124 research outputs found
Leveraging CDR datasets for Context-Rich Performance Modeling of Large-Scale Mobile Pub/Sub Systems
International audienceLarge-scale mobile environments are characterized by, among others, a large number of mobile users, intermittent connectivity and non-homogeneous arrival rate of data to the users, depending on the region's context. Multiple application scenarios in major cities need to address the above situation for the creation of robust mobile systems. Towards this, it is fundamental to enable system designers to tune a communication infrastructure using various parameters depending on the specific context. In this paper, we take a first step towards enabling an application platform for large-scale information management relying on mobile social crowd-sourcing. To inform the stakeholders of expected loads and costs, we model a large-scale mobile pub/sub system as a queueing network. We introduce additional timing constraints such as i) mobile user's intermittent connectivity period; and ii) data validity lifetime period (e.g. that of sensor data). Using our MobileJINQS simulator, we parameterize our model with realistic input loads derived from the D4D dataset (CDR) and varied lifetime periods in order to analyze the effect on response time. This work provides system designers with coarse grain design time information when setting realistic loads and time constraints
20 years of turbo coding and energy-aware design guidelines for energy-constrained wireless applications
During the last two decades, wireless communication has been revolutionized by near-capacity error-correcting codes (ECCs), such as turbo codes (TCs), which offer a lower bit error ratio (BER) than their predecessors, without requiring an increased transmission energy consumption (EC). Hence, TCs have found widespread employment in spectrum-constrained wireless communication applications, such as cellular telephony, wireless local area network, and broadcast systems. Recently, however, TCs have also been considered for energy-constrained wireless communication applications, such as wireless sensor networks and the `Internet of Things.' In these applications, TCs may also be employed for reducing the required transmission EC, instead of improving the BER. However, TCs have relatively high computational complexities, and hence, the associated signal-processing-related ECs are not insignificant. Therefore, when parameterizing TCs for employment in energy-constrained applications, both the processing EC and the transmission EC must be jointly considered. In this tutorial, we investigate holistic design methodologies conceived for this purpose. We commence by introducing turbo coding in detail, highlighting the various parameters of TCs and characterizing their impact on the encoded bit rate, on the radio frequency bandwidth requirement, on the transmission EC and on the BER. Following this, energy-efficient TC decoder application-specific integrated circuit (ASIC) architecture designs are exemplified, and the processing EC is characterized as a function of the TC parameters. Finally, the TC parameters are selected in order to minimize the sum of the processing EC and the transmission EC
Performance of data aggregation for wireless sensor networks
This thesis focuses on three fundamental issues that concern data aggregation protocols for periodic data collection in sensor networks: which sensor nodes should report their data, when should they report it, and should they use unicast or broadcast based protocols for this purpose.
The issue of when nodes should report their data is considered in the context of real-time monitoring applications. The first part of this thesis shows that asynchronous aggregation, in which the time of each node’s transmission is determined adaptively based on its local history of past packet receptions from its children, outperforms synchronous aggregation by providing lower delay for a given end-to-end loss rate.
Second, new broadcast-based aggregation protocols that minimize the number of packet transmissions, relying on multipath delivery rather than automatic repeat request for reliability, are designed and evaluated. The performance of broadcast-based aggregation is compared to that of unicast-based aggregation, in the context of both real-time and delay-tolerant data collection.
Finally, this thesis investigates the potential benefits of dynamically, rather than semi-statically, determining the set of nodes reporting their data, in the context of applications in which coverage of some monitored region is to be maintained. Unicast and broadcast-based coverage-preserving data aggregation protocols are designed and evaluated. The performance of the proposed protocols is compared to that of data collection protocols relying on node scheduling
A review of advances in pixel detectors for experiments with high rate and radiation
The Large Hadron Collider (LHC) experiments ATLAS and CMS have established
hybrid pixel detectors as the instrument of choice for particle tracking and
vertexing in high rate and radiation environments, as they operate close to the
LHC interaction points. With the High Luminosity-LHC upgrade now in sight, for
which the tracking detectors will be completely replaced, new generations of
pixel detectors are being devised. They have to address enormous challenges in
terms of data throughput and radiation levels, ionizing and non-ionizing, that
harm the sensing and readout parts of pixel detectors alike. Advances in
microelectronics and microprocessing technologies now enable large scale
detector designs with unprecedented performance in measurement precision (space
and time), radiation hard sensors and readout chips, hybridization techniques,
lightweight supports, and fully monolithic approaches to meet these challenges.
