Thrust 2.0a
Even though the line-of-sight (LOS) propagation is usually envisioned to be the preferred communication channel in a directional wireless network above 100 GHz, it is susceptible to being completely blocked due to different environmental obstacles. In such a situation, one can envision exploiting a non-line-of-sight (NLOS) path in order to maintain connectivity. Despite the rapidly growing interest in exploiting millimeter and terahertz waves for wireless data transfer, the role of reflected NLOS paths in wireless networking is one of the least explored questions. In this work, we investigate the idea of harnessing these specular NLOS paths for communication in directional networks at mmWave to THz frequencies. We explore several illustrative transmitter architectures, namely, a conventional substrate-lens dipole antenna and a leaky-wave antenna. We investigate how these high-gain directional antennas offer both new challenges and new opportunities for exploiting NLOS paths.
Thrust 2.0b
A new method for link discovery, involved equipping both transmitter and receiver with angularly dispersive antennas (e.g., leaky-wave antennas). Changes in the spectral peak and spectral width of the received signal could be directly correlated with changes in the angle of departure and angle of arrival respectively. This incoherent method for link discovery relied solely on the line-of-sight path from Tx to Rx however we now consider non-line-of-sight paths to a later date.
We constructed a test bed for emulating both LOS and NLOS measurements, in a scale model scenario using low-power ultrabroadband THz transceivers. Students from Knightly’s group worked with students from Mittleman’s group to make measurements in Mittleman’s laboratory. These experiments demonstrated that, when a leaky-wave antenna is employed at the transmitter side, the NLOS path can be extremely valuable, even having a higher Shannon capacity than the LOS path, under certain circumstances, despite the additional losses associated with reflection off of a non-ideal surface. This work was published as an invited article in APL Photonics, and was chosen as a featured article by the editors.
Publications:
Ghasempour, Y., Amarasinghe, Y., Yeh, C.Y., Knightly, E. and Mittleman, D.M., “Line-of-sight and non-line-of-sight links for dispersive terahertz wireless networks,” APL Photonics, 6(4), p.041304, 2021.