Digital TV standards battle: ISDB-T demonstrated in SA
Sentech recently hosted a technical demonstration of the Japanese ISDB-T digital broadcasting standard at their site in Kameeldrift, which was requested by the Brazillians and Japanese to prove that the technology could work under South African conditions.
Integrated Services Digital Broadcasting – Terrestrial (ISDB-T) is a broadcasting standard for digital television that was developed in Japan.
DVB-T and ISDB-Tb: The saga in brief
The South African Department of Communications (DoC) surprised local stakeholders when ex-director general Mamodupi Mohlala announced that South Africa hadn’t selected a standard for digital terrestrial television (DTT) standard.
Many industry players, including e.tv and M-Net, rubbished the DoC’s statement, pointing to the Broadcasting Digital Migration Plan (BDMP) gazetted by the department itself, as well as regulations published by ICASA earlier this year.
Both the BDMP and the regulations addressed Digital Video Broadcasting – Terrestrial (DVB-T) as South Africa’s chosen DTT broadcasting standard.
There has been a back and forth of claims and counter claims by the proponents of DVB-T and ISDB-T/ISDB-Tb, the standards seen as the most likely candidates for digital broadcasting in South Africa.
ISDB-Tb is the Brazillian version of the ISDB-T standard.
The suitability of ISDB-T for South Africa has been questioned. Some of the issues that were raised are:
- Channels in South Africa are 8 MHz wide and ISDB-T has only been deployed in countries with 6 MHz channels.
- Some or all investments in DVB-T systems would be lost.
- ISDB-T set-top box (STB) prices are much higher due to economies of scale.
- South Africa already has the skills needed to run DVB-T and can switch to digital in six to nine months if it sticks to the European standard.
- Policy and regulations for DVB-T already exist. Switching to ISDB-T would delay the migration to digital broadcasting by years.
Configuration and other technical data
A delegation from Japan consisting of representatives from the Association of Radio Industries and Broadcasting (ARIB), Nippon Hoso Kyokai (NHK) and NEC Corporation set up a demonstration for the ISDB-T system at Sentech’s Kameeldrift site.
The objective of the demonstration, they said, was to test the feasibility of 8 MHz ISDB-T with MPEG 4 in South Africa.
For the purposes of the test, 19 radio channels, 4 standard definition (SD) video channels and one low resolution (QVGA, 320×240) “one-seg” (or mobile TV) channel were multiplexed onto a single 8 MHz spectrum channel.
According to the Japanese delegates as well as Sentech, ICASA provided channel 54 at 738 MHz for the purposes of the test and they’re broadcasting at 2 kilowatts.
From the spec sheet provided as well as readings from the test instruments, both QPSK and 64QAM were used to modulate the signals and a guard interval of 1/4 was used.
While not visible on the test instruments, the spec sheets and Japanese delegates indicated that a forward error correction (FEC) rate of 2/3 was used for the QPSK layer and the 64QAM layer used a 3/4 FEC rate.
Unfortunately the exact bitrate of the broadcast couldn’t be provided.
Equipment used
Hiroyuki Furuta, senior engineer at the science and technology research laboratories at NHK explained that they essentially provided four pieces of equipment:
- An ISDB-T multiplexer.
- An ISDB-T exciter.
- A transport player for playing the “one seg” content.
- A set-top box.
According to Furuta everything else was existing infrastructure provided by Sentech. Tebogo Leshope, a project manager at Sentech, confirmed this.
STB price
Masa Sugano, First Secretary of economic and commercial affairs at the Embassy of Japan in South Africa said that the prices of set-top boxes are dependant on industrial policy and competition.
According to Sugano STBs are expensive in Brazil because they decided to manufacture them domestically and not allow imports, and not because they decided to adopt ISDB-T.
ISDB-T set-top boxes could cost as little as $30 (USD), Sugano said.
Skills transfer
Tebogo Leshope, a project manager at Sentech, said that Sentech personnel have been involved in the setup of the ISDB-T demo. If proper processes are followed, a report about the knowledge gained will be written and shared with the SA broadcasting industry, Leshope added.
Shortcomings of the demo
All the measurements were taken straight from the ISDB-T equipment in Sentech’s Kameeldrift base station, rather than from signals transmitted from the base station.
The only video that was received over the air and displayed was the “one-seg” low resolution mobile video.
However, the delegates said that they would be doing a demonstration at the Japanese embassy in Pretoria on Thursday. For the demo signals from Kameeldrift would be received, measured and displayed and the Japanese delegates were confident that it would perform well.
As only one site was set up, the possibility of a running a single frequency network (SFN) on ISDB-T couldn’t be demonstrated. This is when several transmitters simultaneously send out the same signal over the same frequency channel and can allow for more efficient use of spectrum.
Masayuki Ito, director of the broadcasting group at ARIB, said that ISDB-T could be configured to run as a SFN and was used as such in Japan.
Sugano added that SFN configurations were used on ISDB-T in Brazil as well.
Leshope said that should the demo continue at the request of stakeholders the plan is to add an additional two sites to the demonstration network in order to test SFN operation.
Bottom line
ISDB-T seems to be able to work on 8 MHz channels and if the STB cost provided by Sugano is accurate then the set-top boxes for the Japanese standard aren’t necessarily more expensive than those for DVB-T.
A switch to a different standard will still make the DVB-T equipment already procured by broadcasters redundant, however.
South African broadcasters also still have years of experience with DVB-T and the current policies and regulations are all written with DVB-T in mind.
It’s unclear how much a switch in standards would delay our migration to digital TV broadcasting, but industry players have predicted anything from 3 to 5 years.
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