Görg, Carmelita
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Görg, Carmelita
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Görg, Carmelita
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Item type:Publication, Modeling and Implementation of Wireless Sensor Networks for Logistics Applications(2011-06-16); ; Logistics has experienced a long time of developments and improvements based on the advanced vehicle technologies, transportation systems, traffic network extension and logistics processes. In the last decades, the complexity has increased significantly and this has created complex logistics networks over multiple continents. Because of the close cooperation, these logistics networks are highly dependent on each other in sharing and processing the logistics information. Every customer has many suppliers and vice versa. The conventional centralized control continues but reaches some limitations such as the different distribution of suppliers, the complexity and flexibility of processing orders or the dynamics of the logistic objects. In order to overcome these disadvantages, the paradigm of autonomous logistics is proposed and promises a better technical solution for current logistics systems. In autonomous logistics, the decision making is shifted toward the logistic objects which are defined as material items (e.g., vehicles, containers) or immaterial items (e.g., customer orders) of a networked logistics system. These objects have the ability to interact with each other and make decisions according to their own objectives. In the technical aspect, with the rapid development of innovative sensor technology, namely Wireless Sensor Networks (WSNs), each element in the network can self-organize and interact with other elements for information transmission. The attachment of an electronic sensor element into a logistic object will create an autonomous environment in both the communication and the logistic domain. With this idea, the requirements of logistics can be fulfilled; for example, the monitoring data can be precise, comprehensive and timely. In addition, the goods flow management can be transferred to the information logistic object management, which is easier by the help of information technologies. However, in order to transmit information between these logistic objects, one requirement is that a routing protocol is necessary. The Opportunistic relative Distance-Enabled Uni-cast Routing (ODEUR ) protocol which is proposed and investigated in this thesis shows that it can be used in autonomous environments like autonomous logistics. Moreover, the support of mobility, multiple sinks and auto-connection in this protocol enhances the dynamics of logistic objects. With a general model which covers a range from low-level issues to high-level protocols, many services such as real time monitoring of environmental conditions, context-aware applications and localization make the logistic objects (embedded with sensor equipment) more advanced in information communication and data processing. The distributed management service in each sensor node allows the flexible configuration of logistic items at any time during the transportation. All of these integrated features introduce a new technical solution for smart logistic items and intelligent transportation systems. In parallel, a management system, WSN data Collection and Management System (WiSeCoMaSys), is designed to interact with the deployed Wireless Sensor Networks. This tool allows the user to easily manipulate the sensor networks remotely. With its rich set of features such as real time data monitoring, data analysis and visualization, per-node management, and alerts, this tool helps both developers and users in the design and deployment of a sensor network. In addition, an analytical model is developed for comparison with the results from simulations and experiments. Focusing on the use of probability theory to model the network links, this model considers several important factors such as packet reception rate and network traffic which are used in the simulation and experiment parts. Moreover, the comparison between simulation, experiment and analytical results is also carried out to estimate the accuracy of the design and make several improvements of the simulation accuracy. Finally, all of the above parts are integrated in one unique system. This system is verified by both simulations in logistic scenarios (e.g., harbors, warehouses and containers) and experiments. The results show that the proposed model and protocol have a good packet delivery rate, little memory requirements and low delay. Accordingly, this system design is practical and applicable in logistics.doctoral thesis564 244 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Spectrum Sharing Methods in Coexisting Wireless Networks(2012-06-01); ; ; Radio spectrum, the fundamental basis for wireless communication, is a finite resource. The development of the expanding range of radio based devices and services in recent years makes the spectrum scarce and hence more costly under the paradigm of extensive regulation for licensing. However, with mature technologies and with their continuous improvements it becomes apparent that tight licensing might no longer be required for all wireless services. This is from where the concept of utilizing the unlicensed bands for wireless communication originates. As a promising step to reduce the substantial cost