R-3 Repository :: Browsing by Author "Knightly, Edward W."

Browsing by Author "Knightly, Edward W."

Now showing 1 - 20 of 70

A Matter of Perspective: Reliable Communication and Coping with Interference with Only Local Views
(2012-09-05) Kao, David; Sabharwal, Ashutosh; Aazhang, Behnaam; Knightly, Edward W.; Tapia, Richard A.; Chiang, Mung
This dissertation studies interference in wireless networks. Interference results from multiple simultaneous attempts to communicate, often between unassociated sources and receivers, preventing extensive coordination. Moreover, in practical wireless networks, learning network state is inherently expensive, and nodes often have incomplete and mismatched views of the network. The fundamental communication limits of a network with such views is unknown. To address this, we present a local view model which captures asymmetries in node knowledge. Our local view model does not rely on accurate knowledge of an underlying probability distribution governing network state. Therefore, we can make robust statements about the fundamental limits of communication when the channel is quasi-static or the actual distribution of state is unknown: commonly faced scenarios in modern commercial networks. For each local view, channel state parameters are either perfectly known or completely unknown. While we propose no mechanism for network learning, a local view represents the result of some such mechanism. We apply the local view model to study the two-user Gaussian interference channel: the smallest building block of any interference network. All seven possible local views are studied, and we find that for five of the seven, there exists no policy or protocol that universally outperforms time-division multiplexing (TDM), justifying the orthogonalized approach of many deployed systems. For two of the seven views, TDM-beating performance is possible with use of opportunistic schemes where opportunities are revealed by the local view. We then study how message cooperation --- either at transmitters or receivers --- increases capacity in the local view two-user Gaussian interference channel. The cooperative setup is particularly appropriate for modeling next-generation cellular networks, where costs to share message data among base stations is low relative to costs to learn channel coefficients. For the cooperative setting, we find: (1) opportunistic approaches are still needed to outperform TDM, but (2) opportunities are more abundant and revealed by more local views. For all cases studied, we characterize the capacity region to within some known gap, enabling computation of the generalized degrees of freedom region, a visualization of spatial channel resource usage efficiency.
A performance study of deployment factors in wireless mesh networks
(2007) Robinson, Joshua; Knightly, Edward W.
This thesis presents a measurement-parameterized performance study of deployment factors in wireless mesh networks using four performance metrics: client coverage area, backhaul tier connectivity, protocol-dependent throughput, and per-user fair rates. For each metric, I identify and study deployment factors which strongly influence mesh performance via an extensive set of Monte Carlo simulations capturing realistic physical layer behavior. My findings include: (i) A random topology is unsuitable for a large-scale mesh deployment due to doubled node density requirements, yet a moderate level of perturbations from ideal grid placement has minor impact. (ii) Multiple backhaul radios per mesh node is a cost-effective deployment strategy as it leads to mesh deployments costing 50% less than with a single-radio architecture. This work adds to the understanding of mesh deployment factors and their general impact on performance, providing further insight into practical mesh deployments.
A study of opportunistic relaying MAC protocol
(2005) Chawathe, Rahul; Knightly, Edward W.
Recent studies have shown a considerable interest in the development of Medium Access and Control (MAC) protocols for multi-rate wireless networks. The approach of sending the packet to the farthest possible node along the route does not maximize the performance unlike in the case of single-rate wireless networks. The scheme of sending the packet always to the neighbor with best channel quality also does not give the best network throughput. This thesis proposes to exploit the diversity in channel qualities by presenting an Opportunistic Relaying Protocol (ORP) for stationary topologies. Given a route in the form of possible choices for next hops and given the knowledge of the corresponding link channel qualities, we propose to choose the path that minimizes the net transmission delay of the packet. We perform an extensive simulation study of our protocol and present general guidelines in the design of a multi-rate MAC protocol.
Admission control in multi-service wireless networks
(1999) Jain, Rahul; Knightly, Edward W.
