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Chapter 4Simulation and analytical modelling p204*8/42M = 38.9 µs.• Transmission delay of an MPEG2 frame containing an MCI frame (D tx_MPEG ). Thisallows the scheduler to take into account transmission delay of the forthcoming MCIframe.• Interleave delay (D interleave ). This delay is incurred to enable the correction of burstnoise induced errors, protecting against a burst of symbols errors from being sent tothe RS decoder.• Roundtrip propagation delay (2·D prop ). This is the delay incurred to transmit a singlebit of information from the INA to the furthest NIU and vice-versa.• NIU processing delay (D IU_proc ). This is the delay that it takes to the NIU to parsethe MCI frame and translate it into transmission opportunities.Based on the above delays, the scheduler look-ahead delay, D lah , is given by:Dlah= 2 ⋅ D + D + ⋅ D + D(4.18)Tx _ MPEG int erleave2propIU _ procAccording to [34], the interleave delay is given by the following equation,Dint erleaveDS _ size ⋅8⋅(interleave _ depth −1)= (4.19)Dwsbit _ ratewhere DS_size (=204 bytes) is the total size of the MPEG-2 TS frame to be transmitteddownstream including FEC information and the interleave_depth is a constant set to 12for downstream IB modulation. D ws_bit_rate is the downstream data rate set to 42 Mbps.With these values indicated above, the interleave delay results in 427 µs.In order to get the complete scheduler look-ahead time (given by Equation 4.18), theprocessing time of the MCI frame at the NIU (D IU_proc ) is needed. Such delay ishardware specific, but according to the specification [34], this value should be under500 ms. We first consider a short processing delay. Assuming that this delay is about100 ms, then the scheduler look-ahead delay becomes:D lah= 2 ⋅38.9+ 427 + 2 ⋅50+ 100 ≈ 705µs4-24