This letter focuses on the spectrum efficiency (SE) and energy efficiency (EE) of K-tier heterogeneous networks (HetNets), in which massive multiple-input multiple-output (MIMO) is employed in the macro cells. We consider the impact of massive MIMO on flexible cell association. We develop an analytical approach to examine SE and EE of HetNets. We confirm that using flexible cell association can improve the EE of HetNets by offloading data traffic to small cell. This is due to an increase of EE in the macro cell. Moreover, we show that serving moderate number of users in the macro cells with massive MIMO can boost both SE and EE.
One of key 5G scenarios is that device-to-device (D2D) and massive multiple-input multiple-output (MIMO) will be co-existed. However, interference in the uplink D2D underlaid massive MIMO cellular networks needs to be coordinated, due to the vast cellular and D2D transmissions. To this end, this paper introduces a spatially dynamic power control solution for mitigating the cellular-to-D2D and D2D-to-cellular interference. In particular, the proposed D2D power control policy is rather flexible including the special cases of no D2D links or using maximum transmit power. Under the considered power control, an analytical approach is developed to evaluate the spectral efficiency (SE) and energy efficiency (EE) in such networks. Thus, the exact expressions of SE for a cellular user or D2D transmitter are derived, which quantify the impacts of key system parameters such as massive MIMO antennas and D2D density. Moreover, the D2D scale properties are obtained, which provide the sufficient conditions for achieving the anticipated SE. Numerical results corroborate our analysis and show that the proposed power control solution can efficiently mitigate interference between the cellular and D2D tier. The results demonstrate that there exists the optimal D2D density for maximizing the area SE of D2D tier. In addition, the achievable EE of a cellular user can be comparable to that of a D2D user.Index Terms-Massive MIMO, D2D, uplink power control, spectral efficiency, energy efficiency.
Base station (BS) sleeping has been proved to be an effective technique for saving energy consumption in cellular networks. However, BSs in sleeping mode might cause coverage holes, which have a negative impact on the connectivity of the network. In order to overcome this problem, we propose a combined coordinated multi-point (CoMP) transmission and BS sleeping scheme under the heterogeneous networks (HetNets) scenario. The proposed scheme aims at improving energy efficiency as well as increasing coverage probability. In this paper, stochastic geometry analysis is adopted for evaluating the performance of the proposed scheme, instead of the conventional hexagonal grid based approach. Impact of CoMP on energy efficiency in HetNets with a random on/off strategy applied at macro base stations (MBSs) is examined thoroughly. We derived two performance indicators which are coverage probability and energy efficiency in a two-tier HetNets scenario. Numerical results confirm that the combined CoMP and BS sleeping can improve the energy efficiency as well as increase the coverage probability compared with implementing BS sleeping only. The impact of the density ratio of MBSs to Pico BSs (PBSs) on energy efficiency and coverage probability is also quantified.
In this letter, we exploit the implementation of uplink power control and cell range extension for interference coordination in a two-tier massive MIMO enabled heterogeneous cellular network. Our results show that the uplink performance in the massive MIMO macrocells can be significantly improved through uplink power control in the small cells, while more uplink transmissions in the macrocells have mild adverse effect on the uplink performance of the small cells. In addition, the uplink performance of the massive MIMO macrocells can be improved by expanding the small cell range when dozens of users are served in the macrocells.
Index TermsMassive MIMO, heterogeneous cellular networks, uplink interference management.A. He, Y. Chen, and M. Elkashlan are with the
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