Kevin Pietersen admits he is facing the "toughest" challenge of his career as he looks to come to grips with the Decision Review System.

The 31-year-old has struggled with the bat in the United Arab Emirates, scoring just 107 runs in his eight innings to date. Most of his problems have been down to his inability to come to grips with Pakistan's spinners and the controversial DRS.

There were a record 43 lbws decisions given during the three Test matches between Pakistan and England with many of them being given out via referral.

Pietersen feels batsmen are being hard done by the controversial technology as the benefit of the doubt is now being given to the bowlers.

"In my career so far, this is the toughest I've ever found it," he said. "Because of this new DRS system, there are definitely technical issues you have to look at in order to save yourself from batters not getting the benefit of the doubt any more.

"Umpires are giving a lot more lbws, and it just has to be clipping the wickets - like a couple of those games we played in - and you're out. Two, three, four years ago you were never ever out."

He added: "Batters have had to worry about the DRS, worry about the ball hitting your pad and having to change technique to try to counter it. The benefit of the doubt is certainly not with the batter now, which is quite sad."

Pietersen was given out lbw to Pakistan spinner Abdur Rehman in the third Test and he says umpire Simon Taufel admitted afterwards that he made a mistake.

"My dismissal when I got out to Rehman where the ball was clipping leg stump, the umpire Simon Taufel came and apologised to me the next morning. It is fine," he said.

"The decision went with the bowler. When you see a decision and a ball is clipping leg stump that much it should not be umpire's call. If it is crashing into leg stump then out. But when it is clipping like that it is unfair to batters."