Generating two-dimensional turbo codes, with sub-codes at a plurality of different coding rates, there being at least two sub-codes with the same coding rate

摘要

The output of a turbo coder is punctured to produce a sub-code with a lower coding rate than the output of the turbo coder. A puncturing matrix defines which elements of the output of the turbo coder are to be retained in the sub-code. A set of sub-codes is produced in this manner, each sub-code of the set having the same coding rate, but being generated using a different puncturing matrix to any other sub-code. A plurality of different sets of sub-codes are produced, the sub-codes of each set having a different coding rate to the sub-codes of any other set. A first sub-code is sent initially, and an ARQ signal may be returned to indicate that a second sub-code is required. The second sub-code may have the same coding rate as the first sub-code, or a different coding rate to the first sub-code. Subsequent sub-codes may be required. The second sub-code is code combined with the first sub-code at the receiver. The collection of sub-codes produced at the transmitter is referred to in the application as a two-dimensional quasi-complimentary turbo code (QCTC). In one embodiment the order of sub-codes within a set is permuted to ensure a uniform distribution of puncturing. In another embodiment, low rate sub-codes are generated at the transmitter by concatenating a plurality of higher rate sub-codes.