for radio spectrum, different wireless technology based networks are being deployed to operate in the same spectrum bands, particularly in the unlicensed bands, resulting in coexistence. However, uncoordinated coexistence often leads to cases where collocated wireless systems experience heavy mutual interference. Hence, the development of spectrum sharing rules to mitigate the interference among wireless systems is a significant challenge considering the uncoordinated, heterogeneous systems. The requirement of spectrum sharing rules is tremendously increasing on the one hand to fulfill the current and future demand for wireless communication by the users, and on the other hand, to utilize the spectrum efficiently. In this thesis, contributions are provided towards dynamic and cognitive spectrum sharing with focus on the medium access control (MAC) layer, for uncoordinated scenarios of homogeneous and heterogeneous wireless networks, in a micro scale level, highlighting the QoS support for the applications. This thesis proposes a generic and novel spectrum sharing method based on a hypothesis: The regular channel occupation by one system can support other systems to predict the spectrum opportunities reliably. These opportunities then can be utilized efficiently, resulting in a fair spectrum sharing as well as an improving aggregated performance compared to the case without having special treatment. The developed method, denoted as Regular Channel Access (RCA), is modeled for systems specified by the wireless local resp. metropolitan area network standards IEEE 802.11 resp. 802.16. In the modeling, both systems are explored according to their respective centrally controlled channel access mechanisms and the adapted models are evaluated through simulation and results analysis. The conceptual model of spectrum sharing based on the distributed channel access mechanism of the IEEE 802.11 system is provided as well. To make the RCA method adaptive, the following enabling techniques are developed and integrated in the design: a RSS-based (Received Signal Strength based) detection method for measuring the channel occupation, a pattern recognition based algorithm for system identification, statistical knowledge based estimation for traffic demand estimation and an inference engine for reconfiguration of resource allocation as a response to traffic dynamics. The advantage of the RCA method is demonstrated, in which each competing collocated system is configured to have a resource allocation based on the estimated traffic demand of the systems. The simulation and the analysis of the results show a significant improvement in aggregated throughput, mean delay and packet loss ratio, compared to the case where legacy wireless systems coexists. The results from adaptive RCA show its resilience characteristics in case of dynamic traffic. The maximum achievable throughput between collocated IEEE 802.11 systems applying RCA is provided by means of mathematical calculation. The results of this thesis provide the basis for the development of resource allocation methods for future wireless networks particularly emphasized to operate in current unlicensed bands and in future models of the Open Spectrum Alliance.doctoral thesis358 139 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Wireless Multi-hop Ad hoc Networks:Evaluation of Radio Disjoint MultipathRouting(2010-02-09); ; ; In wireless multi-hop ad hoc networks, the simultaneous use of multiple routes may degrade the performance of applications due to mutual interference of discovered paths, irrespective of whether paths are physically node disjoint or link disjoint. Therefore, the selection of noninterfering routes is the main criterion to be addressed when using multiple routes simultaneously. This thesis introduces a new metric to select multiple routes by reducing the effect of interference between paths as far as possible and also selecting the least congested paths. The proposed protocol is named Radio Disjoint Multipath (RDM). The concept of the RDM protocol which can be applied to both reactive and proactive ad hoc protocols is developed and feasibility of the protocol is proven by an implementation and also through an analytical model.Furthermore, this thesis introduces a novel mechanism to distribute multiple flows as well as packets of a single flow based on the properties of the discovered path, which is computed considering the Background Traffic Load (BTL) of each path and the mutual interference between paths. In summary, all investigations presented in this thesis can help to enhance the application performance in different kinds of wireless multi-hop ad hoc networks of Mobile Ad hoc NETworks (MANET), Wireless Sensor Networks (WSN) and Wireless Mesh Networks (WMN), by discovering RDM routes and using them simultaneously.doctoral thesis451 176 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Efficient Communication in Agent-based Autonomous Logistic Processes(2011-06-16); ; ; Transportation of goods plays a vital role for the success of a logistics network. The ability to transport goods quickly and cost effectively is one of the major requirements of the customers. Dynamics involved in the logistics process like change or cancellation of orders or uncertain information about the orders add to the complexity of the logistic network and can even reduce the efficiency of the entire logistics process. This brings about a need of integrating