Abstract: In this work we propose a new unified PON
RAN architecture for LTE mobile backhaul networks,
employing ringbased WDM PONs. The proposed
architecture supports dynamic setup of virtual circ
uits for interbase station communication, over a dedicated
λ
LAN channel. The reservation mechanism is arbitrated by the OLT, which also monitors the traffic imbalances of downstream channels. The proposed architecture also supports load balancing, by dynamically reallocatin
g and sharing the capacity of the downstream wavelengths.
Abstract: In mobile ad-hoc networks (MANETs), the mobility of the nodes is a complicating factor that significantly affects the effectiveness and performance of the routing protocols. Our work builds upon recent results on the effect of node mobility on the performance of available routing strategies (i.e.~path based, using support) and proposes a protocol framework that exploits the usually different mobility rates of the nodes by adapting the routing strategy during execution. We introduce a metric for the relative mobility of the nodes, according to which the nodes are classified into mobility classes. These mobility classes determine, for any pair of an origin and destination, the routing technique that best corresponds to their mobility properties. Moreover, special care is taken for nodes remaining almost stationary or moving with high (relative) speeds. Our key design goal is to limit the necessary implementation changes required to incorporate existing routing protocols in to our framework. We provide extensive evaluation of the proposed framework, using a well-known simulator (NS2). Our first findings demonstrate that the proposed framework improves, in certain cases, the performance of the existing routing protocols.
Abstract: In ad-hoc mobilenetworks (MANET), the mobility of the nodes is a complicating factor that significantly affects the effectiveness and performance of the routing protocols. Our work builds upon the recent results on the effect of node mobility on the performance of available routing strategies (i.e.~path based, using support) and proposes a protocol framework that exploits the usually different mobility rates of the nodes by adopting the routing strategy during execution. We introduce a metric for the relative mobility of the nodes, according to which the nodes are classified into mobility classes. These mobility classes determine, for any pair of origin and destination, the routing technique that best corresponds to their mobility properties. Moreover, special care is taken for nodes remaining almost stationary or moving with high (relative) speeds. Our key design goal is to limit the necessery implementation changes required to incorporate existing routing protocols in our framework. We provide extensive evaluation of the proposed framework, using a well-known simulator (NS2). Our first findings demonstrate that the proposed framework improves, in certain cases, the performance of the existing routing protocols.
Abstract: We propose a MAC protocol for mobile ad hoc networks that
uses power control for the RTS/CTS and DATA frame
transmissions in order to improve energy and capacity
utilization efficiency. Unlike IEEE 802.11, in our scheme the
RTS frames are not sent using the maximum transmission
power to silence neighbouring nodes, and the CTS frames do
not silence all receiving nodes to the same degree. In contrast,
the transmission power of the RTS frames follows a slow
start principle, while the CTS frames, which are sent at
maximum transmission power, prevent the neighbouring
nodes from transmitting their DATA frames with power more
than a computed threshold, while allowing them to transmit at
power levels less than that threshold. This is done by
including in the RTS and the CTS frames additional
information, such as the power of the transmissions, and the
interference tolerance of the nodes. Moreover the DATA
frames are sent at the minimum required transmission power
increased by a small margin to ensure connectivity with the
intended receiver, so as to cause minimal interference to
neighbouring nodes and allow for future interference to be
added to the receiver of the DATA frames. The power to be
used by the transmitter is computed by the recipient of the
RTS frame and is included in the CTS frame. It is expected
that a network with such a power management scheme would
achieve a better throughput performance and more power
savings than a network without such a scheme.
Abstract: We propose a MAC protocol for mobile ad hoc networks that
uses power control for the RTS/CTS and DATA frame
transmissions in order to improve energy and capacity
utilization efficiency. Unlike IEEE 802.11, in our scheme the
RTS frames are not sent using the maximum transmission
power to silence neighbouring nodes, and the CTS frames do
not silence all receiving nodes to the same degree. In contrast,
the transmission power of the RTS frames follows a slow
start principle, while the CTS frames, which are sent at
maximum transmission power, prevent the neighbouring
nodes from transmitting their DATA frames with power more
than a computed threshold, while allowing them to transmit at
power levels less than that threshold. This is done by
including in the RTS and the CTS frames additional
information, such as the power of the transmissions, and the
interference tolerance of the nodes. Moreover the DATA
frames are sent at the minimum required transmission power
increased by a small margin to ensure connectivity with the
intended receiver, so as to cause minimal interference to
neighbouring nodes and allow for future interference to be
added to the receiver of the DATA frames. The power to be
used by the transmitter is computed by the recipient of the
RTS frame and is included in the CTS frame. It is expected
that a network with such a power management scheme would
achieve a better throughput performance and more power
savings than a network without such a scheme.
Abstract: In this paper we present a platform for developing mobile, locative and collaborative distributed games comprised of small programmable object technologies (e.g., wireless sensor networks) and traditional networked processors.
The platform is implemented using a combination of JAVA
Standard and Mobile editions, targeting also mobile phones
that have some kind of sensors installed. We briefly present
the architecture of our platform and demonstrate its capabilities by reporting two pervasive multiplayer games. The key
characteristic of these games is that players interact with each
other and their surrounding environment by moving, running
and gesturing as a means to perform game related actions, using small programmable object technologies.
Abstract: We study the problem of fast and energy-efficient data collection of sensory data using a mobile sink, in wireless sensor networks in which both the sensors and the sink move. Motivated by relevant applications, we focus on dynamic sensory mobility and heterogeneous sensor placement. Our approach basically suggests to exploit the sensor motion to adaptively propagate information based on local conditions (such as high placement concentrations), so that the sink gradually “learns” the network and accordingly optimizes its motion. Compared to relevant solutions in the state of the art (such as the blind random walk, biased walks, and even optimized deterministic sink mobility), our method significantly reduces latency (the improvement ranges from 40% for uniform placements, to 800% for heterogeneous ones), while also improving the success rate and keeping the energy dissipation at very satisfactory levels.
Abstract: Motivated by emerging applications, we consider sensor networks where the sensors themselves (not just the sinks) are mobile. Furthermore, we focus on mobility scenarios characterized by heterogeneous, highly changing mobility roles in the network. To capture these high dynamics of diverse sensory motion we propose a novel network parameter,
the mobility level, which, although simple and local, quite accurately takes into account both the spatial and speed characteristics of motion. We then propose adaptive data dissemination protocols that use the mobility level estimation to optimize performance, by basically exploiting high mobility (redundant message ferrying) as a cost-effective replacement of flooding, e.g. the sensors tend to dynamically propagate less data in the presence
of high mobility, while nodes of high mobility are favored for moving data around. These dissemination schemes are enhanced by a distance-sensitive probabilistic message flooding inhibition mechanism that further reduces communication cost, especially for fast nodes of high mobility level, and as distance to data destination decreases. Our simulation findings
demonstrate significant performance gains of our protocols compared to non-adaptive protocols, i.e. adaptation increases the success rate and reduces latency (even by 15%) while at the same time significantly reducing energy dissipation (in most cases by even 40%). Also, our adaptive schemes achieve significantly higher message delivery ratio and
satisfactory energy-latency trade-offs when compared to flooding when sensor nodes have
limited message queues.
Abstract: Wireless Sensor Networks are by nature highly dynamic and communication between sensors is completely ad hoc, especially when mobile devices are part of the setup. Numerous protocols and applications proposed for such networks
operate on the assumption that knowledge of the neighborhood is a priori available to all nodes. As a result, WSN deployments need to use or implement from scratch a neighborhood discovery mechanism. In this work we present a new protocol based on adaptive periodic beacon exchanges. We totally avoid continuous beaconing by adjusting the rate of broadcasts using the concept of consistency over the understanding of neighborhood that nearby devices share. We propose, implement and evaluate our adaptive neighborhood discovery protocol over our experimental testbed and using large scale simulations. Our results indicate that the
new protocol operates more eciently than existing reference implementations while it provides valid information to applications that use it. Extensive performance evaluation indicates that it successfully reduces generated network traffic by 90% and increases network lifetime by 20% compared to existing mechanisms that rely on continuous beaconing.
Abstract: Motivated by emerging applications, we consider sensor networks where the sensors themselves
(not just the sinks) are mobile. Furthermore, we focus on mobility
scenarios characterized by heterogeneous, highly changing mobility
roles in the network.
