Section: New Results
Cognitive radio and beyond
In cognitive radio networks, secondary (unlicensed) users (SUs) can access the spectrum opportunistically, whenever they sense an opening by the network's primary (licensed) users (PUs). In , we analyzed the minimization of overall power consumption over several orthogonal frequency bands under constraints on the minimum quality of service (QoS) and maximum peak and average interference to the network's PUs. To that end, we proposed a projected sub-gradient algorithm which quickly converges to an optimal configuration if the users' channels are fast fading.
Despite such benefits, the conventional cognitive radio network (CCRN) paradgim is not particularly attractive for opportunistic spectrum access because the network's PUs can recapture SU channels at will, thus interrupting the transmission of the latter. To address this crucial limitation, we proposed in  a semi-cognitive radio network (SCRN) paradigm where PUs are constrained to first use any free channels before being allowed to capture channels that are in use by SUs. These constraints slightly degrade the performance of the network's PUs, but a) they offer remarkable performance improvements to the network's SUs; and b) they can be compensated by imposing a monetary (or other) penalty to the network's secondary owners. In , we provided a game-theoretic analysis of the performance trade-offs involved for both the PUs and the SUs, and we derived both centralized and distributed learning algorithms that allow the system control process to converge to a stable state.