On Optimum Causal Cognitive Spectrum Reutilization Strategy
In this paper, the authors study opportunistic transmission strategies for Cognitive Radios (CR) in which causal noisy observation from a Primary User(s) (PU) state is available. PU is assumed to be operating in a slotted manner, according to a two-state Markov model. The objective is to maximize Utilization Ratio (UR), i.e., relative number of the PU-idle slots that are used by CR, subject to Interference Ratio (IR), i.e., relative number of the PU-active slots that are used by CR, below a certain level. They introduce an a-posteriori LLR-based cognitive transmission strategy and show that this strategy is optimum in the sense of maximizing UR given a certain maximum allowed IR.