But I dont understand what very specific field I am interested in
Excellent, that is a great place to be!
many specific lines one can opt for like FPGAs,System on chip , cognitive interaction
No! You cannot opt. Do not choose anything from a list. Just explore each subject. Then, ask yourself what is important to you? What are you doing here, and what is your religion? You have to dig deep for this part, and really decide about some goal you want to accomplish. It may be slightly unrelated to system design.. stop thinking about systems for a moment, and think about the rest of life.
There must be a reason you chose to enter this field. You have a talent that you can put to use in this field. And you will probably have to sell a lot of your time and talent to some company that becomes your employer, but that is for later.Right now, you have this opportunity to really ask yourself what you can contribute by applying your talent.
So what is it going to be? You will skim through articles that fascinate you... articles written by people in the past 3 years. When you read them, of course each will have a MAIN IDEA that is the author's insight. When you have skimmed through ALL the recent articles about your areas of interest, you will be ready to take the next step by CONTRIBUTING an insight of your own. Contribute to the ongoing conversation. Now that you are gaining some mastery in this field, you are ready to express your own unique contribution. Don't try to force it, just go read another article. :^)