As the communication mode expected to improve system throughput by omitting the specific means to acquire transmit rights, grant free methods, such as NOMA (Non-orthogonal Multiple Access), studied in various mobile networks as systems accommodate many terminals under the expansion of IoT. However, the system, which is premised on many terminals in core networks, has not been sufficiently investigated. Since the terminal location needs to be known and the location registration and its administrative function are particularly needed by mobile communication networks, the system is usually equipped in the core network where the whole network can be accessed easily. As the number of terminals housed in a network increases as the Internet of Things (IoT) expands, the throughput inevitably increases for location registration and the possibility of congestion developing increases. Thus, this article proposes a way to reduce the throughput for location registration where mMTC (massive Machine Type Communication) is prescribed by 5G premised on many simultaneous connection terminals.

High-resolution nowcasting flood prediction using streaming rainfall big data is desired for soft countermeasures against pluvial floods. Although an integrated flood analysis model consisting of a diffusion-wave equation, momentum equations and so on can simulate flood processes accurately, the model is unsuitable for nowcasting flood prediction due to its high computational cost. To realize accurate and computationally inexpensive nowcasting pluvial flood prediction, we have applied the knowledge distillation (KD) technique for training a lightweight neural network with the integrated flood analysis as a teacher. In the previous work, we showed its applicability in terms of prediction time and accuracy. However, this KD-based approach would not be sufficiently accurate in predicting floods caused by rainfall in minor rainfall patterns. To cope with it, we propose a prioritized sampling method that compensates for the imbalance between rainfall patterns. The rainfall patterns are mined from big rainfall data based on the spatiotemporal features of rainfall intensity over a rainfall duration. Compared to random sampling, we show that our prioritized sampling reduces the average prediction error of floods caused by rainfall in a minor rainfall pattern by 37 cm per mesh, which is equivalent to 96% reduction in error rate.

LED-to-camera communication for smartphones promises to enable low-cost, small-size, and intuitive data access to Internet-of-things (IoT) devices. However, for fast and reliable communication under the rolling shutter effect, the packet losses caused by inter-frame gaps and frame drops must be dealt with. In this paper, we introduce LED-to-camera communication between a commercial smartphone and an IoT device with LED flashlight, where the user can intuitively acquire the desired data transmitted from the IoT device to the smartphone. Specifically, we present IoTorch, a fast and reliable LED-to-camera communication that efficiently prevents the packet losses. IoTorch consists of two core mechanisms: 1) a minimum-repetition one-way reliable transmission focusing on the periodicity of inter-frame gaps and 2) an acknowledgement mechanism to overcome frame drops by using a smartphone's built-in flash focusing on its delay characteristics. Additionally, we propose an optimization method to increase the throughput up to 2.92 kbps (i.e., 2.43 times faster than that of the state-of-the-art method that overcomes the inter-frame gaps). Furthermore, we realize a remote wake-up function by using the smartphone's flash as the data transmission trigger. To demonstrate the benefit of IoTorch, we present a sensor data viewer using Arduino and a smartphone console system on TelosB.

TelemetRing is a batteryless and wireless ring-shaped keyboard that supports command and text entry in daily lives by detecting finger typing on various surfaces. The proposed inductive telemetry approach eliminates bulky batteries or capacitors from the ring part. Each ring consists of a sensor coil (the ring part itself), 1-DoF piezoelectric accelerometer, and varactor diode; moreover, it has different resonant frequencies. Typing shocks slightly shift the resonant frequency, and these are detected by a wrist-mounted readout coil. 5-bit chord keyboard is realized by attaching five sensor rings on five fingers. Our evaluation shows that the prototype achieved the tiny (6 g, 3.5 cm^3) ring sensor and 89.7% of typing detection ratio.

As we are surrounded by countless sensing devices, “intuitive” communication, which allows a user to directly obtain information from a device of interest to the user, is needed. Towards this, we present long-range flicker-free LED(lightemitting diode)-to-camera communication in which flickering can be prevented by the rapid switching of LED colors and information can be acquired from remote LEDs that appear as only a few pixels on a camera screen. In the rolling shutter system (typically used in smartphones), the timing of an exposure varies depending on the in-screen position. Hence, the imaging time interval of the LED deviates from the constant frame cycle owing to hand micromotion during communication. Under this condition, when imaging an LED that switches color rapidly, the color captured in the frame changes depending on the degree of hand micromotion. To solve this problem, we present differential color shift keying (DCSK) as a mechanism for correcting the influence of hand micromotion. Experimental results using multiple smartphone models show that the mechanism using DCSK achieves a communication range exceeding 3 m with a throughput of 60 bps from an LED with a diameter of 10 mm compared to several centimeters achieved by state-of-the-art studies.

