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It is expected that mobile-radio systems will play an important role in realizing general personal communication networks through ISDN. In the near future, the so-called mobile ISDN era, it is necessary to have come mon performance objectives between mobile radio links and fixed (or fiber) links and have a common assessment method for data transmission quality. In this paper, based on the ITU-T definition, unavailability statistics are examined in mobile-satellite systems which are characterized by low margin systems. The characteristics of signal degradation due to propagation impairments in maritime, aeronautical, and land mobile sateffite services are examined. Through this analysis, the importance of differentiation between unavailability and 'signal degradation in available time' is emphasized when the digital signal transmission quality is evaluated. [ABSTRACT FROM AUTHOR]

In this paper, a typical mobile communication environment is assumed and the eigenvalue distributions of the correlation matrix of a MIMO channel with the spatial correlation of the multipath taken into account are studied by simulation. Based on this study, a simple method is proposed for accurately deriving the probability distribu- tion of the largest eigenvalue of the correlation matrix. The proposed approximation equation is compared with simu- lation results and good agreement is obtained. In order to understand the information transmission capability of MIMO in a multipath fading environment with spatial correlation, the proposed equation is used for studying the effect of the spatial correlation on channel capacity. Finally, the digital transmission characteristics (relationship be- tween the BER and the CNR) with correlation taken into account are obtained. [ABSTRACT FROM AUTHOR]

In this paper, we propose a beamspace adaptive array antenna for broadband signals with a wide fractional bandwidth. The proposed beamspace adaptive array antenna has a multiple digital beamforming network that preserves spectral components of input broadband signals by using tapped-delay-line circuits. Coefficients of the tapped-delay-line circuits are determined such that each broadband digital beamforming network has the same phase characteristics, and the beam pattern including sidelobe and null characteristics is virtually frequency independent. A few adaptive weights, which are linear combination coefficients of the selected broadband beams, follow a beam selector. The number of adaptive weights for the proposed adaptive array is considerably less than that of an element space structure with tapped-delay-line circuits. We demonstrate by computer simulation that interference suppression by the proposed beamspace adaptive array is as good as that of an element space adaptive array and that it has much faster convergence. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(10): 38–48, 1997 [ABSTRACT FROM AUTHOR]

Adaptive arrays for spatiotemporal signal processing are expected to be effective multipath measures in future high-speed mobile communications systems. However, a problem is the tremendous computational load in a hardware implementation because the number of weights that are adaptively controlled becomes extremely large. Therefore, the key to its practical use is to reduce the computational load. In this paper, an adaptive array for processing subband signals that can substantially reduce the computational load was implemented in hardware by using a commercially available digital signal processor (DSP). First, we illustrated the scale of the hardware by the number of DSPs needed in each unit that performed the required signal processing. Next, we built a simple multipath environment of two waves in an anechoic chamber and performed experiments to demonstrate the basic performance and verified that performance nearly equal to the theoretical values was obtained. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 85(10): 19–30, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.1122 [ABSTRACT FROM AUTHOR]

With a view to application to array antennas for mobile stations in a mobile satellite communication system, a method is proposed for configuration of a receiving diversity array antenna acquiring a communication beam quickly and tracking with stability by means of the digital beam forming (DBF). In this method, an active array is assumed. The receiving phase difference between the antenna elements is detected by digital complex operation for the received baseband signal. Based on this phase difference, the phases of the antenna elements are made in phase in a relative sense so that equal gain or maximal ratio combining is accomplished. As a result, the main beam can be formed in the direction of the arriving wave. In addition, in the case of maximal ratio combining the radiation pattern is oriented toward the multipath arriving waves so that communication quality is improved as the beams are further combined in phase. In this paper, the effectiveness of the present method is demonstrated by the numerical simulation assuming a mobile communication environment with band-limited QPSK signals. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(10): 88–100, 1997 [ABSTRACT FROM AUTHOR]

A digital beam-forming antenna (DBF antenna) used for mobile wireless communications has drawn considerable attention in conjunction with device technology advances. Effective use of the frequency spectrum by means of multibeam antennas and adaptive antennas for mobile communications has also been discussed. With regard to DBF antennas, an offline trial process by means of a workstation and trial fabrication of a general-purpose DSP have been reported. However, to satisfy the high functionality and high-speed operation required for a DBF antenna, an application specific integrated circuit (ASIC) for the digital signal processing section must be realized. The ASIC described here is configured from a digital signal processor that uses a gate array called an FPGA, which can be developed by the user. The gate size necessary for circuit configuration obtained by a trial fabrication is explained and performance for a one-chip ASIC realized with a similar design is discussed. Experimental results are shown for real-time multibeam forming in a large anechoic chamber using the trial system. Confirmation of automatic tracking by means of maximum received beam selection is also shown. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80 (2):100–111, 1997 [ABSTRACT FROM AUTHOR]