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From: vivekananda reddy on 12 Nov 2009 15:53
Q.1. A Binary FSK transmission is given by:

S(t)={Acos(2.pi.f.t),binary1}
{Acos(2.pi.f.t),binary0}

The transmission bandwidth is 100 kHz which spans from 200 to 300 kHz.

(a) Develop a MATLAB program to generate the transmitted waveform. Plot the output waveform showing clearly waveform transitions of the bits and modulated signal. Assume random 100 bits of input data.
(b) Plot power spectrum of the waveform for 163840 samples using a suitable window function. On x-axis plot the frequency in kHz/MHz. On y-axis the power should be in dB. Why do we use 163840 samples? Can we use some other number of samples?

Q.2. A QPSK transmission is given by:
S(t)=1/1.414I(t)cos(2pift)-1/1.415Q(t)sin(2pift)
where s(t) is the modulated waveform, I(t) and Q(t) are the in-phase and quadrature-phase bits. Assuming a suitable bit rate and carrier oscillator frequency:

(a) Develop a MATLAB program to generate the transmitted waveform. Plot the output waveform showing clearly the waveform transitions for the bits and modulated signal. Assume random 100 bits of input data.
(b) Plot power spectrum of the waveform for 163840 samples using a suitable window function. On x-axis plot the frequency in kHz/MHz. On y-axis the power should be in dB.

Q.3. Develop a MATLAB program for a Direct-Sequence (DS) Spread Spectrum (SS) BPSK Modulator. Assume a suitable bit rate and a chip up-sample rate of 4?. Use Maximum Length sequence PN Code. Plot the power spectrum before and after spreading, using a suitable window function. On x-axis plot the frequency in kHz/MHz. On y-axis power should be in dB. Comment on the two power spectrums plotted.


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