| Digital One multiplex has been reconfigured17th October 2006 The Digital One national commercial DAB multiplex has been reconfigured seemingly mainly to increase the bit rate of the 4 mobile TV channels transmitting — they used to be transmitted in a 64 kbps channel, which is ridiculously low for a channel that consists of both video and audio. The main change has been that the DAB-IP mobile TV channels have changed to using the weaker PL4A error protection level from the previously used stronger PL3A. Mobile TV channels are transmitted through DAB data channels, which uses Equal Error Protection (EEP), and the protection levels are subscripted by either A or B, as in PL4A, whereas MP2 radio stations use Unequal Error Protection (UEP), where the protection levels are not subscripted by a letter, so the levels are, e.g., PL3, PL4 etc. The reason why the mobile TV channels can use the weaker protection level 4 when the radio stations are using protection level 3 is due to the fact that there is an additional 'outer layer' of error correction coding used with the mobile TV channels, which is not used for the radio stations. This additional error correction coding is called Reed-Solomon (RS) coding, which is identical to the RS coding used on the DVB-T system (i.e. Freeview), and it will be used as standard on DAB+ for radio stations using AAC+. It is interesting that they're using PL4A for the mobile TV channels, because I've always maintained that the higher-capacity PL4A protection level would be suitable for use with radio stations using AAC+ on DAB+, especially if they're using the MPEG-4 Audio Version 2 Error Resilience tools that are used on DRM/DRM+ and DMB (so they're expected to be used on DAB+ as well). The reason I say this is because video requires a far lower bit error rate (BER) than audio requires for robust reception — i.e. video is far more fragile than audio. In other words, if you can transmit video robustly using PL4A then transmitting AAC+ audio robustly will be a doddle. The new multiplex configuration is as follows (information from the
Wohnort
website):
One ominous fact from the above multiplex configuration, however, is that it looks like the new national jazz station that's going to launch on the Digital One multiplex by the end of the year will be using mono! The reason why it looks like it will transmit in mono is because
DAB multiplexes always have a capacity of 864 CU (DAB multiplex
capacities are measured in CU, not in kbps), so as the current
multiplex consumes 814 CU there is only 50 CU spare, which is enough
to carry one radio station using 64 kbps, which obviously has to be in
mono.
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