The real-time knowledge of mmWave device orientation offers dual benefits for wireless networks and Internet of Things (IoT) applications: it enhances communication and localization performance through link diagnosis, and it enables context inference with asset and wearable tracking. This paper presents MetaPol, a novel system architecture that augments commodity mmWave access points (APs) with a carefully designed ultra-low-cost anisotropic metasurface to non-invasively extract the orientation of client devices, without hindering data reception or modifying hardware. MetaPol leverages the polarization of transmitted electromagnetic (EM) waves as an accurate indicator of the orientation of linearly polarized antenna arrays, prevalent in commercial mmWave mobile and IoT devices. Yet, polarization sensing is rarely supported by commodity APs due to the need for two orthogonally polarized antenna arrays to capture the incident electric field. Instead, MetaPol creates virtual polarization channels to characterize impinging electric fields, through the conversions of wave polarization on the fly as it interacts with the metasurface. To design MetaPol, we model and exploit the properties of a unique anisotropic metamaterial based on C-shaped split-ring resonators. We discover that, when grouped in certain configurations, these meta-elements can convert the incident polarization in a deterministic way. We show that three polarization channels are sufficient for unambiguous orientation sensing, and we provide a corresponding three-shot non-coherent protocol that extracts user orientation by comparing the power received from distinct surface areas. Through extensive over-the-air experiments with more than 1000 measurements in the mmWave band, we demonstrate that MetaPol achieves a mean error of 2.6° across practical settings with negligible compromise to the underlying data communication link.

The integration of communication and sensing functions within mmWave systems has gained attention due to the potential for enhanced passive sensing and improved communication reliability. State-of-the-art techniques separate these two functions in frequency, use of hardware, or time, i.e., sending known preambles for channel sensing or unknown symbols for communications. In this paper, we introduce Panoptic, a novel system architecture for integrated communication and sensing sharing the same hardware, frequency, and time resources. Panoptic jointly detects unknown symbols and channel components from data-modulated signals. The core idea is a new beam manipulation technique, which we call compressive sidelobe forming, that maintains a directional mainlobe toward the intended communication nodes while acquiring unique spatial information through pseudorandom sidelobe perturbations. We implemented Panoptic on 60 GHz mmWave radios and conducted extensive over-the-air experiments. Our results show that Panoptic achieves reflector angular localization error of less than 2° while at the same time supporting mmWave data communication with a negligible BER penalty when compared with conventional communication-only mmWave systems.

Future wireless systems are envisioned to utilize the large spectra available at THz bands for wireless communications. Extremely massive multiple-input multiple-output (MIMO) antennas can be costly and power inefficient for wideband THz communications. An alternative antenna technology, which can achieve low-cost and power-efficient THz signaling, is based on leaky wave antennas (LWAs). In this paper, we explore the usage of the LWAs for wideband downlink multi-user THz communications. We propose a model for LWA-aided communication systems that faithfully captures the antenna operations. We show that LWAs yield frequency-dependent beams, where the equivalent wideband channel induces a dependence between angle, frequency, and spectral lobe width. We identify the LWA’s inherent frequency-selective beamsteering capabilities as motivating multi-band THz communications, in which subbands are allocated among users based on their relative angles. Then, we propose an alternating optimization algorithm for jointly optimizing the LWA configuration along with the spectral division and power allocation to maximize the achievable sum rate performance. Our numerical results show that a single LWA can generate diverse beampatterns, exhibiting performance comparable to costly MIMO architectures in wideband THz multi-user systems.

Orbital Angular Momentum (OAM)-based communication systems offer high-capacity multiplexing in line-of-sight (LOS) scenarios; yet, their performance is sensitive to nodal misalignment, which disrupts modal orthogonality, hindering the data multiplexing gain. To tackle this challenge, we present OrthoVortex, a novel framework that estimates the misalignment angles and applies the appropriate phase correction to restore orthogonality between modes. Unlike purely theoretical prior efforts that rely on impractical fully digital arrays or exhaustive beam scans, OrthoVortex introduces and leverages the cross-modal phase, as a unique signature for identifying the misalignment angles. OrthoVortex is a few-shot alignment technique, making it feasible for real-world implementations. Our key contributions include: (i) a robust angle estimation and phase correction framework based on the physics of OAM propagation that estimates the misalignment and restores modal orthogonality, (ii) the first-ever experimental validation of OAM beam alignment with RF transceivers, and (iii) a comprehensive analysis of practical constraints, including the impact of antenna count and bandwidth. Simulations and over-the-air measurements using low-cost, rapidly prototyped metasurfaces operating at 120 GHz demonstrate that OrthoVortex achieves fast and precise misalignment estimation (mean absolute error of $0.69^{\circ}$ for azimuth and $2.54^{\circ}$ for elevation angle). Further, OrthoVortex can mitigate the inter-modal interference, yielding more than 12 dB increase in signal-to-interference ratio and more than 4.5-fold improvement in link capacity.

