343 research outputs found
Facilitating Flexible Link Layer Protocols for Future Wireless Communication Systems
This dissertation addresses the problem of designing link layer protocols
which are flexible enough to accommodate the demands offuture wireless
communication systems (FWCS).We show that entire link layer protocols with
diverse requirements and responsibilities can be composed out of
reconfigurable and reusable components.We demonstrate this by designing and
implementinga novel concept termed Flexible Link Layer (FLL)
architecture.Through extensive simulations and practical experiments, we
evaluate a prototype of the suggested architecture in both
fixed-spectrumand dynamic spectrum access (DSA) networks.
FWCS are expected to overcome diverse challenges including the continual
growthin traffic volume and number of connected devices.Furthermore, they
are envisioned to support a widerange of new application requirements and
operating conditions.Technology trends, including smart homes,
communicating machines, and vehicularnetworks, will not only grow on a
scale that once was unimaginable, they will also become the predominant
communication paradigm, eventually surpassing today's human-produced
network traffic.
In order for this to become reality, today's systems have to evolve in many
ways.They have to exploit allocated resources in a more efficient and
energy-conscious manner.In addition to that, new methods for spectrum
access and resource sharingneed to be deployed.Having the diversification
of applications and network conditions in mind, flexibility at all layers
of a communication system is of paramount importance in order to meet the
desired goals.
However, traditional communication systems are often designed with specific
and distinct applications in mind. Therefore, system designers can tailor
communication systems according to fixedrequirements and operating
conditions, often resulting in highly optimized but inflexible
systems.Among the core problems of such design is the mix of data transfer
and management aspects.Such a combination of concerns clearly hinders the
reuse and extension of existing protocols.
To overcome this problem, the key idea explored in this dissertation is a
component-based design to facilitate the development of more flexible and
versatile link layer protocols.Specifically, the FLL architecture,
suggested in this dissertation, employs a generic, reconfigurable data
transfer protocol around which one or more complementary protocols, called
link layer applications, are responsible for management-related aspects of
the layer.
To demonstrate the feasibility of the proposed approach, we have designed
andimplemented a prototype of the FLL architecture on the basis ofa
reconfigurable software defined radio (SDR) testbed.Employing the SDR
prototype as well as computer simulations, thisdissertation describes
various experiments used to examine a range of link layerprotocols for both
fixed-spectrum and DSA networks.
This dissertation firstly outlines the challenges faced by FWCSand
describes DSA as a possible technology component for their construction.It
then specifies the requirements for future DSA systemsthat provide the
basis for our further considerations.We then review the background on link
layer protocols, surveyrelated work on the construction of flexible
protocol frameworks,and compare a range of actual link layer protocols and
algorithms.Based on the results of this analysis, we design, implement, and
evaluatethe FLL architecture and a selection of actual link layer
protocols.
We believe the findings of this dissertation add substantively to the
existing literature on link layer protocol design and are valuable for
theoreticians and experimentalists alike
Detection of selfish manipulation of carrier sensing in 802.11 networks
Recently, tuning the clear channel assessment (CCA) threshold in conjunction with power control has been considered for improving the performance of WLANs. However, we show that, CCA tuning can be exploited by selfish nodes to obtain an unfair share of the available bandwidth. Specifically, a selfish entity can manipulate the CCA threshold to ignore ongoing transmissions; this increases the probability of accessing the medium and provides the entity a higher, unfair share of the bandwidth. We experiment on our 802.11 testbed to characterize the effects of CCA tuning on both isolated links and in 802.11 WLAN configurations. We focus on AP-client(s) configurations, proposing a novel approach to detect this misbehavior. A misbehaving client is unlikely to recognize low power receptions as legitimate packets; by intelligently sending low power probe messages, an AP can efficiently detect a misbehaving node. Our key contributions are: 1) We are the first to quantify the impact of selfish CCA tuning via extensive experimentation on various 802.11 configurations. 2) We propose a lightweight scheme for detecting selfish nodes that inappropriately increase their CCAs. 3) We extensively evaluate our system on our testbed; its accuracy is 95 percent while the false positive rate is less than 5 percent. © 2012 IEEE
Exploiting programmable architectures for WiFi/ZigBee inter-technology cooperation
The increasing complexity of wireless standards has shown that protocols cannot be designed once for all possible deployments, especially when unpredictable and mutating interference situations are present due to the coexistence of heterogeneous technologies. As such, flexibility and (re)programmability of wireless devices is crucial in the emerging scenarios of technology proliferation and unpredictable interference conditions.
