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Europe blazes trail for next-generation digital terrestrial

The second-generation digital terrestrial DVB-T2 standard is now being deployed in several European countries after a slow start, driven by competitive pressure from cable, satellite and IPTV, creating demand for extra capacity to carry multichannel HD services. The world is split into four zones for digital terrestrial, each adopting different standards, with ATSC in the whole of North America, ISDB-T in most of South America and Japan, DMB-T/H in China, while the DVB-T and DVB-T2 standards prevail in the largest region including across all of Europe, parts of Africa, Russia, India, the Far East, and Australasia.

Europe has pushed ahead with analogue switch off for terrestrial quickly with most of the continent having adopted an almost self imposed deadline of 2012 for completion, while some countries such as the Netherlands completed the job in 2006. In many countries the switchover was initially to first generation DVB-T, but some such as the UK and Finland are now upgrading to DVB-T2, while among the few countries only just moving from analogue to digital, the Ukraine is jumping straight to the second generation, skipping DVB-T. This makes sense for greenfield countries such as the Ukraine given the recent maturation of DVB-T2 equipment including gateways, modulators and satellite receivers from vendors such as Harmonic, Cisco, Ericsson and T-VIPS. Most importantly, DVB-T2 delivers a significant performance increase of around 65 percent, or even more if the impact of a change from MPEG-2, as typically deployed before, to advanced H.264/MPEG-4 compression is taken into account. DVB-T2 is invariably deployed with H.264/MPEG-4.

But advanced compression is not specific to DVB-T2, with the main contributor to its performance increase being improved FEC, based on the Low-density parity-check (LDPC) method. FEC is required for correcting errors in one way transmission networks where there is no return channel to request additional information, and where retransmissions are impractical or expensive. In that case the signals have to contain enough information from the transmitting device to recover the full data stream in the event of the limited number of errors that can reasonably be expected. This is done in effect by smoothing out the impact of noise across a large number of transmitted codes. The payload data is transformed into a different bit stream for transmission by mathematical techniques that vary according to the particular FEC method used, with the idea being to incorporate enough redundancy to provide a buffer against corruption causing loss of small numbers of the coded bits. The objective is to achieve the required level of redundancy by adding as few extra bits as possible, and in the case of LDPC this is done by trading mathematical complexity for processing power. The algorithm is sophisticated, which is why it has been impossible to deploy DVB-T2 relatively recently, exploiting improvements in signal processing power.

Among the first to start deploying DVB-T2 was the UK's Freeview service delivering free-to-air channels from the BBC, ITV, Channel 4 and others, with the commercial services relying on advertising. However the UK terrestrial TV network run by Arqiva also carries pay TV services alongside Freeview from operators such as Top Up TV and ESPN.

Generally Europe has come round to an FTA model for all DVB-T services, and this has contributed to their increasing success. In Europe a first wave of DTT launches in the early 2000s failed to gain much momentum precisely because they usually were paid services and could not compete against cable and satellite competitors in terms of spectrum capacity. Second time round the focus is on delivering a limited number of popular FTA channels in HD as well as standard definition, relying on IPTV or OTT to provide access to less popular longer tail content. But operators are still under pressure to deliver more channels than before, and more in HD, leading to the growth of DVB-T2. In the UK for example deployment of DVB-T2 is enabling Freeview to roll out HD versions of its main channels across the UK this year and in 2012.

Similarly the Finnish Telco and cable operator DNA is rolling out DVB-T2 to deliver HD, to reach 85 percent of the country's population by the end of 2011. This is also noteworthy because DNA is deploying DVB-T2 in SFM whereby all transmitters use the same frequency to send each channel. Typically DVB-T runs in MFN, using different frequencies to transmit each channel from neighbouring cells to avoid destructive interference resulting in poor quality. SFN uses accurate timing combined with small time gaps called guard intervals between transmitted symbols. This means signals reach each receiver from multiple transmitters with sufficiently close timing such that they interfere constructively, which improves coverage and reduces the power needed.