Sensing friction coefficient is vital for various cyber-physical system applications, including robotic grasping. We present RoboTera, a novel system for the non-contact coefficient of friction (COF) estimation using sub-Terahertz (sub-THz) perception in robotics for the first time. While advanced tactile sensors can provide friction inputs, they require direct contact, which might not be suitable for various applications. Non-contact estimation of friction between the gripper and a target object requires extracting the minute surface perturbations which is unfortunately not supported by existing imaging modalities (such as camera and LiDAR). Our key insight is that sub-THz signals are best suited to infer such information as their sub-millimeter wavelength is comparable with surface perturbations. Hence, impinging sub-THz waves on everyday objects creates diffuse backscattering whose spectral profile hints at surface texture properties. Leveraging this, we use sub-THz wireless signals to extract surface roughness. By integrating sub-THz-estimated roughness inputs with conventional image-based material classification schemes, RoboTera provides a non-contact and precise COF inference framework. Further, we exploit COF inferences to identify stable grasp configurations and improve grasping performance. Our experiments demonstrate an average accuracy of over 92% in COF estimation. We implemented RoboTera on a robotic arm to assess its real-world grasping performance, achieving a 31.8% average improvement across objects with diverse COF profiles and shapes.

Sensing the coefficient of friction (COF) is crucial for robotic and Cyber-Physical System applications, including grasping. We introduce RoboTera, a novel system for non-contact COF estimation using sub-Terahertz (sub-THz) perception in robotics. Unlike tactile sensors that require direct contact, our approach leverages sub-THz signals with sub-millimeter wavelength to capture surface roughness characteristics as an essential factor in non-contact COF inference, that conventional imaging modalities like cameras and LiDAR cannot detect. Our system enables precise COF inference by integrating sub-THz-estimated roughness with image-based material classification. Further, we exploit COF inferences to identify stable grasp configurations and improve grasping performance. Experiments show over 92% accuracy in COF estimation, with a 31.8% improvement in grasp success rates in real-world robotic tasks.

The extended near-field range in future mm-Wave and sub-THz wireless networks demands a precise and efficient near-field channel simulator for understanding and optimizing wireless communications in this less-explored regime. This paper presents NirvaWave, a novel near-field channel simulator, built on scalar diffraction theory and Fourier principles, that precisely captures the propagation evolution of arbitrary user-defined transmit electromagnetic (EM) signals in complex user-defined wireless mediums. NirvaWave offers an interface for investigating novel near-field wavefronts, e.g., Airy beams, Bessel beams, and the interaction of mmWave and sub-THz signals with obstructions, reflectors, and scatterers. The simulation run-time in NirvaWave is orders of magnitude lower than its EM software counterparts that directly solve the Maxwell equations. Hence, NirvaWave enables a user-friendly interface for large-scale channel simulations required for developing new model-driven and data-driven techniques in next-generation communication systems. We evaluated the performance of NirvaWave through direct comparison with EM simulation software. Finally, we have open-sourced the core code-base of NirvaWave in our GitHub repository.

Owing to the substantial bandwidth they offer, the exploration of 100+ GHz frequencies for wireless communications has surged in recent years. These sub-Terahertz channels are susceptible to blockage, which makes reflected paths crucial for seamless connectivity. However, at such high frequencies, reflections deviate from the known mirror-like specular behavior as the signal wavelength becomes comparable to the height perturbation at the surface of the reflectors. Such reflectors are considered electromagnetically “rough” which results in random non-specular reflection components that are not well understood. In this paper, we delve into the fundamentals of rough scattering to analyze its implications for sub-THz wireless networks, including the existence and strength of non-specular links, mobility resilience, and beam reciprocity. Further, we present a novel framework that re-purposes IEEE 802.11ay-like beam sweeps for estimating the surface roughness of a reflector in the vicinity of the communication nodes. Through extensive modeling, simulation, and experiments with everyday reflector samples, we demonstrate the impact of rough scattering on over-the-air data links and evaluate the accuracy of our roughness inference framework.

