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| 科目：通訊系統 | （共1頁 第1頁） |
| 1. | (20%) Consider an AM wave transmitted through an additive white Gaussian channel as shown by  where the noise w(t) is of zero mean and power spectral density N0 / 2. Determine a figure of merit of this AM system. |
| 2. |
(20%) In the filtering scheme for processing side-bands as shown in the following figures, find the condition to recover the message signal m(t) in the coherent receiver.
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| 3. | (10%) Consider an FM signal of carrier frequency  , which is produced by a modulating signal m(t). Assume that is large enough to justify treating this FM signal as a narrow-band signal. Find an expression for Hilbert transform. |
| 4. | (10%) What is the intersymbol interference (ISI) and what is
its effect on a digital communication system? Describe the principles
of the techniques that can be applied to reduce this effect. |
| 5. | (20%) Find the error probability for a BPSK system with a bit
rate of 10 Mbits/s. The received waveforms  ,
are coherently detected with a matched filter. The value of A is 30 mV.
Assume that the single-sided noise power spectral density is N0
= 10-11 W/Hz and that signal power and energy per bit are normalized
relative to a 1 Ω load. |
| 6. | (20%) Design a ternary Huffman code, using 0, 1, and 2 as letters, for a source with output alphabet probabilities: {0.05, 0.11, 0.14, 0.17, 0.19, 0.22, 0.12}. What is the resulting average codeword length? Compare it with the entropy of the source. |
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