In the upcoming generation of mobile networks, femtocells will play a major role because they provide cost-efficient improvement in data rates and coverage. High penetration is expected in the upcoming ultradense 5G networks, increasing the probability of femtocells' clusters. This, in turn, will require interference mitigation techniques to protect nearby non-subscribed users, especially in weak macrocell signal areas. In this paper, we present a mechanism where multiple femtocells coordinate their transmission to serve multiple non-subscribed users through hybrid access. First, we introduce an algorithm that determines the spectrum allocation of femtocells' hybrid access. The algorithm aims to compensate for the performance reduction of subscribed users, due to reduced spectrum. For the second step of the mechanism, we introduce a power control algorithm that balances the impact of hybrid access among all the members of the femtocell cluster. First, we investigate the case where only one femtocell operates in hybrid access, and then we refine the power control algorithm by allowing multiple femtocells in the same cluster to operate in hybrid mode and by taking into account the effect that any change in power transmission will have on neighbouring femtocells. Simulations for the evaluation of the hybrid access algorithm compared with closed and other hybrid access schemes show improvement in the throughput of the non-subscribed users connected to femtocell and the most impacted subscribed users at weak macrocell signal areas and in the fairness of the hybrid access application scheme.

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Abstract-The use of femtocells has been an attractive solution since it achieves better coverage and capacity and low cost for deployment and maintenance. However, their performance can be compromised by the cross-tier interference with existing macrocell infrastructure or between adjacent femtocells, especially in the case of co-channel deployment. One way to address this, is adjusting the transmit power of every femto base station with respect for overall performance. To this direction, we have implemented a framework that simulates femtocell overlays over LTE-Advanced (LTE-A) macrocellular systems. The framework allows power management over user-defined femtocell deployment, deciding their power levels according to three different power schemes. The resulting throughput is presented for every point of the macrocell in a user-friendly GUI. In this paper, we present the design of this framework and discuss the results.