Niovi Pavlidou

Power line communications: state of the art and future trends

This article constitutes an overview of the research, application, and regulatory activities on power line communications. Transmission issues on the power line are investigated and modeling approaches illustrated. Contemporary communication techniques and reliability issues are treated. A description of regulatory activities worldwide is given. Finally, market perspectives and promising applications are covered to assess the viability of this communications environment.

Seamless continuity of real-time video across UMTS and WLAN networks: challenges and performance evaluation

This article addresses several challenges related to the evolution toward seamless interworking of wireless LAN and 3G cellular networks. The main objective is to evaluate the conditions and restrictions under which seamless continuity of video sessions across the two networks is feasible. For this purpose, we formulate a number of practical interworking scenarios, where UMTS subscribers with ongoing real-time video sessions hand over to WLAN, and we study the feasibility of seamless continuity by means of simulation. We particularly quantify the maximum number of UMTS subscribers that can be admitted to the WLAN, subject to maintaining the same level of UMTS QoS and respecting the WLAN policies. Our results indicate that the WLAN can support seamless continuity of video sessions for only a limited number of UMTS subscribers, which depends on the applied WLAN policy, access parameters, and QoS requirements. In addition to this study, we do address several other issues that are equally important to seamless session continuity, such as the QoS discrepancies across UMTS and WLAN, the vertical handover details, and various means of access control and differentiation between regular WLAN data users and UMTS subscribers. The framework for discussing these issues is created by considering a practical UMTS/WLAN interworking architecture.

A TCP Driven CAC Scheme: Efficient Resource Utilization in a Leaky HAP-Satellite Integrated Scenario

An integrated high altitude platform (HAP)-satellite communication system appears to be very suitable for a large set of scenarios including emergency situations, exceptional events, etc. In fact, the satellite capability to provide a broadband and ubiquitous access can be enhanced by the deployment of HAP that allows the use of low-power consuming, cost-efficient, and portable terminals. To obtain an optimum utilization of radio resource, without renouncing to QoS satisfaction, a suitable call admission control scheme must be implemented. Nevertheless, transmission control protocol (TCP) behavior, mainly affected by the high latency and shadowing events, can impact call admission control (CAC) performance. Therefore, it would be desirable that the CAC scheme takes into account also the TCP congestion window real evolution. We present an innovative CAC scheme that uses TCP statistics as one of its inputs and is able to manage different classes of users. Results show that CAC performance is significantly improved by introducing TCP statistics about network congestion as an input parameter.

CAC-TCP Cross-Layer Interaction in a HAPS-Satellite Integrated Scenario

The integration of a satellite system with a HAPS segment appears very suitable to provide communication services, including Internet access, for a large set of applications. In fact, the satellite capability to provide wide coverage and broadband access can be enhanced by the use of cost-effective, mobile/portable and low-power consuming user terminals, when HAPS acts as an intermediate repeater. Moreover, also TCP-based applications, which suffer from long latency introduced by the satellite link and in general by errors, can get benefits in terms of end-to-end performance. In this frame, this paper deals with the introduction, on board the HAPS, of an efficient CAC scheme in order to guarantee an optimal utilization of the precious radio resources. In particular, we propose an innovative TCP driven CAC algorithm, which shall take into account not only the QoS requirements, but also TCP statistics obtained through a proxy installed on the HAPS. Results show that the overall system performance in terms of both average throughput and blocking probability is significantly improved.

Adaptive Handover Management for Multiservice NGSO Satellite Systems

In this paper we propose a handover method for multiservice non-geo satellite systems. The proposed algorithm can be used for satellite handover as well as for cell handover when a fixed amount of resources is allocated to each cell. Specifically, we consider the case in which the satellite system provides services to users of different QoS requirements. The first type of users require the minimization and, if possible, the elimination of the probability of forcing a connection in progress to termination during a handover. On the other hand, the users of the second category do not have any specific handover requirements. The new method is evaluated through extensive simulations and is proved to meet the requirements of the first type of users while at the same time maximizes the system utilization for both types of users.

TCP-Call Admission Control Interaction in Multiplatform Space Architectures

The implementation of efficient call admission control (CAC) algorithms is useful to prevent congestion and guarantee target quality of service (QoS). When TCP protocol is adopted, some inefficiencies can arise due to the peculiar evolution of the congestion window. The development of cross-layer techniques can greatly help to improve efficiency and flexibility for wireless networks. In this frame, the present paper addresses the introduction of TCP feedback into the CAC procedures in different nonterrestrial wireless architectures. CAC performance improvement is shown for different space-based architectures, including both satellites and high altitude platform (HAP) systems.

A satellite-based architecture for internet P2P applications

This paper proposes an architecture for unstructured p2p Internet applications. The paper focuses on applications that use superpeers. The proposed architecture utilizes satellites for building a backbone network for connecting superpeers. This network provides fully meshed connectivity to superpeers, in order to minimize the complexity of the p2p overlay network and at the same time preserves the flexibility in developing new applications. Technical aspects related to the implementation of the proposed architecture are discussed and useful conclusions are drawn.