Communication models for monitoring and mobility verification in mission critical wireless networks

Recent technological advances have seen wireless sensor networks emerge as an interesting research topic because of its ability to realize mission critical applications like in military or wildfire detection. The first part of the thesis focuses on the development of a novel communication scheme referred here as a distributed wireless critical information-aware maintenance network (DWCIMN), which is presented for preventive maintenance of network-centric dynamic systems. The proposed communication scheme addresses quality of service (QoS) issues by using a combination of a head-of-the-line queuing scheme, efficient bandwidth allocation, weight-based backoff mechanism, and a distributed power control scheme. A thorough analysis of a head-of-the-line priority queuing scheme is given for a single-server, finite queue with a batch arrival option and user priorities. The scheme is implemented in the Network Simulator (NS-2), and the results demonstrate reduced queuing delays and efficient bandwidth allocation for time-critical data over non time critical data. In the second part, we introduce a unique mobility verification problem in wireless sensor networks wherein the objective is to verify the claimed mobility path of a node in a co-operating mission critical operation between two allies. We address this problem by developing an efficient power-control based mobility verification model. The simulation framework is implemented in Matlab and the results indicate successful detection of altered claimed paths within a certain error bound --Abstract, page iii

Game-Theoretic Relay Selection and Power Control in Fading Wireless Body Area Networks

The trend towards personalized ubiquitous computing has led to the advent of a new generation of wireless technologies, namely wireless body area networks (WBANs), which connect the wearable devices into the Internet-of-Things. This thesis considers the problems of relay selection and power control in fading WBANs with energy-efficiency and security considerations. The main body of the thesis is formed by two papers. Ideas from probability theory are used, in the first paper, to construct a performance measure signifying the energy efficiency of transmission, while in the second paper, information-theoretic principles are leveraged to characterize the transmission secrecy at the wireless physical layer (PHY). The hypothesis is that exploiting spatial diversity through multi-hop relaying is an effective strategy in a WBAN to combat fading and enhance communication throughput. In order to analytically explore the problems of optimal relay selection and power control, proper tools from game theory are employed. In particular, non-cooperative game-theoretic frameworks are developed to model and analyze the strategic interactions among sensor nodes in a WBAN when seeking to optimize their transmissions in the uplink. Quality-of-service requirements are also incorporated into the game frameworks, in terms of upper bounds on the end-to-end delay and jitter incurred by multi-hop transmission, by borrowing relevant tools from queuing theory. The proposed game frameworks are proved to admit Nash equilibria, and distributed algorithms are devised that converge to stable Nash solutions. The frameworks are then evaluated using numerical simulations in conditions approximating actual deployment of WBANs. Performance behavior trade-offs are investigated in an IEEE 802.15.6-based ultra wideband WBAN considering various scenarios. The frameworks show remarkable promise in improving the energy efficiency and PHY secrecy of transmission, at the expense of an admissible increase in the end-to-end latency

Intelligent Hardware-Enabled Sensor and Software Safety and Health Management for Autonomous UAS

Unmanned Aerial Systems (UAS) can only be deployed if they can effectively complete their mission and respond to failures and uncertain environmental conditions while maintaining safety with respect to other aircraft as well as humans and property on the ground. We propose to design a real-time, onboard system health management (SHM) capability to continuously monitor essential system components such as sensors, software, and hardware systems for detection and diagnosis of failures and violations of safety or performance rules during the ight of a UAS. Our approach to SHM is three-pronged, providing: (1) real-time monitoring of sensor and software signals; (2) signal analysis, preprocessing, and advanced on-the- y temporal and Bayesian probabilistic fault diagnosis; (3) an unobtrusive, lightweight, read-only, low-power hardware realization using Field Programmable Gate Arrays (FPGAs) in order to avoid overburdening limited computing resources or costly re-certi cation of ight software due to instrumentation. No currently available SHM capabilities (or combinations of currently existing SHM capabilities) come anywhere close to satisfying these three criteria yet NASA will require such intelligent, hardwareenabled sensor and software safety and health management for introducing autonomous UAS into the National Airspace System (NAS). We propose a novel approach of creating modular building blocks for combining responsive runtime monitoring of temporal logic system safety requirements with model-based diagnosis and Bayesian network-based probabilistic analysis. Our proposed research program includes both developing this novel approach and demonstrating its capabilities using the NASA Swift UAS as a demonstration platform

Energy Efficiency inWireless Sensor Networks: Transmission Protocols and Performance Evaluation

