WiFi is becoming common in households and digital devices needs to support it. At the same time the devices are getting smaller and the Ethernet port may seem superfluous. When testing these devices the test environment needs to be able to provide WiFi connectivity. The tests may be focused on testing WiFi but it could also be the only network connectivity and thus needs to be very reliable. With a large number of devices in a small physical area a normal WiFi setup would have a density of devices that is too high for today’s1 WiFi standards. A combination of wired physical medium and physical isolation was considered.

In the near future, demand for Heterogeneous Wireless Networking (HWN) is expected to increase. HWNs are formed by integration of different communication technologies, for example the integration of wireless LAN and cellular networks, to support mobile users. QoS provisioning in these networks is a challenging issue given the diversity in wireless technologies and the existence of mobile users with different communication requirements. In this thesis, we consider optimal resource planning and dynamic resource management for HWNs. In the first part of this thesis, we examine the optimal deployment of such networks. We propose a mobility-aware network planning optimization in which the objective is to minimize the rate of upward vertical handovers while maximizing the total number of users accommodated by the network. The optimal placement of Access Points (AP) with respect to these two objectives is formulated as an integer programming problem. Our results show that considering the mobility pattern in the planning phase of network deployment can significantly improve infrastructure performance. In the second part, we investigate optimal admission control policies employed in maintaining QoS in HWNs. Here we consider two cases: integration of cellular overlay with a single WLAN AP, and integration with a WLAN mesh network. A decision theoretic framework for the problem is derived using a dynamic programming formulation. In the case of single WLAN AP and cellular overlay, we prove that for this two-tier wireless network architecture, the optimal policy has a two-dimensional threshold structure. Furthermore, this structural result is used to design two computationally efficient algorithms, Structured Value Iteration and Structured Update Value Iteration. These algorithms can be used to determine the optimal policy in terms of thresholds. Although the first one is closer in its operation to the conventional Value Iteration algorithm, the second one has a significantly lower complexity. In the second case where the underlay is a complex WLAN mesh network, we develop a Partially Observable Markov-Modulated Poisson Process (PO-MMPP) traffic model to characterize the overflow traffic from the underlaying mesh to the overlay. This model captures the burstiness of the overflow traffic under the imperfect observability of the mesh network states. Then, by modeling the overlay network as a controlled PO-MMPP/M/C/C queueing system and obtaining structured decision theoretic results, it is shown that the optimal control policy for this class of HWNs can be characterized as monotonic \emph{threshold curves}. Moreover, these results are used to design a computationally efficient algorithm to determine the optimal policy in terms of thresholds. Extensive numerical observations suggest that, in both cases and for all practical parameter sets, the algorithms converge to the overall optimal policy. Additionally, numerical results show that the proposed algorithms are efficient in terms of time-complexity and in achieving optimal performance by significantly reducing the probability of dropped and blocked calls.

In the near future, demand for Heterogeneous Wireless Networking (HWN) is expected to increase. HWNs are formed by integration of different communication technologies, for example the integration of wireless LAN and cellular networks, to support mobile users. QoS provisioning in these networks is a challenging issue given the diversity in wireless technologies and the existence of mobile users with different communication requirements. In this thesis, we consider optimal resource planning and dynamic resource management for HWNs. In the first part of this thesis, we examine the optimal deployment of such networks. We propose a mobility-aware network planning optimization in which the objective is to minimize the rate of upward vertical handovers while maximizing the total number of users accommodated by the network. The optimal placement of Access Points (AP) with respect to these two objectives is formulated as an integer programming problem. Our results show that considering the mobility pattern in the planning phase of network deployment can significantly improve infrastructure performance. In the second part, we investigate optimal admission control policies employed in maintaining QoS in HWNs. Here we consider two cases: integration of cellular overlay with a single WLAN AP, and integration with a WLAN mesh network. A decision theoretic framework for the problem is derived using a dynamic programming formulation. In the case of single WLAN AP and cellular overlay, we prove that for this two-tier wireless network architecture, the optimal policy has a two-dimensional threshold structure. Furthermore, this structural result is used to design two computationally efficient algorithms, Structured Value Iteration and Structured Update Value Iteration. These algorithms can be used to determine the optimal policy in terms of thresholds. Although the first one is closer in its operation to the conventional Value Iteration algorithm, the second one has a significantly lower complexity. In the second case where the underlay is a complex WLAN mesh network, we develop a Partially Observable Markov-Modulated Poisson Process (PO-MMPP) traffic model to characterize the overflow traffic from the underlaying mesh to the overlay. This model captures the burstiness of the overflow traffic under the imperfect observability of the mesh network states. Then, by modeling the overlay network as a controlled PO-MMPP/M/C/C queueing system and obtaining structured decision theoretic results, it is shown that the optimal control policy for this class of HWNs can be characterized as monotonic \emph{threshold curves}. Moreover, these results are used to design a computationally efficient algorithm to determine the optimal policy in terms of thresholds. Extensive numerical observations suggest that, in both cases and for all practical parameter sets, the algorithms converge to the overall optimal policy. Additionally, numerical results show that the proposed algorithms are efficient in terms of time-complexity and in achieving optimal performance by significantly reducing the probability of dropped and blocked calls.