Supporting Quality of Service (QoS) in mobile networks requires that admission control algorithms incorporate user mobility, and limit the probability that sufficient resources are unavailable when a user must handoff. In this thesis, we develop a framework for designing such admission control algorithms, and using this framework design an admission control algorithm for coarse-grained control of system QoS. We first devise a taxonomy to explore the mathematical structure and practical design tradeoffs encountered in developing admission control algorithms. We next introduce the Perfect Knowledge Admission Control Algorithm, which, while unrealizable in practice, serves as a benchmark for evaluating admission control algorithms by using knowledge of future handoff events to exactly control the admissible region. Third, we present an extensive set of simulations (including trace-driven simulations) and, identify a number of key system parameters for algorithm design, and quantify the fundamental tradeoffs in complexity and accuracy as revealed by the taxonomy. Finally, we introduce a novel coarse grained approach to admission control termed Virtual Bottleneck Cell, which is not only scalable, has low overhead, but also is able to provision QoS in "hot spots" and system bottlenecks. The approach's novelty lies in hierarchical control of the system, without requiring any mobility models or accurate predictions of the users' future locations.
Architecture and algorithms for scalable mobile QoS
(2000) Sadeghi, Bahareh; Knightly, Edward W.
Supporting Quality of Service is an important objective for future mobile systems, and requires resource reservation and admission control to achieve. In this thesis, we introduce a scalable scheme to admission control termed Virtual Bottleneck Cell. Our approach is designed to scale to many users and hand-offs, while simultaneously controlling "hot spots". The key technique is to hierarchically control the virtual system, ensuring QoS objectives are satisfied without requiring accurate predictions of the users' future locations. We develop a simple analytical model to study the system and illustrate several key components of the approach. We formulate the problem of how to group the cells to form the virtual system as an optimization problem and propose a heuristic adaptive clustering algorithm as its solution. Finally, we perform simulations in a two-dimensional network to compare the performance obtained with VBC and adaptive clustering with alternate schemes, including the optimal offline algorithm.
Argos: Practical Base Stations for Large-scale Beamforming
(2012-09-05) Shepard, Clayton; Zhong, Lin; Knightly, Edward W.; Sabharwal, Ashutosh
MU-MIMO theory predicts manyfold capacity gains by leveraging many antennas (e.g. M >> 10) on wireless base stations to serve many users simultaneously through multi-user beamforming (MUBF). However, realizing such a large-scale design is nontrivial, and has yet to be achieved in the real world. We present the design, realization, and evaluation of Argos, the first reported large-scale base station that is capable of serving many (e.g., 10s of) terminals simultaneously through MUBF. Designed with extreme flexibility and scalability in mind, Argos exploits hierarchical and modular design principles, properly partitions baseband processing, and holistically considers real-time requirements of MUBF. To achieve unprecedented scalability, we devise a novel, completely distributed, beamforming technique, as well as an internal calibration procedure to enable implicit beamforming across large arrays. We implement a prototype with 64 antennas, and demonstrate that it can achieve up to 6.7 fold capacity gains while using a mere 1/64th the transmission power.
Audio misinformation encoding via an on-phone sub-terahertz metasurface
(Optica Publishing Group, 2024) Shaikhanov, Zhambyl; Al-Madi, Mahmoud; Chen, Hou-Tong; Chang, Chun-Chieh; Addamane, Sadhvikas; Mittleman, Daniel M.; Knightly, Edward W.
We demonstrate a wireless security application to protect the weakest link in phone-to-phone communication, using a terahertz metasurface. To our knowledge, this is the first example of an eavesdropping countermeasure in which the attacker is actively misled.
Augmenting Wireless Security Using Zero-Forcing Beamforming
(2011) Anand, Narendra; Knightly, Edward W.
We present the design and experimental evaluation of Simultaneous TRansmissions 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 construct simultaneous data streams using Zero-Forcing Beamforming (ZFBF). Instead of using this technique for simultaneous data stream generation, STROBE utilizes ZFBF by allowing an AP to use one stream to communicate with an intended user and the remaining streams to orthogonally "blind" (actively interfere) with any potential eavesdropper thereby preventing eavesdroppers from decoding nearby transmissions. Through extensive experimental evaluation, we show that STROBE reliably outperforms Omnidirectional, Single-User Beamforming (SUBF), and directional antenna based transmission methods by keeping the transmitted signal at the intended receiver and shielded from eavesdroppers. In an indoor Wireless LAN environment, STROBE consistently serves an intended user with a signal 15 dB stronger than an eavesdropper.
