3.4_OOK systems – ASK, FSK, PSK, BPSK, QPSK, applications of Data communication.pptx

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1. SRI KRISHNA COLLEGE OF ENGINEERING AND TECHNOLOGY Kuniamuthur, Coimbatore, Tamilnadu, India An Autonomous Institution, Affiliated to Anna University, Accredited by NAAC with “A” Grade & Accredited by NBA (CSE, ECE, IT, MECH ,EEE, CIVIL& MCT) 20EC611 - COMMUNICATION ENGINEERING Module 3: Digital Communication 3.4 - OOK systems – ASK, FSK, PSK, BPSK, QPSK, applications of Data communication

2. Digital Modulation Techniques Digital Modulation techniques converting digital data into analog modulated signal. Digital Modulation  provides, More information capacity High data security Quicker system availability with great quality communication Hence , digital modulation techniques have a greater demand, for their capacity to convey larger amounts of data than analog modulation techniques.

3. Digital Modulation Techniques Types of digital modulation techniques are, 1. ASK – Amplitude Shift Keying [ On-off keying system ( OOK ) ] 2. FSK – Frequency Shift Keying 3. PSK – Phase Shift Keying Binary Phase Shift Keying  (BPSK) Quadrature Phase Shift Keying  (QPSK) Differential Phase Shift Keying  (DPSK)

4. Amplitude Shift Keying The block diagram of the Amplitude shift keying is,

5. Amplitude Shift Keying In ASK, carrier signal voltage varies according to the input binary signal amplitude. In ASK, the input binary signal is multiplied with the carrier signal along with its time intervals. Between the first time interval of input binary signal multiplied with the first time interval of carrier signal voltage and the same process continues for all time intervals. When the input signal having logic 1, it is multiplied with the carrier signal which is generating the signal. When the input signal having logic 0, during these intervals when the carrier signal multiples with it, zero output will come. 

6. Amplitude Shift Keying

7. Amplitude Shift Keying ASK Modulator The ASK modulator block diagram comprises of the carrier signal generator, the binary sequence from the message signal and the band-limited filter. Following is the block diagram of the ASK Modulator.

8. Amplitude Shift Keying The carrier generator, sends a continuous high-frequency carrier. The binary sequence from the message signal makes the unipolar input to be either High or Low. The high signal closes the switch, allowing a carrier wave. Hence, the output will be the carrier signal at high input. When there is low input, the switch opens, allowing no voltage to appear. Hence, the output will be low. The band-limiting filter, shapes the pulse depending upon the amplitude and phase characteristics of the band-limiting filter or the pulse-shaping filter.

9. Amplitude Shift Keying ASK Demodulation Demodulation is the process of reconstructing the original signal at the receiver level. ASK demodulation can be done in two ways. They are, Coherent detection (Synchronous demodulation) Noncoherent Detection (Asynchronous demodulation) The clock frequency at the transmitter when matches with the clock frequency at the receiver, it is known as a  Synchronous method , as the frequency gets synchronized. Otherwise, it is known as  Asynchronous .

10. Amplitude Shift Keying Coherent ASK Detection In this demodulation process, the carrier signal which is used at the receiver stage is in the same phase with the carrier signal which was used at the transmitter stage. It means the carrier signal at transmitter and receiver stages are the same values. This type of demodulation is called Synchronous ASK detection or coherent ASK detection.

11. Amplitude Shift Keying The receiver receives the ASK modulated waveform from the channel but here this modulated waveform is effected with noise signal because it is forwarded from the free space channel. So this, noise can be eliminated after the multiplier stage by the help of a low pass filter. Then it is forwarded from the sample and hold circuit for converting it into discrete signal form. Then at each interval, the discrete signal voltage is compared with the reference voltage ( Vref ) to reconstruct the original binary signal.

12. Amplitude Shift Keying Non-coherent ASK Detection In this, the only difference is the carrier signal which is using at the transmitter side and receiver side are not in the same phase with each other. By this reason, this detection is called as Non-coherent ASK detection (Asynchronous ASK detection). The ASK modulated input signal is given to the Square law detector. A square law detector is one whose output voltage is proportional to the square of the amplitude modulated input voltage. The low pass filter minimizes the higher frequencies. The comparator and the voltage limiter help to get a clean digital output.

