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Technical Papers

2023

Currently, orthogonal frequency division multiplexing (OFDM), standardized in IEEE 802.15.4, has attracted attention as a transmission scheme for higher data rates, long-distance transmissions, and mobile communications for the expansion of Internet of Things (IoT) applications as well as for legacy IoT applications, such as smart metering systems and home-area networks. In particular, receiving schemes using IEEE 802.15.4-based OFDM have been actively examined to realize mobile communication. This study proposes a receiving scheme for IEEE 802.15.4 OFDM aimed at high-speed mobile IoT communication systems. In the time axis direction, the proposed scheme obtains channel estimates in the same manner as previous schemes. However, in the frequency axis, the proposed scheme obtains the channel estimates by copying estimates of neighboring subcarriers according to the coherence bandwidth of the multipath fading channel to update the channel estimates frequently. Computer simulation results show that the proposed scheme, including delay spread estimation can achieve mobile communication with a data rate of 100 Kb/s at moving speed of 200 km/h in the urban environment.

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In recent years, extensive research has been conducted on the Internet of Things (IoT). Wireless Smart Ubiquitous Network (Wi-SUN) has gained considerable attention as a wireless communication standard for IoT. Wi-SUN Field Area Network (Wi-SUN FAN) is a technical specification of Wi-SUN that can be implemented in both indoor and outdoor IoT communication infrastructure with multi-hop routing. Although Wi-SUN FAN version 1.0 (Wi-SUN FAN 1.0) has been standardized by IEEE 2857–2021, there have been no studies or reviews conducted on the transmission performance of Wi-SUN FAN 1.0 regarding transmission success rate and delay time using computer simulations and experimental evaluation environments involving actual devices. In this study, the specifications of the Wi-SUN FAN are reviewed, and the fundamental transmission performance, such as average transmission success rate and average delay time, is measured using computer simulation as reference data. An experimental evaluation environment involving actual devices is developed to validate the characteristics evaluated by computer simulation. The characteristics determined by the computer simulation and experimental evaluation environment are in good agreement. Using the validated simulator, we evaluate the transmission performance in the wireless IoT environment with one border router and 100 routers randomly arranged in a flat square field with 4,000 m on a side. The average transmission success rate is approximately 1 at 1.00 × 10 −1 s −1 or less. Consequently, Wi-SUN FAN 1.0 can communicate with a higher transmission success rate even when transmitting frequent IoT-data, which is once every ten seconds.

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2022

In recent years, extensive research has been conducted on Internet of Things (IoT). Wireless Smart Ubiquitous Network (Wi-SUN) has gained considerable attention as a wireless communication standard for IoT. Wi-SUN Field Area Network (Wi-SUN FAN) is a technical specification of Wi-SUN that can be implemented in both indoor and outdoor IoT communication infrastructure with multi-hop routing. Although Wi-SUN FAN version 1.0 (Wi-SUN FAN 1.0) has been standardized by IEEE 2857-2021, there have been no studies or reviews conducted on the transmission performance of Wi-SUN FAN 1.0 regarding transmission success rate and delay time using computer simulations and experimental evaluation environments involving actual devices. In this study, the specifications of the Wi-SUN FAN are reviewed, and the fundamental transmission performance, such as average transmission success rate and average delay time, is measured using computer simulation as reference data. An experimental evaluation environment involving actual devices is developed to validate the characteristics evaluated by computer simulation. The characteristics determined by the computer simulation and experimental evaluation environment are in good agreement. Using the validated simulator, we evaluate the transmission performance in the wireless IoT environment with one border router and 100 routers randomly arranged in a flat square field with 4,000 m on a side. The average transmission success rate is approximately 1 at 1.00 × 10–1 s–1 or less. Consequently, Wi-SUN FAN 1.0 can communicate with a higher transmission success rate even when transmitting frequent IoT-data, which is once every ten seconds.