Doktorgradsavhandling, Fakultet for teknologi og realfag, Universitetet i Agder, 2016Energy efficiency is one of the major goals for achieving green wireless communications. The recent growth in ubiquitous wireless connections and multimedia applications demands higher energy efficiency for wireless communications. As a part of this picture, wireless sensor networks (WSNs) need to be more energy efficient since the battery capacity of nodes in such networks is limited in the absence of energy harvesting sources. In general, an energy efficient protocol should perform as few as possible operations when delivering user information successfully across the network. Energy efficient data transmission schemes could utilize network resources more effectively to lower down the energy consumption level. In this dissertation research, we focus on improving energy efficiency for data transmission and medium access control (MAC) protocols in WSNs. While energy consumption is inevitable for transmitting and receiving data in a WSN, the other typical and dominant energy consumption activities are idle listening, overhearing, and retransmissions due to unsuccessful transmission attempts. An energy efficient MAC protocol conserves energy by minimizing all these auxiliary operations in order to prolong network lifetime. On the other hand, balanced energy consumption among nodes which mitigates energy hole across a WSN also helps to extend network lifetime. In this context, we propose two cooperative transmission (CT) based energy balancingMAC protocols for the purpose of WSN lifetime prolongation. The first one is an asynchronous cooperative transmission MAC protocol, in which nodes generate their own wakeup schedules based on their level number in a WSN topology. The second one is a receiver initiated cooperative transmission MAC protocol in which the CT is initiated by a relay node. It is demonstrated that both proposed CT MAC protocols are able to achieve significantly extended network lifetime. In addition, an energy conserving sleeping mechanism for synchronous duty cycling MAC protocols is also proposed in this thesis. It is an eventtriggered sleeping (ETS) mechanism, which triggers the sleep mode of a node based on the incoming traffic pattern to that node. The ETS mechanism eliminates overhearing in a WSN and achieves higher energy efficiency. Furthermore, we apply packet aggregation at the MAC layer in WSNs for achieving more energy efficient data transmission. In aggregated packet transmission (APT), multiple packets are transmitted as a batch in a frame within a single duty cycle instead of transmitting merely one packet per cycle. Numerical results demonstrate that APT achieves higher throughput and shorter delay, in addition to higher energy efficiency. To evaluate the performance of the proposed MAC protocols and transmission schemes, we develop discrete time Markov chain (DTMC) models and verify them by comparing the results obtained from both analysis and discrete-event based simulations. The analytical and simulation results match precisely with each other, confirming the effectiveness of the proposed protocols and schemes as well as the accuracy of the developed models

Exploring Smart Infrastructure Concepts to Improve the Reliability and Functionality of Safety Oriented Connected Vehicle Applications

Cooperative adaptive cruise control (CACC), a form of vehicle platooning, is a well known connected vehicle application. It extends adaptive cruise control (ACC) by incorporating vehicle-to-vehicle communications. A vehicle periodically broadcasts a small message that includes in the least a unique vehicle identifier, its current geo-location, speed, and acceleration. A vehicle might pay attention to the message stream of only the car ahead. While CACC is under intense study by the academic community, the vast majority of the relevant published literature has been limited to theoretical studies that make many simplifying assumptions. The research presented in this dissertation has been motivated by our observation that there is limited understanding of how platoons actually work under a range of realistic operating conditions. Our research includes a performance study of V2V communications based on actual V2V radios supplemented by simulation. These results are in turn applied to the analysis of CACC. In order to understand a platoon at scale, we resort to simulations and analysis using the ns3 simulator. Assessment criteria includes network reliability measures as well as application oriented measures. Network assessment involves latency and first and second order loss dynamics. CACC performance is based on stability, frequency of crashes, and the rate of traffic flow. The primary goal of CACC is to maximize traffic flow subject to a maximum allowed speed. This requires maintaining smaller inter-vehicle distances which can be problematic as a platoon can become unstable as the target headway between cars is reduced. The main contribution of this dissertation is the development and evaluation of two heuristic approaches for dynamically adapting headway both of which attempt to minimize the headway while ensure stability. We present the design and analysis of a centralized and a distributed implementation of the algorithm. Our results suggest that dynamically adapting the headway time can improve the overall platoon traffic flow without the platoon becoming unstable

Applications of graph-based codes in networks: analysis of capacity and design of improved algorithms

The conception of turbo codes by Berrou et al. has created a renewed interest in modern graph-based codes. Several encouraging results that have come to light since then have fortified the role these codes shall play as potential solutions for present and future communication problems. This work focuses on both practical and theoretical aspects of graph-based codes. The thesis can be broadly categorized into three parts. The first part of the thesis focuses on the design of practical graph-based codes of short lengths. While both low-density parity-check codes and rateless codes have been shown to be asymptotically optimal under the message-passing (MP) decoder, the performance of short-length codes from these families under MP decoding is starkly sub-optimal. This work first addresses the structural characterization of stopping sets to understand this sub-optimality. Using this characterization, a novel improved decoder that offers several orders of magnitude improvement in bit-error rates is introduced. Next, a novel scheme for the design of a good rate-compatible family of punctured codes is proposed. The second part of the thesis aims at establishing these codes as a good tool to develop reliable, energy-efficient and low-latency data dissemination schemes in networks. The problems of broadcasting in wireless multihop networks and that of unicast in delay-tolerant networks are investigated. In both cases, rateless coding is seen to offer an elegant means of achieving the goals of the chosen communication protocols. It was noticed that the ratelessness and the randomness in encoding process make this scheme specifically suited to such network applications. The final part of the thesis investigates an application of a specific class of codes called network codes to finite-buffer wired networks. This part of the work aims at establishing a framework for the theoretical study and understanding of finite-buffer networks. The proposed Markov chain-based method extends existing results to develop an iterative Markov chain-based technique for general acyclic wired networks. The framework not only estimates the capacity of such networks, but also provides a means to monitor network traffic and packet drop rates on various links of the network.Ph.D.Committee Chair: Fekri, Faramarz; Committee Member: Li, Ye; Committee Member: McLaughlin, Steven; Committee Member: Sivakumar, Raghupathy; Committee Member: Tetali, Prasa

