Global Navigation: Communication Network With Mobile Nodes

A navigation aid for the mobile nodes of a VHF and microwave-based digital communications network, in which each node has on-board sources for position and universal time information which is available as a real-time input to a special PC expansion card.

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.

Node schematic for a communications network with mobile nodes. 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:

I wrote this software entirely in 'C'.