13. Amplitude Shift Keying Amplitude shift keying applications are, Low-frequency RF applications Home automation devices Industrial networks devices Wireless base stations Tire pressuring monitoring systems

14. Amplitude Shift Keying Advantages of amplitude shift Keying – It can be used to transmit digital data over optical fiber. The receiver and transmitter have a simple design which also makes it comparatively inexpensive. It uses lesser bandwidth as compared to FSK thus it offers high bandwidth efficiency. Disadvantages of amplitude shift Keying – It is susceptible to noise interference and entire transmissions could be lost due to this. It has lower power efficiency.

15. Frequency Shift Keying A digital modulation technique that allows data transmission by changing the frequency of the carrier wave according to the digital modulating signal is known as  frequency shift keying (FSK) . It is the most straightforward and efficient digital signal transmission scheme . The simplest form of FSK is Binary frequency shift keying (BFSK). Here, the carrier is modulated in such a way that high-frequency signal is achieved for high level i.e., 1 of binary data input. Similarly, the low-frequency signal is obtained in case of low level i.e., 0 of the message signal .

16. Frequency Shift Keying

17. Frequency Shift Keying FSK Modulator The figure below shows the generation of FSK modulated wave. The system consists of 2 oscillators that generate high and low-frequency signal separately. A binary message signal is provided to the transmitter circuitry. The carrier wave from the two oscillators and binary modulating signal operates the switch .

18. Frequency Shift Keying W hen the modulating signal bit is high i.e., 1, the switch gets closed forming a path for a high-frequency wave to get transmitted that is generated by oscillator 1. Thus a high-frequency signal is achieved in case of bit 1 of the message signal. When the input bit is level low i.e., 0, the switch now gets closed in a manner to form the path for the low-frequency carrier to get transmitted. This low-frequency carrier is generated by the oscillator 2. Hence , it is clear that a low-frequency signal is achieved in case of a low data bit of the modulating signal. However, in order to eliminate phase discontinuities of the signal at the output, an internal clock is provided to the oscillator. Thus, the high or low-frequency signal is selected according to the digital modulating signal. Thus, an FSK modulated wave is transmitted and achieved at the output.

19. Frequency Shift Keying FSK Demodulator There are different methods for demodulating a FSK wave. These methods are classified into synchronous detection   (coherent )  and  a synchronous detection (non-coherent ). Coherent detection The block diagram for the coherent detection of BFSK signal is,

20. Frequency Shift Keying I t consists of 2 separate mixers followed by the integrators that form the two correlators in the circuit. The output of this correlator is then fed to the decision device. This decision device generates the binary signal which is the original modulating signal. Here, a BFSK waveform is fed to the mixer along with the two separate carriers that are accurately synchronized with the carrier waves at the transmitting end. The output generated by the mixer is then fed to the integrator .

21. Frequency Shift Keying The output of the two separate integrators is then compared by the decision-making device. When the output of integrator 1 is more than that of the integrator 2 then the frequency of the carrier associated with correlator 1 generates the bit symbol. Assume, it to be a high-frequency carrier then a logic high is generated at the output. Similarly, when the output of the integrator 2 exceeds integrator 1 then the carrier frequency associated with correlator 2 generates symbol in favour of that frequency. Let us assume conversely that it is a low-frequency wave then symbol 0 is achieved at the output.

22. Frequency Shift Keying Non-coherent detection In non-coherent detection then no any synchronized carrier is required at the detector. The figure below shows the block diagram for non-coherent detection.

23. Frequency Shift Keying It consists of two separate Band pass filter that is tuned to two different frequencies. The output of this BPF is then fed to an envelope detector which generates two separate output according to the signal achieved from the BPF. A decision-making device then compares the output of the two envelope detector. When the output of detector 1 exceeds detector 2 then logic 1 is obtained and when the output of detector 2 is exceeds by detector 1 then logic 0 is obtained as the output. Thus the original bit stream is generated by the detector .

