小室 信喜

Recently, UWB-based technology providing centimeter-level accuracy has been developed and widely utilized in indoor real-time location tracking systems. However, location accuracy varies due to factors such as frequency interference, collisions, reflected signals, and whether line-of-sight (LOS) conditions are met, and it can be challenging to ensure high accuracy in specific environments. Fortunately, when anchor positions are fixed, the locations of large obstacles such as columns or furniture remain relatively stable, leading to similar patterns of positioning bias at specific points. This study proposes an algorithm that corrects inaccurate positioning to more closely reflect the actual location based on bias and deviation maps generated using natural neighbor interpolation. Initially, positioning bias and deviations at specific points are sampled, and bias and deviation maps are created using natural neighbor interpolation. During location tracking, the algorithm detects candidate clusters and determines the centroid to estimate the actual location by applying the bias and deviation maps to the measured positions derived through trilateration. To validate the proposed algorithm, experiments were conducted in a non-LOS (NLOS) indoor environment. The results demonstrate that the proposed algorithm can reduce the positioning bias of a UWB-based RTLS by approximately 71.34% compared to an uncalibrated system.

Cloud virtual reality (VR) is attracting attention in terms of its lightweight head-mounted display (HMD), providing telepresence and mobility. However, it is still in the research stages due to motion-to-photon (MTP) latency, the need for high-speed network infrastructure, and large-scale traffic processing problems. These problems are expected to be partially solved through edge computing, but the limited computing resource capacity of the infrastructure presents new challenges. In particular, in order to efficiently provide multi-user content such as remote meetings on edge devices, resource provisioning is needed that considers the application’s traffic patterns and computing resource requirements at the same time. In this study, we present a microservice architecture (MSA)-based application to provide multi-user cloud VR in edge computing and propose a scheme for planning an efficient service deployment considering the characteristics of each service. The proposed scheme not only guarantees the MTP latency threshold for all users but also aims to reduce networking and computing resource waste. The proposed scheme was evaluated by simulating various scenarios, and the results were compared to several studies. It was confirmed that the proposed scheme represents better performance metrics than the comparison schemes in most cases from the perspectives of networking, computing, and MTP latency.

Indoor position fingerprint-based location estimation methods have been widely used by applications on smartphones. In these localization estimation methods, it is very popular to use the RSSI (Received Signal Strength Indication) of signals to represent the position fingerprint. This paper proposes the design of a particle filter for reducing the estimation error of the machine learning-based indoor BLE location fingerprinting method. Unlike the general particle filter, taking into account the distance, the proposed system designs improved likelihood functions, considering the coordinates based on fingerprint points using mean and variance of RSSI values, combining the particle filter with the k-NN (k-Nearest Neighbor) algorithm to realize the reduction in indoor positioning error. The initial position is estimated by the position fingerprinting method based on the machine learning method. By comparing the fingerprint method based on k-NN with general particle filter processing, and the fingerprint estimation method based on only k-NN or SVM (Support Vector Machine), experiment results showed that the proposed method has a smaller minimum error and a better average error than the conventional method.

Single image super-resolution attempts to reconstruct a high-resolution (HR) image from its corresponding low-resolution (LR) image, which has been a research hotspot in computer vision and image processing for decades. To improve the accuracy of super-resolution images, many works adopt very deep networks to model the translation from LR to HR, resulting in memory and computation consumption. In this article, we design a lightweight dense connection distillation network by combining the feature fusion units and dense connection distillation blocks (DCDB) that include selective cascading and dense distillation components. The dense connections are used between and within the distillation block, which can provide rich information for image reconstruction by fusing shallow and deep features. In each DCDB, the dense distillation module concatenates the remaining feature maps of all previous layers to extract useful information, the selected features are then assessed by the proposed layer contrast-aware channel attention mechanism, and finally the cascade module aggregates the features. The distillation mechanism helps to reduce training parameters and improve training efficiency, and the layer contrast-aware channel attention further improves the performance of model. The quality and quantity experimental results on several benchmark datasets show the proposed method performs better tradeoff in term of accuracy and efficiency.

