Sonia M. Heemstra de Groot

FEDNETS: Context-Aware Ad-Hoc Network Federations

This paper introduces the concept of fednets. Fednets are temporary ad-hoc federations of networks with the objective of achieving a specific common goal. Fednets are driven by purpose and opportunity. Fednets are constituted by a set of independent networks under mutually agreed rules for cooperation. The rules for cooperation are policies to control under what circumstances (context) with what networks and for what purposes cooperation is allowed. We discuss the concept of fednets by focusing on fednets formed by personal networks (PN), which are person-centric networks connecting personal devices and artefacts regardless of geographical location.

An All-Optical WDM Packet-Switched Network Architecture with Support for Group Communication

The so-called media convergence to the Internet is foreseen. As a consequence of this convergence, MANs will face new demands not only in terms of bandwidth, but also in terms of services. To meet these new demands, new MAN architectures are required. WDM-based MAN architectures that tackle the first problem are available not only in the literature, but also on the market. In this paper we deal with the second problem. Specifically, we describe a novel WDM-based MAN architecture that supports group communication, a service that is expected to increase considerably as new applications converge to the Internet. Based on packet switching, the architecture supports both point-to-point and point-to-multipoint communication in the optical domain.

Vertical handovers among different wireless technologies in a UMTS radio access-based integrated architecture

The demands for accessing services at high data rates while on the move, anyplace and anytime, resulted in numerous research efforts to integrate heterogeneous wireless and mobile networks. The focus was mainly put on the integration of the Universal Mobile Telecommunications System (UMTS) and the wireless local area network (WLAN) IEEE 802.11, which is beneficial in terms of capacity, coverage and cost. With the advent of IEEE 802.16(e) the attention of the research community was shifted to its interworking, on one side, with complementary WLANs, and on the other, with UMTS for extra capacity. In addition, there has been also research on UMTS interworking with different broadcasting systems, including the Digital Video Broadcasting system for handheld devices (DVB-H). All these research activities resulted in various heterogeneous architectures where the interworking was performed at different levels in the network. In this article, we address the integration at the UMTS radio access level, known also as very tight coupling. This integration approach exhibits good vertical handover performance and may allow for seamless session continuity during the handover. However, it is a technology specific solution, where not all the mechanisms applied to the integration of one wireless technology can be straightforwardly reused for embedding another. This integration approach introduces various modifications to UMTS that have to be standardized, which makes it a long-term solution. We present here the general architecture for the integration at the UMTS radio access level and discuss the extension of the architectural framework for various types of access systems with as few as possible additional modifications. The focus of the work is put on the vertical handovers. We discuss various vertical handovers among WCDMA, IEEE 802.11, IEEE 802.16e and DVB-H in the considered heterogeneous architecture. We present new handover types, describe the vertical handover procedures and provide performance evaluation of the vertical handovers in different scenarios and for different combinations of the wireless access technologies.

Proxy-Based Fednets for Sharing Personal Services in Distributed Environments

A Personal Network (PN) is a network of distributed personal devices that communicate with each other independently from their geographical location. By adding extra functionality to PNs it is possible to enable cooperation between PNs forming a group-oriented network called Fednet. A Fednet is a secure, opportunity or purpose driven ad-hoc sharing of personal resources. In this paper, we provide a description of a Fednet and its lifecycle. We introduce a proxy-based functional architecture of a Fednet and the basic processes of the access control in Fednets. Finally, we compare Fednets with related paradigms, such as grids, Virtual Organizations, Secure Virtual Enclaves and P2P networks.

Data Rate based Congestion Control in V2V communication for traffic safety applications

Vehicle-to-Vehicle (V2V) communication systems intend to increase safety and efficiency of the transportation networks. At high vehicle density, the communication channel may become congested, impairing the reliability of the safety applications. As a counter measure, the European Telecommunications Standard Institute (ETSI), proposes the Decentralized Congestion Control (DCC) framework to control the channel load, by tuning message transmission parameters, such as message rate and transmitting power. In this paper, we analyze a congestion control scheme that follows the DCC framework known as Data Rate-DCC (DR-DCC) for various traffic densities. DR-DCC adjusts the data rate based on channel load measurements thus controlling the air time of packets to avoid congestion. Although tuning the data rate has been proposed before we are not aware of any reported work, where its full potential has been investigated in detail. In this paper we intend to provide more insight on the benefits of this approach by analyzing schemes that aim at optimum data rate for various traffic density cases. The objective is not only to avoid congestion but also to provide optimal support to safety applications. We compare the performance of DR-DCC to another DCC approach based on adjusting transmit power for various traffic density cases. DR-DCC outperforms at various traffic densities providing better support to safety applications.