The sub-THz band offers an attractive solution to future wireless networks, thanks to its ultra-low latency as well as its large available bandwidth. However, link blockage remains a major setback towards reliable sub-THz end-to-end communication systems, due to narrow beamwidth and inherently high penetration losses. To achieve blockage mitigation in sub-THz communication, this paper takes advantage of unique near-field properties and manipulates curved wavefront trajectories. Unfortunately, finding the best curved beam configuration is non-trivial due to the lack of a closed-form equation for received power calculation under blockage scenarios, even if the wireless environment is precisely known. To address this, we present a physics-informed learning-based framework that optimizes the phase profile of the transmitting array, such that the resulting wavefront could curve around obstacles and adapt to dynamic environments in real time. Through extensive near-field simulations, we evaluate the performance of our AI-generated curved beams as opposed to optimal Airy beams achieved via impractical exhaustive scans with prohibitively large time and complexity overheads. Importantly, simulated results show that our AI-generated curved wavefront provides an average SNR gain of 19.83 dB compared with conventional beam steering and 2.13 dB compared with near-field beam focusing, across ~400 random and independent test scenarios.

THz communications are expected to play a profound role in future wireless systems. The current trend of the extremely massive multiple-input multiple-output (MIMO) antenna architectures tends to be costly and power inefficient when implementing wideband THz communications. An emerging THz antenna technology is leaky wave antenna (LWA), which can realize frequency selective beamforming with a single radiating element. In this work, we explore the usage of LWAs technology for wideband multi-user THz communications. We propose a model for the LWA signal processing that is physically compliant facilitating studying LWA-aided communication systems. Focusing on downlink systems, we propose an alternating optimization algorithm for jointly optimizing the LWA configuration along with the signal spectral power allocation to maximize the sum-rate performance. Our numerical results show that a single LWA can generate diverse beampatterns at THz exhibiting performance comparable to costly fully digital MIMO arrays.

This paper investigates how an airborne node can eavesdrop on the underwater acoustic communication between submerged nodes. Conventionally, such eavesdropping has been assumed impossible as acoustic signals do not cross the water-air boundary. Here, we demonstrate that underwater acoustic communications signals can be picked up and (under certain conditions) decoded using an airborne mmWave radar due to the minute vibrations induced by the communication signals on the water surface. We implemented and evaluated a proof-of-concept prototype of our method and tested it in controlled (pool) and uncontrolled environments (lake). Our results demonstrate that an airborne device can identify the modulation and bitrate of acoustic transmissions from an uncooperative underwater transmitter (victim), and even decode the transmitted symbols. Unlike conventional over-the-air communications, our results indicate that the secrecy of underwater links varies depending on the modulation type and provide insights into the underlying reasons behind these differences. We also highlight the theoretical limitations of such a threat model, and how these results may have a significant impact on the stealthiness of underwater communications, with particular concern to submarine warfare, underwater operations (e.g., oil & gas, search & rescue, mining), and conservation of endangered species. Finally, our investigation uncovers countermeasures that can be used to improve or restore the stealthiness of underwater acoustic communications against such threats.

This study examines how an airborne device can intercept underwater acoustic signals exchanged between submerged nodes. It challenges the conventional belief that acoustic communications under the water are safe against eavesdropping since acoustics do not cross the water-air boundary. We show that an airborne mmWave radar can detect and decode underwater acoustic signals by picking up minute surface vibrations induced by these signals. The proof-of-concept was tested in controlled (pool) and uncontrolled (lake) environments, proving that an airborne adversary can identify modulation type, bitrate, and decode symbols from an uncooperative underwater transmitter using its radar sensing capabilities. We demonstrate that the secrecy of underwater links depends on modulation type, providing insights into countermeasures to enhance the security of underwater acoustic communications.

