Enhancement of Hybrid Cognitive Approach for Femtocells

The use of femtocells with cognitive capabilities is considered as a promising way for interference mitigation. The femto access point (FAP) accesses the spectrum either in overlay or underlay fashion. In the former case, the FAPs utilize only radio resources currently not occupied by the macrocell. In the latter case, the whole bandwidth may be used but power of the FAPs is restricted. Both spectrum sharing approaches can be coupled to make the protection of primary users (PUs) more efficient. The merging of both ways results in a combined spectrum sharing (CSS). Additional combination of underlay approach and the CSS is known as a hybrid cognitive approach (HCA). In the HCA, the FAPs access the spectrum of the primary cellular operator through the underlay approach while the bandwidth of secondary cellular operators can be accessed by means of the CSS. In this paper, we propose an enhanced hybrid cognitive approach (EHCA), which main objective is to decrease sensing overhead and increase performance of the femtocell users while macrocell users are only minimally negatively affected. The enhancement consists in extension of power control mechanism for femtocells. The simulation results indicate that the sensing overhead can be decreased by the EHCA up to 48% and femtocell users throughput increased by up to 13.5% while the performance of the macrocell users is degraded only negligibly (less than 1.3%) when compared to former HCA scheme.