RTC Magazine

Flying a “swarm” of unmanned aerial vehicles (UAVs) will place demands on both the hardware and software aloft. Indeed it appears the performance envelope for the UAV mission today is established not by airframe, sensor array or propulsion, but by available computing power. The Windows CE operating system, with both real-time and managed code environments, may provide the best path forward to enable the swarm concept of UAV operation.

In the swarm configuration, dozens or even hundreds of UAVs must patrol in unison, and report as a unit to the warfighters on the ground. Likely, these “robots” will work with even more numerous “sta-bots” or sensor platforms recording vibration, RF, sound, images, etc. from many sites. Using today’s sensors, engines and materials, UAVs and sensor platforms can be mass-produced and can reach the cost level of disposable items, like munitions.

What is still needed is enough compute power in both hardware and software to make the swarm largely self-tending and able to work as a unit, under only general guidance from the ground controllers. The swarm should perform as George Bernard Shaw described the Roman military, “And that Legion! It fights like a creature with a thousand arms, one mind and no religion.” -Cleopatra

To deserve such praise, the swarm needs better computers and smarter software than what we are flying today. The systems must be able to assimilate real-time information from attitude, environment and visual sensors and analyze the data—in real time—within a strategic and tactical context established by broad instructions carried throughout the swarm. The swarm moves far past the current UAV notion of “eyes over the next hill”. Available COTS hardware and software components are here today to do this.

Hardware and Software

The current generation of cell phones has mandated the development of powerful 32-bit RISC systems with onboard image, acoustic, RF signal, DSP and parallel processing. If more compute power is needed, the technology to embed special-purpose “soft core” FPGAs, purpose-built CODECs or ASICs for image or spectrum analysis is well developed.

Interestingly, it seems the most expeditious way to tap all this silicon power is via a commercial OS like Windows CE. Windows CE offers several advantages for UAV and sensor-net applications. First, its real-time performance is remarkably good. Windows CE shows a high level of deterministic response, even under high load, down to time windows measured in tens of microseconds. Second, it maintains comprehensive power management, in line with the best of class RISC CPUs. Third, it contains extensive image management software. Fourth, in this same real-time environment, it can host an object-oriented application environment perfect for coordination of swarms of sensor platforms or UAVs.

Real Time

UAVs require millisecond-level real-time determinism. MEMS-based inertial sensors can quickly indicate disturbances to the UAV’s flight path. Efficient dynamic models have been developed to keep the craft on the straight and level—provided the model execution is regular and in phase with servo actuators and sensor systems. Real-time demands will increase; exciting options exist for future integration of optical, perhaps binocular optical subsystems integrated with existing attitude and direction control.

This will allow low-cost UAVs to seek and destroy the fast-moving/low-tech targets such as Rocket Propelled Grenades (RPGs), mortar shells and short-range rockets that have become one of our principle threats. Figure 1 shows the input/output response of a CE system under heavy dynamic load, measured by Maarten Struys and Michel Verhagen of PTS Software (2003). This shows that in the best case, Windows CE latency is 14.0 µseconds, in the worst case the latency is 54.4 µseconds. Jitter—the most important measure of determinism—is only 40.4 µseconds.

Low Power

Low power consumption and power management are important to most UAV and remote sensor applications. Even if power is plentiful aboard some UAVs, low power consumption allows the computer to be enclosed in an environmentally sealed container and run at elevated temperatures if needed. But for many applications, such as electric aircraft, “leave behind” sensor nets and deep-sea submersibles, low power consumption itself is a critical virtue. Windows CE offers extensive power management capabilities, matched to RISC CPUs such as the Intel PXA 27,0 which supports as many as five modes of reduced power operation (including a sleep at .18mW and a deep sleep at .09mW). Reducing long-term power demand to the level of battery leakage is quite possible, and several systems are now deployed for unattended operation for a year or more.

This level of power conservation is obtained only by integrated design throughout the system. The board itself must be partitioned for selective power management. Software drivers need to be power-managed. Power supply design must be efficient and allow for frequent power-up/power-down. Finally, the OS needs power-aware network APIs and similar extensions. The power-thrifty system is engineered to spend most time in “sleep” or some lower power mode, ready to move into full speed computation as dictated by external conditions. Applied Data Systems has further engineered these systems to support an in-built 8-bit CPU with very low power demands that can put the entire system into a “coma” mode drawing only micro amps but ready to return to action with sensor input, serial line input or clock request (Figure 2).