- Main Service Channel -
Main Service Channel
MSC contains the data for all the services within the DRM multiplex. The multiplex may contain between one and
four services, and each service may be either audio or data.
Audio streams comprise compressed audio data blocks or frames. Each audio
frame can also carry a few characters of a radio text message at the end of each frame (last four bytes of a frame - approximately
80 bps). The message is divided into a number of segments and UTF-8 character coding is used.
MSC can be 16-QAM or 64-QAM level. 64-QAM
provides high spectral efficiency whereas 16-QAM provides better performance in the presence of reception errors caused by poor propagation
conditions or interference.
To improve robustness of the OFDM signal against the effects of propagation; interleaving of the
MSC symbols is done. This provides time diversity so that a burst of errors is spread across several symbols/frames to minimise their
destructive effect on the received data.
For moderate propagation conditions, such as medium wave Mode A broadcasts, a short interleaving
of 800 mSec (two frames) is preferred. For more demanding propagation conditions a longer time interleaver of 2.4 seconds can be selected