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Radio communication systems using the frequency-shift keying (FSK) scheme standardized by the IEEE 802.15.4g standard can realize low-power consumption and highly reliable communications and are mainly adopted for smart metering as part of the Internet of Things (IoT). However, smart metering has recently broadened its application expectations, with broadband and long-distance communications now required. To fulfill these requirements, orthogonal frequency-division multiplexing (OFDM) has been incorporated into the IEEE 802.15.4g and 802.15.4x standards. However, comprehensive transmission performance analysis of OFDM under static and multipath fading environments has not been conducted. In this article, we first evaluated the packet error rate (PER) of OFDM assuming fixed communications using computer simulations. We then evaluated the transmission distance of OFDM and showed that OFDM can communicate at transmission distances up to 3.0 times longer than those specified in IEEE 802.15.4g FSK. Next, the PER in a mobile communication environment was evaluated using computer simulations. When only the long training field (LTF) was used to estimate multipath radio channels, the required PER of 10% was not achieved, even in a mobile communication environment at a speed of several km/h. To solve this problem, we proposed a receiving scheme which included a new channel estimation scheme. This scheme successively utilized not only the LTF but also pilot signals inserted into the transmitter to estimate radio propagation characteristics. Computer simulation results showed that the required PER was achieved even in a mobile communication environment at 30–40 km/h by using the proposed scheme.

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The Internet of Things (IoT) has been increasingly realizing communication among diverse devices, in addition to sensors and meters. IoT is equipped with communication functions and entails interconnection via the Internet to collect and use various data. Wireless smart ubiquitous network (Wi-SUN) conforms to the international standard IEEE 802.15.4, and it has therefore been considered a wireless communication standard for IoT. The Wi-SUN uses frequency-shift keying (FSK), standardized in IEEE 802.15.4, and achieves a typical data rate of 100 kbps. However, when Wi-SUN is used in other IoT applications to realize smart cities and smart factories, communications with higher data transmission rates and longer distances are required. Orthogonal frequency division multiplexing (OFDM), standardized in IEEE 802.15.4, has been used as a transmission method to satisfy the associated requirements. In this study, the fundamental transmission characteristics of IEEE 802.15.4 OFDM were first evaluated through computer simulations and laboratory experiments by employing developed evaluation boards. Next, the outdoor transmission performance of IEEE 802.15.4 OFDM was evaluated using the developed evaluation boards. Experimental results indicate that IEEE 802.15.4 OFDM can yield the same transmission distance as that of FSK using a smaller transmit power to achieve the packet error rate (PER) smaller than 10%.

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The wireless smart ubiquitous network field area network (Wi-SUN FAN) is a wireless communication standard for the Internet of things (IoT) in outdoor large-scale multi-hop networks. Currently, frequency shift keying (FSK) standardized in IEEE 802.15.4 is employed as the physical layer of the Wi-SUN FAN. Improving data rate of the physical layer is essential to realize expected requirements toward the next-generation IoT systems. In this paper, we introduce the orthogonal frequency division multiplexing (OFDM) standardized in IEEE 802.15.4 into the Wi-SUN FAN to improve data rate without increasing the system bandwidth. We evaluated the packet error rate (PER) characteristics under inter-signal interference in the transition period of the physical layer from FSK to OFDM through a computer simulation. Results showed that the new interference caused by the mixture of OFDM degraded the PER characteristics, in comparison with the interference between FSKs. However, the interference between different channels was limited because the required carrier-to-interference power ratio to achieve PER=10% was below –10dB. Furthermore, we evaluated the transmission characteristics of the Wi-SUN FAN in the media access control layer and verified that the introduction of the OFDM is effective for improving the maximum system throughput by 1.9 times when performing frequency hopping.

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Recently, there has been a growing demand for the Internet of Things (IoT), which connects all types of devices to the Internet via wireless communications. Wireless Smart Ubiquitous Network Field Area Network (Wi-SUN FAN), a wireless communication standard for the IoT oriented to outdoor infrastructure, is attracting attention. Internet Protocol Version 6, routing protocol for Low-power and Lossy Networks (RPL) is adopted as a routing protocol in Wi-SUN FAN. In RPL, each node autonomously selects a parent node based on the network status and sends data to a root node (border router) via multi-hop communication. To reduce power consumption without degrading connectivity, it is necessary for nodes to adaptively control the transmission power based on the communication environment. This paper proposes an adaptive transmission power control method using Wi-SUN FAN standardized frames that can be applied to an upward link. The transmission success rate and energy required per received bit are evaluated to show that power control effectively reduces power consumption.

