UAV system architectures: The next evolutionStory
August 25, 2010
Network-centricity and recent advances in high-speed serial fabric technologies, along with legacy device bridging methodologies, enable highly flexible UAV system architectures to meet the rapidly changing demands of the 21st century battlefield, while shortening time-to-market and mitigating risks.
The roles of Unmanned Aerial Vehicles (UAVs), like the Global Hawk UAV shown in Figure 1, are expanding. As UAVs’ strategical and tactical mission capabilities continue to expand, there is an ever-increasing need for highly reliable, high-performance electronic systems that can support high-bandwidth network connectivity within the platform – and from the platform to the Command and Control infrastructure. UAVs are increasingly becoming networked systems; they are one element of the entire Unmanned Aircraft System (UAS) that communicates and shares mission-critical payload and sensor information with other elements such as ground control stations and ground/remote terminals to provide a common operating picture.
Figure 1: The demand for UAV technology is ever-increasing, and the Global Hawk is one example of such technology.
(Click graphic to zoom by 1.2x)
This migration from platform-centric to a network-centric systems approach poses new challenges that are met by the use of open architectures. Formerly, UAVs adopted platform-centric architectures that relied on proprietary interfaces. Many of these design concerns can now be overcome by ruggedizing commercial electronics, enabling subsystem technologies containing COTS components and allowing faster time-to-market. The result is rapid battlefield deployment of the newest technologies.
Advances in open standards performance, such as VPX high-speed serial fabrics, along with the ability to bridge legacy devices, make it possible to develop scalable and interoperable network-centric subsystems at significantly lower development and logistical risks.
Network-centricity eases interfacing
Net-centric architecture enables the UAV system designer to standardize the interface between the computing elements and the interface elements. For example, a COTS SBC might not have the needed ADC/DAC onboard, but a network-attached Remote Interface Unit (RIU) with ADC/DAC capabilities can be provided at or near the vehicle’s sensors and actuators. (See Figure 2 for a network-centric reference design.) The RIU in this case would digitize the inputs, communicate with the SBC through a standard network interface such as GbE, and generate analog outputs, therefore creating a standardized interface between the processor and the I/Os. The same approach is also applicable to Network Attached Storage (NAS). NAS improves data accessibility via Network File System (NFS) protocol while making it seamless to grow the storage capacity on the network at a later time. As long as the new device conforms to the same GbE and the file sharing protocols, the rest of the system is not impacted.
Figure 2: A network-centric reference design
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Traditionally, the inputs from platform-specific sensors are either hardwired directly to the processor or transmitted over MIL-STD-1553 or ARINC-429 buses, and the processor board must be designed with dedicated signals such as discrete, analog I/O MIL-STD-1553/ARINC-429 bus interfaces to handle that communication. This introduces an obsolescence risk as the support for these special signals is not standardized by the industry. In other words, a custom product has to be made, which comes at steep nonrecurring and recurring prices. To eliminate those issues, taking the RIU approach, network-attached sensors and effectors can use GbE to communicate through network switches, freeing the processor card from requiring any special onboard I/O. This permits the sensor to stay in place while the processor card or electronic system can be replaced or upgraded separately, with the added benefit of reduced wire counts in the main harness assemblies. Combined with deterministic Ethernet, like ARINC-664/AFDX for avionics, flight control needs can be met.
VPX and high-speed serial fabrics
Another advantage of embracing new open architectures on UAVs is their support for distributed computing. In today’s systems, it is typical for each of the multiple SBCs to be assigned specific functions. Density limits on SBCs, currently at around 18 GFLOPS for a conduction-cooled 3U card, mean that the requirements frequently can’t be addressed in a single slot. A distributed or cluster environment, on the other hand, enables tasks to be shared amongst the SBCs, effectively multiplying CPU power to the 100s of GFLOPS required by video processing and intelligent algorithms. Working in unison with RIUs, the processors can now be physically relocated to practically anywhere within the airframe where CPU power, electronics packaging, power supplies, and cooling capacities can be managed more effectively and where space is available. Figure 3 shows a ruggedized electronic enclosure that supports high-speed interfaces and can be cooled in different ways in accordance with VITA 48.x.
Figure 3: A ruggedized electronic enclosure that can support high-speed interfaces and be cooled in different ways in accordance with VITA 48.x.
This type of processor-to-processor collaboration essentially takes the Symmetric Multi-Processing (SMP) and multicore model beyond the slot level to the chassis level and beyond. This collaboration requires high-speed interconnects, often at multiple Gigabytes-per-second speeds, and is now possible via open standards such as VPX (VITA 46) and its support for serial fabrics such as Serial RapidIO and PCIe. The newer OpenVPX (VITA 65) further refines pinout definition for interoperability. External communications outside the chassis can be achieved with GbE and 10 GbE. One way to satisfy the growing hunger for more processing is to standardize on communications protocols that support distributed computing.
Bridging with legacy devices
As UAV platforms migrate to a network-centric approach, legacy buses such as 1553, RS-232, and CANbus will need to communicate with newer GbE-based interfaces through bridge devices. This approach allows for an incremental upgrade that matches today’s existing budget constraints, because it is unlikely that all older LRUs can be replaced at the same time. There will be a period of time during which new electronic systems and older ones based on the legacy interfaces must coexist.
Curtiss-Wright Controls Electronic Systems’ network bridge technology is used in sensor management and payload management computers to integrate legacy, proprietary, and emerging interfaces in addition to performing data fusion by translating the communications protocols from one side to another. For example, when it is time to upgrade a Remote Terminal (RT) from the 1553 network and put it onto the GbE side, the network bridge can transparently emulate the RT’s I/O as though it were still on the 1553 side. The other LRUs on the UAV won’t even detect that the RT has been transitioned to the GbE side. The same can be achieved for Bus Monitors (BMs) and Bus Controllers (BCs).
The demand for electronic systems with advanced multiprocessor compute technologies on tactical and strategic UAVs creates many challenges. Open interface standards such as VPX (VITA 46), OpenVPX (VITA 65), and VPX-REDI (VITA 48) – along with adoption of standardized high-speed interconnects like GbE and PCIe – enable designers to overcome these challenges. Also critical to the equation is the ability to bridge legacy devices. Hence, now is the time for designers to optimize their electronic systems with a network-centric, open architecture approach to achieve new levels of processing efficiencies and performance.
David W. Lee is a Project Engineer for Curtiss-Wright Controls Electronic Systems. He has more than 12 years of experience in avionics and embedded systems. He holds a degree in Computer Science from the University of Buffalo and an MS in Computer Science from Binghamton University. He can be contacted at [email protected].
Curtiss-Wright Controls Electronic Systems 661-257-4430 www.cwcelectronicsystems.com