Beyond Interference Avoidance: Distributed Sun-network Scheduling in Wireless Networks with Local Views
(2013-09-16) Santacruz, Pedro; Sabharwal, Ashutosh; Aazhang, Behnaam; Knightly, Edward W.; Hicks, Illya V.
In most wireless networks, nodes have only limited local information about the state of the network, which includes connectivity and channel state information. With limited local information about the network, each node’s knowledge is mismatched; therefore, they must make distributed decisions. In this thesis, we pose the following question - if every node has network state information only about a small neighborhood, how and when should nodes choose to transmit? While link scheduling answers the above question for point-to-point physical layers which are designed for an interference-avoidance paradigm, we look for answers in cases when interference can be embraced by advanced code design, as suggested by results in network information theory. To make progress on this challenging problem, we propose two constructive distributed algorithms, one conservative and one aggressive, which achieve rates higher than link scheduling based on interference avoidance, especially if each node knows more than one hop of network state information. Both algorithms schedule sub-networks such that each sub-network can employ advanced interference-embracing coding schemes to achieve higher rates. Our innovation is in the identification, selection and scheduling of sub-networks, especially when sub-networks are larger than a single link. Using normalized sum-rate as the metric of network performance, we prove that the proposed conservative sub-network scheduling algorithm is guaranteed to have performance greater than or equal to pure coloring-based link scheduling. In addition, the proposed aggressive sub-network scheduling algorithm is shown, through simulations, to achieve better normalized sum-rate than the conservative algorithm for several network classes. Our results highlight the advantages of extending the design space of possible scheduling strategies to include those that leverage local network information.
Context in Mobile System Design: Characterization, Theory, and Implications
(2012-09-05) Rahmati, Ahmad; Zhong, Lin; Knightly, Edward W.; Sabharwal, Ashutosh; Kortum, Philip
Context information brings new opportunities for efficient and effective applications and services on mobile devices. Many existing work exploit the context dependency of mobile usage for specific applications, and show significant, quantified, performance gains by utilizing context. In order to be practical, such works often pay careful attention to the energy and processing costs of context awareness while attempting to maintain reasonable accuracy. These works also have to deal with the challenges of multiple sources of context, which can lead to a sparse training data set. Even with the abundance of such work, quantifying context-dependency and the relationship between context-dependency and performance achievements remains an open problem, and solutions to manage the and challenges of context awareness remain ad-hoc. To this end, this dissertation methodologically quantifies and measures the context dependency of three principal types of mobile usage in a methodological, application agnostic yet practical manner. The three usages are the websites the user visits, the phone numbers they call, and the apps they use, either built-in or obtained by the user from the App Store . While this dissertation measures the context dependency of these three principal types of mobile usage, its methodology can be readily extended to other context-dependent mobile usage and system resources. This dissertation further presents SmartContext, a framework to systematically optimize the energy cost of context awareness by selecting among different context sources, while satisfying the system designer’s cost-accuracy tradeoffs. Finally, this thesis investigates the collective effect of social context on mobile usage, by separating and comparing LiveLab users based on their socioeconomic groups. The analysis and findings are based on usage and context traces collected in real-life settings from 24 iPhone users over a period of one year. This dissertation presents findings regarding the context dependency of three principal types of mobile usage; visited websites, phone calls, and app usage. The methodology and lessons presented here can be readily extended to other forms of context and context-dependent usage and resources. They guide the development of context aware systems, and highlight the challenges and expectations regarding the context dependency of mobile usage.
