ThenThe encoder sends three sub-blocks of bits. The first sub-block is the ''m''-bit block of payload data. The second sub-block is ''n/2'' parity bits for the payload data, computed using a [[convolutional code]]. The third sub-block is ''n/2'' parity bits for a known [[permutation]] of the payload data, again computed using a convolutional code. That is, two redundant but different sub-blocks of parity bits for the payload are sent. The complete block has ''m+n'' bits of data with a code rate of ''m/n''.
