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Abstract

LoRaWAN is an upcoming Low Power Wide Area Network (LPWAN) technology for Internet of Things implementations in various application domains. Despite its various advantages, LoRaWAN employs an Aloha-based MAC, which in terms of performance can not guarantee high packet delivery ratio and low latency. To overcome this issue, we propose a time-slotted scheme, called TS-VP-LoRa, which supports multiple transmission times and packet sizes at the same time. In TS-VP-LoRa, scheduling is coordinated by the LoRa gateway, broadcasting beacon frames periodically for the synchronization of LoRa end-devices. A channel hopping mechanism is also proposed in order to minimize the occurrence of collisions and to evenly split the transmission load among all channels. TS-VP-LoRa is evaluated and compared to three other MAC-layer schemes in single gateway simulation scenarios with up to 500 nodes. The proposed scheme has proven to achieve low latency with high packet delivery ratios, significantly minimize collisions and maintain a relatively low energy consumption despite the scaling of the LoRa network.

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... Essa tecnologia é uma tecnologia de Low Power Wide Area Network (LPWAN), baseada na modulação Chirp Spread Spectrum, que podem ser utilizadas para realizar a medição inteligente em cidades, pois, nessa aplicação, os nós podem estar há muitos metros de distância de um determinado gateway, tendo obstáculos. Nesses casos, essa tecnologia pode alcançar longas distâncias, tendo a capacidade de negociar uma sensibilidade do sinal (Triantafyllou;Zorbas;Sarigiannidis, 2022). ...
... Essa tecnologia é uma tecnologia de Low Power Wide Area Network (LPWAN), baseada na modulação Chirp Spread Spectrum, que podem ser utilizadas para realizar a medição inteligente em cidades, pois, nessa aplicação, os nós podem estar há muitos metros de distância de um determinado gateway, tendo obstáculos. Nesses casos, essa tecnologia pode alcançar longas distâncias, tendo a capacidade de negociar uma sensibilidade do sinal (Triantafyllou;Zorbas;Sarigiannidis, 2022). ...
... Essa tecnologia é uma tecnologia de Low Power Wide Area Network (LPWAN), baseada na modulação Chirp Spread Spectrum, que podem ser utilizadas para realizar a medição inteligente em cidades, pois, nessa aplicação, os nós podem estar há muitos metros de distância de um determinado gateway, tendo obstáculos. Nesses casos, essa tecnologia pode alcançar longas distâncias, tendo a capacidade de negociar uma sensibilidade do sinal (Triantafyllou;Zorbas;Sarigiannidis, 2022). ...
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... Nevertheless, some issues must be considered such as extra energy cost of synchronization and the long delay between transmissions in case of long super-frame lengths. [31] proposed a time-slotted scheme, TS-VP-LoRa, considering variable size payload. TS-VP-LoRa arranges channels in 3 dimensional superframes (time, SF, payload). ...
... Compared to ALOHA-LoRaWAN, ETS-LoRaWAN performs better despite the implementation of VHMM-based E-ADR for both schemes. Indeed, ETS-LoRaWAN avoids collision and reduces transmission delay by allocating the earliest available time slot in any channel.Besides the good results of ETS-LoRaWAN, it is interesting to compare it in a future work to time slotted existing works such as TS-LoRa [21] and TS-PV-LoRa [31]. Moreover, the experiments carried out on the various LoRa nodes (Lopy, STM, Semtech) have shown certain loss. ...
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... In addition, to reduce collisions in LPWAN networks, a group of researchers proposed a scheme that supported different transmission times and packet sizes. They also implemented a channel hopping mechanism to decrease the collisions by distributing the packets across the channels [16]. ...