This paper reviews the world-wide effort on these developments.Comment: 84 pages with 46 figures. Review article.For submission to Rep. Prog.
Phy
Low Power Memory/Memristor Devices and Systems
This reprint focusses on achieving low-power computation using memristive devices. The topic was designed as a convenient reference point: it contains a mix of techniques starting from the fundamental manufacturing of memristive devices all the way to applications such as physically unclonable functions, and also covers perspectives on, e.g., in-memory computing, which is inextricably linked with emerging memory devices such as memristors. Finally, the reprint contains a few articles representing how other communities (from typical CMOS design to photonics) are fighting on their own fronts in the quest towards low-power computation, as a comparison with the memristor literature. We hope that readers will enjoy discovering the articles within
Discovery and Group Communication for Constrained Internet of Things Devices using the Constrained Application Protocol
The ubiquitous Internet is rapidly spreading to new domains. This expansion of
the Internet is comparable in scale to the spread of the Internet in the ’90s. The
resulting Internet is now commonly referred to as the Internet of Things (IoT) and
is expected to connect about 50 billion devices by the year 2020. This means that
in just five years from the time of writing this PhD the number of interconnected
devices will exceed the number of humans by sevenfold. It is further expected that
the majority of these IoT devices will be resource constrained embedded devices
such as sensors and actuators. Sensors collect information about the physical world
and inject this information into the virtual world. Next processing and reasoning
can occur and decisions can be taken to enact upon the physical world by injecting
feedback to actuators.
The integration of embedded devices into the Internet introduces new challenges,
since many of the existing Internet technologies and protocols were not
designed for this class of constrained devices. These devices are typically optimized
for low cost and power consumption and thus have very limited power,
memory, and processing resources and have long sleep periods. The networks
formed by these embedded devices are also constrained and have different characteristics
than those typical in todays Internet. These constrained networks have
high packet loss, low throughput, frequent topology changes and small useful payload
sizes. They are referred to as LLN. Therefore, it is in most cases unfeasible to
run standard Internet protocols on this class of constrained devices and/or LLNs.
New or adapted protocols that take into consideration the capabilities of the constrained
devices and the characteristics of LLNs, are required.
In the past few years, there were many efforts to enable the extension of the
Internet technologies to constrained devices. Initially, most of these efforts were
focusing on the networking layer. However, the expansion of the Internet in the
90s was not due to introducing new or better networking protocols. It was a result
of introducing the World Wide Web (WWW), which made it easy to integrate services
and applications. One of the essential technologies underpinning the WWW
was the Hypertext Transfer Protocol (HTTP). Today, HTTP has become a key
protocol in the realization of scalable web services building around the Representational
State Transfer (REST) paradigm. The REST architectural style enables
the realization of scalable and well-performing services using uniform and simple
interfaces. The availability of an embedded counterpart of HTTP and the REST
architecture could boost the uptake of the IoT.
Therefore, more recently, work started to allow the integration of constrained
devices in the Internet at the service level. The Internet Engineering Task Force
(IETF) Constrained RESTful Environments (CoRE) working group has realized
the REST architecture in a suitable form for the most constrained nodes and networks.
To that end the Constrained Application Protocol (CoAP) was introduced,
a specialized RESTful web transfer protocol for use with constrained networks and
nodes. CoAP realizes a subset of the REST mechanisms offered by HTTP, but is
optimized for Machine-to-Machine (M2M) applications.
