DRM+ likely to use 50 - 100 kHz channels

A new web page has appeared on the DRM website containing a summary table of DRM channel bandwidth possibilities. Previously it was common knowledge that 50 kHz channels were being considered, but this page confirms for the first time that 100 kHz channels are being ear-marked as well.

DRM+ is the extension of the current DRM system. The current system only allows transmission up to a maximum frequency of 30 MHz, and DRM+ is the extension to the system to allow it to transmit at frequencies up to 120 MHz -- the web page mentions 108 MHz, which is the top of the current FM band.

The page also mentions that simulations of DRM+ are underway.

The following table shows the results from a short program I wrote last year to estimate what bit rates we could expect to see with different channel bandwidths, while making some assumptions about the OFDM transmission parameters used. 

The assumptions I made were that the maximum speed of the receiver was 100 mph, transmission frequency was 120 MHz, DRM Mode A and (typical) FEC code rate of 0.6 were used. They are only ball-park figures, but I doubt they'll be incorrect by much. 

DRM uses the HE AAC and AAC audio codecs, and as AAC provides good audio quality at 96 kbps and near CD-quality at 128 kbps, DRM+ effectively guarantees the audio quality will be good quality if only one station is transmitted on a 50 ot 100 kHz channel (assuming the audio going into the encoder is good).

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