Multi-Protocol Avionics Systems Require Modular Solutions

Today’s mix of military avionics I/O requirements make system designs a challenge. By leveraging compute-based modular architectures tricky interface problems are smoothed way.



Modern military avionics I/O demands are exploding. From legacy MIL-STD 1553, ARINC 429/717 and 825 to Gbit Ethernet and Fibre Channel, a diverse set of interfaces are used in the plethora of individual systems installed in the aircraft. Because of this diversity, many avionic platforms today find it necessary to integrate Ethernet alongside ARINC 429 and MIL-STD-1553 to meet the varied and growing data demands onboard the aircraft and to support increased bandwidth performance needs of new video processing and sensor-based systems.

It is easy to see the necessity for multi-protocol connectivity with the ability to easily bridge from one protocol to the other. However, it is subsystem performance and flexibility that make these capabilities possible, which is not adequately supported by traditional microcontroller-based subsystems due to their static features and specific command set. Plus, achieving broad interface support is made more difficult by the constant need to satisfy rugged reliability and reduced size, weight and power (SWaP) requirements as more functionality is poured into military aircraft.

Optimizing the I/O Links

Avionics developers must find the most optimal way to link the I/O needs of legacy-based interface systems and make them compatible with higher-performing aircraft subsystems. A practical approach to addressing dynamic interface mix changes is with computer-based avionics solutions that employ the latest highly-integrated processor architectures offering the advantages of lower power consumption.

These new rugged avionics computers process data more efficiently and at the same time deliver an inherently modular, flexible, more powerful, and scalable approach compared with alternative microcontroller solutions. While microcontroller-based subsystems that offer fixed, specific command sets are great for certain applications, these types of solutions do not give users the programmability needed to enable multiple I/O functionality.

Computing Architectures Fill the Need

The 1553 data bus is a standard choice for avionics flight control commands based on its inherent reliability, determinism and a 1 Mbit/s data rate that is more than adequate to support the data communication requirements for flight, sensors, and weapons control (see the sidebar “Why 1553?” in the web version of this article). For avionic applications requiring higher data rates, including video/image transfer, high-speed networks such as gigabit Ethernet and Fibre Channel are often deployed. However, there is a wide range of application requirements from platform to platform, making scalability and programmability of solutions also a critical requirement. Consequently, platform solutions must provide the ability to easily mix and match different I/Os to reduce risk, lower development costs, and help expedite the development process. They also must support the large variety of protocols used and be able to expand as needed into ever smaller form factors, particularly important for long-term system deployment or tech refresh.

What makes all this possible is the ability to provide trusted multi-I/O capabilities in a high-performance avionics solution. The good news is that there are advanced computing architecture platforms that accomplish both demands while providing new capabilities and maintaining legacy interface reliability.

Open Standards Using COMs

Open standards embedded computing platforms based on Computer-on-Modules (COMs) provide an ideal modular framework for enhanced design flexibility. A highly scalable, adaptable and programmable application foundation that allows avionics developers to address dynamic interface mix changes is the application-ready Kontron COBALT (Figure 1). This rugged IP67 fully sealed and compact system delivers the computing performance demanded in today’s military avionics systems. The heart of the COBALT platform is its COM processor board with the complete system including a rugged baseboard, power module, housing and appropriate I/O connectors.

Figure 1 Strict tolerance to shock and vibration has been pre-validated for the COBALT system based on the broad spectrum of UAV and other avionics environments. The unit is also tested to perform reliably in temperatures ranging from -40 to +71 degrees C.

Today’s application-ready platforms simplify this process, enabling defense contractors to use faster Ethernet that then bridges back to 1553 connections. These same platforms also enable the seamless integration of Ethernet technologies and the addition of new devices, which avoids the need to develop new and more costly systems. Furthermore, the capability to support all avionic I/O requirements provided with small footprint computing platforms enables developers to replace several cards or boards with a single form factor thereby delivering significant size, weight, power and cost (SWaP-C) savings.