This paper proposes a Duty-Cycle (DC) control method in order to improve the Packet Delivery Ratio (PDR) for IEEE 802.15.4-compliant heterogeneous Wireless Sensor Networks (WSNs). The proposed method controls the DC so that the buffer occupancy of sensor nodes is less than 1 and assigns DC to each sub-network (sub-network means a network consisting of a router node and its subordinate nodes). In order to use the appropriate DC of each sub-network to obtain the high PDR, this paper gives analytical expressions of the buffer occupancy. The simulation results show that the proposed method achieves a reasonable delay and energy consumption while maintaining high PDR.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. This paper proposes a Medium Access Control (MAC) protocol using directional antennas in wireless ad-hoc networks, which achieves frame-collision reduction, freezing-state duration reduction, and deafness-problem mitigation simultaneously. The idea of the proposed protocol is that Pulse/Tone exchange is applied to the Opportunistic Directional MAC protocol (OPDMAC). By applying the Pulse/Tone exchange prior to Request to Send/Clear to Send (RTS/CTS) handshake, RTS-to-RTS frame collisions are reduced dramatically. Additionally, RTS-to-DATA frame collisions in the OPDMAC are changed to Pulse signal-to-DATA frame overlaps in the proposed protocol. This change makes the DATA-frame transmissions in success because the Pulse signal-to-DATA frame overlaps are regarded as a deafness problem. On that basis, the deafness-problem mitigation can be obtained in the proposed protocol by adaptive transmission-direction switching, which follows the OPDMAC technique. The freezing-state durations can be also reduced by the transmission-direction switching. As a result, the proposed protocol provides high network throughput compared with conventional protocols. Simulation results show the validity and effectiveness of the proposed protocol.

© 2017 Elsevier B.V. It is an effective approach for comprehending network performance is to develop a mathematical model because complex relationship between system parameters and performance can be obtained explicitly. This paper presents generalized analytical expressions for end-to-end throughput of IEEE 802.11 string-topology multi-hop networks. For obtaining expressions, a relationship between the durations of the backoff-timer (BT) decrements and frame transmission is expressed by integrating modified Bianchi's Markov-chain model and airtime expression. Additionally, the buffer queueing of each node is expressed by applying the queueing theory. The analytical expressions obtained in this paper provide end-to-end throughput for any hop number, any frame length, and any offered load, including most of analytical expressions presented in previous papers. The analytical results agree with simulation results quantitatively, which shows the verifications of the analytical expressions.

Green and reliable communication has great significance for Industrial Internet of Things. Unfortunately, because of the loss nature, achieving reliable transmission is challenging. In this paper, a novel hybrid transmission protocol (HTP) is proposed to maximize lifetime while the reliability is still guaranteed. The proposed protocol adopts Send-Wait automatic Repeat-Request protocol in hotspot areas to reduce the energy consumption and network coding based redundant transmission approach with adaptive redundancy level in non-hotspot areas to guarantee the reliability. The proposed protocol could improve the lifetime and shorten the delay on the premise of ensuring the reliability. Comparing with Send-Wait automatic Repeat-Request protocol, it can improve lifetime by 15%-30% under the same reliability and improve the reliability by 12%-45% under the same lifetime. Comparing with network coding based redundant transmission approach, the lifetime has increased by more than one time under the same reliability. (C) 2016 Elsevier Ltd. All rights reserved.

Recently, mobile broadcast services such as DMB, multimedia streaming services and IPTV, caused rapid increase of multimedia services sent over the Internet. It is important to define, measure and evaluate the elements related to the quality of providing the services over the Internet. In this paper, we propose multimedia quality measurement model that evaluates the quality of multimedia from consumers point of view. We selected some parameters that affect the quality of multimedia on application level as well as network level, and then use these parameters to create multiple altered versions of an original video. All videos are then uploaded to YouTube, the popular streaming site. Then each video is viewed by a subject using multiple devices. For each video and device, subjects give Mean Opinion Score (MOS) rating. Then we determined the influence of parameters on videos and devices.

This paper proposes a thread scheduling mechanism primed for heterogeneously configured multicore systems. Our approach considers CPU utilization for mapping running threads with the appropriate core that can potentially deliver the actual needed capacity. The paper also introduces a mapping algorithm that is able to map threads to cores in an O(NlogM) time complexity, where N is the number of cores and M is the number of types of cores. In addition to that we also introduced a method of profiling heterogeneous architectures based on the discrepancy between the performances of individual cores. Our heterogeneity aware scheduler was able to speed up processing by 52.62% and save power by 2.22% as compared to the CFS scheduler that is a default in Linux systems.