In this paper, we focus on the possibility to improve coexistence performance of WiFi and ZigBee networks by exploiting novel programmable architectures of wireless devices able to support run-time modifications of medium access operations. Differently from software-defined radio (SDR) platforms, in which every function is programmed from scratch, our programmable architectures are based on a clear decoupling between elementary commands (hard-coded into the devices) and programmable protocol logic (injected into the devices) according to which the commands execution is scheduled.
Our contribution is two-fold: first, we designed and implemented a cross-technology time division multiple access (TDMA) scheme devised to provide a global synchronization signal and allocate alternating channel intervals to WiFi and ZigBee programmable nodes; second, we used the OMF control framework to define an interference detection and adaptation strategy that in principle could work in independent and autonomous networks. Experimental results prove the benefits of the envisioned solution
A Programmable MAC Based System for Real-time and Non Real-time Flows in Wireless Networks
Wireless networks are increasingly being used to serve both real-time and non real-time flows. The former includes applications such as VoIP and video streaming, while the latter includes applications like file transfer and web browsing. These flows have very different service requirements. On the one hand, real-time flows usually require a strict per-packet delay bound, since late packets may not be useful to the application. On the other hand, non real-time flows do not pose any stringent delay requisites and only demand high throughput.
Serving flows that have heterogeneous requirements necessitates the deployment of algorithms and rules for resource allocation that attempt to satisfy these needs. However, existing hardware does not allow such reconfigurability and is limited to providing a once-size-fits all solution. The objective of this work is to design, develop and demonstrate an architecture, specifically for software reconfigured hardware at the PHY-MAC layers that can provide such functionality at a per-flow and per-packet level, and to illustrate its superior performance to conventionally deployed solutions
A Comprehensive Analysis of Literature Reported Mac and Phy Enhancements of Zigbee and its Alliances
Wireless communication is one of the most required technologies by the common man. The strength of this technology is rigorously progressing towards several novel directions in establishing personal wireless networks mounted over on low power consuming systems. The cutting-edge communication technologies like bluetooth, WIFI and ZigBee significantly play a prime role to cater the basic needs of any individual. ZigBee is one such evolutionary technology steadily getting its popularity in establishing personal wireless networks which is built on small and low-power digital radios. Zigbee defines the physical and MAC layers built on IEEE standard. This paper presents a comprehensive survey of literature reported MAC and PHY enhancements of ZigBee and its contemporary technologies with respect to performance, power consumption, scheduling, resource management and timing and address binding. The work also discusses on the areas of ZigBee MAC and PHY towards their design for specific applications
System level modelling and design of hypergraph based wireless system area networks for multi-computer systems
This thesis deals with issues pertaining the wireless multicomputer interconnection networks namely topology and Medium Access Control (MAC). It argues that new channel assignment technique based on regular low-dimensional hypergraph networks, the dual radio wireless hypermesh, represents a promising alternative high-performance wireless interconnection network for the future multicomputers to shared communication medium networks and/or ordinary wireless mesh networks, which have been widely used in current wireless networks.
The focus of this work is on improving the network throughput while maintaining a relatively low latency of a wireless network system. By means of a Carrier Sense Multiple Access (CSMA) based design of the MAC protocol and based on the desirable features of hypermesh network topology a relatively high performance network has been introduced. Compared to the CSMA shared communication channel model, which is currently the de facto MAC protocol for most of wireless networks, our design is shown to achieve a significant increase in network throughput with less average network latency for large number of communication nodes.
SystemC model of the proposed wireless hypermesh, validated through mathematical models, are then introduced. The analysis has been incorporated in the proper SystemC design methodology which facilitates the integration of communication modelling into the design modelling at the early stages of the system development. Another important application of SystemC modelling techniques is to perform meaningful comparative studies of different protocols, or new implementations to determine which communication scenario performs better and the ability to modify models
to test system sensitivity and tune performance. Effects of different design parameters (e.g., packet sizes, number of nodes) has been carried out throughout this work.
The results shows that the proposed structure has out perform the existing shared medium network structure and it can support relatively high number of wireless connected computers than conventional networks
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
- …