Research on Area Spectrum Efficiency and Energy Efficiency in 3-tier Ultra-Dense Heterogeneous Cellular Networks

Cellular network is usually modeled and analyzed based on two-dimensional space. However, the two-dimensional space model is only appropriate for the scene where base stations are distributed sparsely and has single access node. We aim at dense district with a great of low-power base stations, basing on the theory of stochastic geometry, propose a downlink 3-tier ultra-dense heterogeneous network model in three-dimensional (3D) space. The influence of density of base station on network performance is emphatically analyzed. Firstly, on the basis of this model, the probability density function of the distance between the target user and the base station in 3D space is given. Afterwards, the coverage probability of each layer and the average accessible rate of user in different layers are derived, area spectrum efficiency (ASE) and energy efficiency (EE) are derived at the same time, and the impact of each tier base station density on ASE and EE is analysed. Subsequently, we propose a simple optimization problem. That is when the ASE meets certain constraints, the EE can be maximized by optimizing the density of base station, then they are balanced. It is shown that the density of each tier base station and the density ratio between tiers have huge impact on system performance, and there are thresholds to make the deployment optimal. On the condition of dense environment, the analysis of 3D space heterogeneous network is more precise and practical. We provide more perfect theoretical support for base station deployment and green communication in the next generation mobile communication network.