Edward W. Knightly's research while affiliated with Rice University and other places

Publications (188)

Article
Multi-user transmission in 60 GHz Wi-Fi can achieve data rates up to 100 Gbps by multiplexing multiple user data streams. However, a fundamental limit in the approach is that each RF chain is limited to supporting one stream or one user. In this paper, we scale multi-user 60 GHz WLAN data rate by overcoming this limit and propose SI ngle RF chain M...
Presentation
Wireless Security in next-generation Wi-Fi networks
Preprint
Full-text available
Uncontrolled emissions of gases from industrial accidents and disasters result in huge loss of life and property. Such extreme events require a quick and reliable survey of the site for effective rescue strategy planning. To achieve these goals, a network of unmanned aerial vehicles can be deployed that survey the affected region and identify safe...
Article
Full-text available
We present FALCON, a novel autonomous drone network system for sensing, localizing, and approaching RF targets/sources such as smartphone devices. Potential applications of our system include disaster relief missions in which networked drones sense the Wi-Fi signal emitted from a victim’s smartphone and dynamically navigate to accurately localize a...
Article
Internet speed tests assess end-to-end network performance by measuring throughput for 10’s of MB of TCP uploads and downloads. While such tests provide valuable insights into network health, they are of little use to network administrators since (1) the results are only available on the client that performs the test and (2) the tests can saturate...
Conference Paper
Full-text available
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...
Article
In this article, we first investigate the quality of aerial air pollution measurements and characterize the main error sources of drone-mounted gas sensors. To that end, we build ASTRO+, an aerial-ground pollution monitoring platform, and use it to collect a comprehensive dataset of both aerial and reference air pollution measurements. We show that...
Article
Full-text available
In this paper, we present WACA, the first system to simultaneously measure all 24 Wi-Fi channels that allow channel bonding at 5 GHz with microsecond scale granularity. With WACA, we perform a first-of-its-kind measurement study in areas including urban hotspots, residential neighborhoods, universities, and even a game in Futbol Club Barcelona's Ca...
Article
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 p...
Article
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 a...
Article
In this paper, we present the first cross-layer analysis of wireless LANs operating under downlink multi-user multi-in multi-out (MU-MIMO), considering the fundamental role played by the closed-loop (TCP) traffic. In particular, we consider a scenario in which the access point transmits on the downlink via MU-MIMO, whereas stations must employ sing...
Article
Channel state information (CSI) has been proposed to enhance physical layer security by functioning as a shared secret between a transmitter and a receiver, because it decorrelates over half wavelength distances and cannot be predicted based on locations of the transmitter and receiver in rich scattering environments. Consequently, CSI was employed...
Article
Full-text available
Multiuser 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 article, we...
Conference Paper
Full-text available
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 oo-the-shelf light sensors. We demonstrate that LiSteer maintains beam alignment at the narrowest beamwidth level even in case of device mobility, without incurrin...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
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...
Article
Accurate Channel State Information (CSI) is a key requirement for Massive Multiple-Input Multiple-Output (MIMO) to achieve multi-fold increases in throughput and secrecy rate. Consequently, an adversary targeting the channel sounding process has the potential to significantly degrade performance. In this paper, we first present and model the Pilot...
Conference Paper
We present iTrack, a system which steers mmWave beams at mobile devices by tracking the indicator LEDs on wireless APs to passively acquire direction estimates, and demonstrate that iTrack acquires and maintains beam alignment at the narrowest beamwidth level even in case of device mobility, without incurring any training overhead. Our implementati...
Article
Full-text available
The IEEE 802.11ad amendment to the 802.11 standard ratified in 2012 created the first multi-Gb/s Wi-Fi technology by using the large swath of unlicensed spectrum at the mm-Wave band. While enabling multi-Gb/s wireless local communications was a significant achievement, throughput and reliability requirements of new applications, such as augmented r...
Article
While 802.11 Access Points (APs) can have as many as eight antennas, form factor constraints often limit mobile clients to a single antenna, thereby precluding spatial multiplexing. In this paper, we design, implement, and experimentally evaluate Diverse Spectrum Spatial Multiplexing (DSSM), the first system to enable 802.11 standard-compliant upli...
Conference Paper
Channel State Information (CSI) has been proposed to enhance physical layer security between a transmitter and a receiver because it decorrelates over half wavelength distances in rich scattering environments. Consequently, CSI was employed to generate passwords, to authenticate the source of packets, and to inject artificial noise to thwart eavesd...
Conference Paper
Full-text available
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 s...
