Device-to-device (D2D) Meets LTE-Unlicensed

In this article, we look into how the LTE network can efficiently evolve to cater for new data services by utilizing direct communications between mobile devices and extending the direct transmissions to the unlicensed bands, i.e., device-to-device (D2D) communications in conjunction with LTE-Unlicensed. In doing so, it provides an opportunity to solve the main challenge of mutual interference between in D2D and conventional cellular (CC) transmissions. In this context, we review three interconnected major technical areas of multi-hop D2D: transmission band selection, routing path selection, and resource management. Traditionally, D2D transmissions are limited to specific regions of a cell’s coverage area in order to limit the interference to CC primary links. We show that by allowing D2D to operate in the unlicensed bands with protective fairness measures for Wi-Fi transmissions, D2D is able to operate across the whole coverage area and in doing so, efficiently scale the overall network capacity whilst minimizing cross-tier and cross-technology interference.