The 6ft 6in centre-half headed in his first Arsenal goal in the victory over Tottenham at Emirates Stadium on Saturday.
He said: "I had a very difficult first season with all the settling in and the new things at Arsenal.
"It was quite tough for me, but now I feel much more comfortable with the situation.
"It is much more physical than the Bundesliga so you have to make your mind up about the tackles, about the way you cover your partner, so I set those things up a bit and I feel much better than last season.
"I try to keep on going with that feeling."