The CSMA mode of operation was recently added to the LoRaWAN standard. We investigate, using a queueing model, how the introduction of CSMA in the communication between devices and the gate in LoRaWan may increase the probability of successful transmission. In the proposed model, customers (transmissions) are served by a multichannel station (gate), and the number of channels corresponds to the number of transmissions that can be performed in parallel. We introduce a queueing model with multiple attempts to find a free channel and investigate their impact on transmission throughput and reliability.

Accurate indoor radio propagation modelling is a well-known problem that researchers tend to solve in many ways. Related methods differ in terms of accuracy and complexity. The article’s contribution is a new stochastic propagation model, Universal Indoor Multicharacteristic Propagation (UIMP), which results are statistically consistent with those measured in a real environment. The model could be used to verify real- world applications due to the low computational complexity and high accuracy level compared to state-of-the-art methods. This method can be especially beneficial for the efficient modelling of complex environments shared by many users using discrete events simulations (DES) based on a series of measurements in a real environment. In the article, we describe the method and present how to establish the model. The motivation was to develop an efficient method for use in an actual application: using the Bluetooth Low Energy (BLE) signal to estimate the position of users in indoor environments – the use of the proposed UIMP model allowed for a reliable assessment of the developed functionalities. Therefore we also present how the model was used to evaluate an example, real functionality, showing that the use of simplified models may falsify the assessment of the analyzed method and may lead e.g. to incorrect implementation assumptions.

Low-Power Wide-Area Networks allow long-range communication with Internet-of-Things (IoT) devices. The LoRa (Long Range) is one of the most widely used LP WAN technologies thanks to unlicensed bands, extensive availability of lowcost transceivers and the standardized LoRaWAN networking stack. The messages in LP WANs are rarely extended (e.g. few times a day). The radio link characteristics may change significantly between two consecutive data transmissions due to changes in interference level, collisions with other transmissions or the presence of obstacles on the radio wave transmission path. It makes it very hard to estimate the optimal transmission parameters and delays the detection of any problems in the transmission. We investigate the problem of prediction of the link state, namely the prediction if a packet transmitted by a LoRa arrives at the gateway. We analyze the time sequence of packets delivered to LoRa gateways from a city-wide telemetry network, consisting of 15 gateways and more than 1 mln data points. We evaluate two prediction methods, based on moving averages of received signal strength (RSSI) measurements and using Support Vector Machines (SVMs). Using a time series of 20 days, it is possible to achieve the specificity and sensitivity of the prediction above 0.6 with the SVM method. The mean accuracy of the SVM method is approximately 0.6. Using the comparison of RSSI moving averages, we could predict the link failure with a lower sensitivity, but very high specificity - e.g. prediction of 10% of link breaks with 91% specificity.

The LoRa networks allow building long-range and low power wireless networks using a star of stars topology, with multiple gateways serving low-cost devices. We present the measurements obtained in an urban environment from two independent real-life network topologies located in two Polish cities. These topologies consist of about 6400 and 4400 location points and included more than eight mln data points. We focus on the variability of RSSI (Received Signal Strength Index), SNR (Signal to Noise Ratio), probability of packet delivery, and these measures' dependence on distance. We also present an estimated path loss derived from the measurement data. The analysis shows significant variability of packet delivery probability and the RSSI. Approximately 65% of the population provides > 80% packet delivery probability in setup A, and 85% of the population provides > 80% packet delivery probability in setup B. The calculated path loss model is slightly more pessimistic than shown by most studies, as at longer distances, the measured SNR and RSSI are higher than the actual average since all transmissions with RSSI lower than gateway sensitivity (reception threshold) are not considered in the analysis as there is no data recorded. We also compare the measurements with simulated path loss, showing that commonly used simulation models may overestimate the path loss for larger distances.

The Low-Power Wide-Area Networks allow maintaining connectivity with devices over a distance of a few kilometres. However, due to the presence of obstacles, the communication range in an urban environment may be shorter, which creates multiple blind spots or areas with limited coverage. The nodes acting as relays may solve this problem by forwarding the data from other devices with poor connectivity. We propose and investigate a novel algorithm that assigns devices to the relay role while keeping the battery constraints. We define the algorithm, describe the simulation testbed, and present performance evaluation in several scenarios, including real-life topologies of IoT networks. The proposed relay selection scheme allows increasing the lifetime of the network by selecting the relay taking into account the current battery capacity. Additionally, it outperforms a previously proposed relay selection algorithm for LP WAN, showing an average 4% decrease in transmission time and an order of magnitude lower computation complexity.

The LoRa radio transmission is a popular low power WAN technology due to the use of unlicensed spectrum, low cost and long-range. LoRa devices use different Spreading Factors, which are dynamically selected by an Adaptive Data Rate (ADR) algorithm, based on signal-to-noise ratio (SNR) measurements. We discuss the influence of ADR parameters on the network performance. We use extensive simulations to estimate the probability of message delivery and energy consumption for different configurations of ADR parameters. The analysis has been performed using OMNeT++ Discrete Event Simulator together with FLoRa framework for two types of network topologies: random uniform and based on a sample city-wide LoRa deployment. The results show that there is a significant trade-off between the energy utilization and message delivery ratio probability and that the default configuration of ADR leads to over-optimistic decrease of SF and TX power, as a consequence leading to packet loss ratio >50 %.

