Terahertz Signals Go Around Corners: Reflection and Transmission Unlock Non-Line-of-Sight 6G Links

The terahertz band has long been heralded as the promised land of wireless communications, offering vast swaths of unoccupied spectrum that could carry data at rates approaching those of fiber optic cables. Frequencies between roughly 100 gigahertz and 10 terahertz sit above the millimeter-wave allocations now used in early 5G deployments, and they promise multi-gigabit and even terabit-per-second links for everything from holographic telepresence to wireless data centers. Yet the very physics that makes terahertz spectrum so attractive also makes it notoriously fragile. Signals at these frequencies behave almost like beams of light: they travel in straight lines, they are readily absorbed by the atmosphere, by rain, and even by humidity, and they struggle to penetrate walls, furniture, and the human body. In a typical urban or indoor environment, where a base station and a user device rarely enjoy an unobstructed view of one another, this line-of-sight dependency has been the single greatest obstacle standing between laboratory demonstrations and real-world terahertz networks.

A new analysis published in Communications Engineering examines how two familiar wave phenomena, reflection and transmission, can be harnessed systematically to keep terahertz links alive when the direct path between transmitter and receiver is blocked. The work argues that non-line-of-sight terahertz communication should not be treated as an afterthought or a failure mode, but as a first-class design objective, engineered deliberately into the architecture of future sixth-generation networks. By treating reflective surfaces such as walls, ceilings, glass facades, and even road signs as passive allies, and by exploiting controlled transmission through materials such as drywall and window glass, the study sketches a pathway toward terahertz coverage that survives the shadows cast by everyday obstacles.

The scale of the challenge is rooted in fundamental electromagnetics. As frequency increases, the free-space path loss between two antennas grows with the square of the frequency, so a terahertz link at 300 gigahertz suffers dramatically more spreading loss than a microwave link carrying the same distance. Diffraction, the phenomenon that allows lower-frequency radio waves to bend around corners and fill rooms with coverage, becomes vanishingly weak at terahertz frequencies because the wavelengths, on the order of a millimeter or less, are tiny compared with the edges and gaps of ordinary objects. Scattering from rough surfaces, which would smear energy in many directions at lower frequencies, becomes more specular and directional, meaning that a terahertz wave bounces off a flat wall much the way a billiard ball bounces off a cushion: predictably, but only along a narrow geometric path determined by the law of reflection.

This directional character is a double-edged sword. On one hand, it means that a blocked terahertz link cannot rely on the diffuse, multipath-rich propagation that made older cellular systems robust. On the other hand, it means that reflected paths are stable, identifiable, and potentially very high quality. A signal that bounces once off a well-positioned wall arrives with a predictable delay, a predictable angle of arrival, and, if the surface is sufficiently smooth and conductive, only a modest additional loss. The new analysis emphasizes that in many indoor and street-canyon scenarios, first- and second-order reflected paths can deliver received power levels well within the sensitivity range of modern terahertz receivers, provided that the antenna beams are steered to illuminate and collect from those paths deliberately.

Beam steering is therefore the linchpin of the approach. Terahertz systems almost universally employ highly directional antennas, often implemented as phased arrays of many small radiating elements, to concentrate their limited power into a narrow pencil beam and to overcome path loss. In a line-of-sight world, pointing such a beam is straightforward. In a non-line-of-sight world, the network must first discover which reflective or transmissive paths exist, then select the best one, and then keep the beam locked onto it as people move and doors swing open. The analysis highlights beam management as a central research problem: hierarchical search procedures, machine-learning-assisted path prediction, and the use of out-of-band or sub-6-gigahertz control channels to cue the terahertz beam are all candidate techniques for finding a viable reflected route in milliseconds rather than seconds.

Reconfigurable intelligent surfaces, sometimes called smart metasurfaces, extend this idea from accidental reflectors to engineered ones. These are thin panels studded with subwavelength elements whose electromagnetic response can be tuned electronically, allowing the panel to act as a programmable mirror that redirects an incoming terahertz beam toward a chosen receiver, or even to shape the wavefront in ways a plain wall never could. Mounted on ceilings, building facades, or interior walls, such surfaces could serve as deliberate relay points, stitching together coverage in courtyards, corridors, and factory floors where no natural reflection geometry happens to work. The study situates these engineered surfaces alongside natural reflections as complementary tools in the non-line-of-sight toolkit, noting that their low power consumption and passive operating principle make them attractive for dense deployment.

