This paper presents the first security study of THz networks employing antennas with the angle-frequency coupling property. Using Leaky Wave Antennas (LWAs) as a representative, we explore the unique security properties due to the frequency-dependent radiation. We show via both analytical models and over-the-air experiments that LWA links exhibit non-uniform secrecy capacity across sub-channels, yielding advantages to an eavesdropper at edge frequencies. Yet, because different frequencies emit towards different angles, the eavesdropper is thwarted from easily intercepting an entire wideband transmission. The experiments diverge from the analytical model in that the model underpredicts the eavesdropper’s advantage at angles smaller than the target user and subsequent asymmetric performance across angles. Nonetheless, both the model and measurements show that increasingly wide bandwidth and correspondingly wide beams have only a modest marginal security penalty. Further, we find the LWA link secrecy not only depends on the target user angle (due to nonlinearity of LWA’s frequency-angle coupling), but also the beamwidth of the frequency components that constitute the collective LWA transmission.

With the large bandwidths available in the terahertz regime, directional transmissions can exhibit angular dispersion, i.e., frequency-dependent radiation direction. Unfortunately, angular dispersion introduces new security threats as increased bandwidth necessarily yields a larger signal footprint in the spatial domain and potentially benefits an eavesdropper. This paper is the first study of secure transmission strategies on angularly dispersive links. Based on information theoretic foundations, we propose a transmission strategy that channelizes the wideband transmission in frequency, and performs secure coding across frequency channels. With model-driven evaluations and over-the-air experiments, we show that the proposed method exploits the properties of angular dispersion to realize secure wideband transmissions, despite the increased signal footprint and even for practical irregular beams with side lobes and asymmetry. In contrast, without the proposed cross-channel coding strategy, angularly dispersive links can suffer from significant security degradation when bandwidth increases. In addition, we find that the security degradation due to bandwidth increment for angularly dispersive links is secondary compared to other factors including the selected secrecy rate or the directivity of the link. Nonetheless, we find that a higher angular dispersion level, i.e., a larger angular spread with the same bandwidth, results in a higher security degradation as bandwidth increases.

With the large bandwidths available in the terahertz regime, directional transmissions can exhibit angular dispersion, i.e., frequency-dependent radiation direction. Unfortunately, angular dispersion introduces new security threats as increased bandwidth necessarily yields a larger signal footprint in the spatial domain and potentially benefits an eavesdropper. This paper is the first study of secure transmission strategies on angularly dispersive links. Based on information theoretic foundations, we propose to channelize the wideband transmission in frequency, and perform secure coding across frequency channels. With over-the-air experiments, we show that the proposed method exploits the properties of angular dispersion to realize secure wideband transmissions, despite the increased signal footprint and even for practical irregular beams with side lobes and asymmetry. In contrast, without the proposed cross-channel coding strategy, angularly dispersive links can suffer from significant security degradation when bandwidth increases.

Massive multiple-input and multiple-output (massive MIMO) has the potential to thwart passive eavesdropping as the signals transmitted by large antenna arrays become highly focused. Indeed, the impact of passive eavesdropping has been shown to be negligible when the base station (BS) antenna size approaches infinity for Rayleigh channels. In this paper, we experimentally explore eavesdropping in massive MIMO incorporating real-world factors including a limited BS antenna array size, potential correlation in over-the-air channels, and adaptation of modulating and coding schemes (MCS) over a discrete and finite set. Using a 96-antenna ArgosV2 BS, we first explore scaling the array size and identify eavesdropper (Eve) advantages due to channel correlation. We next identify the “MCS saturation regime” as a vulnerability even with high SNR due to limited MCS levels, and thereby demonstrating the need for power control as a counter-strategy, especially considering Eve’s advantages in the over-the-air channels. We further demonstrate Eve’s gain in optimizing her position, not only via being nomadic and searching for the most favorable position, but also via exploiting predictable line-of-sight (LoS) positional vulnerabilities. Specifically, we demonstrate Eve’s advantage by simply sharing the elevation angle with Bob in the LoS scenario. Finally, we examine how Eve’s advantage due to channel correlation scales with more eavesdropping antennas.

THz communication has the potential to realize an order of magnitude increase in data rates due to the availability of wide THz-scale spectral bands. Unfortunately, establishing and managing highly directional beams in THz networks is challenging as links lack the "pseudo-omni" reception capability of lower bands and the product of AP-client beam resolution is high due to narrow beams of only a few degrees. In this paper, we present One-shot Path discovEry with a THz RAinbow (OPERA), a novel system that identifies dominant paths between the AP and all clients in order to efficiently steer directional beams. The key idea is to embed path direction into the inherent characteristics of signals traveling along each path. To do so, we exploit a single leaky wave antenna and create a THz Rainbow. A THz Rainbow transmission consists of distinct signals with unique spectral characteristics across the angular domain. Leveraging the spatial-spectral signatures in the THz Rainbow, all receivers can correlate the measured signal with the known transmission signatures to discover the sender's path directions in one-shot. Our experiments demonstrate that OPERA achieves average direction estimates within 2° of ground truth for LOS and reflected paths.

