We assume that base stations are immobile and mounted in a safe place (with respect to harmful environmental influences) due to their potential long range (see Section 4.5.2). On the other hand, dust nodes are subject to mobility and other kinds of environmental influences (e.g., LOS obstructions), which can cause faulty location estimates.
However, in Sections 4.5.4 and 4.5.5 we mentioned extensions to the basic system in order to detect and reject such faulty locations estimates with high probability. This leaves us in a situation, where dust nodes either obtain good position estimates or no at all.