To capture these high dynamics of diverse sensory motion
we propose a novel network parameter, the mobility level, which, although
simple and local, quite accurately takes into account both the
spatial and speed characteristics of motion. We then propose
adaptive data dissemination protocols that use the
mobility level estimation to optimize performance, by basically
exploiting high mobility (redundant message ferrying) as a cost-effective
replacement of flooding, e.g., the sensors tend to dynamically propagate
less data in the presence of high mobility, while nodes of high mobility
are favored for moving data around.
These dissemination schemes are enhanced by a distance-sensitive
probabilistic message flooding inhibition mechanism that
further reduces communication cost, especially for fast nodes
of high mobility level, and as distance to data destination
decreases. Our simulation findings demonstrate significant
performance gains of our protocols compared to non-adaptive
protocols, i.e., adaptation increases the success rate and reduces
latency (even by 15\%) while at the same time significantly
reducing energy dissipation (in most cases by even 40\%).
Also, our adaptive schemes achieve significantly
higher message delivery ratio and satisfactory energy-latency
trade-offs when compared to flooding when sensor nodes have limited message queues.
Abstract: Motivated by emerging applications, we consider sensor networks where the sensors themselves
(not just the sinks) are mobile. We focus on mobility
scenarios characterized by heterogeneous, highly changing mobility
roles in the network.
To capture these high dynamics
we propose a novel network parameter, the mobility level, which, although
simple and local, quite accurately takes into account both the
spatial and speed characteristics of motion. We then propose
adaptive data dissemination protocols that use the
mobility level estimation to improve performance. By basically
exploiting high mobility (redundant message ferrying) as a cost-effective
replacement of flooding, e.g., the sensors tend to dynamically propagate
less data in the presence of high mobility, while nodes of high mobility
are favored for moving data around.
These dissemination schemes are enhanced by a distance-sensitive
probabilistic message flooding inhibition mechanism that
further reduces communication cost, especially for fast nodes
of high mobility level, and as distance to data destination
decreases. Our simulation findings demonstrate significant
performance gains of our protocols compared to non-adaptive
protocols, i.e., adaptation increases the success rate and reduces
latency (even by 15\%) while at the same time significantly
reducing energy dissipation (in most cases by even 40\%).
Also, our adaptive schemes achieve significantly
higher message delivery ratio and satisfactory energy-latency
trade-offs when compared to flooding when sensor nodes have limited message queues.
Abstract: We consider sensor networks where the sensor nodes are attached on entities that move in a highly dynamic, heterogeneous manner. To capture this mobility diversity we introduce a new network parameter, the direction-aware mobility
level, which measures how fast and close each mobile node is expected to get to the data destination (the sink). We then provide local, distributed data dissemination protocols
that adaptively exploit the node mobility to improve performance. In particular, "high" mobility is used as a low cost replacement for data dissemination (due to the ferrying of data), while in the case of "low" mobility either a) data propagation redundancy is increased (when highly mobile neighbors exist) or b) long-distance data transmissions are used (when the entire neighborhood is of low mobility) to accelerate data dissemination towards the sink. An extensive performance comparison to relevant methods from
the state of the art demonstrates signi cant improvements i.e. latency is reduced by even 4 times while keeping energy dissipation and delivery success at very satisfactory levels.
Abstract: We investigate the problem of ecient wireless energy recharging in Wireless Rechargeable Sensor Networks (WRSNs). In
such networks a special mobile entity (called the Mobile Charger) traverses the network and wirelessly replenishes the energy
of sensor nodes. In contrast to most current approaches, we envision methods that are distributed, adaptive and use limited
network information. We propose three new, alternative protocols for ecient recharging, addressing key issues which we
identify, most notably (i) to what extent each sensor should be recharged (ii) what is the best split of the total energy between
the charger and the sensors and (iii) what are good trajectories the MC should follow. One of our protocols (
LRP
) performs
some distributed, limited sampling of the network status, while another one (
RTP
) reactively adapts to energy shortage alerts
judiciously spread in the network. As detailed simulations demonstrate, both protocols signi cantly outperform known state
of the art methods, while their performance gets quite close to the performance of the global knowledge method (
GKP
) we
also provide, especially in heterogeneous network deployments.
Abstract: Wireless sensor networks are comprised of a vast number of
ultra-small autonomous computing, communication and sensing devices,
with restricted energy and computing capabilities, that co-operate
to accomplish a large sensing task. Such networks can be very useful
in practice, e.g.~in the local monitoring of ambient conditions and
reporting them to a control center. In this paper we propose a
distributed group key establishment protocol that uses mobile agents
(software) and is particularly suitable for energy constrained,
dynamically evolving ad-hoc networks. Our approach totally avoids
the construction and the maintenance of a distributed structure that
reflects the topology of the network. Moreover, it trades-off
complex message exchanges by performing some amount of additional
local computations in order to be applicable at dense and dynamic
sensor networks. The extra computations are simple for the devices
to implement and are evenly distributed across the participants of
the network leading to good energy balance. We evaluate the
performance of our protocol in a simulated environment and compare
our results with existing group key establishment protocols. The
security of the protocol is based on the Diffie-Hellman problem and
we used in our experiments its elliptic curve analog. Our findings
basically indicate the feasibility of implementing our protocol in
real sensor network devices and highlight the advantages and
disadvantages of each approach given the available technology and
the corresponding efficiency (energy, time) criteria.
Abstract: As a result of recent significant technological advances, a new computing and communication environment, Mobile Ad Hoc Networks (MANET), is about to enter the mainstream. A multitude of critical aspects, including mobility, severe limitations and limited reliability, create a new set of crucial issues and trade-offs that must be carefully taken into account in the design of robust and efficient algorithms for these environments. The communication among mobile hosts is one among the many issues that need to be resolved efficiently before MANET becomes a commodity.
In this paper, we propose to discuss the communication problem in MANET as well as present some characteristic techniques for the design, the analysis and the performance evaluation of distributed communication protocols for mobile ad hoc networks. More specifically, we propose to review two different design techniques. While the first type of protocols tries to create and maintain routing paths among the hosts, the second set of protocols uses a randomly moving subset of the hosts that acts as an intermediate pool for receiving and delivering messages. We discuss the main design choices for each approach, along with performance analysis of selected protocols.
Abstract: In this paper we study the problem of basic communication
in ad-hoc mobilenetworks where the deployment area changes in a
highly dynamic way and is unknown. We call such networks
highly changing ad-hoc mobilenetworks.
For such networks we investigate an efficient communication protocol which extends
the idea (introduced in [WAE01,POMC01]) of exploiting the co-ordinated
motion of a small part of an ad-hoc mobile
network (the ``runners support") to achieve
very fast communication between any two mobile users of the network.
The basic idea of the new protocol presented here is, instead
of using a fixed sized support for the whole duration of the protocol,
to employ a support of some initial (small) size which
adapts (given some time which can be made fast enough) to the
actual levels of traffic and the
(unknown and possibly rapidly changing) network area by
changing its size in order to converge to an optimal size,
thus satisfying certain Quality of Service criteria.
We provide here some proofs of correctness and fault tolerance
of this adaptive approach and we also provide analytical results
using Markov Chains and random walk techniques to show that such
an adaptive approach is, for this class of ad-hoc mobilenetworks, significantly more efficient than a simple non-adaptive
implementation of the basic ``runners support" idea.
Abstract: We introduce a new model of
ad-hoc mobilenetworks, which we call hierarchical,
that are comprised of dense subnetworks of mobile
users (corresponding to highly populated
geographical areas, such as cities),
interconnected across access ports
by sparse but frequently used connections
(such as highways).
For such networks, we present
an efficient routing protocol which extends
the idea (introduced in WAE00) of exploiting the co-ordinated
motion of a small part of an ad-hoc mobile
network (the ``support'') to achieve
very fast communication between any two mobile users of the network.
The basic idea of the new protocol presented here is, instead
of using a unique (large) support for the whole network,
to employ a hierarchy of (small) supports (one for each city)
and also take advantage of the regular traffic
of mobile users across the interconnection highways to communicate
between cities.
We combine here theoretical analysis (average case estimations based on random walk properties) and experimental implementations (carried out using the LEDA platform) to claim and validate results showing that such a hierarchical routing approach is,
for this class of ad-hoc mobilenetworks, significantly more efficient than a simple extension of the
basic ``support'' idea presented in WAE00.
