Millimeter-wave (mmWave) technologies represent a cornerstone for emerging wireless network infrastructure, and for RF sensing systems in security, health, and automotive domains. Through a MIMO array of phased arrays with hundreds of antenna elements, mmWave can boost wireless bit-rates to 100+ Gbps, and potentially achieve near-vision sensing resolution. However, the lack of an experimental platform has been impeding research in this field. We propose to fill the gap with M3 (M-Cube), the first mmWave massive MIMO software radio [1]. M3 features a fully reconfigurable array of phased arrays, with up to 8 RF chains and 256 antenna elements. Despite the orders of magnitude larger antenna arrays, its cost is orders of magnitude lower, even when compared with state-of-the-art single RF chain mmWave software radios. In this demo, we will show M3's hardware modules, and demonstrate its usage in mmWave MIMO communication and sensing.

Embedded devices (e.g., mobile phones, smart watches, etc.) store a large amount of sensitive information. However, Android-based devices may leak a lot of user information if unsafe data deletion. Therefo re, research on secure data deletion for embedded devices has become a practical and urgent issue. In this article, we study the logic structure, operation characteristics, and data management mechanisms of flash memory. Then, we propose a novel method Vacuum that uses a user-space file system and can provide fine-grained file deletion guarantees. Our approach encrypts files on an insecure medium with a unique key that can later be discarded to cryptographically render the data irrecoverable. Additionally, we use TrustZone as a secure key vault, and a garbage collection mechanism is introduced to purge the memory. Finally, we carried out experiments on the Android system, and the results showed that the solution is efficient and can meet the needs of real applications.

Millimeter wave (mmWave) wireless networks are envisioned to bring a very high degree of spatial reuse, i.e., multiple links can operate simultaneously without interference. The vision, however, is becoming doubtful, as recent studies found that non-negligible interference exists due to imperfect beam patterns. In this paper, we extensively measure the spatial reuse issue in a dense 60 GHz mmWave network consisting of multiple access points (AP) and users. Our measurement quantifies the impact of interference on network performance and finds that the existing prediction based on interference-resolving approaches are insufficient. Motivated by the findings, we proposeMDSR, which enhances the spatial reuse in 60 GHz mmWave networks. Instead of relying on interference prediction,MDSRtakes a new measurement principle of building a conflict graph that implicitly takes into account the impact of both beam imperfection and reflections. Using the conflict graph,MDSRimproves the spatial reuse from three dimensions: AP association, user scheduling, and beam selection, which can determine the optimal AP-user-beam combination and minimize interference in each scheduling cycle. We prototype and evaluateMDSRon the testbed using commodity mmWave radios. The evaluation results demonstrate thatMDSRimproves network throughput by multi-folds compared with the state-of-the-art one.

Multi-Gbps 60 GHz millimeter wave (mmWave) networks, are considered as the enabling technology for emerging applications such as untethered VR and 4K/8K Miracast. However, user motion, and even orientation change, can cause mis-alignment between mmWave transceivers’ directional beams and thus severe link outage. Within the practical 3D spaces, the combination of location and orientation dynamics leads to the exponential growth of beam searching complexity, which substantially exacerbates the outage. In this paper, we first measure the impact of 3D motion on 60 GHz link performance in the context of VR and Miracast applications. We find that 3D motion exhibits inherent non-predictability, so conventional beam steering solutions are no longer effective. Therefore, we propose a model-driven 3D beam-steering mechanism called Parallel Scanner (PSCAN), which can maintain high performance for mobile 60 GHz links. To enable PSCAN, we first discover and prove a hidden interaction between 3D beams and the spatial channel profile of 60 GHz radios. Leveraging on which, PSCAN strategically scans the 3D space to reduce the search latency by more than one order of magnitude. Experiment results based on a custom-built 60 GHz platform demonstrate PSCAN’s remarkable throughput gain, up to$5\times $, compared with the state-of-the-art.

