MCQOPTIONS
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MCQOPTIONS
This section includes 84 Mcqs, each offering curated multiple-choice questions to sharpen your Wireless Mobile Communications knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
Half power bandwidth is also called ______ |
| A. | Absolute bandwidth |
| B. | Null to null bandwidth |
| C. | 3 dB bandwidth |
| D. | Zero dB bandwidth |
| Answer» D. Zero dB bandwidth | |
| 2. |
_______ is equal to width of main spectral lobe. |
| A. | Null to null bandwidth |
| B. | Half power bandwidth |
| C. | 3 dB bandwidth |
| D. | Absolute bandwidth |
| Answer» B. Half power bandwidth | |
| 3. |
In digital communication system, in order to increase noise immunity, it is necessary to increase _________ |
| A. | Signal power |
| B. | Signal amplitude |
| C. | Signal frequency |
| D. | Signal magnitude |
| Answer» B. Signal amplitude | |
| 4. |
The performance of modulation scheme is not measured in terms of __________ |
| A. | Power efficiency |
| B. | Bandwidth efficiency |
| C. | Cost and complexity |
| D. | Transmitted power |
| Answer» E. | |
| 5. |
A desirable modulation scheme provides _________ bit error rates at __________ received signal to noise ratios. |
| A. | Low, low |
| B. | Low, high |
| C. | High, high |
| D. | High, low |
| Answer» B. Low, high | |
| 6. |
Modern mobile communication systems use analog modulation techniques. |
| A. | True |
| B. | False |
| Answer» C. | |
| 7. |
For a 10 bit PCM system the signal to quantization noise ratio is 62 dB. If the number of bits is increased by 2, then the signal to quantization noise ratio will |
| A. | Increase by 6 dB |
| B. | Increase by 12 dB |
| C. | Decrease by 6 dB |
| D. | Decrease by 12 dB |
| Answer» C. Decrease by 6 dB | |
| 8. |
A 70 MHz carrier is QPSK modulated by a 1.544 Mbps T1 data stream. The transmitter employs a raised-cosine filter with α = 0.2. What is the transmitted bandwidth of the signal? |
| A. | 3705.6 kHz |
| B. | 1852.8 kHz |
| C. | 308.8 kHz |
| D. | 926.4 kHz |
| Answer» E. | |
| 9. |
A 12-bit ADC has input signal range of ± 1 V. The signal to quantization noise ratio if a sine wave signal with 0.25 V peak voltage is given as input is: |
| A. | 62 dB |
| B. | 72 dB |
| C. | 74 dB |
| D. | 48 dB |
| Answer» B. 72 dB | |
| 10. |
In which modulation does the signal convert its analog information into a binary sequence, i.e., in 1s and 0s |
| A. | Phase shift key modulation |
| B. | Pulse code modulation |
| C. | Analog modulation |
| D. | Frequency modulation |
| Answer» C. Analog modulation | |
| 11. |
A random variable X has X̅ = 0 & σX2 = 1. Form a new random variable Y = 2 X + 1. The values of Y̅ & σY2 are: |
| A. | 0 & 1 |
| B. | 1 & 2 |
| C. | 1 & 4 |
| D. | None of these |
| Answer» D. None of these | |
| 12. |
24 voice channels are sampled uniformly at a rate of 8 kHz and then time division multiplexed. The sampling process uses flat-top samples with 1 μs duration. The multiplexing operation includes the provision of synchronization by adding an extra pulse of 1 μs duration. The spacing between successive pulses of the multiplexed signal is: |
| A. | 4 μs |
| B. | 6 μs |
| C. | 7.2 μs |
| D. | 8.4 μs |
| Answer» B. 6 μs | |
| 13. |
In a 10-bit PCM system, a message signal having maximum frequency of 4 KHz is to be transmitted. If the bit rate of this PCM system is 60 Kbits / sec, the appropriate sampling frequency is |
| A. | 6 kHz |
| B. | 7 kHz |
| C. | 8 kHz |
| D. | 9 kHz |
| Answer» D. 9 kHz | |
| 14. |
If the number bits per sample in a PCM system is increased from; and n to (n + 1), the improvement is signal to quantization noise ratio will be |
| A. | 3 dB |
| B. | 6 dB |
| C. | 2n dB |
| D. | n dB |
| Answer» C. 2n dB | |