Abstract: We investigate basic communication protocols in ad-hoc mobilenetworks. We follow the semi-compulsory approach according to which a small part of the mobile users, the support , that moves in a predetermined way is used as an intermediate pool for receiving and delivering messages. Under this approach, we present a new semi-compulsory protocol called the runners in which the members of perform concurrent and continuous random walks and exchange any information given to them by senders when they meet. We also conduct a comparative experimental study of the runners protocol with another existing semi-compulsory protocol, called the snake, in which the members of move in a coordinated way and always remain pairwise adjacent. The experimental evaluation has been carried out in a new generic framework that we developed to implement protocols for mobile computing. Our experiments showed that for both protocols only a small support is required for efficient communication, and that the runners protocol outperforms the snake protocol in almost all types of inputs we considered.
Abstract: We introduce a new model of ad-hoc mobilenetworks,
which we call hierarchical, that are comprised of
dense subnetworks of mobile users (corresponding to highly
populated geographical areas), interconnected across access
ports by sparse but frequently used connections.
To implement communication in such a case, a possible
solution would be to install a very fast (yet limited) backbone
interconnecting such highly populated mobile user areas, while
employing a hierarchy of (small) supports (one for each lower level
site). This fast backbone provides a limited number of access
ports within these dense areas of mobile users.
We combine here theoretical analysis (average case estimations based on
random walk properties) to claim and validate
results showing that such a hierarchical routing approach is,
for this class of ad-hoc mobilenetworks, significantly
more efficient than a simple extension of the
basic ``support'' idea presented in [WAE00,DISC01].
Abstract: Collecting sensory data using a mobile data sink has
been shown to drastically reduce energy consumption at the cost of increasing delivery delay. Towards improved energy-latency trade-offs, we propose a biased, adaptive sink mobility scheme, that adjusts to local network conditions, such as the surrounding density, remaining energy and the number of past visits in each network region. The sink moves probabilistically, favoring less visited areas in order to cover the network area faster, while adaptively stopping more time in network regions that tend to produce more data. We implement and evaluate our mobility scheme via simulation in diverse network settings. Compared to known blind random, non-adaptive schemes, our method achieves
significantly reduced latency, especially in networks with nonuniform sensor distribution, without compromising the energy efficiency and delivery success.
Abstract: Collecting sensory data using a mobile data sink has been shown to drastically reduce energy consumption at the cost of increasing delivery delay. Towards improved energy-latency trade-offs, we propose a biased, adaptive sink mobility scheme, that adjusts to local network conditions, such as the surrounding density, remaining energy and the number of past visits in each network region. The sink moves probabilistically, favoring less visited areas in order to cover the network area faster, while adaptively stopping more time in network regions that tend to produce more data. We implement and evaluate our mobility scheme via simulation in diverse network settings. Compared to known blind random, non-adaptive schemes, our method achieves significantly reduced latency, especially in networks with nonuniform sensor distribution, without compromising the energy efficiency and delivery success.
Abstract: Collecting sensory data using a mobile data sink has
been shown to drastically reduce energy consumption at the cost of increasing delivery delay. Towards improved energy-latency trade-offs, we propose a biased, adaptive sink mobility scheme, that adjusts to local network conditions, such as the surrounding
density, remaining energy and the number of past visits in each network region. The sink moves probabilistically, favoring less visited areas in order to cover the network area faster, while adaptively stopping more time in network regions that tend to
produce more data. We implement and evaluate our mobility scheme via simulation in diverse network settings. Compared to known blind random, non-adaptive schemes, our method achieves
significantly reduced latency, especially in networks with nonuniform sensor distribution, without compromising the energy efficiency and delivery success.
Abstract: We examine multi-player pervasive games that rely on the
use of ad-hoc mobile sensor networks. The unique feature in
such games is that players interact with each other and their
surrounding environment by using movement and presence
as a means of performing game-related actions, utilizing sen-
sor devices. We brie
y discuss the fundamental issues and
challenges related to these type of games and the scenar-
ios associated with them. We have also developed a frame-
work, called Fun in Numbers (FinN) that handles a number
of these issues, such as such as neighbors discovery, local-
ization, synchronization and delay-tolerant communication.
FinN is developed using Java and is based on a multilayer ar-
chitecture, which provides developers with a set of templates
and services for building and operating new games.
Abstract: The problem of communication among mobile nodes is one of the most fundamental problems in ad hoc mobilenetworks and is at the core of many algorithms, such as for counting the number of nodes, electing a leader, data processing etc. For an exposition of several important problems in ad hoc mobilenetworks. The work of Chatzigiannakis, Nikoletseas and Spirakis focuses on wireless mobilenetworks that are subject to highly dynamic structural changes created by mobility, channel fluctuations and device failures. These changes affect topological connectivity, occur with high frequency and may not be predictable in advance. Therefore, the environment where the nodes move (in three-dimensional space with possible obstacles) as well as the motion that the nodes perform are \textit{input} to any distributed algorithm.
Abstract: We survey here some recent computational models for networks of tiny artifacts. In particular, we focus on networks consisting of artifacts with sensing capabilities. We first imagine the artifacts moving passively, that is, being mobile but unable to control their own movement. This leads us to the population protocol model of Angluin et al. (2004) [16]. We survey this model and some of its recent enhancements. In particular, we also present the mediated population protocol model in which the interaction links are capable of storing states and the passively mobile machines model in which the finite state nature of the agents is relaxed and the agents become multitape Turing machines that use a restricted space. We next survey the sensor field model, a general model capturing some identifying characteristics of many sensor network¢s settings. A sensor field is composed of kinds of devices that can communicate one to the other and also to the environment through input/output data streams. We, finally, present simulation results between sensor fields and population protocols and analyze the capability of their variants to decide graph properties
Abstract: Here we survey various computational models for Wireless Sensor Networks (WSNs). The population protocol model (PP) considers networks of tiny mobile finite-state artifacts that can sense the environment and communicate in pairs to perform a computation. The mediated population protocol model (MPP) enhances the previous model by allowing the communication links to have a constant size buffer, providing more computational power. The graph decision MPP model (GDM) is a special case of MPP that focuses on the MPP's ability to decide graph properties of the network. Another direction towards enhancing the PP is followed by the PALOMA model in which the artifacts are no longer finite-state automata but Turing Machines of logarithmic memory in the population size. A different approach to modeling WSNs is the static synchronous sensor field model (SSSF) which describes devices communicating through a fixed communication graph and interacting with their environment via input and output data streams. In this survey, we present the computational capabilities of each model and provide directions for further research.
Abstract: In this work we introduce two practical and interesting models of ad-hoc mobilenetworks: (a) hierarchical ad-hoc networks, comprised of dense subnetworks of mobile users interconnected by a very fast yet limited backbone infrastructure, (b) highly changing ad-hoc networks, where the deployment area changes in a highly dynamic way and is unknown to the protocol. In such networks, we study the problem of basic communication, i.e., sending messages from a sender node to a receiver node. For highly changing networks, we investigate an efficient communication protocol exploiting the coordinated motion of a small part of an ad-hoc mobile network (the ldquorunners supportrdquo) to achieve fast communication. This protocol instead of using a fixed sized support for the whole duration of the protocol, employs a support of some initial (small) size which adapts (given some time which can be made fast enough) to the actual levels of traffic and the (unknown and possibly rapidly changing) network area, by changing its size in order to converge to an optimal size, thus satisfying certain Quality of Service criteria. Using random walks theory, we show that such an adaptive approach is, for this class of ad-hoc mobilenetworks, significantly more efficient than a simple non-adaptive implementation of the basic ldquorunners supportrdquo idea, introduced in [9,10]. For hierarchical ad-hoc networks, we establish communication by using a ldquorunnersrdquo support in each lower level of the hierarchy (i.e., in each dense subnetwork), while the fast backbone provides interconnections at the upper level (i.e., between the various subnetworks). We analyze the time efficiency of this hierarchical approach. This analysis indicates that the hierarchical implementation of the support approach significantly outperforms a simple implementation of it in hierarchical ad-hoc networks. Finally, we discuss a possible combination of the two approaches above (the hierarchical and the adaptive ones) that can be useful in ad-hoc networks that are both hierarchical and highly changing. Indeed, in such cases the hierarchical nature of these networks further supports the possibility of adaptation.
Abstract: In this work we investigate the problem of communication among mobile hosts, one of the most fundamental problems in ad-hoc mobilenetworks that is at the core of many algorithms. Our work investigates the extreme case of total absence of any fixed network backbone or centralized administration, instantly forming networks based only on mobile hosts with wireless communication capabilities, where topological connectivity is subject to frequent, unpredictable change.
For such dynamically changing networks we propose a set of protocols which exploit the coordinated (by the protocol) motion of a small part of the network in order to manage network operations. We show that such protocols can be designed to work correctly and efficiently for communication by avoiding message flooding. Our protocols manage to establish communication between any pair of mobile hosts in small, a-priori guaranteed expected time bounds. Our results exploit and further develop some fundamental properties of random walks in finite graph.
