Uploads from Travis Goodspeed, tagged 80211b

Data Scrambler 7'b1111111

nobody@flickr.com (Travis Goodspeed) — Sat, 05 Nov 2011 18:35:23 -0700

The 802.11B data scrambler can begin at any state except 7'b1111111.

The upper view shows a legal start state of 7'b0000000 while the lower view shows the illegal state. In the first case, the output symbols are randomized, while in the illegal case, the output consists of only 1's until the SFD.

802.11B Preamble

nobody@flickr.com (Travis Goodspeed) — Fri, 04 Nov 2011 22:25:10 -0700

Travis Goodspeed posted a photo:

The 802.11B Preamble consists of 128 scrambled 1's. This zoomed-out view of a couple thousand 1's shows what different regions of the preamble might look like.

The descrambler self-synchronizes to the scrambler, so the starting state isn't terribly important. All starting states except 0b1111111 are valid, as that state produces only 1's as output when given them as inputs.

802.11B Scrambler Test Bench

nobody@flickr.com (Travis Goodspeed) — Sat, 05 Nov 2011 17:23:11 -0700

Travis Goodspeed posted a photo:

This is a byte from the 802.11B SFD, including scrambler and descrambler states. (The descrambler is delayed a bit, so it is still showing an 0xFF from the preamble.)

802.11B PLCP Scrambler, Descrambler

nobody@flickr.com (Travis Goodspeed) — Sat, 05 Nov 2011 17:18:37 -0700

Travis Goodspeed posted a photo:

This shows an 802.11B scrambler a PLCP header as input and producing a scrambled output, which is then fed to a descrambler. The middle wave is the version as it might appear on the air at 1Mbps BPSK.

802.11B Scrambler Synch

nobody@flickr.com (Travis Goodspeed) — Sat, 05 Nov 2011 16:26:18 -0700

Travis Goodspeed posted a photo:

This test bench shows an 802.11B descrambler self-synchronizing to the state of the scrambler. The X's here representing unknown or unreliable state.