Nokia(s nok) 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(s eric).

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.

Lately Nokia's been reclaiming ground in the U.S., last year beating out rival Ericsson for Sprint's(s s) Spark LTE rollout. In 2011, it scooped up Motorola's network business in part to increase its clout with U.S. carriers. SAC happens to be located in the same northwest Chicago suburbs as its Motorola's former network HQ, which is now Nokia's North American R&D center.

SAC specializes in deploying small cells and distributed antenna systems in dense highly trafficked areas. That should give Nokia an advantage as mobile networks migrate away from the big cell towers and rooftops and move down to street level and indoors.