According to the bitrate chart on my website, which was sourced from ETSI, the maximum theoretical payload of DVB-T2 in a 8MHz channel in PP7 mode is 50.3Mbps with a FEC of 5/6. Obviously that FEC rate is not very robust so in practice that mode would be unlikely to be used for terrestrial broadcasting.
The currently used FEC of 2/3 is reasonable for a PSB mux.
If a DVB-T2 multiplex could be stretched to 50.3Mbps maximum capacity without affecting the FEC rate badly, and the BBC wasn't so budget constrained, we could have BBC One HD, BBC Two HD, ITV1 HD/STV HD/UTV HD, Channel 4 HD/S4C HD, eventually Channel 5 HD and BBC News HD, (after all the new BBC News studios in Salford are HD ready).
According to the bitrate chart on my website, which was sourced from ETSI, the maximum theoretical payload of DVB-T2 in a 8MHz channel in PP7 mode is 50.3Mbps with a FEC of 5/6. Obviously that FEC rate is not very robust so in practice that mode would be unlikely to be used for terrestrial broadcasting.
The currently used FEC of 2/3 is reasonable for a PSB mux.
the max payload depends entirely on estimated sig to noise ratio - hence viterbi error rate - at furthest away reception point using standard aerial. so its not a fixed thing. increasing tx power always lets you up data rate as one possible option .......
dtt is entirely about the digital cliff. a consequence of convolutional coding without which digital boadcasting would be physically impossible.
the max payload depends entirely on estimated sig to noise ratio - hence viterbi error rate - at furthest away reception point using standard aerial. so its not a fixed thing. increasing tx power always lets you up data rate as one possible option .......
dtt is entirely about the digital cliff. a consequence of convolutional coding without which digital boadcasting would be physically impossible.
Surely the maximum payload in a given RF bandwidth will be determined by the channel coding & modulation scheme, the receive S/N plays no part. The maximum payload achievable for a given BLER will indeed depend heavily on receive S/N though.
Convolutional coding isn't an essential part of digital broadcasting either, just an important one.
the max payload depends entirely on estimated sig to noise ratio - hence viterbi error rate - at furthest away reception point using standard aerial. so its not a fixed thing. increasing tx power always lets you up data rate as one possible option .......
dtt is entirely about the digital cliff. a consequence of convolutional coding without which digital boadcasting would be physically impossible.
DVB-T2 uses Low-Density Parity Check for its inner coding, not convolutional coding as used in DVB-T. The outer coding is the more general BCH code compared to the more specific Reed-Solomon code of the original standard. (No, I don't know why the 'inner' and 'outer' are that way round, the 'outer' coding is actually applied first and carried inside the 'inner' coding.) In both cases the terrestrial standard has followed the corresponding satellite techniques.
Of the 66% capacity increase from DVB-T 64QAM 2/3 to DVB-T2 256QAM 2/3, the higher modulation density accounts for 33% (8 bits per carrier per symbol compared to 6). The reduction in scattered pilots from 1 in 12 to 1 in 24 carriers (pilot pattern 7), and only 2 of every four frames rather than every frame, is (I think) 6.8%. Extended bandwidth adds an extra 288 carriers to the 27,265 in 32K mode, or about 1.06%. The other 25% is purely down to the more efficient error correction.
Increasing the transmitter power of all transmitters would do nothing for the signal-to-noise ratio, as the limiting factor in most of the UK is the interference from other transmitters, rather than the inherent noise in the receiver. There are certainly lightly-populated valleys where the noise is the dominating factor, but increasing transmitter power to serve them would only cause interference problems elsewhere. In the main, we've increased transmitter power at switchover (relative to the normal cut to 20% of analogue power, -7 dB) to fight off interference from France, or from COM muxes, rather than to increase coverage.
the max payload depends entirely on estimated sig to noise ratio - hence viterbi error rate - at furthest away reception point using standard aerial. so its not a fixed thing. increasing tx power always lets you up data rate as one possible option .......
dtt is entirely about the digital cliff. a consequence of convolutional coding without which digital boadcasting would be physically impossible.
The digital cliff is a moveable feast - in my experience DTT is only about S/N ratio (or C/N ratio as you may prefer).
You can have a standard Yagi with (say) 9dB forward gain sitting on the on the cliff edge.