24. Frequency Shift Keying The main features of the FSK are: High noise immunity. digital radio transmission, in the cellular telephone system. Applications in modems for data transmission. Likelihood of error less than ASK modulation. Applications of frequency shift keying The technique is used in the high-frequency data transmission system. Extensively used in low-speed modems.

25. Frequency Shift Keying Advantages of frequency shift keying FSK provides  better noise immunity . The signal transmission through FSK is quite simple. It is suitable for  long-distance data transmission . Bit error rate performance is better than ASK. Disadvantages of frequency shift keying It utilizes more bandwidth as compared to ASK and PSK thus is not bandwidth efficient. Detection of the signal at the receiver is somewhat complex.

26. Phase Shift Keying A digital modulation technique that transmits data by varying the phase of the carrier wave in accordance with the digital modulating signal, is called Phase Shift Keying (PSK). It is classified into three types. They are Binary Phase Shift Keying (BPSK) Quadrature Phase Shift Keying (QPSK) Differential Phase Shift Keying (DPSK)

27. Binary Phase Shift Keying (BPSK) Principle of BPSK BPSK technique is the simplest among all the PSK techniques. In this, each signaling element is represented by a single data bit. Here , the carrier undergoes two phase reversal such as 0° and 180°. In phase shift keying the digital bit sequence is first converted to NRZ (Non return to Zero) bipolar signal which directly modulates the carrier wave . T his is also called as 2-phase PSK or Phase Reversal Keying. In this technique, the sine wave carrier takes two phase reversals such as 0° and 180 °.

28. Binary Phase Shift Keying (BPSK) Expression for BPSK Let us consider the carrier wave is given as, s(t ) = A cos (2π f c t ) The peak of the carrier wave is represented as A when the load resistance is assumed to be 1 ohm as standard, the power dissipated is given as, A change in phase by 180° is noticed with the corresponding change in the bit sequence. Assume the carrier for symbol 1 is given as,

29. Binary Phase Shift Keying (BPSK) Similarly, in the case of symbol 0, π represents the phase shift of 180° Since,   cos (ɸ + π) = – cos ɸ Thus, s 2 (t) can be written as, Hence , BPSK signal can be written as , b(t) will be +1 in case of transmission of binary 1 and b(t) will be -1 in case of transmission of binary 0.

30. Binary Phase Shift Keying (BPSK) BPSK modulation The figure below shows the block diagram for the generation of a BPSK signal.

31. Binary Phase Shift Keying (BPSK) T he system consists of NRZ encoder along with product modulator and carrier generator. The binary message signal is fed to the bipolar NRZ level encoder that converts the Binary data input into equivalent bipolar NRZ sequence m(t ). This bipolar NRZ signal is fed to the balanced modulator along with the carrier wave. Thus, the binary signal modulates the carrier wave that generates a phase shifted modulated signal termed as BPSK signal . Here, as we can see that, the figure shows phase reversal when the bit sequence gets changed either from 1 to 0 or from 0 to 1. When the bit sequence changes from 0 to 1 then we noticed a positive phase change whereas, when the bit sequence changes from 1 to 0 then a negative change of phase is noticed.

32. Binary Phase Shift Keying (BPSK) The BPSK generated waveform with the binary bit sequence and carrier wave.

33. Binary Phase Shift Keying (BPSK) BPSK Demodulation The block diagram for the coherent detection of BPSK signal is shown below:

34. Binary Phase Shift Keying (BPSK) Let us consider, the signal at the input of the receiver is, The phase shift ɸ is based on the time delay in between transmitter and receiver. The signal is then fed to a square law device that provides Here only the career of the signal is taken into consideration thus the amplitude is neglected. As we know,

35. Binary Phase Shift Keying (BPSK) Expanding the carrier as the above mathematical identity , dc level is showed by ½ This signal is then fed to the BPF. This BPF has a centre frequency of 2f c , eliminates the dc level hence, generates output as cos 2 (2π f c t + ɸ) This signal is then further fed to a frequency divider unit. As it is frequency divider by 2 thus generates a carrier with frequency f c .

