A reduction in mutual coupling (hereafter referred to as decoupling) is required to enhance the transmission performance of antennas in multiple-input multiple-output (MIMO) devices. In our previous study, a decoupling method was proposed that utilizes parasitic elements and a bridge line to reduce the mutual coupling between two planar inverted-F antennas; however, the decoupling principle of the proposed method was not quantitatively discussed. Therefore, in this study, we utilize a method called characteristic mode analysis (CMA) to quantitatively discuss the decoupling principle. Furthermore, based on the clarified decoupling principle, we propose another decoupling method using four inverted-L-shaped elements, which are placed on the ground plane of the PIFAs. As a result, the mutual coupling between two PIFAs can be reduced from −6.6 dB to −10.2 dB. Therefore, the total antenna efficiency can be improved from 77.4% to 86.1%.
If mobile nodes such as vehicles and pedestrians deliver information by direct wireless communication between mobile nodes and movement of mobile nodes carrying information, disordered and unnecessary spread of information arises. To overcome this problem, a method to permit mobile nodes to transmit information only in transmittable areas has been considered. This method is called Information Floating. Theoretical analysis of Information Floating is important because it is necessary for some purposes such as control of the size of a transmittable area, and has been studied in various situations. In this paper, we consider Information Floating by pedestrians walking toward opposite directions along a street, and theoretically analyze performance of Information Floating under the assumption that the communication range changes due to the positional relationship between mobile nodes because the mobile nodes themselves become obstacles. From the numerical results, we show that degree of effects of the assumption that mobile nodes themselves become obstacles on performance of Information Floating depends on the densities of mobile nodes and the difference between the densities of mobile nodes moving toward the opposite directions, and show effectiveness of the proposed theoretical method. Based on these results, we show a method to decide the size of a transmittable area suitable to the situation where mobile nodes themselves become obstacles.
In order to avoid data packet collisions due to hidden terminals, the wireless LANs practically use a method under which short control packets called RTS and CTS are exchanged prior to every data packet transmission. Under the method, since short control packets may collide, the invalid time due to collision will be shortend even if a collision occurs. However, since the transmission time of RTS is much longer than the slot time, the waiting time of a hidden terminal may expier during the RTS transmission. That causes frequent occurrence of collisions especially under many hidden terminals. In this paper, in order to solve that plobrem, we propose a method which reduces collisions by modifying the timing of sending out RTS packets, and show its effectiveness via simulation.
In this study, a three-dimensional flight trajectory simulator of a table tennis ball was developed. The target movement of the table tennis ball is the flying and falling motion after the ball has been hit with a racket. In this flying and falling motion, aerodynamics (drag, lift, fluid torque) act on the table tennis ball in addition to gravity. In this study, the aerodynamic characteristics (drag coefficient, Magnus coefficient, fluid torque coefficient) of the table tennis ball required for the calculations were determined using computational fluid dynamics (CFD) analysis and interpolation. The motion state of the table tennis ball was expressed by a physical motion model considering gravity and aerodynamics. The flight orbits obtained by the simulation showed the expected three-dimensional trajectories of left rotation and downward rotation that were obtained using a physical motion model, whilst reflecting various characteristics.
When a crowd tries to escape from a room in life-threatening situations such as fires, the passage through doors becomes crucial in determining the evacuation efficiency. The architectural designs of the room influence to a large extent the evacuation process. In this paper, we investigate the possibility to reduce the evacuation time by proper placements of suitable shaped obstacles. Our simulation results clearly demonstrate that appropriately placing two pillars on both sides of the door is an effective strategy to make the pedestrian flow smooth, hence facilitating the evacuation process.
In this paper, we verify an improvement of the bipedal robot's locomotion by equipping with mechanical modular devices. We assumed that the robot model consists of five rigid links in sagittal plane, and the robot is assumed to be fully-actuated. The walking gait and the optimal parameters of the devices for the biped model are calculated by the method of trajectory optimization, and the performance of the gait is evaluated by Cost of Transport, which indicates the walking efficiency. We compare the performance of the devised robot model's gait with a nominal five-link model's one with numerical simulation.