Energy efficiency is essential for many industrial and commercial wireless network applications. In this thesis, we propose an analytical framework to model and design protocols for multi-hop wireless networks for industrial control and automation. We study the mutual interaction among medium access control (MAC), routing, and application layers. Accordingly, we provide three main contributions. First, MAC and routing layers are considered. The carrier sense multiple access (CSMA) of the unslotted IEEE 802.15.4 standard is modeled for multi-hop communications using the specifications of the IETF routing over low power and lossy networks (ROLL). The analysis considers the effects induced by heterogeneous traffic due to the routing mechanism and the node traffic generation patterns, and the hidden terminals due to the reduced carrier sensing capabilities. The interde-pendence between end-to-end performance indicators (reliability, delay, and energy consumption) and routing decisions is described. It is shown that routing decisions based on reliability or delay tend to direct traffic toward nodes with high packet generation rates, with significant negative effects on the energy consumption. Second, we propose TREnD, a cross-layer protocol solution that takes into account tunable performance requirements from the control application. An optimization problem is posed and solved to select the protocol parameters adaptively. The objective is to minimize the energy consumption while fulfilling reliability and delay constraints. TREnD is implemented on a test-bed and it is compared to existing protocols. The protocol model and analysis are validated through experiments. It is shown that TREnD ensures load balancing and dynamic adaptation for static and time-varying scenarios. Eventually, a building automation application is presented by considering the design of a robust controller for under floor air distribution system regulation. The communication performance of an IEEE 802.15.4 network is included in the controller synthesis. We show the impact of reliability and delay on the temperature regulation for synchronous and asynchronous networks. / QC 20110121

Multi-connectivity and network densification are two solutions intended to enhance user throughput and reliability. These solutions are critical since 5G NR uses a wide range of frequency bands, which exhibit different varying radio coverage characteristics. This work studies the user equipment (UE) performance using multi-connectivity within an ultra-dense network (UDN) deployed in an urban city environment. By being connected to more than one access node simultaneously, the UE should benefit from increased reliability and data rates at the expense of a potentially increased power consumption. In this letter, we have constructed an urban city environment and a context-aware UE power consumption model. The performance of the UE is assessed with an uplink power control scheme for multi-connectivity and a novel multi-connectivity scheme is proposed. Our simulation results show that dual-connectivity increases performance by up to 44% and 27% in average downlink and uplink throughput, respectively. Similarly, tri-connectivity does the same by up to 45% and 25%. At mid load (forty-five users), the average increase in UE power consumption compared to single-connectivity is 25% and 60% for dual-connectivity and tri-connectivity, respectively. Dual-connectivity increases global UE energy efficiency by up to 30%. Within an urban environment, dual-connectivity decreases the RLF rate by 20% compared to single-connectivity for high speed users. / <p>Presentation done within the 5th PERCCOM Summer School that took place in Skellefteå. </p> / European Erasmus Mundus programme PERCCOM - PERvasive Computing & COMmunications

In the future of intelligent transport systems, vehicles will communicate with other vehicles and infrastructure. Through this communication, vehicles can cooperate in traffic situations such as intersections and highway merging. This communication can also facilitate sharing of information about other vehicles. ETSI provides a protocol for this communication, the ETSI ITS-G5 protocol. With this protocol, these vehicular ad-hoc networks (VANETs) can decrease traffic congestion, road accidents and travelling time. However, communication also comes with a risk. Communication requires trust, otherwise maliciously intended actors can spread false information which if acted upon might lead to traffic jams, traffic crashes and potential deaths. As a countermeasure ETSI has an architecture for reporting suspect abnormal behaviour: misbehaviour reports. Misbehaviour reports are sent to a centralized authority able to discontinue vehicles' involvement in the VANET. ETSI does not include a warning system between vehicles until the misbehaviour report has been analyzed by the authority. After that, all vehicles will have to experience the abnormal behaviour first-hand without warning. A vehicle-to-vehicle warning system would help vehicles heed extra caution when meeting these misbehaving vehicles, decreasing the risk of interacting with them. The challenges of such a system are protecting the reporter's and reported's integrity, bad actors sending false reports and the system being quicker than the authority. To protect the integrity of vehicles in the VANET, this thesis proposes proving the misbehaviour using non-interactive zero-knowledge proofs, allowing to share of evidence without revealing more than necessary to prove the abnormal behaviour.

