Wireless network without coordinator

Projects General Guidance
1

I have an application that we need to have wireless transmission from one Arduino to another. The "network" is in motion (literally) and we need two Arduino's to talk once they are in range. Imagine 30 units that come in and out of range of each other. A traditional XBee radio network needs a coordinator (from what I understand), but this network will be almost a random link. They almost all need to be coordinators and End points.

Thoughts of what direction I should go for radio's?

Due to application I am certain I will be needing a 900MHz device (really crappy terrain that soaks up radio signals)

2

" talk" is a bit vague.
Identify the radio payload in bytes.

3

Payload will be GPS location data, and status of 4 digital switches.

Each unit will transmit its location and the status defined by 4 digital switches. Data rate would be to broadcast every couple seconds (faster is better but not necessary). This same unit will listen for the same data coming form other units broadcasting the same data.

It is an early warning system being developed between multiple moving objects.

4

HAVE YOU HEARD OF DIGIMESH oops, shift key stuck. Get 900MHz pro modules with digimesh firmware from digi directly. Any module acts as a router. Don't try to get their routing gateway. Built to order, lead time 3 to 6 months. Crap!

5

Digi-Mesh seems to fit the bill. No Coordinator required..... And thats posted just as I type this. Funny.

To the interwebs! prices seem reasonable as well.

6

It is an early warning system being developed between multiple moving objects.

oh, the Borg eh ?

7

Nah, its a mother-inlaw detector!

Actually it is going to be an early warning system between race cars (rally). I have to jam a heaping amount of gear into a idiot proof interface (race car drivers are not too bright once we put our helmets on).

8

Digi-mesh firmware is really neat. They also have new radios the 900 MHz pro HP (high power) so don't buy series 2 modules from other places, which are phased out (you can still load earlier digi-mesh firmware to them). If you want to explore the modules, such as checking them out or manually doing some tests or firmware upload, a sparkfun xbee explorer is a must have. The arduino official wireless shield can't properly reset xbees for firmware upload. You will brick them and have to call digi for some help.

9

I assume you know that you will need DGPS for this, since GPS is not nearly accurate enough.

10

3m accuracy for GPS seems more than accurate. Why would you suggest DGPS? I am not docking or trying to park something. just determine distance between two units within an accuracy of 10m would surface. Although there are times when the two units will be approaching each other at 160ish KPH.

I am definitely interested in opinions. I am not trying to be rash it it comes over that way.

11

I assumed that you were trying to avoid collisions with the GPS. If 10 meters is good enough, great.