Consumer digital radio: from concept to reality by W. H. W. Tuttlebee and D. A. Hawkins The commercial advent of digital broadcast radio in the UK is upon us. The concepts and technology of digital audio broadcasting, DAB, originated from the European Eureka 147 project, which began in 1988 and which has created international standards now adopted by ETSl and the ITU. In the UK today the BBC provides DAB coverage t o some 60% of the population. A DAB licence for independent radio broadcasting has recently been awarded to a consortium called Digital 1 which will offer a similar level of coverage within 12 months. Until recently digital radio was held back by a lack of consumer receivers. High-end consumer products are, however, now beginning to appear in the shops. This paper describes the development of a world- leading, credit-card-sized DAB OEM receiver module that is already allowing new players and consumer products to enter the market. 1 Introduction A little heralded press release from the BBC in July 1998 announced the availability of DAB radio products from Grundig, Clarion, Bosch/Blaupunkt, Kenwood and Pioneer, at prices starting from S499, with distribution through the independent High Street shops, including a selection of Dixons Group stores, Britain’s largest electrical retailer. Hi-fi products are also becoming available, such as ARCAM’s new digital tuner, an early example of a product entry by a new player, facilitated by the availability of Roke Manor’s revolutionary g old0 DAB OEM receiver module. Although prices still have to fall before DAB becomes a mass market technology, the advent of consumer digital radio has at last begun. Digital radio broadcasting by the BBC began in the UK in September 1995. Today the BBC’s transmitter network covers 60% of the UK population, over 30 million people’. The BBC simulcasts its five national network channels and also provides additional live sports coverage and live coverage from the House of Commons. Future evolution of the service is likely to encompass multimedia transmissions. Such a service, in the form of an hour-long interactive multimedia music documentary, was demonstrated by the BBC at this year’s Radio Academy Festival in Birmingham in July 1998, alongside other innovative programming material combining audio, still visuals and dynamic text. ‘BBC Now’ is another interesting ASIC CAD CIF CIP COFDM DAB DSP ECP FFT FIB FIC FPGA GPS F-PAD Abbreviations = application specific IC LSF = computer aided design MCI = common interleaved frame MPEG = command interface protocol MSC = coded orthogonal frequency division OFDM multiplexing = digital audio broadcasting PAD = digital signal processor RDI = extended capability port, which meets RISC the IEEE 1284-1994specification SFN = fast Fourier transform SI = fast information block TI1 = fast information channel UEP = fixed programme-associated data WDL = field programmable gate array = Global Positioning System x-PAD = low sample frequency = multiplex configuration information = Moving Pictures Experts Group = main service channel = orthogonal frequency division = programme-associated data = radio data interface = reduced instruction set computer = single frequency network = service information = transmitter identity information = unequal error protection = very high speed IC hardware description = extended programme-associated data multiplexing language ELECTRONICS & COMMUNICATION ENGINEERING TOURNAL DECEMBER 1998 263
Transcript
Consumer digital radio: from concept to reality
by W. H. W. Tuttlebee and D. A. Hawkins
The commercial advent of digital broadcast radio in the UK is upon us. The concepts and technology of digital audio broadcasting, DAB, originated from the European
Eureka 147 project, which began in 1988 and which has created international standards now adopted by ETSl and the ITU. In the UK today the BBC provides DAB
coverage to some 60% of the population. A DAB licence for independent radio broadcasting has recently been awarded to a consortium called Digital 1 which will
offer a similar level of coverage within 12 months. Until recently digital radio was held back by a lack of consumer receivers. High-end consumer products are, however, now beginning to appear in the shops. This paper describes the development of a world-
leading, credit-card-sized DAB OEM receiver module that is already allowing new players and consumer products to enter the market.
1 Introduction
A little heralded press release from the BBC in July 1998 announced the availability of DAB radio products from Grundig, Clarion, Bosch/Blaupunkt, Kenwood and Pioneer, at prices starting from S499, with distribution through the independent High Street shops, including a selection of Dixons Group stores, Britain’s largest electrical retailer. Hi-fi products are also becoming available, such as ARCAM’s new digital tuner, an early example of a product entry by a new player, facilitated by the availability of Roke Manor’s revolutionary g o l d 0 DAB OEM receiver module. Although prices still have to fall before DAB becomes a mass market technology, the
advent of consumer digital radio has at last begun. Digital radio broadcasting by the BBC began in the UK
in September 1995. Today the BBC’s transmitter network covers 60% of the UK population, over 30 million people’. The BBC simulcasts its five national network channels and also provides additional live sports coverage and live coverage from the House of Commons. Future evolution of the service is likely to encompass multimedia transmissions. Such a service, in the form of an hour-long interactive multimedia music documentary, was demonstrated by the BBC at this year’s Radio Academy Festival in Birmingham in July 1998, alongside other innovative programming material combining audio, still visuals and dynamic text. ‘BBC Now’ is another interesting
ASIC CAD CIF CIP COFDM
DAB DSP ECP
FFT FIB FIC
FPGA GPS
F-PAD
Abbreviations = application specific IC LSF = computer aided design MCI = common interleaved frame MPEG = command interface protocol MSC = coded orthogonal frequency division OFDM
multiplexing = digital audio broadcasting PAD = digital signal processor RDI = extended capability port, which meets RISC
the IEEE 1284-1994 specification SFN = fast Fourier transform SI = fast information block TI1 = fast information channel UEP = fixed programme-associated data W D L = field programmable gate array = Global Positioning System x-PAD
