  The development of vehicle-to-vehicle (V2V) communication facil-itates the
study of cooperative positioning (CP) techniques for vehicular applications.
The CP methods can improve the posi-tioning availability and accuracy by
inter-vehicle ranging and data exchange between vehicles. However, the
inter-vehicle rang-ing can be easily interrupted due to many factors such as
obsta-cles in-between two cars. Without inter-vehicle ranging, the other
cooperative data such as vehicle positions will be wasted, leading to
performance degradation of range-based CP methods. To fully utilize the
cooperative data and mitigate the impact of inter-vehicle ranging loss, a novel
cooperative positioning method aided by plane constraints is proposed in this
paper. The positioning results received from cooperative vehicles are used to
construct the road plane for each vehicle. The plane parameters are then
introduced into CP scheme to impose constraints on positioning solutions. The
state-of-art factor graph optimization (FGO) algo-rithm is employed to
integrate the plane constraints with raw data of Global Navigation Satellite
Systems (GNSS) as well as inter-vehicle ranging measurements. The proposed CP
method has the ability to resist the interruptions of inter-vehicle ranging
since the plane constraints are computed by just using position-related data. A
vehicle can still benefit from the position data of cooperative vehicles even
if the inter-vehicle ranging is unavaila-ble. The experimental results indicate
the superiority of the pro-posed CP method in positioning performance over the
existing methods, especially when the inter-ranging interruptions occur.
