Nokia may have one of the biggest mobile network-building operations in the world, but you would have hardly noticed in the U.S. over the last decade. When the 4G revolution kicked off, Nokia landed a single contract: T-Mobile’s LTE network, which it split with Ericsson. But Nokia’s network fortunes are improving in this key global market, and it’s starting to scale its operations to meet new demand. On Wednesday, Nokia announced it is acquiring Chicago-based SAC Wireless, an engineering firm specializing in the planning and logistics of network deployment. Nokia didn’t reveal the financial terms of the deal.