Routing in multi-hop Ad Hoc networks: an Experimental Approach

In this thesis we investigate the efficiency of routing protocols for Mobile Ad Hoc networks (MANETs) by adopting an experimental approach. MANET routing protocols have been mainly evaluated through simulations which often introduce simplifying assumptions (e.g., radio propagation model) and mask important real characteristics. To avoid these modeling approximations, it is necessary to complement simulation with experiments on real MANETs. This work provides a contribution in this direction reporting our experiences learned by these real measurements. By setting up MANET prototypes, firstly we investigate IEEE 802.11 behavior in single­hop MANETs, secondly we focus on an innovative analysis of routing protocols in multi­hop MANETs by varying scenarios. To the best of our knowledge, our medium­scale scenario composed of 23 nodes represents one of the largest MANET testbed. Our experimental results highlight that, in contrast with MANET community, by using proactive routing protocols the overall system gains in scalability, performance and efficiency. These results encourage us identifying in this last class Hazy Sighted Link State (HSLS) as a more suitable protocol. A further contribution of this thesis is hence to design, develop and test an enhanced version of HSLS, strengthened with a mechanism to guarantee the reliability of LSU packets without additional control overhead, and a module to support middleware-network interactions as proposed by the MobileMAN project (EUIST-FP5-FET-Open-IST-2001-38113)

Energy Efficient and Reliable Data Delivery in Urban Sensing Applications: A Performance Analysis

Urban sensing is an emerging application field for Wireless Sensor Networks (WSNs), where a number of static sensors is sparsely deployed in an urban area to collect environmental information. Data sensed by each sensor are, then, opportunistically transmitted to Mobile Nodes (MNs) that happen to be in contact. In the considered scenario, communications between MNs and sensors require paradigms with a minimal synchronization between devices, extremely fast and energy efficient, especially at the sensor side. To deal with the above issues, in [1] we proposed a hybrid protocol for data delivery from sensors to MNs, named Hybrid Adaptive Interleaved Data Protocol (HI). By combining Erasure Coding (EC) with an Automatic Repeat reQuest (ARQ) scheme, the proposed protocol maximizes the reliability of communications while minimizing the energy consumed by sensors. In this paper, we present an in-depth analysis of the HI performance. We provide an analytical evaluation by defining a flexible model to derive the probability of data delivery and exploiting it to investigate the performance over a wide range of parameters. Moreover, we avail of an experimental study to evaluate the HI effectiveness on real sensor platforms. Specifically, we analyze the impact of resource constraints imposed by sensors on data delivery and provide a careful characterization of its actual consumption of resources

Performance modelling of opportunistic forwarding with exact knowledge

The Delay Tolerant Networking paradigm aims to enable communications in disconnected environments where traditional protocols would fail. Opportunistic networks are delay tolerant networks whose nodes are typically the users\u27 personal mobile devices. Communications in an opportunistic network rely on the mobility of users: each message is forwarded from node to node, according to a hop-by-hop decision process that selects the node that is better suited for bringing the message closer to its destination. Despite the variety of forwarding protocols that have been proposed in the recent years, there is no reference framework for the performance modelling of opportunistic forwarding. In this paper we start to fill this gap by proposing an analytical model for the expected delay and the expected number of hops experienced by messages when delivered in an opportunistic fashion. This model seamlessly integrates both social-aware and social-oblivious single-copy forwarding protocols, as well as different hypotheses for user contact dynamics. The proposed framework is used to derive bounds on the expected delay under homogeneous and heterogeneous contact patterns. We found that, in heterogeneous settings, finite expected delay can be guaranteed not only when nodes\u27 inter-meeting times follow an exponential or power law with exponential cut-off distribution, but also when they are power law distributed, as long as weaker conditions than those derived by Chaintreau et al. [1] for the homogeneous scenario are satisfied

Detecting users communities in mobile social networks

In this paper we focus on approaches which aim at discovering communities of people in Opportunistic Networks. We first study the behaviour of three community detection distributed algorithms proposed in literature [1], in a scenario where people move according to a mobility model which well reproduces the nature of human contacts, namely HCMM [2]. By a simulation analysis, we show that these distributed approaches can satisfactory detect the communities formed by people only when they do not significantly change over time. Otherwise, as they maintain memory of all encountered nodes forever, these algorithms fail to capture dynamic evolutions of the social communities users are part of. To this aim we propose AD-SIMPLE, a new solution which captures the dynamic evolution of social communities. By an extensive simulation analysis, we demonstrate that it accurately detects communities and social changes while keeping computation and storage requirements low

A Hybrid Adaptive Protocol for Reliable Data Delivery in WSNs with Multiple Mobile Sinks

In this paper we deal with reliable and energy-efficient data delivery in sparse Wireless Sensor Networks with multiple Mobile Sinks (MSs). This is a critical task, especially when MSs move randomly, as interactions with sensor nodes are unpredictable, typically of short duration, and affected by message losses. In this paper we propose an adaptive data delivery protocol that combines efficiently erasure coding with an ARQ scheme. The key features of the proposed protocol are: (i) the use of redundancy to cope efficiently with message losses, and (ii) the ability of adapting the level of redundancy based on feedbacks sent back by MSs through ACKs. We observed by simulation that our protocol outperforms an alternative protocol that relies only on an ARQ scheme, even when there is a single MS. We also validated our simulation results through a set of experimental measurements based on real sensor nodes. Our results show that the adoption of encoding techniques is beneficial to energy-efficient (and reliable) data delivery in WSNs with Mobile Sinks

