Digital Radio Mondialetechnical and market progression – Australia and International by TJH Systems Pty Ltdpresented byTrevor HarwoodGlen EnglishDecember 2006
Basic overview of DRM • Developed in Europe • MF-HF Specification matured as a standard approx 2 years ago. • Designed for noisy, time dispersive channels with low SNR • Uses COFDM modulation like DVBT and DAB • Ideal for MF services up to 300km • Ideal for HF/ SW Vertical Incidence and international service
DRM overview • Occupied bandwidth 4.5 to 20 kHz which is designed to fit in existing MF and HF planning • Data pipe from 7 to 65kbps depending on robustness and bandwidth • Typical for 9 kHz allocation is 23.6kbps. • MPEG4 AAC-HE and low bit rate speech codecs supported
Broadcaster advantages • Audio signal to noise and frequency response improved compared to current analog MF and HF broadcasting • Can carry multiple programs at different qualities in the one stream. • Program information low data rate channel • Multipath distortion that limits existing coverage improves nighttime service and extends fringe
Advantages cont... • Supports SFN- Single frequency networking – efficient spectral re-use • Power levels, equipment types, antenna technology are similar to existing infrastructure • Network broadcasters will have consistency across their network.
Radio Market • Convergence is the buzzword : • Mature , established digital radio technologies such at DAB, DMB-T provide interactivity, low resolution video, data facilities . • DVB-H is a data pipe platform optimised for mobile delivery in the UHF bands and can provide DMB-T’s facilities and more. • Commercial radio feels the need to keep up with competition from multimedia mobile phone services and personal audio players.
Digital downsides • But this additional multimedia comes at a price-- robustness • Insufficient signal (excessive BER) has a catastrophic effect on program. • Users are used to analog style degradation, and will put up with the odd bit of noise and distortion from time to time • Digital services- nothing graceful about their degradation- dropouts are abrupt and it often takes time to re-synchronize.
Audience retraining ? • Audiences will not tolerate a new medium that has such interruptions and behaviour – this will influence its success. • Audiences cannot easily find a good spot amongst bad spots for their receiver • The better the digital system, the more abrupt the location variability near the threshold.
Big signals required... • This abrupt dropout effect generates a very high reliability requirement and is a headache for planners and operators • Engineers are only recently developing techniques for combating in-building and high local multipath environments • Mature digital radio technologies such as DAB and DMB-T are sub-optimal compared to recently developed technologies
No need to discard DAB related technologies though • Good receiver base • Much experience in the UK with regards to requirements and quality of coverage. • High field strengths developed by high power and/or multiple transmitters can successfully fix these defficiencies for mature technologies. • Generating high field strengths to replicate existing analog coverage unlikely to be practical for rural and wide area services.
Analog Robustness = success • Existing analog radio is robust • Listeners tolerate a little noise, distortion. • The majority of the current audience just want reliable reception everywhere they have it now. • Radio has been successful because the audience listen when they are doing something else, or with their eyes shut. • Radio’ success is also its content which the quality must be held to hold it’s success.
DAB/DMB-T have been successful in Europe, but : • Australia does not have the population density of the European markets • In Europe, broadcasters choose not to cover dispersed population centres as it is impractical and uneconomical to generate the high field strengths. • Australia’s ABC MF services provide blanket coverage over large areas with little infrastructure. • DAB / DMB-T provide an excellent service in well populated cities- but regional application will leave many without a service.
US IBOC Systems • United States has developed their own ‘HD’ named digital system • Uses same spectrum as existing FM services. • Provides ~ 100kbps multiple program MPEG4 audio pipe • Supports SFN • Mitigates dropouts with fade back to analog.
US IBOC Systems • >800 stations on air • FM HD system provides excellent coverage with full digital upgrade path. • AM HD system uses adjacent channel. • Not successful at this time as nighttime propagation prevents the adjacent channel operation.
DRM technologies • MF- DRM useful for duplicating and improving local and wide area AM services • HF –DRM a superior solution to AM or SSB for vertical incidence outback HF services • DRM+ for Band I and Band II is being tested . • DRM+ provides state-of-the-art transmit diversity to mitigate local indoor multipath at VHF frequencies that troubles DAB/DMB-T.
MF DRM • Fits into existing channels • 9kHz bandwidth –half existing 18 kHz analog bandwidth – 2x ch. • High resistance to impulse noise • Skywave’ self fading’ and multipath distortion at fringes can improve performance! • Provides equivalent coverage to analog service at same peak power
Equivalent Service • ‘Equivalent service’ depends on ones’ definition of the minimum service level. • CCIR take this as ~30dB SNR • Most MF listeners would be comfortable at 23dB SNR. • 20dB SNR is the average performance achieved at the currently defined service fringe of 54dBu. • Punters listening to Racing Radio or Cricket fans listening to the 5th day of the Adelaide Ashes test would consider 6dB SNR was a usable signal
HF DRM • Chalk and cheese for international shortwave services. • Half the average power consumed or better. • Tolerates very long delays that can occur on multihop round the world paths. • Broadcaster can transmit multi lingual programs simultaneously. • Eliminates multipath distortion due to multiple hops on outback Vertical Incidence services.
26 MHz band • Existing ITU broadcasting band – recognized internationally. • Seldom used for SW broadcasting except during the peak sunspot years • Ideal for local coverage DRM • Has advantages of low noise and minimum spill beyond line of site- ideal for generating well defined coverage areas.
