2011美赛题目.doc

PROBLEM B: Repeater Coordination The VHF radio spectrum(无线电频谱) involves line-of-sight（可视传输） transmission and reception. This limitation can be overcome by “repeaters(中继器),” which pick up weak signals, amplify（放大） 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（干扰） with one another unless they are far enough apart or transmit on sufficiently separated frequencies. 无线电频谱包括lineofsight的可视传输和接收。这种限制可以通过使用中继器来克服。中继器可以接收弱的信号，放大信号，然后重新以不同的频率传输。因此，使用一个中继器，低功率的用户（比如移动基站）可以同另外一个通信，在两者之间直接通信不能实现的时候。然而，中继站能够干扰另外一个中继站， 除非他们之间的距离足够远或者他们在分隔足够远的频段上通信。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（次声频） 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. 除了地理上的分隔之外，ctscc（连续音频编码静噪系统），有时也被称为专线的技术可以用来减少干扰和冲突。这种系统为每个中继器联接上一个独立的次声频，给每个想通过此中继站通信的用户。中继站只针对收到的附加有它的特殊的专线音调的回应。通过这种系统，两个相邻的中继站能够使用相同的频率的频段对儿（用于接收和发送）。所以更多的中继站和更多的用户能够在一个特定的区域中使用和适应。For a circular flat area of radius 40 miles radius, determine the minimum number of repeaters necessary to accommodate 1,000 simultaneous（同时的） users. Assume that the spectrum（光谱，频谱） 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. 对于一个圆形的，半径为40英里的一个区域，决策能够同时容纳1000个使用者的最小中继站数目。，假设可用的频谱段为145mhz到148mhz，发射器的频率在一个中继器中是高于或者低于接收频率的600mhz，有54个不同的专线调可以使用。How does your solution change if there are 10,000 users? Discuss the case where there might be defects in line-of-sight propagation caused by mountainous areas.( e/ S, K# ! ; I- ) B题中继站的协调 8 a! w. . g! Xs/ q- M甚高频无线电频谱包含信号的发送和接受。这种限制可以被中继站所克服。中继站可以捕捉到微弱的信号，然后把它放大，再用不同的频率重新发送。这样，低功耗的用户，例如移动电话用户，在不能直接与其他用户联系的地方可以通过中继站来保持联系。然而,中继站之间会互相影响,除非彼此之间有足够远的距离或通过充分分离的频率来传送。 & WH) w7 G5 K4 g4 J+ j除了地理的分离、“连续编码音调控制系统”(CTCSS),有时被称为“私人专线”(PL)、通过这项技术可以减轻干扰问题。该系统连接每个中继站，靠的是所有通过同一个中继站连接的用户发送的独立的亚音频音调来连接。中继站只回应接收到的具有特殊PL的语调的信号。通过这个系统,两个附近的中继站可以共享相同的频率对(包括接收和发送);对于更多的中继站(并且更多的用户)可以提供在一个特定的区域。 e% ?. / C U& Q+ k1 m& B在一个半径40英里的圆形区域，请你设计一个方案，用最少量的中继站来容纳1000同时在线用户。假设频谱范围是145到148兆赫,在中继站中的发射机的频率要么是600千赫以上，要么低于接收机频率600千赫、并且这里有54个不同的PL可用。H4 _ 如果这里有10,000个用户，如何改变你的解决方案。 a* x0 E5 Y4 5 T% M3 R- s* I 在由于山区引起信号传播的阻碍的地区，讨论这样的情形。PROBLEM B:Repeater CoordinationThe 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.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.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 re