Digital Communication — Part 2 MCQs with Explanations

6 × 103 is the correct answer to “The minimum sampling frequency (in samples/sec) required to reconstruct the following signal from its samples without distortion $$x\left( t \right) = 5{\left( {\frac{{\sin 2\pi 1000t}}{{\pi t}}} \right)^3} + 7{\left( {\frac{{\sin 2\pi 1000t}}{{\pi t}}} \right)^2}$$ would be”. This question is standard in competitive examination syllabi for Digital Communication.

$${2^{\frac{{2\left( {n + 1} \right)}}{n}}}$$ is the correct answer to “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”. This question is standard in competitive examination syllabi for Digital Communication.

R = 32 kbps, SNRq = 25.8 dB is the correct answer to “A signal is sampled at 8 kHz and is quantized using 8-bit uniform quantizer. Assuming SNR q for a sinusoidal signal, the correct statement for PCM signal with a bit rate of R is”. This question is standard in competitive examination syllabi for Digital Communication.

$$\frac{1}{{700}}\sec $$ is the correct answer to “The Nyquist sampling interval, for the signal sin c(700t) + sin c(500t) is”. This question is standard in competitive examination syllabi for Digital Communication.

π π 0 0 π π is the correct answer to “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 phases of '0' and 'π' for 1's and 0's respectively, in the encoded sequence, the transmitted phase sequence becomes”. This question is standard in competitive examination syllabi for Digital Communication.

Bp = 2B0 is the correct answer to “For a given data rate, the bandwidth B p of a BPSK signal and the bandwidth B 0 of the OOK signal are related as”. This question is standard in competitive examination syllabi for Digital Communication.

12 × 10-6 V2 is the correct answer to “A sinusoidal signal with peak-to-peak amplitude of 1.536 V is quantized into 128 levels using a mid-rise uniform quantizer. The quantization noise power is”. This question is standard in competitive examination syllabi for Digital Communication.

800 is the correct answer to “Four independent messages have bandwidths of 100 Hz, 100 Hz, 200 Hz, and 400 Hz, respectively. Each is sampled at the Nyquist rate, and the samples are Time Division Multiplexed (TDM) and transmitted. The transmitted sample rate (in Hz) is”. This question is standard in competitive examination syllabi for Digital Communication.

4 is the correct answer to “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”. This question is standard in competitive examination syllabi for Digital Communication.

4000 is the correct answer to “In a baseband communications link, frequencies upto 3500 Hz are used for signaling. Using a raised cosine pulse with 75% excess bandwidth and for no inter-symbol interference, the maximum possible signaling rate in symbols per second is”. This question is standard in competitive examination syllabi for Digital Communication.

4 bits/sec is the correct answer to “An analog signal is band-limited to 4 kHz, sampled at the Nyquist rate and the samples are quantized into 4 levels. The quantized levels are assumed to be independent and equally probable. If we transmit two quantized samples per second, the information rate is”. This question is standard in competitive examination syllabi for Digital Communication.

2-8 is the correct answer to “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) = 125t(u(t) - u(t - 1)) + (250 - 125t)(u(t - 1) - u(t - 2)) so that slope-overload is avoided, would be”. This question is standard in competitive examination syllabi for Digital Communication.

-1 sec-1 is the correct answer to “Consider the signal x(t) shown in the figure. Let h(t) denote the impulse response of the filter matched to x(t), with h(t) being non-zero only in the interval 0 to 4 sec. The slope of h(t) in the interval 3 < t < 4 sec is”. This question is standard in competitive examination syllabi for Digital Communication.

Higher signal amplitudes is the correct answer to “Compression in PCM refers to relative compression of”. This question is standard in competitive examination syllabi for Digital Communication.

$$\rho = 0.5,S$$ is required is the correct answer to “If S represents the carrier synchronization at the receiver and p represents the bandwidth efficiency, then the correct statement for the coherent binary PSK is”. This question is standard in competitive examination syllabi for Digital Communication.

(1 - p)8 + 8p(t - p)7 is the correct answer to “In a digital communication system, transmissions of successive bits through a noisy channel are assumed to be independent events with error probability p. The probability of at most one error in the transmission of an 8-bit sequence is”. This question is standard in competitive examination syllabi for Digital Communication.

0.5 ms is the correct answer to “In binary frequency shift keying (FSK), the given signal waveforms are u 0 (t) = 5cos(20000πt); 0 ≤ t ≤ 7 and u 1 (t) = 5cos(22000πt); 0 ≤ t ≤ T, where T is the bit-duration interval and t is in seconds. Both u 0 (t) and u 1 (t) are zero outside the interval 0 ≤ t ≤ T. With a matched filter (correlator) based receiver, the smallest positive value of T (in milliseconds) required to have u 0 (t) and u 1 (t) uncorrelated is”. This question is standard in competitive examination syllabi for Digital Communication.

binary phase shifting key is the correct answer to “BPSK stands for”. This question is standard in competitive examination syllabi for Digital Communication.