Apart from studying the general case, we identify two practical and interesting cases of ad-hoc mobilenetworks: a) hierarchical ad-hoc networks, b) highly changing ad-hoc networks, for which we propose protocols that efficiently deal with the problem of basic communication.
We have conducted a set of extensive experiments, comprised of thousands of mobile hosts in order to validate the theoretical results and show that our protocols achieve very efficient communication under different scenaria.
Abstract: Evaluating target tracking protocols for wireless sensor networks that can localize multiple mobile devices, can be a very challenging task. Such protocols usually aim at minimizing communication overhead, data processing for the participating nodes, as well as delivering adequate tracking information of the mobile targets in a timely manner. Simulations on such protocols are performed using theoretical models that are based on unrealistic assumptions like the unit disk graph communication model, ideal network localization and perfect distance estimations. With these assumptions taken for granted, theoretical models claim various performance milestones that cannot be achieved in realistic conditions. In this paper we design a new localization protocol, where mobile assets can be tracked passively via software agents. We address the issues that hinder its performance due to the real environment conditions and provide a deployable protocol. The implementation, integration and experimentation of this new protocol and it's optimizations, were performed using the WISEBED framework. We apply our protocol in multiple indoors wireless sensor testbeds with multiple experimental scenarios to showcase scalability and trade-offs between network properties and configurable protocol parameters. By analysis of the real world experimental output, we present results that depict a more realistic view of the target tracking problem, regarding power consumption and the quality of tracking information. Finally we also conduct some very focused simulations to assess the scalability of our protocol in very large networks and multiple mobile assets.
Abstract: Wireless sensor networks are comprised of a vast number of devices, situated in an area of interest that self organize in a structureless network, in order to monitor/record/measure an environmental variable or phenomenon and subsequently to disseminate the data to the control center.
Here we present research focused on the development, simulation and evaluation of energy efficient algorithms, our basic goal is to minimize the energy consumption. Despite technology advances, the problem of energy use optimization remains valid since current and emerging hardware solutions fail to solve it.
We aim to reduce communication cost, by introducing novel techniques that facilitate the development of new algorithms. We investigated techniques of distributed adaptation of the operations of a protocol by using information available locally on every node, thus through local choices we improve overall performance. We propose techniques for collecting and exploiting limited local knowledge of the network conditions. In an energy efficient manner, we collect additional information which is used to achieve improvements such as forming energy efficient, low latency and fault tolerant paths to route data. We investigate techniques for managing mobility in networks where movement is a characteristic of the control center as well as the sensors. We examine methods for traversing and covering the network field based on probabilistic movement that uses local criteria to favor certain areas.
The algorithms we develop based on these techniques operate a) at low level managing devices, b) on the routing layer and c) network wide, achieving macroscopic behavior through local interactions. The algorithms are applied in network cases that differ in density, node distribution, available energy and also in fundamentally different models, such as under faults, with incremental node deployment and mobile nodes. In all these settings our techniques achieve significant gains, thus distinguishing their value as tools of algorithmic design.
Abstract: A central problem in distributed computing and telecommunications
is the establishment of common knowledge between two computing
entities. An immediate use of such common knowledge is in the
initiation of a secure communication session between two entities
since the two entities may use this common knowledge in order to
produce a secret key for use with some symmetric cipher.
%
The dynamic establishment of shared information (e.g. secret key)
between two entities is particularly important in networks with no
predetermined structure such as wireless mobile ad-hoc networks.
In such networks, nodes establish and terminate communication
sessions dynamically with other nodes which may have never been
encountered before in order to somehow exchange information which
will enable them to subsequently communicate in a secure manner.
%
In this paper we give and theoretically analyze a protocol that
enables two entities initially possessing a string each to
securely eliminate inconsistent bit positions, obtaining strings
with a larger percentage of similarities. This can help the nodes
establish a shared set of bits and use it as a key with some
shared key encryption scheme.
Abstract: When one engineers distributed algorithms, some special characteristics
arise that are different from conventional (sequential or parallel)
computing paradigms. These characteristics include: the need for either a
scalable real network environment or a platform supporting a simulated
distributed environment; the need to incorporate asynchrony, where arbitrarya
synchrony is hard, if not impossible, to implement; and the generation
of “difficult” input instances which is a particular challenge. In this
work, we identifys ome of the methodological issues required to address
the above characteristics in distributed algorithm engineering and illustrate
certain approaches to tackle them via case studies. Our discussion
begins byad dressing the need of a simulation environment and how asynchronyis
incorporated when experimenting with distributed algorithms.
We then proceed bys uggesting two methods for generating difficult input
instances for distributed experiments, namelya game-theoretic one and another
based on simulations of adversarial arguments or lower bound proofs.
We give examples of the experimental analysis of a pursuit-evasion protocol
and of a shared memorypro blem in order to demonstrate these ideas.
We then address a particularlyi nteresting case of conducting experiments
with algorithms for mobile computing and tackle the important issue of
motion of processes in this context. We discuss the two-tier principle as
well as a concurrent random walks approach on an explicit representation
of motions in ad-hoc mobilenetworks, which allow at least for averagecase
analysis and measurements and may give worst-case inputs in some
cases. Finally, we discuss a useful interplay between theory and practice
that arise in modeling attack propagation in networks.
Abstract: An ad hoc mobile network is a collection of mobile hosts, with wireless communication capabilities, forming a temporary network without the aid of any established fixed infrastructure. In such networks, topological connectivity is subject to frequent, unpredictable change. Our work focuses on networks with high rate of such changes to connectivity. For such dynamically changing networks we propose protocols which exploit the co-ordinated (by the protocol) motion of a small part of the network. We show that such protocols can be designed to work correctly and efficiently even in the case of arbitrary (but not malicious) movements of the hosts not affected by the protocol. We also propose a methodology for the analysis of the expected behavior of protocols for such networks, based on the assumption that mobile hosts (those whose motion is not guided by the protocol) conduct concurrent random walks in their motion space. In particular, our work examines the fundamental problem of communication and proposes distributed algorithms for it. We provide rigorous proofs of their correctness, and also give performance analyses by combinatorial tools. Finally, we have evaluated these protocols by experimental means.
Abstract: An ad hoc mobile network is a collection of mobile hosts, with wireless communication capabilities, forming a temporary network without the aid of any established fixed infrastructure. In such networks, topological connectivity is subject to frequent, unpredictable change. Our work focuses on networks with high rate of such changes to connectivity. For such dynamically changing networks we propose protocols which exploit the co-ordinated (by the protocol) motion of a small part of the network. We show that such protocols can be designed to work correctly and efficiently even in the case of arbitrary (but not malicious) movements of the hosts not affected by the protocol. We also propose a methodology for the analysis of the expected behavior of protocols for such networks, based on the assumption that mobile hosts (those whose motion is not guided by the protocol) conduct concurrent random walks in their motion space. In particular, our work examines the fundamental problem of communication and proposes distributed algorithms for it. We provide rigorous proofs of their correctness, and also give performance analyses by combinatorial tools. Finally, we have evaluated these protocols by experimental means.
Abstract: In this thesis we investigate the problems of data routing and data collection in wireless sensor networks characterised by intense and higly diverse mobility. We propose a set of protocols that takes exploits the motion of the sensors in order to inform the sink about the network topology. We experimentally evaluate these protocolls in a wide range of topologies, including both homogeneous and heterogeneous ones.
We also investigate random walks as simple motion strategies for mobile sinks that perform data collection from static WSN's. We propose three new random walks that improve latency compared to already known ones, as well as a new metric called Proximity Variation. This metric captures the different way each random walks traverses the network area.
Abstract: Through recent technology advances in the eld of wireless energy transmission, Wireless Rechargeable Sensor Networks
(WRSN) have emerged. In this new paradigm for
WSNs a mobile entity called Mobile Charger (MC) traverses
the network and replenishes the dissipated energy of sensors.
In this work we rst provide a formal de nition of the charging
dispatch decision problem and prove its computational
hardness. We then investigate how to optimize the tradeo
s of several critical aspects of the charging process such
as a) the trajectory of the charger, b) the di erent charging
policies and c) the impact of the ratio of the energy
the MC may deliver to the sensors over the total available
energy in the network. In the light of these optimizations,
we then study the impact of the charging process to the
network lifetime for three characteristic underlying routing
protocols; a greedy protocol, a clustering protocol and an
energy balancing protocol. Finally, we propose a Mobile
Charging Protocol that locally adapts the circular trajectory
of the MC to the energy dissipation rate of each sub-region
of the network. We compare this protocol against several
MC trajectories for all three routing families by a detailed
experimental evaluation. The derived ndings demonstrate
signi cant performance gains, both with respect to the no
charger case as well as the di erent charging alternatives; in
particular, the performance improvements include the network
lifetime, as well as connectivity, coverage and energy
balance properties.
