XBee choice and configuration

The wireless transmission is done using the XBee wireless chip.
XBee variants

transmission frequency: The XBee chip is available in various flavours, either for the 900 MHz or 2.4 GHz range. We have only worked succesfully with the 2.4 GHz version. The 900 MHz ones have a different type of firmware with different settings.
range: XBee and XBee [...]