Global navigation satellite system (GNSS)-based attitude determination plays a critical role in various navigation, guidance, and control applications. GNSS attitude determination has been applied in various land, airborne, and maritime scenarios. The goal of GNSS attitude determination is to estimate a vehicle’s or platform’s orientation in a reference coordinate system utilizing multiple GNSS antennas/receivers rigidly mounted on the body frame. To estimate a platform’s attitude, it is critical to resolve the integer ambiguities of the carrier-phase observations correctly, an onerous mission that becomes even harder in urban areas with limited satellite visibility. This dramatically increases the ambiguity search time. In this talk, we explore ways of reducing the time complexity of GNSS ambiguity resolution by improving the optimization techniques and the search algorithms.