Nadia N. Qadri

Improving Propagation Modeling in Urban Environments for Vehicular Ad Hoc Networks

Developing applications, particularly real-time applications, for wireless vehicular ad hoc networks (VANETs) requires a reasonable assurance of the likely performance of the network, at the least in terms of packet loss ratios and end-to-end delay. Because wireless propagation strongly influences performance, particularly in an urban environment, this paper improves on simpler propagation models for simulations by augmenting ray-tracing-derived models of propagation. In the non-line-of-sight (NLOS) component, the propagation distance is more closely calculated according to the reflection distance, the effect of roadside obstacles is included, and for the modeling of fast fading, a phase factor is introduced, all without necessarily overly increasing the computational load. In the line-of-sight (LOS) component, as well as the roadside obstacle modeling, single and double reflections from roadside buildings are added to the standard two-ray ground-propagation model, the distribution of vehicles within a street segment is used to more closely model the ground reflection ray, and the reflection coefficient is also accordingly adjusted to account for reflections from vehicles. The results have been compared with widely used measurement studies of city streets in the literature, which have confirmed the overall advantage of the improvements, particularly in the case of the NLOS component. A simulation case study shows that, in general, optimistic performance predictions of packet loss occur with the two-ray ground-propagation model when indiscriminately applied. This paper therefore represents a way forward for VANET wireless channel modeling in simulations.

Robust Video Streaming over an Urban VANET

Because of restricted mobility patterns, multi-hop routing, and wireless channel conditions, streaming video over a Vehicular Ad Hoc Network (VANET) is a daunting task. This paper demonstrates that H.264 codec Flexible Macroblock Ordering (FMO) with receiver error concealment is capable of streaming good-quality video across a VANET. FMO is shown to be superior to other error resilience techniques but attention should be given to packet size, choice of protocol and the rate the video is released into the network if there are multiple destinations. Settings close to those of the emerging IEEE 802.11p standard for VANETs were emulated for a Manhattan grid mobility model.

Analysis of Pervasive Mobile Ad Hoc Routing Protocols

Mobile ad hoc networks (MANETs) are a fundamental element of pervasive networks and therefore, of pervasive systems that truly support pervasive computing, where user can communicate anywhere, anytime and on-the-fly. In fact, future advances in pervasive computing rely on advancements in mobile communication, which includes both infrastructure-based wireless networks and non-infrastructure-based MANETs. MANETs introduce a new communication paradigm, which does not require a fixed infrastructure – they rely on wireless terminals for routing and transport services. Due to highly dynamic topology, absence of established infrastructure for centralized administration, bandwidth constrained wireless links, and limited resources in MANETs, it is challenging to design an efficient and reliable routing protocol. This chapter reviews the key studies carried out so far on the performance of mobile ad hoc routing protocols. We discuss performance issues and metrics required for the evaluation of ad hoc routing protocols. This leads to a survey of existing work, which captures the performance of ad hoc routing algorithms and their behaviour from different perspectives and highlights avenues for future research.

Robust P2P Multimedia Exchange within a VANET

Multimedia exchange within a Vehicular Ad Hoc Network (VANET) may be facilitated by exploiting the peer-to-peer (P2P) paradigm for which a multi-path routing protocol has been designed to reduce packet loss. Urban VANETs are characterized by restricted vehicle mobility, driver actions, and bunching at obstacles, leading to wireless interference and broken links. Similarly P2P communication relies on distributed sources which are intermittently available. However, routing packets over multiple hops and multiple paths still results in packet losses, resulting in poor quality reconstructed video at a receiver. This paper proposes a novel slice compensation scheme employing spatial Multiple Description Coding to provide error resilience as a solution to these problems. Results show constant good-quality video even if packet losses rates increase.