Mezzanine Option Investments

Scalable integrated building blocks are essential to simplifying the avionics system design process. Designers can further integrate mezzanine options with Computer-on-Module (COMs)-based systems such as Kontron’s COBALT, a self-contained, small form factor rugged computing platform that packages COM Express-based COMs in its rugged housing. COBALT gives designers a configurable application-ready platform capable of meeting a broad range of I/O and network communications requirements. Importantly, the addition of mezzanines enables new systems without significant modification to an original base design, thereby protecting and maximizing technology investments.

Embedded computing platforms based on COMs enable developers to leverage COM Express Type 6 pin-outs, which permit future design options by reallocating legacy PCI pins for digital display interfaces and additional PCI Express lanes. Extra PCI Express lanes can be routed to serial-based mezzanine card slots such as mPCIe and XMC. Expansion slots are created as a result, providing a performance jump compared to earlier pin-out options. This approach also produces an enhanced fourth generation graphics architecture that is essential to support avionics high definition surveillance and imaging applications.

Because the resulting system is modular and upgradable, performance can evolve by swapping out modules to access processor advancements. Developers meet design requirements while avoiding additional customization costs and development resources from the ability to use and reuse platforms in smaller systems. It is important to note the extensive PCIe support in Type 6 highlights the ongoing move away from legacy parallel interfaces and towards pure serial embedded system designs. This trend matches perfectly with the higher bandwidth and reduced latency required by many military avionics applications.

Data and Image Processing

Using persistent surveillance or high resolution imaging applications as examples, application-ready systems demonstrate performance values ideal for unmanned or other avionics applications. With more powerful graphics display and processing features, military professionals can simultaneously access and process multiple displays of information in the field. Incoming general data can be reviewed immediately on-site or stored for later review, while urgent information can be quickly distributed for immediate action.

In this type of high-bandwidth design scenario, ruggedized, thermal performance is validated at the board level. The system includes reliable performance in temperatures ranging from -40° to +85°C. All I/O routed from the baseboard relies on a proven rugged connector, while all external I/O employs a 38999 type MIL circular connector. Developers avoid design requalification or additional PoC requirements because the system’s baseboard stack provides all necessary interconnects between the COM Express board and XMC and mPCIe interfaces. An added advantage for designers is that these systems typically provide native support for all the newest display interfaces, which ultimately simplifies carrier board designs. This adds significant value by reducing time-to-market as well as total cost of ownership for graphics-intensive military applications.

Flexibility in Avionics Subsystems

With high-density embedded computing advancements, flexible avionics subsystems can be achieved that specifically meet the high channel count, extensive I/O mix and high performance required. These small form factor platforms are smaller and lighter saving space, power, weight, and cost and at the same time provide more features and capabilities. Scalable and ruggedized, new avionics subsystems meet specific harsh environment requirements while also providing the ability to easily customize solutions.

Providing a standards-based foundation, these solutions are equipped with advanced firmware and software designed to handle growing demands for connectivity and high density multi-protocol requirements in small form factor rugged enclosures. Optimized application-ready subsystems are pre-qualified but keep design options flexible to enable fast deployment of Proof of Concept (PoC), new systems or system upgrades. The advanced technology integration of COTS Computer-based avionics subsystems also enable developers to comply with field-proven technical readiness level (TRL) mandates allowing them to effectively reduce associated development time and costs.

Exemplified by DDC’s Rugged Avionics Interface Computer (AIC), developers have a flexible and scalable platform that supports a wide range of data network communications. Platforms such as the AIC provide high-density protocol bridging with a high level bridging API and an extensive range of multi-IO channel configurations supported by an embedded XMC module and two mini-PCIe modules (Figure 2). The system combines best-in-class performance from Intel’s embedded computing architecture. For instance, the system can perform based on very low power Intel Atom processors or be deployed as a more powerful Intel Core i7-based system. The I/O flexibility of DDC’s High Density Multi-Protocol XMC and Mini-PCIe modules gives developers the ability to add optimized avionics connectivity in a small form factor, application-ready and rugged enclosure.

