Wireless communications sensing and security above 100 GHz.

The field of sub-terahertz wireless communications is advancing rapidly, with major research efforts ramping up around the globe. To address some of the significant hurdles associated with exploiting these high frequencies for broadband and secure networking, systems will require extensive new capabilities for sensing their environment and manipulating their broadcasts. Based on these requirements, a vision for future wireless systems is beginning to emerge. In this Perspective article, we discuss some of the prominent challenges and possible solutions which are at the forefront of current research, and which will contribute to the architecture of wireless platforms beyond 5G.

Jamming a terahertz wireless link.

As the demand for bandwidth in wireless communication increases, carrier frequencies will reach the terahertz (THz) regime. One of the common preconceived notions is that, at these high frequencies, signals can radiate with high directivity which inherently provides more secure channels. Here, we describe the first study of the vulnerability of these directional links to jamming, in which we identify several features that are distinct from the usual considerations of jamming at low frequencies. We show that the receiver's use of an envelope detector provides the jammer with the ability to thwart active attempts to adapt to their attack. In addition, a jammer can exploit the broadband nature of typical receivers to implement a beat jamming attack, which allows them to optimize the efficacy of the interference even if their broadcast is detuned from the frequency of the intended link. Our work quantifies the increasing susceptibility of broadband receivers to jamming, revealing previously unidentified vulnerabilities which must be considered in the development of future wireless systems operating above 100 GHz.

Single-shot link discovery for terahertz wireless networks.

Of the many challenges in building a wireless network at terahertz frequencies, link discovery remains one of the most critical and least explored. In a network of mobile receivers using narrow directional beams, how do the nodes rapidly locate each other? This direction information is crucial for beam forming and steering, which are fundamental operations for maintaining link quality. As the carrier frequency increases into the terahertz range, the conventional methods used by existing networks become prohibitively time-consuming, so an alternative strategy is required. Using a leaky-wave antenna with a broadband transmitter, we demonstrate a single-shot approach for link discovery which can be accomplished much more rapidly. Our method relies on measurements of the width of a broad spectrum, and does not require any information about the phase of the received signal. This protocol, which relies on a detailed understanding of the radiation from leaky-wave devices, offers a realistic approach for enabling mobility in directional networks.

Security and eavesdropping in terahertz wireless links.

Resiliency against eavesdropping and other security threats has become one of the key design considerations for communication systems. As wireless systems become ubiquitous, there is an increasing need for security protocols at all levels, including software (such as encryption), hardware (such as trusted platform modules) and the physical layer (such as wave-front engineering)1-5. With the inevitable shift to higher carrier frequencies, especially in the terahertz range (above 100 gigahertz), an important consideration is the decreased angular divergence (that is, the increased directionality) of transmitted signals, owing to the reduced effects of diffraction on waves with shorter wavelengths. In recent years, research on wireless devices6-8 and systems9-11 that operate at terahertz frequencies has ramped up markedly. These high-frequency, narrow-angle broadcasts present a more challenging environment for eavesdroppers compared to the wide-area broadcasts used at lower frequencies12,13. However, despite the widespread assumption of improved security for high-frequency wireless data links14-16, the possibility of terahertz eavesdropping has not yet been characterized. A few recent studies have considered the issue at lower frequencies5,12,13,17,18, but generally with the idea that the eavesdropper's antenna must be located within the broadcast sector of the transmitting antenna, leading to the conclusion that eavesdropping becomes essentially impossible when the transmitted signal has sufficiently high directionality15. Here we demonstrate that, contrary to this expectation, an eavesdropper can intercept signals in line-of-sight transmissions, even when they are transmitted at high frequencies with narrow beams. The eavesdropper's techniques are different from those for lower-frequency transmissions, as they involve placing an object in the path of the transmission to scatter radiation towards the eavesdropper. We also discuss one counter-measure for this eavesdropping technique, which involves characterizing the backscatter of the channel. We show that this counter-measure can be used to detect some, although not all, eavesdroppers. Our work highlights the importance of physical-layer security in terahertz wireless networks and the need for transceiver designs that incorporate new counter-measures.