Filter-Based Turbo Equalization with 2X16QAM Trellis Coded Modulation and Partially Iterative Channel Tracking

A system with serially concatenated 2times16QAM multiple trellis coded modulation (MTCM) and linear minimum mean square error (LMMSE) turbo equalization is proposed for an unknown and time-varying intersymbol interference (ISI) channel. The outer and inner codes are a rate 2/3 binary code and a rate 6/8 recursive TCM code respectively. Frequency hopping is included for increased diversity, and each frequency hop channel is initially identified by linear interpolation between two training sequence based estimates. Channel tracking is improved for each new iteration by using a weighted sum of the interpolation based estimate and an estimate made from the soft decoder information. The weights are determined from calculated reliabilities of the estimates. A comparison is made between turbo equalization with this new combined channel estimate, and with only an interpolation based estimate