High-gain narrow-beam antennas or beamformed antenna arrays will likely be used in millimeter-wave (mmWave) bands and 5G to mitigate the high path loss. Since many multipath components may be excluded by the narrow beam, the mmWave radio channel (consisting of the transmit antenna, the propagation channels, and the receive antenna) strongly depends on the beamwidth, orientation, and shape of the narrow beam. In this article, a procedure is proposed to measure and model the channels vs. synthetic beamwidth. Based on experimental data collected at 60 GHz in an indoor hallway/lobby scenario, the results show that the number of multipath components and the delay dispersion of the channel are significantly reduced by the narrow beams. In addition, the path loss can be decreased by more than 20 dB with an optimized beam-center orientation. The impact of the study on future 5G mmWave system design is discussed, including frequency reuse, antenna design, receiver design, equalization, and link budget.

The deployment of a large number of small cells poses new challenges to energy efficiency, which has often been ignored in fifth generation (5G) cellular networks. While massive multiple-input multiple outputs (MIMO) will reduce the transmission power at the expense of higher computational cost, the question remains as to which computation or transmission power is more important in the energy efficiency of 5G small cell networks. Thus, the main objective in this paper is to investigate the computation power based on the Landauer principle. Simulation results reveal that more than 50% of the energy is consumed by the computation power at 5G small cell base stations (BSs). Moreover, the computation power of 5G small cell BS can approach 800 watt when the massive MIMO (e.g., 128 antennas) is deployed to transmit high volume traffic. This clearly indicates that computation power optimization can play a major role in the energy efficiency of small cell networks.