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I am working on an arduino-based robot that might be used in a classroom environment, in which case there could be forty of them in a single room. If I want them to be wireless, what problems might arise that I wouldn't find with just a few systems (e.g. interference)? On the single robot level we were thinking of playing around with nrf, bluetooth, and xbee off-the-shelf systems. What would be the pros and cons of these (and other?) systems in this sort of high density environment?

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    \$\begingroup\$ If the total payload data rate is not very high you could implement a time-sharing scheme with a master and slave system. The master allocates say 40 time slots, 1 for each individual pair of radios. If the actual data rate is 9600 and each controller sends maybe 4 bytes for control of its robot then a 5msec slot would do and every 200msec the controller gets another crack of the whip. \$\endgroup\$ – Andy aka Sep 26 '13 at 22:40
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There are a lot of variables involved. Questions to ask yourself would be:

  1. How many RF channels does the protocol allow?

  2. What is the network topology? Can you get away with multiple masters or peer-to-peer networks? Can a master scan RF channels if a master/slave implementation is needed?

  3. If you are using a off-the-shelf system how many nodes or addresses are allocated to the protocol?

  4. How much data does each protocol allowed to be sent in a packet PLUS the overhead data the protocol needs to send?

  5. How fast do you need to send data?

If you take all of these together you can play a numbers game to see which one would work for your classroom. Maybe a couple of masters with only 10 or 20 devices could get the data rate you need on separate channels?

A quick search on Google shows XBEE has 16 channels and can have a 16 or 64 bit address.

Problems that could arise if these weren't being considered:

  1. Flooded bandwidth
  2. Slower data rate
  3. Not enough addresses for all of the devices (anything over 5 bit addressing should cover it though)
  4. Interference from an outside source such as another network or something like a microwave
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