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#1 2017-Nov-18 03:34:34

barobaro
Member
Registered: 2017-Nov-18
Posts: 1

Advantage of scrambling data ?

Hi everyone.
I read a description about scrambler that payload bits are scrambled to avoid long runs of constant values but I don't understand how does the long run of constant values negative impact the data transmitting and why do we have to use a scrambler to avoid that one?
Please help me, thank you very much.

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#2 2017-Nov-18 12:17:03

murphpo
Administrator
From: Mango Communications
Registered: 2006-Jul-03
Posts: 5159

Re: Advantage of scrambling data ?

Real-world data contains long runs of constant values. The broadcast MAC address, for example, is 48 1's in a row. In an OFDM system constant data would lead to vary large peaks in the time-domain signal (IFFT(constant) -> delta function). Large peaks are bad for analog circuits - most power amplifiers, for example, cannot apply uniform gain over a large dynamic range, and clipping in a PA leads to degraded transmitted waveforms. The 802.11 spec defines the data scrambler to "whiten" the transmitted data, by replacing long runs of constant values with pseudo-random values that (ideally) result in lower PAPR.

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