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The minimal infrastructure requirements of LoRa make it suitable for deployments in remote and disaster-stricken areas. Concomitantly, the modern era is witnessing the proliferation of web applications in all aspects of human life, including IoT and other network services. Contemporary IoT and network solutions heavily rely on web applications to render services. However, despite the recent research and development pivoted around LoRa, there is still a lack of studies focusing on web application access over LoRa networks. Specifically, technical challenges like payload size limitation, low data rate, and contentions in multi-user setups limit the applicability of LoRa for web applications. Hence, we propose LoRaWeb, which enables web access over LoRa networks. The LoRaWeb hardware tethers a WiFi hotspot to which the client devices connect and access the web pages using a web browser. LoRa backbone of the network handles the web page transmission from the requester and receiver devices. LoRaWeb implements a synchronization procedure to address the aforementioned challenges for effective message exchange between requesters and responders. The system implements a caching mechanism to reduce latency and contention. Additionally, it implements a message-slicing mechanism in the application layer to overcome the hardware limitations on the message length. The actual hardware-based implementation results indicate seamless deployment, and the results indicate an average access time of ~0.95S0.95 S for a 1.5KB1.5 KB and ~6S6 S for a 10KB10 KB size web page.
... The EDs transfer through gateway by accessible sub frequency and any of the SFs. The collisions arise when both devices having same channel and SF eventually [10]. Since the network consists of huge count of EDs, the increase of collision rate leads to affects the efficacy of the system. ...
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... Based on the p-ALOHA protocol, various ALOHA variants are generated to further improve the channel utilization as well as the scalability of the LoRa network, e.g. [7,8]. 2) Through Listen before talk (LBT), Semtech has designed Channel activity detection (CAD) mechanism specifically for LoRa end devices, through which terminals and gateways in a LoRa network can communicate according to Carrier Sense Multiple Access (CSMA) protocol [9]. ...
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New Internet of Things (IoT) technologies such as Long Range (LoRa) are emerging which enable power efficient wireless communication over very long distances. Devices typically communicate directly to a sink node which removes the need of constructing and maintaining a complex multi-hop network. Given the fact that a wide area is covered and that all devices communicate directly to a few sink nodes a large number of nodes have to share the communication medium. LoRa provides for this reason a range of communication options (centre frequency, spreading factor , bandwidth, coding rates) from which a transmitter can choose. Many combination settings are orthogonal and provide simultaneous collision free communications. Nevertheless , there is a limit regarding the number of transmitters a LoRa system can support. In this paper we investigate the capacity limits of LoRa networks. Using experiments we develop models describing LoRa communication behaviour. We use these models to parameterise a LoRa simulation to study scalability. Our experiments show that a typical smart city deployment can support 120 nodes per 3.8 ha, which is not sufficient for future IoT deployments. LoRa networks can scale quite well, however, if they use dynamic communication parameter selection and/or multiple sinks.
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While the Internet of Things continues to grow, the LoRaWAN standard is generating special interest due to its open-source nature, ultra-low power consumption and long-range connectivity. Recent works have explored the challenges of implementing LoRaWAN, with scalability being considered one of the major bottlenecks imposed by its Aloha-based MAC layer. Despite much on-going research on LoRaWAN scheduling aimed at alleviating this concern, experimental approaches are rarely found in the literature. In this work, we describe the steps taken and the technical issues overcome to move from a low-overhead synchronization and scheduling concept to its real-world implementation on top of LoRaWAN Class A. Accordingly, an end-to-end architecture was designed and deployed on top of STM32L0 MCUs, which communicate with a central entity responsible for providing synchronization metrics and allocating transmission slots on demand. The clock drift of devices was measured in a temperature-controlled chamber, which served as a basis to define slot lengths in the network. As a result, an operational end-to-end system was implemented and evaluated for different setup scenarios, with 10-millisecond accuracy being achieved. Our experimental results show significant improvements in packet delivery ratios with respect to Aloha-based setups, especially under high network loads (up to 29% for SF12), thereby demonstrating the feasibility of the presented approach.
Article
The employment of Low-Power Wide Area Networks (LPWANs) has proven quite beneficial to the advancement of the Internet of Things (IoT) paradigm. The utilization of low power but long range communication links of the LoRaWAN technology promises low energy consumption, while ensuring sufficient throughput. However, due to LoRa’s original scheduling process there is a high chance of packet collisions, compromising the technology’s reliability. In this paper, we propose a new Medium Access Control (MAC) protocol, entitled the FCA-LoRa leveraging fairness and improving collision avoidance in LoRa wide-area networks. The novel scheduling process that is introduced is based on the broadcasting of beacon frames by the network’s gateway in order to synchronize communication with end devices. Our results demonstrate the benefits of FCA-LoRa over an enhanced version of the legacy LoRaWAN employing the ALOHA protocol and an advanced adaptive rate mechanism, in terms of throughput and collision avoidance. Indicatively, in a single gateway scenario with 600 nodes, FCA-LoRa can increase throughput by nearly 50% while in a multiple gateway scenario, throughput reaches an increase of 49% for 500 nodes.
