Which Module receive the data first

Question

Hello,

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".

Answer 1

When dealing with clock rates, RF, Noise Etc. That is not a simple question to answer. Especially when you consider that the RF data is being sent at rates like 80kbps or 250kbps over the air. It is simply not possible to detect who receive a transmission first with respect to distance. At best, the only thing you can do is to see how much energy was used to get the data packet from A to B including all interference at the time of the transmission.

Comments

In fact I want to know if (in line of sight), the closest see it. I just need the one who is closest (or in the same place) to determinate the position of the point.

Thanks for your answer, it's really explicite and simple. It helps me a lot :)

Answer 2

Ok I got some new from other sources.

The first thing is to separate the protocol Zigbee and the 802.15.4 .
The Serie 2 Xbee are more useful for information transmission and auto routage of network. The Serie 1 is useful for point to point communication.

In my case, i wanted to get the distance between 2 Xbee and the fact that Zigbee use a lot of broadcast, it cause multiple noise and interference. So the RSSI is more stable with S1 than S2.

The RSSI is linear in line of sight ans so we can say which module is closer. When you pass a wall, the one in the room will get better RSSI. So we can easily estimate which module got the data "first" and say which one is closer :p

Thank's mvut for your answer.

Why S1 is better than S2 is here : http://sensor-networks.org/index.php?page=0823123150