The LoRa communication standard allows to transmit data in radio networks over distances of few kilometers. Although the LoRa WAN protocol assumes the use of ALOHA channel access, due to the use of multiple channels and multiple spreading factors in LoRa networks the evaluation of collision probability is challenging. We present the simulation model allowing to estimate the per node probability of successful packet delivery ratio. The model is evaluated for different network topologies, based on random distribution of nodes or based on the real location of meters in sample smart city deployments. The results show that the packet delivery ratio varies significantly depending on the location of the end nodes in the network. Due to the higher spreading factor used, the collision probability is very low for nodes located near to the access point. The use of proposed simulation model allows to identify the nodes which experience high collision probability and react e.g. by reconfiguration.
a978-3-030-21952-9 a978-3-030-21951-2 00307nas a2200121 4500000000100000000000100001008004100002100002200043700001900065700001800084700001700102245006600119 2019 d 1 aKrzysztof Grochla 1 aRafał Marjasz 1 aKonrad Połys 1 aAnna Strzoda 00 aKolizje pakietów w sieciach LoRa w zastosowaniach smart city 01790nas a2200169 4500000000100000000000100001008004100002260001200043100002100055700002200076700001900098700002200117245011500139856004500254490000700299520131400306 2021 d c01/2021 1 aMichał Gorawski 1 aKrzysztof Grochla 1 aRafał Marjasz 1 aArtur Frankiewicz 00 aEnergy Minimization Algorithm for Estimation of Clock Skew and Reception Window Selection in Wireless Networks uhttps://www.mdpi.com/1424-8220/21/5/1768 0 v21 3 aThe synchronization of time between devices is one of the more important and challenging problems in wireless networks. We discuss the problem of maximization of the probability of receiving a message from a device using a limited listening time window to minimize energy utilization. We propose a solution to two important problems in wireless networks of battery-powered devices: a method of establishing a connection with a device that has been disconnected from the system for a long time and developed unknown skew and also two approaches to follow-up clock synchronization using the confidence interval method. We start with the analysis of measurements of clock skew. The algorithms are evaluated using extensive simulations and we discuss the selection of parameters balancing between minimizing the energy utilization and maximizing the probability of reception of the message. We show that the selection of a time window of growing size requires less energy to receive a packet than using the same size of time window repeated multiple times. The shifting of reception windows can further decrease the energy cost if lower packet reception probability is acceptable. We also propose and evaluate an algorithm scaling the reception window size to the interval between the packet transmission
01795nas a2200181 4500000000100000000000100001008004100002260002700043100001900070700001700089700001800106700002200124245006500146856011600211300001200327520125200339022002201591 2021 d c10/2021 bEurosis aRome 1 aRafał Marjasz 1 aAnna Strzoda 1 aKonrad Połys 1 aKrzysztof Grochla 00 aMitigation of LoRa interferences via dynamic channel weights uhttps://www.researchgate.net/publication/356041519_Mitigation_of_LORA_Interferences_via_Dynamic_Channel_Weights a150-154 3 aThe Low Power Wide Area Networks, such as LoRa (Long Range), allow communication over a large area with limited bandwidth and small data rates, using an unlicensed band. LoRa uses multiple channels, but the number of channels available is relatively narrow - e.g. 8 in most countries in Europe. The transmission is subject to interferences due to many other devices transmitting within the same frequencies. In this paper, we evaluate how strong the interferences' influence is by analysing the packet delivery rate in a large scale LoRa network. The measurements have been made over more than seven months and show noticeable variability in packet delivery rate per channel both in space and in time. We propose to estimate the scale of interferences through continuous observation of the number of delivered packets for every channel per LoRa gateway or per selected area. We also discuss how this estimation may mitigate the interferences by assigning the dynamic weights to the LoRa channel selection procedure. We created an algorithm that periodically updates the weights, and a simulation model to evaluate the algorithm. A significant improvement in the efficiency of package delivery is visible, from 12% to 49% less packet loss.