Radio frequency signals have the potential to convey rich information about a node's motion and surroundings. Unfortunately, extracting such information is challenging, previously requiring accurate phase measurement, large antenna array structures, or extensive training. In this paper, we present LeakyTrack, a novel system that enables non-coherent and training-free motion sensing with a single antenna. The key idea is to create unique spectrally coded signals at different spatial directions so that geometric properties of the receiving node, as well as any potential objects in the environment, leave spectral footprints on the collected signal. To do so, we exploit a THz leaky-wave antenna and realize a color-coded scan in which signals with distinct spectral characteristics simultaneously emit across the angular domain. LeakyTrack infers nodal and environmental motion by analyzing the received spectral profile. We evaluate the performance of LeakyTrack via extensive over-the-air experiments.

This paper presents the first security study of THz networks with Leaky Wave Antennas (LWAs). We employ a mix of analytical models and over-the-air experiments to explore the unique security properties of LWA links. We show via both models and experiments that the LWA's angle-frequency coupling leads to non-uniform secrecy capacity across sub-channels yielding advantages to an eavesdropper at edge frequencies. Yet, because different frequencies emit energy at different angles, the eavesdropper is thwarted from easily intercepting an entire wideband transmission. The experiments diverge from the analytical model in that the model underpredicts the eavesdropper's advantage at angles smaller than the target user and subsequent asymmetric performance across angles. Nonetheless, both the model and measurements show that increasingly wide bandwidth and correspondingly wide beams have only a modest marginal security penalty.

The Wireless of the Students, by the Students, and for the Students (S3) Workshop provides a unique venue for graduate students around the world to present, discuss, and exchange ideas on cross-cutting research on mobile wireless networks. As its name suggests, the workshop is organized by students, and the technical sessions are given by student presenters. The workshop aims at fostering early-career development among students and exposing them to the workings of academic life. It provides a venue for students to learn about each other's' work and discover opportunities for collaboration. The workshop invites students to submit papers, posters, and demos. All submissions are peer-reviewed by the student program committee.

When it comes to machine-to-machine (M2M) communications in advanced cellular networks, the resource allocation scheme should be re-examined to satisfy both low-cost M2M and mission-critical M2M. Because most M2M applications are uplink-dominated, we propose a mixed waiting-time auction and price-based dedicated uplink resource allocation framework for the low-cost and mission-critical M2M. The prioritized framework guarantees resources for traditional human-to-human (H2H) communications while meeting the needs of low-cost and mission-critical M2M devices on the basis of either time bids or direct price. In addition, the scheme ensures the existence and uniqueness of the Bayesian Nash equilibrium and the interregional and waiting-time-based truth-telling properties. This indirect mechanism holds with Bayesian-Nash incentive compatibility, interim efficiency, interim individual rationality, and weak budget balance. The results show that low-cost M2M devices with lower energy awareness are more willing to participate in the waiting-time auction, while mission-critical M2M with higher energy awareness turn to directly pay for guaranteed access. The delay in connected mode and the optimal price vary according to the M2M/H2H traffic loads and resource pool partitions. This paper contributes insights that with proper mechanism design, low-cost M2M and mission-critical M2M can be served together, while the operator is financially compensated.

Since Machine-to-Machine (M2M) communications is going to be realized in advanced cellular networks, the resource allocation scheme should be re-examined to satisfy both traditional Human-to-Human (H2H) communications (e.g., voice calls) and M2M communications. Because most M2M applications are delay-tolerant and uplink-dominated, we propose a waiting-line based uplink resource allocation framework in the M2M/H2H co-existence scenario. The proposed scheme guarantees resources for H2H communications while meeting the needs of M2M communications on a first-come first-served basis. In addition, the scheme ensures the existence and uniqueness of the Bayesian Nash equilibrium and the truth-telling property. Results show that M2M devices with lower energy opportunity cost are more willing to participate in the waiting-line based scheme, and the delay in the connected mode varies according to the H2H traffic load and the total number of competitors. However, M2M devices with higher energy opportunity cost may not join this time bid resource allocation scheme. This work contributes insights into the types of resource allocation schemes, bidding with time or bidding with money, for M2M devices with different levels of energy awareness.