Over the last decade, both the Internet and mobile telephony has become parts of daily life, changing the ways we communicate and search for information. These two distinct tools are now slowly merging. The topic of this thesis is TCP over wireless, and the automatic control that is used both within the system, from the link-layer power control to the end-to-end congestion control. It consists of three main contributions. The first contribution is a proposed split-connection scheme for downloads to a mobile terminal. A wireless mobile terminal requests a file or a web page from a proxy, which in turn requests the data from a server on the Internet. During the file transfer, the radio network controller (RNC) sends radio network feedback (RNF) messages to the proxy. These messages include information about bandwidth changes over the radio channel, and the current RNC queue length. A novel control mechanism in the proxy uses this information to adjust the sending rate. The stability and convergence speed of the proxy controller is analyzed theoretically. The performance of the proposed controller is compared to end-to-end TCP Reno, using ns-2 simulations of realistic use cases. It is shown that the proxy control is able to reduce the response time experienced by users, and increase the utilization of the radio channel. The changes are loalized to the RNC and the proxy; no changes are required to the TCP implementation in terminal or server. The second contribution is the analysis of an uplink channel using power control and link-layer retransmissions. To be able to design the link-layer mechanisms in a systematic way, good models for the link-layer processes, and their interaction with TCP, are essential.The use of link-layer retransmissions transforms a link with constant delay and random losses into a link with random delay and almost no losses. As seen from the TCP end points, the difference between such a link and a wired one is no longer the loss rate, but the packet delay distribution. Models for the power control and link-layer retransmissions on the link are used to derive packet delay distribution, and its impact on TCP performance is investigated. The final contribution considers ways to optimize the link-layer processes. The main result is that TCP performance, over a wireless link with random retransmission delays, can be improved by adding carefully chosen artificial delays to certain packets. The artificial delays are optimized off-line and applied on-line. The additional delay that is applied to a packet depends only on the retransmission delay experienced by that same packet, and this information is available locally at the link. / QC 20101216

Personal mobile multimedia services are rapidly become popular. They leverage the combination of mobile and Internet-based communications, the increased capabilities of the third generation of mobile communications (3G), and the flexibility of a common transport and service platform. Cost and quality are critical factors for the success of IP multimedia services. 3G is based on hetereogeneous networks, characterized by a mixture of wired and wireless links with very different requirements on the communication itself. Furthermore, the "always best connected" paradigm requires the design of the new applications to accomodate different types of access. It turns out that the cellular link is typically the most constrained, e.g. in terms of limited bandwidth and high delay, especially when IP is used as transport. Security is an important aspect of the service. Never before has this awareness been more present, not only among technicians, but also among users. Users want the possibility to protect themselves and their data and private matters, in a way that no one else can interfere and that private communications are guaranteed to remain private. The use of the Internet as a common transport backbone, a notoriously open and adverse environment, and in general the use of the IP technology, which is receiving a bad (media) reputation in terms of the security breaches it opens, calls for an end-to-end security solution for IP multimedia services. There are also scenarios where end-to-end protection of other information is an absolute must, for example public safety communication, catastrophe and emergency communication, corporate, or government communication. This research addresses the design of a security solution for IP multimedia, striving in particular for the promotion of end-to-end security on a large scale. This research builds on the concept of a "transport-friendly" security solution: security always comes at a cost, hence it is important to control its impact on services, otherwise security is generally sacrificed. This research focused on the protection of the media traffic. It first identified the requirements that arise from IP multimedia applications in hetereogeneous networks, examined existing security solutions, and concluded that they did not fullfil the requirements raised by 3G environments. This has motivated the design of two new security protocols that are transport-friend to meet the identified requirements, so as to have a low impact on services. These two protocols have then been integrated to provide a security solution for IP multimedia in hetereogeneous networks. The research leading to this licentiate has been mostly conducted in the IETF (a standardisation body), and its results were also adopted byothers, e.g. 3GPP services. / <p>QC 20101125</p>

