Krzysztof Grochla

Energy-Efficient Crowdsensing of Human Mobility and Signal Levels in Cellular Networks.

The paper presents a practical application of the crowdsensing idea to measure human mobility and signal coverage in cellular networks. Currently, virtually everyone is carrying a mobile phone, which may be used as a sensor to gather research data by measuring, e.g., human mobility and radio signal levels. However, many users are unwilling to participate in crowdsensing experiments. This work begins with the analysis of the barriers for engaging people in crowdsensing. A survey showed that people who agree to participate in crowdsensing expect a minimum impact on their battery lifetime and phone usage habits. To address these requirements, this paper proposes an application for measuring the location and signal strength data based on energy-efficient GPS tracking, which allows one to perform the measurements of human mobility and radio signal levels with minimum energy utilization and without any engagement of the user. The method described combines measurements from the accelerometer with effective management of the GPS to monitor the user mobility with the decrease in battery lifetime by approximately 20%. To show the applicability of the proposed platform, the sample results of signal level distribution and coverage maps gathered for an LTE network and representing human mobility are shown.

Review of Mobility Models for Performance Evaluation of Wireless Networks

Performance evaluation of protocols and mechanisms in wireless networks require a good representation of client mobility. The number of mobility models has been developed, to emulate the changes of location in time of mobile wireless devices in communication networks, such as e.g. mobile phones, tablets, netbooks, palmtops.Mobility models are used to verify the protocols and algorithms developed for wireless networks in simulation and using analytical tools. The mobility patterns of such devices converges with human movement patterns, as the mobile devices bearers. Among many propositions of human mobility modeling in the literature this paper presents and reviews techniques which are most commonly used or that give very good estimation of actual mobile device bearer behavior. The models are divided into 3 groups: random, social and hybrid.

Diffusion Approximation Model for the Distribution of Packet Travel Time at Sensor Networks

We propose a model to estimate the probability density function of the distribution of a packet travel time in a multihop wireless sensor network. The model is based on diffusion approximation and it takes into consideration the heterogeneity of the propagation medium and of the distribution of relay nodes. The modeled system parameters, e.g. the packet loss probability or the network topology, may depend on time.

Performance evaluation of CoAP, SNMP and NETCONF protocols in fog computing architecture

Different architectures of interactions between the objects in the Internet of Things have been proposed, based on direct exchange of data between the wireless devices or based on synchronization with fixed network devices or cloud infrastructure. We evaluated how the selection of the communication architecture influences the performance of the data exchange using discrete event simulation. The distribution of time needed to pass information between smart objects is calculated for three popular network management protocols: CoAP, SNMP and NETCONF. The evaluation is executed for 3 types of communication proposed in the fog computing paradigm: direct synchronization between devices, synchronization through the local gateway or synchronization via the cloud servers. The analysis shows that the communication via the cloud infrastructure requires up to the three times longer time than the data exchange through a local gateway and up to 6 times longer than the direct communication between the network nodes. Transmission through CoAP and SNMP introduces similar delay, considerably lower than NETCONF.

Stability and dynamics of TCP-NCR(DCR) protocol in presence of UDP flows

The fluid-flow approximation models investigate with much success the dynamics and stability of TCP/RED connections. Their main assumption is that the fluctuations of variables characterizing the behaviour of the connections are relatively small, that enables the linearization of model and the use of traditional control analysis tools to obtain such measures as Bode gain, phase margins, tracking error or delay margin. In this article, preserving linear fluid-flow model, we propose its extension to the case when a network is composed of wired and wireless part. We consider a variant of TCP algorithm (TCP-DCR or its new version TCP-NCR) and fluid-flow differential equations representing the size of congestion window, mean queue at the bottleneck router and loss probability at a RED queue are supplemented with terms representing constant loss probability due to transmission in wireless part and probability that a fraction of these errors is recovered by a link level mechanism. The decrease of congestion window due to TCP mechanism is delayed to allow the link protocol to deal with the errors. The model considers the presence of uncontrollable UDP flows.

A diffusion approximation model for wireless networks based on IEEE 802.11 standard

The article presents an analytical model of wireless networks using the IEEE 802.11 protocol to access the transport medium. The model allows to determine such key factors of the quality of service as transmission delays and losses. The model is based on diffusion approximation approach which was proposed three decades ago to model wired networks. We show that it can be adapted to take into consideration the input streams with general interarrival time distributions and servers with general service time distributions. The diffusion approximation has been chosen because of fairly general assumptions of models based on it, hard to be represented in Markov models. A queueing network model can have an arbitrary topology, the intensity of transmitted flows can be represented by non-Poisson (even self-similar) streams, the service times at nodes can be defined by general distributions. These assumptions are important: because of the CSMA/CA algorithm, the overall times needed to sent a packet are far from being exponentially distributed and therefore the flows between nodes are non-Poisson. Diffusion approximation allows us also to analyse the of transient behaviour of a network when traffic intensity is changing with time.

Testing and Scalability Analysis of Network Management Systems Using Device Emulation

The network management systems support the network operators by providing automation of common management tasks, fault management and automation of network reconfiguration. The testing and performance analysis of such system is a challenging engineering issue. In this paper the methodology for testing and performance analysis of the network management systems is proposed, based on a software device emulator. The emulator fully represents the managed devices and implements the management protocols to provide the same load on the server as the real devices. The sample results achieved by the proposed framework are presented.

The real-life mobility model: RLMM

The performance evaluation of mobile wireless networks requires a representation of user mobility. Mobility models are the essential part of such evaluation because they assure examples of mobile nodes movement for typical scenarios. Mobility models provide synthetic traces adjusted to users needs. We propose a novel RLMM model that produces synthetic traces of a working human and includes clear division on working days and weekend activities. We describe the model and evaluate it using simulation. The model provides better representation of changes in human behavior on different days than the models available in the literature.

Simulation comparison of active queue management algorithms in TCP/IP networks

Active Queue Management techniques are recommended to overcome the performance limitations of TCP congestion control mechanisms over drop-tail networks. The main objective of this paper is to present the comparative analysis of the performance of 10 different queue management policies using the OMNeT++ simulator. The AQMs have many parameters which influence their behavior, so some results concerning the parameters selection are given. The algorithms are tested in terms of average queue size, packet delay and packet loss rate in presence of TCP traffic.

MAGANET – On the Need of Realistic Topologies for AMI Network Simulations

The article proposes MAGANET (Map-based Generator of AMI Network Topology), new map-based topology generator, designated for Advanced Metering Infrastructure (AMI) networks as well as for the urban wireless sensor networks (WSNs). The correct, reliable representation of network topology is crucial for the correct performance evaluation on large multihop wireless networks. Most of the current work us different random topologies. In the article we describe proposed new tool and its features. The comparison of the properties of topology provided by MAGANET for three different generation modes: uniform random, grid and map based is also presented.