Distributed Hybrid Spectrum Access for Cognitive Femtocells in 5G Mobile Networks
The femto access points (FAPs) with cognitive capabilities, also known as cognitive FAPs, are able to efficiently mitigate interference in two-tier heterogeneous networks. Hence, the concept of cognitive FAPs can be seen as one of the key enablers for future 5G networks, where high density of FAPs is foreseen. However, conventional overlay and underlay spectrum sharing strategies enabling the cognitive FAPs to access spectrum of macrocells have several drawbacks. The main disadvantage of the former one is that its efficiency fully depends on the activity of macrocell users and insufficient resources can remain for the users of the FAP. The main weakness of the latter one is that it can result in low transmission efficiency because transmission power level of the FAPs is restricted. In this paper, we propose a novel hybrid spectrum sharing that allows the FAPs to use both overlay and underlay strategies simultaneously and, thus, increase performance of FAPs' users. The proposed scheme is fully distributed since the FAPs allocate resources autonomously. The results show that the proposed algorithm is able to significantly outperform competitive schemes in terms of served traffic for femtocell users and, simultaneously, served traffic for macrocell users is intact.
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