BITS PILANI – K K BIRLA GOA CAMPUS
FIRST SEMESTER 2015-2016
EEE F311 COMMUNICATION SYSTEMS
Test – I (Closed Book)
TIME: 1 Hr
1.
DATE: 22-09-2015
Marks: 40, Wt: 20%
(a) What is the maximum signaling rate achievable through a noise-free line that acts as a lowpass filter with cut-off frequency W ?
(b) What is the maximum bit rate achievable in a line of limited Bandwidth W assuming the
line acts as a AWGN channel with a signal-to-noise ratio of 40 dB ?
What are (a) granular noise and (b) slope overload in delta modulation ?
Suppose that a white Gaussian noise 𝜔(𝑡) of zero mean and power spectral density 𝑁0/2 is applied
to an ideal low-pass filter of Bandwidth B and passband magnitude response of one. (a) Sketch the
power spectral density of the filter output (b) Sketch the auto-correlation function of the filter
output.
A waveform 𝑚(𝑡) has a Fourier transform 𝑀(𝑓) whose magnitude is shown in the Figure below.
Estimate the essential bandwidth of the signal if the essential bandwidth is to contain 90% of the
signal energy.
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5.
Sketch the magnitude spectrum of the signals at (b), (c), (d) and (e) in the circuit shown below.
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6.
In VSB modulation, the carrier frequency of a video signal is fc= 80 MHz. The baseband video signal
bandwidth is 4.5 MHz. The VSB shaping filter 𝐻𝑖 (𝑓) at the input is shown in the figure. Find the
output filter 𝐻𝑜 (𝑓) required for distortion-less reception.
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7.
A 100 MHz sinusoidal carrier is frequency modulated with a 3-KHz, 3-V peak sinusoid. If the
modulator has a sensitivity of 2 KHz/V, determine:
(a)
the frequency deviation, ∆𝑓
(b)
the deviation ratio, 𝛽
(c)
the approximate signal bandwidth using Carson’s rule
…. Continued.
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2.
3.
4.
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8.
A block diagram of an Armstrong system of generating an FM signal is shown in the figure below.
Find (a) the Oscillator frequency (fo ) at the mixer and (b) the order k of the second multiplier to
generate the final FM signal with specifications fc = 96 MHz and ∆𝑓 = 77 kHz.
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9.
Consider a signal g(t) whose magnitude spectrum is shown in the figure below. The signal has
frequency components between 80 kHz and 100 kHz.
(a) If sampled at Nyquist rate, sketch the spectrum of sampled signal.
(b) What type of filter is required to extract the original signal from the samples ? Mention the cutoff frequencies of the filter.
(c) If the samples are to be quantized with a uniform quantiser with 65,536 levels, what is the
minimum bandwidth required to transmit the binary encoded samples ?
(d) If the original signal g(t) is sampled at 70,000 samples per second (instead of Nyquist rate),
sketch the spectrum of the samples. Can the original signal be extracted from these samples by
using a filter ? If yes, which type of filter will enable this ? Identify the cut-off frequencies. If not
possible, give reasons.
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10. A TDM-PCM system has to accommodate four 300 bits/s (synchronous) digital inputs and one
analog input that has a bandwidth of 500 Hz. Assume that the analog samples will be encoded into
4-bit PCM words. (a) Design a suitable commutator for multiplexing these sources and (b) Find the
minimum bandwidth required to transmit the multiplexed signal.
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