Lenovo is spending large sums to make a belated impact on the mobile device market, as its core PC sector starts to decline. Having agreed to buy Google’s Motorola Mobility arm for $2.91m, it is topping that up with a $100m acquisition of wireless patents from Unwired Planet, formerly Openwave. Smartphone makers increasingly see it as essential to have a good base of IPR, to strengthen their negotiating position with other patent owners and so improve their economics. That has been a factor behind the wave of legal battles of the past two years, and the string of patent-related acquisitions, including Google’s of Motorola’s device business. The search giant gets to keep most of that IPR, so Lenovo is looking…