  This paper proposes a low-cost six Degree-of-Freedom (6-DOF) navigation
system for small aerial robots based on the integration of Global Position
System (GPS) receiver with sensors of inertional Microelectromechanical Systems
(MEMS). In the problem of fusing Inertial Measurement Unit (IMU) with low-cost
GPS, the effect of time synchronization error on attitude estimation is
concerned. A fusion algorithm which can estimate the motion states and the time
synchronization error simultaneously is proposed. This algorithm adds a time
estimation loop to improve estimation accuracy. Compared with another states
augmented estimation approach, this method has the advantages of lower
computation burden, avoidance of the discretization error in the low sample
rate. The estimation algorithm is implemented in an low-cost embedded
microprocessor where the update rate of algorithm can achieve more than 100 Hz,
and therefore high-performance computational units are not necessary. In
robotic experiment, the proposed algorithm serves as the navigation solution
for a small aerial robot. The accuracy and reliability of the self-designed
system are tested when the robot is moving with significant acceleration.