Get almost uniform S/N ratio is the correct answer to “Companding is used in PCM to”. This question is standard in competitive examination syllabi for Digital Communication.

Equal to twice the signal frequency is the correct answer to “For atmost distortionless reception of signal in pulse modulation it is required that the speed should be:”. This question is standard in competitive examination syllabi for Digital Communication.

1 and 2 only is the correct answer to “Which of the following statements about the matched filter in a communication receiver are correct? 1. Its impulse response depends on the signal shape 2. It maximizes the SNR at the detection instant 3. It produces ISI 4. It may produce phase error if synchronization is improper Select the correct answer from the options given below:”. This question is standard in competitive examination syllabi for Digital Communication.

Multipath fading may be substantially increased because the signal is spread over a large spectrum is the correct answer to “Which one of the following statements is not correct regarding the features of CDMA”. This question is standard in competitive examination syllabi for Digital Communication.

2.16 × 103 bits/s is the correct answer to “The outputs of 18 numbers of 20 Hz low pass filters are sampled, multiplexed and A/D converted. If the sampling is at the Nyquist rate of 40 samples/s, corresponding to signal of 20 Hz band-width and if we use 3 bits/sample to represent each voltage sample, the bit rate is”. This question is standard in competitive examination syllabi for Digital Communication.

Pulse code modulation is the correct answer to “The modulation techniques used to convert analog signal into digital signal are”. This question is standard in competitive examination syllabi for Digital Communication.

PAM is the correct answer to “Which of the following is worst affected by Noise”. This question is standard in competitive examination syllabi for Digital Communication.

NRZI with bit stuffing is the correct answer to “Which type of encoding is used in USB”. This question is standard in competitive examination syllabi for Digital Communication.

1 and 2 only is the correct answer to “Which of the following pulse modulation are digital? 1. PCM 2. Differential PCM 3. PWM Select the correct answer using the options given below:”. This question is standard in competitive examination syllabi for Digital Communication.

Reducing the step size is the correct answer to “The granular noise can be reduced by”. This question is standard in competitive examination syllabi for Digital Communication.

a-2, b-1, c-4, d-3 is the correct answer to “Match List-I with List-II and select the correct answer as per the options: List-I List-II a. RF band is divided into small frequency bands 1. TDMA b. Store and forward system 2. FDMA c. Spread spectrum multiple access 3. Navigation technique d. Dead reckoning 4. CDMA”. This question is standard in competitive examination syllabi for Digital Communication.

QPSK is the correct answer to “In a band limited channel higher bit rate can be transmitted with”. This question is standard in competitive examination syllabi for Digital Communication.

49.8 dB is the correct answer to “A message signal with its amplitude uniformly distributed between -2 V and +2 V is transmitted by a 8-bit binary PCM system. The (SNR) q would be”. This question is standard in competitive examination syllabi for Digital Communication.

$${P_e} = Q\left\{ {\sqrt {\frac{{2v{E_b}}}{{{N_0}}}} } \right\}$$ is the correct answer to “The bit error probability for GMSK is given by”. This question is standard in competitive examination syllabi for Digital Communication.

AND gate is the correct answer to “In high speed TDM, the channels are separated in the receiver employing”. This question is standard in competitive examination syllabi for Digital Communication.

10-1 and 10-4 respectively is the correct answer to “Delta modulation and pulse code modulation have a threshold P e , (Considering the impact of errors in various digits).”. This question is standard in competitive examination syllabi for Digital Communication.

R/5 kHz is the correct answer to “The bit rate of digital communication system is R kbits/s. The modulation used is 32-QAM. The minimum bandwidth required for ISI free transmission is”. This question is standard in competitive examination syllabi for Digital Communication.

540 kHz is the correct answer to “Five channels each with 100 kHz bandwidth are to be multiplexed together. What is the minimum bandwidth of the link, if three is a need of a guard band is a need of a guard band of 10 kHz between the channels to prevent interference”. This question is standard in competitive examination syllabi for Digital Communication.

BW = 1.5 fb is the correct answer to “Minimum Bandwidth required for Minimum Shift Keying (MSK)? Where f b is maximum frequency of baseband signal.”. This question is standard in competitive examination syllabi for Digital Communication.

Nyquist criterion is the correct answer to “The criterion used for pulse shaping to avoid ISI is”. This question is standard in competitive examination syllabi for Digital Communication.

ASK is the correct answer to “Which signaling scheme is most affected by noise”. This question is standard in competitive examination syllabi for Digital Communication.

+12 dB is the correct answer to “The received signal level for a particular digital system is -151 dBW and the effective noise temperature of the receiver system is 1500 K. The value of $$\frac{{{{\text{E}}_{\text{b}}}}}{{{{\text{N}}_0}}}$$ required for a link transmitting 2400 bps is:”. This question is standard in competitive examination syllabi for Digital Communication.