UP Paper 1551 US-W-NAT BOTTOM
Filter-Based Turbo Equalization with 2x16QAM Trellis Coded Modulation and Partially Iterative Channel Tracking
Nysaeter,AsgeirKongsberg Defence and Aerospace
Otnes,RoaldNorwegian Defence Research Establishment
A system with serially concatenated trellis coded modulation and linear minimum mean square error (LMMSE) turbo equalization is proposed for an unknown and time-varying channel with intersymbol interference (ISI). The outer and inner codes are a rate 2/3 binary code and a rate 6/8 recursive TCM code respectively. To improve diversity, frequency hopping is performed for the transmitted symbols, and 2x16QAM multiple trellis coded modulation (MTCM) is used with succeeding symbols transmitted on different carrier frequencies. Each frequency hop channel is initially identified by linear interpolation between two training sequence based channel estimates. Channel tracking is improved for each new iteration by using a channel estimate which is a weighted sum of the interpolation based estimate and an estimate from the soft decoder information. The relative weights are determined from calculated reliabilites of the estimates. A comparison is done between turbo equalization with this new combined channel estimate, and with only an interpolation based estimate.
Asgeir Nysaeter is a senior research and development engineer at Kongsberg Defence and Aerospace, working with development of baseband digital signal processing algorithms both for hand-held radios and radio relays, and with FPGA and ASIC implementation.