User's Manual

Screen Service SDT 200UB – SDT 500UB ARK-1 ATSC Operations
July, 2009 v 1.0 Page 3 - 64
3.8 Filter
The Adaptive Filter provides the ARK1 ATSC with an effective adaptive linear
compensation.
The adaptive filter works only in ATSC operative mode.
The developed system is responsible for pre-emptively compensating an ATSC signal in
order to make unimportant the contribution of the system transmission section. The signal
passes through the transmission section and re-enters the system as to determine the
distortion and the compensating adaptive filter.
The system is composed of two main blocks: a Power Calculation block and a 128-tap
Complex FIR. The modulated signal, with IQ format and sampled at ƒc frequency, enters
both blocks:
• Power Calculation block is responsible for estimating the mean power level that will
be restored at both transmitting and receiving sides;
• 128-tap Complex FIR is responsible for linearly pre-correcting the modulated signal.
Filter coefficients are obtained by estimating the channel between the signal before
the transmission section and the signal reentering the system, after the channel
distortion and the A/D conversion.
Fig. 19: Adaptive Filter