing the input frequency to f2 (upper end of the lock range), till PLL tracks the input signal. 5. Now gradually decrease the input frequency till f3 when the PLL is again locked. This is the upper end of the capture range. Keep on decreasing the input frequency till f4 when the loop is unlocked. This is the lower end of the lock range. 6. Compare theoretical and practical values of lock range and capture range.

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CIRCUIT DIAGRAM

68

VIVA QUESTIONS: 1.What is VCO? 2.Define Lock range,Capture range. 3.What are the applications of PLL? 4.Define PLL. 5.What is frequency synthesizer?

RESULT: Thus the PLL characteristics are studied Theoretical Lock range fL=

Theoretical Capture range fC=

Practical Lock range fL=

Practical Capture range fC=

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Exp-No:15 Date:

PRE-EMPHASIS / DE-EMPHASIS AIM: Design and conduct an experiment to test a pre-emphasis and de-emphasis circuit for 75Ps between 2.1KHz to 15KHz and record the results. APPARATUS REQUIRED: IC 741, Capacitors, Resistors, CRO, Bread Board, Power supply Connecting Wires

PROCEDURE: 1. Connections are made as shown in the circuit diagram. 2. Apply a sine wave of 5Vpp amplitude, vary the frequency and note down the gain of the circuit. 3. Plot a graph of normalized gain Vs frequency. DESIGN 1. Pre-emphasis circuit. Given f1 = 2.1 KHz, f2 = 15KHz. f1 = 1/2SrC, f2 = 1/2SRC Choose C = 0.1Pf then r = 820 and R = 100. Also r/R = Rf/R1, then R1 = 2.2K and Rf = 15K. 2. De-emphasis circuit. fC = 1/2SRdCd. Choose Cd = 0.1Pf and fC = f1 = 2.1KHz Then Rd = 820.

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CIRCUIT DIAGRAM PRE-EMPHASIS

DE-EMPHASIS

71

MODEL GRAPH

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TABULATION: PRE-EMPHASIS: Vi= Frequency(Hz)

VO

Gain= VO/ Vi

Gain in dB

VO

Gain= VO/ Vi

Gain in dB

DE-EMPHASIS: Vi= Frequency(Hz)

73

VIVA QUESTIONS: 1.What is advantage of FM over Am? 2.Define Pre-emphasis and De-emphasis. 3.Define capture effect. 4.What are the types of FM? 5.Define transmission efficiency.

RESULT: Thus the Pre-Emphasis and De-Emphasis circuit was designed and analysed using IC741.

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Exp-No:16 Date:

FREQUENCY DIVISION MULTIPLEXING AIM: To study the concept of frequency division multiplexing. APPARATUS REQUIRED: FDM Trainer kit, Patch Chords, CRO

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Exp-No:17 Date:

ERROR CONTROL CODING USING MATLAB AIM: To write a program in MATLAB for error control coding techniques. ALGORITHM: 1.Get the input binary sequcence. 2.Calculate the reundancy bits for the corrosponding code. 3.Transmit the signal that contains message bits+redundancy bits added at the end. 4.Calculate the redundancy bits once again for the received bits. 5.If the redundancy bits=’0’ then no error in the transmission otherwise some error in the transmission.

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PROGRAM: clc; clear all; close all; k=input('Number of message bits'); n=input('Number of coded bits'); P=[1 1 1;0 1 1;1 0 1;1 1 0] G=[eye(k) P] for i=1:2^k str=dec2base(i-1,2,4); for j=1:k m(i,j)=str(j); end end for i=1:(2^k) for r=1:n o=0; for j=1:k o=o+(m(i,j)*G(j,r)); end c(i,r)=mod(o,2); end end e=zeros(n,n) for i=1:n

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e(i,i)=1; end % Syndrome Table H=[P' eye(n-k)]; H1=H'; for i=1:n for r=1:n-k o=0; for j=1:n o=o+(e(i,j)*H1(j,r)); end er(i,r)=mod(o,2); end end for i=1:n rec1=c(2^k,i)+e(1,i); rec(1,i)=mod(rec1,2); end for i=1:1 for r=1:n-k o=0; for j=1:n o=o+(rec(i,j)*H1(j,r)); end sy(i,r)=mod(o,2); 78

end end i=1; j=1; while sy(1,j)==er(i,j)&&sy(1,j+1)==er(i,j+1)&&sy(1,j+2)==er(i,j+2) rec_er=e(i,:); i=i+1; end rec_er %Error Corrected Message for i=1:n Det=rec(1,i)+rec_er(1,i); det_rec(1,i)=mod(Det,2); end det_rec

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RESULT: Thus the error control coding techniques are executed using MATLAB programs.

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Exp-No:18 Date:

DESIGN OF ASK, PSK, QPSK, FSK USING MATLAB AIM: To write a program in MATLAB for design of ASK,PSK,QPSK and FSK.