Transmission, the second pillar of the analysis, is often dismissed at terahertz frequencies because many common building materials attenuate the signal severely. Concrete and brick are effectively opaque, and even wood and glass introduce losses that grow rapidly with frequency and thickness. Yet the picture is nuanced. Drywall, plasterboard, and standard window glass can pass usable fractions of the incident power at the lower end of the terahertz range, particularly near 100 to 140 gigahertz, where several standards bodies are now defining early commercial allocations. A signal that passes through a single interior wall may arrive attenuated but decodable, especially when the transmitter can boost power or the receiver can integrate over longer symbol durations. The analysis argues that material-aware network planning, in which the propagation database records not only reflectivity but also transmissivity of the surfaces in a given environment, allows the network to choose intelligently between penetrating an obstacle and bouncing around it.

The interplay between reflection and transmission also shapes how channel models must evolve. Classical statistical channel models, built for scattering-rich microwave environments, poorly describe terahertz links, which are dominated by a small number of deterministic geometric paths. Ray-tracing simulations, seeded with accurate three-dimensional models of buildings and streets and with measured material parameters, emerge as the preferred planning tool. The analysis stresses that measurement campaigns at terahertz frequencies remain comparatively sparse, and that closing this gap between modeled and measured channel behavior is essential before operators can trust simulated coverage maps. Hybrid approaches that combine sparse measurements with ray-tracing interpolation, updated in real time from the feedback that connected devices report, offer a pragmatic middle path.

The implications reach well beyond faster smartphone downloads. Terahertz non-line-of-sight techniques are critical for industrial wireless networks, where metal machinery guarantees that direct paths will be blocked, and where deterministic, ultra-reliable low-latency communication is a hard requirement for replacing factory cabling. They matter for vehicular networks, where the geometry of a street canyon creates rich reflection opportunities off building walls and parked vehicles, and for integrated sensing and communication, in which the same reflected terahertz signals that carry data can simultaneously image the environment. They also underpin the vision of wireless data centers and chip-to-chip links, where racks and heat sinks create a maze of reflective metal surfaces that a well-designed terahertz system can exploit rather than suffer.

Considerable engineering hurdles remain before reflected and transmitted terahertz paths can be managed at network scale. Phased arrays with thousands of elements consume significant power, and the phase shifters and amplifiers behind them are still costly at these frequencies. Beam alignment protocols must become faster and more energy-efficient, and handover between line-of-sight and non-line-of-sight states must be seamless enough that users never notice the network quietly rerouting their connection around a passing pedestrian. Standardization bodies are actively working to define the measurement, signaling, and beam-management procedures that would let multiple vendors implement interoperable non-line-of-sight behavior. What the new analysis makes clear is that the physics need not be an enemy. The same specular, mirror-like behavior that makes terahertz waves unforgiving also makes them predictable, and predictability is precisely what a carefully engineered network needs. If future 6G systems learn to treat every wall and window as potential infrastructure, the terahertz frontier may arrive not despite the obstacles in its path, but because the network has learned to use them.

Subject of Research: Non-line-of-sight terahertz communications using reflection and transmission for future 6G networks

Article Title: Non-line-of-sight terahertz communications enabled by reflection and transmission

Article References: Liu, F., Seddon, J., Belio-Apaolaza, I., G. Huggard, P., Wang, H., Lia, E., Deborgies, F., Wu, J. E., Munshi, M. N., Fice, M., & Seeds, A. (2026). Non-line-of-sight terahertz communications enabled by reflection and transmission. Communications Engineering. https://doi.org/10.1038/s44172-026-00782-6

Image Credits: AI Generated

DOI: 10.1038/s44172-026-00782-6

Keywords: terahertz communications, non-line-of-sight, 6G, beam steering, reconfigurable intelligent surfaces, reflection, transmission, channel modeling, millimeter wave, wireless networks, Communications Engineering, phased arrays