US forward error correction company Digital Fountain has put out a white paper to demonstrate that with minor tuning, DVB-T networks everywhere might be picked up easily on a handset.
The exact cost of doing this was not estimated, but Digital Fountain used the European Commission funded Celtic Wing TV project as a test bed to prove that it should work. The difficulty now is getting a supplier to come on board and offer any changes need to the transmission scheme.
The paper was written back in January, but is being distributed widely now to educate the community in the run up to trial deployments which should be in place before year end.
Broadcast networks are always a compromise between reach or penetration and payload, and the German DVB-T network was built to send less TV channels, but to have them cope with mobile delivery, specifically to in-car systems. In the German system, transmitters are allowed to belt out a huge 50 kW ERP in Berlin and 20kW elsewhere, and the network is coded in 16QAM instead of the more usual 64QAM or QPSK which would have less penetration, but which would mean each multiplex (piece of spectrum) would deliver more data.
However another way around this is to offer FEC or Forward Error Correction, the most advanced of which is widely accepted to the be Raptor codes developed by Digital Fountain founder Michael Luby over the past decade.
Digital Fountain has already been selected as the FEC of choice for DVB-H and MBMS, the two mobile TV standards, and has since spent time spearheading the FEC approach in IPTV.
FECs are mathematically complex ways of sending some extra data so that if any data is lost on its way to the target receiver, it can be rapidly re-calculated. The Raptor codes are when an outer code is used to transform packets of data, and then a piece of each packet is stored or sent in multiple other packets to allow packet reconstruction even if a network suffers a loss of a considerable amount of that data. The key to Raptor codes is that they are linear and for a 10% loss experienced on a network, you need to send around 110% of these packets, creating a 10% overhead. Other systems have far higher overheads.
The Digital Fountain paper pointed out that just replacing null packets in existing DVB-T transmission would gain a 1% space for Raptor codes, and that this was almost enough to allow a poorly received video packet to be re-constructed. The net result of that would be to allow far greater indoor penetration of TV signals at a handset. This change, accompanied by power savings on DVB-T chips and improvements in their sensitivity could be enough, some think, to completely wreck DVB-H and stop it from ever becoming widely installed.
The paper also says that despite the initial focus on DVB-T, any signal that is sent on an MPEG-2 Transport Stream, and especially other terrestrial systems such as ATSC and ISDB-T, would work in the same way. However ISDB-T has been carefully constructed to have one of 13 segments devoted to a smaller handset signal, so probably wouldn’t benefit too much from this, and ATSC M/H (the mobile handheld standard) is as cheap an upgrade as the Digital Fountain system is likely to be. It is only because the DVB Project decided that building a new network was the only way to go in mobile TV, creating DVB-H, that it is of vital importance for DVB territories.
Whether or not these Raptor codes will mean the end of DVB-H is tough to say, especially since they are the FEC of choice for protecting DVB-H itself. What may happen is that DVB-T networks will give consumers the appetite for TV on their handsets, and that DVB-H will subsequently provide the equivalent of pay TV
Prior to this paper it was obvious that the combination of battery issues and penetration weaknesses would mean that DVB-T would never fly on a handset. There remains the battery issue because DVB-T sends a continuous streams of bits, while DVB-H accepts them in faster than real time, data heavy, bursts and switches the radio off for over 90% of the time, however it is not only the radio which uses up battery and DVB-T reception is likely to use up the battery about four times as fast as DVB-H, no faster.