Explore topic-wise InterviewSolutions in .

The correct answer is (c) Phase

The EXPLANATION is: In DIFFERENTIAL ENCODING, the phase of the present signal waveform is COMPARED with the phase of the previous signal.

The correct OPTION is (a) COHERENT detection

To EXPLAIN I WOULD say: Matched filter is used for coherent detection. It cannot be used for non coherent detection because matched filter output is a function of UNKNOWN angle α.

Correct answer is (a) 1:2

The EXPLANATION: As the LIMIT of k INCREASES, the ratio of PB/PE BECOMES 1:2.

Right answer is (c) (M/2)/M-1

Easy EXPLANATION: The RELATIONSHIP between the PROBABILITY of BIT error and probability of symbol error is (M/2)/M-1 in M-ary orthogonal signalling.

The correct choice is (a) Es=Eb(log2M)

To EXPLAIN I would say: In M-ary PSK SIGNALLING, the ENERGY per symbol is given as Es=Eb(log2M).

Right choice is (b) 1

Easy explanation: For FSK signalling the detection BANDWIDTH is typically EQUAL to SYMBOL RATE 1/T that is WT is nearly equal to 1.

The correct OPTION is (a) More

To explain: In ORTHOGONAL signalling with SYMBOLS having more NUMBER of bits need more power but requirement PER bit is reduced.

Correct OPTION is (c) QPSK

The best explanation: In QPSK bit stream is PORTIONED into even and ODD stream, I and Q bit STREAMS. Each new stream modulates as orthogonal COMPONENT at half bit rate.

Correct OPTION is (b) Improved, degraded

The best EXPLANATION: In M-ary signalling as K increases, the curve moves towards the degraded ERROR performance. It produces improved error performance in CASE of orthogonal signalling and degraded error performance in case of multiple phase signalling.

The CORRECT answer is (b) 4-ary system

Best explanation: The MINIMUM energy noise vector for 4-ary system is SMALLER than 2-ary system. So 4-ary system is more VULNERABLE to noise.

Right choice is (C) Shannon limit

To EXPLAIN: Eb/N0 curve has waterfall shape. Shannon limit GIVES the THRESHOLD value below which reliable COMMUNICATION cannot be maintained.

The CORRECT ANSWER is (B) 1/T

To explain I would say: In non COHERENT detection the minimum tone separation CORRESPONDS to 1/T.

Right OPTION is (a) Center of the spectral main lobe and first ZERO CROSSING

The explanation is: The frequency difference between the center of the spectral main lobe and the first zero crossing is CALLED as the minimum REQUIRED spacing in non coherent detection.

Right choice is (B) Rectifier and LOW pass filter

The EXPLANATION: An envelope detector consists of a rectifier and a low pass filter. The detectors are MATCHED to the envelopes and not to the SIGNAL themselves.

Correct CHOICE is (a) Encoded differentially

For explanation I would say: In this method, the data is encode deferentially that is the presence of binary zero or one is MANIFESTED by symbol’s similarity or DIFFERENCE when COMPARED to that of the previous symbol.

The correct ANSWER is (C) Carrier wave recovery & Phase estimation

Explanation: The phase locked loop circuitry locks on the ARRIVING carrier wave and ESTIMATES its phase.

Correct ANSWER is (a) 1/T

Explanation: The input signal comprises of a PROTOTYPE signal plus NOISE and the bandwidth is 1/2T where T is the symbol TIME and minimum nyquist sampling rate can be GIVEN as 2W or 1/T.

Correct CHOICE is (a) MAXIMUM LIKELIHOOD detector

The best I can explain: Coherent detector considers PHASE as the most IMPORTANT parameter. This coherent detector is also known as maximum likelihood detector.

Right answer is (B) Predetection point

Easy explanation: The first step of the DETECTION process is to reduce waveform into a single or GROUP of random variable. This first step in the transformation of waveform into a point in signal space. This point is CALLED as predetection point.

Correct choice is (a) ASK

The best explanation: In ASK modulation scheme the SIGNAL attains either maximum AMPLITUDE or ZERO point. Thus it is ALSO called as on-off keying.

Right option is (a) Two 180 opposing vector

Best explanation: In BPSK the two VECTORS, the signal SET can be ILLUSTRATED as two 180 opposing vector which is called as ANTIPODAL signal sets.

Right answer is (a) INPHASE

The BEST I can explain: The TWO main PARTS of sinusoid carrier wave – REAL part is called as inphase and the imaginary part is called as quadrature.

The correct answer is (d) All of the mentioned

The explanation is: Some of the examples of COHERENT modulation techniques are phase SHIFT KEYING, AMPLITUDE shift keying, FREQUENCY shift keying and continuous phase modulation.

Right choice is (a) COHERENT detection

The best I can explain: When the receiver USES CARRIER’s phase as major factor for detection then it is called as coherent detection and when carrier is not given importance it is called as NON coherent detection.