Multi-objective optimization in sensor networks

A number of the practical scenarios relating to sensor networks are modeled as multi-objective optimization formulations where multiple desirable objectives compete with each other and the decision maker has to choose one of the tradeoff solutions. These multiple objectives may or may not conflict with each other. Keeping in view the nature of the application, the sensing scenario and input/output of the problem, the type of optimization problem changes. To tackle different nature of optimization problems relating to sensor network design, deployment, operation, planing and placement, there exist a plethora of optimization solution types. We analyze the existing literature to show the trend of the research community with respect to sensor network technologies being used, different engineering applications, simulation tools being used and the research emanating from different geographical areas. We also present a generic resource allocation problem in sensor network which consists of input variables, required output, objectives and constraints. A list of constraints is also tabulated to give an overview of different constraints which are considered while formulating the optimization problem in sensor networks. Keeping in view the multi facet coverage of this article relating to multi-objective optimization, this will open up new avenues of research in the area of multi-objective optimization relating to sensor networks.

Resilient P2P multimedia exchange in a VANET

Multimedia exchange within a Vehicular Ad Hoc Network (VANET) may be facilitated by exploiting the peer-to-peer (P2P) paradigm. Urban VANETs are characterized by restricted vehicle mobility, driver actions, and bunching at obstacles, leading to wireless interference and broken links. Similarly P2P communication relies on distributed sources which are intermittently available. However, routing packets over multiple hops and multiple paths still results in packet losses, resulting in poor quality reconstructed video at a receiver. This paper proposes a slice compensation scheme employing spatial Multiple Description Coding to provide error resilience as a solution to these problems. Results show constant good quality video despite increasing packet loss ratios.

Energy and throughput aware fuzzy logic based reconfiguration for MPSoCs

Multicore architectures offer an amount of parallelism that is often underutilized, as a result these underutilized resources become a liability instead of advantage. Inefficient resource sharing on the chip can have a negative impact on the performance of an application and may result in greater energy consumption. A large body of research now focuses on reconfigurable multicore architectures in order to support algorithms to find optimal solutions for improved energy and throughput balance. An ideal system would be able to optimize such reconfigurable systems to a level that optimum resources are allocated to a particular workload and all the other underutilized resources remain inactive for greater energy savings. This paper presents a fuzzy logic based reconfiguration engine targeted to optimize a multicore architecture according to the workload requirements for optimum balance between power and performance of the system. The proposed fuzzy logic reconfiguration engine is designed around a 16-core SCMP architecture comprising of reconfigurable cache memories, power gated cores and adaptive on-chip network routers for minimizing leakage energy effects for inactive components. A coarse grained architecture was selected for being able to reconfigure faster, thus making it feasible to be used for runtime adaptation schemes. The presented architecture is analyzed over a set of OpenMP based parallel benchmarks and results show significant energy savings in all cases.

Approaching P2P communication in a vehicular ad hoc network

This paper introduces P2P communication across a VANET and seeks to establish under what conditions (mobility, network size, wireless channel) data streaming is feasible. Routing of streamed services over multiple hops and multiple paths may result in significant packet losses, resulting in unacceptable quality of service. This paper examines the impact of differing traffic densities and different road layouts upon a P2P overlay network. The work modeled the emerging IEEE 802.11p for vehicular networks. It is shown that the mobility pattern of the vehicles involved needs to be closely modeled to determine signal reception patterns, as does the wireless channel environment, to avoid over optimistic assessment of communication within a VANET.

Modeling electrical properties for various geometries of antidots on a superconducting film

Electrical properties, specifically critical current density, of a superconducting film carry a substantial importance in superconductivity. In this work, we measure and study the current–voltage curves for a superconducting Nb film with various geometries of antidots to tune the critical current. We carry out the measurements on a commercially available physical property measurement system to obtain these so-called transport measurements. We show that each of the used geometries exhibits a vastly different critical current, due to which repeatedly performing the measurements independently for each geometry becomes indispensable. To circumvent this monotonous measurement procedure, we also propose a framework based on artificial neural networks to predict the curves for different geometries using a small subset of measurements, and facilitate extrapolation of these curves over a wide range of parameters including temperature and magnetic field. The predicted curves are then cross-checked using the physical measurements; our results suggest a negligible mean-squared error—in the order of