The LoRa networks allow building low-cost long-range networks. The selection of LoRa access point locations in large scale networks requires taking into consideration the spatial distribution of clients, radio signal propagation and the limitation of the number of devices served by a single point of access. We propose a heuristic algorithm for the selection of access point locations within for a given set of candidate locations, based on gradient optimization. The proposed method allows selecting a sub-optimal set of locations which provide full coverage and take into consideration the capacity dimensioning based on spreading factor and expected channel utilization. The algorithm is evaluated in random topologies and in real-life scenario based on city-wide smart meters locations. The analysis shows that it outperforms a manual selection of access points locations, allowing to decrease the number of access points providing the full coverage.

The increasing demand for cellular network capacity can be mitigated through the installation of nomadic eNodeB, which serve a temporal increase of traffic volume in specific area. When nomadic cells are deployed, the transmission power of neighbour base stations needs to be optimised to limit the inter‐cell interferences. The authors analyse the problem of neighbourhood selection for the optimisation, to define what part of the networks needs to be reconfigured when new base station is added. They evaluate the iterative approach, with increasing range of neighbouring cells being reconfigured and propose a novel, sampling‐based local TX power reconfiguration method, which is evaluated by a numerical model in both regular (honeycomb) topology and in realistic topology reflecting locations of cells in a city. The analysis confirms that the proposed algorithm allows to select small subset of neighbouring cells to be reconfigured (in majority of the cases cells), and achieve similar efficacy as global optimisation, with total network throughput different by comparing to the global optimisation.

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.

The method for automatic selection of wireless interface on smart phones is presented. We consider the selection between WiFi and LTE / 3G radios to maximize the throughput of the data transmission and minimize the amount of energy used to scan and measure the throughput of the network. The proposed selection algorithm defines when to measure and how to estimate the network throughput to balance between the accuracy of the selection and the battery drain caused by the measurements. The link speed estimation method optimized for LTE and WiFi networks is also demonstrated

Abstract—The paper presents a performance evaluation of message broker system, Rabbit MQ in high availability- en-abling and redundant configurations. Rabbit MQ is a message queuing system realizing the middleware for distributed systems that implements the Advanced Message Queuing Protocol. The scalability and high availability design issues are discussed. Since HA and performance scalability requirements are in conflict, scenarios for using clustered RabbitMQ nodes and mirrored queues are presented. The results of performance measurements are reported. I.

We present an optimization method for automatic selection of downlink transmit power of LTE eNodeB based on the estimated throughput of the network. The procedures provide self optimized network functions to minimize the inter-cell interferences and maximizing the radio resource utilization. We propose a method based on the expected link throughput based on uniform client spatial distribution and compare our approach with solution based on SINR. We show simulation results that prove that the proposed method gives higher average link rate per client and higher total network throughput than optimization methods shown in the literature.

The article discusses topological properties of multihop wireless networks which are deployed as part of the advanced metering infrastructure (AMI). It proposes a network topology generator based on a real map. The generator imports topologies of buildings from a specific world area indicated by geographical coordinates. The described generator is used for analysis of statistical properties of AMI networks' topologies in areas with different urbanization levels. The article presents examples of different areas along with their properties. The resulting topologies are compared to uniform random topologies.

Wireless mesh networks (WMNs) are comprised of nodes with multiple radio interfaces and provide broadband residential internet access or connectivity to temporal events. Our goal is to simplify the network deployment of such a mesh network, and towards that we are presenting procedures for automatic configuration and optimisation of the network. We first present an architecture framework that supports the integration of key mechanisms to ensure the optimisation of the performance of a wireless mesh network. Secondly, we present three key mechanisms, namely auto-configuration, channel assignment and quality of service (QoS) enforcement based on QoS routing. We provide a method for automatic mesh start-up, joining a node into an existing mesh network and automatic repair of temporary connectivity outage, targeting at simplifying the node configuration as much as possible. The second mechanism supports an efficient algorithm for joint channel selection and topology control, supporting different target objective expressed as utility functions. The third mechanism supports QoS, by allowing routing and admission control decisions, in order to ensure that all flows are handled with the demanded QoS. Finally, we give some simulation results that show the increased performance of our framework.

We propose procedures for autoconfiguration of multihop wireless ad-hoc networks based on DHCP protocol. The proposed mechanism provides automatic address and radio parameters set-up for nodes with multiple radio interfaces, allowing to fully automatically form and to start a wireless mesh network and to route packets. The autoconfiguration schema was implemented and tested on OpenWRT platform. The demonstration shows how multiple Mikrotik routerboard with three 802.11g interfaces can fully automatically create a multihop wireless network, assign IP addresses, radio channels. It will also include the automatic visualization of network topology by network management software.

We propose procedures for autoconfiguration of wireless mesh networks based on DHCP protocol. The proposed mechanism provides automatic address and radio parameters set-up for nodes with multiple radio interfaces, allowing us to fully automatically form and to start a wireless mesh network, and to route packets. It supports mesh networks comprised of multiple IP subnets build with multiple networking technologies. Some performance issues of the autoconfiguration procedure are discussed. The autoconfiguration scheme was implemented and tested on OpenWRT platform.