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With the growing power grid needs in recent years, several different Smart Meters (SMs) have evolved to address diverse challenges. However, interoperability for SMs suppliers is challenging due to the diversity of protocols, data models, and interfaces. In this way, the Wireless Smart Ubiquitous Network (Wi-SUN) is the straightforward solution to address such issue.In this work, we present a simple, low-cost, open-source platform to assess the interoperability with Wi-SUN Field Area Network (FAN) devices. This platform allows the testing of devices under different conditions to check their conformance with the Wi-SUN standard.

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In this study, we developed a USB-type radio board equipped with a wireless smart ubiquitous network (Wi-SUN) field area network (FAN) wireless module capable of performing multi-hops for hundreds of units and an integrated evaluation board to evaluate the transmission performance of Wi-SUN FAN with hundreds of wireless devices in the laboratory. The USB-type radio board achieves low power consumption by controlling the operation of the Wi-SUN FAN wireless module mounted on the board from the outside. Therefore, this study measured the current consumption characteristics. Furthermore, fundamental evaluations of the transmission performance, such as the network configuration time and packet transmission success rate, were performed by configuring a large-scale wireless evaluation system with tree and star topologies using 100 USB-type radio boards and the integrated evaluation boards. A transmission success rate of 95% or higher was achieved continuously for 12 h when all terminals sent a UDP data with a packet length of 200 bytes to the border router of Wi-SUN FAN with a data rate of 100 kbps at the intervals of 150 s.

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2021

Due to the merits of simple implementation and low-power consumption, frequency shift keying (FSK) is widely used in wireless communication systems for the Internet of things (IoT) such as Wi-SUN field area network (Wi-SUN FAN). To expand IoT capacity or diversify IoT application scenarios, higher data rates are highly expected. In this paper, we propose a novel design of data rate enhancement for IEEE 802.15.4-based 2-FSK transmission scheme which meets the radio requirements defined by ARIB STD-T108 regulation in Japan. Fundamental evaluations and field experiments with developed integrated circuits (ICs) are conducted to evaluate the transmission performance of FSK with enhanced data rate parameters. Results show that with the ICs, the data rate of 600 kbps is achieved with a required input power increase of 7.0 dB compared with the conventional data rate of 100 kbps, and can achieve the packet error rate (PER) smaller than 10% for 250 m on line-of-sight (LoS) routes in urban environments. Moreover, the frequency interference level of the proposed FSK scheme is measured to evaluate the performance in practical radio conditions. Results provide reference for the channel management to operate FSK-based communication systems.

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In this paper, the world’s first experimental evaluation of the Wi-SUN Japan Utility Telemetering Association (JUTA) profile-compliant feathery receiver-initiated transmission (JUTA F-RIT) protocol is conducted. Firstly, the transmission success rate in an interference environment is evaluated by theoretical analysis and computer simulations. The analysis is derived from the interference model focusing on the carrier sense. The analysis and simulation results agree as regards the transmission success rate of the JUTA F-RIT protocol. Secondly, we develop the dongle-type prototype that hosts the JUTA F-RIT protocol. Measurement results in a cochannel interference environment show that the transmission success rate at the lower MAC layer is around 94% when the number of terminals is 20. When the waiting time for the establishment of the communication link can be extended to exceed 10 s, the JUTA F-RIT protocol can achieve the transmission success rate of over 90% without the re-establishment of the communication link and re-transmission of data frames. Moreover, the experimental results are examined from two viewpoints of the performance of the frame transmissions and the timeout incident, and the feature of the JUTA F-RIT protocol are discussed.

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This paper aims to identify Wi-SUN devices using physical layer fingerprint. We first extract physical layer features based on the received Wi-SUN signals, especially focusing on device-specific clock skew and frequency deviation in FSK modulation. Then, these physical layer fingerprints are used to train a machine learning-based classifier and the resulting classifier finally identifies the authorized Wi-SUN devices. Preliminary experiments on Wi-SUN certified chips show that the authenticator with the proposed physical layer fingerprints can distinguish Wi-SUN devices with 100 % accuracy. Since no additional computational complexity for authentication is involved on the device side, our approach can be applied to any Wi-SUN based IoT devices with security requirements.