Cooperative Strategies for Near-Optimal Computation in Wireless Networks
(2013-07-24) Nokleby, Matthew; Aazhang, Behnaam; Sabharwal, Ashutosh; Knightly, Edward W.; Damjanovic, Danijela
Computation problems, such as network coding and averaging consen- sus, have become increasingly central to the study of wireless networks. Network coding, in which intermediate terminals compute and forward functions of others’ messages, is instrumental in establishing the capacity of multicast networks. Averaging consensus, in which terminals compute the mean of others’ measurements, is a canonical building block of dis- tributed estimation over sensor networks. Both problems, however, are typically studied over graphical networks, which abstract away the broad- cast and superposition properties fundamental to wireless propagation. The performance of computation in realistic wireless environments, there- fore, remains unclear. In this thesis, I seek after near-optimal computation strategies under realistic wireless models. For both network coding and averaging con- sensus, cooperative communications plays a key role. For network cod- ing, I consider two topologies: a single-layer network in which users may signal cooperatively, and a two-transmitter, two-receiver network aided by a dedicated relay. In the former topology, I develop a decode-and- forward scheme based on a linear decomposition of nested lattice codes. For a network having two transmitters and a single receiver, the proposed scheme is optimal in the diversity-multiplexing tradeo↵; otherwise it pro- vides significant rate gains over existing non-cooperative approaches. In the latter topology, I show that an amplify-and-forward relay strategy is optimal almost everywhere in the degrees-of-freedom. Furthermore, for symmetric channels, amplify-and-forward achieves rates near capacity for a non-trivial set of channel gains. For averaging consensus, I consider large networks of randomly-placed nodes. Under a path-loss wireless model, I characterize the resource de- mands of consensus with respect to three metrics: energy expended, time elapsed, and time-bandwidth product consumed. I show that existing con- sensus strategies, such as gossip algorithms, are nearly order optimal in the energy expended but strictly suboptimal in the other metrics. I propose a new consensus strategy, tailored to the wireless medium and cooperative in nature, termed hierarchical averaging. Hierarchical averaging is nearly order optimal in all three metrics for a wide range of path-loss exponents. Finally, I examine consensus under a simple quantization model, show- ing that hierarchical averaging achieves a nearly order-optimal tradeo↵ between resource consumption and estimation accuracy.
Coordination and Interference in 802.11 Networks: Inference, Analysis and Mitigation
(2013-09-16) Magistretti, Eugenio; Knightly, Edward W.; Gurewitz, Omer; Johnson, David B.; Sabharwal, Ashutosh
In the last decade, 802.11 wireless devices data-rates have increased by three orders of magnitude, while communications experiencing low throughput are still largely present. Such throughput loss is a fundamental problem of wireless networking that is difficult to diagnose and amend. My research addresses two key causes of throughput loss: MAC layer protocol overhead and destructive link interference. First, I design WiFi-Nano reducing the channel access overhead by an order of magnitude leveraging an innovative speculative technique to transmit preambles. This new concept is based on simultaneous preamble transmission and detection via a self-interference cancellation design, and paves the way to the realization of the collision detection paradigm in wireless networks. Next, I propose 802.11ec (Encoded Control), the first 802.11-based protocol that eliminates the overhead of control packets. Instead, 802.11ec coordinates node transmissions via a set of predefined pseudo-noise codewords, resulting in the dramatic increase of throughput and communication robustness. Finally, I design MIDAS, a model-driven network management tool that alleviates low throughput wireless links identifying key corrective actions. MIDAS' key contribution is to reveal the fundamental role of node transmission coordination in characterizing destructive interference. I implement WiFi-Nano, 802.11ec, and MIDAS using a combination of WARP FPGA-based radio boards, custom emulation platforms, and network simulators. The results obtained show that WiFi-Nano increases the network throughput by up to 100%, 802.11ec improves network access fairness by up to 90%, and MIDAS identifies corrective actions with a prediction error as low as 20%.
Curving sub-THz Wireless Links around Obstacles
(2023-11-30) Zhao, Bin; Knightly, Edward W.
A key challenge in millimeter-wave and terahertz wireless networks is the blockage of the line-of-sight path between a base station and a user. Blockage of highly directional beams by intervening people or objects can lead to link disruptions and poor quality of service. In this thesis, we propose a solution to this problem that leverages self-accelerating beams that propagate along curved trajectories for link maintenance. To achieve this, we propose the design of a metasurface and a phase plate capable of spatially modulating the incident wavefront, thereby generating these curved beams. We develop a model to analyze and experimentally evaluate the bandwidth limitations imposed by the use of curved beams. We experimentally demonstrate that curved beams suffer fewer power losses compared to steered directional beams and can realize a data-carrying link by curving around an intervening obstacle. These results show that trajectory engineering of wavefronts will be an important tool in future physical layer implementations and open vast new possibilities for wavefront management in Next-Gen wireless communication systems.
