Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> B. LONG-RANGE M2M WIRELESS TECHNOLOGIES <s> We study carefully the IEEE 802.11ah draft standard published in July 2014.We overview use cases of .11ah, especially related to smart cities scenarios.We describe in details novel mechanisms and explain why they are needed in .11ah. Smart technologies play a key role in sustainable economic growth. They transform houses, offices, factories, and even cities into autonomic, self-controlled systems acting often without human intervention and thus sparing people routine connected with information collecting and processing. The paper gives an overview of a novel Wi-Fi technology, currently under development, which aims to organize communication between various devices used in such applications as smart grids, smart meters, smart houses, smart healthcare systems, smart industry, etc. <s> BIB001 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> B. LONG-RANGE M2M WIRELESS TECHNOLOGIES <s> As one of the fastest growing technologies, machine-to-machine (M2M) communications are expected to provide ubiquitous connectivity. M2M devices can be used for a wide range of emerging applications that have various communications requirements. While M2M communications have been developed for many years, major challenges still remain with their efficient implementation from the perspective of low energy consumption and wide coverage. To address these challenges, low power wide area (LPWA) technology is investigated as one of the potential candidate solutions. In this article, we first introduce some typical LPWA M2M application scenarios. Given their requirements, we highlight key techniques and standards that are explicitly designed for LPWA M2M communications. Finally, we present an LPWA prototype system to evaluate its performance and demonstrate its potential in bridging a technological gap for future Internet-of-Things (IoT) applications. <s> BIB002 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> B. LONG-RANGE M2M WIRELESS TECHNOLOGIES <s> The emerging Internet of Things (IoT) is getting closer to reality every day, with standards and protocols tailored to specific applications. Although some technologies follow a ‘make once, fit all’ approach, others are designed for specific applications such as smart-metering where the devices are often stationary with low jitter and throughput requirements. ETSI is already working towards a new standard for such applications, having specified a Specification Group to study what they call Low Throughput Networks (LTN) and propose a communications standard. In the meantime industrial solutions have entered the market such as, among others, Sigfox's and OnRamp Wireless technologies and LoRaWAN. Although this may lead to fragmentation of the IoT, they are worth examining to gain insights from their innovations and approaches to solving problems that are common in IoT technologies, and more specifically, security, energy management and resource constrains. This paper examines the wireless technologies of LoRaWan, Sigfox and OnRamp Wireless, the emerging leaders in IoT smart metering applications. These have so far not been studied in any peer-reviewed paper. Furthermore we discuss the suitability of Low Throughput Networks for certain applications and how the above technologies would work in such scenarios. <s> BIB003 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> B. LONG-RANGE M2M WIRELESS TECHNOLOGIES <s> This paper focuses on the the emerging transmission technologies dedicated to IoT networks. We first analyze the classical cellular network technologies when taking into account the IoT requirements, and point out the need of dedicated technologies for IoT. Then, we present the PHY and MAC layers of the technologies that are already deployed, or likely to be deployed: UNB by SigFox, CSS by LoRa T M , Weighless, and RPMA by Ingenu. We then compare their performances to highlight their pros and cons. Finally, we discuss on the open research challenges that still need to be addressed. <s> BIB004 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> B. LONG-RANGE M2M WIRELESS TECHNOLOGIES <s> Abstract The emerging IEEE 802.11ah is a promising communication standard that supports a massive number of heterogeneous devices in the Internet of Things (IoT). It provides attractive features like improved scalability, low energy consumption, and coverage of large area. In this paper, we analyze the performance of IEEE 802.11ah, and compare it with a prominent alternative, the IEEE 802.15.4. The simulation results show that the new 802.11ah standard performs better than the 802.15.4 in terms of association time, throughput, delay, and coverage range. <s> BIB005 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> B. LONG-RANGE M2M WIRELESS 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> BIB006 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> B. LONG-RANGE M2M WIRELESS 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> BIB007 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> B. LONG-RANGE M2M WIRELESS 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> BIB008
