The project IDOCAS consists of the development of an intelligent, distributed GPS-based obstacle and collision avoidance system for civil air traffic. Its special feature is a collision avoidance for fixed objects like towers, antennas and aerial ropeway cables. To efficiently avoid fixed obstacles, a database with all obstacles in the area is needed. In order to update this database, it should be possible to connect to a web-connected-server via RF.

The purpose of the project was to develop and implement a specialized client-server protocol to guarantee a secured link between server and clients. The client hardware already existed. The server hardware had to be built in order to connect a RF-module to a Personal Computer.

The developed protocol works along the principles of TDMA (Time Division Multiple Access), which allows the server to provide multiple clients at "the same time", over one communication-channel.

The client-hardware consists of a Texas Instruments MSP430 Micro-Controller and a Nordic nRF905 ISM-RF-module. The server-hardware consists of a PC and a RS232-link to an MSP430 with a connected nRF905-module.

The protocol-software of the client is written in C, in the development environment ICC430. The software runs on a Controller without an operation system. It was realized with the techniques of "state-machines". That way it is possible to run through the program without stocking in the code. If there is an application running on the Controller, she would also have the possibility to get CPU-time.

The protocol-software of the server runs on a simple PC with Windows XP. The software is written in C, in MS Visual Studio 6. To allow multiple accesses to the RF-channel, the server-application has to use "Threads". The protocol uses "Semaphores" to protect the driver of the RF-module. "Semaphores" guarantee the access to the RF-module of only one client at a time.