B题简单意译了一下，希望方便大家理解，非精确翻译~

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电梯直达

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发表于 2011-2-11 10:40 |只看该作者 |倒序浏览

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PROBLEM B: Repeater Coordination

The VHF radio spectrum involves line-of-sight transmission and reception. This limitation can be overcome by “repeaters,” which pick up weak signals, amplify them, and retransmit them on a different frequency. Thus, using a repeater, low-power users (such as mobile stations) can communicate with one another in situations where direct user-to-user contact would not be possible. However, repeaters can interfere with one another unless they are far enough apart or transmit on sufficiently separated frequencies.
甚高频无线电波段包括视线传输和接收。信号收发的限制可以被中继器克服，中继器可以将微小信号放大，再通过设定一个不同的频率将它重新传输出去。因此，通过中继器，信号强度不好的用户可以在一些没有通讯信号的地方进行交流。然而，中继器相互之间的干扰只有在足够远的地理间隔和足够大的波段间隔下才能被消除。
In addition to geographical separation, the “continuous tone-coded squelch system” (CTCSS), sometimes nicknamed “private line” (PL), technology can be used to mitigate interference problems. This system associates to each repeater a separate subaudible tone that is transmitted by all users who wish to communicate through that repeater. The repeater responds only to received signals with its specific PL tone. With this system, two nearby repeaters can share the same frequency pair (for receive and transmit); so more repeaters (and hence more users) can be accommodated in a particular area.
除了地理位置的间隔，亚音频技术也可以消除中继器之间的干扰问题。该系统通过分配给每个中继器一个特定的亚音频从而将所有想通过该中继器进行交流的用户连接起来。中继器只接收一个特定的亚音频信号。在这个系统中，两个相邻的中继器可以共用一个频率组来进行收发，由此更多的中继器和用户可以在一个特定区域内被联系起来。
For a circular flat area of radius 40 miles radius, determine the minimum number of repeaters necessary to accommodate 1,000 simultaneous users. Assume that the spectrum available is 145 to 148 MHz, the transmitter frequency in a repeater is either 600 kHz above or 600 kHz below the receiver frequency, and there are 54 different PL tones available.
在一个半径为40英里的圆形平面区域内，要使1000个模拟用户互相连接最少需要多少个中继器？假定可以使用的波段是145~148兆赫，中继器的发送频率或高于或低于接收频率600千赫，而且共有54个亚音频可用。

How does your solution change if there are 10,000 users?
如果要连接10000个用户，怎么改变决策？
Discuss the case where there might be defects in line-of-sight propagation caused by mountainous areas.
讨论一下由于山区造成的视线传输的缺陷

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