Software-defined radios for defense applications

Software-defined radios for defense applications
The Defense Department is embarked on ambitious new programs designed to usher in no less than a new era of integrated seamless communications. Called the Joint Tactical Communications System, Transformational Communications; and Global Information Grid programs, they will rely heavily on a multitiered wireless infrastructure to move much of the data, voice and video to a dramatically more mobile and autonomous force.

Challenges abound in every aspect of transformational communications technologies. But perhaps the most daunting of all is delivering high-performance, broadband analog-to-digital and digital-to-analog conversion subsystems that can support increasingly complex waveforms such as the JTRS Wideband Networking Waveform.

Now a small advanced technology company in Elmsford, N.Y., believes it has an important part of the solution to transformational communications. The company, Hypres Inc., is touting its superconducting microelectronic (SME)-based digital Real-time Traffic Flow Management subsystems being developed as part of the Defense Department's Technology Insertion Challenge Program. The Hypres All Digital Receiver (ADR) project, built under an $8 million contract from the Office of Naval Research, is designed to demonstrate the extremely high performance and technical maturity of these cryogenically-cooled, digital RTFM subsystems. Next year, the ADR project will produce a prototype demonstration system for the JTRS Software Defined Radio (SDR) program that focuses on tactical multichannel radios for the Army Cluster 1, Navy Cluster 3 and Air Force Cluster 4 programs.

The ADR digital RTFM subsystem is intended to extend the current state-of-the-art well beyond that possible in silicon-based A/D converters. This first ADR will target the most used frequency bands in JTRS below 2 gigahertz: high frequency, very high frequency, ultrahigh frequency and L-band. The A/D converters and digital channelizers (running at 40 GHz) will directly digitize signals in these bands and provide in-phase and quadrature-phase carrier rejection data to the Department of Defense's Joint Tactical Radio System software modem. The system is being designed to be operated by the JTRS Technology Laboratory to ensure a complete evaluation and independent verification of the ADR performance.

Hypres digital RTFM technology is based on the digital superconducting technique called Single Rapid Flux Quantum. SRFQ exploits the performance of microminiature Josephson junctions when in a superconducting state (cooled to liquid helium, 4 K, temperatures). Hypres designs and fabricates thin-film niobium-based chips and multichip modules that employ various arrays of thousands of Josephson junctions to perform the RF tasks of A/D or D/A conversion, digital mixing, digital filtering and digital up and down conversion at very high speed with unparalleled accuracy. As an example, a UHF bandpass A/D digitizing 100 megahertz of spectrum can be expected to produce 120 dB of spurious free dynamic range and better than 100 dB of signal-to-noise ratio. A recent Hughes Research Laboratory survey clocked a 13-GHz version of the Hypres A/D near the collective silicon state-of-the-art limit (see chart). The 40-GHz versions to be produced on the ADR project moves the bar well above the best silicon-based performance.

Hypres intends over the next 18 to 24 months to add the transmit circuits and house the system in a military rugged, compact, cooler design. This development is a part of a product definition called the All Digital Transceiver, which Hypres intends to produce in two basic configurations, four channels and 10 channels. Because the superconductive phenomenon takes place only at very low temperatures, use of SME technology requires a cryocooler, currently restricting its planned use to applications where its 100-W to150-W power draw is acceptable, such as multichannel JTRS systems in vehicles, ships, aircraft and other combat platforms. The size and weight of the Hypres digital RTFM subsystems is defined by the cryocooler and conventional "warm" electronics required to interface with the rest of the JTRS radio.

The ADT product definition currently calls for a complete four-channel ADT to be about 500 cubic inches, and a 10-channel version about 650 cubic inches. Smaller systems are on the drawing board that would use a yet to be developed "cryobattery," but they are several years away. Recent advances in cryocoolers have made very reliable compact coolers available for other applications, such as cell phone base stations, making the JTRS versions a low-risk, near-term possibility.

The cost savings advantage of an all-digital RF distribution system more than pays for the development investment cost to insert this "disruptive" technology in defense communications systems. A recent proposal submitted to the Office of the Secretary of Defense showed a saving of more than $250 million in procurement costs and a potential saving of $2 billion in life cycle cost in one major JTRS program alone. If one believes that this can be accomplished within the Systems Design and Development (SD&D) phases of upcoming JTRS procurements, the call for digital superconducting on tomorrow's battlefield is compelling.

Hypres is currently focusing on development of RF facilities for military applications, but there is little inherent difference between them and commercial basestations. This may be a win-win situation: commercial sales will not have to bear the burden of development cost while the military benefits from the economics of scale available with the much larger production runs associated with commercial apparatus. Hypres anticipates that product evaluation for wireless infrastructure applications will take place in 2004. The combined potential of SME technology to affect both defense and commercial wireless systems makes this a technology to watch over the coming months.

Richard Hitt is vice president/general manager at Hypres Inc., Government Products and Systems (Elmsford, N.Y.).>/I>

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