The Electronics Communications Committee (ECC) of CEPT recently released an article outlining how digital radio could be introduced to the Marine VHF bands.
At present, the allocated frequencies are in the frequency band 156.025 MHz to 162.025 MHz and are mostly FM i.e. analogue.
The channel spacing is 25 kHz which means that there is a lot of spectrum on the band not being used and there is the potential to squeeze a lot more channels in.
In the article, it states that "with the exception of the automatic identification system (AIS) on channels AIS1 (161.975 MHz) and AIS2 (162.025 MHz) and digital selective calling (DSC), currently all the remaining listed channels are used for analogue voice communication. With the digital data exchange allocations in future, some channels will be used for data transfer and not for voice communication any longer. New digital radios need to be developed, which is different equipment than the current voice communication radios. As the result, the frequencies in the VHF maritime mobile band will be shared by four different systems: analogue voice telephony, DSC, AIS and digital data exchange."
There is a huge legacy issue though to overcome first. For a business, they can just swap out the gear and radios when they upgrade from FM to digital. With the Marine VHF band, there is a huge decentralised user base that will take years to change over.
The article suggests the use of DMR (dPMR) as introduced in recent years on the amateur bands..."The technical candidate solution is dPMR (digital Private Mobile Radio) – a technology currently used in land mobile communications as a replacement for analogue FM voice communication in both VHF and UHF bands. dPMR has been standardised by ETSI, the European standards organisation."
The article suggests that initially, the new digital channels which take up 6.25 KHz and these would fit between the existing analogue FM channels as shown below on the left.
It not hard to imagine perhaps a transition period where dual mode (FM & DMR) radios would exist and then there would have to be a date whereby everyone would need to changed over to digital.
In tests done in Estonia, they reported..."Participants in the test were generally positive about the introduction of digital communication with the range being the same (or better) than the range for analogue communication. At the maximum distances, the digital communication remained understandable (d = 19,6 NM) while the analogue communication experienced very high noise and was not understandable."
In the tests done in the Netherlands, they reported..."The users and the observers found the digital voice quality the same or better than the analogue one. The users reported back that listening to digital voice with noise reduction made it easier and less intensive to listen. The users concluded that the digital transmission of voice enabled the same functionality of operation of the ship as for an analogue radio system."
Full article... http://apps.cept.org/eccnews/may-2020/index.html