The recent years have seen an enormous advance in wireless communication technology and co-existence of various types of wireless networks, which requires effective inter-networking among the heterogeneous wireless networks in order to support user roaming over the networks while maintaining the connectivity. One of main challenges to achieve the connectivity over heterogeneous wireless networks is potential intermittent connections caused by user roaming. The issue is how to maintain the connection as the user roams and how to ensure service quality in the presence of a long disconnection period. In this dissertation, we apply the delay tolerant network (DTN) framework to heterogeneous terrestrial wireless networks, and propose a system architecture to achieve the connectivity in the presence of excessive long delays and intermittent paths. We study several possible approaches, discuss the applicability of each of the approaches and propose the super node architecture. To demonstrate the effectiveness of the proposed super node architecture, we give a simulation study that compares the system performance under the super node architecture and under the epidemic based architecture. Within the proposed architecture that employs the idea of super nodes, we further study how to effectively route a message over access networks. We present a new routing technique for mobile ad-hoc networks (MANETs) based on the DTN system architecture. We introduce the concept of virtual network topology and redefine the dominating-set based routing for the challenged network environment under consideration. In addition, we propose a time based methodology to predict the probability of future contacts between node pairs to construct the virtual network topology. We present a simulation study that demonstrates the effectiveness of the proposed routing approach as compared with the epidemic routing, and that the time based technique for predicting the future contacts gives better performance compared with that using the number of previous contacts. We further extend the dominating set routing technique through analyzing the underlying node mobility model. We shed some light on how using node mobility model can improve contact probability estimation. Based on our findings we propose a new algorithm that improves the routing performance by minimizing the selected dominating set size. Information security challenges in the super node architecture are introduced. We further address two main security challenges: The first is how to prevent unauthorized nodes from using the network resources, and the second is how to achieve end-to-end secure message exchange over the network. Our proposed solutions are based on asymmetric key cryptography techniques. Moreover, we introduce a new idea of separating the problem of source authentication from the problem of message authorization. We propose a new technique that employs the one-way key chain to use symmetric key cryptographic techniques to address the problems under consideration.

Resource management in wireless networks is one of the key factors in maximizing the overall throughput. Contrary to popular belief, dividing the resources in a dense network does not yield the best results. A method that has been developed recently shares the spectrum amongst all the users in such a way that each node can potentially utilize about half of all the available resources. This new technique is often referred to as Interference Alignment and excels based on the fact that the amount of the network resources assigned to a user does not go to zero as the number of users in the network increases. Unfortunately it is still very difficult to implement the interference alignment concepts in practice. This thesis investigates some of the low-complexity solutions to integrate interference alignment ideas into the existing wireless networks. In the third and fourth chapters of this thesis, it is shown that introducing relays to a quasi-static wireless network can be very beneficial in terms of achieving higher degrees of freedom. The relays store the signals being communicated in the network and then send a linear combination of those signals. Using the proposed scheme, it is shown that although the relays cannot decode the original information, they can transform the equivalent channel in such a way that performing interference alignment becomes much easier. Investigating the required output power of the relays shows that it can scale either slower or faster than the output power of the main transmitters. This opens new doors for the applications that have constraints on the accessible output powers in the network nodes. The results are valid for both $X$ Channel and Interference Channel network topologies. In Chapter Five, the similarities between full-duplex transmitters and relays are examined. The results suggest that the transmitters can play the relay roles for offering easier interference alignment. Similar to the relay-based alignment, in the presented scheme full-duplex transmitters listen to the signals from other transmitters and use this information during the subsequent transmission periods. Studying the functionality of the full-duplex transmitters from the receivers' side shows the benefits of having a minimal cooperation between transmitters without even being able to decode the signals. It is also proved that the degrees of freedom for the $N$-user Interference Channel with full-duplex transmitters can be $\sqrt{\frac{N}{2}}$. The results offer an easy way to recover a portion of degrees of freedom with manageable complexity suited for practical systems.

Body Area Networks (BANs) are emerging as a convenient option for patient monitoring. They have shown potential in improving health care services through a network of external or implanted biosensors and actuators collecting real-time physiological data. Advancements in wireless networking and sensor development are expediting the adoption of BANs. However, real-time patient monitoring still remains a challenge due to network failures and congestion. In order to improve channel loss resilience and thus link availability, a multi-radio systems approach is adopted incorporating Bluetooth and Wi-Fi. In this work, we propose a multi-radio interface designed for a BAN to improve end-to-end communications. A multi-radio BAN controller is introduced to interface between the two wireless protocols (Wi-Fi and Bluetooth), control inter-radio handovers, manage a shared transmission buffer, and overall, route data accordingly through the protocol stacks. Simulations are conducted to study the performance of the system by adjusting handover timing and its effect on link availability. Advancing a handover has the benefit of a higher throughput at the cost of an increase in power consumption and timing overhead. Furthermore, various human mobility models, AP placement arrangements, and network densities are simulated to evaluate the performance of the BAN multi-radio interface. Sparse networks were found to have the most gain from the addition of the secondary Bluetooth radio system, as primary AP coverage was already very limited. Simulation results for various combinations of simulation parameters are presented to illustrate the improvement in BAN dependability through a multi-radio interface.

