Until now the Eureka 147 DAB digital radio standard has always been broadcast using MPEG 1 audio layer II encoding. Since the original introduction of the Eureka 147 digital radio broadcasting standard (commonly referred today as ("Classic DAB"), more efficient coding schemes and algorithms have emerged.
With the official adoption in 2007 of the HE-AAC v2 audio codec for use with the Eureka 147 digital radio standard, DAB+ emerged. DAB + uses MPEG-4 HE-AAC v2 also known as aacPlus v2. This audio codec is the most efficient audio compression scheme available worldwide. It combines 3 technologies:Advanced Audio coding (AAC), Spectral Band Replication (SBR) and Parametric Stereo (PS).MPEG-4 AAC is the core audio codec, SBR a bandwidth extension tool, enhances efficiency by using most of the available bit rate for the lower frequencies of the audio signal. The decoder generates the higher frequencies by analysing the low band and side information provided by the encoder. This side information needs considerably less in terms of bit rate than would be necessary to encode the high band with the core audio codec. With PS a mono down-mix and side information is encoded as opposed to a conventional stereo signal. The decoder reconstructs the stereo signal from the mono signal using the side information.
COFDM technology, (Coded Orthogonal Frequency Division Multiplex) ensures that signals are received reliably and robustly, even in environments normally prone to interference. Using a precise mathematical relationship, the digital data signal is split across 1 536 different carrier frequencies, and also across time. This process ensures that even if some of the carrier frequencies are affected by interference, or the signal disturbed for a short period of time, the receiver is still able to recover the original sound.
The interference which disturbs FM reception, caused by radio signals 'bouncing' off buildings and hills (multi-path) is eliminated by COFDM technology. It also means that the same frequency can be used across the entire country, so no re-tuning of sets is necessary when travelling, or taking a portable receiver to a different area. Instead of having a different frequency for each radio station, DAB+ combines several services together in what is called a multiplex.
FEATURES of DAB+
- DAB+ provides the same perceived audio quality at about 1/3 of the subchannel bitrate needed by MPEG Layer II.
- The same codec is also used in DRM and DMB.
- All the functionality available for MPEG layer II services is also available for DAB+.
- MPEG Layer II and HE-AAC v2 radio stations can coexist in one ensemble.
- The geographical coverage area of radio services using HE-AAC v2 is slightly larger than that for radio services using MPEG Layer II.
- The multimedia information carried in PAD of an HE-AAC v2 radio service is much better protected against transmission errors than PAD data of a radio service using MPEG Layer II.
BENEFITS of DAB+
- Latest MPEG-4 audio codec delivers exceptional performance efficiency
- More stations can be broadcast on each multiplex
- Greater station choice for consumers
- More efficient use of radio spectrum
- Lower transmission costs for digital stations
- New receivers are backwards-compatible with existing MPEG layer II broadcasts
- Current MPEG layer II services and consumers unaffected
- Compatible with existing scrolling text and multimedia services
- Robust Audio Delivery
- Optimised for live broadcast radio
- Broadcasters/regulators can select standard MPEG layer II, DAB+ or both to suit their needs
- Fast retuning response time (low zapping delay)
- MPEG Surround is possible
OTHER SYSTEMS USING AAC
- Apple Ipod
- Digital Radio Mondiale (DRM)
- Intergrated Services Digital Broadcast (ISDB)
- XM Satellite Radio
- Interference free mobile reception Crisp CD like audio quality.
- Seven and more services on one transmitter.
- Multimedia radio that delivers video, audio and data services.
- High spectrum efficiency through SingleFrequency Network operation of transmitters.
- The most established of all the digital radio technologies is based on the Eureka 147 system for Digital Audio Broadcasting.
- The European technology was designed to deliver interference free CD quality audio and data services into the mobile reception environment.
- Several services are multiplexed together and delivered to the receiver with via a new multi-carrier systems.
Large National Networks are operational in the UK, Sweden and Germany.More than 230 million people across the world were by August 2000 served byterrestrial Eureka 147 DAB signals.
Sentech established Africa’s first DAB pilot broadcasts in December 1997 Under the auspices of the Southern African Digital Broadcasting Association (SADIBA) seven services were accommodated on the Sentech pilot transmission. Ongoing investigations under the Sentech pilot transmissionwill include the development and insertion of data services as well SingleFrequency Network test.
The high cost of DAB receivers coupled withregulatory delays, the subsequent slow roll-out of network infrastructure and services has resulted in a relatively slow market introduction of the technologyworld-wide. Combined and co-ordinated marketing efforts in the UK have forthe first time lead to an uptake of DAB and receiver sales into the consumer market. The majority of the DAB receivers available today are car type receivers. Home receivers as well as PCI plug-in cards that will operate with in a Personal Computer are also available. (Refer to Figures 2 and 3).
Eureka 147 is unique in delivering high quality audio and high speed data services. DAB receivers will provide data services either via a colour display on the Radio, a PC screen or a data port.
Data services that can accompany the audio content are called (Programme Associated Data) and may include drawings for a biology lesson, the CD cover of the song playing, a picture of the news event, a graphic showing the day’s stock performance or the advertised product. Interactive services will deliver web-based services while short text services will further enhance the radio experience.In the pipeline are specifications for (Non-Programme Associated Data) services that will deliver data not necessarily part of the audio services such as electronic newspapers or the Internet. DAB technology is poised to merge with other mobile telecommunication technologies such as GSM and UMTS. DAB according to Eureka 147 delivers the multimedia radio of the future.
DMB mobile TV uses exactly the same transmitters and broadcast technology as DAB and DAB+ though allows broadcast of video services. A DMB signal can be transmitted alongside existing DAB and DAB+ signals, using the same network infrastructure. DMB mobile TV is successfully deployed in South Korea and is available in Europe.
For more information visit www.worlddab.org