Deployment and assessment of wireless mesh networks
(2009) Robinson, Joshua; Knightly, Edward W.
Multi-tier wireless mesh network deployments are a popular, cost-effective means to provide wireless broadband connectivity to neighborhoods and cities. Client devices within the coverage area of a mesh network connect wirelessly to fixed mesh nodes, which then forward traffic directly or via multi-hop paths to capacity injection points. The small number of capacity points act as Internet gateways and reduce overall network cost by limiting the amount of costly wired infrastructure needed. Non-uniform wireless signal propagation and the contention caused by multi-hop traffic contribute the challenge of deploying mesh networks with both high performance and low cost. This dissertation presents and evaluates cost-efficient algorithms for deployment planning and measurement-based assessment of wireless mesh networks. The mesh node placement problem requires mesh nodes to provide ubiquitous network coverage to clients, as well as connectivity amongst mesh nodes. The first contribution of this thesis is to present a graph-theoretic formulation of the NP-hard mesh node placement problem. This is the first formulation which considers the case in outdoor networks where signal propagation is non-uniform and enables the design of graph-theoretic approximation algorithms in order to minimize the deployment size or average contention. Secondly, deployment planning must select locations for the placement of capacity points, as their locations determine the path lengths in the networks and the resulting capacity available to transmit data to and from the Internet. To choose capacity point locations, I first present a technique to efficiently calculate network capacity and then two local search algorithms adapted from solutions to the facility location problem. Third, this thesis presents a framework for the measurement-based verification of a deployed network's performance. To avoid relying on expensive and exhaustive measurement studies, I consider the assessment problem with a limited number of measurements. The framework uses terrain-informed estimation, per-node virtual sectorization, and measurement refinement to accurately predict the network's performance at any given location. I evaluate the presented algorithms on realistic network topologies and with a large-scale measurement study of two currently deployed mesh networks: the TFA network and GoogleWiFi network. The thesis results demonstrate the essential nature of incorporating measurements, realistic propagation, and wireless contention into mesh network planning and assessment techniques.
Design and analysis of opportunistic fair downlink schedulers
(2004) Liu, Yonghe; Knightly, Edward W.
Scarce spectrum has been the impeding force for satisfying users' exploding appetite for anywhere, anytime connectivity. Efficient utilization of the scarce resource while providing high quality of service thus is the main challenge for protocol design over wireless networks. Unfortunately, traditional wireline designs, by assuming constant quality channels, often fail in satisfying these objectives when facing lossy and time varying wireless channels. This thesis develops a class of intelligent media access control algorithms that exploits the adaptation capability of underlying physical layer. Particularly, we design opportunistic schedulers to enable the potential gain on channel diversity among multiple users while satisfying provable weighted fairness. Our key technique in designing these schedulers is to jointly exploit the temporal variations in the resource consumption of multiple users to opportunistically select those with greater throughput potential, while also ensuring that fairness constraints are satisfied. First, we design and analyze Wireless Credit-based Fair Queueing (WCFQ), an opportunistic wireless scheduler targeting at multiple access schemes that are based on single-user-at-a-time. We show that WCFQ satisfies provable long- and short-term probabilistic fairness guarantee while significantly improving system throughput. Second, we extend our system model to exploit concurrent scheduling where multiple users can access the system simultaneously. We design MFS-D and MFS-P, a Multichannel Fair Scheduler with Deterministic and Probabilistic fairness constraints respectively. Finally, we perform a comparison between single and multiple channel scheduling. Particularly, we investigate the fundamental capacity of the system given fairness constraints and limitations from underlying physical layer. Through theoretical and numerical investigations we show that multiple channel scheduling may have significant gain over single channel scheduling in certain scenarios.