Although radio repeaters and wireless routers are commonly used, relaying techniques have received a lot of attention in academic publications the last decade. Most of the techniques proposed in the literature are based on relaying terminals. For instance groups of mobile terminals cooperate so as to jointly communicate with an access point, or to another group of mobiles in an (infrastructure-less) mobile ad-hoc network MANET. However, it has also been suggested that these techniques can be applied to hybrid cellular-relaying architecture with fixed relays and that this would reduce the infrastructure costs. The literature shows that the coverage or capacity of a cellular network is enhanced when using relays. A common assumption in these studies is that relays are very low cost, but little attention has been given to how cheap these relays need to be in order for the technical enhancements to translate into an economic gain. It is not obvious that the techniques proposed for mobile relaying are economically feasible when applied to fixed relays. This thesis examines the conditions under which large scale usage of fixed relays leads to lower infrastructure cost than in a purely cellular architecture, how large the benefits of these new techniques are, compared with existing repeater/router techniques, and how sensitive the results are to traditional network design parameters. The analysis is done by means of several study cases in which coverage should be provided for broadband services by building a network from scratch. The results are expressed in terms of how cheap a relay must be with respect to a base station's cost so that the hybrid infrastructure provides the desired service at a lower cost. If in practice this relative relay cost is much lower, then high economic gains are expected. None of the study cases considered yield substantial cost savings when using fixed relays on a large scale. When access points are placed as high as in a cellular network, the hybrid system is feasible only if the total relay cost is 3-20% of the total base station cost. When unplanned relay deployment is used, the impact of the antenna height and/or gain on the results is much greater than the particular type of amplify-and-forward relaying scheme. Planned deployment of a few relays should be used unless the cost of planning is 1-2 times larger than all the other relay costs. A proper trade-off between route-length and how tight the radio channel can be reused is essential for the feasibility of the hybrid system. The results confirm that the planned usage of few relays together with macro-like base stations is an efficient way of providing coverage. Analysis of other scenarios, such as the use of pico base stations for coverage, is left for further studies. / QC 20101125

To support the future requirements on wireless systems in an affordable manner it is commonly believed that multiple radio access technologies have to be combined. These technologies can be deployed by a single operator or, even, be managed by different competing operators. In order to cope with the increased complexity of such a multifaced wireless environment it has been argued that a transfer of Radio Resource Management (RRM) functionalities towards the network edges (access ports and, ultimately, user terminals) may be beneficial. In addition to detecting varying system conditions in a faster manner this would also allow a more responsive service adaptation. In this thesis we evaluate a set of self-organizing regimes, all with the purpose of supporting the distribution of control at the edge node. Particular emphasis is put on the design of a mechanism for dynamically establishing cooperation between different network entities whether these are access ports or user terminals. Terminal cooperation by means of multihopping is considered in the context of service provision in cellular access systems. Previously the opportunity cost associated with sharing own bandwidth, and energy loss have been seen as a major obstacle for relaying other users’ traffic. To mitigate the effects of this selfish behavior the concept of resource delegation is introduced and evaluated in combination with a rewarding scheme designed for compensating the energy losses induced by forwarding. The results show that our proposed schemes not only are capable of fostering significant cooperation among users, but also to create a simultaneous improvement in user utility, data rates as well as in operator revenues. Opening up networks of user-deployed Access Points (APs) for service provision is considered a means to radically lower the cost of future wireless services. However, since these networks are deployed in an uncoordinated manner, only discontinuous coverage will be provided. The question of how dense these networks need to be, to deliver acceptable user perception, is investigated in this thesis for a set of archetypical services. The results show that already at moderate AP densities the investigated services can be provided with sufficient quality. Epidemic exchange of popular content and inter-AP cooperation are also shown to further decrease the required infrastructure density and improve the APs’ utilization respectively. As last contribution, “Word-of-Mouth”, a distributed reputation-based scheme, is investigated in the context of access selection in multi-operator environments. By exchanging information concerning the Quality of Service (QoS) associated with the different networks, terminal agents can collectively reveal the capabilities of individual networks. For a vertical handover scenario we show that our proposed scheme can reward access providers capable of ensuring some degrees of QoS. By introducing a model for collusion, between low performing APs and terminal agents, we show that our proposed scheme is also robust to the dissemination of false information. / QC 20101112

