GATE ECE

Digital Communication Systems

Communications

(Past Years Questions)

Marks 1

More
In a digital communication system, the overall pulse shape p(t) at the receiver before the sampler has the Fourier trans...
GATE ECE 2017 Set 1
Which one of the following statements about differential pulse code modulation (DPCM) is true?
GATE ECE 2017 Set 1
A speech signal is sampled at 8 kHz and encoded into PCM format using 8 bits/sample. The PCM data is transmitted through...
GATE ECE 2016 Set 2
Consider binary data transmission at a rate of 56 kbps using baseband binary pulse amplitude modulation (PAM) tha...
GATE ECE 2016 Set 1
The modulation scheme commonly used for transmission from GSM mobile terminals is
GATE ECE 2015 Set 3
In a code - division multiple access (CDMA) system with N = 8 chips, the maximum number of users who can be assign...
GATE ECE 2014 Set 1
The bit rate of a digital communication system is R kbits/s. The modulation used is 32-QAM. The minimum bandwidth requir...
GATE ECE 2013
In a PCM system, if the code word length is increased from 6 to 8 bits, the signal to quantization noise ratio improves ...
GATE ECE 2004
In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval t1 $$ \le $$ ...
GATE ECE 2004
For a bit-rate of 8 kbps, the best possible values of the transmitted frequencies in a coherent binary FSK system are ...
GATE ECE 2002
A band limited signal is sampled at the Nyquist rate. The signal can be recovered by passing the samples through
GATE ECE 2001
In a PCM system with uniform quantization, increasing the number of bits from 8 to 9 will reduce the quantization noise ...
GATE ECE 1998
Quadrature multiplexing is
GATE ECE 1998
Compression in PCM refers to relative compression of
GATE ECE 1998
For a given data rate, the bandwidth Bp of a BPSK signal and the band width B0 of the OOK signal are related as ...
GATE ECE 1998
The line code that has zero dc component for pulse transmission of random binary data is
GATE ECE 1997
A deterministic signal has the power spectrum given in figure. The minimum sampling rate needed to completely represent ...
GATE ECE 1997
If the number of bits per sample in a PCM system is increased from n to n+1, the improvement in signal-to-quanti...
GATE ECE 1995
The signal to quantization noise ratio in an n-bit PCM system
GATE ECE 1995
The bandwidth required for the transmission of a PCM signal increases by a factor of ________ when the number of quanti...
GATE ECE 1994

