Recently, microwave and millimeter-wave bands have been considered for outdoor applications to cope with the emerging increase in communication traffic. However, a higher the frequency causes larger propagation losses. Consequently, a system that uses UAVs as relay stations to communicate in a line-of-sight (LoS) environment has been studied. In such a system, the numbers of transmitting and receiving antenna elements are different. In this study, we evaluate the performance of an asymmetric LoS-MIMO system with different number of antenna elements for transmission and reception. The effectiveness of the asymmetric LoS-MIMO system is demonstrated by comparing the channel capacity pertaining to the distance between the transmitter and receiver based on a conventional symmetric LoS-MIMO system with an equal number of antenna elements.
The purpose of this research is to share pedestrian information among multiple vehicles by vehicle-to-vehicle communication and detect the positions of all pedestrians around the vehicle. In the past, we have proposed a method of collating shared pedestrian information through image-based person Re-Identification (ReID). In this paper, in order to improve the accuracy of pedestrian information collation, the state-of-the-art ReID network is adapted to our scenario by fine-tuning. In addition, a new pedestrian image dataset for sharing pedestrian information was constructed. In our experiments using our dataset, the proposed method improved the pedestrian information collation accuracy.
In HTTP adaptive bitrate (ABR) streaming, the ABR algorithm is an important factor determining the quality of experience. Traditional ABR methods control the bitrate of individual clients autonomously so that the quality variation occurs even when the bandwidth of a delivery network is managed. Here, we propose a server-side ABR method achieving quality fairness among clients and suppressing a quality variation over time in networks where external applications dynamically control the quality of service. The method controls both the bitrate and delivery bandwidth based on a perceptual quality score. We evaluated the basic performance of the proposed method on an experimental network whose bandwidth could be controlled by the API. We confirmed that the proposed method could maintain the target quality within the upper-limit bandwidth and suppress the quality variation among clients and over time.
A Two-Dimensional (2D) vortex electrons sorting method that can be used for Orbital Angular Momentum (OAM) transmission is proposed, which can separate vortex electrons with different Topological Charges (TCs) into collectors in the 2D space. Compared with the traditional One-Dimensional (1D) sorting, the sorting distance can be increased from micrometer level to millimeter level, which reduces the inter-mode crosstalk and improves the sorting accuracy. Therefore, the better Bit Error Rate (BER) performance can be obtained for OAM wireless transmission demultiplexing.
For frequencies below 30MHz, electromagnetic interference (EMI) measurements are performed by measuring magnetic field components using a loop antenna. The field strength is given by the voltages read by an EMI receiver and the magnetic field antenna factor (MFAF) of the loop antenna. To measure the field strength accurately, the MFAF of the loop antenna is the most important parameter. In this paper, the basic characteristics of the MFAF of loop antennas for EMI measurements are described, especially its definition, height dependence above a metal ground plane, and directivity at frequencies below 30MHz.
Cloud coverage is one of the critical concerns for reliable hybrid free-space optic (FSO)/radio frequency (RF) based satellite communications. This adverse issue poses various challenges to the performance of the physical layer and different upper-layer protocols. This paper addresses the performance of transmission control protocol (TCP), which is one of the most essential transport protocols, over hybrid FSO/RF-based satellite networks in the presence of clouds. Specifically, the TCP throughput performance is analyzed under the impact of different cloud types. Also, different frequency bands of both FSO and RF used for satellite communications are investigated. The obtained results quantitatively demonstrate the severe impact of clouds on TCP performance over hybrid FSO/RF-based satellite networks.
The 5th generation mobile communication system (5G) incorporates the latest technologies such as OFDMA, LDPC codes and millimeter wave in addition to MIMO. In order to evaluate the propagation characteristics of such a complex system, it is very difficult to evaluate the propagation characteristics at multiple frequencies. In this paper, we propose a method for estimating the datarate of wideband MIMO systems such as 5G using narrowband signals such as CW signals. In this paper, we propose an extension of this method to multi-user systems, and show the effectiveness of this method by applying it to measured data.
This letter presents development of a magnetic field generator to evaluation of biological effects. The magnetic field generator has a frequency bandwidth of 85 kHz because it is intended for wireless power supply for electric vehicles. Furthermore, the generator is designed to operate for only one second, and can produce the induced magnetic field of 10 times compared to basic restrictions of the ICNIRP. By applying the magnetic field generator, it is possible to conduct a evaluation and verification of biological effect depending on electromagnetic fields for WPT systems of electric vehicles.
Designing an ICT system providing certain network application services (DICTS), which consists of selecting appropriate equipment for various requirements, optimal arrangements, and correct connections, needs specialized knowledge and enormous human power. Autonomous DICTS technology using deep reinforcement learning (DRL) has an elementary problem of huge learning time caused by accidentally overestimating a specific configuration because of the sparse reward despite a vast combination of selections, arrangements, and connections. This paper applies our improved Double DQN, a typical DRL algorithm to suppress overestimation, to an autonomous DICTS technology named Weaver and demonstrates the possibility of reducing the number of episodes until convergence by 25%.
In this study, we performed indoor location estimation using wireless LAN. The estimation method is based on the Finger Print method . We measure the database (DB) and user data (UD) using wireless LAN radio waves to improve the location estimation accuracy of Finger Print indoor location estimation. The Neural Network (NN) that compares UD and DB is ResNet (Residual Network), which is a derivative of CNN (Convolutional Neural Network). The number of layers that provide the best accuracy varies depending on the environment. To confirm this, we experimentally verified the relationship between the number of layers and the estimation accuracy in different environments, and clarified the design method.
A noncoherent multiple-input multiple-output (MIMO) method that is effective in high mobility environments is proposed based on Grassmannian MIMO signaling, which is a well-known noncoherent MIMO scheme. The proposed method leverages the property that the Grassmannian can be decomposed into non-overlapping parts called Schubert cells, and assigns information to the Schubert cells for transmission. Furthermore, a multi-resolution MIMO system that incorporates the proposed method is developed, and its error performance is evaluated. The results show that the information assigned to each Schubert cell is correctly decoded even at the normalized Doppler frequency fdTs=0.1 in the multi-resolution MIMO system.