Does SA need digital sound broadcasting?

April 23rd, 2018, Published in Articles: EngineerIT, Featured: EngineerIT, Uncategorised articles

Icasa has launched an enquiry into digital broadcasting. Does this mean that South Africa will soon get digital sound broadcasting, which has been available in the rest of the world for decades? If the migration to digital terrestrial television (DTT) is anything to go by, it may still be decades away! Nevertheless, Icasa has started an inquiry about which system would be best suited for South Africa.

Through its enquiry, Icasa aims to examine the prospect of the implementation of digital sound broadcasting services (DBS) in South Africa and to examine the manner in which implementation of DSB services can improve spectrum efficiency and management.

There are two main generations of DSB: digital audio broadcasting (DAB) and digital radio mondiale (DRM). Sentech has carried trials on both systems.

In 2002 the Southern Africa Digital Broadcasting Association (SADIBA) issued a report in which it said that “to remain commercially attractive, radio as a medium will have to deliver improved quality service, greater choice, interactivity and multi-media. Digital radio technologies must rise to the challenge and deliver the multimedia radio of the future”.

Little has happened until 2014 when the subject was extensively discussed at a SADIBA Conference. The 2002 paper re-emerged and DRM came into the limelight, with international speakers and a demonstration of DRM by the BBC. They transmitted a programme in DRM from their shortwave relay station on Ascension Island with CD clarity, no noise and no interference.

In March 2014 Sentech partnered with Radio Pulpit and Broadcom to set up a DRM30 transmitting station on 1440 kHz in Kameeldrif, east of Pretoria in Gauteng.

The objectives were to:

  • Evaluate actual coverage versus predicted coverage (for both ground and sky-wave propagation modes).
  • Evaluate two different low-profile AM antenna systems.
  • Obtain sufficient measurement data to evaluate overall performance of the technology.
  • Determine if, how and where the technology could be applied to benefit broadcasters.
  • Conduct a study on available commercial radio receivers for both fixed and mobile conditions.

DRM30 is an international consortium of broadcasters, manufacturers, research institutes and stakeholders that have decided to work towards a world-standard for digital radio broadcasting in the frequency bands below 30 MHz. A later iteration of DRM30 was designed to fit in with the existing AM broadcast band plan, based on signals of 9 kHz or 10 kHz bandwidth. It also has modes requiring only 4,5 kHz or 5 kHz bandwidth, and modes that can take advantage of wider bandwidths – 18 kHz or 20 kHz – allowing DRM30 to operate alongside AM transmissions.

In later developments engineers have moved ahead and developed DRM+ for application in the FM band (88 to 108 MHz). DRM is widely used in India and some European countries.

The other system under consideration is DAB+, a digital sound standard broadcasting system designed for operating in band III (VHF and L band). DAB+ is an enhanced version of DAB with MPEG 4 AAC+ (advanced audio coding) and equal error protection added as additional features. AAC is an audio coding standard for lossy digital audio compression, designed to be the successor of the MP3 format. AAC generally achieves better sound quality than MP3 at similar bit rates. Although only 2 dB gain is achieved in the coverage area, DAB+ can accommodate three times as many channels per DAB+ Multiplex (MUX)

There are several benefits the DAB+ technology, just to list a few:

  • Good quality service because of advanced audio coding with quality not directly related to the RF signal in the planned coverage area.
  • Cost effective use, as up to 18 different stations can be accommodated on one multiplex requiring only one transmitter for each coverage area.
  • Enhanced user experience as DAB+ offers additional functionality such as electronic programme guide, news feeds and slideshows.
  • The single frequency network allows more efficient use of limited spectrum with more transmitters at different locations.
  • Capable of operating in simulcast mode broadcasting analogue and digital simultaneously. This could assist during analogue to digital migration.
  • Includes hand-over capabilities between different radio platforms such as DAB+ and FM and vice versa.

Sentech is doing DAB+ trials in the Gauteng area in a collaborative initiative with SADIBA and the National Association of Broadcasters (NAB).

LM Radio, which broadcasts from Johannesburg on 702 kHz AM, is part of the Sentech DAB+ trial. In the studio, presenting LM Morning, is Errol Ballantine.

Two high power transmitters were installed, one in Johannesburg on the Brixton Tower and the another one in Pretoria operating in Band III on channel 13f at 239,2 MHz.  The two stations operate in a single frequency network (SFN). The stations were evaluated separately as well as together at 2 kW, 5 kW and 10 kW power levels.

The DAB+ coverage verification exercise was started on 20 January 2015 with the Johannesburg transmitter running at 2 kW. The power was increased and coverage verification trails were run from 22 April till 5 May 2015. The same exercise was conducted from 8 May till 19 May 2015 running 10 kW.

The findings of the trial showed that at 2 kW line-of-sight paths are required to ensure sufficient coverage and good quality of service. Running the transmitter at 5 kW, the coverage and service quality in no-line-of-sight areas greatly improved. Signal penetration into vehicles also improved while penetration into buildings remained problematic. Increasing the power to 10 kW a much denser coverage was seen as well as good building penetration.

The current trial started in November last year and carries 20 radio services from the public, commercial and community sectors. The trial license runs out on 10 May 2018, but there are indications that an application will be made to Icasa to extend the trial period.

DAB+ is by far the most popular system and is widely deployed in Europe, the USA and countries in the Far East. Icasa is asking industry and the public to comment on:

  • Is there a need for DSB technologies in SA?
  • Are the current technical standard for equipment adequate?
  • In absence of a policy directive, should Icasa provide licenses to test other DSB technologies?
  • SA, through its international agreements at ITU and SADC level, agreed on DAB+ and DRM systems. Should any other DSB technologies be considered?

The full document was published in Government Gazette 41534 on 29 March 2018 and available on www.icasa.org.za. The closing date for comment is 11 May 2018.

Send your comments to engineerit@ee.co.za

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