Joint Optimization of EE and SE Considering Interference Threshold in Ultra-Dense Networks

Due to the explosive growth of mobile data traffic, the Ultra-Dense Networks (UDN) becomes one of the hot research technologies in the 5 ^th Generation mobile communication system (5G). With the multi-layer network structure, UDN brings spectrum multiplexing gain and system capacity improvement by densely deployed small cells in hot spot area. In this paper, in order to improve system Energy Efficiency (EE) and Spectrum Efficiency (SE), we propose a joint optimization algorithm considering both EE and SE for small cells in UDN with the constraints of interference threshold and transmission data rate requirement. We first formulate a compromised objective function considering both EE and SE, and then the optimization problem is transformed from the fractional form to subtractive form to simplify the solution procedure, and finally the results of resource allocation and power allocation are obtained by the iteration of Lagrangian dual decomposition method. Simulation results show that both EE and SE performance of the proposed algorithm is much better than the algorithms used in conventional communication systems, and compared with the algorithm to maximize SE in UDN, the EE can be significantly improved with very slightly reduced SE performance.