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The more intelligence that can be acquired to help warfighters, the better they can do their jobs. In today’s military, the data recorders used in military data acquisition applications must capture more intelligence from more sources than ever before, both SIGINT and ELINT. Longer recording times and higher recording speeds are also in demand.
At the same time, since more recorders are being located in the field—including on the ground, in the air and at sea—size, weight and power (SWAP) are becoming even more important. Data recorders are found in ground-based systems, laboratories and radio astronomy sites. They are key components in UAVs, as well as the Army’s Apache helicopters and the Navy’s Aegis Ballistic Missile Defense system (Figure 1).
The results are demands for higher-performance, sometimes smaller and lighter, rugged recorders that can accept a variety of signal types, both digital and analog, in real time and record them continuously on reliable media.
“Almost all of our customers are looking at how they can increase bandwidth and how they can record for longer periods of time,” says Angsuman Rudra, director of systems at ICS Sensor Processing, part of Radstone Embedded Computing. “Gapless recording is also important, and with the increased importance of field-based data capture, portability is important.”
Faster Throughput, Longer Recording Times
Data recorder speeds are currently 400 Mbytes/s to 600 Mbytes/s for sustained, continuous recording and playback. Within the next year, the high end will jump to 800 Mbytes/s.
The very high-end 7U ICS daqPC Data Acquisition, Storage and Network System, for example, delivers a recording and playback speed of 600 Mbytes/s. Aimed at real-time applications that require acquisition, processing and archiving of analog input signals, this system achieves its high-speed record/playback capability using removable hard drives.
At 600 Mbytes/s, up to 1500 channels of data, each digitized with a 16-bit A/D converter, can be recorded in real time at a 200 kHz/channel sample rate. Alternately, three 40 MHz bandwidth (flat-top) signals can be recorded in real time at a 100 MHz sample rate. The daqPC features maximum storage of over 2.8 terabytes, a 1 Gigabit network interface and time-stamping support.
At the front end, sensor data must be captured accurately and safely. “This is real-time data: you can’t ever slow it down or stop it,” says Mike Jadon, Micro Memory’s director of product marketing. The company’s Anvil recorder is an all-digital front-end based on an embedded hardware architecture in a server form-factor. Up to 64 Gbytes of high-throughput, dual-access optimized SDRAM captures sensor data in two 32-Gbyte buffers. Each is full-duplex and can perform simultaneous reads/writes to secondary, external hard disk drive media.
Since sensors tend to be “bursty” and their bursts cannot be predicted, even in a streaming application there will be “dead spots” when no data is coming in. Targeted at radar and SIGINT applications, each of the Anvil’s memory arrays can sustain data transfer rates of over 500 Mbytes/s. When the sensors produce bursts the recorder can accept their data and simultaneously write it to disk. Alternately, the data can be written during dead spots. PCI slots accommodate a variety of sensor input I/O including A/D, serial FPDP and custom LVDS or fiber links, as well as storage output I/O for Fibre Channel, SCSI or SATA.
“Snapshot” recording is becoming more popular in radar applications, especially SAR, says Jadon. Typically data blasts for a while, then stops for an even longer period, so the recorder must take in data faster than it can be sent to disk. A solution like the Anvil is used to receive data, “snapshot” it, and send it to disk, readying the recorder for the next snapshot.
In ground-based systems, data capture and playback is also essential for testing complex military system designs and PXI has become entrenched as a solution. For example, Conduant’s data recorders are aimed primarily at very high-performance systems based on hard disk drives, although they can also accommodate solid state drives and CompactFlash. PCI Express is being used more often because of its advantages: higher bandwidth, full-duplex, point-to-point connections and the fact that it can run over an external cable. The company has introduced PXI-based data recorders and a PXI Express model, the StreamStor PXIe-416.
The 3U StreamStor PXIe-416 has four-lane endpoint connectivity to the host PXIe fabric and can record at 600 Mbytes/s sustained for more than 3.5 hours. It supports more than 8 terabytes of storage with a total of 16 disk drives, each with 500 Gbytes of capacity.
The StreamStor PXIe-416 records and/or plays back as peer-to-peer transfers within the PXIe fabric, eliminating contention with the computer system’s non-real-time elements. A single unit can simultaneously record streams from multiple data sources within the PXIe fabric or simultaneously play back recorded data to multiple destinations in the fabric. Simultaneous recording and playback, as well as event marking, are also featured. Applications include high-speed image acquisition and recording RF signals in the field for later playback/analysis in a lab.
A large part of the need for higher throughput is in intelligence/surveillance/reconnaissance (ISR). Much of this recording activity is moving out of the labs and into ISR platforms, says Tom Bohman, VMetro’s vice president for business development, recording products. For instance, data recorders in UAVs have very long-term ISR capabilities, recording and analyzing data over several days at a time. So SWAP have become major concerns.
VMetro’s VME- and CompactPCI-based recorders use PMC sites that can integrate virtually any kind of I/O and Fibre Channel to go to the storage. Since FC is a storage area network (SAN), multiple recording systems can be connected in an array where any recording device can access any storage device.
Higher Storage Capacity, Improved Media
The need for higher throughput goes hand in hand with the need for higher storage capacities. Solid state media, in particular solid state disks (SSDs), have often been used in rugged environments. Micro Memory’s Anvil data recorders use SDRAM instead of flash because of its higher speeds. Prices are usually comparable, but flash is very low-performance on writes, says Jadon. But SSDs cost more than hard drives.
Many real-time data recording applications depend on hard disk drive arrays, usually JBOD, also known as Just a Bunch of Disks. For example, SANbric, the storage portion of VMetro’s data recorders, is an array of six 3.5-in. disks usually configured as a type of JBOD (Figure 2). Along with the company’s Vortex Data Recorders, SANbric Rugged Storage Systems are being used in Jet Propulsion Laboratory’s UAV SAR program.