An anti-collision algorithm for localization of multiple chirp-spread-spectrum nodes

This paper develops an anti-collision algorithm for localization of multiple chirp-spread-spectrum (CSS) tag nodes. The CSS is a physical layer defined in IEEE 802.15.4a, and can be used for ranging between two CSS nodes. This ranging operation involves measuring the time-of-flight of the chirp-modulated signal. If anchor CSS nodes are installed at the known positions, a tag CSS node can calculate its coordinate based on the distances between these nodes. When there are multiple tag nodes, however, the tag nodes can fail to calculate their locations because their ranging signals collide with each other. Although the CSMA/CA is adopted for the medium access control protocol of IEEE 802.15.4a, it is not suitable for localization because a tag node must measure at least three successive distances for two-dimensional localization. The proposed algorithm uses a back-off time to prevent collisions, and all tag nodes compete to acquire the authority to use a channel. The proposed algorithm uses two special packets to synchronize the tag nodes for localization. For a theoretical evaluation of the proposed algorithm, the probability of the channel occupation of each tag node is analyzed. Through experiments, the performance of the anti-collision algorithm is verified.