The basic thing about this interview is the candidate should be clear about the basics especially for the previous research work done. The panel will be intrested in your depth of knowledge, you should be crystal clear about everything that you have studied, performed or experimented. They will go deeper and deeper during the Q&A sessions and the judgement will be based on that only, the tougher the interview goes the better research topic will be allotted based on your skills and level of understanding which will help you to gain knowledge and experience during your tenure.