System Latency and Real-time Interface Considerations. In vehicle control systems, designers typically should consider all sources of latency to ensure satisfactory handling qualities and system stability. This is particularly true in a UAV system employing manual control of the aircraft. In such systems, a critical area of concern is the total latency between the air vehicle and the operator controls and displays, as this attribute will strongly influence system performance under manual control. In the UCS architecture, real-time UAV and data link control functions (when required) are managed by the VSM. The CUCS performs non-real-time processing, and the DLI specifies neither fixed nor maximum latency in exchanges between the VSM and the CUCS. Though message delivery may be guaranteed, latency is not, and consequently real time performance is not guaranteed for signals passing through the DLI. In general, the DLI physical medium will have sufficiently high data rates to support control and display data needs at reasonable rates for human interaction. However, because the DLI medium may potentially be shared among a number of VSMs simultaneously, messaging rates and overall bandwidth may tend to be variable and should not be relied upon. Several approaches are possible in constituting a UCS-compliant system: • The VSM performs all real-time functionality autonomously, and data interchange needed to support controls and displays are designed to be of a non-real-time nature. In this approach, controls and displays presented to the user are not dependent upon any particular latency. Changes in latency are managed such that they do not affect readability of displays or performance of controls. For instance, integrators in a control stick filter may use dynamic integration time to avoid changes in the timing of data delivery across the DLI. • The system is designed to take advantage of measured throughput available through the DLI and in the CUCS using near real time techniques resulting in no significant delays, but special provisions are incorporated to sense and accommodate excessive latency. This approach is somewhat risky in that the CUCS hardware configuration is variable and some configurations may not support a given function or approach. • Certain manual controls and displays are critical and will be serviced with no noticeable delays (isochronous) process. In this case, processing is performed in the VSM and device interfaces are managed directly by the VSM without passing through the DLI logically or p...