= low sample frequency = multiplex configuration information = Moving Pictures Experts Group = main service channel = orthogonal frequency division
= programme-associated data = radio data interface = reduced instruction set computer = single frequency network = service information = transmitter identity information = unequal error protection = very high speed IC hardware description
= extended programme-associated data
multiplexing
language
ELECTRONICS & COMMUNICATION ENGINEERING TOURNAL DECEMBER 1998 263
Table 1: Global status of DAB2
Country Coverage status as at Summer 1998
Australia
Belgium
Canada
China
Denmark
Finland
France
Germany
Hungary
India
Israel
Italy
Japan
Malaysia
Mexico
Netherlands
Norway
Poland
Portugal
Singapore
Slovenia
South Africa
South Korea
Spain
Sweden
Switzerland
Turkey
UK
USA
Commercial service from January 2001. Test broadcasts in Canberra
70% population coverage, national services
30% population coverage expected by end 1998. Public (CBC) and private broadcasters
Test transmissions in Guangdong Province and Hong Kong
25% population coverage, national services
20% population coverage, national and regional services
17% population coverage, national and regional services
36% population coverage, regional services, both operational and many pilot services. 80% coverage mandatory by 2000
3 million population covered
Test transmissions in Delhi
70% population coverage, pilot project
10% population coverage, 60% by 1999
No decision yet; several manufacturers have developed Eu-147 receivers
Pilot project, 3 transmitters in Kuala Lumpur
Terrestrial and satellite test transmissions
45% population coverage, national services
35% population coverage, national services
8% population coverage
50% population coverage by 1999, national services
Test transmissions, supported by Deutsche Telekom
Test transmissions
Test transmissions
Test completed. Government decision to adopt Eu-147 DAB
5.8 million population covered by end of 1998
75% population coverage for national ensemble. 45% population coverage for regional ensembles
2 million population covered in pilot projects
Test transmissions, late 1998/early 1999
60% population coverage (BBC), national services. London coverage by commercial radio pilot transmissions
CEMA tests favoured Eu-147, but opposed by the National Association of Broadcasters
experimental service, offering ‘news-on-near-demand’. On the independent radio front, in October 1998 Digital
1, a consortium comprising NTL, GWR Group and Talk Radio, was awarded a licence to provide a national commercial radio DAB multiplex. Digital 1 will provide 65% population coverage by October 1999, with services likely to include Talk Radio, Classic FM and Virgin Radio, along with up to five new nationwide digital radio stations. Local digital radio licences will follow a similar pattern of approval; the first tranche of these should be advertised before the end of 1998, meaning that some DAB local radio services could be on air in 1999.
DAB, however, is not a UK phenomenon, nor even simply European. DAB is a mature, and increasingly global, technology. By mid 1998 more than 150 million people around the world were within coverage of a DAB transmitter and over 250 DAB programme services were on the air world-wide, providing high-quality audio, as well
~
as a wide range of innovative data services. Table 1 provides an overview of the global status of DAB.
The transition of broadcast radio from analogue to digital technology will be as profound as has been the case for mobile phones and as will be for television. In this paper we summarise the operation of the Eureka 147 digital radio system, outlining the key system concepts. We then present a marketplace context for DAB receiver products, describing the types of applications and product opportunities which are beginning to emerge. We next describe the development process which has resulted in Roke Manor’s credit-card-sized DAB receiver. The necessary pre-development work which provided a solid foundation for the subsequent product is outlined, along with the various stages of product development - the initial demonstration prototype phase, the first single- board product (the Gold Pack) launched in summer 1997 and finally the credit-card-sized OEM module, launched at
264 ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998
Table 2: DAB operating modes
System parameter Transmission Mode I Transmission Mode I1 Transmhsion Mode 111 Transmission Mode IV
Nominal frequency
Frame duration
Transmitter separation
No. of carriers radiated
Useful symbol duration
Guard interval
Total symbol duration
Symbols per frame
<375 MHz
96 ms
96 km
1536
1 ms
246 ps
1.246 ms
76
<1.5 GHz
24 ms
24 km
384 250 ps
62 ps
312 ps
76
<3 GHz
24 ms 12 km
192 125 ps
31 ps
156 ps
153
<1.5 GHz
48 ms
48 km
768 500 ps
123 ps
623 ps
76
CeBIT 98. We conclude the paper by summarising the actual and anticipated impact of the Roke Manor activity upon the future of the DAB market and provide some indications of future developments.
2 The Eureka 147 DAB system
System overview The Eureka 147 DAB system has been designed as a
reliable multiservice digital broadcasting system for reception by mobile, fixed and portable receivers, is capable of operation at any frequency from 30 MHz to 3 GHz and can be used on terrestrial, satellite, hybrid and cable broadcast networks. Four different modes are allowed, see Table 2, although the system operation of each is essentially identical. For Modes I to I11 parameter values are optimised for performance in different operating frequency ranges; Mode IV, introduced more recently, allows improved coverage range at the expense of poorer Doppler shift capability. The system supports audio programmes over a wide range of sound coding rates and has a flexible multiplex for broadcast of audio, programme- associated data and independent data services, as explained below.
Digital audio compression techniques (MPEG layer I1 and LSF low sample frequency) achieve significant bit rate reduction of the transmitted signal, whilst coding redundancy is applied to provide strong error protection. Transmitted information is spread in frequency and time to eliminate channel distortion and fades, even in severe multipath conditions. System spectrum efficiency may be increased through use of a single-frequency network (SFN), in which signals from multiple different transmitters on the same frequency are constructively combined at a receiver.