Marks 2

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In binary frequency shift keying (FSK), the given signal wave forms are $$\,{u_o}(t) = 5\,\cos \,(20000\,\pi \,t);\,0 ...
GATE ECE 2017 Set 1
The bit error probability of a memoryless binary symmetric channel is $${10^{ - 5}}$$. If $${10^{ - 5}}$$ bits are sent ...
GATE ECE 2016 Set 3
An ideal band-pass channel 500Hz-2000 Hz is deployed for communication. A modem is designed to transmit bits at the rate...
GATE ECE 2016 Set 2
A sinusoidal signal of 2 kHz frequency is applied to a delta modulator. The sampling rate and step-size $$\Delta $$ of t...
GATE ECE 2015 Set 1
The transmitted signal in a GSM system is of 200 kHz bandwidth and 8 users share a common bandwidth using TDMA. If at a ...
GATE ECE 2015 Set 1
An M - level PSK modulation scheme is used to transmit independent binary digits over a band-pass channel with bandwidth...
GATE ECE 2014 Set 4
In a PCA system, the signal $$m(t) = \{ \sin (100\,\pi \,t)\, + \cos (100\,\pi \,t\} $$ V is sampled at the Nyquist rate...
GATE ECE 2014 Set 3
A binary random variable X takes the value of 1 with probability 1/3. X is input to a casade of 2 independent identical ...
GATE ECE 2014 Set 3
The input to a 1-bit quantizer is a random variable X with pdf $${f_x}(x) = 2{e^{ - 2x}}\,\,for\,\,x \ge 0$$ and $${f_x}...
GATE ECE 2014 Set 2
Four messages band limited to W, W, 2 W and 3 W respectively are to be multiplexed using Time Division Multiplexing (TDM...
GATE ECE 2008
A speech signal, band limited to 4 kHz and peak voltage varying between + 5V and - 5V is sampled at the Nyquist rate. Ea...
GATE ECE 2008
A speech signal, band limited to 4 kHz and peak voltage varying between + 5V and - 5V is sampled at the Nyquist rate. Ea...
GATE ECE 2008
A speech signal, band limited to 4kHz and peak voltage varying between +5V and -5V is sampled at the Nyquist rate. Each...
GATE ECE 2008
In delta modulation, the slope overload distortion can be reduced by
GATE ECE 2007
In a GSM system, 8 channels can co-exist in 200 KHz bandwidth using TDMA. A GSM based cellular operator is allocated 5 M...
GATE ECE 2007
The raised cosine pulse p(t) is used for zero ISI in digital communications. The expression for p(t) with unity roll-off...
GATE ECE 2007
In a Direct sequence CDMA system the chip rate is $$1.2288\,\, \times \,\,{10^6}$$ chips per second. If the processing g...
GATE ECE 2007
The minimum step-size required for a Delta-Modulator operating at 32 K samples/sec to track the signal (here u(t) is the...
GATE ECE 2006
Three analog signals, having bandwidths 1200 Hz, 600 Hz and 600 Hz are sampled at their respective Nyquist rates, enocod...
GATE ECE 2004
A source produces binary data at the rate of 10 kbps. The binary symbols are represented as shown in fig. The sourc...
GATE ECE 2004
Choose the correct one from among the alternatives A, B, C, D after matching an item from Group 1 with the most appropri...
GATE ECE 2004
The input to a linear delta modulator having a step size $$\Delta $$ = 0.628 is a sine wave with frequency fm and peak a...
GATE ECE 2003
If S represents the carrier synchronization at the receiver and $$\rho $$ represents the bandwidth efficiency, then the ...
GATE ECE 2003
A signal is sampled at 8 KHz and is quantized using 8-bit uniform quantizer. Assuming $$SN{R_q}$$ for a sinusoidal signa...
GATE ECE 2003
In a digital communication system employing Frequency Shift Keying (FSK), the 0 and 1 bit are represented by sine waves ...
GATE ECE 2000
Four independent messages have bandwidths of 100Hz, 100 Hz, 200Hz and 400Hz respectively. Each is sampled at the Nyquist...
GATE ECE 1999
The number of bits in a binary PCM system is increased from n to n+1. As a result, the signal to quantization noise rat...
GATE ECE 1996
The bit stream 01001 is differentially encoded using 'Delay and Ex OR' scheme for DPSK transmission. Assuming the refere...
GATE ECE 1992
Coherent demodulation of FSK signal can be effected using
GATE ECE 1992
Source encoding in a data communication system is done in order to
GATE ECE 1992
For the signal constellation shown in the figure, the type of modulation is ________. ...
GATE ECE 1991
In a BPSK signal detector, the local oscillator has a fixed phase error of 200. This phase error deteriorates the SNR at...
GATE ECE 1990
In binary data transmission DPSK is preferred to PSK because
GATE ECE 1989
The transfer function of a zero - order hold is
GATE ECE 1988
The message bit sequence input to a DPSK modulator is 1, 1, 0, 0, 1, 1. The carrier phase during the reception of the f...
GATE ECE 1988

Marks 8

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A rectangular pulse existing between t = 0 and t = T and having an amplitude A is to be received by a matched filter (...
GATE ECE 1987

Marks 10

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A signal of bandwidth 3.5 kHz has peak-to-peak and rms amplitudes of 4 V and 0.2 V, respectively. This signal is passed ...
GATE ECE 1989
For the input signal, x(t), shown in Fig. (a) Sketch the impulse response, h(t), of the matched filter. (b) Sketch the...
GATE ECE 1989

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