Filter-based turbo equalization with 2×16QAM trellis coded modulation and partially iterative channel tracking

  • Authors:
  • Asgeir Nysaeter;Roald Otnes

  • Affiliations:
  • Unik-University Graduate Center, Kjeller, Norway;Norwegian Defence Research Establishment, Horten, Norway

  • Venue:
  • MILCOM'06 Proceedings of the 2006 IEEE conference on Military communications
  • Year:
  • 2006

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Abstract

A system with serially concatenated 2x16QAM 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.