trev 2012-Q2 SDR Steigemann

trev 2012-Q2 SDR Steigemann
SOFTWARE DEFINED RADIO
SDR
— a software-defined multi-radio platform
for the auto industry
Mark Steigemann
NXP Semiconductors
Although Software-defined radio (SDR) concepts have been used in military
applications for several years, it is only recently that designers of cost-sensitive
products such as car radios and mobile phones have started developing SDR-based
solutions. One important enabler has been Moore’s Law, and the resulting ability of
millions of transistors to support highly-computational signal processing chips.
However, raw processing power alone is insufficient because, in the real world, radio
performance is also judged by additional metrics such as power consumption, chip
size and the flexibility of the processing core’s architecture to accommodate new
standards.
This article discusses the drivers, motivations and potential of SDR solutions for incar entertainment applications
Thanks to the continuously growing performance of microprocessors, Software Defined Radio
(SDR) can offer new solutions for vehicle OEMs. Migrating the radio functionality from hardware to
software brings cost advantages for global car production, and also offers more flexibility on the
manufacturing side for future radio features.
More than 80 years after the introduction of the first car radio receivers, the auto industry is confronted with larger challenges. Car radios must offer more than most other consumer products: very
long lifetimes, high robustness and performance. Car radios today need to support not only the traditional analogue radio systems (AM and FM) but digital radio systems as well.
One of the main challenges to master is the worldwide diversity of broadcast standards for digital
radio – ranging from DAB(+) to DRM(+) and HD Radio, to name just a few. Countries or regions
have chosen different standards for a variety of reasons (commercial, political, financial, network
considerations, etc). Truly challenging for radio design engineers is the integration of standards
which are based on different broadcast technologies, error protection schemes and coding technologies, which are briefly introduced below.
Current digital radio standards
Digital Radio Mondiale (DRM)
DRM is a digital radio system for short-wave, medium-wave and long-wave radio at frequencies
below 30 MHz. It delivers near-FM sound quality and the ease-of-use that comes with digital transmissions. The improvement over AM radio is immediately noticeable.
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The DRM system uses Coded Orthogonal Frequency Division Multiplex (COFDM). All of the data
produced from the digitally-encoded audio, and associated signalling data, are distributed for transmission across a large number of closely-spaced radio-frequency carriers.
All the carriers are contained within the transmission channel. Time and frequency interleaving is
applied to mitigate fading from multipath disturbances. Various parameters of the OFDM and coding
systems can be varied to allow DRM to operate successfully in many different propagation environments. The maximum bitrate for DRM is 72 kbit/s.
The DRM system uses MPEG-4 High Efficiency Advanced Audio Compression (HE-AAC+ v2) to
provide high audio quality at low data rates. In addition, Code Excited Linear Prediction (CELP) and
Harmonic Vector eXcitation Coding (HVXC) speech compression algorithms provide speech-only
programming at even lower data rates.
DRM+
DRM+ denotes an ongoing development of DRM, and is a standard for digital radio transmissions in
Band I (the old VHF TV band) and Band II (the VHF/FM radio band). Also here, OFDM provides a
highly efficient usage of spectrum and offers undisturbed mobile reception with no interference. With
its bandwidth of 95 kHz, DRM+ fits into the 100 kHz FM channel spacing used in Europe and can
thus be transmitted within the respective gaps in Band ll.
The maximum effective data rate is up to 186 kbit/s per multiplex. HE-AAC+ audio compression permits the integration of up to 4 different audio streams including additional data services or even
video streams on one DRM+ multiplex. DRM+ integrates “smoothly” into DRM.
Digital Audio Broadcasting (DAB)
When the DAB system was designed in the late 1980s, it had five original objectives: (i) to provide
CD-quality radio; (ii) to provide better in-car reception quality than on FM; (iii) to use the spectrum
more efficiently; (iv) to allow tuning by the name of the station rather than by frequency; and (v) to
allow data to be transmitted.
DAB+ and T-DMB, which both originated from DAB, use HE-AAC+ v2 audio compression and ReedSolomon error correction coding with extra interleaving.