Abstract: In this paper we consider communication issues arising in mobilenetworks that utilize Frequency Division Multiplexing (FDM) technology. In such networks, many users within the same geographical region can communicate simultaneously with other users of the network using distinct frequencies. The spectrum of available frequencies is limited; thus, efficient solutions to the frequency allocation and the call control problem are essential. In the frequency allocation problem, given users that wish to communicate, the objective is to minimize the required spectrum of frequencies so that communication can be established without signal interference. The objective of the call control problem is, given a spectrum of available frequencies and users that wish to communicate, to maximize the number of users served. We consider cellular, planar, and arbitrary network topologies. In particular, we study the on-line version of both problems using competitive analysis. For frequency allocation in cellular networks, we improve the best known competitive ratio upper bound of 3 achieved by the folklore Fixed Allocation algorithm, by presenting an almost tight competitive analysis for the greedy algorithm; we prove that its competitive ratio is between 2.429 and 2.5. For the call control problem, we present the first randomized algorithm that beats the deterministic lower bound of 3 achieving a competitive ratio of 2.934 in cellular networks. Our analysis has interesting extensions to arbitrary networks. Also, using Yao's Minimax Principle, we prove two lower bounds of 1.857 and 2.086 on the competitive ratio of randomized call control algorithms for cellular and arbitrary planar networks, respectively.
Abstract: In this paper we consider communication issues arising in cellular (mobile) networks that utilize frequency division multiplexing (FDM) technology. In such networks, many users within the same geographical region can communicate simultaneously with other users of the network using distinct frequencies. The spectrum of available frequencies is limited; thus, efficient solutions to the frequency-allocation and the call-control problems are essential. In the frequency-allocation problem, given users that wish to communicate, the objective is to minimize the required spectrum of frequencies so that communication can be established without signal interference. The objective of the call-control problem is, given a spectrum of available frequencies and users that wish to communicate, to maximize the number of users served. We consider cellular, planar, and arbitrary network topologies.
In particular, we study the on-line version of both problems using competitive analysis. For frequency allocation in cellular networks, we improve the best known competitive ratio upper bound of 3 achieved by the folklore Fixed Allocation algorithm, by presenting an almost tight competitive analysis for the greedy algorithm; we prove that its competitive ratio is between 2.429 and 2.5 . For the call-control problem, we present the first randomized algorithm that beats the deterministic lower bound of 3 achieving a competitive ratio between 2.469 and 2.651 for cellular networks. Our analysis has interesting extensions to arbitrary networks. Also, using Yao's Minimax Principle, we prove two lower bounds of 1.857 and 2.086 on the competitive ratio of randomized call-control algorithms for cellular and arbitrary planar networks, respectively.
Abstract: We investigate the problem of ecient wireless energy recharging in Wireless Rechargeable Sensor Networks (WRSNs). In
such networks special mobile entities (called the Mobile Chargers) traverse the network and wirelessly replenish the energy
of sensor nodes. In contrast to most current approaches, we envision methods that are distributed and use limited network
information. We propose four new protocols for ecient recharging, addressing key issues which we identify, most notably (i)
what are good coordination procedures for the Mobile Chargers and (ii) what are good trajectories for the Mobile Chargers.
Two of our protocols (
DC,DCLK
) perform distributed, limited network knowledge coordination and charging, while two others
(
CC,CCGK
) perform centralized, global network knowledge coordination and charging. As detailed simulations demonstrate,
one of our distributed protocols outperforms a known state of the art method, while its performance gets quite close to the
performance of the powerful centralized global knowledge method.
Abstract: One of the most important applications of wireless sensor
networks is building monitoring and more speci cally, the
early detection of emergency events and the provision of
guidance for safe evacuation of the building. In this pa-
per, we describe a demo application that, in the event of a
re inside a monitored building, uses the information from
the deployed sensor network in order to nd the shortest
safest path away from the emergency and provides naviga-
tion guidance to the occupants (modelled by a mobile robot),
in order to safely evacuate the building. For this demo, we
developed our own ad-hoc robot-sensor interconnection us-
ing expansion connectors and programming in a low-level
language.
Abstract: The energy balance property (i.e., all nodes having the same energy throughout the network evolution) contributes significantly (along with energy efficiency) to the maximization of the network lifespan and network connectivity. The problem of achieving energy balanced propagation is well studied in static networks, as it has attracted a lot of research attention.
Recent technological advances have enabled sensor devices to be attached to mobile entities of our every day life (e.g. smart-phones, cars, PDAs etc), thus introducing the formation of highly mobile sensor networks.
Inspired by the aforementioned applications, this work is (to the best of our knowledge) the first studying the energy balance property in wireless networks where the nodes are highly and dynamically mobile. In particular, in this paper we propose a new diverse mobility model which is easily parameterized and we also present a new protocol which tries to adaptively exploit the inherent node mobility in order to achieve energy balance in the network in an efficient way.
Abstract: In this paper, we demonstrate the significant impact of (a) the mobility rate and (b) the user density on the performance of routing protocols in ad-hoc mobilenetworks. In particular, we study the effect of these parameters on two different approaches for designing routing protocols: (a) the route creation and maintenance approach and (b) the support approach that forces few hosts to move, acting as helpers for message delivery. We study one representative protocol for each approach, i.e. AODV for the first approach and RUNNERS for the second. We have implemented the two protocols and performed a large scale and detailed simulation study of their performance. The main findings are: the AODV protocol behaves well in networks of high user density and low mobility rate, while its performance drops for sparse networks of highly mobile users. On the other hand, the RUNNERS protocol seems to tolerate well (and in fact benefit from) high mobility rates and low densities.
Abstract: We investigate the efficiency of protocols for basic communication in ad-hoc mobilenetworks. All protocols are classified in the semi-compulsory, relay category according to which communication is achieved through a small team of mobile hosts, called the support, which move in a predetermined way and serves as an intermediate pool for receiving and delivering messages. We implement a new semi-compulsory, relay protocol in which the motion of the support is based on a so-called ``hunter" strategy developed for a pursuit-evasion game. We conduct an extensive, comparative experimental study of this protocol with other two existing protocols, each one possessing a different motion for its support. We considered several types of inputs, including among others two kinds of motion patterns (random and adversarial) for the mobile hosts not in the support. Our experiments showed that for all protocols the throughput scales almost linearly with the number of mobile hosts in the network, and that a small support size suffices for efficient communication. An interesting outcome is that in most cases the new protocol is inferior to the other two, although it has a global knowledge of the motion space.
Abstract: We investigate the impact of multiple, mobile sinks on
efficient data collection in wireless sensor networks. To
improve performance, our protocol design focuses on minimizing
overlaps of sink trajectories and balancing the service load
among the sinks. To cope with high network dynamics, placement
irregularities and limited network knowledge we propose three different
protocols: a) a centralized one, that explicitly equalizes spatial coverage;
this protocol assumes strong modeling assumptions, and also serves as a kind
of performance lower bound in uniform networks of low dynamics b)
a distributed protocol based on mutual avoidance of sinks c) a clustering
protocol that distributively groups service areas towards balancing the load per sink.
Our simulation findings demonstrate significant gains in latency, while keeping the success
rate and the energy dissipation at very satisfactory levels even under
high network dynamics and deployment heterogeneity.
Abstract: We study the problem of fast and energy-efficient
data collection of sensory data using a mobile sink, in wireless sensor networks in which both the sensors and the sink move. Motivated by relevant applications, we focus on dynamic sensory
mobility and heterogeneous sensor placement. Our approach basically suggests to exploit the sensor motion to adaptively propagate information based on local conditions (such as high placement concentrations), so that the sink gradually ”learns”
the network and accordingly optimizes its motion. Compared to relevant solutions in the state of the art (such as the blind random walk, biased walks, and even optimized deterministic sink mobility), our method significantly reduces latency (the improvement ranges from 40% for uniform placements, to 800% for heterogeneous ones), while also improving the success rate and keeping the energy dissipation at very satisfactory levels.
Abstract: We discuss two different ways of having fun with two different kinds of games: On the one hand, we present a framework for developing multiplayer pervasive games that rely on the use of mobile sensor networks. On the other hand, we show how to exploit game theoretic concepts in order to study the graph-theoretic problem of vertex coloring.