mmWave antenna array calibration is a necessary yet tedious and costly process in manufacturing to capture the non-idealities in phased arrays, in order to obtain codebooks for accurate and stable beam steering. Unfortunately, predefined codebooks provided by manufacturers to steer beams in a given set of directions do not support the arbitrary beam shapes required for various mmWave communication, sensing, and security applications. To create arbitrary beam patterns, one needs to first find the unknown calibration vector for the particular phased array in use. In this paper, we introduce EiCal, a novel zero-shot technique that leverages the beamforming codebook advertised by the manufacturer to extract the calibration vector at zero cost (i.e., with no additional measurements). The key idea is that the unknown desired calibration vector can be obtained via an appropriately designed eigen-decomposition of the given codebook. We experimentally demonstrate the efficacy of EiCal on a 60 GHz mmWave array for two scenarios: angle estimation using compressive pseudorandom beams, and simultaneous steering of beams and nulls. Our results also point to potential simplifications in the calibration process at the manufacturer.

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.

The ability to assess the quality of fruit and vegetables at scale can revolutionize the agriculture sector and significantly reduce food waste. In this paper, we present AgriTera, a novel solution for accurate non-invasive, and contract-free fruit ripeness sensing via sub-terahertz wireless signals. The key idea is that sugar and water concentrations in fruit (that are associated with fruit ripening) leave unique non-uniform footprints in the wide band spectrum of the reflected signal off of the fruits. AgriTera utilizes the sub-THz bands for its wide bandwidth, sensitivity to water, mm-scale penetration depth, and non-ionizing features that offer high-resolution inferences from the peel as well as the pulp underneath the peel. We develop a chemometric model that translates the reflection spectra to well-known ripeness metrics, namely Dry Matter and Brix. We conduct extensive over-the-air experiments with commercially available sub-THz transceivers. We compare our results with ground truth values captured by a specialized quality sensor and a vision-based scheme that infers ripeness based on changes in the appearance of the fruit. We demonstrate that AgriTera can accurately estimate Brix and Dry Matter in three different types of fruit with an average Normalized RMSE value of 0.55%, an error that yields a negligible impact on taste and is imperceivable by the consumer.

The use of frequencies above 100 GHz has received increasing attention due to the large amount of available bandwidth. Given the high chance of signal blockage, reflected paths play a key role in 100+ GHz networks. Interestingly, at these frequencies, the signal wavelength becomes comparable to the height perturbation in common natural surfaces. Hence, the reflection pattern deviates from mirror-like smooth reflection and exhibits rough scattering patterns that consist of non-specular components. This paper presents an in-depth analysis and experimental demonstration of "rough" surface scattering and its implications for wireless networking, namely in coverage, mobility resilience, and channel reciprocity. Furthermore, we present a novel framework for estimating the surface roughness level from the unique spectral and spatial signatures seen in the reflection spectra. We perform extensive modeling, simulation, and over-the-air experiments using a broadband sub-THz wireless system employing typical indoor/outdoor surfaces such as tile, brick, redstone, and granite.

Food waste is one of the greatest economic and ethical challenges in the world. Empowering consumers with the ability to assess the quality of fruit can be a game changer for reducing waste and motivating a healthier diet. In this paper, we present Meta-Sticker a novel low-cost non-invasive solution for accurate fruit sensing via a sub-THz metamaterial sticker. The key idea is to exploit fruit as a substrate for resonating meta-atoms. Changes in the chemical composite of the fruit over time (e.g., sugar and water concentration) yield variation in the dielectric properties of the fruit (here substrate). Interestingly, this would affect the resonant frequency of the Meta-Sticker. We design Meta-Sticker to resonate in the sub-THz bands for their sensitivity to water, mm-scale penetration depth, and non-ionizing features that offer high-resolution inferences from the inner pulp of the fruit. We develop a model that translates the resonance of Meta-Sticker to well-known ripeness metrics, namely Dry Matter and Brix. We fabricate Meta-Sticker on paper and conduct extensive over-the-air experiments. We demonstrate that our system can estimate Brix and Dry Matter in three different types of fruits with an average Normalized RMSE value of 1.24%, an error that yields a negligible impact on taste and is imperceptible by the consumer. Our design is non-invasive, low-cost (less than a cent), passive, biodegradable, and conformal.