Conference Paper
While 802.11 Access Points (APs) can have as many as eight antennas, form factor constraints often limit mobile clients to a single antenna, thereby precluding spatial multiplexing. In this paper, we design, implement, and experimentally evaluate Diverse Spectrum Spatial Multiplexing (DSSM), the first system to enable uplink spatial multiplexing fo...
Article
The “white space” model allows TV channels not being used regionally by a TV broadcaster to be re-purposed for secondary access. Unfortunately, populated areas have few unused channels. Nonetheless, Nielsen data show severe under-utilization with vast regions in range of TV transmitters having no active TV receivers even at peak TV viewing time....
Conference Paper
High directivity of 60 GHz links introduces new link training and adaptation challenges due to both client and environmental mobility. In this paper, we design, implement and evaluate MOCA, a protocol for Mobility resilience and Overhead Constrained Adaptation for directional 60 GHz links. Since mobility-induced link blockage and misalignment canno...
Conference Paper
Full-text available
Mobile devices have fewer antennas than APs due to size and energy constraints. This antenna asymmetry restricts uplink capacity to the client antenna array size rather than the AP's. To overcome antenna asymmetry, multiple clients can be grouped into a simultaneous multiuser transmission to achieve a full rank transmission that matches the number...
Conference Paper
Today's "white space" model of spectrum sharing applied in the UHF TV band allows channels that are not being used regionally by a TV broadcaster to be re-purposed for unlicensed-style secondary access in 24 hour increments. Unfortunately, populated areas have few unused channels for white space usage. Nonetheless, from the UHF TV viewer's perspect...
Conference Paper
Full-text available
Millimeter-wave communication achieves multi-Gbps data rates via highly directional beamforming to overcome pathloss and provide the desired SNR. Unfortunately, establishing communication with sufficiently narrow beamwidth to obtain the necessary link budget is a high overhead procedure in which the search space scales with device mobility and the...
Article
Congestive heart failure (CHF) is a chronic medical condition, and early detection of acute cardiac events caused by CHF can lead to life saving results. In this paper, we present Blue Scale, a measuring device that allows both patients and their physicians to monitor cardiac health at home on a daily basis by providing the necessary feedback for e...
Article
In this paper, we present the design, implementation, and evaluation of the novel downlink Multi-User MIMO sounding protocol called MUTE. Our protocol decouples the sounding set selection used to collect Channel State Information (CSI), from the transmission set selection in order to minimize or even eliminate the overhead associated with sounding,...
Conference Paper
Full-text available
In this paper, we propose " Virtual Duplex, " a wireless architecture which, like Frequency Division Duplex (FDD), divides spectrum resources into two sub-bands. However, in contrast to FDD, both bands in Virtual Duplex are physically bi-directional, and transmissions are allocated to the bands according to whether they correspond to download or up...
Article
Full-text available
With the ratification of the IEEE 802.11ad amendment to the 802.11 standard in December 2012, a major step has been taken to bring consumer wireless communication to the millimeter wave band. However, multi-gigabit-per-second throughput and small interference footprint come at the price of adverse signal propagation characteristics, and require a f...
Article
While the UHF band exhibits superior propagation characteristics compared to other frequency bands used for broadband communications, limited spectral availability in time and space necessitates high spectral efficiency techniques such as Multi-user MIMO (MU-MIMO). In this paper we design and implement the first open MU-MIMO Software-Defined Radio...
Article
We present a real-time software-defined radio (SDR) platform for prototyping and measuring the performance of broadband UHF radio networks operating over long distances with point-to-multipoint (PTMP) non-line-of-sight (NLOS) networks. Enabled by the Wideband UHF Radio Card (WURC), a custom high-power and frequency-flexible radio transceiver daught...
Article
Full-text available
Spectrum today is allocated in frequency blocks that serve either licensed or unlicensed services. This static spectrum allocation has limited resources to support the exponential increase in wireless devices. In this article, we present the IEEE 802.11af standard, which defines international specifications for spectrum sharing among unlicensed whi...
Article
The IEEE 802.11ac amendment has been proposed to enhance the throughput of IEEE 802.11n beyond gigabit-per-second rates. In this article we present an overview of the most important features proposed in the 802.11ac amendment, including channel bonding mechanisms and multi-user MIMO.
Article
Full-text available
Wireless networks increasingly utilize diverse spectral bands that exhibit vast differences in both transmission range and usage. In this work, we present MAWS (Mobile Access of Wide-Spectrum Networks), the first scheme designed for mobile clients to evaluate and select both APs and spectral bands in wide-spectrum networks. Because of the potential...
