Hiroki Shoki

Comparison of pre-FFT and post-FFT processing adaptive arrays for OFDM systems in the presence of co-channel interference

For future high-speed wireless communications using orthogonal frequency division multiplexing (OFDM), two major system requirements emerge: throughput improvement and elimination of rich interference. Adaptive array antennas can potentially suppress interference by using plural antennas and spatial coefficient adaptation. In addition, in the case of no interference, it is predicted that the adaptive array can improve either data throughput or potential coverage. In general, the pre-FFT (fast Fourier transform) domain diversity or beamforming in an OFDM system could be a reasonable solution for easy implementation with low complexity. However, in rich multipath environments for both desired signal and interference, the performance will deteriorate drastically. In contrast, it is possible for the post-FFT array processing to provide high performance even in such severe environments, at the cost of complexity. This paper presents a comparison of antenna array architectures for OFDM system using pre-FFT and post-FFT domain array processing, and clarifies the dependency of the channel property for each array processing. It is found that the performance of the pre-FFT array processing is strongly dependent on the total number of multipaths and interferences. Also, it is shown that it is possible for the post-FFT array processing to reduce the complexity by decreasing the number of antennas and the corresponding analog components because its performance depends on the number of signal sources, furthermore, since the proposed post-FFT array processing can achieve high performance with much lower complexity by using subcarrier clustering, it is a promising candidate for real implementation.

Optical subcarrier multiplexing transmission for base station with adaptive array antenna

We propose utilizing a radio-over-fiber technique of optical subcarrier-multiplexing transmission for radio base stations (BSs) with adaptive array antennas. The proposed system can be constructed at low cost since only one optical transmitter and receiver is required for a center station and a BS. Moreover, relative phases among antenna branches are insensitive to equivalent length fluctuation of an optical fiber.

Issues and Initiatives for Practical Deployment of Wireless Power Transfer Technologies in Japan

The Broadband Wireless Forum (BWF) was established in Japan under the guidance of the Ministry of Internal Affairs and Communications, Japan, to enhance future wireless technologies through collaboration involving industry, government, and academia. Wireless power transfer (WPT) is one of the key technologies expected to lead to the emergence of new business fields in the near future. In this context, the Wireless Power Transmission Working Group (WPT-WG) was formed in BWF to discuss problems concerning the commercialization of WPT technologies. In this paper, issues and initiatives of WPT-WG are presented.

Efficiency improvement of wireless power transfer via magnetic resonance using transmission coil array

The transfer efficiency between a transmission coil and a reception coil for wireless power transfer via magnetic resonance is a function of the orientation between the coils. When two coils share a single axis, the transfer efficiency is maximal, but otherwise the efficiency becomes lower. In this paper, a wireless power transfer system via magnetic resonance using a transmission coil array is proposed to improve the transfer efficiency. The transmission coils of the array are excited with appropriate phase weights by transmission circuit, according to the orientation among the transmission coils and the receiving coil. The effect of the proposed system is confirmed by simulation by a method of moment and measurement using a vector network analyzer.

A triangular loop antenna mounted adjacent to a lossy Si substrate for millimeter-wave wireless PAN

Millimeter-wave wireless communication is expected to be used for wireless personal area network (WPAN) for which a bit rate of 1Gbps or more is needed. Our goal is the development of an antenna suited to a WPAN terminal. Since a small, low-cost antenna with high radiation efficiency and a high gain in a wide- angle range is required for WPAN, the beam scan becomes unnecessary. In this paper, we propose a novel triangular loop antenna with a simple structure which has a feed point on to a semiconductor substrate.

A method to improve the correlation coefficient and the mutual coupling for diversity antenna

Wireless LAN systems employ diversity antennas to reduce the effects of multipath fading. When several antennas are provided in close proximity, the radiation patterns becomes similar to one another and the diversity gain decreases. Moreover, the radiation efficiency decreases due to mutual coupling between antennas. In order to increase the diversity gain, a method to improve the correlation coefficient among the antenna elements by mutual coupling between antenna elements has been reported (Sawaya, K. et al., 1982). However, this leaves the problem of a decrease in the radiation efficiency caused by mutual coupling. The paper proposes a new method to improve the correlation and the mutual coupling between antennas simultaneously. A slit is provided on a finite ground plane with antennas. The slit changes the current distribution on the ground plane. This change of current distribution causes differences between antennas in the radiation pattern and a pattern diversity effect is achieved. This diversity effect improves the correlation coefficient without applying mutual coupling. Additionally, by changing the current distribution, the mutual coupling is improved and the radiation efficiency increases under low correlation conditions.

Issues and initiatives for practical use of wireless power transmission technologies in Japan

Broadband wireless Forum (BWF) in Japan was established under the guidance of the Ministry of Internal Affairs and Communications, Japan, to enhance future wireless technologies with collaboration of industry, government and academia. Wireless power transmission technology is one of important technologies which will create new business area in the near future. From this background, Wireless Power Transmission Working Group (WPT-WG) was formed in BWF to discuss several problems concerning the commercialization of WPT technologies. In this paper, issues and initiatives of WPT-WG are presented.

A Study of Wideband Built-in Antenna using RF-MEMS Variable Capacitor for Digital Terrestrial Broadcasting

In this paper, the wideband properties of a proposed antenna with the low-voltage-actuated MEMS variable capacitor is shown by calculation and measurement. First the mechanism of the wideband properties of the proposed antenna due to the use of a dual resonant mode is clarified. Then, applying the MEMS variable capacitor, the properties of the proposed antenna are calculated and measured

A study of efficiency improvement of wireless power transfer by impedance matching

In wireless electric power transmission employing magnetic resonant coils, objects or debris in the vicinity of the coil cause impedance mismatching. The mismatching will decrease the transmission efficiency at the frequency for performing electric power transmission. We have investigated the efficiency improvement by impedance matching adjustment using variable lumped capacitors. In the present work, a loop is employed to excite the resonance coil, and a set of variable capacitors are added to the loop on the power transmission side to adjust the matching. For the test against a small object, a small aluminum plate was put close to the transmission coil, and the input impedance of the coil on the transmission side was adjusted by the variable capacitors. The test measurement showed that the adjustment of the input impedance substantially improved the efficiency at the power transfer frequency.

Bonding wire loop antenna built into standard BGA package for 60 GHz short-range wireless communication

The unlicensed 60 GHz frequency band is suitable for high-speed wireless systems with transmission rates of 1 Gbps or more. In this paper, we propose a bonding wire antenna built into a BGA package for 60 GHz short-range wireless communication. This antenna utilizes two bonding wires and a metal plate on an interposer in a BGA package and has a loop shape. The proposed antenna is built into a standard BGA package without special modification, so that it can be fabricated at low cost by conventional BGA package fabrication process. The first and unique evaluation of the antenna fully sealed by encapsulation resin was done by measurement. We describe the operation mechanism of the proposed antenna, the design procedure and the measurement results.