Posts Tagged wireless

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Why wide bandwidth is needed for high data rate?

For high data rate, simply send fast.

Which one is high data rate ? 2 bits for 1 second vs. 2 bits for 6 seconds.

So, if you want a high data rate, your sending rate should be fast.

Time and frequency relationship is reverse.  Short time duration means wide bandwidth.

That’s why wide bandwidth is need for faster transmission.

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Why smaller spreading factor can achieve higher data rate

Think about the definition of spreading factor: the number of chips for each symbol.
Remember that a chip duration is fixed.
What is symbol? Each symbol can represent some amount of bits. e.g., QPSK, each symbol represents 2 bits.

SF: 2SF vs. 512SF
Time: 2*delta vs. 512*delta
Data: 1 symbol vs. 1 symbol

where delta is chip duration.

With 2SF, you are sending symbol fast (my wife cooks very fast, so she can make lots of food)
With 512SF, you are sending symbol slow (I cook very slow, so I can can make less amount of food than my wife)

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