On the benefits of location-based relay selection in mobile wireless networks

We consider infrastructure-based mobile networks that are assisted by a single relay transmission where both the downstream destination and relay nodes are mobile. Selecting the optimal transmission path for a destination node requires up-to-date link quality estimates of all relevant links. If the relay selection is based on link quality measurements, the number of links to update grows quadratically with the number of nodes, and measurements need to be updated frequently when nodes are mobile. In this paper, we consider a location-based relay selection scheme where link qualities are estimated from node positions; in the scenario of a node-based location system such as GPS, the location-based approach reduces signaling overhead, which in this case only grows linearly with the number of nodes. This paper studies these two relay selection approaches and investigates how they are affected with varying information update interval, node mobility, location inaccuracy, and inaccurate propagation model parameters. Our results show that location-based relay selection performs better than SNR-based relay selection at typical levels of location error when medium-scale fading can be neglected or accurately predicted.     

On the Benefits and Challenges of Crowd-Sourced Network Performance Measurements for IoT Scenarios

Wireless Personal Communications - Systems within IoT domains such as ITS, Smart City, Smart Grid and other, often rely on real-time information and communication. These types of systems often...     

Diamond deposition and plasma diagnostics in a 27 MHz inductive coupled reactor (ICP)

An inductive coupled planar radio frequency (rf) reactor (ICP) with separately mounted concentric coils was used to deposit diamond films onto silicon and boron nitride. A grounded Faraday polarizer was mounted on top of the reactor below the rf-coil to prevent capacitive coupling. The electrically heated substrates were immersed in the most intense plasma region shaped like a torus. Mainly two different argon-hydrogen-methane mixtures were used, namely Ar/H₂/CH₄—250/25/0.5 sccm (mixture #I) and Ar/H₂/CH₄—50/50/0.5 sccm (mixture #II). With the conditions of mixture #I, deposition of good quality diamond with relatively high growth rates (0.6–1 μm h⁻¹) has been obtained. During diamond growth, the plasma was investigated by means of a Langmuir probe system (LP), providing radial distributions of several plasma parameters. The energy distributions of the most often occurring ions were analysed by an energy and mass spectrometer (EMS). Correlations between the measured parameters and the grown coatings will be given.     

Context-Sensitive Service Discovery Experimental Prototype and Evaluation

The amount of different networks and services available to users today are increasing. This introduces a need for ways to locate and sort out irrelevant services in the process of discovering available services for a user. In this paper, we describe and evaluate a prototype of an automated discovery and selection system, which locates services that are relevant to a user based on his/her context and the context of the available services. The prototype is based on a multi-level, hierarchical system approach and introduces entities called User-nodes, Super-nodes, and Root-nodes. These entities separates the network into domains that handle the complex distributed service discovery, which is based on dynamically changing context information. In the prototype, a method for performing context-sensitive service discovery has been achieved. The service discovery part utilizes UPnP, which has been extended in order to increase network scalability. The experimental analysis of service discovery times, based on different scenarios is used to optimize parameter settings of the service discovery system in order to achieve short response times.     

Cooperation of Network and Service Layer in Mobile Ad hoc Networks

In this article, we investigate how a service discovery protocol at the service layer in Mobile Ad Hoc Networks can be improved, by utilizing routing information from the network layer. We consider in this article proactive routing protocols as basis for the underlying routing mechanism, and focus on the optimization of proactive service discovery protocols. First we introduce a general framework, enabling the cooperation of service layer and network layer, and then we propose the optimization scheme. The performance evaluation done by simulation shows that the proposed cooperation scheme can optimize the service discovery protocol, i.e. reduce the communication cost of service discovery, by utilizing routing table and topology information.     

Analysis of the (1, lambda)-ES on the parabolic ridge

The progress rate of the (1,+ lambda)-ES (Evolution Strategy) is analyzed on the parabolic ridge test function. A different progress behavior is observed for the (1, lambda)-ES than for the sphere model test function. The characteristics of the progress rate picture for the plus strategy differs little from the one obtained for the sphere model, but this strategy has drastically worse progress rate values than those obtained for the comma strategy. The dynamics of the distance to the progress axis is also investigated. A theoretical formula is derived to estimate the change in this distance over generations. This formula is used to derive the expected value of the problem-specific distance to the ridge axis. The correctness of the formulae is supported by simulation results.     

On three new approaches to handle constraints within evolution strategies

Evolutionary algorithms with a self-adaptive step control mechanism like evolution strategies (ES) often suffer from premature fitness stagnation on constrained numerical optimization problems. When the optimum lies on the constraint boundary or even in a vertex of the feasible search space, a disadvantageous success probability results in premature step size reduction. We introduce three new constraint-handling methods for ES on constrained continuous search spaces. The death penalty step control evolution strategy (DSES) is based on the controlled reduction of a minimum step size depending on the distance to the infeasible search space. The two sexes evolution strategy (TSES) is inspired by the biological concept of sexual selection and pairing. At last, the nested angle evolution strategy (NAES) is an approach in which the angles of the correlated mutation of the inner ES are adapted by the outer ES. All methods are experimentally evaluated on four selected test problems and compared with existing penalty-based constraint-handling methods.     

Connectivity analysis of one-dimensional ad-hoc networks

Application and communication protocols in dynamic ad-hoc networks are exposed to physical limitations imposed by the connectivity relations that result from mobility. Motivated by vehicular freeway scenarios, this paper analyzes a number of important connectivity metrics for instantaneous snapshots of stochastic geographic movement patterns: (1) The single-hop connectivity number, corresponding to the number of single-hop neighbors of a mobile node; (2) the multi-hop connectivity number, expressing the number of nodes reachable via multi-hop paths of arbitrary hop-count; (3) the connectivity distance, expressing the geographic distance that a message can be propagated in the network on multi-hop paths; (4) the connectivity hops, which corresponds to the number of hops that are necessary to reach all nodes in the connected network. The paper develops analytic expressions for the distributions and moments of these random variables for general stationary MAP processes on a one dimensional space. The numerical results compare bursty vehicular traffic with independent movement scenarios described by a Poisson process, illustrate in examples the impact of a random communication range, and demonstrate the usefulness of MAP processes via comparison with vehicular simulation traces.     

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

Relaying 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.     

Evolution strategies – A comprehensive introduction

This article gives a comprehensive introduction into one of the main branches of evolutionary computation – the evolution strategies (ES) the history of which dates back to the 1960s in Germany. Starting from a survey of history the philosophical background is explained in order to make understandable why ES are realized in the way they are. Basic ES algorithms and design principles for variation and selection operators as well as theoretical issues are presented, and future branches of ES research are discussed.