Conference Paper
Virtual Multiple-Input Single-Output (vMISO) systems distribute multi-antenna diversity capabilities between a sending and a cooperating node. vMISO has the potential to vastly improve wireless link reliability and bit error rates by exploiting spatial diversity. In this paper, we present the first design and experimental evaluation of vMISO trigge...
Article
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) has been adopted by the IEEE 802.11 standard and provides good performance when all transmitters are within the range of each other. Unfortunately, in multi-hop topologies, the asymmetric view of the channel state leads to a throughput distribution where a few flows may capture all th...
Article
In 802.11 managed wireless networks, the manager can address underserved links by rate-limiting the conflicting nodes. In order to determine to what extent each conflicting node is responsible for the poor performance, the manager needs to understand the coordination among conflicting nodes' transmissions. In this paper, we present a management fra...
Article
In this paper, we design, implement and evaluate 802.11ec (Encoded Control), an 802.11-based protocol without control messages: instead, 802.11ec employs correlatable symbol sequences, which together with the timing the codes are transmitted, encode all control information and change the fundamental design properties of the MAC. The use of correlat...
Article
Full-text available
This paper proposes a new protocol called Optimal DCF (O-DCF). Inspired by a sequence of analytic results, O-DCF modifies the rule of adapting CSMA parameters, such as backoff time and transmission length, based on a function of the demand-supply differential of link capacity captured by the local queue length. Unlike clean-slate design, O-DCF is f...
Article
The FCC ruled in September 2010 that unused UHF TV channels could be repurposed for unlicensed wireless Internet, a capability often termed "Super WiFi" because UHF bands have much greater range compared to today's GHz WiFi. Yet with so many channels used for TV in populated areas, few and sometimes none are left over in urban areas, severely hinde...
Conference Paper
We present a novel modeling approach to derive closed-form throughput expressions for CSMA networks with hidden terminals. The key modeling principle is to break the interdependence of events in a wireless network using conditional expressions that capture the effect of a specific factor each, yet preserve the required dependences when combined tog...
Article
Full-text available
We present the design and implementation of ADAM, the first adaptive beamforming based multicast system and experimental framework for indoor wireless environments. ADAM addresses the joint problem of adaptive beamformer design at the PHY layer and client scheduling at the MAC layer by proposing efficient algorithms that are amenable to practical i...
Article
We present the design and experimental evaluation of Simultaneous TRansmission with Orthogonally Blinded Eavesdroppers (STROBE). STROBE is a cross-layer approach that exploits the multi-stream capabilities of existing technologies such as 802.11n and the upcoming 802.11ac standard where multi-antenna APs can construct simultaneous data streams usin...
Conference Paper
Full-text available
Visible Light Communication (VLC) is a fast-growing technology to provide data communication using low-cost and omni-present LEDs and photodiodes. In this paper, we examine the key proper-ties in enabling vehicular VLC (V2LC) networks as follows. We first develop a custom V2LC research platform on which we expe-rimentally evaluate the feasibility o...
Conference Paper
Full-text available
By `optimal CSMA' we denote a promising approach to maximize throughput-based utility in wireless networks without message passing or synchronization among nodes. Despite the theoretical guarantees on the performance of these protocols, their evaluation in real networking scenarios has been preliminary. In this paper, we propose a methodical approa...
Conference Paper
Full-text available
In 802.11 managed wireless networks, the manager can address under-served links by rate-limiting the conflicting nodes. In order to determine to what extent each conflicting node is responsible for the poor performance, the manager needs to understand the coordination among conflicting nodes' transmissions. In this paper, we present a management fr...
Article
We have deployed a large-scale multi-tier wireless network in one of Houston's most economically disadvantaged neigh-borhoods. The network serves two objectives: empowering under-resourced communities with access to technology, ed-ucation and work-at-home tools, and providing an unprece-dented platform for research of wireless communication tech-no...
Conference Paper
In this paper, we present WARPLab, a framework for the rapid prototyping and implementation of physical layer algorithms for wireless LANs. WARPLab is based on WARP, an FPGA-based, wireless experimental platform. We first give an overview of WARPLab and then present an example of a physical layer algorithm that we implemented on the framework for o...
Conference Paper
Full-text available
Multi-User MIMO promises to increase the spectral efficiency of next generation wireless systems and is currently being incorporated in future industry standards. Although a significant amount of research has focused on theoretical capacity analysis, little is known about the performance of such systems in practice. In this paper, we present the de...
