In this paper, to efficiently support virtual reality (VR) and extended reality (XR) applications, we propose a novel method for gesture recognition utilizing inertial measurement unit (IMU) and ultra-wideband (UWB) in the commercial off-the-shelf, where three smartphones are used for one head mounted display (HMD) and two wrist-attached devices (WADs). According to the intensive experimental evaluations, our proposed method can provide very high success rate of gesture recognition for pre-defined 10 hand motions. For 8 volunteers participating the data collection, classifier learning, and testing, we observed that the recognition success rate of 100 % is achieved. Moreover, the success rate of 91.9% for new users who did not participate in learning can be achieved. These results can provide meaningful guidelines to adopt the UWB chipset into the HMD and WADs, because UWB significantly improves the success rate of gesture recognition than that result from the IMU only.

The ultra-wideband (UWB) based indoor positioning system (IPS) using downlink-time difference of arrival (DL-TDOA) enables a UWB device to estimate its own location with high accuracy by merely listening to UWB signals of adjacent UWB anchors. From a viewpoint of UWB anchor deployment, due to tens of a few meter coverage of the UWB signal, UWB anchors have to be densely deployed to cover the large-scale area. Also, UWB anchors should be grouped into clusters in the DL- TDOA and each cluster is assigned with the dedicated time resource for UWB signal transmissions in time division manner for interference mitigation. In particular, we have observed that blocking line-of-sight (LOS) ray component between UWB anchors may severely degrade the performance under such a manual configuration. To tackle those problems, we propose a novel algorithm, called ACTION (Anchor Clustering and TIme resOurce assigNment) based on an optimization approach. Experimental results show that ACTION can considerably improve the localization success ratio and accuracy with a feasible duration.

Recently, many researchers and global vendors of mobile devices have paid attention to the ranging technique using IEEE 802.15.4z ultra-wideband (UWB), because it can support a highly precise spatial awareness and indoor localization. In the Internet of Things (IoT) environments, the interval of the ranging attempts for a ranging device (RDEV) affects largely the performance of the RDEV. The proper ranging interval for an RDEV varies according to the IoT applications using the ranging results as well as the type and state of the RDEV (e.g., moving speed and battery status). In the IEEE 802.15.4z, since the ranging for a group of multiple RDEVs is carried out once every ranging block, the ranging interval can be represented by the block length, which should be determined based on the various requirements of RDEVs within the group. In this article, we analyze the requirements on the block length of RDEVs, from the viewpoint of the energy efficiency and the degree of service satisfaction. Considering these requirements, we design a novel decision scheme of the ranging block length, based on the Markov decision process. The simulation results show that the proposed scheme enhances remarkably the energy efficiency and the satisfaction of RDEVs.

As the number of Internet-of-Things (IoT) devices explosively increases, developing the IoT standard is essential to control those devices efficiently. To do this, many vendors and IT companies have established IoT standard organizations. In particular, the Open Connectivity Foundation (OCF), the most influential IoT standard organization, has been actively developing the OCF standard and an open-source software framework called IoTivity. The OCF standard supports interoperability through bridging techniques toward non-OCF devices of other ecosystems, such as ZigBee, Bluetooth low energy, oneM2M, and AllJoyn. Among several bridging techniques, we focus on developing an OCF-to-ZigBee (O2Z) bridging technique which is very important to provide the scalability of the OCF standard. This is because there are many ZigBee devices to construct IoT applications (e.g., lightening, heating, and sensing), and the number of them is steadily increasing. In this article, we introduce the O2Z bridging technique adopted in the OCF standard, and describe how to implement an O2Z bridging plugin as a software component of IoTivity. This work would provide a good guideline for developing other bridging techniques toward other IoT ecosystems.

Recently, video traffic has rapidly increased, and a considerable portion of that is caused by wireless devices. Since video streaming services now require high data rates, IEEE 802.11 has been widely used to support them in the wireless environment. On the other hand, in densely populated areas (e.g., conference rooms), multiple video streaming services using a unicast method can result in exceeding the available capacity. Instead, a multicast method can be considered for video streaming services in these latter conditions, since many users can be served at the same time with a relatively small resource. However, the legacy multicast in IEEE 802.11 does not perform the Automatic Repeat reQuest (ARQ), which leads to many packet losses and the degradation of video quality. To tackle this problem, we investigate the reliable video multicast using the application layer-forward error correction (AL-FEC) technique without the ARQ mechanism. Specifically, based on traffic characteristics of H.264/AVC video streaming, we propose a practical adaptation scheme, which determines the robustness of the FEC and a physical transmission rate of wireless access point. Moreover, we implement a prototype system in practice using the proposed scheme. The experimental results show that the proposed scheme greatly supports the coexistence with unicast transmissions, as well as the reliable video multicast, while satisfying the video quality.

In cellular systems, the relaying technique is used for increasing service coverage, system capacity, and cell- edge user throughput at a relatively low cost. However, the introduction of relay stations (RSs) leads to a more complex intra-cell and inter-cell interference problem between the base station (BS) and RSs. The fractional frequency reuse (FFR) is one of the most simple and efficient (thus, practical) techniques to solve this problem. To heighten the performance of cellular systems with the relaying/FFR combination, the deployment (i.e., the positioning) of RSs should be managed carefully. In this paper, we focus on energy efficiency (EE) as a performance index, which is quantified as the number of bits that can be transmitted per unit of energy consumption. We first derive the EE as a function of the distance between BS and RS. Then, we find out the optimal distance using optimization approach. Based on the numerical results, we provide a guideline in the deployment of RSs.