A novel bandwidth efficient coding scheme employing turbo codes

We have investigated a novel bandwidth efficient channel coding scheme that has a code structure similar to binary turbo codes but employs Ungerboeck codes as component codes. The combination of turbo codes with powerful bandwidth efficient component codes leads to a straightforward encoder structure and allows iterative decoding in analogy to the binary turbo decoder. However, certain special conditions need to be met at the encoder, and the iterative decoder needs to be adapted to the decoding of the component Ungerboeck codes. The scheme has been investigated for 8 PSK and 16 QAM modulation, for which a first attempt at component code optimization was performed. Simulation results are presented and the scheme is compared with Ungerboeck codes on their own and also turbo codes with Gray mapping. The results show that the novel scheme is markedly superior at comparable complexity.