大象传媒

If there is going to be a "DVB-T2-Lite" profile, which is a lower quality profile designed for mobile phones etc., couldn't there also be a "DVB-T2-High Quality" profile introduced that we could have 1080p50, 4K, SHV etc.?

I have not studied DVB-T2 light but at I cannot see how it is possibe to use it for mobile devices. Mobile phones do use these high frequencies but only work because of there small cells. Phones usually are in contact with several cells at the same time so can choose the best cell. Freeview HD uses a relativly small number of transmitters with highly directional receiving aerials. The idea that this problem can be overcome with extra error correction seems some what optimistic. Most Freeview transmitters are horizontally polarized so not really ideal for car reception.

Please can you tell me what the spectral efficiency of your trial is in terms of kbps per khz?

What we don't want is another disaster like DAB with its poor audio quality and error correction.

It has seemed to me the 大象传媒 R&D budget would be better spent on something like DRM for radio services. Most mobile phones have a perfectly good FM tuner in any case.

@trevor: Are you out of your MIND? DRM on radio... seriously... WHY?

Sounds interesting, but wouldn't it be better if creating a new digital mobile TV/radio service to use spare VHF spectrum like Band I, or Band II if/when FM shuts down, rather than taking a significant amount of bitrate that could be much better used for a fifth Freeview HD service? After all, assuming your figures you just posted are representative of what the service would be like, you'd be sacrificing nearly 7Mb/s for the sake of just over 1Mb/s for a mobile service - that's not many video streams, and if it's audio you may as well use DAB.

@Muzer0

I think you may have misunderstood DRM. DRM stands for Digital Radio Mondial which is a radio system which can be used in the LW, MW, SW and FM bands. Infact it can fit into the white space between FM transmitters in Band 2. It is about 2.8 times more spectrally efficient that DAB. Add AAC and you can fit 5 times as many stations in the same space. The 大象传媒 has done reseach into this but have been very quite about it.

FM is not shutting down. The 大象传媒 wants to shutdown it's FM national transmitters but as everyone knows it won't be able to it because most people don't want the inferior DAB system.

HD1080: You're confusing how the bitrate is provided with how it is used. The DVB-T2 scheme can be used to carry practically anything. It is not required to provide HD pictures. The choice of frame size and rate - and encoding method - is made at the video encoder and can be carried in either DVB-T2 or DVB-T2 'Lite' so long as there is enough capacity from the selected transmission mode. Normally multiple services will be carried on one multiplex (e.g. 大象传媒 One HD, 大象传媒 HD, ITV1 HD and 4hd, in England).

The changes for DVB-T2 Lite are to save battery power, by requiring less complex circuits, and reduce the doppler problem - that a receiver moving relative to the transmitter experiences a frequency shift, which changes the relationships of the carriers and therefore causes interference that wouldn't occur if the receiver was stationary. If the receiver is moving quickly enough, it can't decode the signal. For even standard definition TV, you can be going too fast on an Intercity train or even in a car (perhaps not legally!) for it to work.

But surely they are using more bandwidth to give a more robust signal for mobile digital TV. Surely stationary TV could use that bandwidth for a better quality picture than currently (including higher definition picture) and wouldn't need to be as robust a signal.

So surely this DVB-T2 light is wasting bandwidth to give a small low quality mobile picture (using more bandwidth to give it a more robust mobile picture) that could be used for a much higher quality stationary digital TV system that wouldn't need as robust a signal.

HD1080: This is not a change to the Freeview HD signals transmitted from those transmitters which have switched over, and the early HD services at Crystal Palace, Emley Moor, Pontop Pike and Lichfield. This is a short-range low-power test from one site. The public Freeview HD multiplex is running at the highest capacity possible, within the rules of DVB-T2, for equivalent coverage to the other two Public Service multiplexes (for sites that have switched over). This is just enough, at the moment, for four HD TV services.

The 大象传媒 were required to make three slots available, for the regional ITV company, Channel 4 or S4C (in Wales), and Channel 5. At the time Freeview HD launched, Channel 5 turned down the offer, allowing the 大象传媒 to reclaim the capacity and launch 大象传媒 One HD. It's hoped that improved compression will allow a fifth slot to be created by the end of next year, which again will be offered to Channel 5 first.

More capacity could only be achieved by using less error protection, which would require power increases to keep the same coverage - which would need to be co-ordinated between different regions in the UK and with our neighbours, primarily Ireland, the Netherlands, Belgium and France. Beyond a certain point, adding a new multiplex would be easier, though again any new frequency allocations would have to be co-ordinated across the country and across Europe, and many frequencies now used for TV are being sold off for mobile phone services.

This trial is to see how *technically* feasible it is to slice up the transmission into high and low-capacity parts. Freeview already carries 大象传媒 National Radio stations which take up about 5% of the 大象传媒 A multiplex (for regions that have switched over). However, the receiver has to have fully robust stationary reception in order to play back the radio portion. The time-slicing used in this trial would deliver three-quarters of the HD TV capacity *and* allow the radio stations to be received by portables, from the same frequency allocation. The capacity delivered in the mobile part is too low for TV.

The background is that the radio spectrum regulator, Ofcom, keeps talking about releasing more and more spectrum for mobile phones and wireless broadband, even where that isn't a sensible use for that frequency range (87.5 - 108 MHz will deliver no useful broadband service), and the broadcasters may find themselves having to cram things in where they can, rather than having ranges dedicated to radio and TV.

why the data rate is limited to 4 Mbit/s in T2 lite?

you have defined the followed configuration " 8K 1/32 QPSK 陆 with L_DATA = 46". and This gives a bitrate of 1.02 Mbit/sec for the mobile service. my question is how did you calculate this data rate ?

