Digital Communication MCQ Questions & Answers | ECE

A signal x(t) = 100cos(24π × 10³)t is ideally sampled with a sampling period of 50 psec and then passed through an ideal lowpass filter with cutoff frequency of 15 kHz. Which of the following frequencies is/are present at the filter output?

In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval t₁ ≤ t ≤ t₂. This indicates that during this interval

A BPSK scheme operating over an AWGN channel with noise power spectral density of $$\frac{{{N_0}}}{2},$$  uses equiprobable signals
$${s_1}\left( t \right) = \sqrt {\frac{{2E}}{T}} \sin \left( {{\omega _c}t} \right)$$     and $${s_2}\left( t \right) = \sqrt {\frac{{2E}}{T}} \sin \left( {{\omega _c}t} \right)$$
over the symbol internal (0, T). If the local oscillator in a coherent receiver is ahead in phase by 45° with respect to the received signal, the probability of error in the resulting system is

Consider a sample signal
\[y\left( t \right) = 5 \times {10^{ - 6}}x\left( t \right)\sum\nolimits_{ - \infty }^{ + \infty } {\delta \left( {t - n{T_s}} \right)} \]
where x(t) = 10cos(8π × 10³)t and T_s =100 μsec. When y(t) is passed through an ideal lowpass filter with a cutoff frequency of 5 kHz, the output of the filter is

The Nyquist sampling frequency (in Hz) of a signal given by 6 × 10⁴sinC³(400t) ∗ 10⁶sinC³(100t) is

In a PCM system, if the code word length is increased from 6 to 8 bits, the signal to quantization noise ratio improves by the factor

Three analog signals, having bandwidths 1200 Hz, 600 Hz and 600 Hz, are sampled at their respective Nyquist rates, encoded with 12-bit words, and time division multiplexed. The bit rate for the multiplexed signal is

The peak-to-peak input to an 8-bit PCM coder is 2 Volts. The signal power-to-quantization noise power ratio (in dB) for an input of 0.5cos(ω_mt) is

The Nyquist sampling rate for the signal $$s\left( t \right) = \frac{{\sin \left( {500\pi t} \right)}}{{\pi t}} \times \frac{{\sin \left( {700\pi t} \right)}}{{\pi t}}$$      is given by

The bit rate of digital communication system is R kbits/s. The modulation used is 32-QAM. The minimum bandwidth required for |S| free transmission is