For public safety or military purposes, it is needed to introduce a unified architecture of multi-hop wireless networks that include both flat (ad-hoc) networks and hierarchical (mesh) networks, where devices can access multiple channels using multiple radio interfaces thanks to the advance of mobile devices. In such networks, it is a challenging issue how to assign channels in a distributed manner by avoiding interference and maintaining connectivity. In this paper, we propose a distributed heuristic channel assignment scheme, based on channel utilization and even adaptive against jamming. We use the OPNET simulator to perform a rigorous simulation and confirm that the performance of the proposed scheme outperforms existing schemes.

This paper proposes a Watts and Strogatz-model based routing method for wireless sensor network along with link-exchange operation. The proposed routing achieves low data-collection delay because of hub-node existence. By applying the link exchanges, node with low remaining battery level can escape from a hub node. Therefore, the proposed routing method achieves the fair battery-power consumptions among sensor nodes. It is possible for the proposed method to prolong the network lifetime with keeping the small-world properties. Simulation results show the effectiveness of the proposed method.

This paper presents a Multi-channel MAC protocol with channel grouping for multi-channel ad-hoc networks. The proposed protocol has both concepts of the multiple rendezvous and the single control channel protocols, which were proposed as a MAC protocol for multi-channel ad-hoc network without centralized stations. In the proposed protocol, all the channels are divided into some groups and each group has a control channel. Network nodes circulate among the groups and channel negotiations are carried out on a control channel of the group. By applying the channel grouping, it is possible to enhance network throughput without reducing the channel-usage probability. Because there is an optimum group number for obtaining the highest throughput, this paper gives analytical expressions of maximum network throughput for the proposed protocol as a function of system parameters. The effectiveness of the proposed protocol is shown from simulation results. In addition, the validity of the analytical expressions is confirmed from quantitative agreements between analytical predictions and simulation results.

This paper presents an analytical model for network throughput of WLANs, taking into account heterogeneous conditions, namely network nodes transmit different length frames with various offered load individually. The airtime concept, which is often used in multihop network analyses, is firstly applied for WLAN analysis. The proposed analytical model can cover the situation that there are saturation and non-saturation nodes in the same network simultaneously, which is the first success in the WLAN analyses. This paper shows the network throughput characteristics of four scenarios. Scenario 1 considers the saturation throughputs for the case that one or two length frames are transmitted at the identical offered load. Scenarios 2 and 3 are prepared for investigating the cases that all network nodes transmit different length frames at the identical offered load and identical length frames at the different offered loads, respectively. The heterogeneous conditions for not only frame length but also offered load are investigated in Scenario 4.

This paper proposes the analytical expressions for the IEEE 802.11 string-topology multi-hop networks using Markov-chain model. For achieving that, the proposed analysis procedure includes two proposals, which are: (i) Bianchi's Markov-chain model is modified for considering a relationship between the backoff timer and frame length, and (ii) the interferences, such as hidden node collision and carrier sensing, among network nodes are expressed by merging the proposed Markov-chain model and airtime expression. The analytical expressions are verified by comparisons with simulation results.

String-topology multi-hop network is often selected as an analysis object because it is one of the fundamental network topologies. The purpose of this paper is to establish expression for end-to-end delay for IEEE 802.11 string-topology multi-hop networks. For obtaining the analytical expression, the effects of frame collisions and carrier-sensing effect from other nodes under the non-saturated condition are obtained for each node in the network. For expressing the properties in non-saturated condition, a new parameter, which is frame-existence probability, is defined. The end-to-end delay of a string-topology multi-hop network can be derived as the sum of the transmission delays in the network flow. The analytical predictions agree with simulation results well, which show validity of the obtained analytical expressions.

This paper proposes analytical expressions of end-to-end throughput for IEEE 802.11e Enhanced Distributed Channel Access (EDCA) wireless string-topology multi-hop networks. For obtaining the IEEE 802.11e EDCA performance, internal collisions between Access Categories (ACs) in a node, frame collisions with external nodes, and frame-existence probabilities of buffers at each AC are expressed as functions of EDCA access parameters. Therefore, it is possible to obtain the effects of the EDCA access parameters to Quality of Service (QoS) support in the EDCA. It is possible to obtain the end-to-end throughput at any offered load with respect to each AC because the buffer states can be expressed according to ACs. The obtained analytical expressions are verified by showing the quantitative agreements with simulation results.