Coding gains (dB) over the corresponding uncoded QAM system over AWGN channels

Detection is based on the choice of the codeword which is nearest to the received sequence in the Euclidian distance sense. A particular case of BCM can improve the coding gain in a range of BER from 10^3 to 10^4 without greatly increasing the number of redundant bits, by introducing block codes into multi-state modulation schemes. In the case of a 256-QAM signal transmission system, the introduction of block codes into only 2 of the 8 bit baseband signal streams can improve error correction performance. This is because this method enables the addition of four times the number of redundant bits than conventional error correction schemes.

The code bits (2 bits) are used as “sub-set” signals and the remaining uncoded bits (6 bits) are mapped into signal space to maximize the Euclidean distance based on the Ungerboeck’s set-partitioning method. Sub-set signals are decoded in a process based on a conventional error correcting algorithm. Error correction of uncoded bits is performed only if the sub-set signal is

corrected. At the specific time-slot, the uncoded bits are decoded by selecting a signal point that is located nearest to the received signal point from the coded sub-set signals using soft-decision information.

When the BCH (31,11) code is employed as the above-mentioned block code modulation, a coding gain of about 5 dB can be obtained at a BER of 10^4. The application of block code modulation has led to a coding gain of about 5 dB at a BER of 10^4.