Reputation-Based Systems within Computer Networks

The topic on using reputation has received considerable research attention in the field of networking and communications. In this survey paper, we discuss the various ways the systems can benefit from using reputation information. We provide the examples of existing reputation-based systems discussing their functional implementations. Based on our observations, we list minimum requirements for benefiting from reputation-based systems in computer networks. This survey is suited as a tutorial for both researchers and practitioners, willing to build reputation systems, equipped with the knowledge and experience have been made in the field.

Policy-Based Hybrid Approach to Service Provisioning in Federations of Personal Networks

A Personal Network (PN) is a network of geographically distributed personal devices, which creates a distributed environment of a user and provides access to personal resources and services regardless the location of the user. A Federation of Personal Networks (Fednet) is a peer-to-peer cooperation of PNs of different users to share personal resources and services. Until now little research has been conducted on the service provisioning in Fednets. Based on the current status of the research on Fednets, the service provisioning can be done directly at the personal device (network overlay approach), or at a specific entry point of a PN, called a service proxy (service proxy approach). While the network overlay approach provides quick service access and provisioning, the service proxy approach provides a more elegant solution for service provisioning by preventing direct access of other PNs to the PN’s services and by enabling the control over the access to personal services at a single point of a PN. In this paper, to leverage the advantages of both approaches, we propose a hybrid approach to service provisioning in Fednets, which combines both approaches to provide an optimal and flexible solution for service provisioning in Fednets.

Supporting IP dense mode multicast routing protocols in WDM all-optical networks

Recent developments in all-optical networking and wavelength division multiplexing technologies allow for the support of optical multicasting, a missing feature towards the optical Internet. In this paper we propose a protocol to construct source-rooted WDM multicast trees. The protocol works under dense mode multicasting routing IP protocols and supports network nodes with different degrees of light splitting, wavelength conversion, and add/drop capabilities.

Architectures for intra-personal network communication

Personal Networks (PN) is a new concept related to pervasive computing with a strong user-focus view. The key to a successful PN realization is a general network architecture that is capable of bridging different current and future technologies and offers a homogeneous and clear view to the end-user. In this paper, we focus on forming a PN by connecting remote personal devices using infrastructure-based IP networks, including 3G networks and WLAN hotspots. One way is to upgrade the current access networks with new functionality to support PNs. Since many devices in PNs are mobile and battery powered, this may help them to achieve a faster service and to save energy. However, to deploy such functionality is not easy and may hamper the adoption of PNs altogether. Therefore, we propose an intra-PN communication architecture that will work over current IP networks. To discern the above proposal we also give a detailed picture of PN network architecture and infrastructure supported PNs. We believe that this will help the success of PNs.

Measurements and performance of large MIMO systems at 2.4 GHz for indoor WLAN

Large MIMO is a new and promising technique for boosting wireless link capacity. Currently, the research of large MIMO focuses on the theoretical aspects while work on the practical implementations and analysis are very limited. In this paper, we present some critical investigations on the behaviors of large MIMO in real propagation environment based on extensive channel measurements. On the one hand, our analysis has verified the advantages that the MIMO channel vectors between users tend to be orthogonal and the optimal capacity approximates the theoretical upper bound as the antenna array size grows. On the other hand, we observe that the practical limitations of allowable antenna array size and achievable spatial degrees of freedom in the physical channel have significant impacts. Furthermore, in order to enable the utilization of linear precoding techniques in such high-dimensional MIMO systems to achieve close-to-optimal capacity, a large ratio between the antenna array size of the large MIMO system and the number of simultaneously served users should be maintained.