Replacing it with a large extra-gain aerial increases the forward gain to (say) 15-17dB - lifting the signal to (say) 6-8dB above the cliff edge - insufficient for bad weather - but the side lobes will decrease the S/N ratio and you will may be no better off.
Replacing the standard Yagi with (say) 8dB forward gain log-periodic may seem a retrograde step - but add a 15dB - 20dB amplifier and you will be well clear of the cliff with a S/N ratio under normal circumstances of at least 20dB.
I have used everything from simple Yagis to a Triax Unix 100 WB (and a 52 group A) with and without various levels of amplification and nothing has beaten a simple 16dB amplified log-periodic. The only circumstances where a log will be a problem is with a strong interfering signal within its 90deg front acceptance angle - either direct or reflected. Careful positioning here enabled us to receive group A signals from Stockland Hill Iand high C/D from Mendip) - whilst rejecting group A from Rowridge reflections.
I must admit that I am not sure about using the LogPeriodic as a VP aerial pointed at Rowridge. (which I will cover in another thread)
Comments
...as are the new ones at Broadcasting House (which will sustain the TV news channel daytime/evening/overnight soon)
the max payload depends entirely on estimated sig to noise ratio - hence viterbi error rate - at furthest away reception point using standard aerial. so its not a fixed thing. increasing tx power always lets you up data rate as one possible option .......
dtt is entirely about the digital cliff. a consequence of convolutional coding without which digital boadcasting would be physically impossible.
Surely the maximum payload in a given RF bandwidth will be determined by the channel coding & modulation scheme, the receive S/N plays no part. The maximum payload achievable for a given BLER will indeed depend heavily on receive S/N though.
Convolutional coding isn't an essential part of digital broadcasting either, just an important one.
DVB-T2 uses Low-Density Parity Check for its inner coding, not convolutional coding as used in DVB-T. The outer coding is the more general BCH code compared to the more specific Reed-Solomon code of the original standard. (No, I don't know why the 'inner' and 'outer' are that way round, the 'outer' coding is actually applied first and carried inside the 'inner' coding.) In both cases the terrestrial standard has followed the corresponding satellite techniques.
Of the 66% capacity increase from DVB-T 64QAM 2/3 to DVB-T2 256QAM 2/3, the higher modulation density accounts for 33% (8 bits per carrier per symbol compared to 6). The reduction in scattered pilots from 1 in 12 to 1 in 24 carriers (pilot pattern 7), and only 2 of every four frames rather than every frame, is (I think) 6.8%. Extended bandwidth adds an extra 288 carriers to the 27,265 in 32K mode, or about 1.06%. The other 25% is purely down to the more efficient error correction.
Increasing the transmitter power of all transmitters would do nothing for the signal-to-noise ratio, as the limiting factor in most of the UK is the interference from other transmitters, rather than the inherent noise in the receiver. There are certainly lightly-populated valleys where the noise is the dominating factor, but increasing transmitter power to serve them would only cause interference problems elsewhere. In the main, we've increased transmitter power at switchover (relative to the normal cut to 20% of analogue power, -7 dB) to fight off interference from France, or from COM muxes, rather than to increase coverage.
You can have a standard Yagi with (say) 9dB forward gain sitting on the on the cliff edge.
Replacing it with a large extra-gain aerial increases the forward gain to (say) 15-17dB - lifting the signal to (say) 6-8dB above the cliff edge - insufficient for bad weather - but the side lobes will decrease the S/N ratio and you will may be no better off.
Replacing the standard Yagi with (say) 8dB forward gain log-periodic may seem a retrograde step - but add a 15dB - 20dB amplifier and you will be well clear of the cliff with a S/N ratio under normal circumstances of at least 20dB.
I have used everything from simple Yagis to a Triax Unix 100 WB (and a 52 group A) with and without various levels of amplification and nothing has beaten a simple 16dB amplified log-periodic. The only circumstances where a log will be a problem is with a strong interfering signal within its 90deg front acceptance angle - either direct or reflected. Careful positioning here enabled us to receive group A signals from Stockland Hill Iand high C/D from Mendip) - whilst rejecting group A from Rowridge reflections.
I must admit that I am not sure about using the LogPeriodic as a VP aerial pointed at Rowridge. (which I will cover in another thread)