Creating Zigbee Ad-hoc Network in a dynamic environment

Question

We are working on a project to create a V2V ad-hoc network between vehicles. Basically we are deploying Raspberry Pis in vehicles and we are using Xbee modules and Zigbee protocol in order to exchange data between vehicles if they are near from each other.

Our ad-hoc network is completely dynamic and decentralized (We cannot have any static nodes in the network). Our problem is that the topology of the mesh network created by the Zigbee protocol requires a coordinator to be always in the network and the network will fail in case this coordinator failed down.

It seems that using Zigbee protocol requires knowing the topology of the network beforehand.

We do not know whether it is feasible to create our dynamic network using the Zigbee protocol without knowing the topology of the network beforehand and without the requirement of the coordinator. Can we have more than 1 coordinator in the network to overcome this problem? Thanks in advance.

Answer 1

Is there a particular reason you are looking to use Zigbee? if you are after a truely decentralised network you would be better off using either a different protocol (one that has no need for a coordinator) or by defining your own using basic RF modems (which is a lot more complicated)

however XBee modules are configurable by AT commands, with a bit of work you could probably set them up to periodically change mode (when it is running as coordinator) to check for other coordinators and if it finds one then stay as a standard node, and if the coordinator drops out (stops replying) then steps up to be coordinator.

this approach would require you to solve a few issues though:

1. how do the remaining modules in the network decide which becomes coordinator
2. how often would the coordinator scan for other coordinators in order to effect a reasonable response time, yet not disrupt data flow

i would suggest that you provide a bit more information relevant to the question such as:

1. how much data is being transferred?
2. how often is this data being transferred?
3. how are you planning to define where the data gets sent (addresses? or multicast to everywhere?)

hopefully this helps you in the right direction, but in the mean time i'd suggest you look at the XBee datasheets for the AT commands and what is possible (has been a while since i used them)

James