Rasmus Løvenstein Olsen

Probabilistic models for access strategies to dynamic information elements

In various network services remote access to dynamically changing information elements is a required functionality. Three fundamentally different strategies for such access are investigated in this paper: (1) a reactive approach initiated by the requesting entity, and two versions of proactive approaches in which the entity that contains the information element actively propagates its changes to potential requesters, either (2) periodically or (3) triggered by changes of the information element. This paper develops probabilistic models for these scenarios, which allow to compute a number of performance metrics, with a special focus on the mismatch probability. In particular, we use matrix-analytic methods to obtain explicit expressions for the mismatch probability that avoid numerical integration. Furthermore, limit results for information elements spread over a large number of network nodes are provided, which allow one to draw conclusions on scalability properties. The impact on mismatch probability of different distribution types for the network delays as well as for the time between changes of the information element are obtained and discussed through the application of the model in a set of example scenarios. The results of the model application allow for design decisions on which strategy to implement for specific input parameters and specific requirements on the performance metrics.

A Generic Context Management Framework for Personal Networking Environments

In this paper we introduce a high level architecture for a context management system for personal networks (PN). The main objective of the context management framework (CMF) described in this paper is to support the interactions between context information sources and context aware components, services and applications in a generic manner, independently of their nature and operation area. To this end, we propose a structure consisting of a context management interface, context access manager module, processing and storage module, and a data source abstraction layer. Nodes provide a certain set of these modules depending on their computational capabilities and their role within the system. We differentiate between basic context nodes (BCN), enhanced context nodes (ECN) and context management nodes (CMN) within the CMF. CMNs operate on two levels, i.e., local/cluster level and PN level. In the paper we also describe how these entities will interact with each other and how different context information will be exchanged within the personal network. Finally, we provide an outlook of the work and issues that need to be addressed in order to complete the described framework

Heterogeneous services and architectures for next-generation wireless networks

Even though it is named as the successor of the previous cellular generations, the fourth generation of wireless mobile communication systems (4G) is predominantly presented as a convergence platform that provides clear advantages in terms of coverage, bandwidth, energy consumption and a variety of heterogeneous services, ranging from pop-up advertisements to location-based and interactive or on-demand ones (so called IP datacasting). Based on the above vision of 4G, in this paper we propose innovative services and architectures that may achieve enhanced security, energy efficiency, and just-for-you and just-in-time content delivery. Furthermore, since the state-of-the-art technologies do not appropriately cover the needs required for 4G, a context sensitive service discovery that can operate in a wireless as well as in a wired network environment, ranging from local to global distances, is described and applied to the case of the proposed services.

QRP01-5: Quantitative Analysis of Access Strategies to Remote Information in Network Services

Remote access to dynamically changing information elements is a required functionality for various network services, including routing and instances of context-sensitive networking. Three fundamentally different strategies for such access are investigated in this paper: (1) a reactive approach initiated by the requesting entity, and two versions of proactive approaches in which the entity that contains the information element actively propagates its changes to potential requesters, either (2) periodically or triggered by changes of the information element (3). This paper first develops a set of analytic models to compute different performance metrics for these approaches, with special focus on the so-called mismatch probability. The results of the analytic models allow for design decisions on which strategy to implement for specific input parameters (change rate of the information element, network delay characterization) and specific requirements on mismatch probability, traffic overhead, and access delay. Finally, the analysis is applied to the use-case of context-sensitive service discovery.

Network aware dynamic context subscription management

Context-awareness is a key requirement in many of todays networks, services and applications. Context management systems are used to provide access to distributed, dynamic context information. The reliability of remotely accessed dynamic context information is impacted by network delay, packet drop probability, its information dynamics and the access strategy used. Due to the characteristics of the different access strategies, different levels of reliability of context information can be ensured, but at the same time, these strategies lead to different access traffic which impacts also the network performance, and hence feeds back to the reliability of the information. Furthermore, different levels of QoS may be available and used in order to mitigate the impact of network performance degradation on the reliability of the dynamic context information. In this paper we describe a system and algorithms that are capable of configuring effectively context access strategies in order to maximize reliability of all accessed dynamic context information. The framework utilizes and extends existing information reliability models, and it can utilize different network performance models. Simulation results of scenarios in which the framework uses finite-buffer bottleneck performance models demonstrate the effectiveness of our algorithm to increase reliability. Furthermore, the framework is applied to a scenario with QoS classes that allows to trade off delay and loss via different buffer-size configurations.

