PULSE WIDTH MODULATIONA modulation technique in which pulse of the carrier signal is changed in accordance with the amplitude comparison of message signal with carrier signal. Code ExplanationA message signal of particular frequency is defined then carrier signal of the form sawtooth is defined. Now desired result is obtained by comparing the amplitudes of message and carrier signals i.e if message signal is less than carrier signal pulse of output signal is zero otherwise pulse of the output signal is one. Matlab CodefrequencyMessage=50;
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Frequency Shift Keying Code ExplanationIn frequency shift keying the amplitude of the resultant signal is varied in accordance with the input bit sequence that we have defined. If the bit sequence is 0 the resultant signal is an analog signal of a defined frequency 20 for a defined range of time. If the bit sequence is 1 the resultant signal is an analog signal of a defined frequency 50 for a defined range of time. Matlab CodebitStream=[0 1 0 1 0 0];%defining a bit stream Amplitude Shift KeyingIn amplitude shift keying the amplitude of the resultant signal is varied in accordance with the amplitude of the input bit sequence that we have defined. If the bit sequence is 0 the amplitude of the resultant signal is zero otherwise the resultant signal is an analog signal of a defined frequency for a defined range of time. Matlab CodebitStream=[0 1 0 1 0 0];%defining a bit stream Under Sampling?Now decreasing the sampling rate of already sampled signal is called the process of under sampling (down sampling). In some applications we require under sampling. Two different methods are used for this kind under sampling (down sampling). Following code and output shows the concept explained. Matlab Codef_origional=60; Over SamplingNow increasing the sampling rate of already sampled signal is called the process of up sampling. In some applications we require upsampling. Two different methods are used for this kind over sampling (upsampling). Following code and output shows the concept explained. Matlab Codef_origional=60; Sampling ProcessWhen sampling process is done by using Nyquist criteria to avoid aliasing i.e the sampling frequency should be two times the frequency of the origional signal, the this is called Nyquist Sampling. Following code and its output shows the concept explained Matlab Codetime=-.05:.001:.05; Bipolar Coding Scheme?Bipolar coding scheme is a type of line coding (a technique of converting digital data to digital signals). In bipolar coding scheme a ‘0’ bit represents a ‘0’ voltage level and a ‘1’ bit represents an alternative voltage level i.e if previously the voltage level was +1, now it would be -1 and if previously it was -1, now it would be +1. Matlab Codex=[1 0 1 1 0 1]; Polar Coding Scheme?Polar coding scheme is a type of line coding (a technique of converting digital data to digital signals). In polar coding scheme a ‘0’ bit representation could be a positive ‘1’ voltage level and a ‘1’ bit representation could be a negative ‘1’ voltage level. Matlab Codex=[1 0 1 1 0 1]; ExplanationUni Polar Coding scheme is a type of line coding (a technique of converting digital data to digital signals). In uni polar coding scheme simply a ‘0’ bit represent a zero voltage level and ‘1’ bit represents a positive 1 voltage level. Matlab Code:x=[1 0 1 1 0 1]; |
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