CODED MODULATION WITH GENERALIZED MULTIPLE CONCATENATION OF BLOCK-CODES

Block coded modulation schemes can be obtained by generalized concatenation of the modulation and block codes of length N. The modulation is considered as a code in the euclidean space IR2. One obtains a concatenated code in the euclidean space IR2N using binary block codes. In this paper the obtained code is taken as an inner code, which is concatenated with block codes once again. The advantage of this multiple concatenation compared to single concatenation is the use of very short (easy to decode) outer codes such as repetition codes and even weight codes. The construction of multiple concatenated codes is presented. A decoding method is given which uses soft decision decoding for the outer codes. As examples twice concatenated codes are designed for QPSK and 8-PSK modulation. Computer simulations have been performed in order to compare multiple concatenated codes to single concatenated codes of equal length and rate. The multiple concatenated codes investigated here are found to be better than the single concatenated codes as far as the symbol error probability as well as the decoding effort is concerned.