Abbreviations
AAC
AM
AVC
BIFS
BSAC
CELP
CMOS
COFDM
CPU
DAB
DAB+
DMB
DRM
DRM+
Advanced Audio Coding
Amplitude Modulation
(MPEG-4) Advanced Video Coding, part 10
(aka H.264)
BInary Format for Scene description
Bit Sliced Arithmetic Coding
Code-Excited Linear Prediction
Complementary Metal-Oxide Semiconductor
Coded Orthogonal Frequency Division
Multiplex
Central Processing Unit
Digital Audio Broadcasting (Eureka-147)
http://www.worlddab.org/
DAB using the AAC codec
Digital Multimedia Broadcasting
http://www.worlddab.org/
Digital Radio Mondiale
http://www.drm.org/
DRM for the higher frequency bands, up to
174MHz
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DSP
DVB
EPG
ETSI
FM
HE-AAC
HVXC
HW
IC
OEM
OFDM
PS
R&D
SBR
SDR
SW
T-DMB
Digital Signal Processor / Processing
Digital Video Broadcasting
http://www.dvb.org/
Electronic Programme Guide
European Telecommunication Standards
Institute
http://pda.etsi.org/pda/queryform.asp
Frequency Modulation
High Efficiency AAC
(MPEG) Harmonic Vector eXcitation Coding
Hardware
Integrated Circuit
Original Equipment Manufacturer
Orthogonal Frequency Division Multiplex
Pseudo Stereo
Research & Development / Design
Spectral Band Replication
Software Defined Radio
Software
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DAB+
The primary difference between DAB and DAB+ is that a DAB digital radio broadcast uses MPEG-2
Audio Layer II audio compression while DAB+ uses HE-AAC+ v2 audio compression.
HE-AAC+ v2 is a superset of the AAC core audio compression. This superset structure permits
three options depending on the required bitrate: (i) plain AAC for high bitrates; (ii) AAC and Spectral
Band Replication (SBR) i.e. HE-AAC for medium bitrates; or (iii) AAC, SBR and Pseudo Stereo (PS)
i.e. HE-AAC+ v2 for low bitrates.
Each audio super frame is carried in five consecutive logical DAB frames which enable easy synchronization and management of reconfigurations.
T-DMB
T-DMB is also based on the conventional DAB transmission system according to the ETSI standard,
EN 300 401. This means that the DAB transmission system can be used for T-DMB transmissions
by adding a T-DMB video encoder to the existing DAB system. Since T-DMB and DAB are delivered
via the same system, T-DMB devices can receive not only T-DMB multimedia services but also DAB
audio services.
T-DMB uses Bit Sliced Arithmetic Coding (BSAC) or HE-AAC+ v2 audio coding for audio services,
Advanced Video Coding (AVC) for video services and Binary Format for Scene (BIFS) for interactive
data-related services.
HD Radio
HD Radio is a method of broadcasting digital radio signals on the same channel and at the same
time as the conventional AM or FM signal (in-band, on-channel, or IBOC).
HD Radio is a proprietary transmission system which uses a COFDM system to create a set of digital sidebands on each side of
the normal AM/FM signal.
The combined AM/FM and digital radio signal fits into the
same spectral mask as specified for conventional AM/FM.
The system allows for growth
towards eventual full utilization
of the spectrum by the digital
signal in three steps: Hybrid,
Extended Hybrid and Full Digital.
Global market
Figure 1
Production chain using dedicated single devices for each standard
Although car production is
more-or-less global, the market
for car radios is regional, due to digital radio standards being deployed on a regional basis. Thus,
each market requires a dedicated digital radio solution (Fig. 1). This diversity is expensive and time
consuming since, for each market, different combinations of radio components need to be evaluated,
tested and integrated.
More flexible
Hitting the sweet spot with the right combination of flexibility and cost efficiency can be accomplished with the right mixture of powerful embedded DSPs (= flexibility) and dedicated HW acceleraEBU TECHNICAL REVIEW – 2012 Q2
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SOFTWARE DEFINED RADIO
tors
(= cost
efficiency).
Software Defined Radio is not a
new idea as such but, so far,
pure SW-based radio systems
have been used mainly for academic purposes.
Key for a commercially-attractive digital radio system is a
proper hardware/software partitioning, along with the following
thoughts:
 Moving the digitization as
close as possible to the
Figure 2
antenna input (digital is
Leaner supply chain using SDR technology
more flexible);
 Processing steps which
need fixed and regular number-crunching should be implemented in HW (e.g. digital filtering).
