How to design a cheat proof content rating system

I am planning to code a feature to a site where mostly user generated content is presented. I want to give the logged in users a way to rate the content. In order to prevent cheating of the system i am planning to give users rating points according to their activity. What would be the best way to design a system to make it cheat proof as much as possible? do you know any case studies about cheat proof rating systems or any algorithms for such systems?