Main system fiatures The DAB transmission signal occupies a bandwidth of
1.536 MHz and carries a multiplex of several digital services simultaneously. The gross transmission data rate is 2.3 Mbit/s, and the net bit rate varies from 0.6 to 1.8 Mbit/s depending on the convolutional code rate, which can vary from application to application. Typically the multiplex has a useful bit rate capacity of around 1.3 Mbit/s
in a complete ensemble at an average code rate of l/2. A variable coding overhead of between 25% (rate 3/4) to 200% (rate 1/3) may be applied, depending on the broadcaster’s quality-of-service delivery requirements. The ensemble may contain several audio channels, programme- associated data (PAD) for each audio channel and, optionally, other independent data services. The fast information channel (FIC) is a part of the multiplex that contains information on how the multiplex is actually configured, multiplex configuration information (MCI), and informs the receiver of upcoming reconfigurations,
The market for digital radios
Key results fiom UK market research. Source: Market research commissioned by the BBC, as reported in Reference 6.
73% of interviewees expressed interest or keen interest in purchasing a digital radio
0 77% of the early adopter groups expressed such interest
0 People are prepared to pay a premium for digital radio, of:
25% for a car radio 30% for a hi-fi tuner 60% for a portable radio
0 Early adopters will be predominantly male, 50% aged <35, who already own surround sound TV, DCC (Digital Compact Cassette), mobile phone and a PC
0 First buyers of digital radio products will be: affluent gadget enthusiasts (cf above items) hi-fi enthusiasts serious music fans owners of in-car CD equipment Internet-PC owners
0 New stations, dynamic text and visuals will act as purchase triggers for digital radio, with improved sound quality acting as a ‘post purchase’ reward
ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998 265
along with service information (SI) about the current and any new services. Flexible audio coding bit rates are allowed, from 64 kbit/s (32 kbit/s single channel) to 384 kbit/s (at 48 kHz sample frequency) and from 8 kbit/s to 160 kbit/s (at 24 kHz sample frequency, LSF).
A typical multiplex has 4 or 5 high-quality stereo audio services with a few low bit rate mono audio services, and up to 20% non-audio related data services. Data services can be separately defined streams or may be further divided by means of a packet structure. Programme-associated data (PAD) is embedded in the MPEG audio bit stream (e.g. song title and artist, name and details of a person being interviewed, details of a phone-in number) for display at the receiver.
The way in which the DAB transmission signal is created is described in more detail below; this may be best understood with reference to Fig. 1 which shows the conceptual building blocks of a DAB transmitter. For a full description of the standard see Reference 3.
Audio services Normal CD quality audio using PCM coding generates a
bit stream of 44.1 x 16 kbit/s per channel, i.e. 1.4 Mbit/s for stereo. DAB uses a low bit rate subband coding system enhanced by a psychoacoustic model - MPEG layer I1 (MUSICAM) - which .makes use of the fact that only those parts of the audio spectrum above the masking threshold of a given sound contribute to its perception by the ear. Acoustic action occurring at the same time, but with less intensity, and thus under the threshold, will not be heard because it is masked by the main sound event. This process allows a bit rate reduction from 0.7 Mbit/s per channel to about 100 kbit/s per channel. The operation of MPEG audio coding has been described in some detail in a recent article in this journal4 and so is not repeated here.
Data services Each audio programme may contain programme-
associated data (PAD) with a variable capacity. The data rate ranges from 667 bit/s (F-PAD) to 65 kbit/s @-PAD). For 24 kHz sampling, these rates are halved. The PAD channel is incorporated at the end of the DAB audio frame, so PAD data is synchronous to the audio. (Data in frame n refers to audio in frame n+l.) Typical examples of PAD applications are:
0 dynamic range control information (F-PAD) dynamic labels - Radiotext @-PAD) speech/music indication and origin (F-PAD)
0 text and graphics, e.g. a CD album cover, an artist bibliography, news headlines during a news bulletin @-PAD).
In addition to PAD, general data may be transmitted as separate independent data services. Such services are carried in the main service channel (MSC) and can either be a continuous stream, segmented into 24 ms logical frames with data rates normally between 8 and 64 kbit/s, or alternatively, for services requiring much lower data rates, packet mode data. Examples of independent data services
are traffic information, correction data for differential GPS, up-to-the-minute stock market information, paging, electronic newspapers and car navigation systems.
Service information and multiplex control Service information (SI) which is essential for the
listener, and for control of the receiver, is carried in the FIC (fast information channel), along with the MCI (multiplex configuration information). The following SI elements are available:
0 service label - the name of the service, e.g. ‘BBC RI Digital’
0 programme type label, e.g. ‘News’, ‘Sport’, ‘Classical Music’ time and date, for display or recorder control
0 programme number for recorder control 0 switching to traffic reports, news flashes or
announcements on other services 0 frequency information and cross-referencing to the
same service in another DAB ensemble or on FM.
The user accesses the service components carried in a multiplex by selecting a service. The organisation of the subchannels, services and service components is managed by the MCI (multiplex configuration information) which has five principal functions:
UL
service
U- DAB I
pADj , audio MPEG
audio encoder Layer II
Fig. 1 Creation of a DAB transmission signal
266 ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998
0 definition of the subchannel organisation, in terms of their size and position within the CIF (common interleaved frame) and their error protection
0 listing the services available in the ensemble 0 establishing links between service and service
component 0 establishing links between service components and
Energy dispersal scrambling Energy dispersal is applied to the data representing each
of the programme services, and to the FIC. The process involves selectively complementing bits in the logical frame to reduce the possibility that systematic patterns result in unwanted regularity in the transmitted signal. This randomises the shape of the DAB signal, thereby improving the efficiency of the transmitter power amplifiers. The inputs to the energy dispersal scramblers are scrambled by a modulo 2 addition with a pseudorandom binary sequence (PRES), prior to convolutional encoding.
