The Wallenberg laboratory for research on Information Technology and Autonomous Systems

System Architecture

The first version of the WITAS UAV command and control architecture (CCSA) was developed for the 1997 and 1998 demo systems, which are described in a separate menu item here. Based on the experience of that early work we defined a revised architecture that is the basis for the continued work and that is described in a detailed report that was published by Linköping University Electronic Press.

The following is a brief summary of the WITAS CCSA. It can be characterized as a three-layered hybrid deliberative/reactive architecture with functionality and structure similar in spirit to, but not the same as, the three-layered architectures proposed by Firby and Gat. The CCSA contains the following layers which function as three separate asynchronous computational processes:

• Deliberative Layer -- The deliberative layer is responsible for computation intensive tasks such as plan generation, plan monitoring, high-level episode recognition, diagnosis, and responding to queries from other parts of the system. Time and space complexity for tasks executed in the deliberative layer are theoretically unrestricted, although the nature of the application obviously places bounds on these parameters.

• Reactive Layer -- The reactive layer is responsible for the contingent sequencing, parameterization, and execution of tasks associated with the achievement of temporally extended goals explicitly generated during run-time by the deliberative layer and implicitly defined at compile-time by the system designers in the reactive layer. Time and space complexity for tasks executed in the reactive layer are restricted to have much tighter bounds then the deliberative layer, with very little use of world state and limited time bounds on computation.

• Process Layer -- The process layer is responsible for the concurrent computation of collections of feedback control loops tightly coupling sensing with actuation. Time and space complexity are tightly bounded with essentially no use of world state and very short sampling periods.

In addition, the CCSA contains a Knowledge and Data Repository (KDR) storing two types of knowledge and data:

• Static KD -- This part of the KDR contains longer term symbolic knowledge structures such as those found in Geographic Information Systems, assertional knowledge bases, or reactive task description repositories.

• Ephemeral KD -- This part of the KDR contains shorter term knowledge structures and caches used by the different CCSA layers to implement both low and high-level functionality. For example, the dynamic data structures used by the image processing system and scene information manager in the vision module create short term ephemeral KD structures during image interpretation.

In general, much of the knowledge and data used by the system is stored in a local manner, especially in the lower layers of the architecture. Global knowledge and data can be retrieved and updated by all three layers of the CCSA via access to a central data bus, although the lower layers primarily use and update the ephemeral KD structures and the deliberative layer uses and updates the static KD structures. In addition, it is the responsibility of the deliberative layer to fuse ephemeral KD structures with static KD structures when this is deemed useful.

Maintenance information: Latest update 10.5.2000 by WITAS secretariat. Edit mode aml, position code D.witas.info.arch. To proceed, click other item in menue