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When an adaptive array antenna is used in cellular and other mobile communication base stations for the purpose of improving SINR, the array antenna itself sometimes falls into a fading valley, resulting in failure to obtain an adequate improvement effect. While this problem can be solved by increasing the aperture length of the array antenna, simply increasing the aperture length alone increases the number of antenna elements, so that a large-scale adaptive array antenna becomes required, leading to the problem of failure of the weighting to track changes in the environment during fast fading. In this paper, we try to solve the first issue by making the element spacing nonuniformly aligned, reducing the number of elements. For the second issue, the weighting is divided into two layers, resolving the problem through both use of MMSE to eliminate interference and use of EGC for diversity combining. In a slow fading environment, however, favorable characteristics can be obtained when the entire weighting is controlled by MMSE. In this paper, we estimate the fading speed by the amount of envelope fluctuation in the desired signal after elimination of interference by the initial layer MMSE, and propose during slow fading the use of MMSE batch control, and during fast fading a control that incorporates both MMSE and EGC diversity combining. Finally, we use a computer simulation to evaluate the validity. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(12): 13–21, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20397 [ABSTRACT FROM AUTHOR]

The authors previously proposed a TDMA with parallel transmission (TDMA/PT) system in which several terminals can send packets in parallel in the TDMA system by controlling the transmission power of each terminal. In TDMA/PT, packets can be transmitted in parallel unless the packet sent by a terminal collides with that transmitted by the preceding terminal. Each terminal understands the positions of other terminals and can obtain transmission information about the preceding terminal. Hence, if a directional antenna is used in the TDMA/PT, it is possible to improve the performance by increasing the probability of parallel transmission. In this paper, a transmission algorithm is proposed in which directional antennas are used in conjunction with TDMA/PT. In TDMA/PT, only the parallel transmission of two terminals with contiguous IDs is considered, so that the probability of parallel transmission cannot be made very high. In this paper, a transmission algorithm allowing the parallel transmission of more than three terminals is proposed, and its performance improvement effect is discussed. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(1): 11–21, 1999 [ABSTRACT FROM AUTHOR]

Recently, the superresolution method has attracted significant attention as a high-resolution method of estimation of the electromagnetic wave propagation environment for mobile communications as well as various kinds of wireless communications. With regard to the array shape used in the estimation problem of direction of arrival, various array configurations in addition to equally spaced arrays have been studied. Weiss and colleagues have proposed a method of realizing a virtual equally spaced array by applying the EM method and the IQML method to nonuniform arrays. In this paper, the EM-MODE method based on this algorithm is proposed for estimation of the direction of arrival of the coherent wave by a nonuniform array and for improved processing. It is shown that improvement of the estimation success rate is possible by applying the improved processing in cases where estimation by the conventional EM-MODE method is difficult. The errors in estimation of the direction of arrival when this method is applied are studied. It is shown that much better characteristics can be obtained than when real elements are equally spaced. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(8): 47–56, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1117 [ABSTRACT FROM AUTHOR]

In cellular mobile communication, the same channel is shared by a number of cells. Up to now, the model has been considered where the same channel is used with a sufficient separation, so that the radiowave interference is sufficiently small for any call generated in the cell. Recently, on the other hand, a model has been proposed where the same channel is assigned independently of the specified cell separation, as long as the carrier-interference ratio is above a certain value. Although the assignment algorithm has been discussed for the traditional model, no report has been made on the detailed assignment procedure for the new model. With such a situation as the background, this paper proposes an application of Hopfield's neural net as an approach to the channel assignment in the new model and derives the energy function. Several results of computer simulation are shown where the proposed neural net is applied to the mobile communication model. It is not always true that the neural net produces the optimal solution, but it is interesting that an unexpected improvement of the channel utilization is observed in the communication traffic as far as the result of computer simulation is concerned. [ABSTRACT FROM AUTHOR]

In this paper, we applied combination channel assignment using the genetic algorithm (GA) to the channel assignment problem in mobile communications and performed evaluation tests. Combination channel assignment is a method combining the three assignment methods of repetition channel assignment, grouped channel assignment, and maximum channel assignment. A computer simulation tested a model with four patterns of the number of requested channels for 49 cells. In addition, the three assignment methods independently performed the channel assignment and at least two combined methods performed the channel assignment. The result showed that the number of channels used could be reduced by combination channel assignment compared to independent channel assignment using GA. And we demonstrated the ability to assign channels with hardly any effect on the assignment time when the number of cells was increased. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(7): 20–28, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20183 [ABSTRACT FROM AUTHOR]

To use finite spectral resources more efficiently, the cellular mobile communications method reuses frequencies (radio channels) repeatedly. With the cellular method, channel assignment that efficiently allocates radio channels to each base station while guaranteeing fixed communication quality becomes harder as the number of base stations grows, making it difficult to achieve optimization in a short time. This paper looks at the autonomous function for learning the channel used by each base station in autonomous distributed channel assignment and proposes a new channel assignment algorithm for determining channel assignments from the results that are obtained. It also clarifies the application results in a channel assignment system that incorporates the proposed algorithm. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 59–71, 2003; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ecja.1162 [ABSTRACT FROM AUTHOR]

