Which Module receive the data first

Question

My question is simple, is it the closest Xbee that will receive data (from a broadcast) first ?

I'm working on a simple way to estimate the position of a module but I need to know which one is the closest from my module which Broadcast. So the first to read the data will send a message to the broadcaster to say him "Hi, i'm first?" and wait for the reply "yes, you are the Xth to ask me that".

Thanks

Answer 1

That won't be reliable for at least two reasons:

• Broadcast messages are sent three times to ensure receipt by all nodes on the network. You don't know which retransmission a node actually receives.
• Host processing likely introduces variable latency on each node -- how often is the host polling for bytes on the XBee module? That latency is likely high compared to the speed at which the RF signal travels through the air.

Most distance estimation on 802.15.4 networks makes use of the received signal strength indicator (RSSI). In an open-air environment with identical antennas, a lower RSSI should indicate a greater distance between nodes. For example, Freescale has published a paper on Position Location Monitoring Using IEEE® 802.15.4/ZigBee® technology.