technology and making the system more autonomous to handle these dynamics and to reduce the complexity. Therefore, the distributed logistics routing protocol (DLRP) was developed at the University of Bremen. In this thesis, DLRP is extended with the concept of clustering of transport goods, two novel routing decision schemes and a negotiation process between the cluster of goods and the vehicle. DLRP provides the individual logistic entities the ability to perform routing tasks autonomously e.g., discovering the best route to the destination at the given time. Even though DLRP seems to solve the routing problem in real-time, the amount of message flooding involved in the route discovery process is enormous. This motivated the author to introduce a cluster-based routing approach using software agents. The DLRP along with the clustering algorithm is termed as the cluster-based DLRP. In the latter, the goods are first clustered into groups based on criteria such as the common destination. The routing is now handled by the cluster head rather than the individual transport goods which results in a reduced communication volume in the route discovery. The latter is proven by evaluating the performance of the cluster-based DLRP approach compared to the legacy DLRP. After the routing process is completed by the cluster heads, the next step is to improve the transport performance in the logistics network by identifying the best means to transport the clustered goods. For example, to have better utilization of the transport capacity, clusters can be transported together on a stretch of overlapping route. In order to make optimal transport decisions, the vehicle calculates the correlation metric of the routes selected by the various clusters. The correlation metric aids in identifying the clusters which can be transported together and thereby can result in better utilization of the transport resources. In turn, the transportation cost that has to be paid to the vehicle can be shared between the different clusters. The transportation cost for a stretch of route is calculated by the vehicle and offered to the cluster. The latter can decide based upon the transportation cost or the selected route whether to accept the transport offer from the vehicle or not. In this regard, different strategies are developed and investigated. Thereby a performance evaluation of the capacity utilization of the vehicle and the transportation cost incurred by the cluster is presented. Finally, the thesis introduces the concept of negotiation in the cluster based routing methods. The negotiation process enhances the transport decisions by giving the clusters and the vehicles the flexibility to negotiate the transportation cost. Thus, the focus of this part of the thesis is to analyse the negotiation strategies used by the logistics entities and their role in saving negotiation time while achieving a favorable transportation cost. In this regard, a performance evaluation of the different proposed strategies is presented, which in turn gives the logistics practitioners an overview of the best strategy to be deployed in various scenarios. Clustering of goods aid in the negotiation process as on the one hand, a group of transport goods have a stronger basis for negotiation to achieve a favorable transportation price from the vehicle. On the other hand it makes it easier for the vehicle to select the packages for transport and helps the vehicle to operate close to its capacity. In addition, clustering enables the negotiation process to be less complex and voluminous. From the analytical considerations and obtained results in the three parts of this thesis, it can be concluded that efficient transport decisions, though very complex in a logistics network, can be simplified to a certain extent utilizing the available information of the goods and vehicles in the network.doctoral thesis433 101 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Enhanced Forwarding Strategies in Information Centric Networking(2015-04-24); ; ; Content Centric Networking (CCN), a "Clean Slate" architecture to Information Centric Networking (ICN) , uses new approaches to routing named content, achieving scalability, security and performance. This thesis proposes a design of an effective multi-path forwarding strategy and performs an evaluation of this strategy in a set of scenarios that consider large scale deployments. The evaluations show improved performance in terms of user application throughput, delays, adoptability and scalability against adverse conditions (such as differing background loads and mobility) compared to the originally proposed forwarding strategies. Secondly, this thesis proposes an analytical model based on Markov Modulated Rate Process (MMRP) to characterize multi-path data transfers in CCN. The results show a close resemblance in performance between the analytical model and the simulation model.doctoral thesis601 184 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Long Term Evolution-Advanced and Future Machine-to-Machine Communication(2014-12-12); ; ; Long Term Evolution (LTE) has adopted Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) as the downlink and uplink transmission schemes respectively. Quality of Service (QoS) provisioning is one of the primary objectives of wireless network operators. In LTE-Advanced (LTE-A), several additional new features such as Carrier Aggregation (CA) and Relay Nodes (RNs) have been introduced by the 3rd Generation Partnership Project (3GPP). These features have been designed to deal with the ever increasing demands for higher data rates and spectral efficiency. The RN is a low power and low cost device designed for extending the coverage and enhancing spectral efficiency, especially at the cell edge. Wireless networks are facing a new challenge emerging on the horizon, the expected surge of the Machine-to-Machine (M2M) traffic in cellular and mobile networks. The costs and sizes of the M2M devices with integrated sensors, network interfaces and enhanced power capabilities have decreased significantly in recent years. Therefore, it is anticipated that M2M devices might outnumber conventional mobile devices in the near future. 