Global Navigation: Communication Network With Mobile Nodes

Each node continually scans for the presence of all nodes of the network using a transponder scheme which is 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 is provided of the imminent loss of a link due to a node being about to move out of range. This allows the link to be safely closed down and the network reconfigured.

For this purpose, a database is 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 are not network nodes are also held as additional sources of positional reference.

To minimise processing, the rate at which a node is tested for range as a candidate for transponder interrogation is 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 is provided 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'.