Main Service Channel - mattpascoe135/dab GitHub Wiki
Main Service Channel (MSC): used to carry audio and data service components. The MSC is a time-interleaved (see clause 12 in etsi) data channel divided into a number of sub-channels which are individually convolutionally coded, with equal or unequal error protection (see clause 11.3 in etsi). Each sub-channel may carry one or more service components. The organization of the sub-channels and service components is called the multiplex configuration.
##Coding in the Main Service Channel In this clause the details of the puncturing procedure are specified in terms of protection profiles and protection levels.
A protection profile associates the various blocks of a mother codeword with a collection of puncturing indices. For each of the allowed values of the audio or data bit rate a number of permissible protection profiles are defined. The set of protection profiles allows for audio and data broadcasting over radio frequency channels or cable networks with a level of protection suited to the requirements of the transmission channel.
Each protection profile is associated with a protection level indicating the relative level of protection provided. Protection level 1 indicates the highest level of protection within each set of profiles. The protection levels defined in clauses 11.3.1 and 11.3.2 (set A and set B) are independent of each other.
###Unequal Error Protection (UEP) coding
Each logical frame at the output of the energy dispersal scrambler (according to clause 10.3) corresponding to the processing of an audio service component, consists of a I-bit vector 
, where I is a function of the audio bit rate.
NOTE: UEP profiles are designed for audio, but the use of UEP profiles for other applications is not excluded.
Each vector shall be processed as defined in clause 11.1.1. The first 4I bits of the serial mother codeword U are split into L consecutive blocks of 128 bits, as defined in clause 11.1.2.
The value of L for each possible audio bit rate shall comply with table 30.
The first L1 blocks shall be punctured as defined in clause 11.1.2, according to the puncturing index PI1.
The next L2 blocks shall be punctured as defined in clause 11.1.2, according to the puncturing index PI2.
The next L3 blocks shall be punctured as defined in clause 11.1.2, according to the puncturing index PI3.
The remaining L4 blocks shall be punctured as defined in clause 11.1.2, according to the puncturing index PI4.
Finally the last 24 bits of the serial mother codeword shall be punctured as described in clause 11.1.2.
Each quadruple (L1, L2, L3, L4) associated to a quadruple (PI1, PI2, PI3, PI4), defines a protection profile.
Five protection levels P (P = 1, 2, 3, 4, 5) are defined.
The permissible protection profiles are specified as a function of the audio bit rate and the protection level P in table 31 (see also table 6 of clause 6). To ensure a word length of a multiple of 64 bits at the output of the encoding process, a certain number of "zero value" padding bits shall be appended at the end of the punctured codeword for certain protection profiles, as specified in table 31.
The resulting convolutional codeword for a given logical frame is denoted 
.
Table 32 gives the approximate value of the resulting average code rate as a function of the audio bit rate and the protection level P. In this table, the options denoted by X are not provided.