3GPP standards like LTE-A have primarily been developed for broadband data services with mobility support. However, M2M applications are mostly based on narrowband traffic. These standards may not achieve overall spectrum and cost efficiency if they are utilized for serving the M2M applications. The main goal of this thesis is to take the advantage of the low cost, low power and small size of RNs for integrating M2M traffic into LTE-A networks. A new RN design is presented for aggregating and multiplexing M2M traffic at the RN before transmission over the air interface (Un interface) to the base station called eNodeB. The data packets of the M2M devices are sent to the RN over the Uu interface. Packets from different devices are aggregated at the Packet Data Convergence Protocol (PDCP) layer of the Donor eNodeB (DeNB) into a single large IP packet instead of several small IP packets. Therefore, the amount of overhead data can be significantly reduced. The proposed concept has been developed in the LTE-A network simulator to illustrate the benefits and advantages of the M2M traffic aggregation and multiplexing at the RN. The potential gains of RNs such as coverage enhancement, multiplexing gain, end-to-end delay performance etc. are illustrated with help of simulation results. The results indicate that the proposed concept improves the performance of the LTE-A network with M2M traffic. The adverse impact of M2M traffic on regular LTE-A traffic such as voice and file transfer is minimized. Furthermore, the cell edge throughput and QoS performance are enhanced. Moreover, the results are validated with the help of an analytical model.doctoral thesis507 144 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Performance Evaluation and Improvement of the Mobile Internet Protocol: A Study of Hand-offs, Transport Layer Performance and Flow Mobility(2006-05-05); ; TCP/IP was originally designed without any considerations for mobile computing. The greatest technical difficulties are encountered in the routing service of the IP layer. Mobile IP is an enhancement to the IP protocol which allows for transparent routing of traffic to mobile nodes in the Internet. In this manner, mobile nodes may vary their point of attachment between Internet administrative domains without having to interrupt active communications.Mobile IP introduces several overheads including extended packet loss during Mobile IP/IP layer hand-offs. Moreover, Mobile IP was designed focusing on mobile nodes equipped with a single access interface, capable of maintaining a single point of attachment to the Internet.This thesis focuses on evaluating and improving the performance of Mobile IP and of other protocols in conjunction with Mobile IP. Different types of Mobile IP hand-offs have been investigated. It was determined that all standardised Mobile IP hand-off techniques introduce a service disruption unacceptable for real time communications such as Internet telephony or for file transfer and WWW. In an effort to accelerate Mobile IP hand-offs, new hand-off types were introduced and proposals were made regarding the hierarchical organisation of Mobile IP infrastructure. It was shown that TCP, the primary and reliable, transport layer protocols of TCP/IP, misinterprets all packet loss experienced during Mobile IP hand-offs as the effect of network congestion and curtails the amount of offered load to the connection every time that a mobile node migrates. New protocol extensions were proposed and evaluated, aiming at resolving the incompatibilities between TCP and Mobile IP.The thesis demonstrates how Mobile IP can be deployed to introduce Internet mobility management facilities to WAP, the industrial de facto standard for Internet access to mobile phones. The demonstration involves a migration scenario between two heterogeneous wireless technologies, i.e. Wireless LANs and GSM. It was shown that Mobile IP inherits the interconnecting property of the Internet Protocol. In this manner, the problem of integrating heterogeneous protocols, above and below it, is reduced into a matter of routing.Considering the ever increasing availability of mobile devices equipped with multiple wireless access interfaces the inability of Mobile IP to take advantage efficiently of this property was considered a major drawback. A significant part of this thesis is devoted to the introduction of flow mobility management facilities that allow for dynamic distribution of flows or parts of a flow (datagrams) between the available interfaces in mid-session. Through extensive experimental evaluation it was shown that both data and telecommunications services can benefit from this approach.doctoral thesis239 139 