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# 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