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# One Shot Marathon Series Test - Communication Systems

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Question 1

Consider an 8-PSK system ope with an information bit rate 24 kbps. Bandwidth efficiency of the system (in bits per cycle) is _____

Question 2

A carrier is AM modulated by a combination of two sinusoidal modulating signals of different frequencies with individual modulation indices 0.3 and 0.4. The power in the sidebands as percentage of the total power of the modulating signal is:

Question 3

An AM signal with full carrier is generated using a carrier signal 15cos (6π × 105 t) and message signal . Find the maximum value of discharging time constant of envelope detector required to demodulate AM signal without diagonal chipping distortion if the AM signal is 50% modulated.

Question 4

Consider a signal s(t) given as

If N0 = 4 × 10–11 W/Hz then find the signal to noise ratio of output of the matched filter.

Question 5

The input to the quantizer is a random variable ‘X’ with probability density function as shown in figure below. The quantizer characteristics are shown in figure below. The output of quantizer is a random variable ‘Y’.

Find the probability of quantization level Y = – 3.

Question 6

The capacity of AWGN channel with a bandwidth of 1MHz and signal to noise ratio of 40dB is ____ Mbps. [up to 2-decimal point]

Question 7

Suppose that binary PSK is used for transmitting information over an AWGN with power spectral density of N0/2 = 10–10W/Hz. The transmitted signal energy is Eb = A2T/2, where T is the bit interval and A is the signal amplitude. Determine the signal amplitude in mV required to achieve an error probability of 10–6, if the data rate is 10 kbps, given that Q(x) = 10–6 for x = 4.75 .

Question 8

Power spectral density (PSD) of a random process X(t) is given as,

Find the ratio of and i.e., where, E represents expectation.

Question 9

The power received by an antenna system is described by an exponential random variable X. the pdf of X is

Where A is the average amount of received power. The probability that the received power is larger than the power received on the average is _______.

Question 10Multiple Correct Options

A two level waveform is made analog because of the effect of additive Gaussian noise as X : N(1, 1).

A decoder samples the analog waveform x(t) at t0 and decodes according to the following rule.

Which of the following is/are correct for the above conditions?

Question 11

A data stream of 500 Mbps is to be transmitted through a wireless channel using 32–PSK technique. Find the minimum bandwidth requirement of wireless channel.

Question 12

Which of the following is false regarding the white noise.

Question 13

The message signal m(t) is given to both frequency and phase modulator. Find such that maximum frequency deviation of resultant PM and FM signals are same.

Question 14

An FM signal has a carrier frequency of 110 MHz and upper frequency of 110.009 MHz of modulated signal, the carriers swing is

Question 15

In amplitude modulation, the modulation envelop has a peak value which is double the unmodulation carrier value. What is the value of the modulation index?

Question 16

The channel capacity under the Gaussian noise environment for a discrete memory less channel with a bandwidth of 8 MHz and SNR of 63 is ____ Mbps

Question 17

An analog signal is quantized and transmitted using a PCM system. The maximum allowable quantization error in sample amplitudes 0.2% of peak to peak value of the message signal. The minimum number of bits required to encode each sample is ______

Question 18

An AM transmitter is to transmit a message signal having a bandwidth of 20kHz and an average power of 1W over a transmission channel charcterized by an additive white noise of 2-sided PSD of 0.5´ 10-15 W/Hz and a total transmission loss of 100dB. If the amplitude sensitivity is 1 and demodulated signal has SNR of 104, then the average transmitted power is _______in kW.

Question 19

A binary source generates symbols which are transmitted over a noisy channel. The probability of transmitting the both symbols is equal.Input to the threshold detector is The probability density function of the noise is shown below.

If the detection threshold is zero, then the probability of error (correct to two decimal places) is ____________.

Question 20

A binary PAM system uses an envelope rectangular pulse of duration Tb and amplitude ± A to transmit digital information at a rate Rb = 104 bps. If PSD of two-sided AWGN is 5 × 10–2 W/Hz (If Q(x) = 10–7 for x = 4.5), the value A that is required to achieve Pe = 10–7 is ______________

Question 21

12 Band-pass message signals are to be frequency multiplexed over a band-pass channel of bandwidth B, with each message signal having a bandwidth of 2 kHz. A guard band of 200 Hz is needed and no guard band is provided at the edges of overall channel, the minimum Band-pass bandwidth B (in kHz) needed is

Question 22

The voice signal in delta modulator is sampled at a rate 20.000 samples/sec. The normalized quantization noise power at the receiver output will be ______W.

Considering step size D such slope overload error will not occur.

Question 23

A 4th order device has the input-output relation y(t) = x4(t), where x(t) and y(t) are the input and output signals.

This device is fed with an input signal having bandwidth of 10 kHz with maximum frequency deviation kept less than 50 kHz. The bandwidth (in kHz) of the signal obtained at output of this device is

Question 24Multiple Correct Options

If X be a Bernoulli random variable with P[X = 0] = p and P[X = 1] = q. Probability density function (PDF) of X can be represented as fX(x) = pδ(x) + qδ(x – 1), another R.V. Y is defined as Y = X – 1. Considering the above conditions which of the following is/are correct?

Question 25Multiple Correct Options

A delta modulator is designed to operate on speech signals limited to 3 .4 kHz. The sampling rate is 8 times the Nyquist rate of the speech signal. The step size is 100 mV. The modulator is tested with a 1 kHz sinusoidal test signal. Which of the following is/are correct?
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