Abstract: In this work we study the implementation of multicost rout-
ing in a distributed way in wireless mobile ad hoc networks.
In contrast to traditional single-cost routing, where each
path is characterized by a scalar, in multicost routing a
vector of cost parameters is assigned to each network link,
from which the cost vectors of candidate paths are calcu-
lated. These parameters are combined in various optimiza-
tion functions, corresponding to different routing algorithms,
for selecting the optimal path. Up until now the performance
of multicost and multi-constrained routing in wireless ad hoc
networks has been evaluated either at a theoretical level or
by assuming that nodes are static and have full knowledge
of the network topology and nodes� state. In the present
paper we assess the performance of multicost routing based
on energy-related parameters in mobile ad hoc networks by
embedding its logic in the Dynamic Source Routing (DSR)
algorithm, which is a well-known fully distributed routing
algorithm. We use simulations to compare the performance
of the multicost-DSR algorithm to that of the original DSR
algorithm and examine their behavior under various node
mobility scenarios. The results confirm that the multicost-
DSR algorithm improves the performance of the network in
comparison to the original DSR algorithm in terms of energy efficiency. The multicost-DSR algorithm enhances the
performance of the network not only by reducing energy
consumption overall in the network, but also by spreading
energy consumption more uniformly across the network, pro
longing the network lifetime and reducing the packet drop
probability. Furthermore the delay suffered by the packets
reaching their destination for the case of the multicost-DSR
algorithm is shown to be lower than in the case of the orig
inal DSR algorithm.
Abstract: In this book chapter we will consider key establishment protocols for wireless sensor networks.
Several protocols have been proposed in the literature for the establishment of a shared group key for wired networks.
The choice of a protocol depends whether the key is established by one of the participants (and then transported to the other(s)) or agreed among the participants, and on the underlying cryptographic mechanisms (symmetric or asymmetric). Clearly, the design of key establishment protocols for sensor networks must deal with different problems and challenges that do not exist in wired networks. To name a few, wireless links are particularly vulnerable to eavesdropping, and that sensor devices can be captured (and the secrets they contain can be compromised); in many upcoming wireless sensor networks, nodes cannot rely on the presence of an online trusted server (whereas most standardized authentication and key establishment protocols do rely on such a server).
In particular, we will consider five distributed group key establishment protocols. Each of these protocols applies a different algorithmic technique that makes it more suitable for (i) static sensor networks, (ii) sensor networks where nodes enter sleep mode (i.e. dynamic, with low rate of updates on the connectivity graph) and (iii) fully dynamic networks where nodes may even be mobile. On the other hand, the common factor for all five protocols is that they can be applied in dynamic groups (where members can be excluded or added) and provide forward and backward secrecy. All these protocols are based on the Diffie-Hellman key exchange algorithm and constitute natural extensions of it in the multiparty case.
Abstract: In this paper we examine the problem of searching for some information item in the nodes of a fully
interconnected computer network, where each node contains information relevant to some topic
as well as links to other network nodes that also contain information, not necessarily related to
locally kept information. These links are used to facilitate the Internet users and mobile software
agents that try to locate specific pieces of information. However, the links do not necessarily point
to nodes containing information of interest to the user or relevant to the aims of the mobile agent.
Thus an element of uncertainty is introduced. For example, when an Internet user or some search
agent lands on a particular network node, they see a set of links that point to information that is,
supposedly, relevant to the current search. Therefore, we can assume that a link points to relevant
information with some unknown probability p that, in general, is related to the number of nodes
in the network (intuitively, as the network grows, this probability tends to zero since adding more
nodes to the network renders some extant links less accurate or obsolete). Consequently, since there
is uncertainty as to whether the links contained in a node?s Web page are correct or not, a search
algorithm cannot rely on following the links systematically since it may end up spending too much
time visiting nodes that contain irrelevant information. In this work, we will describe and analyze
a search algorithm that is only allowed to transfer a fixed amount of memory along communication
links as it visits the network nodes. The algorithm is, however, allowed to use one bit of memory at
each node as an ?already visited? flag. In this way the algorithm has its memory distributed to the
network nodes, avoiding overloading the network links as it moves from node to node searching for
the information. We work on fully interconnected networks for simplicity reasons and, moreover,
because according to some recent experimental evidence, such networks can be considered to be a
good approximation of the current structure of the World Wide Web.
Abstract: We extend here the Population Protocol model of Angluin et al. [2004,2006] in order to model more powerful networks of resource-limited agents that are possibly mobile. The main feature of our extended model, called the Mediated Population Protocol (MPP) model, is to allow edges of the communication graph to have states that belong to a constant size set. We then allow the protocol rules for pairwise interactions to modify the corresponding edge state. Protocol specifications preserve both uniformity and anonymity. We first focus on the computational power of the MPP model on complete communication graphs and initially identical edges. We provide the following exact characterization for the class MPS of stably computable predicates: A predicate is in MPS iff it is symmetric and is in NSPACE(n^2)$. We finally ignore the input to the agents and study MPP's ability to compute graph properties.
Abstract: We extend here the Population Protocol model of Angluin et al. [2004] in order to model more powerful networks of very small resource-limited artefacts (agents) that are possibly mobile. Communication can happen only between pairs of artefacts. A communication graph (or digraph) denotes the permissible pairwise interactions. The main feature of our extended model is to allow edges of the communication graph, G, to have states that belong to a constant size set. We also allow edges to have readable only costs, whose values also belong to a constant size set. We then allow the protocol rules for pairwise interactions to modify the corresponding edge state. Thus, our protocol specifications are still independent of the population size and do not use agent ids, i.e. they preserve scalability, uniformity and anonymity. Our Mediated Population Protocols (MPP) can stably compute graph properties of the communication graph. We show this for the properties of maximal matchings (in undirected communication graphs), also for finding the transitive closure of directed graphs and for finding all edges of small cost. We demonstrate that our mediated protocols are stronger than the classical population protocols, by presenting a mediated protocol that stably computes the product of two positive integers, when G is the complete graph. This is not a semilinear predicate. To show this fact, we state and prove a general Theorem about the Composition of two stably computing mediated population protocols. We also show that all predicates stably computable in our model are (non-uniformly) in the class NSPACE(m), where m is the number of edges of the communication graph. We also define Randomized MPP and show that, any Peano predicate accepted by a MPP, can be verified in deterministic Polynomial Time.
Abstract: We present here, Fun in Numbers, a framework for developing multiplayer pervasive games that rely on the use of ad hoc mobile sensor networks. The unique feature in such games is that players interact with each other and their surrounding environment by using movement and presence as a means of performing game-related actions, utilizing sensor devices. We present the fundamental issues and challenges related to these type of games and the scenarios associated with them is provided. Our framework is developed using Java and is based on a multilayer architecture, which provides developers with a set of templates and services for building and operating new games. Our framework handles a number of challenging fundamental and practical issues, such as synchronization, network congestion, delay-tolerant communication and neighbors discovery. We also present our platform and identify issues that arise in pervasive games which utilize sensor network nodes. The implemented games show how to use non-conventional user interface methods to breathe new life into familiar concepts, like the multiplayer games played out in open space.
Abstract: Wireless Sensor Networks (WSNs) constitute a recent and promising new
technology that is widely applicable. Due to the applicability of this
technology and its obvious importance for the modern distributed
computational world, the formal scientific foundation of its inherent laws
becomes essential. As a result, many new computational models for WSNs
have been proposed. Population Protocols (PPs) are a special category of
such systems. These are mainly identified by three distinctive
characteristics: the sensor nodes (agents) move passively, that is, they
cannot control the underlying mobility pattern, the available memory to
each agent is restricted, and the agents interact in pairs. It has been
proven that a predicate is computable by the PP model iff it is
semilinear. The class of semilinear predicates is a fairly small class. In
this work, our basic goal is to enhance the PP model in order to improve
the computational power. We first make the assumption that not only the
nodes but also the edges of the communication graph can store restricted
states. In a complete graph of n nodes it is like having added O(n2)
additional memory cells which are only read and written by the endpoints
of the corresponding edge. We prove that the new model, called Mediated
Population Protocol model, can operate as a distributed nondeterministic
Turing machine (TM) that uses all the available memory. The only
difference from a usual TM is that this one computes only symmetric
languages. More formally, we establish that a predicate is computable by
the new model iff it is symmetric and belongs to NSPACE(n2). Moreover, we
study the ability of the new model to decide graph languages (for general
graphs). The next step is to ignore the states of the edges and provide
another enhancement straight away from the PP model. The assumption now is
that the agents are multitape TMs equipped with infinite memory, that can
perform internal computation and interact with other agents, and we define
space-bounded computations. We call this the Passively mobile Machines
model. We prove that if each agent uses at most f(n) memory for f(n)={\`U}(log
n) then a predicate is computable iff it is symmetric and belongs to
NSPACE(nf(n)). We also show that this is not the case for f(n)=o(log n).
