MAP-algorithm with fixed-point representation for software radios

The international mobile communication system IMT2000 will enable very flexible communication, which means variable data rates from 8 kbit/s speech up to 2 Mbit/s for data transmission. In November 1999 five modes of IMT2000 have been specified. In several modes turbo codes are proposed to enable bit error rates (BER) as low as 10/sup -6/ for high quality data services. Usually for this type of channel coding two MAP-algorithms, based on the maximum a posteriori criterion, are used for decoding. The MAP-algorithm utilizes soft input information and produces soft output information. The practical implementation of the MAP-algorithm, respectively its computational reduced version log-MAP and max-log-MAP, is investigated.