  In this paper, we propose a molecular communication system to localize an
abnormality in a diffusion based medium. We consider a general setup to perform
joint sensing, communication and localization. This setup consists of three
types of devices, each for a different task: mobile sensors for navigation and
molecule releasing (for communication), fusion centers (FC)s for sampling,
amplifying and forwarding the signal, and a gateway for making decision or
exchanging the information with an external device. The sensors move randomly
in the environment to reach the abnormality. We consider both collaborative and
non-collaborative sensors that simultaneously release their molecules to the
FCs when the number of activated sensors or the moving time reach a certain
threshold, respectively. The FCs amplify the received signal and forward it to
the gateway for decision making using either an ideal or a noisy communication
channel. A practical application of the proposed model is drug delivery in a
tissue of human body, in order to guide the nanomachine bound drug to the exact
location. The decision rules and probabilities of error are obtained for two
considered sensors types in both ideal and noisy communication channels.
