Visible Light Positioning (VLP) provides a promising means to achieve indoor localization with sub-meter accuracy. We observe that the Visible Light Communication (VLC) methods in existing VLP systems rely on intensity-based modulation, and thus they require a high pulse rate to prevent flickering. However, the high pulse rate adds an unnecessary and heavy burden to receiving devices. To eliminate this burden, we propose the polarization-based modulation, which is flicker-free, to enable a low pulse rate VLC. In this way, we make VLP light-weight enough even for resourceconstrained wearable devices, e.g. smart glasses. Moreover, the polarization-based VLC can be applied to any illuminating light sources, thereby eliminating the dependency on LED. This paper presents the VLP system PIXEL, which realizes our idea. In PIXEL, we develop three techniques, each of which addresses a design challenge: 1) a novel color-based modulation scheme to handle users’ mobility, 2) an adaptive downsampling algorithm to tackle the uneven sampling problem of wearables’ low-cost camera and 3) a computational optimization method for the positioning algorithm to enable real-time processing. We implement PIXEL’s hardware using commodity components and develop a software program for both smartphone and Google glass. Our experiments based on the prototype show that PIXEL can provide accurate realtime VLP for wearables and smartphones with camera resolution as coarse as 60 pixel 80 pixel and CPU frequency as low as 300MHz.

/pdf/wearables-can-afford-light-weight-indoor-positioning-with-54z10zkb1f.pdf

Wearables Can Afford: Light-weight Indoor Positioning with Visible Light (Best Paper Candidate, Best Video Presentation Award)

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.

https://dl.acm.org/doi/pdf/10.1145/3372224.3380892

M-Cube: a millimeter-wave massive MIMO software radio

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.

https://dl.acm.org/doi/pdf/10.1145/3241539.3241542

LiSteer: mmWave Beam Acquisition and Steering by Tracking Indicator LEDs on Wireless APs

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.

https://dl.acm.org/doi/pdf/10.1145/3241539.3241556

Multi-Stream Beam-Training for mmWave MIMO Networks

Millimeter-wave (mmWave) networking represents a core technology to meet the demanding bandwidth requirements of emerging connected vehicles. However, the feasibility of mmWave vehicle-to-everything (V2X) connectivity has long been questioned. One major doubt lies in how the highly directional mmWave links can sustain under high mobility. In this paper, we present the first comprehensive reality check of mmWave V2X networks. We deploy an experimental testbed to mimic a typical mmWave V2X scenario, and customize a COTS mmWave radio to enable microscopic investigation of the channel and the link. We further construct a high-fidelity 3D ray-tracer to reproduce the mmWave characteristics at scale. With this toolset, we study the mmWave V2X coverage, mobility and blockage, codebook/beam management, and spatial multiplexing. Our measurement debunks some common misperceptions of mmWave V2X networks. In particular, due to the constrained roadway network structures, we find the beam management can be handled easily by the often-denounced beam scanning schemes, as long as the codebook is properly designed. Blockage can be almost eliminated through proper basestation deployment and cooperation. Highly effective spatial multiplexing can be realized even without sophisticated MIMO radios. Our work points to possible ways to realize efficient and reliable mmWave networks under high mobility, while maintaining the simplicity of standard network protocols.

https://dl.acm.org/doi/pdf/10.1145/3372224.3419208

Demystifying millimeter-wave V2X: towards robust and efficient directional connectivity under high mobility

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-User Multi-Stream mmWave WLANs With Efficient Path Discovery and Beam Steering

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.

/pdf/search-light-tracking-device-mobility-using-indoor-183475l3oo.pdf

Search Light: Tracking Device Mobility using Indoor Luminaries to Adapt 60 GHz Beams

Overhead Constrained Joint Adaptation of MCS, Beamwidth and Antenna Sectors for 60 GHz WLANs with Mobile Clients

Wireless communication in mmWave bands with wide bandwidths and directional links is crucial for high data rate demands of future networks. A key challenge in mmWave networking is maintaining beam alignment under device mobility such as rotation or translation. We present LiSteer, a novel system which acquires and 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, and 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 custom hardware and simulation platforms shows LiSteer achieves direction estimates within 2.5 degrees of ground truth on average, and achieves beam steering accuracy of more than 97% while in tracking mode.

https://dl.acm.org/doi/pdf/10.1145/3264877.3264884

Muhammad Kumail Haider

Papers

Multi-Stream Beam-Training for mmWave MIMO Networks

Multi-User Multi-Stream mmWave WLANs With Efficient Path Discovery and Beam Steering

Search Light: Tracking Device Mobility using Indoor Luminaries to Adapt 60 GHz Beams

Overhead Constrained Joint Adaptation of MCS, Beamwidth and Antenna Sectors for 60 GHz WLANs with Mobile Clients

mmWave Beam Steering via Visible Light Sensing