Millimeter-wave (mmWave) technologies represent a cornerstone for emerging wireless network infrastructure, and for RF sensing systems in security, health, and automotive domains. Through a MIMO array of phased arrays with hundreds of antenna elements, mmWave can boost wireless bit-rates to 100+ Gbps, and potentially achieve near-vision sensing resolution. However, the lack of an experimental platform has been impeding research in this field. This paper fills the gap with M3 (M-Cube), the first mmWave massive MIMO software radio. M3 features a fully reconfigurable array of phased arrays, with up to 8 RF chains and 288 antenna elements. Despite the orders of magnitude larger antenna arrays, its cost is orders of magnitude lower, even when compared with state-of-the-art single RF chain mmWave software radios. The key design principle behind M3 is to hijack a low-cost commodity 802.11ad radio, separate the control path and data path inside, regenerate the phased array control signals, and recreate the data signals using a programmable baseband. Extensive experiments have demonstrated the effectiveness of the M3 design, and its usefulness for research in mmWave massive MIMO communication and sensing.

Millimeter-wave (mmWave) technologies represent a cornerstone for emerging wireless network infrastructure, and for RF sensing systems in security, health, and automotive domains. Through a MIMO array of phased arrays with hundreds of antenna elements, mmWave can boost wireless bit-rates to 100+ Gbps, and potentially achieve near-vision sensing resolution. However, the lack of an experimental platform has been impeding research in this field. We propose to fill the gap with M3 (M-Cube), the first mmWave massive MIMO software radio. M3 features a fully reconfigurable array of phased arrays, with up to 8 RF chains and 256 antenna elements. Despite the orders of magnitude larger antenna arrays, its cost is orders of magnitude lower, even when compared with state-of-the-art single RF chain mmWave software radios. In this demo, we will show M3's hardware modules, and demonstrate its usage in mmWave MIMO communication and sensing.

Millimeter wave (mmWave) wireless networks are envisioned to bring a very high degree of spatial reuse, i.e., multiple links can operate concurrently without interference. The vision, however, is becoming doubtful, as recent studies found that non-negligible interference exists due to imperfect beam patterns generated by commodity mmWave radios and strong reflections. In this paper, we conduct an extensive measurement on the spatial reuse issue in a dense 60 GHz mmWave network consisting of multiple access points (AP) and users. Our measurement quantifies the impact of interference on network performance and finds that the existing prediction-based interference-resolving approaches are insufficient. Motivated by the findings, we propose mmMuxing, which enhances the spatial reuse in 60 GHz mmWave networks. Instead of relying on interference prediction, mmMuxing takes a new measurement principle of building a conflict graph that implicitly takes into account the impact of both beam imperfectness and reflections. Using the conflict graph, mmMuxing designs a joint user-beam selection algorithm, which can determine the optimal user-beam combination and lead to the minimum interference in each schedule. We prototype and evaluate mmMuxing over testbed using commodity mmWave radios. The evaluation results demonstrate that mmMuxing improves network throughput by multi-folds compared with the state-of-the-art.

The emerging millimeter-wave (mmWave) networking technology promises to unleash a new wave of multi-Gbps wireless applications. However, due to high directionality of the mmWave radios, maintaining stable link connection remains an open problem. Users' slight orientation change, coupled with motion and blockage, can easily disconnect the link. In this paper, we propose RoMil, a robotic mmWave relay that optimizes network coverage through wireless sensing and autonomous motion/rotation planning. The robot relay automatically constructs the geometry/reflectivity of the environment, by estimating the geometries of all signal paths. It then navigates itself along an optimal moving trajectory, and ensures continuous connectivity for the client despite environment/human dynamics. We have prototyped RoMil on a programmable robot carrying a commodity 60 GHz radio. Our field trials demonstrate that RoMil can achieve nearly full coverage in dynamic environment, even with constrained speed and mobility region.

