Ferdinand, 35, is a free agent following the expiration of his contract at Manchester United, and Goal revealed in June that the former West Ham trainee was close to agreeing a deal at Loftus Road.
Reports had suggested that a potential QPR move for the centre-back was in jeopardy due to the former England international's wage demands.
However, Redknapp has dismissed those rumours, stating that a deal for Ferdinand - who is currently working as a television pundit at the Fifa World Cup in Brazil - is close to being completed.
"Rio has agreed to join us and we're hopeful of getting that one over the line when he gets back from the World Cup," Redknapp told The Daily Telegraph.
"I can't foresee any problems with it and we'd be delighted if we can get it done soon.
"He's been a player at the top of the list since he left Manchester United and he would give the whole place a lift with his quality and experience."
Redknapp is keen to pair Ferdinand with Caulker, who he worked with during his time at Tottenham, at the heart of the QPR defence.
But QPR's hopes of signing the Cardiff City man could be scuppered by apparent interest from Liverpool, Everton and Southampton.
"We've agreed a fee with Cardiff and it's now up to Steven to decide his next move," Redknapp added.
"I know him well from Spurs and he's always been a tremendous prospect. Hopefully that's another one we can get done."