Jointly optimal spectrum deployment and cognitive access for ase maximization of macro-femto HetNets

To achieve higher spectral efficiency in future wireless networks, small cells have been conceived to be deployed over conventional macrocell networks, generating heterogeneous networks (HetNets). However, interference between different tiers of HetNets is the main bottleneck for high spectral efficiency. Spectrum access, including spectrum deployment and channel access, is one of the most powerful methods to manage the interference. Unfortunately, the optimal spectrum access scheme for macro-femto HetNets remains unknown. By allowing femtocells to dynamically access the available macro-tier spectrum in addition to their dedicated femto-tier spectrum through cognitive spectrum sensing, we propose a novel spectrum access scheme, which takes the existing schemes as special cases. By jointly optimizing three important system parameters, we maximize the area spectral efficiency (ASE) and determine the optimal spectrum access scheme for macro-femto HetNets. Analytical results imply that the optimal spectrum access scheme is determined by the optimum number of active links per unit area, which governs the interference level in each unit area. Simulation results validate the obtained analytical results and show that the proposed scheme outperforms existing schemes in terms of ASE.