Archive for June, 2010
Today we launched the promised Hands On section of Low-Power Wireless. Check out our first (mostly video) review of Silicon Labs’ low-power wireless development kit:
Silicon Labs is known for its low-power microcontrollers as well as its wireless devices. So it’s only natural that they’d focus on low-power wireless, for which the Si1000 is their flagship product. Introduced earlier this year, Silicon Labs claims the chip exhibits both lower sleep- and active-mode power than competing chips (and you know who they are). When you have 10 minutes to spare and a fresh cup of coffee, check out the video here where we check out the Si1000.
OK, not yet but soon. Check back for more reviews for dev kits from Microchip, TI, Atmel, Lattice, Redpine Signals, Xilinx and who knows who else. If you have a dev kit you’d like us to review–and a bit of patience–drop us a line and we’ll look into it. Also any feedback on our reviews would be more than welcome. BTW this post is the place to post them, since WordPress hasn’t figured out how to accept comments on pages (at least I haven’t).
This week (June 8, 2010) as part of its Green Radio program IMEC introduced a reconfigurable cognitive radio baseband architecture (COBRA) that promises to meet 4G requirements at up to 1 Gbit/s throughput with multiple asynchronous concurrent data streams on mobile handsets, basestations and small cells.
The COBRA architecture can be customized to meet the requirements for Wi-Fi (WLAN (IEEE802.11n to .11ac), cellular (LTE to LTE-advanced), and broadcasting (DVB-T/H to DVB-T2) and other air interfaces. With idle power in the range of 2mW in 65nm low-power CMOS technology for the baseband platform, COBRA could prove to be a boon for both handset makers and carriers alike.
It’s hard to see how multi-band, multi-protocol handsets can be implemented without software-defined radio (SDR) techniques. To date the major problem has been that SDR radios have been power hungry, since realizing a bullet-proof front end with sufficient bandwidth means cranking up the power to the ADC. In that regard alone IMEC’s SDR implementation is a big step forward.
SDR also offers carriers the possibility of doing a simple firmware update over phone lines to thousands of cellular basestations when they want to introduce a new air interface instead of spending millions of dollars doing truck rolls to upgrade the hardware.
The RF Front End
Scaldio-2B consists of a reconfigurable frequency synthesizer and receiver in 40nm digital TSMC CMOS technology. The single-chip flexible receiver is fully software configurable across all channels in the frequency bands between 100MHz and 5GHz. Its properties (such as the RF carrier frequency, channel bandwidth, noise figure, linearity, filter characteristics) can be adapted to the requirements of the standards that are used.
To meet the additional demands implementing a cognitive radio in 4G, COBRA has added a novel ASIP (application-specific integrated processor)-based digital front end enabling hierarchical platform activation—presumably to swap in different waveform images from software as the need arises—in addition to flexible filtering, synchronization and spectrum sensing. According to Liesbet Van Der Perre, IMEC’s Program Director for Wireless Communication, the goal of COBRA is to enable “Devices that can negotiate and switch between frequencies to optimally use the available spectrum. Devices that switch between standards, choosing the best option depending on location, user environment and user application.”
Cognitive SDR techniques will enable both multi-band, multi-mode handsets as well as far more efficient use of available spectrum—a major issue as the number of cell phone users continues to increase geometrically.
COBRA utilizes IMEC’s 3rd generation reconfigurable ADRES processor (Architecture for Dynamically Reconfigurable Embedded Systems). ADRES is a processor architecture designed for wireless and multimedia processing in single- and multiprocessor systems. Through an XML template, designers can create the ADRES processor instance that is best suited for their applications. Applications for an ADRES processor can be completely programmed in a high-level programming language (C) and compiled with IMEC’s DRESC C compiler.
The 2nd generation ADRES processor was designed to support 600Mbps 802.11.n on two cores with a total power use of 220mW using 40nm technology. For this application IMEC got rid of the central bus and went to a crossbar architecture and added multi-threading and wide SIMD (single instruction, multiple data) capabilities. They also added support in their DRESC compiler for instruction-, data- and task-level parallelism, which in itself is a major step forward. According to Van Der Perre, “We expect to have a first instantiation of this processor ready in the course of 2010”.
To cope with a diversity of high-speed protocols, IMEC has added a flexible forward-error-correction (FlexFEC) processor template to achieve both high-speed turbo and low-density parity check (LDPC). An LDPC-specific instance for multi-standard broadcasting has also been derived to further optimize power and area.
IMEC’s COBRA architecture is far from the only SDR architecture out there, but to my knowledge it’s the first one to bring cognitive techniques close to the silicon. It’s also a big step forward in terms of energy efficiency. With IMEC partners Samsung, Renasas, Panasonic and TSMC working on implementing CORBA in both software and silicon, commercial products shouldn’t be far off.
The June issue of the MIT Technology Review has a short article on how to build your own cellular network (registration required). The idea of going into competition with Verizon for a few hundred dollars was just too much fun to overlook.
Far from being just a fun hack, OpenBTS’s founders Harvind Samra and David Burgess set out to design a cellular basestation that would reduce the cost of GSM service provision in rural areas and the developing world to below $1 per month per subscriber. They’ve already successfully field tested their DIY basestation at the Burning Man festival in Nevada and on the tiny island nation of Niue in the South Pacific. Now you can put your own island on the digital map for around $1,000 or so, depending on your patience and your junkbox.
OpenBTS is an open-source Unix application that uses the Universal Software Radio Peripheral (USRP) to present a GSM air interface to standard GSM handset and uses the Asterisk software PBX to connect calls. The combination of the ubiquitous GSM air interface with VoIP backhaul could form the basis of a new type of cellular network that could be deployed and operated at substantially lower cost than existing technologies in greenfields in the developing world.
OpenBTS systems draw only about 60W, which can easily be supplied by a few marine batteries in remote locations, topped up by solar panels or a small wind generator. And while the USRP hardware—which is the basis for a large number of SDR deployments—can be programmed for many waveforms other than GPS, GPS is the dominant standard worldwide—particularly in developing countries—and besides Asterisk is based on it. And Asterisk, which can run on a notebook computer, is free vs. $250,000 or so for comparable commercial infrastructure.
Your output power and antenna will clearly determine—or be determined by—the range you wish to cover. The USRP’s WBX daughterboard puts out a modest 50-100mW (17-20dBm) from 50 MHz to 1.2 GHz, which covers most international cellular bands, though 100mW won’t get you very far. Add a PA and a small array of yagis and the sky’s the limit.
There is, however, the little matter of FCC approval. For the Burning Man field test in 2008 the FCC issued Experimental Special Temporary Authorization license WD9XKN to Kestrel Signal Processing Inc., Samra and Burgess’ consulting firm. The FCC issued a second temporary license for a larger test at the 2009 Burning Man festival. Both tests proved quite successful. OpenBTS is now providing cell phone coverage to Niue’s 1,700 residents and an unknown number of tourists, using Telecom Niue for Internet backhaul. Tests are currently under way in South America and Asia.
Ready to roll your own basestation? Samra and Burgess have the Burning Man covered, but maybe you could talk the FCC into letting you cover Coachella or Austin’s South by Southwest (SXSW) music festival. You can download all the necessary software here and browse for hardware at the Kestrel OpenBTS store. You’re on your own for the batteries.
Good luck, have fun and don’t forget to call!