36. Binary Phase Shift Keying (BPSK) This carrier is then multiplied with the input signal , This signal is then given to the integrator and bit synchronizer unit. The signal is integrated over the 1-bit period by the integrator by making use of bit synchronizer. It manages the bit duration. After a completed bit duration, synchronizer closes S 2  and the output of the integrator acts as input to the decision device. Further, processing continues when S 2  gets open and S 1  gets closed for some time, resetting the voltage of the integrator to 0. Then the next bit is integrated by the integrator and the cycle repeats. The decision device then generates the equivalent binary data, the actual message signal.

37. Quadrature Phase Shift Keying (QPSK) This is the phase shift keying technique, in which the sine wave carrier takes four phase reversals such as 0°, 90°, 180°, and 270°. The   QPSK  is a variation of BPSK, and it is also a Double Side Band Suppressed Carrier   DSBSC  modulation scheme, which sends two bits of digital information at a time, called as  bigits . Instead of the conversion of digital bits into a series of digital stream, it converts them into bit pairs. This decreases the data bit rate to half, which allows space for the other users.

38. Quadrature Phase Shift Keying (QPSK) QPSK Modulator The QPSK Modulator uses a bit-splitter, two multipliers with local oscillator, a 2-bit serial to parallel converter, and a summer circuit. Following is the block diagram for the same. At the modulator’s input, the message signal’s even bits (i.e., 2 nd  bit, 4 th  bit, 6 th  bit, etc.) and odd bits (i.e., 1st bit, 3 rd  bit, 5 th  bit, etc.) are separated by the bits splitter and are multiplied with the same carrier to generate odd BPSK (called as  PSK I ) and even BPSK (called as  PSK Q ). The  PSK Q  signal is phase shifted by 90° before being modulated.

39. Quadrature Phase Shift Keying (QPSK) The QPSK waveform for two-bits input is as follows, which shows the modulated result for different instances of binary inputs.

40. Quadrature Phase Shift Keying (QPSK) QPSK Demodulator The QPSK Demodulator uses two product demodulator circuits with local oscillator, two band pass filters, two integrator circuits, and a 2-bit parallel to serial converter. Following is the diagram for the same. The two product detectors at the input of demodulator simultaneously demodulate the two BPSK signals. The pair of bits are recovered here from the original data. These signals after processing, are passed to the parallel to serial converter.

41. Phase Shift Keying  (PSK ) Advantages of Phase shift keying It allows more efficient transmission of radio frequency signal. Better noise immunity is noticed in the case of BPSK technique. Less bandwidth is utilized by the BPSK signal in comparison to BFSK. Disadvantages of Phase shift keying Detection of a BPSK signal is quite complex. Phase discontinuity sometimes leads to variation in amplitude of the signal. Applications of Phase shift keying PSK modulation technique used in biometric operations, bluetooth connectivity, wireless local area networks and in telemetry operations.

42. DIGITAL DATA COMMUNICATION Advantages of Digital Communication The effect of distortion, noise, and interference is much less in digital signals as they are less affected. Digital circuits are more reliable. Digital circuits are easy to design and cheaper than analog circuits. The hardware implementation in digital circuits, is more flexible than analog. The occurrence of cross-talk is very rare in digital communication. The signal is un-altered as the pulse needs a high disturbance to alter its properties, which is very difficult. Signal processing functions such as encryption and compression are employed in digital circuits to maintain the secrecy of the information.

43. DIGITAL DATA COMMUNICATION Advantages of Digital Communication The probability of error occurrence is reduced by employing error detecting and error correcting codes. Spread spectrum technique is used to avoid signal jamming. Combining digital signals using Time Division Multiplexing  TDM is easier than combining analog signals using Frequency Division Multiplexing  FDM. The configuring process of digital signals is easier than analog signals. Digital signals can be saved and retrieved more conveniently than analog signals. Many of the digital circuits have almost common encoding techniques and hence similar devices can be used for a number of purposes. The capacity of the channel is effectively utilized by digital signals.

44. DIGITAL DATA COMMUNICATION Application of digital communication systems It is used in military application for secure communication and missile guidance. It is used in image processing for pattern recognition, robotic vision and image enhancement. It is used in digital signal processing. The digital communication systems used in telephony for text messaging. It is used in space communication where a spacecraft transmits signals to earth. It is used in video compression. It is used in speech processing. It is used in digital audio transmission. It is used in data compression.

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