a978-9-492-85918-1 00421nas a2200145 4500000000100000000000100001008004100002260001200043100001900055700001900074245012300093856003800216490000700254022001400261 2021 d c10/2021 1 aWojciech Kempa 1 aRafał Marjasz 00 aStudy on Transient Queue-Size Distribution in the Finite-Buffer Model with Batch Arrivals and Multiple Vacation Policy uhttps://doi.org/10.3390/e23111410 0 v23 a1099-4300 00485nas a2200145 4500000000100000000000100001008004100002260001200043100002000055700002000075700001900095245017000114856004900284490000600333 2021 d c10/2021 1 aWojciech. Kempa 1 aKamil Książek 1 aRafał Marjasz 00 aOn Time-Dependent Queue-Size Distribution in a Model With Finite Buffer Capacity and Deterministic Multiple Vacations With Applications to LTE DRX Mechanism Modeling uhttps://ieeexplore.ieee.org/document/9591613 0 v9 01878nas a2200169 4500000000100000000000100001008004100002260005900043100001900102700001800121700001700139700002200156245004500178856006700223520140000290020001801690 2021 d bAssociation for Computing Machinery aNew York, NY, USA 1 aRafał Marjasz 1 aKonrad Połys 1 aAnna Strzoda 1 aKrzysztof Grochla 00 aImproving Delivery Ratio in LoRa Network uhttps://dl.acm.org/doi/10.1145/3479241.3486698?cid=99659913397 3 aThe LoRa (Long Range) radio communication provides large coverage areas, low bandwidth, small data rates, and transmitting limited data sizes, with very low energy usage. Multiple transmission channels are used, but the number of channels available is fairly limited - e.g. 8 in most countries in Europe. The amount of interferences may be estimated by the continuous observation of the number of delivered packets and the received signal strength. We propose to aggregate and analyse those metrics per channel and geographical area. When the proportion of received packets per some of the areas decreases, it is subjected to heavier interferences than other parts of the network and should be used less intensively. Thus we propose to allocate the weights for each channel per geographic area and/or device, defining the probability of the channel usage. Furthermore, we created an algorithm that periodically updates the weights and a simulation model using OMNeT++, FloRa, taking into account possible packets collisions. The algorithm has been validated for both random and realistic network topologies. The simulation evaluations show a significant improvement in the package delivery efficiency, by almost 50% in scenarios with very high interference level simulated and by more than 13% in scenarios fed with real-life measurements of packet delivery probability changes in time.
a9781450390798 01607nas a2200193 4500000000100000000000100001008004100002260001200043100002200055700001700077700001900094700002300113700002000136700002700156245006100183856005900244490000700303520110300310 2022 d c11/2022 1 aKrzysztof Grochla 1 aAnna Strzoda 1 aRafał Marjasz 1 aPrzemysław Głomb 1 aKamil Książek 1 aZbigniew Łaskarzewski 00 aEnergy-Aware Algorithm for Assignment of Relays in LPWAN uhttps://dl.acm.org/doi/10.1145/3544561?cid=99659913397 0 v18 3 aThe 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 communication technology has been developed for data transmission, but recent research papers showed that it could also be used to estimate the transmitting devices' location. The location can be found with reasonable accuracy, with median error as low as tens of meters; however, in many cases, it is evaluated in very optimistic transmission conditions, e.g. using line-of-sight communication and on a small data set. We estimate how LoRa localization performs in a realistic scenario, using an extensive data set of a telemetric network of a few thousand devices to calculate the location using the trilateration and estimate the error of the calculation. Within the analysed dataset the true-range multilateration provides highly inaccurate location estimation, with a median error of 588.64 m and an average error of 808.57 m. We argue that the LoRa localization in real-life conditions is ineffective, as the estimation of the distance between the node and the gateway changes heavily depending on the location of the node and radio channel attenuation.
a9781450394826 01594nas a2200145 4500000000100000000000100001008004100002260005400043100001700097700001900114700002200133245006800155856004700223520117800270 2022 d c12/2022 bInfocommunications Journal aNice, France 1 aAnna Strzoda 1 aRafał Marjasz 1 aKrzysztof Grochla 00 aLoRa Positioning in Verification of Location Data's Credibility uhttps://www.infocommunications.hu/2022_4_8 3 aThe LoRa is a novel radio communication technology
providing low power and a high range of data transmission.
The LoRa transmission may be used for a low-cost localization
to estimate the network nodes’ location. Some recent research
showed that the location could be found with reasonable accuracy,
with median error as low as tens of meters. Still, such results are
achieved in a controlled environment with low interferences. We
first evaluate the LoRa localization using an extensive data set
of a telemetric network of a few thousand devices. We show that
although the direct positioning based on trilateration provides
limited accuracy, the measurement of LoRa transmission may
be successfully used to evaluate the credibility of location information.
The information about which gateways received the data
and the RSSI measurements allow us to verify if the potential
coordinates of a location are accurate. We propose a metric for
location verification and estimate its credibility on a sample of
measurements from the LoRa telemetry network.
Detecting water leaks in distribution networks is crucial for conserving resources and preventing infrastructure damage. However, one of the most basic and significant challenges before employing any leak detection method is collecting data from the water distribution network. The sensors used for data collection are usually battery-powered; thus, the energy consumption of these devices is an essential factor. In this paper, we analyze the battery consumption of real devices placed in an operational water distribution network, and based on the obtained data, we perform a series of complex simulations to validate the preliminary assumptions we plan to use in further research of leak detection methods.
