Turbo Decoding With Early State Decisions

Sammanfattning: Turbo codes was first presented in 1993 by C. Berrou, A. Glavieux and P. Thitimajshima. Since then this class of error correcting codes has become one of the most popular, because of its good properties. The turbo codes are able to come very close to theoretical limit, the Shannon limit. Turbo codes are for example used in the third generation of mobile phone (3G) and in the standard IEEE 802.16 (WiMAX). There are some drawbacks with the algorithm for decoding turbo codes. The deocoder uses a Maximum A Posteriori (MAP) algorithm, which is a complex algorith. Because of the use of many variables in the decoder the decoding circuit will consume a lot of power due to memory accesses and internal communication. One way in which this can be reduced is to make early decisions. In this work I have focused on making early decision of the encoder states. One major part of the work was also to be sure that the expressions were written in a way that as few variables as possible are needed. A termination condition is also introduced. Simulations based on estimations of the number of memory accesses, shows that the number of memory accesses will significantly decrease.