Convolutional coding (Fig. 2) The channel encoding process is based on punctured
convolutional encoding, which allows for both equal and unequal error protection (UEP), matched to bit error
FIC
main service
multiplexe
r transmitter
frame multiplexer 1 I
FIC & MSC (frequency interleaved)
symbol generator
synchronisation channel symbol
generator
signal generator
TI1 signal generator
sensitivity characteristics. The FIC is coded using equal error protection, with the added redundancy being equivalent to a code rate of 1/3. The audio frame is divided into four sections, each of which may be coded at one of 24 different levels of redundancy. A choice of five UEP profiles is available for each audio coding bit rate, allowing robustness to be traded against transmission capacity.
Main service multiplex and transmission frame multiplexing (Fig. 3)
The encoded and interleaved data from all the service channels is fed to the main service multiplexer (MUX) where every 24 ms the data is gathered into sequences and time interleaved. The combined bit-stream output is known as the main service channel (MSC). The transmission frame multiplexer takes the FIC, comprising a number of fast information blocks (FIBS), and the MSC, comprising a number of common interleaved frames (CIFs), and combines them. To this is added a synchronisation channel, comprising a null symbol for coarse synchronisation (when no RF signal is transmitted) and a phase reference synibol to facilitate differential demodulation and fine synchronisation.
Orthogonal frequency division multiplexing (Fig. 4) The DAB system uses a multicarrier scheme known as
OFDM. Prior to transmission, the fully multiplexed information is divided into a large number of bit-streams, each with a low bit rate. These modulate individual orthogonal carriers using differential QPSK (DQPSK) in such a way that the corresponding symbol duration becomes larger than the delay spread of the transmission channels. A guard interval is inserted between successive symbols so that channel selectivity and multipath propagation will not cause intersymbol interference. The large number of carriers, readily generated using a fast Fourier transform process, is known as a DAB block. The spectrum is roughly rectangular, Gaussian noise like, and occupies a bandwidth of 1.536 MHz. A fuller description of the application of coded OFDM to DAR may be found in Reference 5.
Transmitter identification information (TII) , which uniquely identifies each transmitter in an SFN, may also be optionally added at this final stage. During the null symbol period, certain numbers of pairs of adjacent carriers of the OFDM signal are transmitted. Each transmitter is assigned a main and a sub ID, which can be identified by a receiver. This information, in conjunction with service information, can also be processed to provide an estimate of the receiver’s location.
3 The market for consumer digital radio
What products and who will buy them? To answer this question we use the LJK market as an
example. Many of the arguments presented are generic and applicable to other European, and other, countries. We use the UK example because hard market research has been undertaken to substantiate what might otherwise
ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998 267
Fig. 2 Error protection across an MPEG audio frame
x C
U 3 U ??
Fig. 3 Transmission frame multiplexing
header bit allocation scale factors audio subband samples PAD SFCRC
Sync. channel
DAB audio frame
SFCRC = scale factor cyclic redundancy check
fast information main service channel channel
FIB ..........
simply be speculation. Within the UK some 12 million radios are purchased
each year. Although broadcast radio is not a medium that attracts great attention, still some 85% of the population are regular radio listeners (defined as at least once per week). With the potential to transmit HTML (Web format) pages, dynamic text, still visuals, real-time traffic information and many other as-yet-unthought-of data services, DAB has a significant potential to revolutionise this market in the next few years.
Eureka 147 DAB is the first broadcast radio standard to have been developed specifically to accommodate the multipath propagation conditions of the mobile environment. From the outset the in-car application was seen as a top priority, reflecting the fact that every car sold today includes a radio - a significant ongoing volume market. The fact that DAB can support in-car near-CD- quality audio as the vehicle traverses the country, with no fades or flutters or need for retuning, is a clear attraction. However, whilst many manufacturers have focused almost exclusively on this market segment it is by no means the only or earliest one.
From the perspective of establishing a broad consumer DAB radio market, the hi-fi industry is a key player. The compact disc, for example, began with expensive CD player products aimed at the high-end audio market; the CD player became widespread as the technology matured,
CIF . ....... *. CIF
volumes increased and prices fell. We may expect the same with DAB.
Another, less obvious but very important, market is that for PC-card DAB receivers. The capability of DAB to simultaneously support dynamic text accompanying audio broadcasts has tremendous advertising potential. The prospect of accessing a generation of net-surfing teenagers and flashing a ticker saying ‘the music you are listening to can be purchased on-line by clicking here now!’ has obvious commercial attractions. A host of other PC- supported commercial applications using the data capability of DAB also exists, operating both independently of, and combined with, the Internet.
Portable radios, small domestic units through to ghetto blasters, are also of course an important market segment, albeit one that will probably be addressed slightly later than the others, since power supply constraints on such products (battery capacity) demand low power consumption, something hard to achieve in any new and complex high-technology product.