Wireless sensor networks allow us to instrument our world in novel ways providing detailed insight that had not been possible earlier. Since these networks provide an interface to the physical world, it is necessary for each sensor node to learn its location in the physical space. The availability of location information at individual sensor nodes allows the network to provide higher layer services such as location stamped event reporting, geographic routing, in-network processing etc. A wide range of these sensor network protocols do not require absolute node coordinates and can work with relative node positions. This motivates for the need of anchor free localization algorithms that localize the individual sensor nodes with respect to each other in a local coordinate system. Such algorithms allow the sensor networks to be decoupled from external infrastructure and become truly place and play systems. The primary contributions of this thesis include two anchor free localization algorithms and one location refinement algorithm for ad-hoc wireless sensor networks. Our distributed anchor free localization algorithms do not require any external infrastructure in the form of landmark or manually initialized anchor nodes. These algorithms use measured inter-node distances among some node pairs and localize the entire network in a local coordinate system up to a global translation, rotation and reflection. The relative or virtual coordinates assigned by these algorithms can be readily used with a range of sensor network services like geographic routing, data aggregation, topology control etc. Our first localization algorithm is based on a distributed collaborative approach where all of the nodes in the network collaborate with each other to select a set of nodes. These nodes are localized and then used as reference nodes for the remaining sensor nodes. The novelty of this approach is that instead of solving the localization problem for the entire network upfront, first a small well-formed localization problem is solved and then these results are used to solve the localization problem for the remaining nodes in the network. Our second localization algorithm borrows ideas from the data visualization field and exploits the general undirected graph drawing theory to solve the sensor network localization problem. This algorithm divides the network into a large number of small overlapping clusters and creates local coordinate systems for each of the clusters. These clusters are then merged together in a single coordinate system using a novel distributed algorithm that seeks to minimize the error during this merge process. Our final contribution is a distributed location refinement algorithm that can be used with any of the range based localization algorithms to refine the sensor node coordinates to conform to the measured inter-node distances. We model this coordinate refinement problem as an unconstrained non-linear optimization problem and then transform this optimization problem into an aggregate computation problem. We propose two different approaches to solve this aggregate computation problem in a distributed manner. We evaluate our algorithms with detailed simulations using both Matlab and TinyOS simulator TOSSIM. We also validate our simulation results with experimentation carried out on a real network of MIT Cricket motes. We conclude this thesis with lessons learned during this research and discuss some future directions which can be explored to advance the research in sensor network localization.

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 234-249.

We consider an online learning scenario in which the learner can make predictions on the basis of a fixed set of experts. We derive upper and lower relative loss bounds for a class of universal learning algorithms involving a switching dynamics over the choice of the experts. On the basis of the performance bounds we provide the optimal a priori discretization of the switching-rate parameter that governs the switching dynamics. We demonstrate the algorithm in the context of wireless networks.

Αντικείμενο της διπλωματικής αυτής εργασίας είναι η μελέτη ενός ZigBee ασύρματου δικτύου βιοαισθητήρων και η δυνατότητα διασύνδεσης του με μεγαλύτερα δίκτυα όπως το Ίντερνετ. Αρχικά γίνεται μια αναφορά στην χρησιμοποίηση δικτύων τηλεϊατρικής, στη σπουδαιότητά τους για τον άνθρωπο καθώς και σε ολοκληρωμένες λύσεις που έχουν προταθεί. Έπειτα παρουσιάζονται και περιγράφονται βιοαισθητήρες που χρησιμοποιούνται σε ένα WBAN όπως και η λειτουργία τους. Στη συνέχεια γίνεται εκτεταμένη ανάλυση όλων των επιπέδων του πρωτοκόλλου Zigbee/802.15.4 στοχεύοντας πιο συγκεκριμένα στη ζώνη μετάδοσης των 2,4 GHz και το πως αυτή μπορεί να χρησιμοποιηθεί κρατώντας υψηλό το QOS , απαραίτητη προϋπόθεση ενός δικτύου τηλεϊατρικής . Τέλος μελετώνται οι πιθανοί τρόποι διασύνδεσης δικτύων αισθητήρων και γίνεται προσομοίωση ενός TCP/IP δικτύου στο οποίο καταλήγουν τα δεδομένα τα οποία συγκεντρώνονται από μια σειρά αισθητήρων με σκοπό τη μελέτη της δυνατότητας χρήσης ενός τέτοιου συστήματος. / Subject of this diploma work is to study a ZigBee wireless biosensor network and connectivity with other networks like the internet. Initially is made a reference to the use of telemedicine networks, the importance for man as well as integrated solutions that have been proposed. Then there are presented and described biosensors used in a WBAN as their function. Then is made an analysis of all levels of the protocol Zigbee/802.15.4 targeting the particular zone of 2,4 GHz and how it can be used while holding a high QOS. Finally are examined possible ways of interconnecting networks of sensors and is made a simulation of a TCP / IP where the collected data from the sensors end.