<p>The successful deployment of Universal Mobile Telecommunication System (UMTS) is heavily dependent on Quality of Service (QoS) to be achieved. This thesis addresses a few facets of the QoS issues in UMTS, including traffic shaping and policing, conformance consistency, Call Admission Control (CAC) and resource allocation.</p><p>The main focus of this thesis is traffic conditioning related issues for QoS provisioning in UMTS. Assuming an end-to-end QoS scenario supported by IntServ or/and Diffserv architectures, the thesis initially presents an all nodes traffic conditioning-enabled framework in UMTS. Under this framework, the traffic generated at each User Equipment (UE) is regulated by a traffic shaper in the form of a token bucket, and the conformance of the traffic flow is policed at the policing node. The performance of imposing traffic shaping at the UE is studied and compared with the case without shaping. Next, having observed that the performance of the traffic conditioned system is sensitive to the values of the token bucket parameters, the thesis proposes a heuristic approach for searching local and global QoS-aware token bucket parameters. By tuning the system operating at the obtained ’optimal’ shaping parameters, the requirements for all concerned QoS attributes are guaranteed. Furthermore, the thesis studies conformance consistency in a traffic conditioned multi-hop network, by monitoring the conformance status of a traffic flow using an identical token bucket for both traffic shaping and policing. In the presence of variable packet size, the thesis gives a quantitative result, for a simple case, on how much percent of the originally conformant packets may misbehave at further policing node(s). The performance of the aggregated traffic flows and the measures to minimize the effect of conformance deterioration are also studied in the thesis.</p><p>Another facet of the QoS issues in UMTS, CAC together with resource allocation, is also studied in the thesis. A priority-oriented framework for QoS management of multimedia services in UMTS is proposed. Based on a traffic class priority definition, the framework is implemented through a priority-oriented CAC, channel congestion control and adaptive bandwidth allocation.</p>

The successful deployment of Universal Mobile Telecommunication System (UMTS) is heavily dependent on Quality of Service (QoS) to be achieved. This thesis addresses a few facets of the QoS issues in UMTS, including traffic shaping and policing, conformance consistency, Call Admission Control (CAC) and resource allocation. The main focus of this thesis is traffic conditioning related issues for QoS provisioning in UMTS. Assuming an end-to-end QoS scenario supported by IntServ or/and Diffserv architectures, the thesis initially presents an all nodes traffic conditioning-enabled framework in UMTS. Under this framework, the traffic generated at each User Equipment (UE) is regulated by a traffic shaper in the form of a token bucket, and the conformance of the traffic flow is policed at the policing node. The performance of imposing traffic shaping at the UE is studied and compared with the case without shaping. Next, having observed that the performance of the traffic conditioned system is sensitive to the values of the token bucket parameters, the thesis proposes a heuristic approach for searching local and global QoS-aware token bucket parameters. By tuning the system operating at the obtained ’optimal’ shaping parameters, the requirements for all concerned QoS attributes are guaranteed. Furthermore, the thesis studies conformance consistency in a traffic conditioned multi-hop network, by monitoring the conformance status of a traffic flow using an identical token bucket for both traffic shaping and policing. In the presence of variable packet size, the thesis gives a quantitative result, for a simple case, on how much percent of the originally conformant packets may misbehave at further policing node(s). The performance of the aggregated traffic flows and the measures to minimize the effect of conformance deterioration are also studied in the thesis. Another facet of the QoS issues in UMTS, CAC together with resource allocation, is also studied in the thesis. A priority-oriented framework for QoS management of multimedia services in UMTS is proposed. Based on a traffic class priority definition, the framework is implemented through a priority-oriented CAC, channel congestion control and adaptive bandwidth allocation.

Univ., Diss.--Hamburg, 1992.