Homework 2 - Chapter 2

Answer the following questions. Each question is worth 2 points.

1. A constellation diagram has points at (1, 1) and (2, 2). Is this using phase modulation, amplitude modulation or both?
2. A constellation diagram has points arranged in a circle centered around origin (0,0). Is this using phase modulation, amplitude modulation or both?
3. Consider an aDSL modem that allocates 32 channels to upstream and the remainder to downstream. 1% of the channels in each stream are unusable due to noise. Assuming the remainder of the channels can use QAM-64 modulation and sample at 4000 baud, what is the capacity of each stream?
4. If a trunk has 2-MHz bandwidth, what is the maximum number of calls that can be multiplexed onto the line using FDM? Assume each call has a 4kHz bandwidth.
5. Consider a variation on FDM that has guard bands between each frequency band. Assuming that the frequency bands are still 4kHz wide and that the guard bands are 400Hz wide, how many calls can now be put on the above 2-Mhz trunk?
6. What percentage of an OC-1 line is overhead? What percentage is available for user data?
7. You are being asked by your boss to decide whether to use a T3 or OC-1 line for the office. What factors would you consider while making this decision?
8. What is the primary difference between message switching and packet switching?
9. With DSL, each house is connected to the central office by the local loop, which creates a point-to-point link between the two. With cable modems, each house is connected to a shared coax line, which is a broadcast network. Give the strengths and weaknesses of each approach (point-to-point and broadast).
10. A cable company advertises a 7Mbps download cable modem plan. The company has allocated 192Mbps per coax cable to carry cable modem downloads. There are 500 houses per coax line. If the company wants to make sure that all users could simultaneously download at 7Mbps, what percentage of houses could subscribe to the cable modem service?