The emerging millimeter-wave (mmWave) networking technology promises to unleash a new wave of multi-Gbps wireless applications. However, due to high directionality of the mmWave radios, maintaining stable link connection remains an open problem. Users' slight orientation change, coupled with motion and blockage, can easily disconnect the link. In this paper, we propose miDroid, a robotic mmWave relay that optimizes network coverage through wireless sensing and autonomous motion/rotation planning. The robot relay automatically constructs the geometry/reflectivity of the environment, by estimating the geometries of all signal paths. It then navigates itself along an optimal moving trajectory, and ensures continuous connectivity for the client despite environment/human dynamics. We have prototyped miDroid on a programmable robot carrying a commodity 60 GHz radio. Our field trials demonstrate that miDroid can achieve nearly full coverage in dynamic environment, even with constrained speed and mobility region.

Multi-user MIMO (MU-MIMO) can serve multiple users concurrently, and is the key technology to enable ultra-high-speed wireless access. However, in practice MU-MIMO networks are far from their full potential due to the poor scalability problem, including high computational complexity at PHY layer and large-overhead channel contention at MAC layer. Moreover, cross-cell interference among multiple MU-MIMO cells also counteracts network performance. In this paper, we perform a systematic study on MU-MIMO and propose a fully scalable MU-MIMO user selection protocol called Guidepost. In contrast with previous works, Guidepost builds on a novel principle of indirection channel orthogonality evaluation, so as to decouple and simplify the complicated computational/contention interaction among users. Based on the principle, Guidepost first achieves scalable MU-MIMO user selection with only linear computational complexity. Second, Guidepost realizes distributed user selection through a two-dimensional prioritized contention mechanism, which can single out the best concurrent users efficiently by utilizing both the time and frequency domain resources. Third, Guidepost incorporates a lightweight AP-assisted contention mechanism to handle cross-cell interference in distributed MU-MIMO (netMIMO) where users are widely distributed and cannot sense each other. Software-radio based implementation and experimentation show that Guidepost significantly outperforms state-of-the-art methods under various traffic patterns and node mobility.

60 GHz networks, with multi-Gbps bitrate, are considered as the enabling technology for emerging applications such as wireless Virtual Reality (VR) and 4K/8K real-time Miracast. However, user motion, and even orientation change, can cause mis-alignment between 60 GHz transceivers' directional beams, thus causing severe link outage. Within the practical 3D spaces, the combination of location and orientation dynamics leads to exponential growth of beam searching complexity, which substantially exacerbates the outage and hinders fast recovery. In this paper, we first conduct an extensive measurement to analyze the impact of 3D motion on 60 GHz link performance, in the context of VR and Miracast applications. We find that 3D motion exhibits inherent non-predictability, so conventional beam steering solutions, which targets 2D scenarios with lower search space and short-term motion coherence, fail in practical 3D setup. Motivated by these observations, we propose a model-driven 3D beam-steering mechanism called Orthogonal Scanner (OScan), which can maintain high performance for mobile 60 GHz links in 3D space. OScan discovers and leverages a hidden interaction between 3D beams and the spatial channel profile of 60 GHz radios, and strategically scans the 3D space so as to reduce the search latency by more than one order of magnitude. Experiment results based on a custom-built 60 GHz platform along with a trace-driven emulator demonstrate OScan's remarkable throughput gain, up to 5×, compared with the state-of-the-art.

Current VR headsets are tethered to computers which limits mobility and poses a tripping hazard. Delivering VR content over a wireless link is challenging due to the high data rates and stringent time delivery requirements. Millimeter wave communication at 60 GHz (WiGig) can meet these requirements, but, it is unreliable due to blockages and beam misalignments. In this poster, we present an idea of using both WiFi and WiGig interfaces to transmit the VR content. We divide a video frame into tiles and prioritize the tiles in the user's field of view. Based on the wireless link conditions, the tiles are encoded with varying qualities and transmitted over either WiFi or WiGig interface. We formulate an optimization framework to deliver the VR video with high reliability and low latency.

