Early this year, Google bought 188 patents and 29 patent applications related to mobile phones from IBM but did not disclose how much it paid. Last year, IBM sold Google 2000 or so patents ranging from mobile software to computer hardware and processors. Google has been strengthening its patent portfolio as the fight for dominance in the booming smartphone and tablet computer markets increasingly involves patent lawsuits - with Apple a prime litigator. The technology titan behind Android mobile device software last year transferred patents to smartphone giant HTC to help the Taiwan-based company in an intellectual property clash with iPhone maker Apple. Apple has accused HTC and other smartphone makers using Google's Android mobile operating system of infringing on Apple-held patents.