**6. Channel coding**

In the 802.16e definition channel coding constitutes the sum of steps including data randomization, channel coding, rate matching, Hybrid Automatic Repeat reQuest (HARQ), and interleaving . At the beginning of each FEC block is a modulo-2 shift-register of maximum-length whose output is used to randomize the data. This randomization is purely for data integrity by providing PHY encryption and avoiding accidental decode by unintended receivers. In cases where HARQ is used the initial seed of the shift-register is kept the same over the period to allow for joint FEC decoding over several transmissions.

Channel coding is performed on every FEC block, which is n integer long sub-channels and whose maximum depends on channel coding scheme and the modulation constellation. Should the required number of FEC block sub-channels exceed this maximum, then segmentation is done to produce multiple FEC sub-blocks. Encoding and rate matching is done separately for these sub-blocks and then concatenated sequentially [10].