Figure 2 The rugged Avionics Interface Computer (AIC) offers three modes of bridging capability. Remote Access Mode uses Ethernet to communicate to the AIC on the airframe and control the 1553 and 429 interfaces, eliminating the need to run long 1553 or 429 cabling.

Maximizing technology investments and reduced time to market are key challenges for military avionics systems developers. Leveraging integrated building block computing architecture for rugged avionics applications provides the sound basis for successful configurable platforms capable of meeting a broad range of I/O and network communications requirements. Scalable by design, the latest avionics multi-protocol platforms allow reuse enabling customized solutions that speeds design to deployment of new or system upgrades while reducing long-term costs and engineering resources.

Long-Term Design Strategies

U.S. Army Training and Doctrine Command states “military power in the 21st century will be defined by our ability to adapt.” As modern avionics system designs advance, it will be important to adapt and support all relevant military avionics interface schemes from 1553 networks to an Ethernet-centric topology. Taking a COTS computing approach that uses COMs’ standard LAN, SATA, video, audio, GPIO, configurable serial ports, and multiple USB features, permits variable I/O to be designed in through application-specific customization on the carrier board.

Integrating these benefits, new avionics subsystems such as the Rugged AIC from DDC, enable remote multi-interface connections to help fulfill this transformation. Enhancing avionics system design options, maximizing portability of the application and increasing data application performance, these next-generation subsystems provide flexibility in system design topologies and reduce both initial and recurring development costs.

While there is no “one solution fits all” for modern avionics networking, multi-protocol avionics computers flexibly fill the gap in many design scenarios. Leveraging configurable computer-based platforms allows these latest computing-based systems meet the full complement of avionics I/O, save precious SWaP and reduce costs as well-all in a single small form factor. Significantly in this age of reduced budgets, proven designs can be reused, giving defense developers a competitive advantage in meeting design requirements while reducing the need for development resources and avoiding additional customization costs.



Why 1553?

Inherent reliability and determinism are the most important qualities of the 1553 data bus. That reliability, and the vast number of existing and sometimes relatively old defense systems that depend on it, ensures that military designers will continue to specify 1553 on new applications for years to come. Thirty years ago, MIL-STD-1553 started out as the primary data carrier between subsystems on high-performance aircraft. Today, it often plays a secondary role in relatively low-bandwidth deterministic, assured-delivery applications, and often complements modern super-fast serial data buses.

A 1553 data bus can virtually guarantee delivery of all messages, thanks to its simplicity, highly robust physical layer, and its redundant two-channel architecture. A key attribute of the 1553 physical layer is its large budget for signal attenuation; the transmitter produces a large voltage signal, while the receiver at the other end is very sensitive, so the message still gets through even if it loses strength along the way. Further, 1553 includes a very robust common mode rejection spec of 45 dB minimum. The required use of isolation and bus coupling transformers provides strong common mode rejection, along with inherent immunity from ESD and lightning disturbances.

MIL-STD-1553 is enduring because it fills a need in many applications, offering the low-cost and robust interoperability that is optimized for low-speed sensors, engine controls, and flight surfaces. 1553 continues to be the popular choice for military command and control applications requiring high levels of determinism and reliability, and where 1 Mbits/s provides adequate speed. Over the past 30 years, 1553 has been widely implemented in command and control applications, principally for Air Force weapons platforms, but also for Army, Navy, and NASA and other space applications. These include a long list of fighter, attack, and bomber aircraft; helicopters, missiles, ground vehicles, ships, and satellites; and the International Space Station.

Data Device Corp.
Bohemia, NY.
(631) 567-5600

Kontron America
Poway, CA
(858) 677-0877