position locator using zigbee

Question

I am working on a project to count the number of cars in a specified region. I would like to use a Zibee/Xbee module. As far as I've learned, Xbee modules are used as stationary nodes and Zigbee modules are arranged in the car. There is a gateway node that receives the data in terms of RSSI values of the signal received through the stationary node.

1)How to use that data to find the position of the car?

2)A Xbee unit can take how many readings at same time?

3)What is the range of this position locator

For the first question I studied a lot on the web and there is no certain information about how to do it. All I know is a mobile node requires three stationary nodes to locate it and it is measured through RSSI value of signal received. If I am wrong somewhere please correct me.

Answer 1

1. Triangulate. you have 3 known points, 1 unknown but with 3 RSSI readings. Assuming all parameters are the same, RSSI is proportional to the distance via Friis transmission equation. Caution though: things rarely stay the same outside the simulation.

2. What readings? what unit of time?

3. That depends on your link budget and local conditions.

Answer 2

1) It is not going to work out if you want to use zigbee to triangulate a car's exact position ,like in which parking slot. The rssi is heavily affected by the environment, antenna direction, wall, construction materials, and other existing signals like wifi, bluetooth...