Conference Paper
Full-text available
IEEE 802.11-based mesh networks can yield a throughput distribution among nodes that is spatially biased, with traffic originating from nodes that directly communicate with the gateway obtaining higher throughput than all other upstream traffic. In particular, if single-hop nodes fully utilize the gateway's resources, all other nodes communicating...
Conference Paper
In this paper, we consider routing in multi-hop wireless mesh networks. We analyze three standardized and commonly deployed routing mechanisms that we term "node-pair discovery" primitives. We show that use of these primitives inherently yields inferior route selection, irrespective of the protocol that implements them. This behavior originates due...
Article
Full-text available
Significant progress has been made in understanding the behavior of TCP and congestion-controlled traffic over CSMA-based multihop wireless networks. Despite these advances, however, no prior work identified severe throughput imbalances in the basic scenario of mesh networks, in which a one-hop flow contends with a two-hop flow for gateway access....
Conference Paper
A class of CSMA protocols used in a broad range of wireless applications uses synchronized contention where nodes periodically contend at intervals of fixed duration. While several models exist for asynchronous CSMA contention used in protocols like IEEE 802.11 MAC, no model exists for synchronized CSMA contention that also incorporates realistic f...
Article
Countering distributed denial of service (DDoS) attacks is becoming ever more challenging with the vast resources and techniques increasingly available to attackers. In this paper, we consider sophisticated attacks that are protocol-compliant, non-intrusive, and utilize legitimate application-layer requests to overwhelm system resources. We charact...
Conference Paper
Full-text available
Accurately selecting modulation rates for time-varying channel conditions is critical for avoiding performance degradations due to rate overselection when channel conditions degrade or underselection when channel conditions improve. In this paper, we design a custom cross-layer framework that enables: 1) implementation of multiple and previously un...
Conference Paper
In order to evaluate, improve, or expand a deployed, city- wide wireless mesh network, it is necessary to assess the network's spatial performance. In this paper, we present a general framework to accurately predict a network's well- served area, termed the metric region, via a small number of measurements. Assessment of deployed networks must ad-...
Conference Paper
Full-text available
Previous work has shown that CSMA-based protocols such as the IEEE 802.11 can yield flow starvation in multi-hop wireless networks. While prior protocol designs alleviated such starvation by utilizing MIMO, they require global synchronization to temporally align transmissions and require per-packet distribution of the complete channel state informa...
Article
Multi-hop wireless networks employing random access protocols have been shown to incur large discrepancies in the throughputs achieved by the flows sharing the network. Indeed, flow throughputs can span orders of magnitude from near starvation to many times greater than the mean. In this paper, we address the foundations of this disparity. We show...
Article
Significant progress has been made towards making ad hoc networks secure and DoS resilient. However, little attention has been focused on quantifying DoS resilience: Do ad hoc networks have sufficiently redundant paths and counter-DoS mechanisms to make DoS attacks largely ineffective? Or are there attack and system factors that can lead to devasta...
Article
Full-text available
Today, municipalities are planning to deploy metro-scale two-tier wireless mesh networks at a rapid pace. Fittingly, the IEEE 802.11s standard is being developed to allow interoperability between heterogeneous mesh network devices. In this article we describe and discuss how the initial standard addresses key factors for standardization of these ne...
Conference Paper
Full-text available
Deployments of city-wide multi-hop 802.11 networks intro- duce challenges for maintaining client performance at vehic- ular speeds. We experimentally demonstrate that current network interfaces employ policies that result in long out- age durations, even when clients are always in range of at least one access point. Consequently, we design and eval...
Conference Paper
Full-text available
Significant progress has been made in understanding the behavior of TCP and congestion-controlled traffic over multi- hop wireless networks. Despite these advances, however, no prior work identified severe throughput imbalances in the basic scenario of mesh networks, in which one-hop flows contend with two-hop flows for gateway access. In this pape...
Conference Paper
Full-text available
In this paper, we perform an extensive measurement study on a multi-tier mesh network serving 4,000 users. Such dense mesh deployments have high levels of interaction across heterogeneous wireless links. We find that this heterogeneous backhaul consisting of data-carrying (forwarding) links and non- data-carrying (non-forwarding) links creates two...
Conference Paper
Full-text available
This paper addresses channel assignment and random medium access design for single-radio multi-channel mesh networks. Two prior approaches include: (i) designing MAC protocols that dynamically select channels based on local information and (ii) partitioning the mesh into subnetworks with different channels and using 802.11 as the medium access prot...