Polarization-Based Multi-Dimensional Resource Optimization for Spectrum Sharing in Dense Heterogeneous Networks

Dense heterogeneous networks (HetNets) have recently emerged as a promising paradigm to fulfill the ever increasing demand for huge capacity of wireless communication systems. Nevertheless, critical issue of interferences arises including co-tier and cross-tier interferences. As an enabling solution to address interference issue, spectrum sharing in cognitive radio is envisioned to enhance spectrum efficiency of dense HetNets. Traditionally, spectrum sharing typically works in time, frequency, space and power domains. In this paper, polarization, an under-utilized resource domain in wireless communications, is exploited to increase the degrees of freedom for spectrum sharing. Through joint optimization of multi-dimensional resources including polarization, power and frequency resources, we propose a polarization-based multi-dimensional resource allocation (PMRA) scheme, which maximizes the downlink capacity of densely-deployed small cells and avoid harmful cross-tier interference to an existing macrocell. Towards this end, an iterative approach is employed in which transmitting polarization states, power and subcarriers are optimized and allocated iteratively. Simulation results demonstrate the performance advantage of PMRA scheme compared with traditional spectrum sharing schemes in dense HetNets as well as existing polarization-based spectrum sharing schemes, which verifies the promising potential of exploiting polarization in dense HetNets.