A Boundary Condition-Based Algorithm for Locating Construction Site Objects Using RFID and GPS

Construction site is rugged, dynamic, and complex, involving a large number of objects that continuously change their locations and occupied spaces. Being able to accurately locate site objects and track site dynamics is critical to project control. Automated locating technologies such as Radio Frequency Identification (RFID) have proven to be beneficial in tracking some construction site objects. The biggest challenge in applying the RFID technology is that the received signal strength (RSS) varies over time and location, and there is no direct relationship between signal strength and detection range, leading to low positional accuracies in the estimated tag locations. This paper presents an algorithm termed BConTri that combines a "boundary condition method" and the trilateration concept to estimate tag location in three-dimensional (3D) real world coordinates from four or more RFID readers equipped with GPS. A comprehensive assessment of the positional accuracy was applied to field experiment results and a high accuracy of the algorithm was observed. A measure of the spatial dilution of reader distribution was proposed, which has a linear relationship with the resulting accuracy of the estimated tag location. This could help in estimating the accuracy and quality control of RFID-based locating and tracking systems in construction.