Service information describing the transmission is added to the transport stream. This stream is then randomized prior to routing to an outer R-S error correction coder that adds redundancy to the data. A convolutional interleave process then reorders the data so that adjacent data in the transport stream are not adjacent in the transmission. An inner trellis coder is then used to produce a multi-level signal for the VSB modulator. Figure 8.10 shows a DVB-T transmitter.
Service information is added as before, followed by the randomizing stage for energy dispersal.
Outer R-S check symbols are added prior to interleaving. The modulator output is then upconverted to produce the RF output. At the receiver, the bit clock is extracted and used to control the timing of the whole system. The channel coding is reversed to obtain the raw data plus the transmission errors. The inner code corrects random errors and may identify larger errors to help the outer coder after deinterleaving.