Xbee sequential sensor network: finding nearest neighbor

Hi all

For a project I need to build a sequential wireless sensor network. With sequential I mean that all sensor nodes are placed one after another on a straight line, with around 50m (164ft) of clear LOS between nodes. Each node will contain a PIR sensor. When it detects something, it has to send a signal to its two nearest neighbors (the one on the left and the one on the right).

Each node will have an Arduino for sensor interfacing and logging the amount and time of sensor trips. Every few hours a central node will poll all nodes for the number of sensor trips.

The sensor network also needs to be expandable quite flexible: new sensor nodes must be able to be added at the end of the existing sequential network without having to reconfigure the existing network or the Arduino in each node.

I would appreciate any tips or suggestions on how to implement this. Right now, I'm looking into the Xbee Series 2 modules. In mesh networking mode, they should be able to build and maintain the wireless network and support addition of new nodes with zero configuration (granted the Xbee radio is properly configurated). It should also allow easy polling of each node: when every Xbee module is configured as router they can relay the polling messages from the coordinator through the network.

To find the nearest neighbors, I would make Arduino keep a log of each radio address that sends packets to the node and the RSSI of each of these radios. The two radios with the strongest RSSI should be the two nearest nodes.

Of course this is theoretical speculation because I have yet to implement it. Would the above be possible and/or practical? Or are there better ways of implementing this project?

I also read that Xbee series 2 don't have the possibility of communicating the RSSI of each packet when in API mode. Is this correct?