| 91年 4月12日 11:30 ~ 12:30 電子系通訊組 | 誠實是我們珍視的美德， 我們喜愛「拒絕作弊，堅守正直」的你！ |
| 科目：通訊系統 |
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1.
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Assuming a message signal 
and carrier signal 
, determine the following modulated signals. |
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(a)DSB-SC (5%) (b)SSB (5%) (c)PM (5%) (d)FM (5%) |
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2.
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Model of AM receiver is given in Fig. 1. where |
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is a zero mean white Gaussian noise with power spectral density  |
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Assuming s(t) is larger compared with the noise terms nI(t) and nQ(t). Find: |
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(a) (SNR)c (10%) |
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(b) (SNR)o (10%) |
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3.
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A PCM system uses a uniform quantizer followed by a 7-bit
binary encoder. The bit rate of the system is equal to 
b/s. |
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(a) What is the maximum message bandwidth for which the system operates satisfactorily？ (10%) |
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(b) Determine the output signal to (quantization) noise ratio when a full-load sinusoidal modulating wave of frequency 1 M Hz is applied to the input. (10%) |
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4.
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The average probability of error is  ,
where P0,P1,are a priori
probabilities. Find the optimum threshold  to
minimize Pe. (20%) |
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5.
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A discrete memoryless source has an alphabet of seven symbols where probabilities of occurrence are as described here: |
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(a) Compute the Huffman Code for this source, moving a "combined" symbol as high as possible. (10%) |
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(b) Explain why the computed source code has an efficiency of 100 percent？ (10%) |
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