Goodput and throughput comparison of single-hop and multi-hop routing for IEEE 802.11 DCF-based wireless networks under hidden terminal existence

We investigate how multi-hop routing affects the goodput and throughput performances of IEEE 802.11 distributed coordination function-based wireless networks compared with direct transmission (single hopping), when medium access control dynamics such as carrier sensing, collisions, retransmissions, and exponential backoff are taken into account under hidden terminal presence. We propose a semi-Markov chain-based goodput and throughput model for IEEE 802.11-based wireless networks, which works accurately with both multi-hopping and single hopping for different network topologies and over a large range of traffic loads. Results show that, under light traffic, there is little benefit of parallel transmissions and both single-hop and multi-hop routing achieve the same end-to-end goodput. Under moderate traffic, concurrent transmissions are favorable as multi-hopping improves the goodput up to 730% with respect to single hopping for dense networks. At heavy traffic, multi-hopping becomes unstable because of increased packet collisions and network congestion, and single-hopping achieves higher network layer goodput compared with multi-hop routing. As for the link layer throughput is concerned, multi-hopping increases throughput 75 times for large networks, whereas single hopping may become advantageous for small networks. The results point out that the end-to-end goodput can be improved by adaptively switching between single hopping and multi-hopping according to the traffic load and topology. Copyright © 2015 John Wiley & Sons, Ltd

Applied Formal Methods in Wireless Sensor Networks

This work covers the application of formal methods to the world of wireless sensor networks. Mainly two different perspectives are analyzed through mathematical models which can be distinct for example into qualitative statements like "Is the system error free?" From the perspective of quantitative propositions we investigate protocol optimal parameter settings for an energy efficient operation

Applicability of network coding with location based addressing over a simplified VANETmodel

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2016The design and implementation of network coding into a location based ad- dressing algorithm for VANET has been investigated. Theoretical analysis of the network coding algorithm has been done by using a simplified topology called the ladder topology. The theoretical models were shown to describe the way that network coding and standard location based addressing works over the VANET network. All tests were performed over simulation. Network coding was shown to improve performance by a factor of 1.5 to 2 times in both simulation and theoretical models. The theoretical models demonstrate a fundamental limit to how much network coding can improve performance by, and these were confirmed by the simulations. Network coding does have a susceptibility to interference, but the other benefits of the techniques are substantial despite this. Network coding demonstrates strong possibilities for future development for VANET protocols. The ladder topology is an important tool for future analysis.G

Performance Prediction and Tuning for Symmetric Coexistence of WiFi and ZigBee Networks

Due to the explosive deployment of WiFi and ZigBee wireless networks, 2.4GHz ISM bands (2.4GHz-2.5GHz) are becoming increasingly crowded, and the co-channel coexistence of these two networks is inevitable. For coexistence networks, people always want to predict their performance (e.g. throughput, energy consumption, etc.) before deployment, or even want to tune parameters to compensate unnecessary performance degradation (owing to the huge differences between these two MAC protocols) or to satisfy some performance requirements (e.g., priority, delay constraint, etc.) of them. However, predicting and tuning performance of coexisting WiFi and ZigBee networks has been a challenging task, primarily due to the lack of corresponding simulators and analytical models. In this dissertation, we addressed the aforementioned problems by presenting simulators and models for the coexistence of WiFi and ZigBee devices. Specifically, based on the energy efficiency and traffic pattern of three practical coexistence scenarios: disaster rescue site, smart hospital and home automation. We first of all classify them into three classes, which are non-sleeping devices with saturated traffic (SAT), non-sleeping devices with unsaturated traffic (UNSAT) and duty-cycling devices with unsaturated traffic (DC-UNSAT). Then a simulator and an analytical model are proposed for each class, where each simulator is verified by simple hardware based experiment. Next, we derive the expressions for performance metrics like throughput, delay etc., and predict them using both the proposed simulator and the model. Due to the higher accuracy of the simulator, the results from them are used as the ground truth to validate the accuracy of the model. Last, according to some common performance tuning requirements for each class, we formulate them into optimization problems and propose the corresponding solving methods. The results show that the proposed simulators have high accuracy in performance prediction, while the models, although are less accurate than the former, can be used in fast prediction. In particular, the models can also be easily used in optimization problems for performance tuning, and the results prove its high efficiency