The Extension of DRM to VHF Frequencies
DRM+ is the name applied to the DRM standard when used in the VHF frequencies. The initiative to extend DRM began with a vote at the 2005 General Assembly to begin the design, verification and testing of the parameters needed to allow DRM to operate in the VHF broadcasting bands between; primarily Band I and Band II.
The design process began shortly afterwards and key decisions were made to ensure that the extension completely shared the successful design philosophy of DRM – it is “DRM but at higher frequencies”.
Therefore, it has:
- The same multiplex and signalling scheme
- The same OFDM design (with new parameters)
- The same audio codecs
DRM+ is implemented in the standard as robustness mode E. Its spectrum usage parameters are determined from the internationally agreed norms in the FM band (88 to 108 MHz). Therefore it has an occupied bandwidth of 96 kHz and a frequency grid of 100 kHz.
DRM+ provides bit rates from 35 kbps to 185 kbps at SNRs from 2 dB to 14dB and, like DRM, permits up to four services. It is therefore a flexible solution allowing single or small numbers of audio services to be broadcast together.
Field Trial Results
During the process of gaining endorsement from the ITU for DRM’s extension to the VHF bands, test results from various field trials conduscted around the world were submitted. Some of the reports are avaialbel below: