Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> IV. NEED FOR HORIZONTAL INTEGRATION AMONG LPWA TECHNOLOGIES <s> The emergence of low-cost connected devices is enabling a new wave of sensorization services. These services can be highly leveraged in industrial applications. However, the technologies employed so far for managing this kind of system do not fully cover the strict requirements of industrial networks, especially those regarding energy efficiency. In this article a novel paradigm, called Low-Power Wide Area Networking (LP-WAN), is explored. By means of a cellular-type architecture, LP-WAN–based solutions aim at fulfilling the reliability and efficiency challenges posed by long-term industrial networks. Thus, the most prominent LP-WAN solutions are reviewed, identifying and discussing the pros and cons of each of them. The focus is also on examining the current deployment state of these platforms in Spain. Although LP-WAN systems are at early stages of development, they represent a promising alternative for boosting future industrial IIoT (Industrial Internet of Things) networks and services. <s> BIB001 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> IV. NEED FOR HORIZONTAL INTEGRATION AMONG LPWA TECHNOLOGIES <s> Low power wide area (LPWA) networks are attracting a lot of attention primarily because of their ability to offer affordable connectivity to the low-power devices distributed over very large geographical areas. In realizing the vision of the Internet of Things, LPWA technologies complement and sometimes supersede the conventional cellular and short range wireless technologies in performance for various emerging smart city and machine-to-machine applications. This review paper presents the design goals and the techniques, which different LPWA technologies exploit to offer wide-area coverage to low-power devices at the expense of low data rates. We survey several emerging LPWA technologies and the standardization activities carried out by different standards development organizations (e.g., IEEE, IETF, 3GPP, ETSI) as well as the industrial consortia built around individual LPWA technologies (e.g., LoRa Alliance, Weightless-SIG, and Dash7 alliance). We further note that LPWA technologies adopt similar approaches, thus sharing similar limitations and challenges. This paper expands on these research challenges and identifies potential directions to address them. While the proprietary LPWA technologies are already hitting the market with large nationwide roll-outs, this paper encourages an active engagement of the research community in solving problems that will shape the connectivity of tens of billions of devices in the next decade. <s> BIB002 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> IV. NEED FOR HORIZONTAL INTEGRATION AMONG LPWA TECHNOLOGIES <s> A new breed of wireless technologies has emerged under the generic name of low-power, wide-area (LPWA), with a number of common characteristics that make these technologies uniquely suitable for Internet of Things (IoT) applications. These common characteristics include a power-optimized radio network, a simplified network topology, frame sizes in the order of tens of bytes transmitted a few times per day at ultralow speeds, and a mostly upstream transmission pattern that allows the devices to spend most of their time in low-energy deep-sleep mode. These characteristics enable a range of several kilometers and long battery lifetimes, possibly ten years of operation on a single coin-cell. It also enables simple and scalable deploymen <s> BIB003 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> IV. NEED FOR HORIZONTAL INTEGRATION AMONG LPWA TECHNOLOGIES <s> Low-power wide area networking technology offers long-range communication, which enables new types of services. Several solutions exist; LoRaWAN is arguably the most adopted. It promises ubiquitous connectivity in outdoor IoT applications, while keeping network structures and management simple. This technology has received a lot of attention in recent months from network operators and solution providers. However, the technology has limitations that need to be clearly understood to avoid inflated expectations and disillusionment. This article provides an impartial and fair overview of the capabilities and limitations of LoRaWAN. We discuss those in the context of use cases, and list open research and development questions. <s> BIB004 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> IV. NEED FOR HORIZONTAL INTEGRATION AMONG LPWA TECHNOLOGIES <s> Abstract By 2020, more than twenty five billion devices would be connected through wireless communications. In accordance with the rapid growth of the internet of things (IoT) market, low power wide area (LPWA) technologies have become popular. In various LPWA technologies, narrowband (NB)-IoT and long range (LoRa) are two leading technologies. In this paper, we provide a comprehensive survey on NB-IoT and LoRa as efficient solutions connecting the devices. It is shown that unlicensed LoRa has advantages in terms of battery lifetime, capacity, and cost. Meanwhile, licensed NB-IoT offers benefits in terms of QoS, latency, reliability, and range. <s> BIB005 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> IV. NEED FOR HORIZONTAL INTEGRATION AMONG LPWA TECHNOLOGIES <s> Low Power Wide Area Networks (LPWANs) are thought to provide low-cost coverage for massive numbers of devices. Due to the many business opportunities ahead, the market is currently highly fragmented with many competing waveforms. In order to establish a basis for the comparison of LPWAN waveforms, we present the first open-source, standards-compliant implementation of the IEEE 802.15.4 Low Energy Critical Infrastructure Monitoring (LECIM) Direct Sequence Spread Spectrum (DSSS) physical layer including the fragmentation sublayer in the GNU Radio framework. This Software Defined Radio-based testbed enabled us to conduct the first field trials evaluating the performance in the highly-congested 2.4 GHz band with different configurations at various receiver locations. Our results indicate that there is a considerable potential for LPWANs in the 2.4 GHz range, even in the presence of many uncontrolled Wi-Fi access points. <s> BIB006 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> IV. NEED FOR HORIZONTAL INTEGRATION AMONG LPWA TECHNOLOGIES <s> Motivated by the increasing variance of suggested Internet of Things (IoT) applications and the lack of suitability of current wireless technologies in scalable, long range deployments, a number of diverging Low Power Wide Area (LPWA) technologies have been developed. These technologies promise to enable a scalable high range network on cheap low power devices, facilitating the development of a ubiquitous IoT. This paper provides a definition of this new LPWA paradigm, presents a systematic approach to defined suitable use cases, and undertakes a detailed comparison of current LPWA standards, including the primary technologies, upcoming cellular options, and remaining proprietary solutions. <s> BIB007
There are a number of LPWA technologies, each with common and unique features. The reason for this diversity in features and operations is that most LPWA solutions have been designed by the industry to fulfill certain market demands and have not gone through the SDOs. Many efforts are now being undertaken by IEEE, 3GPP, IETF and ETSI to bring these technologies closer together. A proper understanding of and compatibility among these diverse technologies will be necessary to make interoperability possible. Whereas gateways, backend base stations, IoT middleware and virtualization have been proposed to facilitate interoperability between LPWA technologies BIB002 , we investigate the cause of this diversity and argue the need for interoperability between various technologies. In this section, issues related to the compatibility among LPWA technologies are discussed, and the need to address this diversity and achieve better integration is explained. Diversity mainly arises due to the ways in which these technologies address the MAC and physical layers, more specifically, the bands they operate in, the modulation and MAC mechanisms, the payload formats and sizes, the communication modes, and the techniques used for forward error correction (FEC) and security. LoRa and SigFox operate in unlicensed ISM radio bands, but each uses a different type of radio. SigFox's UNB uses a thin peak of the spectrum, whereas LoRa's CSS spans the entire available bandwidth BIB003 . By contrast, Telensa uses its own patented UNB radio technology operating in the license exempt spectrum. RPMA uses the global 2.4 GHz band, resulting in more interference and propagation loss at high frequencies. The robustness of physical layer enables this technology to operate in these challenging environments  . Most LPWA solutions operate in the ISM band and thus have an advantage over NB-IoT, which operates in licensed cellular bands, because they do not require the involvement of mobile operators BIB004 . This variety in radio technologies may be to the benefit of IoT applications in providing the service that fits best. RPMA is not suitable for applications powered by battery due to the high processing power consumption of its underlying topology. SigFox, on the other hand, is not suitable for devices that require regular transmission due to its traffic limits, as mentioned in Section II-B.2. Moreover, SigFox's on-air transmission makes it non-compliant with some countries' regulations. The US, for example, imposes a maximum of 0.4 s of on-air transmission, which is much less than SigFox's approximate on-air transmission time of 2 s BIB001 . In addition, the band used in the US is less robust against interference than the band used in Europe. SigFox and Telensa lack the guarantee of QoS and thus limit the options for services demanding this feature. On the other hand, LoRaWAN and SigFox require a subscription to use cloud services BIB005 , BIB007 . A possible issue that may arise from this diversity, particularly for solutions that are not standard-based, is complexity. Some of this complexity arises from the ways in which these technologies secure their communications and manage their services. An additional layer above the radio layer for the sake of convergence, similar to the IP layer of the Internet, has been proposed to mitigate this complexity. IPv6 and the constrained application protocol (CoAP)  are two potential protocols for providing connectivity among LPWA devices regardless of their underlying radio technologies BIB003 . This would allow Internet-based services to be provided to applications running on end devices. Each LPWA solution offers a variety of characteristics that may or may not exist in other solutions. For example, WiSUN  , a global industry alliance aimed at the standardization of wireless technologies for IoT applications already supports IPv6 through the IETF IPv6 stack for IPv6-based LoWPAN (6LoWPAN), but additional work will be required on security and identity management, as IoT devices are protected differently from computers. The IoT-based attack on KrebsOnSecurity.com could serve as evidence of this threat BIB003 . The PHY and MAC layers of RPMA are based on the IEEE 802.15.4k standard  . The standard targets long-range and low-energy critical infrastructure monitoring networks. The IEEE 802.15.4k standard has been amended to adopt DSSS modulation in the PHY and MAC layers BIB006 . It also provides a QoS guarantee by prioritizing traffic BIB002 . Both SigFox and Telensa use UNB modulation, and LoRa uses the orthogonal sequence spread spectrum (OSSS) modulation technique. The goal of ETSI's low throughput network (LTN) technology is to standardize bidirectional low-rate LPWA technologies. According to the LTN specifications  , either the UNB or OSSS modulation scheme can be deployed by LPWA solutions in sub-GHz ISM band. However, it is recommended to use binary phase shift keying (BPSK) on the UL and Gaussian frequency shift keying (GFSK) on the DL for UNB implementation and OSSS for bidirectional communications. The LTN approach has motivated a few LPWA providers, including SigFox, Telensa, and Semtech, to standardize their solutions while maintaining proprietary modulation schemes BIB002 . The data rate of LoRaWAN depends on the SF and bandwidth. To avoid collision, simultaneous transmissions must select different SFs and channels. In addition to PHY/MAC constraints, the performance of LoRaWAN is limited by duty cycle regulations in the ISM bands. A key constraint for LPWA technologies operating in unlicensed bands is the restriction imposed on the duty cycle, which limits an end device's occupation of the channel. SigFox, Telensa and LoRa devices are restricted to a maximum 1% duty cycle in the EU 868 ISM band BIB004 . The maximum transmission time for each end device operating in each EU 868 ISM sub-band was computed to be 36 s/h. Another issue that arises from the duty cycle restriction is that the channel selection must be compliant with the maximum duty cycle BIB004 .