Reconfigurable surfaces enable on-demand manipulation of electromagnetic wave properties in a controllable manner. These surfaces have been shown to enhance mmWave wireless networks in many ways, including blockage recovery. In this paper, we investigate the security vulnerabilities associated with the deployment of reconfigurable surfaces, i.e., an adversary may deploy new rogue surfaces or tamper with already-deployed surfaces to maliciously engineer the reflection pattern. In particular, we introduceMetasurface-enabled Sideband Steering (MeSS), a new metasurface-in-the-middle attack in which the spectral-spatial properties of the reflected wavefront are manipulated such that a concealed sideband channel is created in the spectral domain and steered toward the eavesdropper location, while maintaining the legitimate link toward the victim intact. We fabricate a custom reconfigurable surface prototype and evaluate MeSS through theoretical analysis as well as over-the-air experiments at the 60 GHz band. Our results indicate that MeSS significantly reduces empirical secrecy capacity (up to 81.7%) while leaving a small power penalty at the victim that can be masked under normal channel fluctuations.

The first low earth orbit satellite networks for internet service have recently been deployed and are growing in size, yet will face deployment challenges in many practical circumstances of interest. This paper explores how a dual-band, electronically tunable smart surface can enable dynamic beam alignment between the satellite and mobile users, make service possible in urban canyons, and improve service in rural areas. Our design is the first of its kind to target dual channels in the Ku radio frequency band with a novel dual Huygens resonator design that leverages radio reciprocity to allow our surface to simultaneously steer energy in the satellite uplink and downlink directions, and in both reflective and transmissive modes of operation. Our surface, Wall-E, is designed and evaluated in an electromagnetic simulator and demonstrates 94% transmission efficiency and a 85% reflection efficiency, with at most 6 dB power loss at steering angles over a 150 degree field of view for both transmission and reflection. With 75cm2 surface, our link budget calculations predict 4 dB and 24 dB improvement in the SNR of a link entering the window of a rural home in comparison to the free-space path and brick wall penetration, respectively.

The spectrum above 100 GHz has the potential to enable accurate 3D wireless localization due to the large swath of available spectrum. Yet, existing wide-band localization systems utilize the time of arrival measurements requiring strict time synchronization. In this paper, we present 123-LOC, a novel non-coherent system for one-shot dual-polarized 3D localization above 100 GHz. Our key idea is to create unique asymmetric THz fingerprints in 3D so that a wireless node can jointly infer its angular position and distance by taking hints from the measured power-spectrum profile. We introduce a dual-polarized dual-slit waveguide structure that emits out signals into free-space with a key feature that the beam pattern depends on the frequency of the signal and the geometry of the slit. To distinguish the emissions from the two slits, we use polarization diversity and manipulate the aperture geometry of the two slits so that they transmit slightly different angular-spectral signatures. Our over-the-air experiments demonstrate that 123-LOC achieves an average angle estimation error of 1° together with millimeter-scale ranging resolution, solely through non-coherent power measurements.

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.

Multi-stream 60 GHz communication can potentially achieve data rates up to 100 Gbps via multiplexing multiple data streams. Unfortunately, establishing multi-stream directional links is a high overhead procedure as the search space increases with the number of spatial streams and the product of AP-client beam resolution. In this paper, we present MUlti-stream beam-Training for mm-wavE networks (MUTE) a novel system that leverages channel sparsity, GHz-scale sampling rate, and the knowledge of mm-Wave RF codebook beam patterns to construct a set of candidate beams for efficient multi-stream beam steering. MUTE repurposes the mandatory periodic beam sweeps in 60 GHz WLANs to discover the dominant paths of the mmWave channel between the AP and any client with zero additional overhead. Coupling path estimates with beam pattern knowledge, MUTE selects a set of candidate beams that capture diverse or ideally orthogonal paths to obtain maximum stream separability. Our over-the-air experiments demonstrate that MUTE achieves 90% of the maximum achievable aggregate PHY rate while incurring only 1.2% of exhaustive search's training overhead.