This PhD research builds upon CoAP to enable a better integration of constrained
devices in the IoT and examines proposed CoAP solutions theoretically
and experimentally proposing alternatives when appropriate. The first part of this
PhD proposes a mechanism that facilitates the deployment of sensor networks
and enables the discovery, end-to-end connectivity and service usage of newly
deployed sensor nodes. The proposed approach makes use of CoAP and combines
it with Domain Name System (DNS) in order to enable the use of userfriendly
Fully Qualified Domain Names (FQDNs) for addressing sensor nodes. It
includes the automatic discovery of sensors and sensor gateways and the translation
of HTTP to CoAP, thus making the sensor resources globally discoverable and
accessible from any Internet-connected client using either IPv6 addresses or DNS
names both via HTTP or CoAP. As such, the proposed approach provides a feasible
and flexible solution to achieve hierarchical self-organization with a minimum
of pre-configuration. By doing so we minimize costly human interventions and
eliminate the need for introducing new protocols dedicated for the discovery and
organization of resources. This reduces both cost and the implementation footprint
on the constrained devices.
The second, larger, part of this PhD focuses on using CoAP to realize communication
with groups of resources. In many IoT application domains, sensors
or actuators need to be addressed as groups rather than individually, since individual
resources might not be sufficient or useful. A simple example is that all
lights in a room should go on or off as a result of the user toggling the light switch.
As not all IoT applications may need group communication, the CoRE working
group did not include it in the base CoAP specification. This way the base protocol
is kept as efficient and as simple as possible so it would run on even the most
constrained devices. Group communication and other features that might not be
needed by all devices are standardized in a set of optional separate extensions. We
first examined the proposed CoAP extension for group communication, which utilizes
Internet Protocol version 6 (IPv6) multicasts. We highlight its strengths and
weaknesses and propose our own complementary solution that uses unicast to realize
group communication. Our solution offers capabilities beyond simple group
communication. For example, we provide a validation mechanism that performs
several checks on the group members, to make sure that combining them together
is possible. We also allow the client to request that results of the individual members
are processed before they are sent to the client. For example, the client can
request to obtain only the maximum value of all individual members.
Another important optional extension to CoAP allows clients to continuously
observe resources by registering their interest in receiving notifications from CoAP
servers once there are changes to the values of the observed resources. By using
this publish/subscribe mechanism the client does not need to continuously poll the
resource to find out whether it has changed its value. This typically leads to more
efficient communication patterns that preserve valuable device and LLN resources.
Unfortunately CoAP observe does not work together with the CoAP group communication
extension, since the observe extension assumes unicast communication
while the group communication extension only support multicast communication.
In this PhD we propose to extend our own group communication solution to offer
group observation capabilities. By combining group observation with group
processing features, it becomes possible to notify the client only about certain
changes to the observed group (e.g., the maximum value of all group members has
changed).
Acknowledging that the use of multicast as well as unicast has strengths and
weaknesses we propose to extend our unicast based solution with certain multicast
features. By doing so we try to combine the strengths of both approaches to obtain
a better overall group communication that is flexible and that can be tailored
according to the use case needs.
Together, the proposed mechanisms represent a powerful and comprehensive
solution to the challenging problem of group communication with constrained devices.
We have evaluated the solutions proposed in this PhD extensively and in
a variety of forms. Where possible, we have derived theoretical models and have
conducted numerous simulations to validate them. We have also experimentally
evaluated those solutions and compared them with other proposed solutions using
a small demo box and later on two large scale wireless sensor testbeds and under
different test conditions. The first testbed is located in a large, shielded room,
which allows testing under controlled environments. The second testbed is located
inside an operational office building and thus allows testing under normal operation
conditions. Those tests revealed performance issues and some other problems.
We have provided some solutions and suggestions for tackling those problems.
Apart from the main contributions, two other relevant outcomes of this PhD are
described in the appendices. In the first appendix we review the most important
IETF standardization efforts related to the IoT and show that with the introduction
of CoAP a complete set of standard protocols has become available to cover the
complete networking stack and thus making the step from the IoT into the Web
of Things (WoT). Using only standard protocols makes it possible to integrate
devices from various vendors into one bigWoT accessible to humans and machines
alike.
In the second appendix, we provide an alternative solution for grouping constrained
devices by using virtualization techniques. Our approach focuses on the
objects, both resource-constrained and non-constrained, that need to cooperate
by integrating them into a secured virtual network, named an Internet of Things
Virtual Network or IoT-VN. Inside this IoT-VN full end-to-end communication
can take place through the use of protocols that take the limitations of the most
resource-constrained devices into account. We describe how this concept maps to
several generic use cases and, as such, can constitute a valid alternative approach
for supporting selected applications
- …