Introductions of dynamic control of the systems are expected for mobile communications in time, space, and frequency domains. The adaptive antenna is effective for control in space. The dynamic zone configuration will be a new application area in which, depending on the distributions of the users, the zone shape is varied.
In this study, we examined the microwave power transfer to sensors in car engine compartment. First, we calculated the transmission efficiency in free space. We changed a transmission distance, and confirmed a theoretical limit value of the transmission efficiency in free space. Second, we simulated the transmission efficiency using the cuboid engine compartment model. From simulation results, we confirmed that transmission efficiency was increased by the multiple reflections and that transmission efficiency was decreased by the engine between transmitting (Tx) and receiving (Rx) antennas. Finally, we simulated transmission efficiency using the real engine compartment model. Changing the direction of the antennas, and obtained 2.8% of the highest transmission efficiency in the required antenna position. In addition, changing the position of the Tx antenna, we obtained 7.2% of the highest transmission efficiency.
Effective use of frequency is extremely important for land mobile communication where the number of users is steadily increasing. One means of achieving frequency efficiency is to employ the microcell in which the service area is subdivided into a minimum unit to increase geographical frequency reuse. One implementation of the microcell system is to position the base-station antenna at a level below the tops of surrounding buildings. Estimation of the radio wave propagation characteristics is indispensable for implementing such a microcell system.In this paper, a method of estimating the wave propagation characteristics between arbitrary transmission and reception points based on a building database is modeled theoretically on a computer using geometrical optical methods such as the geometrical theory of diffraction (GTD). Up to two reflections and diffractions are considered. Comparison of theoretical and measured results of the estimated propagation loss show that the estimated average error was less than about f 10 dB for distances of less than 500 m from the transmitter to the receiver for streets on which the transmitting antenna is visible from the receiving antenna. By contrast, the error was about +20 dB to -10 dB within 600 m on a street crossing one where the transmitting antenna is visible.
Fax: $81 423 27 6953 ,4bst~act-To realize wireless multimedia communication networks, new MAC (Medium Access Control) protocols are required and the MAC protocols for the integration of voice/data are now being studied. This paper proposes a MA4C protocol called R-ISMA (Reserved Idle Signal Multiple Access) for the integration of voiceldata in wireless information networks. To meet the requirements of wireless multimedia communication. the R-ISMA protocol can handle both the voice traffic and data traffic from various sources, i.e., from terminals with different generation rates. We describe this protocol, then evaluate the system performance by using the TFA (Transient Fluid Approximation) analysis. The R-ISMA is shown to perform better than the I-ISMA (ISMA for Integrated services) protocol.
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