MCQ
Paper - II (xv) — Basics of communication MCQ - Practice Questions with Answers
Solve 44 Paper - II (xv) — Basics of communication questions for RAS/RPSC preparation.
Practice questions
Q1For a brief technical introduction to GSM radio access, which pairing is most accurate?
GSM is a 2G digital cellular system. Its radio access is typically introduced as GMSK modulation with TDMA signalling over paired frequency-division duplex carriers. Confusing GSM with CDMA is a common exam trap: GSM divides users into time slots on radio carriers, whereas CDMA separates users primarily through codes.
Q2A uniform plane electromagnetic wave in free space travels in the +z direction. At a particular instant and point, its electric field is along +x. Which statement is correct?
In a plane electromagnetic wave propagating through free space, the electric field, magnetic field, and direction of propagation are mutually perpendicular. The direction of energy flow follows E × B, so +x crossed with +y gives +z. The amplitude relation is E0/B0 = c, the speed of light in free space.
Q3In a linear delta modulator with step size Delta and sampling interval Ts, which condition most directly indicates slope-overload distortion for an input x(t)?
Delta modulation transmits whether the reconstructed staircase should move up or down by a fixed step. During one sampling interval it can change only by Delta, so its maximum trackable slope is Delta/Ts. If the message slope exceeds that value, the staircase lags behind the input and slope-overload distortion appears. Increasing step size or sampling rate can reduce this particular error, though too large a step increases granular noise.
Q4In a link budget, a cable section has input power 20 mW and output power 2 mW. Immediately after it, an amplifier provides +13 dB gain. Ignoring all other losses, what is the net effect of the two stages?
Attenuation is represented as a negative power gain when output power is less than input power. Here the cable ratio is 2/20 = 0.1, which is -10 dB using 10 log10(Pout/Pin). Cascaded dB values add algebraically, so -10 dB + 13 dB = +3 dB.
Q5Which description most accurately captures wavelength division multiplexing in optical communication?
WDM is a frequency-domain multiplexing technique at optical frequencies: distinct data streams modulate different wavelengths, which are combined into the same fibre and later separated optically. It should not be confused with time slots in TDM or spreading codes in CDMA. This makes it a high-capacity fibre technique rather than a source-coding method.
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More questions
6A band-limited AWGN channel has bandwidth B hertz and received signal-to-noise ratio S/N expressed as a linear ratio. Which statement correctly captures the Shannon capacity implication for this channel?
7In a CDMA uplink cell, a mobile close to the base station can drown out a distant mobile if both arrive with very different received powers. Which mechanism is primarily used to control this near-far impairment?
8In a simple delta modulator, the staircase output cannot follow a rapidly rising input even though the sampling rate is unchanged. Which design change directly reduces this specific error, and what trade-off can it worsen during slowly varying portions?
9Which statement best captures the central idea and a key design issue of CDMA-based communication systems?
10A speech signal band-limited to 4 kHz is encoded using uniform PCM with 256 quantization levels. Using the Nyquist sampling rate, what minimum raw PCM bit rate is obtained before line coding or compression?
11In a digital communication link, which impairment is best modelled as random additive disturbance that directly reduces SNR and hence lowers Shannon capacity, without necessarily shifting the carrier frequency?
12An electromagnetic wave propagates through free space at approximately 3 x 10^8 m/s. If its frequency is 150 MHz, what is its wavelength?
13A noiseless low-pass channel of bandwidth 4 kHz is used with 16 distinguishable signalling levels. According to the Nyquist bit-rate expression for a noiseless channel, what is the maximum bit rate?
14For an ideal band-limited AWGN channel, bandwidth is 3 kHz and the received signal-to-noise ratio is 30 dB. Which value is closest to the Shannon channel capacity?
15A receiver input is -20 dBm. The signal then passes through a 6 dB feeder loss, a 20 dB low-noise amplifier, and a 2 dB connector loss. Ignoring mismatch, what is the output power level?