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This paper proposes a novel routing method considering load balancing to improve transmission characteristics of a large-scale Wi-SUN field area network (Wi-SUN FAN) based on IEEE 802.15.4. Wi-SUN FAN is a wireless communication standard that enables the interconnection of many Internet-of-Things (IoT) devices outdoors. Wi-SUN FAN prevents packet collisions by frequency hopping in the media access control (MAC) layer. Besides, Wi-SUN FAN constructs multi-hop networks autonomously using Internet protocol version 6 routing protocol for low-power and lossy networks (RPL) at the network layer. In RPL, each node determines its parent node based on the quality of communication. Therefore, many nodes are likely to choose the same parent node with good radio reachability, resulting in many packets being sent to the parent node. The heavy load for the specific node makes frequency hopping not work effectively, and transmission characteristics deteriorate. The proposed routing method with a load-balancing algorithm eliminates the load concentration and improves the average transmission success rate by approximately 9.4% on the specific nodes.

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Radio interference or jamming can cause isolated area in advanced metering infrastructure (AMI) based on Wire-less smart utility network (Wi-SUN), in which conventional recovery techniques cannot cope with. In this paper, we deploy narrowband internet-of-things (NB-IoT) interface to some smart meters to act as emergency gateway, called ResiLite. An optimal ResiLite placement algorithm for enhancing network resilience is proposed. We define an implicit resilience metric based on path diversity and cluster closeness. The defined metric is used to form an integer linear programming (ILP) problem, then we solve the ILP to obtain optimal ResiLite placement. Simulation results show that the optimal ResiLite placement improves Wi-SUN AMI network resilience (defined as the number of surviving nodes with packet delivery ratio (PDR) above 99% under disturbance) by up to 167% compared to an AMI without ResiLite, and up to 29% compared to uniformly random ResiLite placement, respectively.

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2020

In this paper, we propose a heterogeneous wireless management scheme for a home area network (HAN) system. The HAN system integrates multiple wireless systems (e.g., the Wi-Fi operating in the 2.4 GHz-band and the Wi-SUN field area network (Wi-SUN FAN) operating in the sub-GHz-band) for the in-home health care management system. The system assumes a medical care and proactive health management, and a variety of data such as the vital data, the environment data, and the user activity data are collected to a coordinator by using IoT gateways (IoT-GWs). For the transmission scheme between the loT-GWs, we compare two schemes; the conventional FAN scheme and the proposed fast-path scheme. In the FAN scheme, all of the measured data are collected by using the Wi-SUN FAN multi-hop transmission. On the other hand, the proposed fast-path scheme uses both the Wi-Fi and the Wi-SUN FAN, and a part of the data is offloaded to the Wi-Fi from the Wi-SUN FAN. These two schemes are evaluated by computer simulations. In the case that only the vital and environmental data are collected to the coordinator, these data can be collected with the end-to-end (E2E) transmission success rate of 98 % in the proposed fast-path scheme compared with 92 % in the conventional FAN scheme.

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Advanced metering infrastructure (AMI) based on Wireless Smart Utility Network (Wi-SUN) employs carrier sense multiple access (CSMA), hence suffers from poor network performance when the number of nodes increases but without proper design of data collection scheduling. In this paper, we introduce an interference-aware TDMA-like optimal data collection scheduling, in which a link-timeslot assignment problem is formed by considering interference constraint to achieve better spatial timeslot reuse. A constraint for achieving consecutive flow for multi-hop transmission is also introduced to avoid modifications on the original CSMA protocol, and hence the proposed scheduling is standard compliant. Our results show that the proposed scheduling reduces the total data collection time of Wi-SUN AMI network with 100(200) smart meters by 59%(48%), 33%(32%), and 19%(13%), respectively, when compared with conventional Wi-SUN AMI, conventional TDMA scheduling and heuristic scheduling based on 2-rank distance interference model.

