I need some help with selecting a wireless board for my project. The requirements are:
A. Able to detect collisions on transmit. B. Able to work in point-to-point fashion (802.11 centralized fashion might be an advantage, but probably will be an overkill). C. Error detection is an advantage.
A little bit of a background on the project: those units will be used to connect sensors, all across the place. Therefore, they will be used to transmit a relatively small amounts of data, in a congested spectrum - at the very least, 2 units just might start transmitting simultaneously. Hence, I'm interested in a solution, that is able to detect collisions - just like the Ethernet protocol do. I'm fully aware that some sort of higher level protocol might solve it with some sort with ACK/NACK exchange solution, but since collisions are expected (there will be many sensor, communicating with the central unit, in the same place), I find it more reliable to use collision detection - that way, the sender knows it didn't get through.
Some sort of 802.11 (WiFi) might be an advantage but for transmitting a couple of bytes of sensor status, it just seems to be an overkill. Additionally, sensors should continue to be operational, even in case of electrical grid shutdown - and while I can provide those units with a power supply able to switch from from main grid power to batteries, THE ROUTER in center of that WiFI network, will probably not have that ability and will go down, shutting down the entire network. Additionally, 802.11 forcing me to implement complicated higher level protocols (TCP/IP) and generally, takes the price high, very high.
I've been thinking about connecting those cheap 214Mhz units, to 2 different arduinos - providing them with logic that commands both of them to work simultaneously (the Rx one will be actual collision detector, in case it didn't got the correct message, probably another unit was transmitting at the same time) and the issue is, it do not cheap either and quite complicated (inter arduino communication).
So my question is, is there any boards out there, that can reliably transmit the message by themselves? Without me taking care of collision detection, error detection and such? Any suggestion will be welcome.