| 15. |
Arrange in increasing order of Null-to-Null bandwidth (Hz) of the following binary bandpass signals.(i) QPSK(ii) MSK(iii) FSK(iv) ASK |
| A. | (iii), (iv), (ii), (i) |
| B. | (iv), (i), (ii), (iii) |
| C. | (i), (ii), (iv), (iii) |
| D. | (iv), (ii), (i), (iii) |
| Answer» D. (iv), (ii), (i), (iii) | |
| 16. |
PAM, PPM, PWM are examples of _______. |
| A. | altitude modulation |
| B. | angular modulation |
| C. | digital modulation |
| D. | analogue modulation |
| Answer» E. | |
| 17. |
In PCM system |
| A. | a large bandwidth is required |
| B. | the biggest disadvantage is its incompatibility with TDM |
| C. | companding is used to overcome quantising noise |
| D. | none of the above |
| Answer» B. the biggest disadvantage is its incompatibility with TDM | |
| 18. |
In digital transmission, the modulation technique that requires the minimum bandwidth is: |
| A. | PCM |
| B. | PAM |
| C. | DPCM |
| D. | Delta modulation |
| Answer» E. | |
| 19. |
If the synchronization between transmitter and receiver fails which of the following pulse systems would be affected? |
| A. | PAM |
| B. | PDM |
| C. | PPM |
| D. | none of these |
| Answer» D. none of these | |
| 20. |
Which of the following statements is correct? |
| A. | Bandwidth requirement of DPCM is more than PCM |
| B. | Bandwidth requirement of DPCM is equal to PCM |
| C. | Bandwidth requirement of DPCM is less than PCM |
| D. | Both DPCM and PCM have no Bandwidth requirement |
| Answer» D. Both DPCM and PCM have no Bandwidth requirement | |
| 21. |
A 13 bit PCM system performance is better than an 8 bit PCM system because: |
| A. | Noise is lower and is proportional to reciprocal of bandwidth |
| B. | Bandwidth is larger and detection is easier |
| C. | Quantization noise is lesser other things being equal |
| D. | Quantization noise is nearly zero since 213 levels are available |
| Answer» E. | |
| 22. |
Bandwidth of an N-bit binary coded PCM signal for modulating a signal sampled at ‘f’ Hz is |
| A. | f/N Hz |
| B. | f/N2 Hz |
| C. | Nf Hz |
| D. | N2f Hz |
| Answer» D. N2f Hz | |
| 23. |
If the number of bits per sample in a PCM system is increased from 8 to 16, then the bandwidth will be increased by |
| A. | 2 times |
| B. | 4 times |
| C. | 8 times |
| D. | 16 times |
| Answer» B. 4 times | |
| 24. |
Directions: The item consists of two statements, one labelled as the ‘Assertion (A)’ and the other as ‘Reason (R)’.You are to examine these two statements carefully and select the answers to the item using the codes given below:Assertion (A): When coding signals like speech signals a-law or μ-law quantizers are used.Reason (R): A-law and μ-law quantizers occupy smaller bandwidth than uniform quantizers. |
| A. | Both A and R individually true and R is the correct explanation of A |
| B. | Both A and R are individually true but R is not the correct explanation of A |
| C. | A is true but R is false |
| D. | A is false but R is true |
| Answer» D. A is false but R is true | |
| 25. |
Output data ratio of a 8-bit PCM-TDM system sampling 24 voice channels, comparing these using μ-law at the rate of 8 kHz with a 1 frame alignment word, is: |
| A. | 1.2 × 106 bit/sec |
| B. | 1.4 × 106 bit/sec |
| C. | 1.6 × 106 bit/sec |
| D. | 1.8 × 106 bit/sec |
| Answer» D. 1.8 × 106 bit/sec | |
| 26. |
For a given data rate, the bandwidth required with m-ary transmission is smaller than that for binary transmission by |
| A. | log2m |
| B. | \(\frac{log_2m}{m}\) |
| C. | \(\frac{2}{log_2m}\) |
| D. | \(\frac{log_2m}{2}\) |
| Answer» B. \(\frac{log_2m}{m}\) | |
| 27. |
A PCM system is to have a signal-to-noise ration of 40 dB. The signals are speech and an rms-to-peak ratio of – 10 dB is allowed for. The number of bits per code word is |
| A. | 6 bits |
