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# 大學 計算機概論 網路資訊問題 煩請高手火速解答

1. If the baud rate of a line were 9600 and 16 different is signaling levels were used, what is the equivalent bit rate of the line? What will happen if 4906 different signaling levels were used for the same situation?

2. Approximately, how long does it take to download a compressed file of size 20

MB using a medium with a bandwidth of 512 Kbps?

3. If P_final is one nanoWatt(1* 10的負九次方Watts)and P_ref is one milliWatt(1* 10的負三次方 Watts), what is the gain or loss in decibels? Is this value positive or negative? Does the value represent a gain or a loss in power?

Update:

Rating

(1a) bits/sym = log2(signal levels);

so the bit rate = 9600 * log2(16) = 9600*4

(1b) if the signal level is 4906 (4096?)

bit rate = 9600 * log2(4906) = 9600 * 12.26

(2) if you ignore the followings:

+ signaling errors

time t = file_size/medium_rate

=20MB/512Kb/s

=160Mb/512Kb/s

=320s

(3a) -60dB

(3b) negative

(3c) loss of 60dB.

2009-11-10 05:09:05 補充：

(3a) dB = 10 * log10(p_final/p_ref)

= 10 * log10(1x 10^-9/ 10^-3)

= 10 * (-6)

= -60dB