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The wireless smart ubiquitous network field area network (Wi-SUN FAN), a wireless communication standard for Internet of Things (IoT) applications, such as smart metering and monitoring, has been attracting attention. Conventionally, the information transmitted by the Wi-SUN FAN is numerical values and/or character strings, such as metering information. It has been thought that the Wi-SUN FAN cannot transmit video images because the data rate is at most in hundreds of kbps. However, owing to improvements in video compression and transmission technologies in recent years, video images can be transmitted at a transmission rate of hundreds of kbps. In this study, the feasibility of video transmission over the Wi-SUN FAN is evaluated using low-rate video compression and transmission technology. First, several network topologies for video transmission by the current Wi-SUN FAN with multi-hop are evaluated by computer simulations. Consequently, adequate numbers of nodes and multi-hops in the Wi-SUN FAN are recommended. Subsequently, using a recommended value, an experimental system is configured and the video transmission performance over the Wi-SUN FAN is evaluated experimentally.

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The wireless smart ubiquitous network (Wi-SUN) field area network (FAN) attracts attention as a wireless communication standard for large-scale Internet of Things (IoT) systems. Currently, frequency shift keying (FSK) defined in IEEE 802.15.4 is adopted in the physical layer of the Wi-SUN FAN. To improve the network performance toward next-generation IoT systems, a data rate enhancement scheme for FSK has been proposed. However, there is no evaluation of data rate improvement effect by adopting the data rate enhanced FSK on the transmission characteristics of the Wi-SUN FAN. Besides, introducing the data rate enhanced FSK causes the bandwidth to increase. For multiple systems to coexist in limited frequency bands, it is necessary to achieve high spectral efficiency even when the Wi-SUN FAN adopts the data rate enhanced FSK. In this paper, we evaluate the transmission characteristics of the Wi-SUN FAN adopting the high-speed FSK of 600 kbps by computer simulations. The simulation results show that the system throughput improves by 2.5 times, but the bandwidth also increases by 2.5 times compared to the existing system. Furthermore, we propose highly-dense frequency hopping based on a novel channel arrangement scheme to improve spectral efficiency and compatibility with the existing system design while the data rate enhanced FSK is adopted. The evaluation results show that the system throughput in the proposed scheme is 2.4 times of the existing system while using less than half of the bandwidth compared to the conventional channel arrangement scheme.

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Wireless smart utility network field area network (Wi-SUN FAN), which configures very large-scale multi-hop networks, has been standardized to promote interoperable open standards for machine-to-machine (M2M) communication. In the media access control (MAC) layer, Wi-SUN FAN adopts a carrier sense multiple access with collision avoidance (CSMA/CA) and a channel hopping (CH) to avoid interferences between devices. A channel schedule controls the operational channel of CH and it is dominant for both unicast and broadcast transmission performances. In this paper, the impact of channel schedule on the network performance is studied to enhance the unicast transmission throughput. The transmission throughput of a Wi-SUN FAN system in four multiple tandem topologies are evaluated by computer simulations in various channel schedule schemes. The simulation results show that by adopting CH and setting the broadcast interval (BI) coefficient to the optimal value that depends on the network topology, higher unicast throughput can be achieved and the transmission interval of broadcast control frames can be preserved at 131 s. In the case of a multiple tandem topology that consists of 33 devices, by adopting CH and setting the BI coefficient to be 30, the unicast throughput increases by up to 12.2% compared to the case of default parameter configuration recommended in Wi-SUN FAN standard.

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Prior to 2020

This paper summarizes Wi-SUN communication systems and their physical (PHY) layer and media access control (MAC) specifications. Firstly, the Wi-SUN communication systems are categorized into three. The key PHY and MAC standards, IEEE 802.15.4g and .4e, that configure the systems are explained, and fundamental transmission performances of the systems in the PHY layer and MAC layer are evaluated by computer simulations. Then, the Wi-SUN alliance and the Wi-SUN profiles that include IEEE 802.15.4g and .4e are explained. Finally, to understand the transmission performance of actual IEEE 802.15.4g Wi-SUN radio devices, PER performances under AWGN and multipath fading environments are measured by using IEEE 802.15.4g compliant and Wi-SUN alliance certified radio modules. This paper is an instruction paper for the beginners of the Wi-SUN based communications systems.

