First, start with the systems architecture. You need to design the system considering cost, safety, ease of development.
After that, for each item, main features are defined. This defines the high-level architecture of software elements (platform-side, maintenance computer or controller softwares).
The question is most probably about the main (vehicle) software, which conducts the most important calculations.
The main software architecture depends a lot on what one wants to accomplish. Is it a remotely-operated-vehicle? is it an autonomous system? how autonomous?
After that, software architecture is defined, taking into consideration any dictated or selected data interfaces.
The software architecture functionally resembles the systems architecture, because the main computer interacts with almost all of the elements of the robot.
Sample architecture for a robot racer
There are several studies regarding autonomous vehicle system and software solutions. You can dive deeper into the topic by visiting Google.