Design criteria on a mmWave-based small cell with directional antennas

Due to spectrum shortage in the conventional microwave bands, millimeter wave (mmWave) bands have been attracting great attention as an additional spectrum band for 5G cellular networks. In this paper, we show the feasibility of using a mmWave-based small cell with directional antennas. We investigate the effect of the number of antennas, n_ant, on the capacity and coverage probability, and propose an antenna clustering scheme (ACS) to utilize the antennas more efficiently. For a given n_ant, we also investigate the effect of the number of clusters, n_cluster, on the capacity and coverage probability. In addition, we propose two design criteria: a capacity-maximization criterion (CapMC) and a coverage-maximization criterion (CovMC), in the mmWave-based small cell. Each design criterion is formulated as a joint optimization problem to find the optimal values of n_ant and n_cluster to maximize each objective function while satisfying system requirements such as capacity and coverage probability. Performance evaluation shows that CapMC can achieve the highest capacity while satisfying a given coverage probability requirement and CovMC can achieve the highest coverage probability while satisfying a given capacity requirement.