On the Capacity of the Cognitive Tracking Channel

We explore the capacity of opportunistic secondary (cognitive) communication over a spectral pool of two independent channels. Due to the distributed nature of the primary user´s spectral activity, the cognitive receiver does not have full knowledge of the channel used at the transmitter for secondary communication. Tracking the transmitter state at the receiver is therefore a primary issue in such channels. The problem is further complicated as the channel availability changes with time. The tracking uncertainty also makes decoding at the receiver non-trivial. Using genie based outer bounds and training based lower bounds, we estimate the capacity of the secondary link. The capacity analysis shows that the benefits of spectral pooling are lost in dynamic spectral environments