| B. | 7 bits |
| C. | 8 bits |
| D. | 10 bits |
| Answer» C. 8 bits | |
| 28. |
In an ADC, the minimum Effective Number of Bits (ENOB) requires to represent each quantization level to achieve Signal to Noise and Distortion Ratio (SINAD) of 70 dB is |
| A. | 8 bits |
| B. | 10 bits |
| C. | 11 bits |
| D. | 12 bits |
| Answer» E. | |
| 29. |
________ is mostly preferred for telegraphy. |
| A. | Single tone modulation |
| B. | On-off keying |
| C. | Frequency shift keying |
| D. | Pulse code modulation |
| Answer» D. Pulse code modulation | |
| 30. |
In digital communication, Inter Symbol Interference (ISI) is a form of distortion where one symbol interferes with subsequent symbols. An eye diagram is used to study the extent of ISI in a communication channel. Which of the following is FALSE? |
| A. | The eye diagram can be observed in an oscilloscope |
| B. | Width of the eye-opening indicates an interval where the wave can be sampled without ISI |
| C. | Height of the eye-opening at a specific sampling time defines the margin over the noise |
| D. | Band-limiting the channel helps to reduce ISI |
| Answer» E. | |
| 31. |
In a PCM system, if N is the number of levels and Z is the step size, then mean square quantization error is given by: |
| A. | NZ/12 |
| B. | Z2/12 |
| C. | Z2/12N |
| D. | NZ2/12 |
| Answer» C. Z2/12N | |
| 32. |
Direction: The following item consists of two statements, one labeled as ‘Statement (I) and the other as ‘Statement (II). You are to examine these two statements carefully and select the answers to these items using the code given below:Statement (I): PCM requires very complex encoding and quantization circuitry.Statement (II): PCM requires less bandwidth compared to analog systems. |
| A. | Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I) |
| B. | Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I) |
| C. | Statement (I) is true but Statement (II) is false |
| D. | Statement (I) is false but Statement (II) is true |
| Answer» D. Statement (I) is false but Statement (II) is true | |
| 33. |
Pulse code modulation employing 4-bit code is used to transmit a data signal having frequency components from dc to 2 KHz. The minimum bandwidth of the carrier channel should be |
| A. | 2 kHz |
| B. | 4 kHz |
| C. | 8 kHz |
| D. | 16 kHz |
| Answer» D. 16 kHz | |
| 34. |
An AM Scheme is working with a modulation index of 0.8. Power efficiency of this modulation Scheme is |
| A. | 24% |
| B. | 48% |
| C. | 12% |
| D. | 18% |
| Answer» B. 48% | |
| 35. |
Comparing Delta Modulation (DM) with PCM systems, DM requires:1. a lower sampling rate2. a higher sampling rate3. least bandwidth4. simpler hardware |
| A. | 1, 2 and 4 only |
| B. | 1, 2 and 3 only |
| C. | 2, 3 and 4 only |
| D. | 1, 3 and 4 only |
| Answer» D. 1, 3 and 4 only | |
| 36. |
It is assumed that quantization error, e(n) is a sequence of random variables where1. The statistics do not change with time.2. It is a sequence of uncorrelated random variables.3. It is uncorrelated with the quantizer input x(n).4. The probability density function is uniformly distributed over the range of values of quantization error.Which of the above statements are correct? |
| A. | 1, 2 and 3 only |
| B. | 1, 2 and 4 only |
| C. | 3 and 4 only |
| D. | 1, 2, 3 and 4 |
| Answer» C. 3 and 4 only | |
| 37. |
How many bits are required to divide 10V into 0.001V intervals? |
| A. | 14 bits |
| B. | 20 bits |
| C. | 1024 bits |
| D. | 100 bits |
| Answer» B. 20 bits | |
| 38. |
Match the following:Column AColumn B a. FSK modem1. 2400 bpsb. 4-DPSK modem2. 9600 bpsc. 8-DPSK modem3. 1200 bpsd. 16 QAM modem4. 4800 bps |
| A. | a – 3; b – 1, c – 4, d - 2 |
| B. | a – 1; b – 3, c – 4, d - 2 |
| C. | a – 2; b – 4, c – 1, d - 3 |