How real is the market for such products? Will people really wish to trade in their familiar analogue radio for the new ‘digital’ service? Is ‘near-CD-quality audio’ really a pull for the listener? To quantify these issues, and to understand the public’s expectations, the BBC commissioned a range of market research during 1997, which indicated a very positive response, suggesting that
268 ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998
Fig. 4 Composition of the OFDM transmission frame
DSP software
development
transmission frame made up of OFDM symbols
DSP software refinement
-
fast information ( "7 nservicechannel
synchronisation channel channel
interval useful part I I
algorithm development
and simulation
TS 4 c
single chip firmware custom IC development - VHDUFPGA VH DUASlC development - consolidation
the public response to digital radio will indeed be favourable. The key results are summarised in the panel T h e market for digital radios' on page 265.
prototype receiver
complexity and technology
evaluation
Receiver availability Innovations in high-technology industry mean change,
sometimes even a change in fundamental ground rules of competition - for this reason possible market development strategies are viewed differently depending upon the category of industry player. In the case of DAB, pioneering broadcasters such as the BBC have clearly and understandably been disappointed at the lack of early availability of receivers in the market at reasonable prices. Established manufacturers who have funded the innovation wish to recover their investments in technology development and could prefer a slow transition, creaming profit with high-priced products. Other established manufacturers who have not pioneered the innovation but realise that change is coming may recognise the need to adapt, but again, for different reasons, may prefer a slow transition to allow them time to go down the learning curve. Both of these categories of player are concerned to avoid cannibalisation of their existing market and products.
Technological change, however, often opens the door to a third category - new market entrants, who have no
Gold Pack goldCARD receiver receiver
legacy of prior investment or product to protect. Such players may be fleet of foot and see the baggage of the historic market incumbents working to their advantage. For such players a technology shift offers a once-in-a- decade opportunity to secure position in what for them is a virgin market; a strategy of early low-price product, if achievable, is a rational and realistic route to this goal. For DAB, given the potential size of the market, the prize is great.
Such a strategy was adopted, for example, in the early days of GSM (Global System for Mobile) cellular radio, where the launch of GSM terminals in Germany at a price below the existing analogue products enabled a new entrant to secure a strong foothold in a new (for that player) market, upsetting existing market shares. The impact was profound, with all the players rapidly learning how to take cost out of their designs. The resultant growth in the GSM market exceeded expectations and was a major factor contributing to its success in Europe and subsequent expansion to become a de facto global standard?.
Until recently, the lowest price DAB radio on the market was E2000-2500, hardly a consumer product. The key early players were Philips, with their 452 test receiver, Grundig and Bosch. Such products were large, with a box of advanced processing mounted in the boot of
prototype RF design
RF technology evaluation
RF optimisation
I
Fig. 5 Development overview
ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998 269
m simulation A
I I I fixed point lgo"are lcOmParebl VHDL for prototype 1 Ccode . FPGAs receiver
I SH-DSP 120mParelcomParq VHDLfor assemblv code ASIC receiver
Gold Pack I SH-DSP SH-DAB goldCARD
integration integration receiver
Fig. 6 DAB processing development flow
the car, driven from a dash-mounted car-radio-style panel unit. It was this scenario, and the evident need for consumer products if DAB was to succeed, which prompted Roke Manor Research to present at the UK DAB Forum Plenary in September 1994 its proposal to develop, jointly with its partner Ensigma, a consumer DAB receiver module.
manufacturers initially chose to sit on the fence, rather than buy in to the development, not fully convinced that DAB would become a real market. Nonetheless, numerous very useful discussions were held with many of the industry players in the subsequent months which eventually led to a way forward, albeit introducing some delay into the timescales that could have been achieved if funding had been secured at an earlier stage. Eventually the situation emerged where Roke Manor Research and Ensigma jointly undertook for Hitachi development of a DAB processing chip, the SH-DAB chip. Development of an early reference design was supported in part by the UK Department of Trade and Industry. Further substantial
investment by Roke Manor Research finally resulted in the goldCARD OEM product, via the development route described below; the first consumer products using this module were launched in autumn 1998.
4 From concept to product
The consumer DAB receiver development initiative The announcement of plans to develop a consumer
OEM DAB receiver was widely welcomed. Despite this, the initiative did not move as quickly as had originally been hoped. The initial concept had been to create a club of members who would jointly fund the module development, with silicon development subcontracted to a suitably qualified semiconductor manufacturer. Members of the club would have access to the OEM module and customise their products by means of the product packaging, user interface, control aspects etc.
With hindsight, the timing of the launch of the initiative was slightly premature, being prior to the formal endorsement of DAB by ETSI and by the ITU and prior to the BBC's public commitment to DAB. Thus many
To successfully develop a consumer high-technology product requires a comprehensive set of technical, engineering and product management skills. The original proposal recognised the existing backgrounds of Roke Manor Research in DAB RF engineering and design for volume manufacture of GSM and DECT (Digital Enhanced Cordless Telecommunications) telephones and of Ensigma in DAB system simulation and algorithms. Encouraged by the BBC, with whom both parties already had links, both companies recognised that the match of skills was uniquely suited to such a development. Close liaison with the BBC, an early and key player in DAB, clearly was an asset in terms of gaining an early appreciation of the subtleties of the system, as was membership of the Eureka 147 consortium. The advent of Hitachi, with a well-matched silicon DSP
engine, formed the final piece in the technology jigsaw.
From the outset it was recognised that the receiver had to be dual-band (L- band/Band HI), in view of the likely allocation of different spectrum in different countries. The original target size was for a module 150 x 150 mm - in practice this was achieved with the Gold Pack design, launched in August 1997, and surpassed by a considerable margin with the goldCARD product.
The complex DAB requirement necessitates advanced signal process- ing, and evaluation of the best technological approaches to this formed a high priority at the start of the programme'; this led to the identifica- 2 tion of the Hitachi SH-DSP programm-
Fig. 7 The original DAB receiver demonstration platform able DSP engine as being well suited to
270 ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998
the requirement. The second key activity at this stage was an assessment of the applicability of low-cost RF technology, developed for personal comm- unications markets, to the DAB application. The third key predevelopment . activity was construction of a comprehen- sive reference simulation of the Eureka-147 system and creation of the necessary demodulation, decoding and processing algorithms.