The ever-growing computational performance of embedded processor technologies has changed
quite a bit. That is true, also for SDR. Today it is still not possible to run pure SDR on a multipurpose
processor. However, in the future, more and more processing elements can be mapped on processors, helping OEMs further to reduce HW costs and to increase the maturity of their products.
More economic
SDR technology provides a more economic way. Instead of developing a dedicated solution for each
standard, customers can use a single chip which supports multiple standards. It will simplify the
logistical effort and lower the R&D investment for
chip development, SW validation and module
manufacturing.
An example of such a solution is the Digital Radio
Co-Processor, SAF356x, from NXP (Fig. 3) which
supports standards such as HD Radio, DAB,
DAB+,T-DMB as well as DRM and DRM+. The
individual standards can be activated through programming at the end of the car production lines.
You have to run only once through the costly integration process for the HW, regardless of where
the radio will be used in the world.
The goal is not yet to run a complete radio on a
general-purpose processor. Such a system would
not be economical with today’s technology. HowFigure 3
ever, it is all about making the chip design in such
Multi-standard Digital Radio SAF356x for
a way that each function is executed by the promultiple markets
cessing unit which is technically and commercially
the most suited, regardless if it is in HW or SW. Thus, a Multi-standard radio system is always composed of a component that carries the traditional AM/FM radio function and a second component
which can, through SDR, realise all the digital radio standards that are required in the region.
More support during transition
There is another challenge and that is the combination of different technologies, customer support
services and performance requirements.
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One of the confusions in the car industry occurred when the codecs had to be changed with the
introduction of DAB+. Although the installed base of in-car DAB radios wasn’t that big when DAB+
was introduced, there were already quite a number of cars in the market with a DAB-only solution
which could not be upgraded to DAB+. The switch to a new codec for DAB+ turned out to be a problem, simply because the radio-frequency and audio processing was not flexible enough to allow a
reconfiguration. Furthermore, many solutions simply didn’t offer a mechanism for upgrading the
chipset with new SW, once installed in the car. Here, SDR solutions – in combination with efficient
chip design – can help car manufacturers and providers of system solutions to react to challenges
quickly. Furthermore, SDR can increase the adoption speed of new standards and features in the
automotive world, because it provides faster inroads for e.g. consumer market features which have
a higher evolution rate.
It does not help the adoption of new digital radio standards if the listening experience is hampered
by audible effects, when the radio switches from analogue to digital reception (or vice versa)
because of the delay in broadcasting between the same programmes on analogue (e.g. FM) and
digital (e.g. DAB). That is why modern radio systems require to have functions like “DAB-FM blending” which enables a seamless roaming between analogue and digital reception without any interruption. The radio will always switch to the best reception available, based on reception quality
parameters.
Being in the digital domain has yet another advantage. It is possible to create time-shift functions
which allow the continuation of radio programmes, just from the point when the listener got interrupted, e.g. by an incoming telephone call. However, SDR technology can also bear risks for the
supply chain of customers. For traditional radio systems there is usually a semiconductor company
to provide help and services during integration. However, with a growing amount of SW components
for various standards, the situation can become more complex, since the SW may come from different suppliers. It makes sense to ensure that there is a reliable supply and service network behind the
silicon vendor.
More digitization and even more innovations to come
As long as Moore’s Law 1 is valid, the value of SDR technology will continue to grow. SW-based
innovation will be the driver for tomorrow’s in-car entertainment innovations. There will be new ways
to do things and shorter design cycles to introduce new features. Even updates over the air are possible as we already know from satellite receivers in the home. Software-defined radio technology will
develop further in the field of vehicle electronics, bringing new applications, because SDR allows us
to unify the chip technology development: we’ll be able to migrate from application-specific signal
processing to a broader more universal platform which encapsulates radio-standard-specific processing in SW.
Implementing a single digital radio standard such as DAB(+) or T-DMB may not be enough to
address reception as well as geographical aspects for radio in the future. Some regions may decide
to pursue a dual strategy such as using DAB in urban areas and DRM in rural areas, due to its larger
coverage. The co-existence of different standards and services will be a further challenge for radio
system designers in the future. For example, when coming from a rural area into a city with a different radio standard and different radio services, will require a seemless audio handover.
