Robert J Morton

Personal Project Mobile Communications Network: a navigation aid for the mobile nodes of a VHF and microwave-based digital communications network in which each node had on-board sources for position and universal time information which was available as a real-time input to a special PC expansion card.

Each node continually scanned for the presence of all nodes of the network using a transponder scheme which was able to identify all network members which were sufficiently within range for a digital radio link to be established and maintained between them. Conversely, warning was provided of the imminent loss of a link due to a node being about to move out of range. This allowed the link to be safely closed down and the network reconfigured.

For this purpose, a database was constructed within each node's PC to hold the details of all the nodes of the network including self. Details of waypoints (navigation stations and prominent geographic features) which were not network nodes were also held as additional sources of positional reference.

To minimise processing, the rate at which a node was tested for range as a candidate for transponder interrogation was a function of its last known distance from the circle of maximum safe useable range and its velocity component towards that circle.

A special access/editing function was written to enable the database to be scanned at various rates for various items of data in real-time, while being able concurrently to accept keyboard updates. Other functions provided included:

• range and bearing calculation using spherical geometry
• conversion of degrees + minutes to radians and vice versa
• computing screen co-ordinates from range and bearing
• computing ellipsoidity and tilt of a displayed node
• annotating nodal ellipse with the node or feature name
• displaying currently established links to remote nodes
• displaying information source status and credibility
• displaying universal time and own lat, long, height

I wrote this software entirely in 'C'.