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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.

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.

Group detection (GD), the combination of maximum likelihood (ML) decoding and linear processing for multiple antenna systems, has been shown to attain reasonable performance and practical complexity. However, the diversity gain of conventional GD degrades since the degrees of freedom at the receive antennas are exploited for the linear processing before the local ML search. This paper proposes a novel GD with overlapped grouping. The proposed GD employs selection diversity within the overlapped signals by using the likelihood value, after the local ML search. Therefore, the proposed GD can achieve higher diversity gain compared with the conventional GD.

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.

This paper proposes a new path diversity method using an adaptive array with directional antennas for high bit rate mobile communications. The proposed scheme selects some optimum elements from plural directional antennas based on the results of all delay profile estimation, and combines some outputs of the adaptive array for each delayed wave. Therefore, interference waves can be suppressed by this space-time processing approach with less processing power. Computer simulations show that the performance of the proposed scheme can be improved drastically by the path diversity combining method which minimizes mean square errors, even if delayed waves are incident from the same directions as a direct wave.

This paper reports the configuration of a smart antenna receiver testbed for land mobile communication base stations and the experimental results obtained for it. The antenna pattern and bit error rate (BER) are measured in a radio anechoic chamber. These results show the interference can be suppressed effectively by beamforming using an adaptive algorithm, e.g., LMS or CMA.

MUSIC (multiple signal classification) has been widely used to estimate the direction of arrivals (DOAs) accurately. However, this method requires a large calculation time for eigen-decomposition of the covariance matrix. This paper presents a high-speed DOA estimation based on the beamspace MUSIC, which can reduce the order of the covariance matrix. The proposed method implements a two-step DOA estimation. The first step is the coarse estimation in which the DOAs are roughly estimated. The second step is the fine estimation in which the result of the coarse estimation is exploited and the DOAs are accurately estimated.

A new adaptive null forming algorithm for phased arrays has been proposed. The algorithm to control phase weights, based on constrained power minimization (CPM), uses only the array output power and does not require the complex baseband signals from individual array elements. The derivation of parameters for the iterative control from the deviation of the array output power by phase weight perturbation is described. Numerical simulations show that the proposed algorithm can direct a null to an interferer while maintaining the gain to the desired signal.

The analysis of a cross-slot-coupled circular microstrip antenna is presented. The approach is based on the reciprocity theorem and the exact Green's functions for the antenna structure. The equivalent circuit of the antenna was obtained. The calculated results for antenna input impedance were compared with the measured data.