ASK,FSK and M-PSK using Matlab


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ASK,FSK and M-PSK using Matlab

  1. 1. ABSTRACT Three types of digital modulation techniques, namely Amplitude shift keying (ASK), Frequency shift keying (FSK) and phase shift keying (FSK) are observed and investigated in this experiment. ASK,FSK and M-PSK modulated signals are produced using MATLAB software and Simulink. The coding for MATLAB are troubleshoot from the questions given to produce modulated signals. For ASK, FSK and PSK amplitude, frequency and phase of carrier signal is varied to represent binary 1 and 0 respectively.
  2. 2. INTRODUCTION Modulation is one of a technique of converting digital data to an analog signal. Analog signal takes a discrete number of signal level. Discrete analog signals operate with a discrete number of levels like digital signals. Discrete modulation technique begins with simple modulation technique(shift keying) and ends with more complex techniques used for systems (quadrature amplitude modulation). The simplest modulation technique is amplitude shift keying. ASK imparts to a sinusoid two or more discrete amplitude level. By modulating a high-frequency sinusoid or carrier, a spectrum of a signal can be shifted to a higher frequency range. s(t)=A cos 2π𝑓𝑐 for binary =1 and s(t)=0 for binary=0. A data value 1 (higher amplitude) and a data value 0 (lower amplitude) represented by two different amplitudes of a signal as shown in figure 1. During each period, amplitude of the signal is constant. The amplitude levels can also be represented in 2 bits (Figure 2). Every time amplitude changes, 2 bits are transmitted. It is more efficient than one that require two signal changes every bit. ASK is susceptible to sudden noise impulses. The signal will experience significant increase in amplitude. Hence, ASK is least efficient in systems that require high transmission rate.  A cos(2f ct ), binary 1 s(t )   binary 0 0,
  3. 3. Frequency shift keying (FSK) uses two different frequency ranges to represent data values of 0 and 1 as in figure. The lower frequency might represent a 1 and the higher frequency might represent a 0. The frequency of signal is controlled by baseband signal. FSK does not affected by noise impulses. However, it is subjected to intermodulation distortion which will create new frequencies when the frequencies of two or more signals mix together.  A cos(2f1t ), binary 1 s (t )    A cos(2f 2t ), binary 0 Phase shift keying is the third modulation technique. It represents 0s and 1s by different changes in the phase of a waveform. A 0 cannot be a phase change , while a 1 can be phase change of 180 degrees. It does not affected by amplitude changes or intermodulation distortion. PSK can be used at a high frequency. PSK is accurate that the signal transmitter can increase efficiency by introducing multiple phase shift angle.
  4. 4. binary 1  A cos(2f c t ), s (t )    A cos(2f c t   ), binary 0 binary 1  A cos(2f c t ),    A cos(2f c t ), binary 0  Ad (t ) cos(2f c t ), d (t )  1 In MPSK, the data bits to be modulated is grouped into symbols 𝑙𝑜𝑔2 M bits and take m possible values 0,1,..,m-1. The modulator shifts the carrier to one m possible values of the input symbol during each interval.