These activities were follow- ed by three phases of develop- ment, as shown in Fig. 5: firstly a demonstration platform, secon-
DSP software
high-level control
Firmware I I
dynamic range control
rate control
-- RDI and audio
interface interfaces
Fig. 8 DAB processing software and hardware functionality
dly the first product - the Gold Pack - and finally the highly integrated goldCARD product. The first phase was implemented, ignoring size constraints, using an SH-DSP evaluation board, programmable logic (FPGAs) and basic functionality RF stages. For the Gold Pack receiver, the FPGA and other peripheral functionality was integrated into a custom ASIC, alongside the SH-DSP, together with optimisation of the RF circuitry using low-cost designs similar to those used in personal communications products. In the third stage the SH-DSP, its firmware, the custom ASIC and memory were consolidated into a single device, the SH-DAB IC, alongside further cost reduction and optimisation of the RF design.
Predevelopment activities
System simulation and algorithm development: One of the first activities was the construction of a DAB system simulation and the development of appropriate receiver algorithms, which would be key to silicon-efficient implementation. This reference simulation was used extensively in the later phases, as a means of validating receiver software, see Fig. 6.
and DMA controller peripherals.. The predevelopment studies confirmed that the SH-DSP
could perform the tasks of DAB synchronisation and OFDM demodulation for both the FIC and a high-quality stereo subchannel, but not all the remaining tasks, such as the error control decoding. It was recognised however that the SH-DSP could potentially be combined with standard- cell logic to produce an efficient single-chip DAB baseband processor. Further, at a subchannel data rate of 256 kbit/s, the SH-DSP could perform the MPEG audio decoding as well as OFDM demodulation. It was concluded that the SH- DSP capability was well matched to that required for a DAB audio receiver, offering a very flexible development path and a cost-effective solution, offering both good silicon area efficiency and low power consumption.
RF technology appraisal: The consumer cordless and cellular telephony markets (DECT and GSM1800/1900) have encouraged RF technology development at L-band and above, resulting in the availability of high- performance, low-cost components. An early activity was therefore assessment of the suitability of such devices
DAB processing: Having established the required algorithms and their processing requirements, the different possible implementation approaches which could be adopted for the DAB baseband processing could be evaluated. This identified a preferred silicon implementation architecture'. Following initial evaluation, the Hitachi SH-DSP, a member of the SH family of RISC processors, was examined in more detail. The basic SH-DSP provides 60 MIPS of processing, consumes 135 mW at 60 MHz and supports a power saving mode at times when its full processing capacity is not required. It offers general-purpose RISC instructions and specialised DSP functions, and contains timer, serial ports
ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998
Fig. 9 The Gold Pack DAB receiver board
271
reference oscillator
converter
demod
J 1 h
I
Fig. 10 Architecture of the Gold Pack receiver
and design approaches to the DAB receiver Demonstration receiver requirement.
A related early task was examination of receiver functional partitioning between the digital processing and the RF/analogue parts. The architectural approach identified and subsequently adopted resulted in significant simplification of the overall design (using only a single voltage-controlled crystal oscillator, for example).
The above initial activities provided a sound basis of engineering choices for the subsequent development phases.
Having identified the preferred technical approach, development of a demonstration platform, to validate the system concepts and algorithms in the real-life radio propagation environment, was a high priority.
'The platform was constructed as a 'three board sandwich', each board 150 x 250 mm, comprising the SH-USP evaluation board, a second digital board implementing the 'dedicated processing' functionality of Viterbi, MPEG, etc., and a third board of RF circuitry. The
I " -- " x ~ ~ ."."-"/ "--- - I -- 4. 44.
Fig. 11 The Gold Pack controller software allows easy display of the wide range of available DAB services
Fig. 12 Detailed technical information on the received DAB services may be displayed
272 ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMKEK 1998
processing on one side and RF circuitry on the other, Fig. 9. The architecture of this receiver is shown in Fig. 10.
The receiver used an SH-DSP chip, now without its support environment, together with a custom ASIC, designed by Roke Manor Research for Hitachi, which implemented the additional functions of the prototype
receiver digital board, drama- tically reducing both size and component count. The custom ASIC design was based upon the high-level hardware description VHDL code from the prototype receiver FPGA implementation, thereby ensuring correctness. The basic SH-DSP code, proven on the prototype receiver, was used in the Gold Pack design,
improvements in code efficiency. MPEG audio decoding was also
Fig. 13 The BBC Digital Radio tuner uses the with algorithm OptimiSatiOnS and Gold Pack (Courtesy of BBC Digital Radio)
and other tasks, presenting a processor on startup. This allowed the receiver to be
Approaches borrowed from mobile phone design were
converters and external processing functionality was
filtering technique was developed in-house. IF filtering embodied a commercially available surface mount surface
approach facilitated a calculated in high-volume production and command correspondingly
on the SH-DSP an italhardwareisshowninFig.8. SP software functionality, were integrated into the
(CIP) via an RS232 link to a standard PC, running a Windows-based man-machine interface (although other control devices can of course be used). The software is
a hardware-independent platform uent enhancements to receiver of the software with the prototype
a limited capacity/functionality r field testing of the receiver and its
audio and data compatible DAB receiver within minutes of
relatively simple RF designs were ceiver, to accelerate development ation and cost reduction being
seen as a r
The Gold Pack
273
external hardware
decoder (optional)
ii converter (optional)
Fig. 15 The goldCARD architecture
unpacking from the box. The CIP offers a rich command set which allows both
simple and elaborate man-machine interfaces to be implemented. The control software provided with the receiver offers point-and-click selection of a new ensemble or station, control of audio/data outputs, as well as detailed diagnostic data from the receiver. The receiver decodes and provides information such as fast information channel (FIC) , programme-associated data (PAD) and transmitter identity information (TII) . Signal strength, receiver AGC operation, and estimates of error rate (CIF) derived from the Viterbi decoding as well as the ensemble construction - a list of stations on each multiplex, with type
goldCARD OEM module, launched at the CeBIT show in Hanover in March 1998. A key step in this was the consolidation into a single silicon device of the SH-DSP IC, the custom ASIC and various memory chips used in the earlier design. The consolidated IC was fabricated by Hitachi with strong design support to their in-house team from Roke Manor Research and Ensigma, resulting in the new SH-DAB IC.
