Update README.md

README.md

@@ -33,6 +33,7 @@ To find the sequence you just need to search through the signal one sample at a
 ## Coarse CFO Detection/Adjustment
 Without knowing the ZC sequence parameters, all that remains are the cyclic prefixes, and cross correlating the ZC sequence halves
 Neither is great as both are spread pretty far apart.  Nothing like the 16 sample IEEE 802.11 preambles that are amazing for coarse CFO.  Perhaps the second ZC sequence can be used?  In the time domain it looks like it repeats itself over and over rapidly.
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 Update: I've skipped this step as my primary goal is to get to bits.  For some reason my logic that uses the cyclic prefix is off by a factor of 9.  For now I have done the correction by hand.
 
 ## Fine CFO Detection/Adjustment
@@ -41,6 +42,7 @@ Update: I've skipped this as well.  My corrections from the Coarse CFO have take
 
 ## Phase Correction
 Another one that needs a known sequence in the burst.  The good news is that all of the data carriers are QPSK, so there's only 4 ways to rotate the constellation.
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 Update: I've skipped this too.  Handily the burst I am looking at right now didn't need much in the way of phase adjustments
 
 ## Symbol Extraction
@@ -48,10 +50,12 @@ This is super simple and just requires being time and frequency aligned with kno
 
 ## Descrambling
 Rumor is that there is a scrambler in use.  It's not clear to me if the scrambler is before or after FEC, but it will need to be dealt with.  Supposedly it's LTE standard.
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 Update: the scrambler is definitely before the FEC.  I found a really nice writeup about it at https://www.sharetechnote.com/html/Handbook_LTE_PseudoRandomSequence.html.  The scrambling sequence seems to be made out of two Linear Feedback Shift Registers (LFSRs) combined together.  The intital state of the first LFSR is a constant value, but the second LFSR needs certain parameters that relate to the link.  Unfortunately I don't have those parameters.  The only good news is that is *only* a 31-bit exhaust to brute force.  So ~ 2.5 billion attempts and you're assured success!  In the event that the Turbo decoder parameters are magically known then maybe this won't be so bad.
 
 ## Turbo Product Code Removal
 It is assumed that the demodulated data contains an LTE standard TPC.  There are libraries that can handle this (hopefully)
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 A new wrinkle here is that under the Turbo code is going to be "Rate Matching" bits.  I have no idea if that's going to be a standard process that doesn't vary depending on link parameters that aren't already known.
 
 ## Deframing