SDR looks to new middleware

COLORADO SPRINGS, Colo. — Dreams of a fully reconfigurable integer CPU or baseband DSP for software-defined radio are all but dead. But as SDR for military, public safety and even consumer markets continues to develop, middleware specialists are looking for new ways to optimize existing architectures for SDR applications.

Objective Interface Systems Inc. (OIS; Herndon, Va.), with expertise in object request broker software, is expanding from traditional Common Object Request Broker Architecture (Corba) interfaces for SDR to new VHDL models for FPGAs used in radio channelization and baseband functions for cognitive radio. VHDL models for Virtex-4 FPGAs from Xilinx Inc., launched in November, will be followed this year by models for additional architectures, both from Xilinx and competing FPGA companies.

For a decade, the biggest interest in SDR has come from the Defense Department, which defined a software-communication architecture (SCA) that only characterized the interfaces for the part of the design implemented in general-purpose microprocessors. The key contracts involving SDR have been in the Pentagon's Joint Tactical Radio Systems (JTRS) program. Prime contractors have not aggressively demanded high-level behavioral models for the DSP or FPGA portions of design, so OIS's bread and butter has been traditional Corba tools.

For example, OIS has worked for years with the National Security Agency, Air Force Research Labs and several prime contractors on a security-critical request-broker product, PCSexpress, which is used to implement middleware for multiple independent levels of security, or MILS, programs. The real-time Corba base of PCSexpress will continue to have a strong market base in the high-security community for some time.

SDR Forum members want to expand cognitive radio into high-volume markets. Eighteen-year-old OIS works with the SDR Forum and its member companies to promote SDR outside military JTRS applications. OIS executive vice president Joe Jacob said the company is fully prepared to offer software in small footprints, with small power requirements, at prices appropriate to commercial applications. There are two basic markets outside the Defense Department for SDR: public-safety communications and general digital cellular/consumer applications.

In the post-Katrina environment, as the federal Project 25 effort to define public-safety standards has accelerated, local police and public safety representatives are pushing suppliers to consider anything that eases interoperability with federal counterparts.

"Most of these groups have no money, which actually helps drive a move to SDR," said Jacob. "It is absolutely critical for public safety networks to talk to JTRS. The federal MILS program will help in that regard, but there needs to be bigger adoption of SDR overall."

As for programmable SDR architectures in basestations and handsets for commercial cellular, Jacob said there is a camp that sees SDR as inevitable, and another camp that says handset OEMs are nervous about the potential for SDR to commoditize functions. Once the ability to reprogram baseband functions and radio channels is made as affordable as multiband DSP and RF chips based on traditional designs, he said, the adoption of SDR will accelerate.

Jacob emphasized that the traditional OEM market in SDR is not yet ready to move full-steam to device models. This week, for instance, OIS will announce a key design win for ORBexpress RT, its original real-time object request broker tool, with General Dynamics Corp.'s C4 Systems group. C4 will standardize on the OIS broker for all its JTRS products, including handheld, manpack and small form-fit cluster radios. All 14 C4 radios meet the Pentagon's SCA standard for SDR frameworks.

The need to move to VHDL models stemmed from the SCA focus on general-purpose integer microprocessors, Jacob said, with little attention paid to DSP and FPGA architectures. OIS created a dedicated model development team after examining the modem-hardware abstraction layer defined by SCA, which was subject to International Traffic in Arms Regulations (ITAR) restrictions, and could not be used in commercial or foreign-developed projects.

An original effort by OIS to develop Corba products for commercial general-purpose processors, broadened to an examination of products for DSPs and FPGAs. The OIS development team realized that the concepts of partial reconfiguration of an FPGA, one of the features that made newer FPGAs so appealing to SDR developers, could be mapped into VHDL descriptions.

Creating a separate engineering group for this effort "means that we are looking at all aspects of using behavioral models," Jacob said. "That doesn't mean we'd be getting into silicon ourselves anytime soon, but this could expand our IP licensing approaches for silicon partners."

The high-security MILS market could leap to VHDL soon. The federal agencies involved in MILS are familiar with VHDL models, Jacob said, and FPGA spinoffs of the PCSexpress program are likely.

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