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I'm new to EE, and I was reading an introduction book which says:

long-distance communication requires wide bandwidth

Can anyone give me an intuitive example to understand it? I only know that bandwidth is determined by the signal rate( which is determined by bit rate), but long-distance communication doesn't necessarily mean larger big rate, isn't it?

P.S The context is : Biphase schemes that are suitable for dedicated links between stations in a LAN are not suitable for long-distance communication because of their wide bandwidth requirement.

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    \$\begingroup\$ hehehe which book says that? .. - .. ... .-- .-. --- -. -.. Here is long distance communication at 160 bps. space.stackexchange.com/questions/24338/… \$\endgroup\$
    – user16324
    May 31, 2020 at 14:59
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    \$\begingroup\$ Please post more context from the book, perhaps also book title and author. In general, the opposite of what the book claims is true. \$\endgroup\$
    – AndrejaKo
    May 31, 2020 at 15:02
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    \$\begingroup\$ It is far more nuanced than that; as noted by others, the title and author may help with context. \$\endgroup\$ May 31, 2020 at 15:15
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    \$\begingroup\$ yeah, none of the things stated in your question are true as written... context, context, context! \$\endgroup\$ May 31, 2020 at 16:15
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    \$\begingroup\$ hmm googing the book was easy to understand, nrz vs biphase twice the bandwidth. And as everyone has pointed out and knows that wont get you very far. Therefore "Biphase schemes that are suitable for dedicated links between stations in a LAN are not suitable for long-distance communication because of their wide bandwidth requirement." \$\endgroup\$
    – old_timer
    Jun 1, 2020 at 3:44

1 Answer 1

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"long-distance communication requires wide bandwidth"

This statement is not true. The achievable distance of a wireless link depends on several factors: transmit power, gain of transmit antenna, gain of receive antenna, minimum receive power for a given bit error rate.

Usually white noise is assumed. This means that the noise power per Hertz bandwidth is constant or that with greater bandwidth, we observe more noise power. To achieve the same bit error rate, the received power must be increased. With everything else being the same, the achievable distance decreases.

Long story short: the greater the bandwidth, the smaller the achievable distance.

By the way, the bandwidth is not directly connected to the bit rate but rather the symbol rate. M-ary modulation techniques transmit several bits in one symbol. Since the bandwidth depends on how often the symbol changes, we can get a higher bit rate with the same bandwidth. Unfortunately, in general the bit error rate will get worse.

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