Evaluating the Impact of User Behavior on D2D Communications in Millimeter-Wave Small Cells

Abstract

Small cells in millimeter-wave (mmWave) band are able to provide multigigabit access data rates and have emerged as a cost-efficient solution to offer interference-free device-to-device (D2D) communications. In order to improve system performances and enhance user experiences, direct transmissions between devices need to be scheduled properly. We first propose a transmission scheduling scheme for radio access of small cells in the mmWave band, termed directional D2D medium access control (D3MAC), whereby a path-selection criterion is designed to enable D2D transmissions. Through extensive simulations, we demonstrate that D3MAC achieves near-optimal performances and outperforms other schemes significantly in terms of delay and throughput. Based on this near-optimal scheme, we then evaluate the impact of user behaviors, including the traffic mode and traffic load, as well as user density, denseness, and mobility, on the performance of D2D communications in mmWave small cells. Our study reveals that the performance of D2D communications is improved, as the user density and denseness increase, but this effect is only obvious under heavy traffic loads. Furthermore, user mobility is shown to be another important factor that influences the performance of D2D communications. The system performance is first improved, as the average user speed increases from static, but the performance is degraded significantly when the user speed becomes high.