At last week’s SMPTE conference ACMA’s Acting Manager of Broadcast Engineering in the Broadcast Planning Branch, Alastair Gellatly gave the regulator’s perspective on digital radio.
In a speech to the conference, Gellatly provided an update on the available digital radio technologies including, and touched on the latest on what is happening in relation to digital radio in Australia and elsewhere in the world.
The paper drew on the work of the Digital Radio Study Group (DRSG) report titled Digital Radio Technology Update, which was released in September 2003.
Gellatly told the conference most of the standards remain unchanged since 2003, however, there are some new developments.
“Firstly, there are two new standards, and secondly receiver availability and prices are constantly changing for the operational systems. The new DMB and DVB-H standards are both primarily targeted at mobile video or multimedia, however, they also have potential as technology platforms for the delivery of digital radio… The DMB standard is a variant of the existing DAB digital radio standard but offers the ability to use more advanced audio coding.”
Gellatly says there are quite a range of possible technologies for digital radio, but concludes there is “really only one choice if you were to start a service now,” and that standard is known as DAB (Digital Audio Broadcasting) also known as Eureka 147.
DAB is a digital radio system developed in Europe. One of the strengths of DAB is that it is a mature technology with established standards implemented widely, in Canada, the UK, Germany and other parts of Europe. DAB is a broadband system requiring a 1.5 MHz channel, that can offer five simultaneous CD quality services at 224 kilobits per second (kbit/s) or considerably more services at lower quality.
In the UK, digital radio operators are currently providing a mixture of five to six stereo services at 128 kbit/s or 160 kbit/s; three to six mono services at 64 kbit/s or 80 kbit/s and some data services in each 1.5 MHz channel. Although DAB was designed to operate over a wide spectrum range from 30 3000 MHz, it has only been commercially implemented in two spectrum bands, VHF Band III and L Band.
But there is a disadvantage to DAB says Gellatly:
“As an older technology, however, its audio compression techniques are less efficient than more recently developed digital radio technologies. This means that fewer audio programs can be transmitted within a given bandwidth.
“DAB uses spectrum currently used for analog and digital television, defence services and radiocommunication services. Although the future return of analog television spectrum may present an opportunity for DAB, finding sufficient spectrum in the meantime poses challenges because of current use by other services. If DAB was to be implemented in Australia, there is in general more capacity in L Band than in VHF Band III. However, L Band is seen as a less attractive proposition than the VHF band, due to its inferior propagation properties in urban areas.
“This shortage of VHF spectrum suitable for wide coverage poses problems for both augmentation and conversion models of digital radio introduction using DAB, as L Band DAB would require numbers of new transmission sites within each major city and may not be an economically viable way to provide wide area coverage in regional areas, where many L Band transmitters would be required to replicate the coverage of a single VHF Band III transmitter. Meanwhile, the supply of VHF spectrum currently available in advance of analog television switch off is extremely limited. ”
Only 6 MHz of VHF Band III channel 9A, is available in each of the five major cities and in many of the existing radio markets that are adjacent to them. Trials of DAB services in Sydney have demonstrated that a 6 MHz channel 9A can support three DAB multiplexes. However, to minimise the potential for interference to or from adjacent channel television services, DAB transmissions on VHF channels need to be constrained to the same transmission sites as VHF television services and limited in power to less than 15 kW effective radiated power.
Gellatly told the conference that the World DAB Forum and the Digital Radio Mondiale (DRM) have formed a strategic alliance with the potential for common DRM/DAB receivers to be developed.
Radioscape Ltd in June 2005 announced the development of a analog/DAB/DRM radio module that would be available in August. Radioscape forecast that multi-standard receivers using the module could be available as early as December 2005 for around A$340.
The price of DAB receivers is continuing to fall according to Gellatly, with the cheapest home/portable receivers falling from A$250 to A$108.
The price of the cheapest car receivers fell from A$750 to A$445 and the cheapest ‘hand-held’ receivers fell from A$355 to A$140.
With increasing interest in DMR, and the possibility of an official trial of that digital broadcast technology in Canberra soon, Gellatly also explained how DRM workd:
“Digital Radio Mondiale is a narrowband digital radio system designed for use in the low frequency (LF) medium frequency (MF) and high frequency (HF) terrestrial broadcasting bands below 30 MHz. DRM was originally designed as a green-fields solution in that it requires a clear frequency to operate effectively. It was designed to augment existing services by operating with the existing channel spacing employed for amplitude modulated (AM) broadcasting and for HF broadcasting worldwide. It can carry audio and/or data with the flexibility to trade off between audio quality, data capacity and signal robustness. A version of the DRM system has also been designed to facilitate conversion of analog services by permitting simulcasting in analog and digital modes. Under this system, the analog and DRM transmissions would occupy a similar bandwidth to an ordinary AM MF service. The feasibility and practical implications of DRM’s simulcast operation has also yet to be established.
“DRM operates on very low bit rates, typically of the order of 20-25 kbit/s, however due to the use of AAC+ audio coding it can provide audio quality comparable to FM radio. Other audio coding standards are provided that allow for multiple voice only services at bit rates from 2.4 kbit/s to 6.4 kbit/s.”
Currently, no consumer DRM receivers are readily available. The Mayah 2010 is the closest thing to a consumer receiver and costs approximately A$1500. Most other DRM receivers are software based and require a computer to process the signal.
According to Gellatly, the biggest advantage of DRM is its ability to cover large areas and its modern audio coding.
He also spoke about the American IBOC system, saying there are “fewer operational concerns with IBOC FM” as the same FM channel arrangements are used in Australia and the US, however, the US does not use any frequency offsets (ie. the decimal place in the MHz frequency is always an odd number) and this could lead to some receivers not being able to tune to some of the offset stations like 103.2 MHz in Sydney. He referred to the IBOC tests at SMPTE (reported on radioinfo last week).
Commenting on radio’s increasingly significant competitor, the internet, he said:
“The Internet is sometimes touted as a future competitor to digital radio in the provision of digital audio entertainment and information. ‘Internet radio’ or audio streaming via the Internet to PCs has been available for some time. Radio content available on the Internet is already being included in ratings statistics in the UK when considering the number of people accessing digital radio (alongside DAB and digital television broadcasts)…
“Though the Internet makes radio services from all over the world available, it suffers from lack of mobility, low sound quality, cost of bandwidth and limitations on the number of PCs to which services can be streamed simultaneously.
The mobility problem may be partially addressed by Wi Fi systems…
A Wi-Fi like system is being deployed in a number of Australian cities under the name ‘iBurst’, which can provide mobile broadband to computer modems travelling up to 100 km/h. ”
In future there is likely to be increasing migration of Internet applications to mobile platforms such as telephones and Personal Digital Assistants (PDAs), although whether these applications will ultimately include streamed audio entertainment is unclear according to Gellatly.
“Indeed, there are indications a more likely hybrid in the short term could be mobile telephones that contain digital radio receivers.
“A relatively recent competitor for radio listeners are the IPOD and MP3 player, and the ability to down load ‘Podcasts’. Podcasting refers to the practice of program material being made available for down loading over the internet for listening to later on the IPOD or MP3 player.”
He is hopeful of some official policy announcement about digital radio in the near future.