Based on these, we show that for f(n)={\`U}(log n) there exists a space
hierarchy like the one for classical symmetric TMs. We also show that the
latter is not the case for f(n)=o(loglog n), since here the corresponding
class collapses in the class of semilinear predicates and finally that for
f(n)={\`U}(loglog n) the class becomes a proper superset of semilinear
predicates. We leave open the problem of characterizing the classes for
f(n)={\`U}(loglog n) and f(n)=o(log n).
Abstract: Motivated by the problem of efficiently collecting data from
wireless sensor networks via a mobile sink, we present an accelerated
random walk on Random Geometric Graphs. Random
walks in wireless sensor networks can serve as fully local,
very simple strategies for sink motion that significantly
reduce energy dissipation but introduce higher latency in the
data collection process. While in most cases random walks
are studied on graphs like Gn,p and Grid, we define and experimentally
evaluate our newly proposed random walk on
the Random Geometric Graphs model, that more accurately
abstracts spatial proximity in a wireless sensor network. We
call this new random walk the \~{a}-stretched random walk, and
compare it to two known random walks; its basic idea is
to favour visiting distant neighbours of the current node
towards reducing node overlap. We also define a new performance
metric called Proximity Cover Time which, along
with other metrics such as visit overlap statistics and proximity
variation, we use to evaluate the performance properties
and features of the various walks.
Abstract: An ad-hoc mobile network is a collection of mobile hosts, with
wireless communication capabilities, forming a temporary network
without the aid of any established fixed infrastructure.
In such networks, topological connectivity is subject to frequent,
unpredictable change. Our work focuses on networks with high
rate of such changes to connectivity. For such dynamic changing
networks we propose protocols which exploit the co-ordinated
(by the protocol) motion of a small part of the network.
We show that such protocols can be designed to work
correctly and efficiently even in the case of arbitrary (but not
malicious) movements of the hosts not affected by the protocol.
We also propose a methodology for the analysis of the expected
behaviour of protocols for such networks, based on the assumption that mobile hosts (whose motion is not guided by
the protocol) conduct concurrent random walks in their
motion space.
Our work examines some fundamental problems such as pair-wise
communication, election of a leader and counting, and proposes
distributed algorithms for each of them. We provide their
proofs of correctness, and also give rigorous analysis by
combinatorial tools and also via experiments.
Abstract: In this paper we demonstrate the significant impact of (a) the mobility rate and (b) the user density on the performance of routing protocols in ad-hoc mobilenetworks. In particular, we study the effect of these parameters on two different approaches for designing routing protocols: (a) the route creation and maintenance approach and (b) the "support" approach, that forces few hosts to move acting as "helpers" for message delivery. We study one representative protocol for each approach, i.e., AODV for the first approach and RUNNERS for the second. We have implemented the two protocols and performed a large scale and detailed simulation study of their performance. For the first time, we study AODV (and RUNNERS) in the 3D case. The main findings are: the AODV protocol behaves well in networks of high user density and low mobility rate, while its performance drops for sparse networks of highly mobile users. On the other hand, the RUNNERS protocol seems to tolerate well (and in fact benefit from) high mobility rates and low densities. Thus, we are able to partially answer an important conjecture of [Chatzigiannakis, I et al. 2003].
Abstract: We propose a new theoretical model for passively mobile Wireless Sensor Networks. We
call it the PALOMA model, standing for PAssively mobile LOgarithmic space MAchines. The main
modification w.r.t. the Population Protocol model [2] is that agents now, instead of being automata, are
Turing Machines whose memory is logarithmic in the population size n. Note that the new model is still
easily implementable with current technology. We focus on complete communication graphs. We define
the complexity class PLM, consisting of all symmetric predicates on input assignments that are stably
computable by the PALOMA model. We assume that the agents are initially identical. Surprisingly, it
turns out that the PALOMA model can assign unique consecutive ids to the agents and inform them
of the population size! This allows us to give a direct simulation of a Deterministic Turing Machine
of O(n log n) space, thus, establishing that any symmetric predicate in SPACE(n log n) also belongs
to PLM. We next prove that the PALOMA model can simulate the Community Protocol model [15],
thus, improving the previous lower bound to all symmetric predicates in NSPACE(n log n). Going
one step further, we generalize the simulation of the deterministic TM to prove that the PALOMA
model can simulate a Nondeterministic TM of O(n log n) space. Although providing the same lower
bound, the important remark here is that the bound is now obtained in a direct manner, in the sense
that it does not depend on the simulation of a TM by a Pointer Machine. Finally, by showing that a
Nondeterministic TM of O(n log n) space decides any language stably computable by the PALOMA
model, we end up with an exact characterization for PLM: it is precisely the class of all symmetric
predicates in NSPACE(n log n).
Abstract: We propose a new theoretical model for passively mobile Wireless Sensor Networks, called PM, standing for Passively mobile Machines. The main modification w.r.t. the Population Protocol model [Angluin et al. 2006] is that agents now, instead of being automata, are Turing Machines. We provide general definitions for unbounded memories, but we are mainly interested in computations upper-bounded by plausible space limitations. However, we prove that our results hold for more general cases. We focus on \emph{complete interaction graphs} and define the complexity classes PMSPACE(f(n)) parametrically, consisting of all predicates that are stably computable by some PM protocol that uses O(f(n)) memory in each agent. We provide a protocol that generates unique identifiers from scratch only by using O(log n) memory, and use it to provide an exact characterization of the classes PMSPACE(f(n)) when f(n) = Ω(log n): they are precisely the classes of all symmetric predicates in NSPACE(nf(n)). As a consequence, we obtain a space hierarchy of the PM model when the memory bounds are Ω(log n). We next explore the computability of the PM model when the protocols use o(loglog n) space per machine and prove that SEM = PMSPACE(f(n)) when f(n) = o(loglog n), where SEM denotes the class of the semilinear predicates. Finally, we establish that the minimal space requirement for the computation of non-semilinear predicates is O(log log n).
Abstract: We propose a new theoretical model for passively mobile Wireless Sensor Networks, called PM, standing for Passively mobile Machines. The main modification w.r.t. the Population Protocol model [Angluin et al. 2006] is that the agents now, instead of being automata, are Turing Machines. We provide general definitions for unbounded memories, but we are mainly interested in computations upper-bounded by plausible space limitations. However, we prove that our results hold for more general cases. We focus on complete interaction graphs and define the complexity classes PMSPACE(f(n)) parametrically, consisting of all predicates that are stably computable by some PM protocol that uses O(f(n)) memory in each agent. We provide a protocol that generates unique identifiers from scratch only by using O(log n) memory, and use it to provide an exact characterization of the classes PMSPACE(f(n)) when f(n)=Omega(log n): they are precisely the classes of all symmetric predicates in NSPACE(nf(n)). As a consequence, we obtain a space hierarchy of the PM model when the memory bounds are Omega(log n). Finally, we establish that the minimal space requirement for the computation of non-semilinear predicates is O(log log n).
Abstract: This Volume contains the 11 papers corresponding to poster and demo presentations
accepted to the 7th ACM/IEEE International Symposium on Modeling,
Analysis and Simulation ofWireless and Mobile Systems (MSWiM 04),
that is held October 4-6, 2004, in Venice, Italy.
MSWiM 2004 (http://www.cs.unibo.it/mswim2004/) is intended to provide
an international forum for original ideas, recent results and achievements on
issues and challenges related to mobile and wireless systems.
A Call for Posters was announced and widely disseminated, soliciting posters
that report on recent original results or on-going research in the area of wireless
and mobilenetworks. Prospective authors were encouraged to submit interesting
results on all aspects of modeling, analysis and simulation of mobile and
wireless networks and systems. The scope and topics of the Posters Session
were the same as those included in the MSWiM Call for Papers (see above).
Poster presentations were meant to provide authors with early feedback on
their research work and enable them to present their research and exchange
ideas during the Symposium.
All submissions to the call for posters as well as selected papers submitted
to MSWiM 04 were considered and reviewed. The review process resulted in
accepting the set of 11 papers included in this Volume. Accepted posters will
also be on display during the Symposium.
