My research area is WSN in agriculture "Data issues and aggregation analysis in WSNs ", So for this what is the best simulator and where i can download it?
In my opinion, Omnet++ (open source) with Castalia module is best for this kind of applications, since you can control almost everything, from network topology, MAC and routing protocols, channel model and even node movement. Furthermore, it is written in C, so the learning curve is very fast, and it is not node-platform specific.
Ns2, ns3, Omnet++ and optnet are well-knew and excelent simulador. But thay are to simulations of protocols and interactions among nodes. There are in Agricuture weather variables and plants behavior those extremily dificult to sensoring. Maybe If you create the data from a Agricutural Simulator like http://www.sciencedirect.com/science/article/pii/0308521X9400055V and put these in node enter you have a better simulation. Thais paper perheps help you: http://ifsa2012.dk/?page_id=357.