Chapter 12: Digital Modulation and Modems

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Malcolm Moody
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1 Chapter 12: Digital Modulation and Modems MULTIPLE CHOICE 1. FSK stands for: a. Full-Shift Keying c. Full-Signal Keying b. Frequency-Shift Keying d. none of the above 2. PSK stands for: a. Pulse-Signal Keying c. Phase-Signal Keying b. Pulse-Shift Keying d. Phase-Shift Keying D 3. QAM stands for: a. Quadrature Amplitude Modulation c. Quadrature Amplitude Marking b. Quadrature Amplitude Masking d. none of the above 4. In the equation I = ktb, I is measured in: a. amperes c. bits b. amperes per second d. bits per second 5. In the equation C = 2Blog 2 M, M is the: a. margin of noise c. number of possible states per symbol b. modulation index d. maximum number of symbols per second 6. An "eye pattern" shows a good channel when: a. the eye is maximally open c. the eye is half open b. the eye is maximally closed d. the eye alternately opens and closes 7. What you see in an eye pattern is the effect of: a. too many bits high c. intermodulation distortion b. too many bits low d. intersymbol interference D 8. High-frequency radioteletype systems commonly use: a. FSK c. PSK b. AFSK d. QAM

2 9. Instead of a single bit, a QPSK symbol contains: a. a byte c. a dibit b. 4 bits d. a Q-bit 10. To reduce the need for linearity, π/4 DQPSK uses: a. angles of 0, 90, 180, and 270 degrees c. angles of π/4, 2π/4, 3π/4, and 4π/4 b. angles of 45, 135, 225, and 315 degrees d. double phase-shift angles 11. For QAM, a "constellation diagram" shows: a. location of symbols in "symbol space" c. effects of noise on symbols b. separation of symbols in "symbol space" d. all of the above D 12. For QAM, the two dimensions of its symbol space are: a. amplitude and frequency c. frequency and phase angle b. amplitude and phase angle d. I-bits and Q-bits 13. The specs of the old Bell type 103 modem were: a. 300 bps, full-duplex, FSK c bps, full-duplex, FSK b. 600 bps, full-duplex, FSK d bps, half-duplex, FSK 14. ITU is an abbreviation for: a. International Telephony Unit c. International Telecommunications Union b. International Telephony Union d. International Telecommunications Units 15. The ITU is under the auspices of: a. CCITT c. IEEE b. the U.N. d. ANSI 16. High-speed modems equalize the line to compensate for: a. noise and interference b. uneven phase and frequency response c. low SNR d. inconsistent bit rates at either end of channel 17. The bits sent to allow equalization are called: a. Gaussian bits c. a training sequence b. random bits d. a random sequence

3 18. The V.90 standard is issued by: a. the EIA c. the ITU b. the TIA d. the ISO 19. MNP2, MNP3, MNP4, and MNP10 are all: a. data-compression schemes c. both a and b b. error-correction protocols d. none of the above 20. MNP5 and V.42 bis are both: a. data-compression schemes c. both a and b b. error-correction protocols d. none of the above 21. In RS-232, flow control is done using: a. RTS/CTS handshake c. both a and b b. XON/XOFF characters d. none of the above 22. The official name for RS-232C is: a. RS-232C c. ISO-232C/D b. EIA-232D d. ANSI-232C 23. In RS-232, a modem would be: a. a DTR c. a DCE b. a DSR d. a DTE 24. In RS-232, a personal computer would be: a. a DTR c. a DCE b. a DSR d. a DTE D 25. On a DB-9 RS-232 connector, signal ground is pin: a. 1 c. 5 b. 3 d On a DB-25 RS-232 connector, signal ground is pin: a. 1 c. 5 b. 3 d. 7

4 D 27. The minimum lines required for RS-232 are: a. TD and RD c. TD, RD, DSR, and signal ground b. TD, RD, and signal ground d. TD, RD, RTS, CTS, and signal ground 28. Hardware flow control uses: a. XON and XOFF c. RTS and CTS b. TD and RD d. DSR and DCD 29. Software flow control uses: a. XON and XOFF c. RTS and CTS b. TD and RD d. DSR and DCD 30. Which voltage represents a binary zero on an RS-232 data pin: a. +15 volts c. +9 volts b. +12 volts d. all of the above D 31. DSL stands for: a. Data Signal Line c. Digital Subscriber Line b. Digital Signal Line d. Double-Speed Loop 32. ADSL stands for: a. Asynchronous DSL c. Analog DSL b. Asymmetrical DSL d. All DSL 33. In a CATV system, HFC stands for: a. Head Frequency Control c. Hybrid Fiber-Coax b. Hybrid Frequency Control d. Hybrid Fiber Control 34. In a CATV system, CMTS stands for: a. Cable Modem Terminal Server c. Cable Modem Terminal System b. Cable Modem Transmission System d. Cable Modem Transmission Server 35. A "splitter" at the subscriber end is not required for: a. Any DSL scheme c. ADSL Lite b. ADSL d. none of the above

5 COMPLETION 1. RTS means Request To. Send 2. The response to RTS is. TS 3. FSK stands for Frequency-Shift. Keying 4. DSR stands for Set Ready. Data 5. QAM stands for Amplitude Modulation. Quadrature 6. The number of symbols per second is called the rate. baud 7. The 2 bits of information in a QPSK symbol is called a. dibit 8. QPSK uses different phase angles. four 9. DPSK stands for PSK. Delta 10. The QAM amplitude-phase combinations are shown with a diagram. constellation 11. ITU stands for International Union. Telecommunications 12. In QAM modems, coding adds extra bits to improve performance on a noisy line.

6 Trellis 13. is used in a high-speed modem to compensate for uneven frequency and phase response on a line. Equalization 14. The maximum allowed speed for a modem on a dial-up line is about bps. 54k 15. The nominal maximum speed on an RS-232 cable is bps. 20k 16. In RS-232, the line is asserted when the analog carrier from another modem is being received. CD DCD RLSD 17. Between hardware flow control and software flow control, flow control is preferred. hardware 18. A voltage higher than volts should be considered a high on an RS-232 receiver A modem cable is used to connect two DTEs via their serial ports. null 20. ADSL stands for DSL. symmetrical 21. A typical CATV system is organized as a network. tree 22. In a CATV system using cable modems, a is used to put several channels of data onto a fiber-optic backbone. MTS 23. is the process of synchronizing transmitted data from cable modems to a CMTS.

7 Ranging 24. systems send high-speed data over a POTS line while sharing the line with dialup service. DSL 25. The version of ADSL does not require a splitter at the subscriber end. lite 26. modulation divides the line bandwidth into many narrow bands called tones or bins for ADSL. DMT 27. A DSLAM is a DSL Access. Multiplexer SHORT ANSWER 1. Calculate the bits per second capacity of a system sending 1000 symbols per second with 16 possible states per symbol How many points will be on the constellation diagram of a QAM system using 8 phase angles and 2 amplitude levels? A CATV system has 100 cable-modem customers sharing a single channel with a data rate of 36 Mbps. If half the modems are active at any given time, what bit rate can a customer expect? 720 kbps 4. A DMT system uses 4.3-kHz bins on a 1-MHz cable. Approximately how many bins are there? Assuming a maximum symbol rate of 400 per second, how many possible states must a symbol have to achieve a data rate of 1200 bps?

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