  5. 5. Results TASK 1 Matlab program for ASK modulated signal before troubleshoot %b is the input binary bit stream %f is the frequency of the carrier n= length(b); %determine the length of bit stream t=0:0.01: n-0.01; %time axis for i=1:n bw(((i-1)*100+1:i*100)=b(i); %loop end carrier= cos(2*pi*f*t); %carrier signal modulated = bw.*carrier; %modulated signal
  6. 6. Matlab program for ASK modulated signal after troubleshooting:
  7. 7. Enter binary bit stream=[1 -1 1 -1 1] Enter carrier frequency=0.8 Hz Enter binary bit stream= [1 -1 1 -1 1] Enter carrier frequency=10Hz
  8. 8. Discussions: In ASK modulation, the amplitude of carrier is varied to create signal elements. In this lab, the input of binary bit stream is entered by users. In this case the input is [1 -1 1 -1]. This is because as in the question wants the graph to be plotted for amplitude of binary code A=1V and A=-1V. In ASK, the amplitude of carrier assumes one of the two amplitudes dependent on the logic stream of the input bit stream. When the message signal is 1 or high, the modulated signal will show and high frequency, but when message signal is 0 or low, the modulated signal will still remain at zero.Next, when troubleshooting, a change is made that the value of x is added so that, x = 1:1:(n+1)*100. This is to complete the formula for binary bit stream in the y-axis which is incomplete in this coding. Hence the formula declared in the loop is bw(x(i*100:(i+1)*100)) = b(i). So it will loop to get the signal value for ASK. The output graphs show that the first waveform is a message which initiates the second waveform is an ASK signal. The third waveform is modulated signal. In this lab, two values carrier frequencies are entered to compare the outputs waveforms of different values. The first carrier frequency entered is 0.9 Hz. Digital signal is transmitted, modulates a carrier signal and varies its amplitude in such a way as to make it coincide with the logical 1 and the logical 0, two different amplitudes of the carrier. When the carrier frequency is change to a bigger value, which is 10 Hz. The value of carrier frequency is higher than the amplitude of modulating signal. The modulation index, m>1. Hence, overmodulation occur which in turns causing distortion. Both frequency and phase remains constant while amplitude changes. The bandwidth required is two times the highest frequency content including any harmonics for binary pulse modulating signals. Conclusions ASK is generated using matlab program. The most important characteristic of ASK signal is that the two binary values, 1 and 0 are represented by two different amplitudes of the carrier frequency. When changes from 1 to 0, the amplitude of modulated frequency also changes. In matlab, if the input carrier frequency is high, modulation index,m will be greater than 1. Then distortion occurs.The source signals are generally referred to as baseband signals. It sends analogue and digital signals directly over a medium. The low-frequency signal is often frequency-translated to a higher frequency range for efficient transmission. . The three basic ways of modulating a sine wave carrier for binary digital modulation, are called binary amplitude-shift keying (BASK), binary frequency-shift keying (BFSK) and binary phaseshift keying (BPSK). Modulation also leads to the possibility of frequency multiplexing. ASK is more susceptible to noise and inefficient to use for modulation technique. Instead, it is used typically used only up to 1200 bps for voice-grade lines.The ASK technique is used to transmit digital data over
  9. 9. optical fiber, where one signal element is represented by a light pulse while the other signal element is represented by the absence of light. TASK 2 Frequency shift keying (FSK)
  10. 10. Enter binary bit stream to [1 0 1 0 1] Enter carrier frequency = 0.8 Hz Enter binary bit stream [1 0 1 0 1] Enter carrier frequency=10 Hz
  11. 11. Discussions: In FSK, frequency of carrier signal is varied to represent binary signal 1 or 0. A frequency shift keyed transmitter has its frequency shifted by the message. In this lab, the input of binary bit stream is entered by users. In this case the input is [1 0 1 0 1]. In FSK, two frequencies are transmitted which is one corresponding to binary 1(mark) and another one is 0 (space). In this lab, two values of carrier frequencies are entered. Frequency is shifted while amplitude and phase remains constant in each bit interval. The first value is 0.8Hz. The results of modulated signal shows that the frequency is shifted when data is transfer from binary signal 1 to 0. There is difference in frequency in the modulated signal when going from 1 to 0.The two possible carriers with different frequencies that are coupled to logical binary values 1 and 0 .When the frequency of carrier entered is 10Hz, it can be seen that there is distortion or noise presence in carrier signal 1 and carrier signal 2. The modulation index, m>1. Hence, overmodulation occur which in turns causing distortion. However it still can be seen that at modulated signal there is difference in frequency in the modulated signal when going from 1 to 0. Conclusions: Matlab code obtained for ASK modulated signal can be altered to produce Matlab code for FSK signal. Higgher frequency of carrier will produce distortion and noise, however the FSK modulated signal is still can be seen when it is shifted from 1 to 0. The most common form of FSK is binary FSK (BFSK), in which the two binary values are represented by two different frequencies near the carrier frequency. There are three common form of FSK, that is Binary Frequency Shift Keying, BFSK, Multiple Frequency Shift Keying, BFSK. BFSK literally implies using a pair of discrete frequencies to transmit binary (0s and 1s) information. With this scheme, the "1" is called the mark frequency and the "0" is called the space frequency. BFSK is less susceptible to error than ASK. On voice-grade lines, it is typically used up to 1200 bps. It is also commonly used for high-frequency (3 to 30 MHz) radio transmission, also be used at even higher frequencies on local area networks that use coaxial cable.