IEEE 802.11 Ad Hoc Networks: Performance Measurements

In this paper we investigate the performance of IEEE 802.11b ad hoc networks by means of an experimental study. An extensive literature, based on simulation studies, there exists on the performance of IEEE 802.11 ad hoc networks. Our analysis reveals several aspects that are usually neglected in previous simulation studies. Firstly, since different transmission rates are used for control and data frames, different transmission ranges and carrier-sensing ranges may exist at the same time in the network. In addition, the transmission ranges are in practice much shorter than usually assumed in simulation analysis, not constant but highly variable (even in the same session) and depends on several factors. Finally, the results presented in this paper indicate that for correctly understanding the behavior of an 802.11b network operating in ad hoc mode, several different ranges must be considered. In addition to the transmission range, the physical carrier sensing range is very important. The transmission range is highly dependent on the data rate and is up to 100 m, while the physical carrier sensing range is almost independent from the data rate and is approximately 200 m. Furthermore, even though stations are outside from their respective physical carrier sensing range, they may still interfere if their distance is lower than 350 m

Modelo de corriente de fuga en estructuras de unión p-n fabricados a base de nitruros del grupo III en fase cubica

Mediante mediciones de SIMS, encontramos evidencia de difusión de impurezas residuales hacia el bulto de películas de GaN cubico no intencionalmente dopadas. El análisis de imágenes de espectroscopía de masas de iones secundarios (SIMS) revela que la difusión es propiciada por las fallas de apilamiento. La profundidad a la que las impurezas residuales difunden, concuerda con la distancia a la que la densidad de fallas de apilamiento alcanza su valor mínimo. Mediciones de microscopía electrónica en transmisión (TEM) muestran una alta densidad de fallas de apilamiento en las zonas de contacto ohmico de diodos de unión p-n fabricados con GaN cúbico. De acuerdo con datos reportados en la literatura que indican conducción parásita a través de defectos estructurales y con base en estos resultados, se propone un modelo de corriente de fuga en diodos de unión p-n de GaN cúbico que degradan su desempeño y/o provocan su falla

Minimum-Delay Service Provisioning in Opportunistic Networks

Opportunistic networks are (ad hoc) networks created dynamically by exploiting contacts between pairs of mobile devices that come within communication range. This networking paradigm overcomes main limitations of conventional MANETs, related to the fact that, due to mobility and energy conservation issues, it is often not practical to maintain connected multihop paths among nodes. While forwarding in opportunistic networking has been explored, investigations into asynchronous service provisioning are unique contributions of this paper. Mobile devices are typically heterogeneous, possess disparate physical resources, and can provide a variety of services. During opportunistic contacts, the pairing peers can cooperatively provide (avail of) its (other peer\u27s) services. This service provisioning paradigm is a key feature of the emerging opportunistic computing paradigm. We develop an analytical model to study the behaviors of service seeking nodes (seekers) and service providing nodes (providers) that spawn and execute service requests, respectively. The model considers the case in which seekers can spawn parallel executions on multiple providers for any given request, and determines: i) the delays at different stages of service provisioning; and ii) the optimal number of parallel executions that minimizes the expected execution time without saturating providers\u27 resources. The analytical model is validated through simulations, and exploited to investigate the performance of service provisioning over a wide range of parameters

Exploiting opportunistic contacts for service provisioning in bandwidth limited opportunistic networks

Opportunistic computing has emerged as a new paradigm in computing, leveraging the advances in pervasive computing and opportunistic networking. Nodes in an opportunistic network avail of each others\u27 connectivity and mobility to overcome network partitions. In opportunistic computing, this concept is generalised, as nodes avail of any resource available in the environment. Here we focus on computational resources, assuming mobile nodes opportunistically invoke services on each other. Specifically, resources are abstracted as services contributed by providers and invoked by seekers. In this paper, we present an analytical model that depicts the service invocation process between seekers and providers. Specifically, we derive the optimal number of replicas to be spawned on encountered nodes, in order to minimise the execution time and optimise the computational and bandwidth resources used. Performance results show that a policy operating in the optimal configuration largely outperforms policies that do not consider resource constraints

Beta-agonist stimulation ameliorates the phenotype of spinal and bulbar muscular atrophy mice and patient-derived myotubes

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease characterized by the loss of lower motor neurons. SBMA is caused by expansions of a polyglutamine tract in the gene coding for androgen receptor (AR). Expression of polyglutamine-expanded AR causes damage to motor neurons and skeletal muscle cells. Here we investigated the effect of β-agonist stimulation in SBMA myotube cells derived from mice and patients, and in knock-in mice. We show that treatment of myotubes expressing polyglutamine-expanded AR with the β-agonist clenbuterol increases their size. Clenbuterol activated the phosphatidylinositol-3-kinase (PI3K)/Akt/mechanistic target of rapamycin (mTOR) pathway and decreased the accumulation of polyglutamine-expanded AR. Treatment of SBMA knock-in mice with clenbuterol, which was started at disease onset, ameliorated motor function and extended survival. Clenbuterol improved muscle pathology, attenuated the glycolytic-to-oxidative metabolic alterations occurring in SBMA muscles and induced hypertrophy of both glycolytic and oxidative fibers. These results indicate that β-agonist stimulation is a novel therapeutic strategy for SBMA