The main requirements of the IoT applications are long distance coverage, high network capacity, low data rates, low power consumption, and affordable devices. The technologies discussed in Subsection II-A are limited by the transmission range and number of devices. LPWA technology is considered a potential solution for M2M communications. M2M limitations on coverage and inefficient energy consumption force IoT providers to rely on LPWA networks for diverse IoT applications. The IEEE 802.11ah Task Group has been assigned by the IEEE 802 LAN/MAN standards committee (LMSC) to work on extending the range and data rate of the IEEE 802.11ah standard so that it achieves energy efficient protocols suitable for IoT applications BIB001 . IEEE 802.11ah is a WiFi based low data rate and low-energy consumption solution that can cover up to 1 km with 200 mW default transmission power at a minimum data rate of 100 kbps operating in frequency bands less than 1 GHz (TV White Space bands are excluded)  . Using efficient modulation and coding schemes (MCSs) and proper propagation characteristics and operating in relatively narrow bands enable this technology to provide hundreds of Mbps (subject to channel conditions) and to be energy efficient BIB001 . The IEEE 802.11ah physical (PHY) layer is based on the IEEE 802.11ac and adopted to the use of sub bands. It uses orthogonal frequency division multiplexing (OFDM), multiple-input multiple-output (MIMO) downlink multi-user MIMO (DL MU-MIMO) and MCSs similar to IEEE 802.11ac. To cover long distances between a large number of low power nodes, the PHY and MAC layers implement a number of innovative approaches including hierarchical association identification, restricted access window, traffic indication map and segmentation, target wake time, and smaller headers BIB005 , BIB001 . IEEE 802.11ah is a promising communication solution for outdoor WiFi devices; however, it cannot be deployed in environments such as remote or underground areas BIB002 . LPWA networks have been proposed to replace short-range M2M wireless technologies. They have emerged to close the gap between local wireless and mobile wide area network technologies. They have features that are particularly attractive for IoT devices and applications, which will enable them to play a significant role over the next few years. LPWA technologies utilize various mechanisms to satisfy the requirements of modern IoT applications. Main characteristics of the LPWA networks are summarized below: • Long-range coverage LPWA networks offer optimized coverage for longrange communications, with a +20 dB gain over legacy cellular networks. This allows end devices to stay connected to their base stations over tens of kilometers BIB007 ( Figure 2 ). • Low data rates LPWA networks target services that are not sensitive to losses and delays. For most of the use-cases presented in Section V, single signals of a few bits are usually reported, which, in most cases, correspond to an ''OK'' status ( Figure 2 ). • Low power consumption Power consumption is a major concern with respect to mobile end devices. LPWA networks are designed to prolong battery lifetimes by placing devices in lowenergy sleep mode and only waking them when they need to communicate with the gateway (Figure 3 ). This makes it possible for devices to operate on a single coin cell for several years BIB008 . LPWA applications operate over power-optimized radio networks. • Low-cost end devices Since complex processing is mainly offloaded to the base station and the end devices are awake only when they have data to report, the cost of such a device can be as low as ten dollars or even less ( Figure 3 ). SigFox's packet would have been 15% longer if the message was decoded on the end devices BIB003 . For example, LoRa wide area network (LoRaWAN) and SigFox devices cost approximately $2-5 each. • Large numbers of end devices Two of the design goals for LPWA networks are high network capacity and scalability. Billions of devices are predicted for IoT deployment scenarios  , in which a base station may be connected to hundreds of thousands of devices  . LPWA technologies use a number of techniques to support such massive numbers of devices. Some of these techniques include the use of ultra narrow band (UNB) communication, which enables the coexistence of a large number of devices within a cell while controlling interference and adaptive data rates and channel selection BIB007 . • Usage of unlicensed spectrum Most LPWA technologies use free licensed spectrum resources within the ISM band. Therefore, LPWA providers do not need to pay for licensing, thus lowering the cost of deployment. • Simplified network topology LPWA networks are deployed in a simple star topology (instead of the mesh or tree topologies used by other technologies), in which end devices are directly connected to the base station through their modems. This simple deployment scheme allows devices to operate over a thin and scalable infrastructure that spans a range of several kilometers. This also simplifies the installation of hardware. Additional base stations can be used to further extend the coverage. A star-of-stars topology can also be used to connect a cluster of base stations via gateways or concentrators BIB006 . There are currently a number of LPWA providers, such as Semtech [39] , SigFox [40] , Ingenu  , Silver Spring  and Telensa [42] . The diversity in the LPWA technologies is mainly due to the difference in the PHY and MAC specifications. The SDOs have exerted much effort to enable communication between these diverse technologies through standardizing or amending the design of the PHY and MAC layers. Some (e.g., Telensa) have already begun standardization of their LPWA technologies BIB007 . The PHY/MAC challenges of SigFox, LoRa, Weightless and RPMA for the IoT have been analyzed in BIB004 . In this section, we explore LoRaWAN, SigFox, RPMA  , Telensa and NB-IoT [45] . We refer readers interested in other LPWA technologies to BIB006 and BIB007 .