12,229 research outputs found
Cross-Layer Techniques for Efficient Medium Access in Wi-Fi Networks
IEEE 802.11 (Wi-Fi) wireless networks share the wireless medium using a
Carrier Sense Multiple Access (CSMA) Medium Access Control (MAC) protocol.
The MAC protocol is a central determiner of Wi-Fi networks’ efficiency–the
fraction of the capacity available in the physical layer that Wi-Fi-equipped
hosts can use in practice. The MAC protocol’s design is intended to allow
senders to share the wireless medium fairly while still allowing high utilisation.
This thesis develops techniques that allow Wi-Fi senders to send more data
using fewer medium acquisitions, reducing the overhead of idle periods, and
thus improving end-to-end goodput. Our techniques address the problems we
identify with Wi-Fi’s status quo. Today’s commodity Linux Wi-Fi/IP software
stack and Wi-Fi cards waste medium acquisitions as they fail to queue enough
packets that would allow for effective sending of multiple frames per wireless
medium acquisition. In addition, for bi-directional protocols such as TCP,
TCP data and TCP ACKs contend for the wireless channel, wasting medium
acquisitions (and thus capacity). Finally, the probing mechanism used for
bit-rate adaptation in Wi-Fi networks increases channel acquisition overhead.
We describe the design and implementation of Aggregate Aware Queueing
(AAQ), a fair queueing discipline, that coordinates scheduling of frame transmission
with the aggregation layer in the Wi-Fi stack, allowing more frames per
channel acquisition. Furthermore, we describe Hierarchical Acknowledgments
(HACK) and Transmission Control Protocol Acknowledgment Optimisation
(TAO), techniques that reduce channel acquisitions for TCP flows, further
improving goodput. Finally, we design and implement Aggregate Aware Rate Control (AARC), a bit-rate adaptation algorithm that reduces channel acquisition
overheads incurred by the probing mechanism common in today’s
commodity Wi-Fi systems. We implement our techniques on real Wi-Fi hardware
to demonstrate their practicality, and measure their performance on real
testbeds, using off-the-shelf commodity Wi-Fi hardware where possible, and
software-defined radio hardware for those techniques that require modification
of the Wi-Fi implementation unachievable on commodity hardware. The techniques
described in this thesis offer up to 2x aggregate goodput improvement
compared to the stock Linux Wi-Fi stack
Mobileflow: Applying SDN to Mobility in Wireless Networks
Wireless technology has become an increasingly popular way for network access. Wireless networks provide efficient, reliable service; supporting a broad range of emerging applications including multimedia streaming and video conferencing.
Currently, there are two dominant technologies for providing wireless network access: cellular broadband networks and wireless local area networks (Wi-Fi). Cellular networks offer ubiquitous coverage, high reliability, and support mobility; yet such networks require expensive specialized equipment and expensive spectrum bands.
In contrast, Wi-Fi networks utilize unlicensed frequency bands; relying on commodity equipment. As a result, Wi-Fi infrastructure operational costs are lower than cellular network costs. Wi-Fi networks however, have limited coverage, do not support mobility, and are less reliable than cellular networks.
Recently, software-defined-networking architectures are gaining interest. The Software-Defined Networking (SDN) approach separates control (forwarding decisions) and data plane (packet processing). This approach provides an abstraction of a network switch and an interface for manipulating this abstraction with clear semantics. The SDN approach enables applications to control underlying network services without knowing the low-level details of specific network equipment. Thus, this approach allows network programming by modifying the behavior of the routers and switches to meet network application requirements.
This thesis introduces a reference architecture that supports user mobility through integration of the SDN technology into Wi-Fi networks. This project then implements a mobility manager application on top of an SDN controller to handle clients’ handoff between access points. It proposes an algorithm for mobility prediction, allowing the network operator to minimize packet loss and delays during handoffs. Algorithm validation uses real data traces from the Texas A&M University network. Trace analysis was conducted to extract mobility patterns to build a prediction model which was implemented as an application in the SDN controller.
The approach was tested by measuring packet loss that was decreased by approximately nine times. Collected mobility traces were used to analyze our prediction model performance, whose accuracy reached 65% and 95% when selecting five users with Last-in-First-out scheme with a high- and low-load access point, respectively.