60 GHz millimeter-wave networking has emerged as the next frontier technology to provide multi-Gbps wireless connectivity. However, the intrinsic directionality and limited field-of-view of 60 GHz antennas make the links extremely sensitive to user mobility and orientation change. Hence, seamless coverage, even at room level, becomes challenging. In this paper, we propose Pia, a robust 60 GHz network architecture that can provide seamless coverage and mobility support at multi-Gbps bitrate. Pia comprises multiple cooperating access points (APs). It leverages the pose information on mobile clients to proactively select the AP and manage multi-link spatial reuse. These decisions require a model of the pose/location of the APs and ambient reflectors. We address these challenges through a set of AP-pose sensing and compressive angle estimation algorithms that fuse the pose measurement with link quality measurement on the client. We have implemented Pia using commodity 60 GHz platforms. Our experiments show that Pia reduces the occurrence of link outage by 6.3x and improves the spatial sharing capacity by 76%, compared to conventional schemes that only use in-band information for adaptation.

Increasing popularity of mobile devices and upload-intensive applications is rapidly driving the uplink traffic demand in wireless LANs. Network MIMO (netMIMO) can potentially meet the demand by enabling concurrent uplink transmissions to an AP cluster (APC) comprised of multiple access points. NetMIMO's PHY-layer communication algorithms have been well explored, but the MAC-level signaling procedure remains an open issue: prior to uplink transmission, a group of clients must gain channel access, and ensure synchronization and channel orthogonality with each other. But such signaling is fundamentally challenging, because netMIMO clients tend to be widely distributed and may not even sense each other. In this paper, we introduce the first signaling protocol, called NURA, to meet the challenge. NURA clients employ a novel medium-access-signaling mechanism to realize group-based random access and synchronization, without disturbing ongoing uplink transmissions. The APC leverages a lightweight user-admission mechanism to group users with orthogonal channels (and hence high uplink capacity), without requiring costly channel-state feedback from all users. We have implemented NURA on a software-radio based netMIMO platform. Our experiments show that NURA is feasible, efficient, and can readily serve as the a priori signaling mechanism for distributed asynchronous netMIMO clients.

3D orientation tracking is an essential ingredient for many Internet-of-Things applications. Yet existing orientation tracking systems commonly require motion sensors that are only available on battery-powered devices. In this paper, we propose Tagyro, which attaches an array of passive RFID tags as orientation sensors on everyday objects. Tagyro uses a closed-form model to transform the run-time phase offsets between tags into orientation angle. To enable orientation tracking in 3D space, we found the key challenge lies in the imperfect radiation pattern of practical tags, caused by the antenna polarity, non-isotropic emission and electromagnetic coupling, which substantially distort phase measurement. We address these challenges by designing a set of phase sampling and recovery algorithms, which together enable reliable orientation sensing with 3 degrees of freedom. We have implemented a real-time version of Tagyro on a commodity RFID system. Our experiments show that Tagyro can track the 3D orientation of passive objects with a small error of 4°, at a processing rate of 37.7 samples per second.

Orientation tracking is an essential ingredient for many Internet-of-Things applications. In this work, we introduce Tagyro, which attaches an array of passive RFID tags as orientation sensors on everyday objects. Tagyro uses a closed-form model to transform the run-time phase offsets between tags into orientation angle, and addresses the unexpected deviation of phase measurement distorted by imperfect radiation pattern of practical tags. We have implemented a real-time version of Tagyro on a commodity RFID system. In this demo, we show that Tagyro can handle the phase distortion by sensing the effective layout tag array, an use the sensed layout to track the orientation of objects in high accuracy.

Leveraging the redundancy and parallelism from multiple RF chains, MIMO technology can easily scale wireless link capacity. However, the high power consumption and circuit-area cost prevents MIMO from being adopted by energy-constrained wireless devices. In this paper, we propose Halma, that can boost link capacity using multiple antennas but a single RF chain, thereby, consuming the same power as SISO. While modulating its normal data symbols, a Halma transmitter hops between multiple passive antennas on a per-symbol basis. The antenna hopping pattern implicitly carriers extra data, which the receiver can decode by extracting the index of the active antenna using its channel pattern as a signature.