Design and Evaluation of Primitives for Passive Link Assessment and Route Selection in Static Wireless Networks
(2012-09-05) Miskovic, Stanislav; Knightly, Edward W.; Johnson, David B.; Sabharwal, Ashutosh
Communication in wireless networks elementally comprises of packet exchanges over individual wireless links and routes formed by these links. To this end, two problems are fundamental: assessment of link quality and identification of the least-cost (optimal) routes. However, little is known about achieving these goals without incurring additional overhead to IEEE 802.11 networks. In this thesis, I design and experimentally evaluate two frameworks that enable individual 802.11 nodes to characterize their wireless links and routes by employing only local and passively collected information. First, I enable 802.11 nodes to assess their links by characterizing packet delivery failures and failure causes. The key problem is that nodes cannot individually observe many factors that affect the packet delivery at both ends of their links and in both directions of 802.11 communication. To this end, instead of relying on the assistance of other nodes, I design the first practical framework that extrapolates the missing information locally from the nodes' overhearing, the observable causal relationships of 802.11 operation and characterization of the corrupted and undecodable packets. The proposed framework employs only packet-level information generally reported by commodity 802.11 wireless cards. Next, I design and evaluate routing primitives that enable individual nodes to suppress their poor route selections. I refer to a route selection as poor whenever the employed routing protocol fails to establish the existing least-cost path according to an employed routing metric. This thesis shows that an entire family of the state-of-the art on-demand distance-vector routing protocols, including the standards-proposed protocol for IEEE 802.11s mesh networks, suffers from frequent and long-term poor selections having arbitrary path costs. Consequently, such selections generally induce severe throughput degradations for network users. To address this problem, I design mechanisms that identify optimal paths locally by employing only the information readily available to the affected nodes. The proposed mechanisms largely suppress occurrence of inferior routes. Even when such routes are selected their durations are reduced by several orders of magnitude, often to sub-second time scales. My work has implications on several key areas of wireless networking: It removes systematic failures from wireless routing and serves as a source of information for a wide range of protocols including the protocols for network management and diagnostics.
Design and Experimental Evaluation of Next-Generation Multi-User WLANs from Millimeter-Wave to Terahertz
(2022-08-22) Dasala, Keerthi Priya; Knightly, Edward W.
The use of millimeter-wave and terahertz frequencies (30 GHz to 1 THz) for wireless links is rapidly emerging as one of the accepted paradigms for future (5G and beyond) wireless networks. Driven by increased spectrum availability, millimeter-wave (mmWave) and terahertz (THz) communications are envisioned as the key building block to realizing the next order of magnitude in data rate and user densities for next-generation wireless networks. As a key challenge for maintaining directional links, mmWave bands have exploited large antenna arrays to overcome higher path loss and reflection loss and enhance link budget to provide a multi-Gbps data rate for a single point-to-point transmission. Unfortunately, RF chains become the limiting resource in mmWave bands due to numerous hardware and power constraints that make it challenging to have a separate RF chain and data converter for each antenna. Consequently, to date with Wi- Fi, a single RF chain has precluded Multi-User (MU) communication and supports only one stream/ one user at a time. Furthermore, scaling multi- user data rates at THz bands introduce new challenges beyond mmWave: The wider THz spectrum exhibits a unique property of angular dispersion, i.e., frequency-dependent radiation direction with different propagation characteristics, thus requiring different system and node architectures for multi-user communication. By leveraging the unique capabilities of mmWave/THz wireless signals, namely, the ability to flexibly access a large swath of spectrum, sparse scattering, and the possibility of directionality in small form factors (i.e., large antenna arrays or high-frequency antenna structures), this thesis presents the design, implementation, and experimental evaluation of novel solutions to achieve scalable multi-user directional networking in mmWave to THz spectrum in unprecedented ways. In this thesis, I design and experimentally demonstrate for the first time how to support MU downlink and uplink in mmWave WLANs using only a single RF chain. To realize this, I propose (i) mmWave WLAN architecture in which the number of supported simultaneous users and streams exceed the number of RF chains, thus removing the RF-chain limitation on MU scaling, (ii) Scalable Multi-User Constellations that enable single beamformed MU transmission and reception at the AP, and (iii) Novel User and Beam adaptation framework that targets aggregate rate maximization with beam training and computation overhead design tradeoffs. Then, I design and implement the key components of the first multi- user THz WLAN system based on a novel node architecture built on leaky-wave antennas, a promising structure for THz networks. By exploit- ing electromagnetics of antennas to protocol design, signal processing, and end-to-end system design, I demonstrated a contention-free and scheduler- free THz-scale multi-user communication scheme that supports up to 11 simultaneous users in practice, achieving Tb/s aggregate data rates using just a single-element antenna link. Together, these above designs address the key challenges of directional networking and demonstrate scalable multi-user mmWave and THz systems with minimal device cost and power consumption with the potential to enable ultra-high-speed connectivity with millisecond latency and massive scalability, thus yielding a paradigm change in the design and development of next-generation multi-user wireless systems.
