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hw2 - CS/ECE 438 Communication Networks for Computers...

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CS/ECE 438: Communication Networks for Computers Spring 2010 Problem Set 2 Due: start of class, Wednesday, February 10 th . Direct Link Networks and Error Correction Codes Assigned reading: Peterson and Davie: Chapter 2.1 2.4. All problems carry equal weight. 1. Noisy Channel Data Rates The decibel is a measure of the ratio between two signal levels: N db = 10 log 10 (P 2 /P 1 ), where N db = the number of decibels, P 1 = the input power level and P 2 = the output power level. a. A telephone line is known to have a loss of 20db. The input signal power is measured as 0.50 watt and the output noise is measured as 8 watt. Using this information, calculate the output signal-to-noise ratio in dB. b. What is the capacity of this phone line with a frequency range of 100 Hz 1000 Hz? c. If the attenuation rate of this phone line is 2db/km, and the minimum output signal is 0.00025 watt, given the input signal from part a), how long can the phone line be before requiring a repeater? 2. Encoding, Channel Capacity and Modulation a. Show the NRZ, Manchester, NRZI and 4B/5B encoding signals (the resulting NRZI signal for 4B/5B), using a diagram similar to that in Figure 2.10, p. 82, P&D, for the data bit sequence 10111 10100 11011 10110. To be definite, suppose the NRZI signals begin at a low voltage.

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