Related Questions Works with only Tags ?

Hi,

Related Questions only working with Tags.

So Now say i dont have any tags for a question then there is no related questions appears.

Every time users are not using tags in the questions. so related questions showing empty.

1. I want Related questions to work with category instead of tags if there were No tags in that questions.
2. Also Related Questions needs to be shown randomly but same Related Q&A appearing in the next/previous questions.

Please suggest for the above two points

Thanks