Loudspeakers are widely used in conferencing and infotainment systems. Private information leakage from loudspeaker sound is often assumed to be preventable using sound-proof isolators like walls. In this paper, we explore a new acoustic eavesdropping attack that can subvert such protectors using radio devices. Our basic idea lies in an acoustic-radio transformation (ART) algorithm, which recovers loudspeaker sound by inspecting the subtle disturbance it causes to the radio signals generated by an adversary or by its co-located WiFi transmitter. ART builds on a modeling framework that distills key factors to determine the recovered audio quality. It incorporates diversity mechanisms and noise suppression algorithms that can boost the eavesdropping quality. We implement the ART eavesdropper on a software-radio platform and conduct experiments to verify its feasibility and threat level. When targeted at vanilla PC or smartphone loudspeakers, the attacker can successfully recover high-quality audio even when blocked by sound-proof walls. On the other hand, we propose several pragmatic countermeasures that can effectively reduce the attacker's audio recovery quality by orders of magnitude.

Radio-based passive-object sensing can enable a new form of pervasive user-computer interface. Prior work has employed various wireless signal features to sense objects under a set of predefined, coarse motion patterns. But an operational UI, like a trackpad, often needs to identify fine-grained, arbitrary motion. This paper explores the feasibility of tracking a passive writing object (e.g., pen) at sub-centimeter precision. We approach this goal through a practical design, mTrack, which uses highly-directional 60 GHz millimeter-wave radios as key enabling technology. mTrack runs a discrete beam scanning mechanism to pinpoint the object's initial location, and tracks its trajectory using a signal-phase based model. In addition, mTrack incorporates novel mechanisms to suppress interference from background reflections, taking advantage of the short wavelength of 60 GHz signals. We prototype mTrack and evaluate its performance on a 60 GHz reconfigurable radio platform. Experimental results demonstrate that mTrack can locate/track a pen with 90-percentile error below 8 mm, enabling new applications such as wireless transcription and virtual trackpad.

Poor scalability is a long standing problem in multi-user MIMO (MU-MIMO) networks: in order to select concurrent uplink users with strong channel orthogonality and thus high total capacity, channel state information (CSI) feedback from users is required. However, when the user population is large, the overhead from CSI feedback can easily overwhelm the actual channel time spent on data transmission. Moreover, due to spontaneous uplink traffic, uplink user selection cannot rely on the access point's central assignment and needs a distributed realization instead, which makes the problem even more challenging.

High-quality, speaker-location-aware audio capturing has traditionally been realized using dedicated microphone arrays. But high cost and lack of portability prevents such systems from being widely adopted. Today's smartphones are relatively more convenient for audio recording, but the audio quality is much lower in noisy environment and speaker location cannot be readily obtained. In this paper, we design and implement Dia, which leverages smartphone cooperation to overcome the above limitations. Dia supports spontaneous setup, by allowing a group of users to rapidly assemble an array of smartphones to emulate a dedicated microphone array. It employs a novel framework to accurately synchronize the audio I/O clocks of the smartphones. The synchronized smartphone array further enables autodirective audio capturing, i.e., tracking the speaker's location, and beamforming the audio capturing towards the speaker to improve audio quality. We implement Dia on a testbed consisting of 8 Android phones. Our experiments demonstrate that Dia can synchronize the microphones of different smartphones with sample-level accuracy. It achieves high localization accuracy, and similar beamforming performance compared with a microphone array with perfect synchronization.

In cognitive radio network, cooperation between primary users and secondary users can improve their data rate and achieve dynamic spectrum sharing. This paper proposes a novel spectrum sharing model to solve the opportunistic access problem in cooperative cognitive radio network (CCRN). In this model, primary users select sets of secondary users as their relays and allocate channel resource to secondary users according to their cooperative transmitting power. Secondary users have their own data rate requirement, and they have to determine their optimal relay power to satisfy their requirement. Primary users have to select the best relay group and maximize their throughput. We model this problem as a Stackelberg game and prove the existence and uniqueness of Nash Equilibrium. A low-complexity algorithm is proposed to realize the cooperative transmission mechanism. Simulation results show significant throughput enhancement in the primary network and more opportunities for secondary users to get access into the spectrum.