In addition, significant effort went into cost-optimisation of the RF design, reviewing component choice whilst ensuring appropriate design tolerancing. Circuit layout was a critical factor in achieving the final size, whilst simultaneously minimising cost. The strong in-house CAD team, working
summer 1997 and has since board was double-sided, of been widely used world- dimensions just 85 x 50 wide by broadcasters for Fig. 16 The ARCAM hi-fi tuner launched at LIVE 98 in mm, marginally smaller service development and September 1998 uses the goldCARD” (Courtesy of than a credit card, see Fig.
14. As may be gathered ARCAM) by radio manufacturers to evaluate use of the subsequent, but pin-compatible, credit- from the above, the overall architecture of the goldCARD is card-sized OEM goldCARD receiver module in their own very similar to that of the earlier receiver, see Fig. 15. end products. Fig. 13 shows one of the BBC Digital Radio’s Clearly EMC issues are an important factor with such a demonstration products based around the Gold Pack compact and yet complex RF design, requiring receiver, constructed by Ensigma. considerable care at all stages. Appropriate choice of
overall radio architecture - including choice of oscillator, The goldCARD synthesiser and filter frequencies - is vital in this respect,
as is good physical board layout and screening design. Further miniaturisation, circuit optimisation and cost Extensive experience of GSM and DECT radio product reduction in the next development phase resulted in the design paid dividends in minimising EMC problems
274 ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998
during the development process, as did the phased development approach.
The same physical interface connector is used on the goldCARD as on the Gold Pack receiver. It also uses the same command set (CIP), typically over a 38.4 kbit/s asynchronous serial port, using a simple command/ response protocol. Easy and interchangeable connection of both receivers to a range of host controllers for development and end-product implementation is possible in this way. High-bandwidth transfer of data to a host processor or to further data processing circuits is possible via a PC ECP parallel port. The Eureka 147 RDI, which carries the decoded data from the main service channel (MSC) and FIC of the DAB ensemble, as well as the TI1 if requested, is also supported.
These powerful and flexible interfaces, together with the data and audio functionality and compact size, mean that the goldCARD OEM is ideally suited for use in a wide range of end products.
Performance: The specification targets for the Roke Manor DAB receivers were derived from the ETSI specifications and various published 'Receiver Guideline' documents. These are shown in Table 3, alongside the values typically achieved.
The performance achieved has in many cases exceeded the initial targets, notably in the critical areas of RF sensitivity and dynamic range. Channel scanning and ensemble acquisition times in particular are rapid compared with other products on the market. The capability for off-board audio and data decoding also allows for easy experimentation, standards evolution or extensions for real-time data service applications.
5 Impact and future developments
Digital radio is here and is coming. The BBC coverage in the UK is already substantial and the coming year will see the launch of new commercial services and the beginnings of new multimedia programming. High-end hi-fi products and car radios will begin to seed the market and create a knock- on effect in terms of market demand; such products are already beginning to find acceptance by the early adopters.
In one respect the goldCARD product is only just beginning to have its impact in the end-product consumer marketplace. The product has substantially removed two major entry barriers to the DAB market, i.e. technology risk and product development investment"'. Small manufacturers, who would otherwise be excluded from the market by these factors, are able to purchase modules for inclusion within their own products. The first commercial product in the UK to do so, from ARCAM, was launched at LIVE 98 in September 1998, see Fig. 16.
Customisation of the design, e.g. for PC card products, is available. For high-volume manufacturers wishing to have full control in-house, licensing of the design is available. The SH-DAB IC developed for Hitachi is available on the open market and indeed is leading the field. Manufacturers considering their future product developments have the option of using the SH-DAB IC and licensing a proven design
Table 3: Receiver specification and performance
Specification parameter TargeVtypical value
Overall system parameters
Operating modes Eureka 147, all modes I, (I, 111, IV
Channel frequencies Programmable grid centre frequencies
Ensemble acquisition Model: 600ms time (warm acquisition; Mode II: 440 ms slightly longer required Mode 111: 400 ms at initial power up) Mode IV: 480 ms
Software data decoding MSC, FIC, PAD, TI1
Radio frequency performance
RF interface
RF sensitivity
RF maximum signal handling capability
RF dynamic range
Adjacent channel rejection
Adjacent channel protection ratio
Image rejection
Audio
Software audio decoding
Audio output - analogue
Audio output - digital
Interfaces
Serial
Parallel port
RDI
Physical
Dimensions
Temperature range
Single interface 50 R VSWR <1.5:1 in passband
Target: -90 dBm; typical: -100 dBm
Target: 0 dBm; typical: 0 dBm
Target: 90 dB; typical: 100 dB
Typical: > 50 dB
Target: > 35 de; typical: 50 dB
Target: > 50 de; typical: >50 dB
MPEG Layer 2 (external decoder may be used via digital interface)
Stereo 775 mV into 600 R goldCARD: 12S Gold Pack: RS422 in AESIEBU, IEC958, S/PDIF or E lAJ CP-340
RS 232
IEEE 1284-1994 ECP reverse mode
RS 485
8 5 x 5 0 ~ 1 1 mm
-40/+85 "C
around it, thereby saving themselves perhaps ayear in terms of time-to-market, whilst still retaining the option of evolving their own in-house design, if they wish, for a later product evolution. The availability of this wide variety of commercial options will result in many new players and products entering the DAB radio market during the coming year and will accelerate the growth of the market, not only in the UK, but globally. The goldCARD represents the state-of-the-art in
ELECTRONICS & COMMUNICATION ENGINEERING JOURNAL DECEMBER 1998 275
Walter Tuttlebee is Business Development Manager for the expanding Radio Communica- tions Business Unit at Roke Manor Research, a Siemens company. Walter launched Roke Manor’s consumer DAB rec- eiver development initiative in late 1994 and has since presented several papers on its progress at international conf- erences, including the Inter- national Broadcasting Conven- tion events IBC 96 and IBC 98. He holds BSc and PhD degrees from the University of Southampton and an MBA from Cranfield University. As a radio engineer Walter contributed to and led feasibility studies, definition studies and product development teams on several successful radio communication systems during the 1980s prior to assuming responsibility for a range of R&D in the field of personal communications - GSM, DECT and UMTS -on which he has published widely. His recent book ‘Cordless telecommunications worldwide’ describes global perspectives of applications, standards, markets and technologies. He is a frequent conference speaker, most recently in the emerging field of software radio. He is an IEE Fellow.