Multi-stream 60 GHz communication has the potential to achieve data rates up to $100$ Gbps via multiplexing multiple data streams. Unfortunately, establishing multi-stream directional links can be a high overhead procedure as the search space increases with the number of spatial streams and the product of AP-client beam resolution. In this paper, we present MUlti-stream beam-Training for mm-wavE networks (MUTE) a novel system that leverages channel sparsity, GHz-scale sampling rate, and the knowledge of mm-Wave RF codebook beam patterns to construct a set of candidate beams for multi-stream beam steering. In 60 GHz WLANs, the AP establishes and maintains a directional link with every client through periodic beam training. MUTE repurposes these beam acquisition sweeps to estimate the Power Delay Profile (PDP) of each beam with zero additional overhead. Coupling PDP estimates with beam pattern knowledge, MUTE selects a set of candidate beams that capture diverse or ideally orthogonal paths to obtain maximum stream separability. Our experiments demonstrate that MUTE achieves 90% of the maximum achievable aggregate rate while incurring only 0.04% of exhaustive search's training overhead.

We present LiSteer, a novel system that steers mmWave beams at mobile devices by repurposing indicator LEDs on wireless Access Points (APs) to passively acquire direction estimates using off-the-shelf light sensors. We demonstrate that LiSteer maintains beam alignment at the narrowest beamwidth level even in case of device mobility, without incurring any training overhead at mobile devices. Our extensive evaluation on a custom dual-band hardware platform comprising highly directional horn antennas as well as practical phased antenna arrays with electronic beam steering shows that LiSteer achieves direction estimates within 2.5 degrees of ground truth on average. Moreover, it achieves beam steering accuracy of more than 97% while in tracking mode, without incurring any client beam training or feedback overhead.

We present SearchLight, a system that enables adaptive steering of highly directional 60 GHz beams via passive sensing of visible light from existing illumination sources. The key idea is to simultaneously track a mobile device's position and orientation using intensity measurements from lighting infrastructure, and to adapt client and AP beams to maintain beam alignment, without training overhead or outages in the 60 GHz band. Our implementation on custom dual-band hardware with 2 GHz wide channels and 24-element, electronically steerable phased array antennas shows that SearchLight successfully tracks client mobility and achieves up to 3× throughput gains compared to an in-band training strategy, and eliminates millisecond-scale in-band training epochs.

In this paper we formulate a general link packing problem for mmWave networks. Each link is a 4-tuple determined by the choice of receiving user, transmitting access point, transmit beamforming vector and receive beamforming vector. The problem seeks to optimize the weighted sum over active links, where each link is allowed to have any arbitrarily chosen weight or priority and an active link must satisfy a minimum link quality threshold. Our formulation models a practical scenario in which blockages due to arbitrarily placed obstacles in the propagation environment are allowed to occur, where we note that mmWave transmissions are extremely susceptible to blockages. This is a key departure from the classical link packing problem where only the signal attenuation based on propagation distance is modeled. We exploit the sparsity induced by the directional nature of propagation due to beamforming, limited diffraction and the significant signal attenuation due to high path, penetration losses. We propose a novel technique that exploits this sparsity and considers an alternate formulation which is a column-sparse binary packing problem. This alternate formulation is in general conservative and we derive sufficient conditions under which it is equivalent to the original problem. We construct an efficient iterative algorithm and show that it outperforms other heuristics and guarantees a constant factor approximation for input instances that are likely to occur in mmWave networks.

We introduce X60, the first SDR-based testbed for 60 GHz WLANs, featuring fully programmable MAC/PHY/Network layers, multi-Gbps rates, and a user-configurable 12-element phased antenna array. These features provide us with an unprecedented opportunity to revisit the most important aspects of 60 GHz signal propagation and obtain new insights on performance expected from practical 60 GHz systems. X60's unique capabilities make it an ideal platform for experimentation and prototyping across layers.

Multi-user transmission at 60 GHz promises to increase the throughput of next generation WLANs via both analog and digital beamforming. To maximize capacity, analog beams need to be jointly configured with user selection and digital weights; however, joint maximization requires prohibitively large training and feedback overhead. In this paper, we scale multi-user 60 GHz WLAN throughput via design of a low-complexity structure for decoupling beam steering and user selection such that analog beam training precedes user selection. We introduce a two-class framework comprising (i) single shot selection of users by minimizing overlap of their idealized beam patterns obtained from analog training and (ii) interference-aware incremental addition of users via sequential training to better predict inter-user interference. We implement a programmable testbed using software defined radios and commercial 60 GHz transceivers and conduct over-the-air measurements to collect channel traces for different indoor WLAN deployments. Using trace based emulations and high resolution 60 GHz channel models, we show that our decoupling structure experiences less than 5% performance loss compared to maximum achievable rates via joint user-beam selection.