# Digital Communication Systems · Communications · GATE ECE

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## Marks 1

GATE ECE 2022
Let H(X) denote the entropy of a discrete random variable X taking K possible distinct real values. Which of the following statements is/are necessari...
GATE ECE 2022
A symbol stream contains alternate QPSK and 16-QAM symbols. If symbols from this stream are transmitted at the rate of 1 mega-symbols per second, the ...
GATE ECE 2022
Consider a channel over which either symbol xA or symbol xB is transmitted. Let the output of the channel Y be the input to a maximum likelihood (ML)...
GATE ECE 2017 Set 1
In a digital communication system, the overall pulse shape p(t) at the receiver before the sampler has the Fourier transform P(f). If the symbols are ...
GATE ECE 2017 Set 1
Which one of the following statements about differential pulse code modulation (DPCM) is true?
GATE ECE 2016 Set 2
A speech signal is sampled at 8 kHz and encoded into PCM format using 8 bits/sample. The PCM data is transmitted through a baseband channel via 4-lev...
GATE ECE 2016 Set 1
Consider binary data transmission at a rate of 56 kbps using baseband binary pulse amplitude modulation (PAM) that is designed to have a raised...
GATE ECE 2015 Set 3
The modulation scheme commonly used for transmission from GSM mobile terminals is
GATE ECE 2014 Set 1
In a code - division multiple access (CDMA) system with N = 8 chips, the maximum number of users who can be assigned mutually orthogonal signatu...
GATE ECE 2013
The bit rate of a digital communication system is R kbits/s. The modulation used is 32-QAM. The minimum bandwidth required for ISI free transmission i...
GATE ECE 2004
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
GATE ECE 2004
In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval t1 $$\le$$ t $$\le$$ t2. This indicates...
GATE ECE 2002
For a bit-rate of 8 kbps, the best possible values of the transmitted frequencies in a coherent binary FSK system are
GATE ECE 2001
A band limited signal is sampled at the Nyquist rate. The signal can be recovered by passing the samples through
GATE ECE 1998
GATE ECE 1998
Compression in PCM refers to relative compression of
GATE ECE 1998
In a PCM system with uniform quantization, increasing the number of bits from 8 to 9 will reduce the quantization noise power by a factor 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 1997
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 this signal is ...
GATE ECE 1995
If the number of bits per sample in a PCM system is increased from n to n+1, the improvement in signal-to-quantization noise ratio will be
GATE ECE 1995
The signal to quantization noise ratio in an n-bit PCM system
GATE ECE 1994
The bandwidth required for the transmission of a PCM signal increases by a factor of ________ when the number of quantization levels is increased fro...