David Hawkins is Product Manager for Roke Manor’s DAB product line, where he has been responsible for the highly successful Gold Pack receiver development kit (which is now being replaced by the Mk I1 version), for the goldCARD DAB OEM receiver module and for Roke Manor’s new DAB monitoring receiver. David represents Roke Manor within the Eureka 147 consortium and within WorldDAB. He also sits on the Steering Board of the UK Digital Radio Forum and represents Roke Manor Research within Digital Radio Mondiale, the digital shortwave consortium. After securing an honours degree in Electronic Engineering in 1977 from Portsmouth University, David worked for Marconi Space and Defence Systems and subsequently Marconi Underwater Systems Ltd. In 1988 he joined Hampshire Video Services, a multimedia facilities company making training programmes on Laservision discs. He went on in 1992 to become Design Manager at Cray Technology, where he was responsible for a variety of projects, prior to joining Roke Manor Research in 1996. He is an IEE Associate Member.
cost-effective DAB receiver design at the present time. Looking to the future, Roke Manor Research has recently
announced the availability of a full multiplex test receiver based on a combination of goldCARD technology and Radioscape’s software receiver - a high-end product intended to support the broadcast industry as it rolls out DAB transmissions networks. This new product allows avariety of important metrics to be displayed on a PC in real time. For example, the channel impulse response can be displayed and monitored automatically, so that should a transmitter start to drift out of the guard band an alarm can be raised, preventing the transmission network from malfunctioning.
In addition, the goldCARD development itself is ongoing, with work in hand to identify further options for cost
reduction. An RF ASIC is being developed which will reduce the component count in the RF part, leading to further reductions in module size and cost reduction in the future. The days of a pocket DAB portable radio, providing CD-quality audio and multimedia services, are not far away. In ten years time we may remember the days of VHF/FM and wonder Was there a day when radio was just audio?’
Acknowledgments
The authors would like to thank the many colleagues within the engineering teams at Roke Manor Research, Ensigma and Hitachi who have made possible the successful developments described above. The ongoing support, collaboration and friendship of Adrian Anderson (Ensigma) and Volker Politz (Hitachi) is particularly appreciated. The support of the DTI, in the form of a SMART award to Ensigma, is also acknowledged. Roke Manor Research is a member of WorldDABand the Eureka 147 consortium and would also like to acknowledge the major contribution of these organisations in the definition and global promotion of DAB. Permission to use photographs from BBC Digital Radio and ARCAM, Figs. 13 and 16, is appreciated.
References
1 GLEAVE, M.: ‘Digital radio takes off, IEE Review, November
2 WorldDAB Newsletter, No. 8, June 1998, supported by additional information from the WorldDAB website, www.worlddab.org
3 ETS 300 401: ‘Radio broadcasting system: digital audio broadcasting (DAB) to mobile, portable and fixed receivers’ (European Telecommunications Standards Institute, Sophia Antipolis, 1997)
4 AMBIKAIWAH, E., DAVIS, A. G., and WONG, W. T. K.: ‘Auditory masking and MPEG-1 audio compression’, Electron. Commun. Eng. J., August 1997,9, (4), pp. 165-175
5 SHELSWELL, P.: T h e COFDM modulation system: the heart of digital audio broadcasting’, Electron. Commun. Eng. J. June 1995,7, ( 3 ) , pp. 127-136
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Digital Audio Broadcasting Conference, IIK, October 1995, London, UK
8 ANDERSON, A.: ‘Towards a one chip DAB solution’. Audio Engineering Society Conference on ‘DAB: the future of radio’, May 1995, London, UK
9 ANDERSON, A., ANDREWS, E., CHAMBERS, G. W., and TUTTLEBEE, W. H. W.: ‘Development of a compact DAB receiver design for the consumer market’. International Broadcasting Convention, September 1996, Amsterdam, The Netherlands, IEE Conf: Publ. No. 4282
10 HAWKINS, D. A. and TUTTLEBEE, W. H. W.: ‘Digital audio broadcasting: removing the entry barriers’. International Broadcasting Convention, September 1998, Amsterdam, Netherlands
11 For more details of the ARCAM DAB tuner visit http://www.arcam.co.uk/products/tualpha 10.html
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