Digital Communications

1. Which of the following is rarely used in digital communication systems?a. ASKb. FSKc. PSKd. QAMAnswer:

2. Information capacity is directly proportional to a. Bit rateb. Baud ratec. C/Nd. Bandwidth Answer:

3. Which of the following does not makes efficient use of available bandwidth?a. FSKb. PSKc. QAMd. ASKAnswer:

4. Which of the following is used extensively in high-frequency radio teletype transmission?a. QAMb. FSKc. PSKd. ASKAnswer:

5. QAM usesa. PSKb. ASKc. PCMd. MSKAnswer:

6. Digital amplitude modulation is calleda. ASKb. FSKc. MSKd. PSKAnswer:

7. A system that provides high-speed internet access using regular telephone lines.a. ISDNb. DSLc. WAPd. Wi-FiAnswer: B

8. Downstream speeds of ADSL typically range from a. 64 kbps to 1.5 Mbpsb. 56 kbps to 8 Mbpsc. 768 kbps to 9 Mbpsd. 128 kbps to 2 MbpsAnswer:

9. Upstream speeds of ADSL typically range from a. 64 kbps to 1.5 Mbpsb. 56 kbps to 8 Mbpsc. 768 kbps to 9 Mbpsd. 128 kbps to 2 MbpsAnswer:

10. In DSL technology, it is the proprietary technology trademarked by Rockwell International. ?a. IDSLb. CDSLc. RDSLd. ADSLAnswer:

11. Uses the advanced signal modulation techniques of DSL and combines them with the half-duplex "burst" packet nature of Ethernet. a. xDSLb. EthernetLoopc. ISDNd. WAPAnswer:

12. A type of DSL in which the upstream and downstream speeds are unequal or uneven.a. RDSLb. ADSLc. HDSLd. IDSLAnswer:

13. Which xDSL generally used as a substitute for T1/E1?a. HDSLb. SDSLc. IDSLd. RADSLAnswer:

14. A lower data rate version of Asymmetric Digital Subscriber Line (ADSL) was been proposed as an extension to ANSI standard T1.413 by the UAWG (Universal ADSL Working

Group) led by Microsoft, Intel, and Compaq. a. RDSLb. SDSLc. G.lited. EthernetLoopAnswer:

15. A two-wire implementation of HDSLa. SDSLb. MDSLc. IDSLd. xDSLAnswer:

16. Uses 2B1Q line coding and typically supports data transfer rates of 128 kbps?a. RDSLb. IDSLc. HDSLd. SDSLAnswer:

17. A DSL technology which uses pulse amplitude modulation (PAM) on a 4-wire loop?a. RADSLb. HDSLc. SDSLd. G.liteAnswer:

18. The name has become more generic over time to refer to symmetric service at a variety of rates over a single loop. a. RADSLb. SDSLc. MDSLd. All of the aboveAnswer:

19. It uses carrier-less amplitude and phase modulation (CAP).a. RADSLb. MDSLc. SDSLd. IDSLAnswer:

20. xDSL which has a data rate that exceeds 10 Mbps and proposed at a short local loops.a. VDSLb. MDSLc. SDSLd. HDSL

Answer: 21. What is the other name for a multiplier

circuit?a. Balanced modulatorb. Digital Subscriber Linec. Limiter d. Discriminator Answer:

22. MDSL stands fora. Main Digital Subscriber Lineb. Multi-rate Digital Subscriber Linec. May Daga Sa Lunggad. None of the aboveAnswer:

23. High Bit-rate Digital Subscriber Line 2 was designed to transport T1 signaling at 1.544 Mb/s over a single copper pair. HDSL2 uses a. CRCb. OPTISc. MPEG-2d. MPEG-4Answer:

24. The bandwidth of one D channel isa. 16 kbpsb. 64 kbpsc. 56 kbpsd. 128 kbpsAnswer:

25. The bandwidth of one bearer channel isa. 56 kbpsb. 64 kbpsc. 128 kbpsd. 16 kbpsAnswer:

26. A DSL technology where the uplink rate depends on the downlink rate, which is a function of line conditions and signal to noise ratio (SNR). a. RADSLb. MDSLc. SDSLd. IDSLAnswer:

27. The data transmission rate of a modem is measured ina. Bits per secondb. Bytes per secondc. Bit rated. Baud rateAnswer:

28. To permit the correct selection of 1 out of 2048 equal-probability events, how many bits are required?a. 5b. 9c. 11d. 16Answer:

29. Which of the following is a feature of a smart modem?a. Auto dialb. Accepts commandc. Auto fallbackd. All of the aboveAnswer:

30. Two bits of information is calleda. Dual-bitb. Dibit c. Twin-bitd. Sa-bitAnswer

31. Four bits of information is also calleda. Quadbitb. Nibblec. Half byted. All of the aboveAnswer:

32. 16-PSK uses how many phases?a. 4b. 16c. 2d. 8Answer:

33. DPSK means _____ PSK.a. Differentialb. Deltac. Duald. DoubleAnswer:

34. How many points will be on the constellation diagram of a QAM system using 16 phases and 2 amplitude levels?a. 2b. 8c. 16d. 32Answer:

35. GMSK meansa. Greatest Maximum Shift Keyingb. Gaussian Minimum Shift Keyingc. Graded-Multimode Step Keying

d. None of the aboveAnswer:

36. What is a special case of FSK that achieves the minimum bandwidth possible for a two-frequency system at a given data rate?a. DFSKb. GMSKc. DPSKd. FLASKAnswer:

37. The _____ is equal to twice the highest frequency component of the analog signal.a. Nyquist rateb. Hall ratec. Bit rated. Dollar rateAnswer:

38. A type of digital modulation which has only one bit transmitted per cycle.a. Bitb. PPMc. PDMd. Delta Answer:

39. Broadband ISDN data rate for H21 channel.a. 32.768 Mbpsb. 43 Mbpsc. 138.24 Mbpsd. 132 MbpsAnswer:

40. Broadband ISDN data rate for H22 channel.a. 32.768 Mbpsb. 43 to 45 Mbpsc. 138.24 Mbpsd. 132 MbpsAnswer:

41. Broadband ISDN data rate for H4 channel.a. 32.768 Mbpsb. 43 to 45 Mbpsc. 132 to 138.24 Mbpsd. None of the aboveAnswer:

42. A means by which data can enter and exit the B-ISDN network in an asynchronous fashion.a. TCP/IP

b. ATMc. DSLd. ADMAnswer:

43. B-ISDN is outlined ina. I.119b. I.120c. I.121d. I.122Answer:

44. ATM breaks data into small chunks of fixed size cells of how many bytes?a. 48 bytesb. 5 bytesc. 64 bytesd. 128 bytesAnswer:

45. In PCM, what follows the input bandpass filter?a. ADCb. Sample-and-holdc. Low-pass filterd. DACAnswer:

46. During times when there is no analog input signal, the only input to the PAM is random, thermal noise calleda. Overload distortionb. Idle channel noisec. Slope overloadd. Quantization errorAnswer:

47. Results if the magnitude of the sample exceeds the highest quantization interval.a. Overload distortionb. Idle channel noisec. Slope overloadd. Quantization errorAnswer:

48. An error which results from the rounding the magnitude of the sample to the nearest valid code.a. Overload distortionb. Idle channel noisec. Slope overloadd. Quantization errorAnswer:

49. Results when the input signal frequency is higher than the DAC can handle.a. Overload distortion

b. Idle channel noisec. Slope overloadd. Quantization errorAnswer:

50. A problem associated with delta modulation.a. Granular noiseb. Overload distortionc. Quantization noised. None of the aboveAnswer:

51. A type of sampling where the sample voltage is held at a constant amplitude during the A/D conversion time; this is done by sampling the analog signal for a short period of time.a. Natural samplingb. Constant samplingc. ADC samplingd. Flat-top samplingAnswer:

52. A type of sampling, the sample time is made longer and the analog-to-digital conversion takes place with changing analog signal. This introduces more aperture distortion and requires a faster A/D converter?a. Natural samplingb. Constant samplingc. ADC samplingd. Flat-top samplingAnswer:

53. If the sampling frequency is less than twice the maximum analog input frequency, which of the following will occur.a. Aliasing b. Foldover distortionc. Crossover distortiond. A and B aboveAnswer:

54. Magnitude of the minimum step size.a. Quantization b. Resolution c. Pixel d. All of the aboveAnswer: