I'm renewing my search for a point-to-multipoint radio system, preferably based on the nRF51822. Basically, I need to be able to connect up to 32 (or more!) nodes to a master hub. The nodes each pass requests to via the master hub out to the internet and a response is delivered back within a second or so. Requests/responses are typically no more than 128 bytes.
Additionally, I need the master hub to be able to send unsolicited (reverse!) requests to any given node (addressed by BT/MAC addr). The master hub should be able to handle up to 7-8 concurrent connections and for both the nodes and the master hub, the interface to the nRF51822 module would be via the UART.
I'm particularly attracted to Bluetooth's spread spectrum frequency hopping design and range of up to 100ft for it's robustness in radio noisy environments (eg. vs wifi).
I've asked this same question about BLE before on this site and the conclusion was that it was quite difficult. I've looked at Gazelle, but it doesn't seem clear on how to make it scale beyond 8 nodes (and I don't think it can handle the unsolicited requests initiated by the master hub back to a node).
I have seen several posts on this forum regarding custom protocols, so my question is, is this really the way to go? Or am I really re-inventing the wheel here. The application level protocol already handles encryption as well as retries/timeouts. I'm prepared to roll up my sleeves and dig into designing a protocol if necessary.
Finally, are there any examples/samples of implementing a custom radio protocol on the nRF51822?