PROGRAM: ASK: clc clear all; close all; N=10; x=randint(1,N); k=1; for t=0.01:0.01:10 c(k)=sin(2*pi*t); k=k+1; end for j=1:1:N if x(j)==0 for i=(j-1)*100+1:1:j*100 y(i)=0; tr(i)=0; end end if x(j)==1 for i=(j-1)*100+1:1:j*100 y(i)=1; tr(i)=c(i); end end end for i=1:1:1000 re(i)=tr(i)*c(i); end for j=1:1:N d=0; 81

for i=(j-1)*100+1:1:j*100 d=d+re(i) end if d>0.5 det(j)=1; else det(j)=0; end end for j=1:1:N if det(j)==0 for i=(j-1)*100+1:1:j*100 det(i)=0; end end if x(j)==1 for i=(j-1)*100+1:1:j*100 det(i)=1; end end end subplot(5,1,1); plot(y); title('message Signal'); subplot(5,1,2); plot(c); title('Carrier Signal'); subplot(5,1,3); plot(tr); title('Transmitted Signal'); subplot(5,1,4); plot(re); title('Received Signal'); subplot(5,1,5); plot(det); title('Detected Signal');

FSK 82

clc clear all close all N=10; x=randint(1,N); k=1; for t=0.01:0.01:10 c1(k)=sin(2*pi*t); c2(k)=sin(4*pi*t); k=k+1; end for j=1:1:N; if x(j)==0 for i=(j-1)*100+1:1:j*100 y(i)=0; tr(i)=c2(i); end end if x(j)==1 for i=(j-1)*100+1:1:j*100 y(i)=1; tr(i)=c1(i); end end end for i=1:1:1000 re(i)=tr(i)*c1(i)*c2(i); end for j=1:1:N d=0; for i=(j-1)*100+1:1:j*100 d=d+re(i); end if d>0.5 det(j)=1; else det(j)=0; end 83

end for j=1:1:N if det(j)==0 for i=(j-1)*100+1:1:j*100 det(i)=0; end end if x(j)==1 for i=(j-1)*100+1:1:j*100 det(i)=1; end end end subplot(6,1,1); plot(y); title('message signal'); subplot(6,1,2); plot(c1); title('Carrier Signal-1'); subplot(6,1,3); plot(c2); title('Carrier Signal-2'); subplot(6,1,4); plot(tr); title('Transmitted Signal'); subplot(6,1,5); plot(re); title('Received Signal'); subplot(6,1,6); plot(det); title('Detected Signal');

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PSK clc clear all; close all; N=10;%No.of Data x=randint(1,N); k=1; for t=0.01:0.01:10 c(k)=2*sin(2*pi*t); k=k+1; end for j=1:1:N if x(j)==0 for i=(((j-1)*100)+1):1:(j*100) y(i)=0; tr(i)=-c(i); end else for i=(((j-1)*100)+1):1:(j*100) y(i)=1; tr(i)=c(i); end end end for i=1:1:1000 re(i)=tr(i)*c(i); end for j=1:1:N d=0; for i=(((j-1)*100)+1):1:(j*100) d=d+re(i) end if d>=0 det(j)=1; else det(j)=0; end end for j=1:1:N 85

if det(j)==0 for i=(((j-1)*100)+1):1:(j*100) det(i)=0; end end if x(j)==1 for i=(((j-1)*100)+1):1:(j*100) det(i)=1; end end end subplot(5,1,1); plot(y); title('Message Signal'); subplot(5,1,2); plot(c); title('Carrier Signal'); subplot(5,1,3); plot(tr); title('Transmitted Signal'); subplot(5,1,4); plot(re); title('Received Signal'); subplot(5,1,5); plot(det); title('Detected Signal');

86

QPSK clc clear all; close all; N=20; X=randint(1,N); L=100; l=(N/2*L*0.01)-0.01 i=1; for t=0:0.01:1 I(i)=cos(2*pi*t); i=i+1; end i=1; for t=0:0.01:1 Q(i)=sin(2*pi*t); i=i+1; end for i=1:N/2 if X((i-1)*2+1)==1 for j=((i-1)*L+1):(i*L) y(j)=1; QMI(j)=y(j)*I(j); end else for j=((i-1)*L+1):(i*L) y(j)=-1; QMI(j)=y(j)*I(j); end end k=((i-1)*2)+2; if X(k)==1 for j=((i-1)*L+1):(i*L) y(j)=1; QMQ(j)=y(j)*Q(j); end else for j=((i-1)*L+1):(i*L) y(j)=-1; QMQ(j)=y(j)*Q(j); 87

end end end for i=1:(N/2*L) QP(i)=QMI(i)+QMQ(i); end for i=1:(N/2*L) re1(i)=QP(i)*I(i); reQ(i)=QP(i)*Q(i); end k=1; for i=1:N/2 rI=0; rQ=0; for j=((i-1)*L+1):(i*L) rI=rI+re(j); rQ=rQ+reQ(j); end if rI>=0 real(i)=1; else real(i)=0; end if rQ>=0 imag(i)=1; else imag(i)=0; end det(k)=real(i); det(k+1)=imag(i); k=k+2; end

88

RESULT: Thus the ASK,PSK,QPSK and FSK was designed using MATLAB.

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