"I think it doesn't make any sense to be anything other than optimistic. I need to believe in my qualities and my abilities and I need to believe that I can repeat the success.
"Of course it is going to be an incredibly difficult task to achieve, but you never know, nothing is really impossible."
Nadal lost his top ranking to Djokovic in 2011 and cut a world-weary figure as the year came to an end, having played 84 matches - more than any of his rivals.
But the 25-year-old, whose French Open triumph was his 10th major and sixth at Roland Garros, believes leading Spain to a fifth Davis Cup has helped reignite his hopes for 2012.
He is also determined to adopt a new approach to his trade.
"I tell myself: 'If I do a bit more, I will be nearly back to winning things again.' That is the motivation. Recovering the extra will that makes you give a bit more of yourself," he said.
"I have to get back to my cruising altitude, which should be higher. From Indian Wells to Wimbledon and the Olympic Games is where I have to recover my best level."
Federer, meanwhile, defied those who believe that having celebrated his 30th birthday in 2011, his best was behind him.
The Swiss won his first title in Doha in January before picking up three more in the home straight in Basel, Paris and a sixth World Tour finals trophy.
He will go into 2012, his 13th year on the tour, on the back of a 17-match winning run.
"My passion for competition and my love for tennis has a lot to do with it," Federer told The National newspaper in Abu Dhabi.
"I have always said that the minute you decide or think that you cannot improve is the time that you should stop playing.
"The good news for me is that I feel like I still have things to learn and parts of my game to improve, so I am excited for the future."
The three-day tournament at the Abu Dhabi International Tennis Complex in Zayed Sports City also features Spain's David Ferrer and French duo Jo-Wilfried Tsonga and Gael Monfils.
- AAP
