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Fragmented Broadcast World: Myth or Reality?DVB-T, a Digital Terrestrial Television (DTT) standard, was first published in 1997 and broadcasted in the UK in 1998. Since this date, many new Digital TV & Radio standards appeared in several countries as seen on the following world map:
This landscape may seem, at first glance, as a nightmare for chipset and device manufacturers who must invest significant amounts of money to develop devices for each standard with a relatively limited market opportunity. However a comparative analysis of the DTT standards structures shows that there is more convergence than it would appear to be at first. Despite this so-called fragmented Broadcast World, it is possible to find strong commonalities between the various standards thus allowing manufacturers to implement all these standards into a single programmable chip with minimum overhead costs as what has been previously done with modulators chipsets.
In order to facilitate the comparison between all the DTT standards, the set of configurable parameters (M-QAM, FFT size, Guard Interval, Inner and Outer codes rates, bandwidth) are listed in columns in the next two pages, together with the bit rate calculation formulas. In addition, the last column shows that some standards offer the possibility of In-band Mobile TV applications thanks to availability of sub-channels or Multi-Pipes.In practice, the last table synthesizes the performances of the most used DTT configuration in the World and a final graph compares their spectrum efficiency versus the carrier-to-noise signal C/N required.
Most of the DTT standards use the same frequency band, and the same modulation scheme composed of COFDM Multi-carriers or Single Carrier modulated in M-QAM, associated with inner code (Viterbi, Turbo code or LDPC) and outer code (Reed Solomon or BCH).The following Block-diagram shows the required range of parameters of a programmable “multistandards” chipset, capable of demodulating in one IC, all the existing DTT World Standards. For any given standard to work, the receiver only has to download the associated microcode. There is therefore no need to change the Hardware.
ConclusionThis paper shows similarities between the world DTT standards, allowing the design of a programmable “multistandard“ chipset that can cover all standards with minimum overhead. For manufacturers, the fragmented Broadcast world is no longer a challenge, but an opportunity. In the very near future, one might think of a car that can drive anywhere and be capable of receiving all Radio and TV standards wherever it is driving, one might dream of a Tablet
It has to be noted that the chosen configurations are the most used, but they are not necessarily optimal in terms of spectral efficiency. Also, it appears clearly on this graph that the new DVB-T2 is the standard which has the best performance with respect to the spectral efficiency criteria.
In the next figure the spectral efficiency of DTT standards configurations analysed in the previous table are plotted versus their required Gaussian C/N and compared to the theoretical Shannon limit.
Currently deployed bit rates and Gaussian (C/N) by standard in some countries
In the following table the previous formulas are used to calculate the bit rate of most used DTT configurations used in the World. Some specified/measured values of C/N (Gaussian and TU6@10Hz Doppler) are also given in the last columns.
0
1
2
3
4
5
6
7
0 2 4 6 8 10 12 14 16 18 20
ISDB-T 12 SEG
DVB-T2 UK
DVB-T 64QAM 3/4
DVB-T 16QAM 2/3
ISDB-T 1 SEG CMMB DAB
CTTB SC 0.8
ATSC
DVB-T2 Lite 16QAM DVB-T2 Lite QPSK
CTTB 4k 0.6
CTTB 4k 0.8
DVB-SH
Spectral Efficiency C/N
(C/N) [dB]
Spec
tral E
ffici
ency
(bit/
s/H
z)
that can receive HD TV signals anywhere without the constraints of which standard is available in that area. Despite the initial industry and political lobbying, one can see that Digital Communications always end up with somewhat the same scheme. And as history shows, sooner or later, semiconductor designers can implement everything at a reasonable consumer cost.