但是，在实际中发现，用某种“特定”方法连接起来的最优信源编码器和信道编码器，并不一定能构成最佳通信系统。

But, it may be not a optimum system using an "AD hoc" method to combine the optimum source with channel coders in practical communication systems.

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由于传输环境的剧烈变化，移动通信系统不能工作在最佳的信源编码速率和信道编码速率。

Due to the intense change of the transmission environment, the mobile communication system can not work in the optimal source coding rate and channel coding rate.

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