Physical Layer Building Blocks. In this section, we will provide an overview of the physical
layer operations. We begin with a block diagram of the function performed in DVB-H transmission.
The input MPEG transport stream (TS) is essentially scrambled by a Pseudo Random Binary
Sequence (PRBS) having a generator polynomial equal to g(x) x15 x14 1. Concatenated error
correction is used in order to get required performance to deliver the intended services. Recall in
an earlier chapter concatenated coding performance results were presented for the RS CC scenario.
This is accomplished by having an outer Reed-Solomon FEC code and an inner convolutional
FEC code separated by a convolutional interleaver operating on bytes of data having a depth
of 12 (see Fig. 9.12).
In order to support variable bit rates the inner convolutional code is punctured. The convolutional
code has a native rate of R 1/2 with a constraint length of K 7. This rate is punctured to allow 2/3,
3/4, 5/6, and 7/8 rates. A puncturing patterns table is provided in the DVB standard.
488 CHAPTER NINE
IP
MPE MPE-FEC
MPEG-2 Transport
DVB-T DVB-H
Network Layer
Link Layer
Physical Layer
FIGURE 9.11 DVB-H protocol architecture.
The Reed-Solomon code is a RS(204,188) with error correction capability of t 8 bytes; this is
shortened from the RS(255, 239) code by inserting 51 bytes of all zero value to the 188 input data.
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