User:Ryan Cooley/DAB

Rough Draft. Probably take a month to look like anything.

Digital Audio Broadcasting (DAB, or EUREKA-147) is a standard for transmitting lossy encoded digital audio.

History

The EUREKA (European Research Coordination Action) project is a pan-European, intergovernmental initiative, for industrial (non-military) research and development. It does not have any association with the European Union (EU), even though the two share many common goals.

DAB has been in development since 1981, initially by Institut für Rundfunktechnik (IRT).

In 1987 the E!147 project started, taking 6 years to define the DAB standard, and several more to implement it. The DAB standard was publish February 1995, and experimental broadcasts began a few months later (such as the BBC in London). The project ended in 2000, costing a total of 89.2 million Euros. Germany and France contributing the majority, at 36% each.

DAB, DAB+ and DMB are all part of the Eureka-147 family of standards. http://www.dab-digitalradio.ch/?lang=en&c=db_gl#DAB+

"The EBU and the Eureka 147 DAB (Digital Audio Broadcasting) project set up a joint group in 1992, in order to evaluate the performance of the Eureka 147 DAB system."

So the WorldDAB Forum decided in June 2005 to start the development of an alternative audio system for DAB ­ the Technical Committee set up the Task Force, New Audio System. The result of 1.5 years of enthusiastic work ­ the norm "Transport of Advanced Audio Coding (AAC) audio" was published by ETSI in February 2007 and was announced publicly as DAB+ at the same time.

Adoption/Stats: http://www.ebu.ch/en/technical/trev/trev_311-dab_dmb.pdf

 Electronic Program Guide (EPG)
 Intellitext

DMB...

DAB+ was published in February 2007

RF

OFDM:

 Multipath, Doppler Shift, Interference.
 Inter-Symbol Interference (ISI)
 Fast Fourier Transform (FFT)
 Differential QPSK 
   4 quad. phases (0°, 90°, 180°, 270°.)
   no channel equalization needed
   (up to) 1536 (narrowband) carriers
 Guard Interval 
   1/4th symbol length interval
     copies end of symbol before start of symbol
   Multipath
   Single-Frequency Networks (FSN)
 Synchronization
   Null symbol
   Phase Reference Symbol (PRS)

Frequency-Domain Multipath

 (Punctured) Convolutional Coding (COFDM)
   Forward-error correction (FEC)
   Normally; half-rate. == 1.2Mb/s
   Viterbi decoder (put the digital signal in the correct chronological order and check the signal for transmission errors)
 Bit-stream re-ordering; Pre-determined patterns
   Temporal:  Between Frames; depth 360ms
   Frequency: Interleaving.  

 The performance of this modulation scheme in

various channels is described in ETSI 101 758: Digital Audio Broadcasting (DAB); Signal strengths and receiver parameters; Targets for typical operation. For an MPEG-1 Layer II codec, the C/N for non-audio impairment is 14 dB for the majority of locations in urban and rural environments and at speeds below 130 km/h.

-15 db average loss indoor reception

UEP 3 (~0.5)

4 transmission modes, 1,2,4,8KHz wide

 Mode 1: Band III (4x1.54MHz DAB in 7MHz UKTV space)  
   70km max SFN antenna spacing
 Mode 2: L-Band (1452-1492MHz, world) 
   est 17km max SFN antenna spacing
 Mode 3: up to 3GHz for satellite
   est 8km max SFN antenna spacing
 Mode 4: L-Band, sometimes appropriate (L-Band SFNs)
   est 35km max SFN antenna spacing

useful payload (0.6 - 1.7 Mbit/s) available. 6 x 192Mb/s MP2 = 1.2Mb/s Fast Information Channel (FIC) - Non-interleaved

 Multiplex configuration information 
 reference frequency and timing information
 overhead and control. 
 Multiplex Configuration Information (MCI).

?Service Information (SI) Main Service Channel (MSC)

 MP2 audio

Packet Demux for datacasts 24ms frames

Data Services

"ETSI specification, EN 300 401 (Second Edition) specifies the transmitted DAB signal."

