Wireless Oom

1. Binary XOR operation allows the original symbol reconstruction.
Do spread:
symbol sequence X  (XOR) some code Y => some signal Z
Do despread:
some signal Z (XOR) some code Y => symbol sequence X

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2. Let’s assume there are 10 users who want to send its data X1, X2, …, X10.
Let’s assume they have their own codes Y1, Y2, [...]

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 [...]

First, think about the definition of spreading factor (SF): the number of chips for each symbol.
Second, remember that a chip duration is fixed.
Third, what is symbol? Each symbol can represent some amount of bits. e.g., QPSK, each symbol represents 2 bits.
SF: 2 SF vs. 512 SF
Time: 2*delta vs. 512*delta
Data: 1 symbol vs. 1 symbol
where delta [...]