A fundamental shift in wireless communication is underway, and nowhere is this evolution more evident than in the field of digital radio. Ten years ago, the avionics industry and a few satellite-radio visionaries were the only ones investing in digital radio technology. In the last two years, however, digital radio has taken off as a cost-effective, flexible platform for communications and entertainment systems for commercial and consumer applications.

Among the first embedded-processor vendors to recognize the vast potential of Software Defined Radio (SDR), Analog Devices, Inc. (ADI) committed R&D and market resources to establish a market-leading technology portfolio for SDR equipment makers. Among the results of that focus is that ADI's Blackfin Processor includes architectural and feature characteristics that are ideal for enabling low cost digital radio products for high volume markets like automotive AM/FM/shortwave, and consumer portable entertainment units.


What's Past is Prologue
In the mid-1990s, a move began to transform aircraft fleets from analog to modern digital communication systems. Airborne digital radio technology demonstrations began in 1996, and by the turn of the century, a national network of weather transmitter sites were developed to disseminate real-time textual and graphical weather information to the entire U.S. fleet of aircraft.

At the same time, companies like American Mobile Radio Corporation (now XM Satellite Radio) were laying the foundation for providing consumer radios through satellites.

Choosing the Blackfin Processor
AeroStream Communications was founded specifically to embrace Software Defined Radio (SDR), a technology that was beginning to make its way into commercial applications from its original military roots. SDR provides an efficient and comparatively inexpensive solution to the problem of building software-reconfigurable multimode, multifunctional wireless devices that can be field updated or enhanced to support different air interfaces and traffic requirements.

Software Defined Radios (DSRs)

A number of enabling technologies have been used to develop platforms for SDR systems, including ASIC-based approaches, reconfigurable logic (FPGAs), and programmable embedded processors.

The ASIC-based approach was incompatible with AeroStream's software-reconfigurability goal, and FPGAs take too long to reconfigure for time-sensitive wireless applications. High development costs for ASICs and FPGAs were also unsuitable for AeroStream's tightly-managed R&D budget.

Once AeroStream decided to take an off-the-shelf embedded processor approach for its SDR technology, there was no question which processor the company would use. "Blackfin is the answer in the DSP world because of size, power and cost," said AeroStream president, Don Moore. "The technology we're developing today is 75 percent less costly than what we were developing six years ago. It is less complex because it is more highly-integrated, and the core modules are not only more cost effective, but smaller and less power hungry."

The power of the Blackfin processor allows AeroStream to execute the baseband SDR signal processing in the programmable software domain, while part of the SDR signal chain is implemented in the analog domain (portions of the RF and IF circuits). AeroStream felt this approach would save time and money, simplify development, and – most importantly – allow for maximum programmability and reconfigurability.

AeroStream Board Image

Because it is fully programmable, the Blackfin processor allows AeroStream to deal with multiple standards of digital radio across the world. It also allows for a high degree of flexibility; one can add video, MPEG, and additional capabilities as needed. But not all embedded processors are created equal, and Blackfin has two significant advantages for SDR applications. The first is price/performance – Blackfin is the only processor that can provide enough MIPS to implement a digital radio in the $5-$6 range (in volume). Secondly, Blackfin has the lowest power consumption of any processor in its class, which is especially crucial for power-constrained portable radios.

SDR design challenges are far from trivial: the processing engine must deal with a harsh mix of radio static, signal fade, pops and hisses, adjacent station interference and limited listening range from existing signals – all the while providing the listener with impeccable audio clarity and volume. And if this is true for the aviation market, the audio quality requirements are multiplied dramatically for the consumer digital radio market, where listeners are accustomed to "CD quality." Here again, the Blackfin processor's superior software architecture provided AeroStream with the ability to execute medium range to high performance digital radio audio processing and tuning algorithms simultaneously on a single processor/software thread.

The Blackfin Processor is architecturally ideal for SDR implementations, and AeroStream was able to take advantage of features including the PPI bus for interfacing with high-speed converters, zero overhead loops for block filtering, 2-dimensional DMA for zero-overhead "ping-pong" buffering, hardware "Ones Population Count" for data radio parity checks, run-time model specification for custom RTOS context switching, and block-floating-point manipulation for perceptual audio coders (like MP3).

AD9874 Interface

Implementing SDR with Blackfin
AeroStream began developing an SDR using the Blackfin embedded processor and the Analog Devices AD9874 IF subsystem. The marriage of these two products allowed AeroStream to achieve the programmability and multimode functionality they needed.

The AD9874 IF subsystem connects directly to Blackfin, and the code-compatible family members share the fundamental core attributes of high-performance, low power consumption, and the ease-of-use advantages of a microcontroller instruction set.

Using ADI EZ-Kit development tools and ADI's floating-point library, AeroStream had Blackfin processor boards up-and-running real-time filters within six months of its initial SDR development. AeroStream also uses the Blackfin processor to implement an RS-232 communications protocol for use with a PC or PDA control program. The processor also runs a full complex quadrature demodulation from the AD9874 and a high-sample-rate (384kHz) demodulation process in order to sample the full 75kHz deviation of FM broadcast, for mono, stereo and radio data service (RDS) channels.

The company's main processing is in blocks of 1K samples, which are decimated after demodulation as necessary. Linear-phase FIR filters are applied during demodulation, and fast IIR filters handle back-end processing (using a customize transformation algorithm for optimum audio performance). AeroStream has also developed software building blocks for all sorts of other demodulations such as AM, narrow-band FM, Single Sideband, and various data demodulators.

The result is a complete, standard RF/baseband radio processor from AeroStream, with a family of receiver cards to define multiple uses within each target group. Receiver cards currently in development include an AM-SW-FM stereo receiver, a VHF all-mode receiver, and VHF all-mode transceiver, and a special purpose multi-mode transceiver.

The company's communications products can demodulate any radio signal from the FM broadcast band, including AM, shortwave, NOAA, single-sideband hand, and digital modes. Add-on features are also an option, such as MP3, video or voice capabilities, as well as over-the-air repair and update capabilities.

The Sky is Not the Limit
AeroStream's technology soars beyond the founder's aviation roots, with its SDR product lineup spanning the full spectrum of communications, information and entertainment systems. From marine radios to car stereos and automotive applications, AeroStream's products offer a complete SDR platform for mobile and portable environments. Because of the scalability afforded by the Blackfin processor, all of these products have the functionality to be reprogrammable, multiband/multimode, networkable, and support data and voice simultaneously.

By taking advantage of the breadth of ADI's SDR offerings, AeroStream accomplished its goal of building a very small, very low-cost data radio that can be programmed for multiple applications – by enabling a single platform, bill-of-materials, and form factor for multiple markets and applications, the Blackfin processor lets AeroStream leverage economies of scale to achieve previously unreachable price points for digital radio. As the evolution of wireless communication continues, the Blackfin processor will play a key role in the widespread adoption of SDR and digital radio technology, making it more affordable and accessible for commercial and consumer applications.

For more information, visit Aerostream.

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