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发表于 2011-2-11 22:08 |只看该作者 |倒序浏览

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PROBLEM B: Repeater Coordination

中继器协调

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.

VHF（甚高频）无线电频谱要牵涉到视距传播与接收。这方面的限制可以通过“中继器”来解决。中继器可以接收到一个比较弱的无线电信号，对其进行放大，然后通过一个不同的频率重新传送这个信号。这样，通过中继器，低功率的移动设备用户（比如移动电台）可以与另一个无法实现直接通讯的用户联络。然而，两台中继器之间会产生干涉，除非两台中继器之间的距离足够远或者它们使用的频率相差很大。

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.

除了距离上的隔离，“连续音频编码静噪系统”（CTCSS，一般昵称“专用线路”）可以缓解中继器的干涉问题。这个系统将想通过某一中继器进行通讯的用户所发出的单独的次音频发送给那个中继器。那个中继器只对它自己特定专用线路的信号进行回应。通过这个系统，两个邻近的中继器可以使用相同的频率进行接收和传播，这样更多的中继器和移动设备可以在同一个区域内正常工作。

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.

现有一个直径40英里的圆形区域，如果同时有1000个用户要进行通讯，需要最少多少中继器？假设无线电的频率范围是145到148MHZ（兆赫），中继器的发射装置频率高于或低于接收装置频率600kHZ（|发射频率-接收频率|>600kHz），有54条专用线路可供使用

How does your solution change if there are 10,000 users?

如果区域内的用户变为10 00个，结论有什么变化？

Discuss the case where there might be defects in line-of-sight propagation caused by mountainous areas.

讨论在视距传播（用户之间直线传播无线电）会产生缺陷的山区中的情况。

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