Xbee or other wireless communication methods

I'm trying to have a small robot car sending data about its position relative to a reference point in real-time. While I know Xbee can be used for wireless data transfer between two transceivers, I'm not sure about the following:

a) how well XBee chips handle distances that are close to the limit (100 m for Xbee, 1 mile = 1.60 km for Xbee Pro), as the power usually drops off as a 1/r^2 relationship?
b) whether the signal strength received is proportional to the distance
c) how the propagated waves carrying the signals generated by the transceivers are propagating through/around a wall corner that the car would encounter during the course?

Are there other wireless communication similar to Xbee that would allow me to determine real-time position of an object? Thanks in advance.

I am also thinking of putting a Xbee repeater somewhere in the path to ensure the signal is strong enough to be received properly. I would welcome any suggestions. Thanks.

Are there other wireless communication similar to Xbee that would allow me to determine real-time position of an object? Thanks in advance.

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You cannot determine position based on a single signal strength. Best bet is to have xbee transmit GPS info.

b) whether the signal strength received is proportional to the distance

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One would think so but, No

Aren't GPS chips usually very expensive? or do you have any recommendations for affordable chips that I can use?

A quick google pulled this up.
Low cost DIY XBee/GPS plane locator - RC Groups

Does that help?

Yes. The ones that I have found weren't low-cost enough. Thanks for the tip again.

Mikebits said:

One would think so but, No

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In my opinion the answer should be yes , however many factors influence this .
What frequency, what influences are in the locality. How good is the measuring equipment

Thanks. Regarding GPS chips, how well does it work if I am running the GPS-equipped car indoors?

Zigbee's main offering is the application profile. Unless you want your rotobotic car to talk to your ceiling fan it is overkill. Look into MiWi.