I am new to Wireless Sensor Networks so please dont mind my ignorance.
I am assigned to research the feasibility of using XBEE 900 Pro HP for using on an embedded collar for cattle. The RSSI values of signals from the XBEE 900 will be used by 3 base stations for trilateration to determine the location of the animal.
XBEE is being used for localization instead of a GPS device for cost effectiveness.
My question:
Is trilateration based on XBEE 900 pro with 300mW transmit power an effective technique for 10m accuracy?
How is the estimation of distance from RSSI effected by distance? My required range is 16-18km?
What you are trying to accomplish is feasible, just not the way you approached the problem. What you want is radio direction finding, the details of this process are outside the scope of this forum but basically you would need each "cow" to have a separate frequency modulated(FM) transmitter frequency, a frequency that is easily discernible by your 3 receiver stations, and at each of these receiver stations you have an electronically switched antenna array. The cow's direction from the receiver can then be determined based on a tone produced by electronically switching between antennas to the input of your receiver, it would be the same thing as mechanically swinging a single antenna in a circle. Based on the received direction of the cow from each of your receiver stations, you could then triangulate the cow's position on a map. This would not be possible with a spread spectrum transmitter such as the zigbee, you would need something more low-tech that transmits FM every so often.
You can do it with spread spectrum, but then you'd be reliant on timing of signals rather than RSSI. The timing would be more accurate, but I doubt you've got the resolution you need cost effectively.....
Im also not sure if zigbee can do multicasting?
For the resolution you can do the maths yourself, based on time differenece of receipt. Its going to require some very accurate clocks.... and very accurate timing on the processing of signals too (you're way outside arduino world now)
There may be other ways to do it, but you'd need to provide some scope; Size of area the cattle can roam over... availability of power etc.
XBEE is being used for localization instead of a GPS device for cost effectiveness.
Strange statement when a Ublox Neo6 are $10 - $15. Couple this with an RF module to transmit the GPS serial and you know where the beef is located. All for under $20 (less battery, etc.)