have to design a embedded circuitry that can calculate the time of travel between two wireless devices.
what is the time taken by two wireless module and that time should send to server(MQTT).
you have to design only part of communication.
in a parking lot there is lots of place and lots of vehicles, if any one wants to find out where is the vehicle it is most probably difficult to find out. so, in these case that vehicle have a dynamic node and the parking lot have some static node. so, when some try to find out he/she have a mobile app and send a request to server to pin up the location of vehicle.
but here you have to work with what time take to communication between static and dynamic nodes of each.
And that time will send to server. THATS IT..