I think it's great that you are experimenting with DVB-T2-Lite.
However I think it is a shame that nobody seem to be considering using it in Band III. There seems to be a number of unused DAB channels, and as far as I understand DVB-T2 has a mode with a bandwidth suitable to be used in these channels. So I assume that T2-Lite could also be used in Band III channels in this way.

HD1080: DVB-T2 lite is a much more efficient use of available bandwidth than DAB.

@ RichardEvans67

There are no unused blocks in VHF Band III. Most of the blocks in sub-bands I and II are used by PMR & PMSE providers and these users are protected until 2015. In their latest review document (22 June) Ofcom identified Block 5A as being available for local DAB in some areas. If any others become available these will also be used for local DAB to minimise frequency re-use and reduce co-block interference between multiplexes.

Block 11A is spare as Channel 4 DAB handed the licence back without launching the service, but Ofcom still hope to use it for a national DAB service.

To answer the question in comment 8 asked by 鈥淒VB-T2 Man鈥�

First the data rate is limited to 4 Mbit/s in T2-Lite because Section I.10 of the DVB-T2 specification says 鈥淎dditionally, for the TS case, the maximum input TS bit rate shall be 4 Mbit/s.鈥� The reason this limitation is imposed is to allow for simplifications in the FEC decoder implementation.

To calculate the data rate of the T2-Lite service, you need to calculate how many information bits are transmitted and divide that by the amount of time it takes to transmit them.

The information bits are broken up into FEC blocks and, in this mode, there are 38 FEC blocks in an interleaving frame.

The mode we are using is QPSK 陆 which according to table I.1 means that Kbch = 7032. Now each FEC block has an 80 bit header, so the number of information bits in a FEC block is 7032-80 = 6952 bits. So the total number of information bits in 38 FEC blocks is 6952 * 38 = 264176 bits. However type B in-band signalling is mandatory in T2-Lite, so the number of bits in an interleaving frame is reduced by 102 which gives 264176 鈥� 102 = 264074 bits.

The next question is how long does it take to transmit those information bits.

If we work in units of T (7/64 us), then the duration of the T2-Lite frame is ((46+2)*8448)+2048 = 407552. There are 46 data symbols and 2 P2 symbols (in 8K). The FFT size in 8K is 8192 and the guard interval is 1/32 which means that the number of samples of T in a symbol is (33/32)*8192 = 8448. Finally the P1 symbol is 2048 samples of T in duration.

The length of the FEF (which is the T2 base) is 33024*60+2048 = 1983488.
So the total duration is 407552 + 1983488 = 2391040 T = 261.52 ms.

Finally, because we are operating in high efficiency mode, the data rate is increased by (188/187) because of the removal of the transport stream sync bytes.

So the data rate = (188/187) * 264074 / 0.26152 = 1.015166 Mbit/sec.

Thank you Justin for the clear explanations about data rate calculation.

@ RichardEvans67 and Brian Gregory :

According to DVB.org, Open Channel company in Denmark plans to start DVB-T2 Lite tests in 1,7 MHz bandwidth channels.

See

Bearer performances for DVB-T2 Lite outperform existing DAB systems (still based on old Eureka 147 developments). It could be an efficient way for getting more capacity or a better quality of coverage, specially in countries where nothing has been still deployed for digital radio.

Comments from Justin (and others) are welcome !

Question to Andrew: Hi.
1) does Lite version has common PLP and Data PLP?
2) MUX of TSPS and TSPSC: does it require to alter PMT table to include common PLP TS PID also part of services that are connected to data PLP of that particaulr channel?
3) Does L1 signal still required for Lite version. SInce most of the parameters are fixed then why we need L1 signal
thanks a lot in advance
[Personal details removed by Moderator]

on CommonPLP:
1) Is it correct in saying "Common PLP" will carry only EIT and SDT TS packets?
In case yes, suppose one component is common to all channels and also have same time synch. In this case, ( as a rule 1), we can seprate this component and put it common PLP. If we do this then, is it require toalter PMT. or is it true that data PLP PMT will have information on Common PLP service as well ( this might be not true in general)... thus question is ...is it require to alter or revise PMT and PAT, we we MUX TSPS and TSPSC?

Q on CSP implementation of RX
Hi , in a function "t2_rx_dvbt2blrotcondmap" , after de-rotation there is need to put back imag part of array . Fro example following code
% undo imag shift
u2 = reshape(imag(DataRx.data), CELLS_PER_FEC_BLOCK, []);
u2 = u2([2:end 1], :);
u2 = reshape(u2, 1, []);
appears be doing exactly what is required at receiver end. But
VV007-16KFFT_TP08a_CSP.txt appears to not matching. Is there any issues in test vecot at TP08a.txt. But above code appears to be clean and good.. any advice on the above.
thanks in advance /jk

I have executed transmitter. I am not getting VV007-16KFFT_TP016_CSP.txt file which is not mentioned in DVB-T2-ReferenceStreamsDocumentation and its not showing any error too. May I know what to do.

Thanks and Regards,
Anbarasu.P.

I got error in the files
VV007-16KFFT_TP025_CSP.txt and VV007-16KFFT_TP032_CSP.txt
when i compared with the Reference streams which are given in ftp://ftp.kw.bbc.co.uk/t2refs/.

The mistake i found in the power not in values.
eg: 7.00002e00
7.00002e000
Kindly help me to clear it.

Thanks and Regards,
Anbarasu.P.