New Technologies Drive Diverse Solutions

As sensor processing hardware like data converters, FPGAs and CPUs evolve to handle more channels with higher signal bandwidths, designers can develop powerful distributed signal acquisition and pre-processing subsystems in small form factor (SFF) enclosures located right next to the sensors. They connect to central processing or storage resources using wideband gigabit serial links, now often exploiting low cost, standardized optical cables and interfaces. Major benefits include high signal quality over long distance, improved maintainability, and easier insertion of new technology. Since these same benefits apply across many different applications and installations, SFF system vendors now offer a bewildering array of enclosures targeting the unique requirements of each customer.

Small form factor systems mounted up on the mast are extremely effective in handling digitized radar and communications signals to and from shipborne antennas by eliminating signal degradation through long RF cables. Digital optical links between the equipment room and the mast provide immunity to EMI from powerful transmitters and other noise sources commonly found on large ships.

What Are SFF Systems?

In the existential struggle to maintain military and aerospace superiority, embedded systems must constantly evolve to counter new threats, deal with new constraints, embrace the latest technologies, and develop new implementation strategies. Together, these mandates invariably steer systems engineers towards designs that deliver effective solutions. After early adoption and user validation, the best solutions survive to become industry standards.

Standard open architecture embedded systems such as VME, VPX, and CompactPCI, offer flexibility and modularity so that systems integrators can choose standard boards, backplanes and chassis from several different vendors to create each application. These benefits, along with easier system upgrades, new technology insertion, and simpler maintenance, are all fully consistent with the COTS philosophy.

However, a large, diverse, and growing class of highly-effective solutions, collectively, and often arbitrarily, dubbed “small form factor”, have largely foiled traditional standardization efforts. Although several VITA and PICMG standards have emerged, each is supported by only a small handful of different vendors, even after many years. Indeed, SFF system enclosures come in all shapes and sizes, with a variety of backplanes, interconnect schemes, circuit board definitions, and environmental specifications.

As a result, SFF systems are often proprietary architectures that satisfy a single, well-defined function with limited availability from multiple vendors. Compared to traditional open architecture systems, SFF systems are smaller, less expensive, lighter, lower power, easier to install, and capable of supporting tough operating environments – all significant and often critical advantages!

Gaining Popularity

Pentek Model 5973 3U OpenVPX FMC carrier with VITA 66.4 optical backplane interface supports 12 GBytes/sec of traffic in and out of the module over 24 optical fibre lanes to a remote SFF subsystem.

Customers are naturally attracted to SFF systems for two major reasons. Obviously, any embedded system with improved SWaP metrics opens up new application spaces and markets where those factors are critical. In addition, larger embedded systems are now being split up into smaller distributed sub-systems, each handling a portion of the system tasks. These two trends are gaining momentum and changing the landscape of embedded system offerings from traditional full size rack mount chassis.

For these distributed systems, several business factors drive make-or-buy decisions for each element:

  • If the required technology is outside the scope of the prime contractor's capabilities, he may not want to invest in developing internal engineering skills and expertise. A good example is a compact high-speed recording subsystem, capable of storing wideband analog or digital output signals from the signal processing system.
  • Even if the prime contractor does have engineers capable of a complex or technically challenging sub-system, he may decide to purchase an SFF solution to reduce risk or time to market, even if the estimated cost to develop it himself might be a bit lower. An example might be a sensitive RF receiver small enough to fit within the confines of a UAV.
  • Customers are increasingly willing to accept compact SFF enclosures and boards that do not follow embedded system standards. This is especially true for distributed systems if the vendor can successfully argue that the main portion of the system is a standards-based platform, while the SFF sub-systems are “just peripherals”.
  • For larger distributed architectures, SFF sub-systems make it much easier for systems integrators to replace these SSF peripherals to easily accommodate new requirements for a similar system, but installed in a completely different platform with different sensors, topologies, and environments.

SFF and Optical Links

Apart from the business reasons above, SFF systems can significantly improve performance levels, simplify installations, and reduce maintenance costs. Whether for radar, communications, or telemetry, overall system performance is limited by the dominant source of noise or interference at any point in the signal path.

Embedded systems have traditionally used the same system chassis to house the processing boards and the sensor interface boards. Many of these must support analog I/O using RF circuitry and precision data converters to maintain the highest levels of signal fidelity and dynamic range. Isolating and shielding these sensor interfaces from conducted and radiated emissions from powerful signal processor boards, graphic processors, and switching power supplies operating at several hundreds of watts is extremely challenging. Analog signals flowing from remote antennas or sensors suffer degradation from cable losses and susceptibility to interference from transmitters and power generation equipment. These chronic problems can be largely eliminated using the latest SFF strategies.

Removing the sensor interfaces from the chassis by using a SFF subsystem to relocate them as close as possible to the sensors solves the first problem of system noise contamination. With sensitive RF circuitry and data converters inside the SFF enclosure, the link to the main system is now digital. This is a good first step, but digital copper cables still suffer from loss and interference, both of which only get worse over distance. New optical interfaces are often an excellent solution to this second problem.