## Marks 2

GATE ECE 2017 Set 1
In binary frequency shift keying (FSK), the given signal wave forms are $$\,{u_o}(t) = 5\,\cos \,(20000\,\pi \,t);\,0 \le \,\,t\, \le \,T,$$ and $$... GATE ECE 2016 Set 3 The bit error probability of a memoryless binary symmetric channel is$${10^{ - 5}}$$. If$${10^{ - 5}}$$bits are sent over this channel, then the pr... GATE ECE 2016 Set 2 An ideal band-pass channel 500Hz-2000 Hz is deployed for communication. A modem is designed to transmit bits at the rate of 4800 bits/s using 16-QAM. ... GATE ECE 2015 Set 1 A sinusoidal signal of 2 kHz frequency is applied to a delta modulator. The sampling rate and step-size$$\Delta $$of the delta modulator are 20,000 ... GATE ECE 2015 Set 1 The transmitted signal in a GSM system is of 200 kHz bandwidth and 8 users share a common bandwidth using TDMA. If at a given time 12 users are talkin... GATE ECE 2014 Set 4 An M - level PSK modulation scheme is used to transmit independent binary digits over a band-pass channel with bandwidth 100 kHz. The bit rate is 200 ... GATE ECE 2014 Set 3 In a PCA system, the signal$$m(t) = \{ \sin (100\,\pi \,t)\, + \cos (100\,\pi \,t\} $$V is sampled at the Nyquist rate. The samples are processed by... GATE ECE 2014 Set 3 A binary random variable X takes the value of 1 with probability 1/3. X is input to a casade of 2 independent identical binary symmetric channels (BSC... GATE ECE 2014 Set 2 The input to a 1-bit quantizer is a random variable X with pdf$${f_x}(x) = 2{e^{ - 2x}}\,\,for\,\,x \ge 0$$and$${f_x}(x) = 0\,\,for\,\,x\, < \,0...
GATE ECE 2008
Four messages band limited to W, W, 2 W and 3 W respectively are to be multiplexed using Time Division Multiplexing (TDM). The minimum bandwidth requi...
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. Each sample is quantized and rep...
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. Each sample is quantized and rep...
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 sample is quantized and repres...
GATE ECE 2007
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 MHz bandwidth. Assuming a frequ...
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 factor is given by $$p(t) = ... GATE ECE 2007 In a Direct sequence CDMA system the chip rate is$$1.2288\,\, \times \,\,{10^6}$$chips per second. If the processing gain is desired to be at least ... GATE ECE 2006 The minimum step-size required for a Delta-Modulator operating at 32 K samples/sec to track the signal (here u(t) is the unit-step function) x(t) = 1... GATE ECE 2004 Three analog signals, having bandwidths 1200 Hz, 600 Hz and 600 Hz are sampled at their respective Nyquist rates, enocodes with 12 bit words, and time... GATE ECE 2004 A source produces binary data at the rate of 10 kbps. The binary symbols are represented as shown in fig. The source output is transmitted using t... GATE ECE 2004 Choose the correct one from among the alternatives A, B, C, D after matching an item from Group 1 with the most appropriate item in Group 2. Group ... GATE ECE 2003 The input to a linear delta modulator having a step size$$\Delta $$= 0.628 is a sine wave with frequency fm and peak amplitude Em. If the sampling f... GATE ECE 2003 If S represents the carrier synchronization at the receiver and$$\rho $$represents the bandwidth efficiency, then the correct statement for the cohe... GATE ECE 2003 A signal is sampled at 8 KHz and is quantized using 8-bit uniform quantizer. Assuming$$SN{R_q}$$for a sinusoidal signal, the correct statement for P... GATE ECE 2000 In a digital communication system employing Frequency Shift Keying (FSK), the 0 and 1 bit are represented by sine waves of 10 KHz and 25 KHz respectiv... GATE ECE 1999 Four independent messages have bandwidths of 100Hz, 100 Hz, 200Hz and 400Hz respectively. Each is sampled at the Nyquist rate, and the samples are tim... GATE ECE 1996 The number of bits in a binary PCM system is increased from n to n+1. As a result, the signal to quantization noise ratio will improve by a factor GATE ECE 1992 The bit stream 01001 is differentially encoded using 'Delay and Ex OR' scheme for DPSK transmission. Assuming the reference bit as a '1' and assigning... GATE ECE 1992 Coherent demodulation of FSK signal can be effected using GATE ECE 1992 Source encoding in a data communication system is done in order to GATE ECE 1991 For the signal constellation shown in the figure, the type of modulation is ________. ... GATE ECE 1990 In a BPSK signal detector, the local oscillator has a fixed phase error of 200. This phase error deteriorates the SNR at the output by a factor of ... GATE ECE 1989 In binary data transmission DPSK is preferred to PSK because GATE ECE 1988 The transfer function of a zero - order hold is GATE ECE 1988 The message bit sequence input to a DPSK modulator is 1, 1, 0, 0, 1, 1. The carrier phase during the reception of the first two message bits is$$\pi...

## Marks 8

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

## Marks 10

GATE ECE 1989
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 through a linear PCM coder and...
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 output, y(t), of the matched ...
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