2. Most individual data communicating devices require relatively modest datarate support.2.15 How is interference avoided by using frequency division multiplexing?6).Each signal requires a certain bandwidth centered on its carrier frequency, referredto as a channel. To prevent interference, the channels are separated by guard bands,
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which are unused portions of the spectrum (not shown in the figure).2.16 Explain how synchronous time division multiplexing works.synchronous TDM, referring to the fact that time slots are preassigned and fixed. Hence thetiming of transmission from the various sources is synchronized. In contrast, asynchronousTDM allows time on the medium to be allocated dynamically. Unless otherwise noted, the termTDM will be used to mean synchronous TDM.A number of signals [mi(t), i = 1, n] are to be multiplexed onto the same transmissionmedium. The signals carry digital data and are generally digital signals. Theincoming data from each source are briefly buffered. Each buffer is typically one bitor one character in length. The buffers are scanned sequentially to form a compositedigital data stream mc(t). The scan operation is sufficiently rapid so that each bufferis emptied before more data can arrive. Thus, the data rate of mc(t) must at leastequal the sum of the data rates of the mi(t). The digital signal mc(t) may be transmitteddirectly, or passed through a modem so that an analog signal is transmitted. Ineither case, transmission is typically synchronous.
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