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This paper proposes and develops a wide area wireless smart utility network (Wi-SUN) system and measures the transmission performance of the system by field experiments. In the wide area Wi-SUN system, a high performance base station (BS) can expand the direct communication distance to wireless devices with sensors and meters by enriching BS functions, i.e. in the down link (DL), transmission power is enlarged, and in the up link (UL), high gain directional antennas are used. Field experiments of the system are carried out to validate effectiveness and availability of the proposed system. The experimental systems are compliant with the regulation for Japan, namely transmission powers of BS and devices are 250 mW and 20 mW respectively, modulation scheme is Gaussian frequency shift keying (GFSK) and the operational frequency band is 920 MHz. Experimental results show that the proposed system expand the direct communication distance around 4.33 times longer than that of conventional system in the practical urban environment.

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Recently, the sub-gigahertz band (e.g. 920 MHz in Japan) has been extensively used for the wireless Internet of Things (IoT) because of its advantages such as excellent radio wave reachability, less interference, and many developments and implementations of large-scale wireless multi-hop networks by using interference avoidance technologies such as the media access control (MAC) protocol and frequency hopping. There are two types of the wireless communication systems for IoT: Wi-SUN FAN, as an asynchronous wireless system, and MAC protocol with time-slotted channel hopping (TSCH), as a synchronous wireless system. Wi-SUN FAN and TSCH systems have already been commercialized and installed to the several IoT environments and are expected to expand in scale in the future. Since both systems are operated in the same frequency band of the sub-gigahertz band, the intersystem interference is a concern for the coexistence of systems. In this paper, the possibility of the coexistence between the systems is examined. The intrasystem and intersystem interferences are evaluated by computer simulations in the case of operating the two systems by themselves and that of operating the systems simultaneously in the same frequency channel.

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Wi-SUN FAN (wireless smart utility network field area network) is a technical specification of Wi-SUN that introduced multi-hop M2M (machine-to-machine) transmission for advanced smart city infrastructure. To construct a multihop network, the RPL (IPv6 routing protocol for low power and lossy networks) and the ETX (expected transmission count) are adopted as routing protocol and routing metric, respectively, in Wi-SUN FAN. The combination of the RPL and the ETX may cause a node to change its parent frequently. If a node selects a parent with lower link quality, communication reliability becomes lower. To avoid the frequent parent changing problem, parent candidates of each node should be selected appropriately. In this paper, we propose two schemes to select parent candidates for each node (i.e., optimized RSL (received signal level) threshold scheme and MAC (media access control) address filtering scheme) to stabilize the multi-hop routing construction in the Wi-SUN FAN systems. The proposed schemes are experimentally evaluated in a real field in an office building using the IoT-GWs (internet of things gateways) with Wi-SUN FAN module. By using the optimized RSL threshold scheme, the number of parent changes can be reduced by up to 96% compared to the case with unoptimized RSL threshold. Also, the number of parent changes can be reduced by up to 77% with the proposed MAC address filtering scheme compared to without the proposed scheme.

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Wireless Smart Utility Network (Wi-SUN) has been standardized to provide Machine-to-Machine (M2M) communication in Low power and Lossy Networks (LLNs). Wi-SUN Field Area Network (FAN) is the specification that maintains a wireless multi-hop communication on the advanced smart city infrastructure. Wi-SUN FAN has adopted the Internet Protocol version 6 (IPv6) Routing Protocol for LLNs (RPL) which has been successfully optimized in fixed terminals. To establish the embedded smart city, mobile nodes are required to implement the RPL as well. Nevertheless, the RPL fails to choose the appropriate routing node when the terminal moves, resulting in high packet loss. To improve the transmission performance, the system simulator of Wi-SUN FAN with the Expected Transmission Count (ETX) based algorithm is firstly developed to evaluate the end-to-end transmission success rate via multi-hop transmission and the simulation result clarifies that the critical factor causing low transmission performance is the unsmooth handover of the receiver node at first hop. Then, a dynamic routing algorithm based on ETX transition is proposed and the simulation result finally assures the smooth handover, resulting in the improved transmission performance.

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