Fig. 3

Error modeling of cell-id and mean cell-id techniques. This figure illustrates a hypothetical instant when the maper is observed. Lengths are typed with normal font and vectors with bold. The region under the coverage of the nth RFID tag’s signal, \(1\le n\le N\), is shaded and comprises a circle centered on its true position \(\mathbf {P_{n}}\) and radius r. The greatest distance from the corridor’s borders to the line passing through the estimated positions of the tags \(\mathbf {X_{n-1}X_{n}}\) is denoted by L and the smallest distance by \(l_{0}\). The white circle centered in the estimated position \(\mathbf {X_{n}}\) of the nth tag, \(1\le n\le N\), shows the uncertainty of the tag’s position and has a radius \(\varepsilon\) for all tags. Depending on the technique employed, the maper at the very situation illustrated might be \(X_{1}\), \(X_{2}\) or \(X_{3}\).