A list sphere decoder based turbo receiver for groupwise space time trellis coded (GSTTC) systems

A list sphere decoder (LSD) based turbo receiver is introduced for groupwise space time trellis coded (GSTTC) systems. It can approach the single-user bound by iteratively exchanging soft information between the LSD and the soft-input soft-output (SISO) maximum a posteriori (MAP) space time trellis (STT) decoder. The LSD approximates the SISO maximum likelihood (ML) channel detector using only a subset of hypotheses, and thus greatly reduces the computational complexity. Simulation results show that good FER and BER performances as well as fast convergence can be achieved with a very small list for simple STT codes with a small number of states. For more powerful codes with more states, a large list is required. Compared with the linear minimum mean square error (LMMSE) turbo receiver, the proposed receiver is more flexible and converges faster. Its performance can always be improved by increasing the list size, but at the cost of increased complexity. For higher order modulation, the performance gain is larger.