Computer Science 851
                           Quiz 2           Name _______________________


1. What bandwidth is required to support a bit rate of 100,000 BPS
   on a channel with a 30dB SNR?









2. Suppose a PCM scheme supports a bit rate of  49,000 bps and
   quantizes the signal into 127 distinct levels.  What is the
   highest frequency that it can carry?









3. What bit rate is required to support a new "hi-fi" PCM phone
   that supports frequencies to 16Khz and quantizes the signal
   into 4096 discrete levels.









4. The use of very small slot sizes in a TDM multiplexing scheme is:

   a. Inefficient and shouldn't       b. Generally shouldn't be used for
      be used in either STDM or ATDM     SDTM but is OK for ATDM

   c. Generally shouldn't be used     d. Perfectly OK for both
      for ATDM but is OK for STDM

5.  Recall the Bell 212A modem discussed in class.  It signalled using
    4 phase angles, 45, 135, 225, and 315 degrees.
    When a long burst of 00000000000000000000 is transmitted,

   a. The modem will emit a             b. There will be a +45 degree
      pure sine wave of the form           phase shift in the signal
      f(t) = sin(wt + 45deg)               every bit time.
      for the duration of the burst

   c. There will be a +45 degree
      phase shift every other bit
      time.

6. Which best characterizes the DS-0,1,2, and STS-1,2,3 telephone
   carriers

   a. they all use the same frame       b. they all use the same frame
      rate and the same frame size         rate but different frame sizes

   c. they all use the same frame size  d. they all use different frame
      but different frame rates.           rates and frame sizes.


7. QAM-64 sends

   a. 2 bits per baud time             b. 4 bits per baud time

   c. 6 bits per baud time             c. 8 bits per baud time


8. In QAM 64 the each of the two carriers use

   a. 2 different amplitudes           b. 4 different amplitudes

   c. 8 different amplitudes           d. 16 different amplitudes


9. With currently deployed WDM technology, the aggregate bit rate that can
    be carried by a single optical fiber is closest to:

    a. one million bits / sec           b. one billion bits /sec

    c. ten billion bits / sec           d. one trillion bits / sec


The Bit rate = buad_rate x log2(V)

10. The maximum baud rate on a channel is primarily constrained by

    a. the bandwidth                    b. the SNR

    c. both equally                     d. neither one is a direct factor

11. The number of possible signalling states V is primarily constrained by

    a. the bandwidth                    b. the SNR

    c. both equally                     d. neither one is a direct factor


12. The main reason digital channels have much lower error rates than analog
   when used over long distances is:

   a. Digital signalling is baseband   c. Digital signals are amplified
      instead of analog.                  rather than regenerated.

   b. Digital signals are regenerated  d. Digital channels have much higher
      rather than amplified.              SNR's than analog.