Sharing systems for personal mobility devices (PMDs) with batteries are gaining popularity because of their advantages in terms of maneuverability and low environmental burdens. However, PMDs suffer from a small battery capacity, a lack of charging stations, and the inconvenience of plugging in for charging. To solve these problems, we propose retrofitting city spaces into wireless power transfer (WPT) stations/pads by placing sheet-like transmitters in available open spaces. Many studies have considered WPT for electrical vehicles; however, little attention has been given to WPT for PMDs, although they have many unique characteristics to consider (e.g., light weight, form factor, sharing ecosystems, and random running routes). In this study, we investigated a form of WPT via magnetic resonant coupling for PMDs through coil design, analysis, and measurements based on two scenarios: (1) charging PMDs at charging stations and (2) charging in-motion PMDs from chargers placed on the road. Based on these considerations, we confirmed that around 90 % transfer efficiency can be obtained in laboratory setups, whereas practical setups achieved around 70% efficiency.

Magnetic resonant coupling wireless power transfer (MRC- WPT) using transmitter arrays is expected to be applied to power electric vehicles and electronic devices. Transmitter arrays can maintain power transfer efficiency despite lateral misalignment between the transmitter and receiver. However, methods of using transmitter arrays while reducing magnetic field leakage have not been studied. A new method of using transmitter arrays is necessary for electromagnetic compatibility and user safety. In this study, we optimized the input currents at transmitter arrays and the load at the receiver to reduce magnetic field leakage and maintain power transfer efficiency even with lateral misalignment between the transmitter arrays and the receiver. Simulations showed that the proposed method can reduce magnetic field leakage by more than 10 dB and 38 dB, with and without ferrite plates, respectively, compared to the existing method of maximizing power transfer efficiency.

LoRa networks achieve a remarkably wide coverage as compared to that of the conventional wireless systems by employing the chirp spread spectrum (CSS). However, single-hop LoRa networks have limited penetration in indoor environments and cannot efficiently utilize the multiple-access dimensions arising from different spreading factors (SF) because the star topology is typically used for LoRa. On the other hand, a multi-hop LoRa network has the potential to realize extensive network coverage by utilizing packet relaying and improving the network capacity by utilizing different SFs. We evaluated the LoRa receiver performance under co-technology interference via simulation and experiments to realize these potentials. The results show that LoRa can survive interference from time-synchronized packets transmitted by multiple transmitters with an identical SF. Furthermore, we examined the orthogonality between different SFs by evaluating the required signal-to-interference ratio (SIR). Finally, we demonstrated the possibility of employing different SFs to construct the pipeline in a multi-hop relay network to increase network efficiency.

In this paper, we propose a passive and contactless epidermal pressure sensor patch printed on a paper substrate with silver nano-particle ink. This disposable patch can be used to measure the pressure between the clothes and the human body. Different from the conventional pressure sensors, the pressure can be measured wirelessly without disturbing the motion of the users. The sensor circuit pattern is printed by a conductive inkjet printer and the sensor's pressure value is detected by a reader coil through the change of the capacitance of an LC resonant circuit. We propose a sensor design method that minimizes the effect of the human body. We demonstrate our sensor patch by measuring the pressure exerted by compression garments whose pressure distribution is important for the wearer's health.

Full-duplex wireless information and power transfer allows the implementation of wireless sensor networks without batteries. In a full-duplex wireless network, an access point and sensor nodes transmit information and power signals simultaneously. However, this simultaneous transmission leads to a collision problem. To solve this collision problem, we propose a media access control (MAC) protocol, namely the Full-Duplex Simultaneous Wireless Information and Power Transfer Medium Access Control (FD-SWIPT MAC) protocol, for full-duplex wireless information and power transfer. The evaluation results show that the proposed FD-SWIPT MAC protocol outperforms other MAC protocols.