U.S. Army Case Study
Airborne Router Evaluation and Problem Identification
A global defense contractor was developing an implementation of the Multi-Role Tactical Common Data Link (MR-TCDL) specification for an airborne router application. Field trials for evaluating the technology were planned using a fixed ground node, an on-the-move (OTM) software test environment (a modified HMWV), and NASA WB-57 high altitude research aircraft. The trials were to be conducted at the Mountain Home AFB in Idaho.
The US Army wanted thorough validation of the MR-TCDL implementation but also wanted to minimize the expense of live flight tests. The contract allowed for a maximum of seven flight test days to identify the problems during the initial flight tests. During the first day of the live flight testing, the system experienced unexpected intermittent link drops.
EXata was used to create a high-fidelity virtual network model of the test environment. The model incorporated the actual Inter-Platform Communications Manager (IPCM) software used in the live routers. The model also included real code to emulate aircraft attitude (yaw, pitch and roll) and antenna behavior (both directional and omni). The model was overlaid on accurate DTED 1 terrain.
Before the first flight tests, a series of network simulation scenarios were run to establish a networking system performance envelope. A range of parameter variations were analyzed to identify different predicted sensitivity levels, enabling the engineers to optimize the live flight experiments. In particular, the virtual network model allowed for detailed analysis of antenna/weather/terrain effects on signal strength and link quality. When the intermittent link drops were discovered, the model was used to explore potential causes.
After the first day of flight tests where the intermittent link drop issue was observed, additional use of the virtual network model enabled engineers to quickly narrow the cause down to wing shadowing of the primary antenna as the aircraft executed its flight patterns. This shadowing lowered the signal strength below the keep-alive threshold level.
Subsequent flight tests confirmed both this predicted behavior and the effectiveness of the system modifications that mitigated the issue. Leveraging the EXata simulation model with system-in-the-loop emulation, the entire validation exercise for the Multi-Role Tactical Common Data Link was completed successfully in only three live flight test days.
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