  12. 12. TASK 3 M-PSK Simulink Block Diagram: Graph Results: i)Noise ii)
  13. 13. Results After Troubleshooting: Changes that have been made i)Change Bernoulli Binary Generator to Random Integer Generator Change sample time to 1e-7 ii)AWGN Channel Change symbol period to Symbol period=log2(M)*1e-7
  14. 14. iii)Error Rate Calculation Change maximum number of symbols=1e8 Simulink block diagram:
  15. 15. Graph Results: Discussions PSK is a modulation where there is only one carrier so that two numerical values 1 and 0 are coupled to two different phases of the same frequency 0° and 180° respectively. In this lab, the Simulink is triggered to produce a 8-PSK modulator. When troubleshooting, the Bernoulli Binary Generator is changed to Random Integer Generator. Also the value of sample time is changed to 1e-7. The reasons Random Integer Generator is used instead of Bernoulli Binary Generator is because it generates random integers in the range [0, M-1], where M is the M-ary number defined in the dialog box. As in this lab, 8ary is need to be generated. Meanwhile, Bernoulli Binary Generator only can generate m binary numbers using a Bernoulli distribution. That is why before we troubleshoot, the results is only 2-PSK instead of 8-PSK. This is generally because it could not produce other than m-binary numbers. Next the sample time is changed to 1e-7 because a smaller sample time can produce a more precise result. This is also the same as in AWGN Channel and Error Rate Calculation where the sample time/ maximum number of symbols is changed. The output at discrete time plot shows a 8 plotted M-PSK. This plot refers as 8 phase. The phase start with 0 degree, and it changes every 45 degree. M-ary number refers to the 8-PSK. In PSK, the phase of the carrier is shifted to represent data. It use two phase (0 and 180) to represent the two binary digits. When M=8, so the output of binary bit is equal to 3 bit. This 3 bit encoded, formatting titbits and producing 3 different output phase. The data next to the scatter plot is Gaussian Noise that presents to process zero mean and single-side power density spectral.
  16. 16. Conclusions: Using Simulink can create a Phase Shift Keying modulation. In PSK, the phase of the carrier signal is shifted to represent data. M-PSK where M=8 is popular on straight-forward extension of QPSK. 8=2^3. Hence,3 bits fit into every symbol. If M>8, the distance between constellation point is small and Eb/No ratio has to become larger to attain target BER. The mapping from the data bits arbitrary but generally some data bits are used. In M-PSK constellation, every constellation point is always has two neighbors with equal probabilities of an error to either neighbor. BER is for every symbol error there is one bit error assumed but there are 4 bits per symbol. In PSK, the demodulator must be able to determine the phase of received sinusoid with respect to some reference phase. PSK is less susceptible to errors than ASK, while it requires the same bandwidths as ASK. Besides, it is more efficient to use bandwidth which is a high data rate. One of the disadvantages of PSK includes it is more complex signal detection or recovery process than ASK and FSK. References: 1) B.P. Lathi : Modern Digital and Analog Communication, Oxford University Press, New York, 1998 2) Wayne Tomasi : Electronics Communications System, Prentice Hall, New Jersey, 2004 3) Blake: Electronics Communications System 2nd Edition, CENGAGE Learning, Delmar, 2002 4) N Vlajic: , ASK,FSK,PSK,QAM, Fall 2010. 5) Harjot Kaur: Comparative Performance Analysis of M-ary PSK Modulation Schemes using Simulink, September 2011