Software Defined Radio (SDR) Configured as a cognitive radio using GNU Radio companion as the software development toolkit. Just need to know the correct code blocks to use

I need to design a cognative radio using the GNU radio companion toolkit. The hardware i have is 2 each of the following: Raspberry Pi 3, RTL-SDR dongle, eRA connect2-pi transceiver. In the scenario, rather than avoiding Primary users, the radio is trying to avoid large amounts of noise/interference as the current infrastructure is rendered useless following a natural disaster. The have the blocks to get the RTL-SDR to scan the spectrum and display the results. We now need to get the radio to find the gap in the spectrum/available channel and dynamically select that channel to transmit on. The receiver must be able to pick out the tx signal over the noise to rx the signal. The sent data can be very small (large enough to reduce the error rate) so maybe 3 bits? 1 way traffic only is required. Research suggests OFDM with QPSK and cyclostationary feature detect as the way forward. I have no coding or GNU experience so hoping someone out there can provide the flow graph? The flow-chart will need custom source/sink blocks for the eRA Connect2Pi transceiver as I don't beleive they exist yet. We are proving our concept in the 433MHz unlicensed band but the system should have the capability to expand further into the spectrum with a change of hardware. We only have until 27 Mar 17. Many thanks.