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.

Baseband Processing

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.

Looking Ahead

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.