Distance-1 constrained channel assignment in single radio wireless mesh networks
(2008) Aryafar, Ehsan; Knightly, Edward W.
This thesis 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 IEEE 802.11 as the medium access protocol. Both of these approaches suffer from limited throughput improvement: the first approach due to wrong or incomplete channel state information that inherently arises in a multi-hop wireless environment, while the second approach due to high interference within each subnetwork. In this thesis. I first introduce. D1C-CA, Distance-1 Constrained Channel Assignment. D1C-CA statically assigns channels to a set of links as a function of physical connectivity, contention, and the unique gateway functionality of mesh networks. i.e. all internet (non-local) traffic has a gateway node as its source or destination. To design D1C-CA, I model the channel assignment problem as a new form of graph edge coloring in which edges at distance one are constrained. I prove that the problem is NP-complete and design an efficient heuristic solution for mesh networks. Second, I design an asynchronous control-channel-based MAC protocol that solves multi-channel coordination problems and employs the proposed channel assignment algorithm. Finally, I investigate the performance of my approach through extensive simulations and show considerable performance improvements compared to alternate schemes.
Distributed and scalable physical layer and medium access design for uplink multiuser multiple-input, multiple-output (MU-MIMO) in wireless local area network (WLAN) systems
(2020-11-10) Flores Miranda, Adriana B.; Knightly, Edward W.; Rice University; United States Patent and Trademark Office
A client device includes a processor and an antenna. The client device obtains an announcement that specifies a winning client of a channel contention competition; identifies a group association of the client device using an identity of the winning client; transmits a preamble modulated by an entry of a preamble interference nullification matrix, the entry is based on the group association; and transmits, after transmitting the preamble, a data transmission. The preamble is transmitted at the same time as a second preamble is transmitted by a second client device.
Distributed Full-duplex via Wireless Side Channels: Bounds and Protocols
(2013-09-16) Bai, Jingwen; Sabharwal, Ashutosh; Aazhang, Behnaam; Knightly, Edward W.
In this thesis, we study a three-node full-duplex network, where the infrastructure node has simultaneous up- and downlink communication in the same frequency band with two half-duplex nodes. In addition to self-interference at the full-duplex infrastructure node, the three-node network has to contend with the inter-node interference between the two half-duplex nodes. The two forms of interferences differ in one important aspect that the self-interference is known at the interfered receiver. Therefore, we propose to leverage a wireless side-channel to manage the inter-node interference. We characterize the impact of inter-node interference on the network achievable rate region with and without a side-channel between the nodes. We present four distributed full-duplex inter-node interference cancellation schemes, which leverage the device-to-device wireless side-channel for improved interference cancellation. Of the four, bin-and-cancel is asymptotically optimal in high signal-to-noise ratio limit which uses Han-Kobayashi common-private message splitting and achieves within 1 bits/s/Hz of the capacity region for all values of channel parameters. The other three schemes are simpler compared to bin-and-cancel but achieve the near-optimal performance only in certain regimes of channel values. Asymptotic multiplexing gains of all proposed schemes are derived to show analytically that leveraging the side channel can be highly beneficial in increasing the multiplexing gain of the system exactly in those regimes where inter-node interference has the highest impact.

Browsing by Author "Knightly, Edward W."

Results Per Page

Sort Options