Training-sequence Assisted QAM-concepts Digital Terrestrial TV Transmission

The performances of different computer simulated QAM concepts for a 7 MHz transmission channel are presented and hndamentals of the theory are explained. Each considered concept uses a periodically inserted training sequence to update the complex coefficients of an adaptive equalizer. The multipath propagation channel is modeled according to the COST 207 channel models [l]. Introduction With an accurate model for the modulation schemes and channels, it becomes feasible to optimize and compare various designs by analysis and / or simulations rather than by extensive field measurements with experimental hardware. The performance of a modulation scheme is mainly determined by a correct carrier recovery because a frequency or phase offset in the demodulated signal will cause degradation to the performance of the receiver. In this sense we distinguish the considered QAM concepts in designs with and without an additive pilot tone for synchronous demodulation. In order to use a computer to simulate a QAM transmission the complete simulation requires a complex baseband version of the real-valued bandpass signals. QAM Transmitter Following the error protection in the ATSC Digital Television Standard [2] we consider a t=10 (207487) Reed-Solomon and 2/3 trellis encoded data stream. Using a periodically inserted data segment sync at the beginning of each data segment for synchronization and a data field sync as a training sequence for adaptation of equalizer coefficients in the receiver leads to a QAM transmitter shown in Figure 1