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The definition of signal rate is number of signal elements (timewise shortest unit) sent in 1s. The book says that the signal rate of all 1s or all 0s may be different from a data pattern of alternating 0s and 1s. (And there can be three cases : best, worst and average) The strange thing is, it means that the signal rate changes in real time. Data rate and signal rate are interconnected by a formula : S = N/r How does the signal rate change dynamically even if N(data rate) and r(number of data elements per one signal element) are static?

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Data Communications and networking (of Forouzan)

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    \$\begingroup\$ "the book"? Is there only one? We need more context. Is it talking about error recovering encoding schemes? \$\endgroup\$ – PlasmaHH Sep 17 '18 at 8:14
  • \$\begingroup\$ @PlasmaHH Well it seems that there's no extra explanation. The chapter introduces the basic terminology like data rate and signal rate. It does not look like being related to error recovering maybe. \$\endgroup\$ – Riddle Aaron Sep 17 '18 at 9:06
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    \$\begingroup\$ Which book? There are many, many books on communications systems and modulation theory of widely varying quality. Give us a cite for the bit you are talking about and maybe someone can either explain what the book is trying to say or tell you that the book is just plain wrong (It happens). \$\endgroup\$ – Dan Mills Sep 17 '18 at 10:59
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Even if the transmitter sends the same "signal" (the more common term is "symbol") several times in a row, it does not mean that the signal rate (baud rate) has changed.

However, if the receiver is relying on signal changes in order to perform clock recovery, long strings of the same signal could present problems. Many communications systems employ data scrambling circuits in order to minimize the probability of this happening.

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  • \$\begingroup\$ Then do you mean that signal rate is static too? \$\endgroup\$ – Riddle Aaron Sep 17 '18 at 11:29
  • \$\begingroup\$ Yes, that is the misconception in the book. \$\endgroup\$ – Dave Tweed Sep 17 '18 at 11:31
  • \$\begingroup\$ One more, are signal rate and baud rate different notion? I searched it on Google and I found that the symbol rate(=baud rate) is the number of symbol in the time unit, which is a different description from the book \$\endgroup\$ – Riddle Aaron Sep 17 '18 at 11:33
  • \$\begingroup\$ No, that part is correct. Baud rate is the number of signals (symbols) per second. \$\endgroup\$ – Dave Tweed Sep 17 '18 at 11:34

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