1,721,227 research outputs found
Multi-AP coordination in Wi-Fi 7 exploiting time resources sharing
No full textThe multi-AP coordination is a key feature of Wi-Fi 7 (EHT) and is a promising approach to improving the utilization of limited radio resources. However, the APs coordination requires the exchange of information among the APs in the coordination set in order to make the optimal sharing decision with regard to specific performance parameters. In this work, we present the control frames defined for this purpose and the transmission procedures defined in EHT for the multi-AP coordination. We implemented the new frames and EHT procedures in ns-3. Furthermore, we designed and implemented a scheduler with the aim to improving the performance of EHT network in non-saturated conditions by sharing the time resources, i.e., C-TDMA. Then, we assessed the performance of the proposed scheduler in ns-3. Multi-AP coordination through C-TDMA allows for reduction of the network latency of one order of magnitude while keeping the network throughput stable
A Thorough Study of LoRaWAN Performance under Different Parameter Settings
No full textLoRaWAN is an emerging low-power wide-area network (LPWAN) technology, which is gaining momentum thanks to its flexibility and ease of deployment. Conversely to other LPWAN solutions, LoRaWAN indeed permits the configuration of several network parameters that affect different network performance indexes, such as energy efficiency, fairness, and capacity, in principle making it possible to adapt the network behavior to the specific requirements of the application scenario. Unfortunately, the complex and sometimes elusive interactions among the different network components make it rather difficult to predict the actual effect of a certain parameters setting, so that flexibility can turn into a stumbling block if not deeply understood. In this article, we shed light on such complex interactions for a single-gateway (GW) system by analyzing the effect of some built-in features and configurations, including the GW's limitations in terms of duty cycle and the number of parallel reception paths, the number of allowed retransmissions for confirmed traffic, and the preconfigured data rate used in downlink transmissions. The simulation-based analysis reveals various tradeoffs and highlights some inefficiencies in the design of the LoRaWAN standard. Furthermore, we show how significant performance gains can be obtained by wisely setting the system parameters, possibly in combination with some novel network management policies (e.g., enabling selective prioritization of downlink transmissions at the GW)
Correction of non-common path aberrations in pyramid wavefront sensors to recover the optimal magnitude gain using a deformable lens
No full textAdaptive optics (AO) correction based on pyramid wavefront sensors (P-WFSs) has been successfully implemented in several instruments for astronomical observation due to the P-WFS advantages in terms of sensitivity with respect to other WFSs, such as the Shack-Hartmann. The correction of non-common path aberrations (NCPAs) between the sensing and the scientific arm, commonly performed introducing offsets to the Zernike coefficients of the measured wavefront in the AO closed loop, reduces the sensitivity of P-WFSs causing a loss in sky coverage and scientific throughput. We propose a technique to exploit the full capabilities of P-WFSs compensating the NCPAs up to the fourth order on the WFS channel by means of a multi-actuator adaptive lens (MAL). We show the preliminary results obtained in a dedicated laboratory test bench
Performance Evaluation of 802.11ax OFDMA through Theoretical Analysis and Simulations
No full textWith the introduction of Orthogonal Frequency Division Multiple Access (OFDMA) in 802.11ax, the role of the Access Point (AP) in Wi-Fi networks changes significantly, thanks to the opportunity of implementing more complex scheduling logic to handle Downlink (DL) traffic flows and simultaneously act as coordinator of Multi User (MU) Uplink (UL) transmissions. In this context, it becomes necessary to develop reliable network analysis and simulation tools that allow for an in-depth investigation of the trade-offs involved in the usage of OFDMA, especially considering that the standard leaves much of the actual scheduling algorithmic details to vendor-specific implementation. In this work we present a series of results highlighting how several network settings have an impact on throughput and Head-of-Line Delay, in a network that employs multiple 802.11ax features such as OFDMA and the MU Enhanced Distributed Channel Access (EDCA) Parameter Set, while also containing legacy devices. The results are obtained via both the newly re-designed ns-3 wifi module and an original analytical framework, based on the well-established Bianchi 802.11 model
Validation of the ns-3 802.11ax OFDMA implementation
No full textThe introduction of Orthogonal Frequency Division Multiple Access (OFDMA) in 802.11ax signifies a change in role for the Access Point (AP) in WiFi networks, with the opportunity to implement more complex scheduling logic to handle Downlink (DL) traffic flows and simultaneously act as coordinator of Multi User (MU) Uplink (UL) transmissions. In this context it becomes necessary to develop reliable network analysis and simulation tools that allow for an in-depth analysis of the trade-offs involved in the usage of OFDMA, especially considering that the standard leaves much of the actual scheduling algorithmic details to vendor-specific implementation. In this work we validate the recent OFDMA implementation in ns-3's wifi module, within the context of a re-design effort to improve modularity and support for future WiFi amendments. ns-3 based OFDMA performance evaluation via simulation is shown to match the predictions of an analytical approach in some simplified scenarios
A Configurable Mathematical Model for Single-Gateway LoRaWAN Performance Analysis
Full text linkLoRaWAN is a Low Power Wide Area Network technology featuring long transmission ranges and a simple MAC layer, which can support sensor data collection, control applications and reliable services thanks to the flexibility offered by a large set of configurable system parameters. However, the impact of such parameters settings on the system’s performance is often difficult to predict, depending on several factors. To ease this task, in this paper, we provide a mathematical model to estimate the performance of a LoRaWAN gateway serving a set of devices that may or may not employ confirmed traffic. The model features a set of parameters that can be adjusted to investigate different gateway and end-device configurations, making it possible to carry out a systematic analysis of various trade-offs. The results given by the proposed model are validated through realistic ns-3 simulations that confirm the ability of the model to predict the system performance with high accuracy, and assess the impact of the assumptions made in the model for tractability
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Performance Analysis of LoRaWAN in Industrial Scenarios
No full textIn this work, we evaluate the performance of a LoRaWAN network in industrial scenarios where different Industrial Internet of Things (IIoT) end nodes communicate to a central controller in order to provide monitoring and sensing information to optimize the efficiency of industrial processes and reduce costs. In particular, we consider confirmed and unconfirmed traffic, multi-gateway deployments, the usage of different classes of devices, and a non-standard channel plan. Furthermore, we analyze the higher-layer impact of different models of LoRa PHY layer with industrial channel models. We show that, with proper configuration, LoRaWAN is able to serve IIoT sensing applications with a packet success rate over 90%, providing at the same time limited communication delays
Collaboration of LoRaWAN and Underwater Acoustic Communications in Sensor Data Collection Applications
No full textThe Robotic Vessels as-a-Service (Robo VaaS) project aims to provide innovative services in a harbor scenario, exploiting new technologies to enhance different aspects of harbor activities. In this paper we analyze the data collection service from underwater sensor nodes. Specifically, we assess the End-To-End (E2E) communication, from sensor nodes deployed in the harbor to the gateway placed on the shore. The sensor data is collected by an autonomous underwater vehicle (AUV), and then forwarded to one or more surface buoys. Finally, the buoys convey the received data to the shore. Communication from the underwater sensors to the AUV and from the AUV to the surface buoys is performed through acoustic links, while the communication from the surface buoys to the shore gateway is performed via LoRaWAN. In this scenario we evaluate the performance of the E2E communication, by simulating both the underwater and the above water network
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