Spectrogram


spectrograms show the performance of the Aerospace cognitive radio testbed under different scenarios.

These spectrograms show the performance of the Aerospace cognitive radio testbed under different scenarios. In the first scenario, the primary licensed user of the spectrum begins transmitting, and one of the two cognitive radios must immediately vacate that region. There is no longer enough free spectrum to maintain the full bandwidth, so the radio adaptively drops its bandwidth and shifts into the remaining unused space (without adaptive bandwidth control, the radio would have to stop transmitting altogether). When the primary user stops transmitting, the radio is once again able to use the unclaimed spectrum. In the second scenario, the primary user starts transmitting, and the first radio must reduce its bandwidth. The user changes to a different frequency, forcing the second radio to reduce its bandwidth, but enabling the first radio to return to its full bandwidth. The third scenario is the most complex. After a few seconds, the primary user starts transmitting, but switches unpredictably from frequency to frequency. Nonetheless, both cognitive radios are able to react in time, changing their center frequency and bandwidth to maximize their own throughput without causing interference for the primary user or for each other.  More »