Combating the Distance Problem in the Millimeter Wave and Terahertz Frequency Bands

In the millimeter-wave (30-300 GHz) and terahertz (0.1-10 THz) frequency bands, the high spreading loss and molecular absorption often limit the signal transmission distance and coverage range. In this article, four directions to tackle the crucial problem of distance limitation are investigated, namely, a distance-aware physical layer design, ultra-massive MIMO communication, reflectarrays, and intelligent surfaces. Additionally, the potential joint design of these solutions is proposed to combine the benefits and further extend the communication distance. Qualitative and quantitative evaluations are provided to illustrate the benefits of the proposed solutions. The feasibility of mmWave and THz band communications up to 100 m in both line-of-sight and nonline- of-sight areas are demonstrated.