Along with several colleagues at GTRI, I have spent the last year working on GNU Radio-based waveforms for the DARPA Spectrum Challenge competition. The final tournament was last week and we finished in a respectable 2nd place in the competitive competition. You can find the full results at MarmotE's website.
We developed two waveforms, one based on differential OFDM for the cooperative tournament, and another based on direct sequence spread spectrum for the competitive tournament. Both waveforms dynamically adjust to their environment based on sensed information. The video below shows our cooperative entry (the red team) and how it dynamically adapts to the blue team's static spectrum allocation. You can see that the sensing robustly minimizes wasted white space to maximize the joint spectral efficiency.