Next-generation radar applications will drive performance demands that will have architectural implications for radar computing and electronics. Advanced multi-function radar (MFR) systems, which will be deployed in harsh and demanding environmental conditions inside unmanned aerial vehicles (UAVs), manned aircraft, and ship- and ground-based radar systems must simultaneously provide multi-mode search, multi-target tracking, synthetic aperture radar (SAR) imaging, and space time adaptive processing (STAP). Both the performance and ruggedization requirements make it challenging to service MFR applications using yesterday's commercial- off-the-shelf (COTS) technologies.

COTS solutions based on open standards are now meeting these requirements. The blend of massive fabric bandwidth, field programmable gate array (FPGA) processing power, PowerPC high-compute-density farms, and standards-based I/O housed in a conduction-cooled system address the simultaneous requirements of performance within an enclosure that can withstand the extremely hazardous field conditions found in deployed radar. VPXREDI, a next-generation standard that combines the VITA 46 and VITA 48 standards with the RapidIO open-standard switched fabric, significantly advances the robustness and performance of COTS sensor computing.

Figure 1. Complete data acquisition and signal processing applied technology chain.

Actual implementation depends upon a number of basic capabilities:

• Multi-element antenna (8 to 100 elements),
• Separate receiver channel and A/D for each element/channel,
• Efficient mapping of dedicated hardware for the pulse compression algorithms on field programmable gate array (FPGA) modules,
• Tightly coupled fabric connectivity for corner-turning operations, and
• Data exchanges with the high-compute density processing modules for the final STAP and data processing.

Figure 2. Computationally intensive beam-forming requirements for a single pulse return data set.

Open-Standard COTS Systems

Figure 3. Application of adaptive weighting techniques to pattern null interference and jamming.

A system host carrier module is required to orchestrate and synchronize the radar receiver/exciter and data collection control, and to prosecute the I/O distribution among the various FPGAs for signal conditioning and general-purpose processors for data processing and image formation. The switching fabric connects all of the modular components in the system, enabling the quick and efficient exchange of data between processors, and enabling the implementation of corner-turning for the SAR algorithm and all-to-all data exchanges at the maximum data rates of the packetswitched serial RapidIO fabric in the aggregate range of 16 Gigabytes per second or greater as a measure of systemwide bisection bandwidth.

Algorithm Challenges

Figure 4. 3D data block signal processing chain including I/O-intensive corner-turning operations.

The corner turn shown in Figure 4 is one of the greatest challenges facing radar processing systems. VPX-REDI introduces a new module format based on a new set of high-speed differential signaling connectors. The adoption of a new connector set in the VPX-REDI standard paves the way for higher-speed signaling, greater power budgets, and an enormous increase in I/O capabilities. VPX-REDI systems can achieve hundreds of Gigabytes per second of system throughput using high-speed serial fabric interconnects.

A key difference in the architecture of VPX-REDI is its ability to support an expansive, full-mesh compute fabric topology through an increased number of serial fabric links on each module. The full mesh provides all-to-all connectivity without requiring a dedicated fabric- switching slot, as is the general case in other form factor architectures, namely VXS (VITA 41). There also is support for an interconnected common set of building block technologies including standard I/O mezzanine cards, PowerPC processors, FPGAs, and the RapidIO fabric.

Two-Level Maintenance
New radar systems require two-level maintenance (2LM) when a failure occurs and end users swap out individual electronics modules in the field. VPX-REDI provides the electrical and mechanical infrastructure that protects individual electronics modules from electrostatic discharge (ESD) when they are being handled by personnel. This includes specially designed backplane connectors, carefully placed GND signals to sink excess current, and robust module covers.

Ruggedization
Mobile applications impose certain constraints on computing. Ground mobile vehicles can operate in regions of extreme temperature and where the air is dusty, or worse, chemically contaminated. This environment precludes the use of air convection cooling. Conduction cooling provides passive means by which heat can be conducted for the card to the outside wall of the chassis. The chassis wall can be cooled with a fan, but this has none of the implied problems of blowing air directly across the board. The conduction-cooling board exoskeleton also provides reinforcement for high shock and vibration applications.

Airborne applications tend to prefer air cooling since it is lighter in terms of weight than conduction cooling. However, tactical fighters that achieve heights of 70,000 feet may have difficulty cooling electronics at low pressure. Despite the disadvantage of weight, these types of airborne applications also choose to make use of conduction cooling.

The Solution
The radar compute subsystem addressing these requirements comprises a VPX-REDI chassis and three basic processing modules connected via a serial RapidIO backplane fabric and other backplane interconnects. The system's conduction-cooled modules include an I/O mezzanine carrier, a PowerPC signal processing card, and an FPGA compute resource card. The VPX-REDI backplane provides a means for each slot to transfer data to any of 16 other slots via a RapidIO fabric interface without the use of a central switch card.

The I/O carrier module is a smart (processor-based) I/O mezzanine carrier that also serves as the scalar data and control processor for the radar receiver/ exciter. It contains two MPC8548 processors that can serve as application processors or I/O engines servicing respective mezzanine card sites. The two mezzanine cards support PMC-X or XMC interfaces, providing systems integrators with a wide and established ecosystem of option cards that may be incorporated.

The high-compute-density (HCD) module is a quad PowerPC AltiVec processor resource board. Each MPC7448 processor on the HDC operates at 1.4 GHz with a 400-MHz DDR2 memory interface. Each HCD module contains four PowerPC compute nodes (CNs) connected by a low-latency RapidIO crossbar to implement the network of fully connected floating point processors necessary to provide the GFLOPS of processing power for SAR and STAP algorithms.

The FPGA resource board houses three user-programmable Xilinx Virtex-4 FPGAs and can be delivered with an FPGA Developer's Kit (FDK). This kit puts the basic building blocks needed for system integration at the fingertips of developers: RapidIO fabric and serial FPDP bridge end-point IP, data movement functionality, memory controllers, etc.

Multi-function radars present enormous challenges for system integrators, but COTS solutions based on open standards are now meeting them. The combination of massive fabric bandwidth, FPGA processing power, PowerPC highcompute- density farms, and standardsbased I/O housed in a conductioncooled system can address the simultaneous requirements of performance within an enclosure that can face the extremely hazardous field conditions found in deployed radar.

This article was written by James Meyer, Senior Systems Applications Engineer at Mercury Computer Systems, Chemlsford, MA. For more information, visit http://info.hotims.com/10962-841.