MF and 26 MHz DRM • Majority of receivers operate LF, MF to HF (30 MHz) • Transmissions contain alternate frequency information so that receivers can auto-search-tune. • MF can be used for wide area blanket coverage • 26 MHz band can be used as fill-in cells where noise and man made interference in heavily built up areas makes MF coverage impractical. • Localized community and commercial radio
World wide development - HF • HF – Shortwave services- many players • Over 5000 hours per week are broadcast • Radio New Zealand- > 100 hours per week. • Immediate success
International Development – MF and 26 MHz • Over 10 full time stations in Europe. • Not as developed as HF-SW, but growing • Many countries from Finland to Mexico have both MF and 26 MHz tests in progress • European local market broadcasters considering DRM to compliment DAB services where DAB coverage is impractical.
Australian Development of DRM • Since May 2006 , TJH Systems have had a 24 hour facility at Wollongong on 1386 kHz transmitting ABC local radio. • 1kW power using Broadcast Electronics transmitter and DRM exciter designed by the author. • Combined into co-sited MF service DA.
DRM Wollongong Test • Demonstrated coverage similar to 2kW ABC service next door. • Can be received daytime in Sydney south of the harbour, much of NSW at night. Has been received in Adelaide • Phase one complete, full results online at : www.drmtrial.com.au • Phase two through summer investigates impact of thunderstorms on service level requirements.
Impulse response of Wollongong DRM Test received in Sydney Late afternoon Early evening
Constellation of Wollongong received in Sydney early evening- 16QAM mode A
Aust. development cont.. • Canberra test on 1440kHz by Broadcast Australia. Short test and no results of this test have been published. • Radio Australia have an HF facility at Brandon which is currently in commissioning stage. • TJH Systems have 26 MHz tests planned for 1st Q 2007.
Planning Issues- MF • Basic study shows the current spectrum can accomodate a DRM transmission for every existing program, with the following adjustments to MF broadcasting : • a) A reduction of fringe area (54 dBu) night time co-channel protection from 30dB to 23dB. • Existing fringe nighttime SNR’s are less than 23dB due to atmospherics, man made noise, and poorly functioning DA’s. • Analog signal quality will be generally unchanged
MF planning adjustments.. • b) Modulation bandwidth limiting from 9kHz audio response to 4.5kHz, thus halving the transmit bandwidth. • The large majority of radios have 10dB bandwidths of less than 4.5kHz • Some have 3dB bandwidth of < 2.5kHz ! • Modern audio processors can develop very aggressive pre-emphasis and brick wall responses which largely negates the losses of the transmitter high frequency(>4.5kHz) components
MF planning adjustments.. • The number of channels available is therefore approximately doubled. • Night time signal quality for all analog services will be vastly improved as adjacent channel splatter (which is a result of 9 kHz spacing and 18kHz transmitted bandwidth) will no longer occur.
MF DRM • DRM supplimentry licences provided for existing services would be allocated to allow a low degree of difficulty combining the service into existing infrastructure. • Like ABC services can operate as SFN’s providing improved coverage with less spectrum utilisation. • Therefore a statewide program may save over 10 channels. • Biggest headache for MF-DRM is the spectral pollution that has gone unchecked for many years.
26 MHz Band Planning • MF planning is ‘hard’ – 26 MHz band planning can be simplified by : • ERP restrictions : approx 50W • HAAT restrictions. • The right combination will yield reuse at less than 200km • Will provide planning staff simple rules and readily computer optimised. • Skywave propagation features in this band. • If coverage requirements and power is limited, interference by skywave will be minimal.
Receivers ? • Receivers tune a station based on a program or service name, not frequency or channel. • Are becoming ‘software defined’- that is the logic gets programmed at startup time to perform a particular decoding function, eg : DAB or DRM. • We are seeing all mode DRM, DAB, AM, FM units.
Receivers - • Two streams of receivers currently : • Morphy Richards, Roberts, some German fixed receivers • approx 199 Euros ~ AUD$360 • based on Radioscape integrated tuner • Feature multi mode- DRM, DAB FM and AM • Performance is acceptable for a first generation design.
Receivers • Himalaya – Hong Kong designed DRM / AM compact desktop • Mayah – compact unit ran a short production. • Other receiver options on the www.drm.org website.
Receivers • Second Stream : Software Decoders- • Open source software and PC sound card with modified conventional tuner . • “DREAM”, “Fraunhofer decoder” • ‘Enthusiast’ software defined radios such as : • WINRADIO – built in decoder. • SatSchnieder DRT-1 • Elad FDM77
Limitations, restrictions. • Power consumption of these receivers is still a full order of magnitude too high. • This is in line with DAB receivers which have similar impractical power consumption for small portable devices. • Power consumption will drop dramatically as ASICs are developed. • DRM is low bandwidth and requires less power than older digital technologies.
Chicken and Egg • Consumers bitten by AM-Stereo .The industry got behind it-, the receiver manufacturers didnt. • It was easier and more profitable building $1 radios than competing with a $3 radio. • Digital radios will never(?) be a cheap as analog radios but what is being delivered is generally whole lot better than what the analog radio can deliver. Apples for apples and consumer education required. • Currently mainstream receiver manufacturers are hesitant to commit to large runs (and price drops) until they see broadcasters putting signals to air.
Success ? • FM was a huge success because in the cities, it was a tremendous improvement on AM of the day • FM stereo was modern and hip, receivers were available. • DRM will succeed for the same reason- it is so much better than the technology it surpasses . • DCC/DAT failed as it was not that much better than compact cassette for the average consumer • CD was a success due to its enormous advantages over Vinyl. • There are numerous industry examples of this trend