Patent ID: 7530011

Claim:
A turbo decoding method for decoding an N-bit turbo-encoded signal by repeating element decoding including steps of performing a backward probability calculation which is a repetitive calculation from back to front, performing a forward probability calculation which is a repetitive calculation from front to back and performing a joint probability calculation, an a posteriori probability calculation, and an external-information likelihood calculation using N-number of results of the backward probability calculation and N-number of results of the forward probability calculation, comprising the steps of: providing M-number of element decoders in parallel; dividing, into M-number of divided signals, the N-bit signal to be decoded; applying element decoding to i-th divided signal (i=1, 2, . . . , M) in respective one of the element decoders in parallel; alternately interleaving and deinterleaving the M-number of results of element decoding collectively; and performing turbo decoding by repeating the above operation a prescribed number of times, wherein the step of applying element decoding includes the steps of: performing the backward probability calculation backwards by an excess amount B as an amount of overlap in overlapping windows using (i+1)-th divided signal neighboring to the i-th divided signal, and then performing the backward probability calculation using the i-th divided signal and storing backward probabilities of this backward probability calculation in a memory; performing the forward probability calculation forwards by the excess amount B using (i−1)-th divided signal neighboring to the i-th divided signal, and performing the forward probability calculation using the i-th divided signal; and executing element decoding processing using the forward probabilities calculated after the excess forward probability calculation and the backward probabilities calculated after the excess backward probability calculation which are stored in said memory; the method further comprising the steps of: when the N-bit signal to be decoded is divided into M-number of divided signals, making division size toward the end greater than other division sizes; and performing the backward probability calculation and the forward probability calculation with overlap of the amount B with regard to the other division sizes, and performing the backward probability calculation and the forward probability calculation continuously without overlap with regard to the division size toward the end.