Configurable FPGAs: More than a point solution
Two major challenges confront developers of military radar-processing systems. The first challenge is that modern multiband radar sensors produce huge amounts of data that need to be brought into the system's digital-processing stage as accurately and rapidly as possible in order to generate actionable data for the warfighter. The second challenge in this arena is the rapid rate of change that missions must respond to, as adversaries continually morph and evolve their tactics and develop more sophisticated technologies.
As recently as ten years ago, legacy radar sensors might have only supported a single band, such as KU-Band, X-Band, or S-Band. These single-band point solutions produced a particular data rate which had specific downstream data and processing effects. Each radar system would have a fixed set of functions and attack only a particular band of operation within which intelligence had identified that adversaries were operating.
As threats have become more sophisticated, radar sensors have, too. Now, radar signal detection must be performed over multiple bands, meaning that the sensors have had to become much smarter and more sensitive. The result? Radar sensors today are collecting and sending significantly more data to the radar processor. To support these new sensors, radar-system developers want to use underlying digital processing technology that can accept and handle data from a broad variety of different sources. This approach, compared to the earlier point solution, effectively eliminates the cost and time needed to develop a unique digital processor every time a new threat is identified.
The point solution
Sensor requirements for radar, electronic warfare (EW), and signal intelligence (SIGINT) applications usually differ from application to application. The investment required to develop a new system from the ground up for every application can be costly and time-intensive. For instance, every antenna design differs depending on the application space or where in the electromagnetic spectrum the system designer is trying to attack, sense, or operate.
FPGA [field-programmable gate array] devices, a key component in radar-processing systems, are continuing to evolve and add more capability such as floating-point math, increased local memory, faster sensor I/O channels, local processors, and embedded RF analog I/O. Functions such as digital down converters (DDC) are particularly well suited for FPGAs, enabling extraneous data to be removed or dynamically scanned, ensuring that later processing chains are not flooded with data that slows the system down. FPGAs almost uniquely have the ability to support the high processing speeds needed to handle and process the vast sensor data bandwidths typical of radar-system applications. That capability makes these devices exceptional technology for the front end of any high-performance system.
FPGAs are ideal for performing math-intensive algorithms such as Fast Fourier Transforms (FFT) on the incoming raw sensor data stream. After the key data has been extracted by the FPGAs, it can be sent to devices such as DSPs [digital signal processors] or GPGPUs [general-purpose graphics processing units] that can provide even more sophisticated processing, but on smaller data sets better suited to the throughput limits of those device types.
For many years, radar system designers turned to in-house-designed FPGA module solutions that targeted a specific application. In the past, radar systems often used costly custom or semicustom FPGA technology, in a system designed with a specific program or purpose in mind. While dedicated point solutions have their place, such systems lack the flexibility needed to address a wide variety of applications. To support multiband radar, a processing system needs to be flexible and – ideally – reconfigurable. One downside to custom and semi-custom FPGA module developments is that they tend to require large amounts of resources to develop and maintain. Moreover, because they are typically designed for a specific point solution, it’s rarely practical to leverage the investment in these devices across multiple applications.
Today, due to more sophisticated mission requirements and the costs associated with point solutions, system designers are increasingly turning to commercial off-the-shelf (COTS) reconfigurable FPGA modules. Using a commercially available and reconfigurable FPGA processor hosted on an open architecture form factor such as 3U or 6U VPX, the system designer is freed from the hassle of developing independent and unique sensor-processing solutions for every antenna design. What’s more, investment in flexible FPGA technology often leads to downstream benefits with respect to system reuse. Another benefit is that using COTS FPGAs enables designers to track future technology roadmaps to help future-proof their application.
Configurable COTS FPGA solutions can handle the performance
Today’s configurable, user-programmable FPGA solutions are designed to meet the needs of challenging embedded high-performance sensor-processing applications. To complement the FPGA processing capability, large amounts of backplane I/O bandwidth is useful in interconnecting different system elements. The amount of onboard memory, as well as its type, speed, and depth, are also key considerations. Standard interfaces such as PCI Express (PCIe), Ethernet, and Aurora provide a reliable connection to other system processing elements. The combination of a sizeable amount of processing density and flexible I/O, as well as expansion sites for daughtercards like FPGA mezzanine cards (FMCs), help to make configurable FGPA modules ideal for use in wide variety of rugged embedded applications.
Let there be light: the optical fiber advantage
Another recent development that helps to make COTS FPGA modules a compelling choice for radar-system designers is the availability of optical fiber interfaces on the modules themselves, enabling huge amounts of sensor data to be brought directly into the VPX backplane and then sent to the FPGA for digital processing. This approach enables the radar system to absorb as much of the raw sensor data as possible without having to introduce any intermediary conversion stages. Instead, data is sent directly from the sensors and over the backplane to the optical sensor on the FPGA.
At that point, the sensor data has entered the digital-processing realm, and the algorithms can be performed. This approach – defined by the VITA 66 standard – completely eliminates the need for fiber-optic rear-transition modules that plug into the back of VPX backplane or a separate media-conversion module. Formerly, such a module would be required to perform the fiber-optic conversion before sending the data over the VPX backplane to the digital processor. This intermediary transition module took up space, introduced complexity, and complicated logistics. Instead, using VITA 66, the transition module goes away, enabling the chassis depth to be reduced and improving overall size, weight, and power (SWaP) stats. In addition to being able to handle huge amounts of bandwidth, optical fiber connectivity delivers major benefits such as enhanced security because they create no EMI or noise that might enable hacking. For the warfighter, the faster access to greater amounts of radar data delivers the possibility for longer fields of view, a more accurate and quicker ability to locate targets in the environment, and the ability to operate over a much wider spectrum.
Example of a reconfigurable FPGA solution
To address rapidly changing requirements, a COTS configurable FPGA module, such as Curtiss-Wright’s CHAMP-FX4 (Figure 1), offers system designers a solution that enhances sensor processing capability for multiple applications. The 6U OpenVPX board hosts three Xilinx Virtex-7 FPGAs, and is designed to serve as the core of a sensor-processing subsystem that can integrate with multiple antennas or applications for radar systems.
Another key element in a flexible radar-processing system is a high-speed transceiver module to handle the synchronization of analog-to-digital and digital-to-analog conversion synchronization. The 3U VPX VPX3-534 module is a 6 Gs/sec transceiver card that provides multiboard synchronization. Powered by a Kintex UltraScale FPGA, the module combines high-speed multichannel analog I/O, user-programmable FPGA processing, and local processing in a single 3U VPX slot for direct RF wideband processing to 6 Gs/sec. (Figure 2.)
A moving target
As threats become more complex and sophisticated, the use of reconfigurable FPGAs in radar systems provides a flexible technology that helps system designers keep up with rapidly evolving challenges. Support for direct input from the sensor via optical fiber connectivity speeds the ability to turn greater amounts of analog sensor data into actionable intelligence. The nature of these applications is that the amount of sensor data will continue to grow while the sophistication of the adversary will continue to expand. COTS FPGAs help system designers keep pace with this rapidly changing landscape.
Curtiss-Wright Defense Solutions www.curtisswrightds.com