In this particular case, the radio has to continue audio service playback of the current radio standard
while, in the background, extracting the service-linking information of an alternative channel which
has the same audio content. Then, it needs to start a secondary radio reception to initiate decoding
of the alternative radio service in the background and to determine the broadcast delay (which can
be up to 5-10 seconds). In the final step, the radio performs a seamless handover between the two
time-aligned audio services.
1. Moore’s Law states that the CPU power doubles with each CMOS process node.
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The result for the customer will be continuous listening to the selected audio services; the switch to a
new reception standard may only be visible to the listener because of the availability of new services
such as, for example, album cover art, weather maps, etc.
The described scenario can be seen as just one of many possible cases involving the co-existence
of different radio standards, depending on the region. Many other possible combinations and scenarios are thinkable, not only limited to digital radio. Combinations of digital radio with digital TV
standards, (DVB-T, DVB-T2, DVB-SH) could make sense when exchanging EPG (Electronic Programme Guide) data or linking to a TV or radio service.
However, such a use case can
hardly be built using traditional
radio technologies that process
only single standards: the cost
of such a radio would not be
economical anymore. Instead,
software-defined radio technology can help to reduce system
diversity and costs for the auto
industry.
Fig. 4 sketches a solution using
SDR technology to overcome
Figure 4
the problem of radio reception
Reduction of Radio reception pipe diversity using SDR technology
pipe diversity. The SAF356x follows this approach by implementing DAB, HD Radio and DRM baseband and audio decoding in a programmable architecture, in
combination with a universal tuner which can cover all reception bands from AM up to L Band.
Internet access
In addition to digital radio broadcasts, there is another important medium coming to the car – internet
access, which will offer a vast variety of new services and opportunities to obtain music and other
content, even on a personalized basis.
Internet access can be enabled via a GSM (e.g. 3G) connection or via a Wi-Fi connection (utilising
stationary or mobile Wi-Fi as planned in Car2X concepts using the 802.11p standard). Regardless of
how the content enters the car, there are many new options available, because most of the major
radio services in Europe offer live or time-shifted audio streams to access over the Internet. Thus,
new ways of combining broadcast radio and Internet radio are possible, which will make SDR technology even more valuable in the future.
Conclusions
The variety of new digital broadcast standards requires a refined approach for automotive applications. It must consider the needs for leaner supply chains of electronic components and systems.
There is no uniform one-size-fits-all solution which can sufficiently cover all aspects of an appealing
entertainment system, including:
 attractive cost;
 lean and global component design;
 feature and performance differentiation between markets and radio systems.
In a world where the lifetime of new features and performance benchmarks are measured in months
– defined by the availability of new smartphones and tablets – Software-Defined Radio technology is
set to offer a turnaround for automotive Broadcast Radio entertainment.
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Mark Steigemann is Technology Manager & Lead Architect in the Automotive Business unit at NXP Semiconductors, where his main responsibility includes product
architecture definition for worldwide digital radio systems such as DRM(+), HD
Radio, DAB(+), T-DMB, ISDB-T (and others). This involves closely working with
leading automotive manufacturers and Tier-One automotive suppliers, as well as the
coordination of research and technology programmes required for Digital Radio
product development (RFCMOS, SDR).
Prior to this, Mr Steigemann held various positions in NXP dealing with product concept development, innovation and technology management in the consumer TV and
3D GFX business.
It has been shown that SDR can be used successfully to create momentum in a market which tries
to be on a par with the latest consumer product features, while maintaining important additional
requirements for the automotive environment, such as long life-time, high reliability and extreme
robustness (temperature, humidity, mechanical stability, outstanding support).
The illustrated example of NXP’s Digital Radio processor solution (SAF356x) can handle the dynamics of new standards, still-emerging features, and market and product differentiation, by providing a
platform which enables a lean supply chain for module makers and OEMs. The chosen HW/SW partitioning offers flexibility where needed and shields complicated real-time signal processing from the
programmer’s interface.
This version: 26 June 2012
Published by the European Broadcasting Union, Geneva, Switzerland
ISSN: 1609-1469
Editeur Responsable: Lieven Vermaele
Editor:
Mike Meyer
E-mail:
tech@ebu.ch
The responsibility for views expressed in this article
rests solely with the author
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