Arikan 2009: synthetic channels W_N^(i) polarize — as N→∞, each channel is either perfect (Z→0) or useless (Z→1). Rate = fraction of good channels used.
Bhattacharyya parameter Z evolution through polarization stages. Orange=good channels, gray=frozen.
Sorted Bhattacharyya params for each synthetic channel. Info (blue) vs frozen (gray).