Article
Automation and data capture in manufacturing, known as Industry 4.0, requires the deployment of a large number of wireless sensor devices in industrial environments. These devices have to be connected via a reliable, low-latency, low-power and low operating-cost network. Although LoRaWAN provides a low-power and reasonable-cost network technology, its current ALOHA-based MAC protocol limits its scalability and reliability. A common practise in wireless networks is to solve this issue and improve scalability through the use of time-slotted communications. However, any time-slotted approach comes with overheads to compute and disseminate the transmission schedule in addition to ensuring global time synchronisation. Affording these overheads is not straight forward with LoRaWAN restrictions on radio duty-cycle and downlink availability. Therefore, in this work, we propose TS-LoRa, an approach that tackles these overheads by allowing devices to self-organise and determine their slot positions in a frame autonomously. In addition to that, only one dedicated slot in each frame is used to ensure global synchronisation and handle acknowledgements. Our experimental results with 25 nodes show that TS-LoRa can achieve more than 99% packet delivery ratio even for the most distant nodes. Moreover, our simulations with a higher number of nodes revealed that TS-LoRa exhibits a lower energy consumption than the confirmable version of LoRaWAN while not compromising the packet delivery ratio.
Article
LoRaWAN promises to provide wide-area network access to low-cost devices that can operate for up to ten years on a single 1000-mAh battery. This makes LoRaWAN particularly suited for the data collection applications (e.g., monitoring applications), where device lifetime is a key performance metric. However, when supporting a large number of devices, LoRaWAN suffers from a scalability issue due to the high collision probability of its Aloha-based MAC layer. The performance worsens further when using acknowledged transmissions due to the duty-cycle restriction at the gateway. For this, we propose FREE , a fine-grained scheduling scheme for reliable and energy-efficient data collection in LoRaWAN. FREE takes advantage of applications that do not have hard delay requirements on data delivery by supporting the synchronized bulk data transmission. This means data are buffered for transmission in scheduled time slots instead of transmitted straight away. FREE allocates spreading factors, transmission powers, frequency channels, time slots, and schedules slots in frames for LoRaWAN end-devices. As a result, FREE overcomes the scalability problem of LoRaWAN by eliminating collisions and grouping acknowledgments. We evaluate the performance of FREE versus different legacy LoRaWAN configurations. The numerical results show that FREE scales well and achieves almost 100% data delivery and the device lifetime is estimated over ten years independent of traffic type and network size. In comparison to poor scalability, low data delivery and device lifetime of fewer than two years for acknowledged data traffic in the standard LoRaWAN configurations.
Article
Wireless networks have been widely deployed for many Internet-of-Things (IoT) applications, like smart cities and precision agriculture. Low Power Wide Area Networking (LPWAN) is an emerging IoT networking paradigm to meet three key requirements of IoT applications, i.e., low cost, large scale deployment and high energy efficiency. Among all available LPWAN technologies, LoRa networking has attracted much attention from both academia and industry, since it specifies an open standard and allows us to build autonomous LPWAN networks without any third-party infrastructure. Many LoRa networks have been developed recently, e.g., managing solar plants in Carson City, Nevada, USA and power monitoring in Lyon and Grenoble, France. However, there are still many research challenges to develop practical LoRa networks, e.g., link coordination, resource allocation, reliable transmissions and security. This article provides a comprehensive survey on LoRa networks, including the technical challenges of deploying LoRa networks and recent solutions. Based on our detailed analysis of current solutions, some open issues of LoRa networking are discussed. The goal of this survey paper is to inspire more works on improving the performance of LoRa networks and enabling more practical deployments.
