Weighted Rank Constrained Rank Minimization Interference Alignment for Three-Tier Downlink Heterogeneous Networks

摘要

Heterogeneous networks (HetNets) technology is one of the main emerging technologies that are expected to be applied in next generation cellular networks to achieve higher capacity. However, applying HetNets introduces a significant amount of interference among different tiers within the same cell. In this paper, we propose a weighted rank constrained rank minimization (WRCRM) based interference alignment (IA) approach in three-tier HetNets. The concept of RCRM is applied in a different way to deal with the nature of tiers with different interference vulnerability. In the proposed WRCRM approach, interference from different tiers is weighted with different weighting factors (WFs) to reflect their vulnerability to interference. Firstly, we derive an inner and a loose outer bound on the achievable degrees of freedom (DoFs) for the three-tier system that is modeled as a three-user mutually interfering broadcast channel (MIBC). Then, the derived bounds along with the well-known IA feasibility conditions are used to evaluate the effectiveness of the proposed WRCRM approach. Results show that there exists an optimal value of the WFs at which the proposed WRCRM approach outperforms the conventional RCRM approach in terms of the average sum rate and the average number of DoFs. Moreover, adjusting the required number of DoFs according to the derived bounds improves the performance of WRCRM approach.