Yes, we will retune DTT again, but it will not be soon

The Second Digital Dividend has just ended . Since October 31, 2020, the 700 MHz band has been fully released so that operators can start operating in it with 5G coverage . The auction will be held in March, and it will be the second time that DTT has given way to mobile telephony, as has already happened with the 800 MHz of 4G. However, this is not going to be the last time it will happen.

The DTT National Technical Plan , approved by Royal Decree in June 2019, guarantees that DTT will continue to operate in Spain at least until 2030 in the same bands that it is currently doing. Thus, there will be no Third Digital Dividend or loss of bands by DTT in the next 9 years.

DTT will not lose bands until at least 2030

As explained by the Ministry of Economic Affairs and Digital Transformation, the allocation of new uses for frequency bands is coordinated at the international level in the World Radiocommunication Conferences (WRC) held by the International Telecommunications Union (ITU) . These conferences are held every three to four years, the last being held in October and November 2019 in Egypt. The previous one was held in Geneva in November 2015, the same as those of 2003 and 2007.

In 2019, there was no talk of any change in DTT frequency bands for other uses. Therefore, it is not expected that this issue will be discussed until at least 2022 or 2023, which is when the next World Conference on the matter will be held. In addition, in the event that something is discussed there, it will be the European Union that will have to establish the deadlines to release the bands.

In 2023 there will be no SD channels

What we will see on January 1, 2023 is that all DTT channels will be in HD, leaving behind the SD and the MPEG2 standard that they use. What is not known is whether the use of the current DVB-T standard and the MPEG4 codec (H.264) will continue, or whether it will give way to DVB-T2 and HEVC, which allow the use of spectrum to be cut in half with the same current quality. They also allow you to offer higher quality, as well as add more channels.

With the elimination of the SD channels, enough spectrum would already be freed up to improve the bitrate, which would make it not essential to switch to DVB-T2 . In the future, in the event that, for example, the 600 MHz band becomes used by mobile telephony, then it would be necessary to use a new technology that uses the spectrum more efficiently, since otherwise channels would be lost .

Will 5G replace DTT?

Therefore, it is clear that at least we are going to have to retune DTT once more in the next two years to eliminate SD channels and stay only with HD. From there, can we touch buy a decoder or a TV with DVB-T2 because, since the summer of 2019, all new TVs must carry one integrated, or we can continue using the DVB-T HD today for a little longer.

DTT currently uses 8 MHz channels with a bitrate of up to 19.91 Mbps. This figure is obtained as a result of the modulation parameters used in Spain, where 64QAM is used, a guard interval of 1/4, 6.048 useful carriers, and a 2/3 encoding rate. This rate indicates that, of every three bits sent, two are valid and one of them is used as redundancy if one fails to deliver. If it were not for that, 30 Mbps of bitrate could be used, although the channels would present errors in the transmission.

Each HD channel has a bitrate that reaches 4.5 Mbps, as is the case with SD, which tend to have slightly lower figures around 3.5 or 4 Mbps. Thanks to better encoding efficiency, H. 264 can compress a higher resolution image than SD and use almost the same spectrum.

For this reason, each multiplex only accepts up to four HD channels, with three being the maximum that we currently see combined with a DTT channel. To this we must add that there is a percentage that is also used for radio stations, programming guides, teletext, and other services accessible via DTT.

Therefore, until changes are made in that way of encoding and compressing the signals, it is not possible to add more channels or use the spectrum more efficiently. If we multiply the 9 multiplexes currently used in DTT by the 19.91 Mbps of each one, we have that DTT uses 179.19 Mbps distributed in 224 MHz of spectrum from 470 to 694 MHz. In this case of 5G, in that same spectrum, it is possible to reach speeds of several thousand Mbps.

Thus, things that are difficult to predict may occur between now and 2030. For example, it is possible that some technology will be implemented at a European level that allows the broadcasting of television signals through 5G, which has a technology called FeMBMS  ( Further evolved Multimedia Broadcast Multicast Service ). This would allow receiving the TV signal anywhere thanks to mobile phones, and without having to depend on external tuners, as well as not having to use programs to watch DTT on PC . FeMBMS technology has been tested for years in Germany, where emissions have already been made in tests that have shown that this technology is viable.


by Abdullah Sam
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