02017nas a2200157 4500000000100000000000100001008004100002260001200043100001900055700002200074700001800096245013600114856005500250490000700305520154700312 2024 d c06/2024 1 aRafał Marjasz 1 aKrzysztof Grochla 1 aKonrad Połys 00 aA Comprehensive Algorithm for Vertical Positioning in Multi-Building Environments as an Advancement in Indoor Floor-Level Detection uhttps://www.nature.com/articles/s41598-024-64824-9 0 v14 3 aThe proliferation of smartphones has catalyzed diverse services, mainly focusing on indoor localization to determine users’ and devices’ positions within buildings. Despite decades of exploration, the seamless integration of wireless technologies in tracking devices and users has become pivotal in various sectors, including health, industry, disaster management, building operations, and surveillance. Extensive research in laboratory and industrial settings, particularly in wireless sensor networks and robotics, has informed indoor localization techniques. This paper, referencing surveys and original literature reviews, proposes an innovative indoor location system amalgamating GPS and barometer readings. GPS identifies entry through doors, while barometer readings facilitate accurate floor-level tracking. The integration promises continuous real-time location updates, enhancing security, navigation, and emergency response. Notably, the algorithm is infrastructure-independent, relying on the smartphone’s barometer, and versatile, detecting elevator travel when Wi-Fi AP or LTE signals are available. Results indicate high accuracy, with building entry exceeding 93%, elevator recognition achieving 75% sensitivity and 97% specificity, and floor change detection surpassing 95% sensitivity and nearly 98% specificity (which translates to nearly 97% accuracy). This comprehensive solution, emphasizing the critical role of precise vertical positioning, signifies an advancement in tracking within urban structures.
01016nas a2200145 4500000000100000000000100001008004100002260004200043100002100085700001900106700002200125245012700147520057400274020002200848 2024 d c06/2024 bEUROSIS-ETI aValencia, Spain 1 aMichał Gorawski 1 aRafał Marjasz 1 aKrzysztof Grochla 00 aPerformance evaluation of the secure multi-tenancy system for smart city IoT environment using open LDAP and Apache Kafka. 3 aSupporting multiple users and operators in a single IoT system is vital for large-scale commercial deployments. This involves servicing numerous network operators with one IT system and set of devices, ensuring each operator can manage, reconfigure, and change device settings securely. This paper evaluates a multi-tenancy solution in our test system (TS), utilizing Apache Kafka as a message broker and OpenLDAP as an authorizer. It describes the system design, methods to ensure data separation, security and results of performance evaluation in simulation.
a978-9-492859-30-3 02487nas a2200157 4500000000100000000000100001008004100002260001200043100001900055700001900074700002200093245016400115856016500279490000700444520187800451 2025 d c03/2025 1 aRafał Marjasz 1 aWojciech Kempa 1 aViacheslav Kovtun 00 aQuantification of system resilience through stress testing using a predictive analysis of departure dynamics in a M^X/G/1/N queue with multiple vacation policy uhttps://www.nature.com/articles/s41598-025-95478-w?utm_source=rct_congratemailt&utm_medium=email&utm_campaign=oa_20250326&utm_content=10.1038/s41598-025-95478-w 0 v15 3 aThe study investigates the departure counting process in a finite-buffer queueing system with batch arrivals and multiple vacation policy, focusing on quantifying system resilience through stress testing and predictive analysis. A representation for the mixed double transform of the number of departures up to a fixed time moment is obtained in explicit form by applying an analytic approach based on integral equations and linear algebra. We perform a comparative analysis of numerical calculations and simulations made in OMNeT++ Discrete Event Simulator. The attached numerical study aims to understand how the queueing system copes under challenging conditions, examining the impact of various system parameters on the behaviour of the mean number of packets processed within a fixed time frame. Utilizing numerical experiments, the study analyzes the influence of vacation duration, initial buffer state, arrival intensity, and processing rate on the departure process. This enables the understanding of system recovery dynamics, particularly in how critical infrastructures can be optimized for resilience against disruptions. Results reveal significant dependencies between these parameters and the transient behaviour of the queueing system. Notably, the service speed parameter demonstrates the most substantial influence on the mean number of processed packets, followed by the arrival rate. Conversely, variations in vacation duration and initial packet count exhibit comparatively minor effects on system behaviour. Overall, the findings provide valuable insights into the dynamics of departure processes in finite-buffer queue systems with batch arrivals and multiple vacation policies, offering implications for system optimization, performance enhancement strategies, and resilience assessment in the face of potential system failures or disasters.