Conference Paper
LoRa-based transmissions suffer from extensive collisions even for low node numbers due to unregulated access to the medium. In order to tackle this problem, we propose a collision-free time-slotted scheduling approach where each node autonomously decides when to transmit a packet based on its unique identifier which is converted to a slot number using a modulo operation. We report through simulations and real experiments that this approach can provide very high reliability when the nodes are synchronized. Moreover, it does not require any additional communication overhead apart from a broadcast packet emitted by the gateway. Our comparison with the native LoRa, as well as to a slotted-LoRa version, shows significant performance gains in terms of packet delivery ratio, especially in the case of low node populations.
Conference Paper
LoRa-based transmissions suffer from extensive collisions due to the ALOHA-style transmission policy. As a consequence , delivering a high number of packets in a short amount of time becomes an unfeasible task. To tackle this problem we propose to schedule node transmissions in slots of different size depending on the Spreading Factor (SF). Transmissions with the same SF are scheduled in different slots to avoid collisions while those with different SF can occur in parallel. In this paper, we propose two algorithms executed in an offline manner to allocate SFs to nodes aimed at minimising the total data collection time while respecting the radio duty cycle restriction. The examined simulation scenarios and our comparison with LoRaWAN show an up to 101% improvement in terms of data collection time and an up to 250% improvement in terms of energy consumption combined with a nearly 100% packet delivery ratio.
Conference Paper
LoRa, an abbreviation of Long Range, is a Low-Power Wide Area Network (LPWAN) radio technology that has quickly gained popularity as a communications means for the Internet-of-Things (IoT). LoRa is typically used together with the MAC protocol LoRaWAN and operates in the license-free ISM-bands. As such, anyone is allowed to deploy their own LoRaWAN network, provided that they adhere to the LoRaWAN specification and ISM regulations. However, an uncoordinated deployment of LoRaWAN networks may cause neighboring networks to interfere and LoRaWAN frames to collide. In this paper, we present an in-depth investigation of LoRaWAN frame collisions -- and the capture effect in particular -- through various experiments. Contrary to previous research, we focus on correct reception of data at the application, instead of at the gateway, and we consider multi-gateway, multi-provider, and dense scenarios to obtain insight into collisions within actual networks.
Article
Providing low power and long range connectivity is the goal of most IoT networks, e.g., Long Range (LoRa), but keeping communication reliable is challenging. LoRa networks are vulnerable to the capture effect. Cell-edge nodes have a high chance of losing packets due to collisions, especially when high spreading factors are used that increase time on air. Moreover, LoRa networks face the problem of scalability when they connect thousands of nodes that access the shared channels randomly. In this work, we propose a new MAC layer – RS-LoRa – to improve reliability and scalability of LoRa Wide-Area Networks (LoRaWANs). The key innovation is a two-step lightweight scheduling: (1) a gateway schedules nodes in a coarse-grained manner through dynamically specifying the allowed transmission powers and spreading factors on each channel; (2) based on the coarse-grained scheduling information, a node determines its own transmission power, spreading factor, and when and on which channel to transmit. Through the proposed lightweight scheduling, nodes are divided into different groups, and within each group, nodes use similar transmission power to alleviate the capture effect. The nodes are also guided to select different spreading factors to increase the network reliability and scalability. We have implemented RS-LoRa in NS-3 and evaluated its performance through extensive simulations. Our results demonstrate the benefit of RS-LoRa over the legacy LoRaWAN, in terms of packet error ratio, throughput, and fairness. For instance, in a single-cell scenario with 1000 nodes, RS-LoRa can reduce the packet error ratio of the legacy LoRaWAN by nearly 20%.
Chapter
OMNeT++ (www.omnetpp.org) is an extensible, modular, component-based C++ simulation library and framework which also includes an integrated development and a graphical runtime environment. Domain-specific functionality (support for simulation of communication networks, queuing networks, performance evaluation, etc.) is provided by model frameworks, developed as independent projects. There are extensions for real-time simulation, network emulation, support for alternative programming languages (Java, C#), database integration, SystemC integration, HLA and several other functions.
Improving delay and capacity of TS-LoRa with flexible guard times
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