Turbo-codes and turbo-coded modulation in CDMA mobile radio systems for short frame transmission

Binary parallel concatenated recursive convolutional codes termed turbo-codes have received great attention due to their amazing error correcting capabilities. Nevertheless, reaching near Shannon limit performance is only possible with very large interleavers prohibiting an application in speech-transmission. This paper presents simulation results for a short-frame data transmission system based on DS-CDMA (direct-sequence code division multiple access) employing turbo-codes. Furthermore, the performance of a turbo-coded modulation scheme is investigated with respect to the typical conditions of DS-CDMA systems. As a result, it is shown that turbo-codes are no longer superior to classical convolutional codes if the same decoding costs are assumed. Additionally, simulation results illustrate that coded modulation schemes are not well suited for the application in CDMA systems. Finally, it is proved that an accurate channel estimation is necessary for allowing high coding gains