This paper addresses the problem of decentralized, outdoor formation coordination with multiple quadcopters. The problem is formulated as a receding horizon, mixed-integer non-linear program (RH-MINLP). Each quadcopter solves this RH-MINLP to generate its time-optimal speed profile along a minimum snap spline path while coordinating its position in a desired formation with other quadcopters. Constraints on quadcopter kinematics, dynamics, collision avoidance, wireless communication connectivity, and geometric formations are modeled. Communication connectivity is modeled as a constraint on maximum separation distance based on a minimum viable received signal strength in the presence of path loss attenuation. The resulting RH-MINLP is non-convex, and is solved using an outer-approximation branch and bound solver with a warm-starting scheme. The framework is validated via Hardware-in-the-Loop (HITL) and outdoor flight test with up to 6 quadcopters. Results demonstrate the effect of number of quadcopters and formation type on total transit time. Average radio packet loss statistics during transit indicate robust network performance for a round robin communication scheduling scheme.