The set of papers in this Proceedings covers a wide range of important topics
in wireless and mobile computing, including channel allocation in wireless
networks, quality of service provisioning in IEEE 802.11 wireless LANs, IP
mobility support, energy conservation, routing in mobile adhoc networks, resource
sharing, wireless access to the WWW, sensor networks etc. The performance
evaluation techniques used include both analysis and simulation.
We hope that the poster papers included in this Volume will facilitate a fruitful
and lively discussion and exchange of interesting and creative ideas during
the Symposium.
We wish to thank the MSWiM Steering Committee Chair Azzedine Boukerche
and the Program Co-Chairs ofMSWiM 04 Carla-Fabiana Chiasserini and
Lorenzo Donatiello for their valuable help in the selection procedure. Also, the
MSWiM 04 Publicity Co-Chairs Luciano Bononi, Helen Karatza and Mirela
Sechi Moretti Annoni Notare for disseminating the Call for Posters.
We wish to warmly thank the Poster Proceedings Chair Ioannis Chatzigiannakis
for carefully doing an excellent job in preparing the Volume you now
hold in your hands.
Abstract: The 8th ACM/IEEE International Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems Symposium (MSWiM 2005) solicits posters that report on recent original results or on-going research in the area of wireless and mobilenetworks.
Abstract: The 9th ACM/IEEE International Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems Symposium (MSWiM 2006) solicits posters that report on recent original results or on-going research in the area of wireless and mobilenetworks.
Abstract: The population protocol model (PP) proposed by Angluin et al. [2] describes sensor networks consisting of passively mobile finite-state agents. The agents sense their environment and communicate in pairs to carry out some computation on the sensed values. The mediated population protocol model (MPP) [13] extended the PP model by communication links equipped with a constant size buffer. The MPP model was proved in [13] to be stronger than the PP model. However, its most important contribution is that it provides us with the ability to devise optimizing protocols, approximation protocols and protocols that decide properties of the communication graph on which they run. The latter case, suggests a simplified model, the GDM model, that was formally defined and studied in [11]. GDM is a special case of MPP that captures MPP's ability to decide properties of the communication graph. Here we survey recent advances in the area initiated by the proposal of the PP model and at the same time we provide new protocols, novel ideas and results.
Abstract: In this paper we demonstrate the significant impact of the user mobility rates on the performance on two different approaches for designing routing protocols for ad-hoc mobilenetworks: (a) the route creation and maintenance approach and (b) the "support" approach, that forces few hosts to move acting as
"helpers" for message delivery. We study a set of representative protocols for each approach, i.e.~DSR and ZRP for the first approach and RUNNERS for the second. We have implemented the three protocols and performed a large scale and detailed simulation study of their performance. Our findings are: (i) DSR achieves low message delivery rates but manages to deliver messages very fast; (ii) ZRP behaves well in networks of low mobility rate, while its performance drops for networks of highly mobile users; (iii) RUNNERS seem to tolerate well (and in fact benefit from) high mobility rates.
Based on our investigation, we design and implement two new protocols that result from the synthesis of the investigated routing approaches. We conducted an extensive, comparative simulation study of their performance. The new protocols behave well both in networks of diverse mobility motion rates, and in some cases they even outperform the original ones by achieving lower message delivery delays.
Abstract: Data propagation in wireless sensor
networks is usually performed as a multihop process.
Thus,
To deliver a single
message, the resources of many sensor nodes are used and
a lot of energy is spent.
Recently, a novel approach is catching momentum because of important applications;
that of having a mobile sink move inside the network area and collect
the data with low energy cost.
Here we extend this line of research by proposing and evaluating three new protocols.
Our protocols are novel in
a) investigating the impact of having {many} mobile sinks
b) in weak models with restricted mobility, proposing and evaluating
a mix of static and mobile sinks and c) proposing a distributed
protocol that tends to {equally spread the sinks} in the network to
further improve performance.
Our protocols are simple, based on randomization and assume locally
obtainable information. We perform an extensive evaluation via simulation; our
findings demonstrate that our solutions scale very well with respect to the number of sinks
and significantly reduce energy consumption and delivery delay.
Abstract: We investigate the impact of different mobility rates on the
performance of routing protocols in ad-hoc mobilenetworks. Based
on our investigation, we design a new protocol that results from
the synthesis of the well known protocols: ZRP and RUNNERS. We have implemented the new protocol as well as
the original two protocols and conducted an extensive, comparative
simulation study of their performance. The new protocol behaves
well both in networks of diverse mobility motion rates, and in
some cases even outperforms the original ones by achieving lower
message delivery delays.
Abstract: In this work, we discuss multiplayer pervasive
games that rely on the use of ad hoc mobile sensor networks.
The unique feature in such games is that players interact
with each other and their surrounding environment by using
movement and presence as a means of performing game-related
actions, utilizing sensor devices. We discuss the fundamental
issues and challenges related to these type of games and the
scenarios associated with them. We also present and evaluate
an example of such a game, called the “Hot Potato”, developed
using the Sun SPOT hardware platform. We provide a set of
experimental results, so as to both evaluate our implementation
and also to identify issues that arise in pervasive games which
utilize sensor network nodes, which show that there is great
potential in this type of games.
Abstract: We propose and evaluate the performance of a new MAC-layer protocol for mobile ad hoc networks, called the Slow Start Power Controlled (abbreviated SSPC) protocol. SSPC improves on IEEE 802.11 by using power control for the RTS/CTS and DATA frame transmissions, so as to reduce energy consumption and increase network throughput and lifetime. In our scheme the transmission power used for the RTS frames is not constant, but follows a slow start principle. The CTS frames, which are sent at maximum transmission power, prevent the neighbouring nodes from transmitting their DATA frames at power levels higher than a computed threshold, while allowing them to transmit at power levels less than that threshold. Reduced energy consumption is achieved by adjusting the node transmission power to the minimum required value for reliable reception at the receiving node, while increase in network throughput is achieved by allowing more transmissions to take place simultaneously. The slow start principle used for calculating the appropriate DATA frames transmission power and the possibility of more simultaneous collision-free transmissions differentiate the SSPC protocol from the other MAC solutions proposed for IEEE 802.11. Simulation results indicate that the SSPC protocol achieves a significant reduction in power consumption, average packet delay and frequency of RTS frame collisions, and a significant increase in network throughput and received-to-sent packets ratio compared to IEEE 802.11 protocol.
Abstract: In this paper we study the threshold behavior of the fixed radius random graph model and its applications to the key management problem of sensor networks and, generally, for mobile ad-hoc networks. We show that this random graph model can realistically model the placement of nodes within a certain region and their interaction/sensing capabilities (i.e. transmission range, light sensing sensitivity etc.). We also show that this model can be used to define key sets for the network nodes that satisfy a number of good properties, allowing to set up secure communication with each other depending on randomly created sets of keys related to their current location. Our work hopes to inaugurate a study of key management schemes whose properties are related to properties of an appropriate random graph model and, thus, use the rich theory developed in the random graph literature in order to transfer ?good? properties of the graph model to the key sets of the nodes.
Partially supported by the IST Programme of the European Union under contact number IST-2005-15964 (AEOLUS) and the INTAS Programme under contract with Ref. No 04-77-7173 (Data Flow Systems: Algorithms and Complexity (DFS-AC)).
Abstract: Today we are experiencing a major reconsideration of the computing
paradigm, as witnessed by the abundance and increasing frequency
of use of terms such as {\em ambient intelligence}, {\em ubiquitous computing}, {\em disappearing computer}, {\em grid
computer}, {\em global computing} and {\em mobile ad-hoc
networks}. Systems that can be described with such terms are of a
dynamic, with no clear physical boundary, nature and it seems that
it is impossible (or, at least, difficult) to define sharply a
number of important properties holding with certainty as well as
holding throughout the whole lifetime of the system.
%
One such system property, which is important for the viability of
a system, is {\em trust}. Our departure point is the assumption
that it seems very difficult to define static system properties
related to trust and expect that they hold eternally in the
rapidly changing systems falling under the new computing paradigm.
One should, rather, attempt to define trust in terms of properties
that hold with some limiting probability as the the system grows
and try to establish conditions that ensure that ``good''
properties hold {\em almost certainly}. Based on this viewpoint,
in this paper we provide a new framework for defining trust
through formally definable properties that hold, almost certainly,
in the limit in randomly growing combinatorial structures that
model ``shapeless'' computing systems (e.g. ad-hoc networks),
drawing on results that establish the threshold behavior of
predicates written in the first and second order logic.