This research lays out groundwork for enhancing the functionality of WiFi networks, including mobility support, while maintaining their advantages in terms of lower cost, flexibility, and user of off-the-shelf components
JAG: Reliable and Predictable Wireless Agreement under External Radio Interference
Wireless low-power transceivers used in sensor networks typically operate in unlicensed frequency bands that are subject to external radio interference caused by devices transmitting at much higher power.communication protocols should therefore be designed to be robust against such interference. A critical building block of many protocols at all layers is agreement on a piece of information among a set of nodes. At the MAC layer, nodes may need to agree on a new time slot or frequency channel, at the application layer nodes may need to agree on handing over a leader role from one node to another. Message loss caused by interference may break agreement in two different ways: none of the nodes uses the new information (time slot, channel, leader) and sticks with the previous assignment, or-even worse-some nodes use the new information and some do not. This may lead to reduced performance or failures. In this paper, we investigate the problem of agreement under external radio interference and point out the limitations of traditional message-based approaches. We propose JAG, a novel protocol that uses jamming instead of message transmissions to make sure that two neighbouring nodes agree, and show that it outperforms message-based approaches in terms of agreement probability, energy consumption, and time-to-completion. We further show that JAG can be used to obtain performance guarantees and meet the requirements of applications with real-time constraints.CONETReSens
Experimentation with MANETs of Smartphones
Mobile AdHoc NETworks (MANETs) have been identified as a key emerging
technology for scenarios in which IEEE 802.11 or cellular communications are
either infeasible, inefficient, or cost-ineffective. Smartphones are the most
adequate network nodes in many of these scenarios, but it is not
straightforward to build a network with them. We extensively survey existing
possibilities to build applications on top of ad-hoc smartphone networks for
experimentation purposes, and introduce a taxonomy to classify them. We present
AdHocDroid, an Android package that creates an IP-level MANET of (rooted)
Android smartphones, and make it publicly available to the community.
AdHocDroid supports standard TCP/IP applications, providing real smartphone
IEEE 802.11 MANET and the capability to easily change the routing protocol. We
tested our framework on several smartphones and a laptop. We validate the MANET
running off-the-shelf applications, and reporting on experimental performance
evaluation, including network metrics and battery discharge rate.Comment: 6 pages, 7 figures, 1 tabl
Efficient AoA-based wireless indoor localization for hospital outpatients using mobile devices
The motivation of this work is to help outpatients find their corresponding departments or clinics, thus, it needs to provide indoor positioning services with a room-level accuracy. Unlike wireless outdoor localization that is dominated by the global positioning system (GPS), wireless indoor localization is still an open issue. Many different schemes are being developed to meet the increasing demand for indoor localization services. In this paper, we investigated the AoA-based wireless indoor localization for outpatients’ wayfinding in a hospital, where Wi-Fi access points (APs) are deployed, in line, on the ceiling. The target position can be determined by a mobile device, like a smartphone, through an efficient geometric calculation with two known APs coordinates and the angles of the incident radios. All possible positions in which the target may appear have been comprehensively investigated, and the corresponding solutions were proven to be the same. Experimental results show that localization error was less than 2.5 m, about 80% of the time, which can satisfy the outpatients’ requirements for wayfinding
Towards efficient coexistence of IEEE 802.15.4e TSCH and IEEE 802.11
A major challenge in wide deployment of smart wireless devices, using
different technologies and sharing the same 2.4 GHz spectrum, is to achieve
coexistence across multiple technologies. The IEEE~802.11 (WLAN) and the IEEE
802.15.4e TSCH (WSN) where designed with different goals in mind and both play
important roles for respective applications. However, they cause mutual
interference and degraded performance while operating in the same space. To
improve this situation we propose an approach to enable a cooperative control
which type of network is transmitting at given time, frequency and place.
We recognize that TSCH based sensor network is expected to occupy only small
share of time, and that the nodes are by design tightly synchronized. We
develop mechanism enabling over-the-air synchronization of the Wi-Fi network to
the TSCH based sensor network. Finally, we show that Wi-Fi network can avoid
transmitting in the "collision periods". We provide full design and show
prototype implementation based on the Commercial off-the-shelf (COTS) devices.
Our solution does not require changes in any of the standards.Comment: 8 page
Coordinated Dynamic Spectrum Management of LTE-U and Wi-Fi Networks
This paper investigates the co-existence of Wi-Fi and LTE in emerging
unlicensed frequency bands which are intended to accommodate multiple radio
access technologies. Wi-Fi and LTE are the two most prominent access
technologies being deployed today, motivating further study of the inter-system
interference arising in such shared spectrum scenarios as well as possible
techniques for enabling improved co-existence. An analytical model for
evaluating the baseline performance of co-existing Wi-Fi and LTE is developed
and used to obtain baseline performance measures. The results show that both
Wi-Fi and LTE networks cause significant interference to each other and that
the degradation is dependent on a number of factors such as power levels and
physical topology. The model-based results are partially validated via
experimental evaluations using USRP based SDR platforms on the ORBIT testbed.
Further, inter-network coordination with logically centralized radio resource
management across Wi-Fi and LTE systems is proposed as a possible solution for
improved co-existence. Numerical results are presented showing significant
gains in both Wi-Fi and LTE performance with the proposed inter-network
coordination approach.Comment: Accepted paper at IEEE DySPAN 201
- …