'CD quality' using bit-rates of 192 kbit/s or above for stereo

Transmission mode I is intended for terrestrial Single Frequency Networks (SFN) and loca-area broadcasting in Bands I, II and III. Transmission mode II is intended to be used for terrestrial local-area broadcasting in Bands I, II, III, IV, V and in the 1,452-1,492 MHz frequency band (i.e. L-Band).

The DAB signal comprises a succession of transmission frames of 96 ms duration in mode I and of 24 ms duration in mode II. Within these transmission frames, the synchronization channel occupies approximately the first 2.544 ms in mode I, and approximately 0.636 ms in mode II.

(Mode I) ... permits the use of relatively widely-spaced transmitters, whereas in transmission mode II the However, mode II has fewer radiated carriers; also, for mobile reception in L-Band, the greater frequency seperation of the carriers is intended to reduce the effect of Doppler shifting for reception in moving vehicles, especially at the higher speeds. There are 1,536 radiated carriers in mode I, and 384 carriers in mode II, in a system bandwidth of about 1.54 MHz.

Ensemble - A 1.536MHz block of carriers. ETSI - European Telecom Standardization Institute.

Forward Error Correction Levels: Error Protection Level FEC Rate Capacity required for a 192 kbits/s MP2 channel 1 0.34 568 kbits/s 2 0.43 448 kbits/s 3 0.51 384 kbits/s 4 0.62 312 kbits/s 5 0.75 256 kbits/s

Protection level one offers the best protection with a coding rate of approximately 1/3. Level five offers the least protection and has a coding rate of approximately 3/4.

Examples of SI are

• Service identifier.
• Programme type.
• Radio frequencies of associated FM, MF and digital radio services.
• Announcement switching (linked to announcement channels in an ensemble).

FIC 96 kbit/s (fixed 64 kbits/s ECC) MSC 2.304 Mbit/s

The time and frequency interleaving procedure ensures that bits which are adjacent in time in the sub-channel bit stream are not adjacent in time and frequency when coded onto the 1536 carrier of digital radio signal.

Data Coding

MPEG-1 Layer II audio at 48kHz or 24kHz

A 192kbit/s DAB channel can cost from 2 to 20 million Euros, depending on how well utilized each transmitter is.

insert PAD into the Musicam frames

UK

 "The BBC covers 85% of the UK population" 

 "In the United Kingdom, 12.5 MHz of Band III spectrum from 217.5 - 230 MHz has been allocated to DAB. This will accommodate seven multiplexes. The BBC has been allocated one of these channels for its national DAB multiplex"

 "RDS travel bulletins to interrupt listening,"

World

 "100 million people" circa 2007

DAB+

 MPEG-4 HE-AAC v2

 Reed-Solomon additional ECC 8.3% overhead
 Marginally better fringe reception due to R-S
 Muting instead of artifacts

 Stream and Packet Mode. The ten parity bytes per 110 data bytes ­ equivalent to an over-head of 8.3%­ lead to an ability of correcting up to five erroneous bytes in those 120 bytes (Fig. 9).

 DAB+ was published in February 2007 as ETSI TS 102563 "Digital Audio Broadcasting (DAB); Transport of Advanced Audio Coding (AAC) audio".

 HE-AAC v2 provides the same perceived audio quality at about one third of the sub-channel bitrate needed by MPEG Audio Layer II.

DAB+ Bullshit

Moser AAC+ Bullshit. Does not mention MP2 at all Ridiculously low AAC bitrates are cited are based on ITU-R BS. 1534 MUSHRA (Multiple Stimulus Hidden Reference and Anchor) testing, versus ITU-R BS.1116-1 testing for older, higher MP2 bitrates.

For traditional DAB, SBR can be combined with MP2 to provide better audio quality at a given bitrate (to newer receivers equipped with SBR decoding), while legacy decoders would still be able to listen to a lower quality audio signal. This would eliminate the need for the 8% overhead of reed-solomon codes, and maintain backwards compatibility with DAB receivers already sold. Tests by IRT have shown that DAB reception is not affected by SBR.

CTAAC+ http://www.ebu.ch/trev_291-dietz.pdf DRM http://www.ebu.ch/trev_286-stott.pdf

External Links

• ETSI List of DAB Standards
• WorldDMB List of DAB Standards