On the impact of information delay on location-based relaying: A Markov modeling approach

For centralized selection of communication relays, the necessary decision information needs to be collected from the mobile nodes by the access point (centralized decision point). In mobile scenarios, the required information collection and forwarding delays will affect the reliability of the collected information and hence will influence the performance of the relay selection method. This paper analyzes this influence in the decision process for the example of a mobile location-based relay selection approach using a continuous time Markov chain model. The model is used to obtain optimal relay policies via a heuristically reduced brute-force search. Numerical results show how forwarding delays affect these optimal policies.

Bandwidth analysis of smart meter network infrastructure

Advanced Metering Infrastructure (AMI) is a network infrastructure in Smart Grid, which links electricity customers to utility company. Compared to a network where different amount of data is send, AMI network sends small amount of data at different time intervals. This network enables smart services by making it possible for the utility company to get an overview of their customers power consumption and also control devices in their costumers household e.g. heat pumps. The problem investigated in this paper is what bandwidth requirements can be expected when implementing such network to utilize smart meters and which existing broadband network technologies can facilitate this smart meter service. Initially, scenarios for smart meter infrastructure are identified. The paper defines abstraction models which cover the AMI scenarios. A general overview of the bandwidth requirements are analysed. For this analysis assumptions and limitations are defined. The results show the bandwidth provided by GPRS technology is sufficient. However, from a delay point of view, GPRS has its limits, therefore, xDSL or 3G can be used for faster transfer but will rarely utilize the available bandwidth from these technologies. The aggregator which is responsible to collect all the data from the different smart meters can become a bottleneck as the aggregated amount of data is high, thus the bandwidth for the data concentrator has to be high. These results are interesting to look at, as they show there are different bandwidth requirements from a smart meter and aggregator point of view and that, the aggregator is a vital element in the network and it has to be studied further.

Utilizing network QoS for dependability of adaptive smart grid control

A smart grid is a complex system consisting of a wide range of electric grid components, entities controlling power distribution, generation and consumption, and a communication network supporting data exchange. This paper focuses on the influence of imperfect network conditions on smart grid controllers, and how this can be counteracted by utilizing Quality of Service (QoS) information from the communication network. Such an interface between grid controller and network QoS is particularly relevant for smart grid scenarios that use third party communication network infrastructure, where modification of networking and lower layer protocols are impossible. This paper defines a middleware solution for adaptation of smart grid control, which uses network QoS information and interacts with the smart grid controller to increase dependability. In order to verify the methodology, an example scenario of a low voltage grid controller is simulated under imperfect network conditions.

Analysis of Information Quality in Event Triggered Smart Grid Control

The integration of renewable energy sources into the power grid requires added control intelligence which imposes new communication requirements onto the future power grid. Since large scale implementation of new communication infrastructure is infeasible, we consider methods of increasing dependability of existing networks. We develop models for network delays and information dynamics, and uses these to model information quality for three given information access schemes in an event triggered control scenario. We analyse the impact of model parameters, and show how optimal choice of information access scheme depends on network conditions as well as trade-offs between information quality, network resources and control reactivity.

Location-quality-aware policy optimisation for relay selection in mobile networks

AbstractRelaying can improve the coverage and performance of wireless access networks. In presence of a localisation system at the mobile nodes, the use of such location estimates for relay node selection can be advantageous as such information can be collected by access points in linear effort with respect to number of mobile nodes (while the number of links grows quadratically). However, the localisation error and the chosen update rate of location information in conjunction with the mobility model affect the performance of such location-based relay schemes; these parameters also need to be taken into account in the design of optimal policies. This paper develops a Markov model that can capture the joint impact of localisation errors and inaccuracies of location information due to forwarding delays and mobility; the Markov model is used to develop algorithms to determine optimal location-based relay policies that take the aforementioned factors into account. The model is subsequently used to analyse the impact of deployment parameter choices on the performance of location-based relaying in WLAN scenarios with free-space propagation conditions and in an measurement-based indoor office scenario.