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, LTE Optimization and Resource Management in Wireless Heterogeneous Networks(2013-05-14); ; ; Mobile communication technology is evolving with a great pace. The development of the Long Term Evolution (LTE) mobile system by 3GPP is one of the milestones in this direction. This work highlights a few areas in the LTE radio access network where the proposed innovative mechanisms can substantially improve overall LTE system performance. In order to further extend the capacity of LTE networks, an integration with the non-3GPP networks (e.g., WLAN, WiMAX etc.) is also proposed in this work. Moreover, it is discussed how bandwidth resources should be managed in such heterogeneous networks. The work has purposed a comprehensive system architecture as an overlay of the 3GPP defined SAE architecture, effective resource management mechanisms as well as a Linear Programming based analytical solution for the optimal network resource allocation problem. In addition, alternative computationally efficient heuristic based algorithms have also been designed to achieve near-optimal performance.doctoral thesis475 352 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Optimization and Performance Analysis of High Speed Mobile Access Networks(2010-11-17); ; ; The end-to-end performance evaluation of high speed broadband mobile access networks is the main focus of this work. Novel transport network adaptive flow control and enhanced congestion control algorithms are proposed, implemented, tested and validated using a comprehensive High speed packet Access (HSPA) system simulator. The simulation analysis confirms that the aforementioned algorithms are able to provide reliable and guaranteed services for both network operators and end users cost-effectively. Further, two novel analytical models one for congestion control and the other for the combined flow control and congestion control which are based on Markov chains are designed and developed to perform the aforementioned analysis efficiently compared to time consuming detailed system simulations. In addition, the effects of the Long Term Evolution (LTE) transport network (S1and X2 interfaces) on the end user performance are investigated and analysed by introducing a novel comprehensive MAC scheduling scheme and a novel transport service differentiation model.doctoral thesis292 274 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Future Mobile Communications: LTE Optimization and Mobile Network Virtualization(2012-07-06); ; ; Providing QoS while optimizing the LTE network in a cost efficient manner is very challenging. Thus, radio scheduling is one of the most important functions in mobile broadband networks. The design of a mobile network radio scheduler holds several objectives that need to be satisfied, for example: the scheduler needs to maximize the radio performance by efficiently distributing the limited radio resources, since the operator's revenue depends on it. In addition, the scheduler has to guarantee the user's demands in terms of their Quality of Service (QoS). Thus, the design of an effective scheduler is rather a complex task. In this thesis, the author proposes the design of a radio scheduler that is optimized towards QoS guarantees and system performance optimization. The proposed scheduler is called Optimized Service Aware Scheduler (OSA). The OSA scheduler is tested and analyzed in several scenarios, and is compared against other well-known schedulers. A novel wireless network virtualization framework is also proposed in this thesis. The framework targets the concepts of wireless virtualization applied within the 3GPP Long Term Evolution (LTE) system. LTE represents one of the new mobile communication systems that is just entering the market. Therefore, LTE was chosen as a case study to demonstrate the proposed wireless virtualization framework. The framework is implemented in the LTE network simulator and analyzed, highlighting the many advantages and potential gain that the virtualization process can achieve. Two potential gain scenarios that can result from using network virtualization in LTE systems are analyzed: Multiplexing gain coming from spectrum sharing, and multi-user diversity gain. Several LTE radio analytical models, based on Continuous Time Markov Chains (CTMC) are designed and developed in this thesis. These models target the modeling of three different time domain radio schedulers: Maximum Throughput (MaxT), Blind Equal Throughput (BET), and Optimized Service Aware Scheduler (OSA). The models are used to obtain faster results (i.e., in a very short time period in the order of seconds to minutes), compared to the simulation results that can take considerably longer periods, such as hours or sometimes even days. The model results are also compared against the simulation results, and it is shown that it provides a good match. Thus, it can be used for fast radio dimensioning purposes. Overall, the concepts, investigations, and the analytical models presented in this thesis can help mobile network operators to optimize their radio network and provide the necessary means to support services QoS differentiations and guarantees. In addition, the network virtualization concepts provides an excellent tool that can enable the operators to share their resources and reduce their cost, as well as provides good chances for smaller operators to enter the market.doctoral thesis319 177