In digital mobile radio, it is well known that the error control by block codes is effective for improving the code error performance in the multipath fading channel. Chase has proposed efficient soft decision decoding algorithms for block codes. In this paper, the word error rate performance of Chase's second algorithm using the received carrier level as CMI (channel measurement information) is described in the Rayleigh fading. First, the upper and lower hounds of the word error rate in the Rayleigh fading channel are derived theoretically assuming independent variations of received carrier level corresponding to each bit in a received block. The computer simulation results agree well with the theoretical results. Next, for the case where received carrier level variations are correlated, the word error rate performance is obtained by computer simulation using the Golay code as an example, and the bit-interleaving size required to make the variations of the received CNR statistically independent, and to randomize the errors occurring in a received block is calculated. [ABSTRACT FROM AUTHOR]

This paper considers the adaptive maximum-likelihood sequence estimation (MLSE) equalizer as a means of delay distortion compensation that is indispensable in high-speed signal transmission of megabit order in mobile communications. Improvement of the processing speed and reduction of the circuit scale are discussed. As a method for channel estimation we propose the quantized variable-gain least-mean-squares (QVLMS) algorithm, in which multiplication processes are eliminated by approximating the gain function in the VLMS algorithm by a power of 2. A method for reducing the circuit scale is also proposed, utilizing symmetry of mapping rotation in the PSK/QAM modulation. Based on the proposed method, a two-tap equalizer for QPSK modulation was constructed in the laboratory, and it is shown that the circuit can be realized at a scale of approximately 40 kgates even at the FPGA level. An equalizer was also constructed for a two-wave independent multipath Rayleigh fading channel with a transmission rate of 1.5 Mbits/s and a delay spread of 650 ns, and excellent performance was realized, reducing the floor error to less than 10–5 and completing initial convergence in eight symbols. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(10): 40–49, 1999 [ABSTRACT FROM AUTHOR]

One of the important problems in the development of digital land mobile communication is the suppression of the adjacent channel interference. Several methods have been proposed in the fixed microwave link and in other communication systems, which attempt to eliminate the interference wave to cope with the adjacent channel interference. In the land mobile communication link, however, the transmission characteristics are unknown and time-varying, for which no detailed investigation has been made. From such a viewpoint, this paper considers a system, such as land mobile communication, where the transmission characteristics are unknown, and proposes a method of optimal rejection of the adjacent channel interference, where the Wiener filter is constructed using the transversal adaptive equalizer. The effectiveness of the method as well as the de- tailed design are discussed. BPSK is employed as the modulation scheme with the data transmission rate of 16 kbit/s. Kalman algorithm is applied to the adaptive equalizer. The static characteristics are simulated by computer. It was confirmed as a result that the proposed method can suppress the distortion due to the adjacent channel interference and the intersymbol Interference by approximately 15 dB, for the channel spacing of 25 kHz and D/U = -30 dB. [ABSTRACT FROM AUTHOR]

Recently, land mobile communication has advanced significantly. In order to carry out transmission at higher speeds than ever, the problem of frequency-selective fading due to multipath propagation must be addressed. As a remedy, the use of an adaptive array is investigated. Of these adaptive arrays, the CMA adaptive array is known to have excellent interference suppression characteristics. The CMA was originally conceived for constant-modulus signals. However, from the point of view of efficient frequency use, the characteristics of the CMA for signals of nonsteady modulus such as 16 QAM signals have been recognized and operating examples have been reported. However, to date no discussion has been reported as to the excellent operation of the CMA for QAM signals. In this paper, by using the two-wave model, an operation analysis (multipath suppression and convergence) of the CMA for QAM signals is carried out theoretically. Also, computer simulation is carried out to verify the validity of the theoretical analysis. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 1, 80(11): 11–21, 1997 [ABSTRACT FROM AUTHOR]

Some means to cope with frequency-selective fading is indispensable to the realization of a wideband digital mobile communication, and various investigations have been made to this end. For example, the decision feedback equalizer (DPE) is considered promising, since it requires smaller- scale equipment and is versatile in applications. The application of DPE to mobile communication requires tracking to the times varying channel as well as the fast initial adaptation. Thus, comprehensive investigations, including the construction of the equalizer and tap-updating algorithm are needed. The Kalman algorithm is employed as the tap-updating algorithm. By introducing the memory factor into the algorithm, the tracking performance to the time-varying channel is improved as well as the speed of the initial adaptation. A computer simulation is made for the proposed method based on the model of 256 kbit/s TDNA system with QPSK modulation. It is verified that DFE is useful in compensate ing for the frequency-selective fading in mobile communication. [ABSTRACT FROM AUTHOR]

An antenna pattern diversity reception system was constructed experimentally as a means to cope with multipath fading in mobile communication, where the four-direction antenna is used as the diversity branches, which themselves have the fading reduction effect. The variable threshold switching method is employed as the output scheme from the diversity branches. The switching algorithm for the four-branch multithreshold reception is discussed. From the computer simulation based on the actually measured fading data, the optimal values for the parameters of the branch switching control algorithm are determined. A field experiment is made using the experimental system, and it is verified that the short-term fading is improved in the actual multipath environment with the value close to the theoretical value, for the selection switching by four receivers using uncorrelated branches with Rayleigh distribution. [ABSTRACT FROM AUTHOR]