IS250 Computer Based Communications Networks and Systems

Spring 2010

Assignment 2

Assignment 2 is due at 2pm (before start of class) on Tuesday 2/16. Please see grading policy on course homepage for additional details regarding early/late submissions.

Please submit your answers in plain text (no attachments) to i250hw@ischool.berkeley.edu.

1. In the lecture slides, we discussed how a data string "10110010" is encoded by USB using a NRZ-I scheme.

(a) Show how the same data string is encoded by Ethernet, using the Machester Encoding scheme.

(b) In what way is the Machester Encoding scheme superior (or not) to the NRZ-I scheme?

2. Channel capacity:

(a) If two signal levels are used, what is the data rate that can be sent over a coaxial cable that has an analog bandwidth of 6.2MHz? (Comer 7.22)

(b) If a telephone system can be created with a signal-to-noise ratio of 40dB and an analog bandwidth of 3000 Hz, how many bits per second can be transmitted? (Comer 7.25)

3. Using Shannon's Theorem, explain why practical amplitude modulation systems keep the carrier near maximum strength. (Comer 10.3)

4. What is the difference between modulation and multiplexing?

Note: For Question 1(a), you can show the resulting waveform using a fixed-width font (see example below) or attach an image file to your submission.

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