| D. | a – 3; b – 2, c – 4, d - 1 |
| Answer» B. a – 1; b – 3, c – 4, d - 2 | |
| 39. |
Indicate which of the following system is digital |
| A. | PPM |
| B. | PCM |
| C. | PWM |
| D. | PFM |
| Answer» C. PWM | |
| 40. |
If the channel is band limited to 6 kHz and signal to noise ratio is 16, what would be the capacity of channel? |
| A. | 15.15 kbps |
| B. | 24.74 kbps |
| C. | 30.12 kbps |
| D. | 52.18 kbps |
| Answer» C. 30.12 kbps | |
| 41. |
A signal is band-limited to 3.6 kHz and three other signals are band-limited to 1.2 kHz each. These signals are to be transmitted by means of time-division multiplexing. If each signal is sampled at its Nyquist rate, then the speed of the commutator (by assuming 6 samples per rotation) is |
| A. | 864000 r.p.m. |
| B. | 144000 r.p.m. |
| C. | 86400 r.p.m. |
| D. | 14400 r.p.m. |
| Answer» E. | |
| 42. |
Following constellation diagram represents: |
| A. | 16 PSK |
| B. | 16 QAM |
| C. | 16 APSK |
| D. | All of above |
| Answer» C. 16 APSK | |
| 43. |
In ASK modulation: |
| A. | A finite number of amplitude are used |
| B. | A finite number of frequencies are used |
| C. | A finite number of two phases are used |
| D. | A finite number of phases are used |
| Answer» B. A finite number of frequencies are used | |
| 44. |
In a PCM system, the amplitude levels are transmitted as 7 bit code-words. The sampling is done at 10 kHz. The bandwidth of the system is |
| A. | 10 kHz |
| B. | 20 kHz |
| C. | 35 kHz |
| D. | 70 kHz |
| Answer» E. | |
| 45. |
In QAM, both ________ of a carrier frequency vary. |
| A. | frequency and amplitude |
| B. | phase and amplitude |
| C. | phase and frequency |
| D. | Phase and frequency |
| Answer» C. phase and frequency | |
| 46. |
Multiplexing scheme which uses carrier phase shifting and synchronous detection to permit two DSB signals to occupy the same frequency band is called |
| A. | NBFM |
| B. | CDMA |
| C. | QAM |
| D. | FDMA |
| Answer» D. FDMA | |
| 47. |
A special PCM system uses 32 channels of data, one whose purpose is an identification (ID) and synchronization. The sampling rate is 4 kHz. The word length is 5 bits. Find the serial data rate. |
| A. | 1280 kHz |
| B. | 160 kHz |
| C. | 320 kHz |
| D. | 640 kHz |
| Answer» E. | |
| 48. |
In a communication system, noise due to quantization error is |
| A. | Linear and signal-dependent |
| B. | Nonlinear and signal-dependent |
| C. | Linear and signal independent at low frequencies only |
| D. | Non-linear and signal-dependent at low frequencies only |
| Answer» C. Linear and signal independent at low frequencies only | |
| 49. |
Direction: Given question consists of two statements, one labeled as the 'Assertion (A)' and the other as 'Reason (R)'. You are to examine these two statements carefully and select the answers to these items using the codes given below.Assertion (A): The basic group in an FDM system occupies a band of 60 kHz to 108 kHz in frequency.Reason (R): The voice channels in FDM are band-limited to 4 kHz and carrier frequencies fc = 60 + 4 × n kHz are used for 12 channels in the basic group. |
| A. | Both A and R are individually true and R is the correct explanation of A |
| B. | Both A and R are individually true but R is NOT the correct explanation of A |
| C. | A is true but R is false |
| D. | A is false but R is true |
| Answer» B. Both A and R are individually true but R is NOT the correct explanation of A | |
| 50. |
Determine the number of bits/sec generated by a PCM system if the bandwidth of TV video and audio signal of 4.5 MHz is to be converted to PCM stream with 1024 quantization levels. Assume signal is sampled at 20% above Nyquist rate. |
| A. | 108 × 106 |
| B. | 18 × 104 |
| C. | 80 × 106 |
| D. | 81 × 105 |
| Answer» B. 18 × 104 | |