Comparison of Underlay and Overlay Spectrum Sharing Strategies in MISO Cognitive Channels
The authors consider an extension of the cognitive radio channel model in which the secondary transmitter has to obtain ("Learn") the primary message in a first phase rather than having non-causal knowledge of it. They propose an achievable rate region that combines elements of decode-and-forward relaying with coding for the pure cognitive radio channel model. Moreover, they find the choice of parameters that maximize the secondary rate under a primary rate constraint. Finally, they compare numerically the performance of their system to that of an underlay scheme that combines beamforming, rate splitting, and successive decoding.