Linear Minimum Mean Square Turbo Equalization with 16QAM Multiple Trellis Coded Modulation

Linear minimum mean square error (LMMSE) turbo equalization with Gray mapped rate 3/4 1times16QAM and rate 6/8 2times16QAM trellis coded modulation (TCM) are compared on an unknown and time-varying frequency-selective channel. Frequency hopping is used for increased diversity, and the channel is tracked by linear interpolation between training sequence based estimates where a training sequence is inserted into the start and end of each frequency hop block. The TCM codes are optimized with regard to good low SNR performance. Turbo equalization with 2times16QAM TCM shows the best bit error performance, due to increased diversity relative to 1times16QAM TCM and better low SNR performance. The search procedure for finding optimum 2times16QAM codes is described.