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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]

This paper proposes a beam pattern selection diversity technique using an adaptive array antenna. In the system using an adaptive array antenna, beam control in the uplink is carried out for all terminals in the cell. Hence, it is necessary to determine the antenna weights for all terminals at the base station, so that the amount of computation is increased and the base station configuration becomes complex in a cellular system that seeks to be capable of handling as many terminals as possible. In this paper, the beam patterns are generated only for a limited number of terminals in the cell, while other terminals share the generated radiation patterns, so that the amount of computation can be reduced substantially. In general, in a system using an adaptive array antenna, the interference suppression capability is significantly affected by the angle of arrival of the propagation channel. In this paper, the angle of arrival of the channel is modeled by a normal distribution and the proposed system is investigated in a micro-cell environment. As a result of numerical simulation, it is found that the proposed method can reduce the processing effort by 20% in the micro-cell environment, while the characteristics are sufficiently competitive with the results obtained when optimum radiation patterns are generated for all terminals. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(5): 32–41, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10020 [ABSTRACT FROM AUTHOR]

In cellular communication systems, every call is carried through a base station, and when the communication path to the base station is obstructed by buildings or other obstacles, the communication may not be established. It is expected that ad hoc relaying of such an obstructed call will increase the performance of the network as a whole. This paper discusses how to theoretically analyze the communication traffic performance of a cellular system with ad hoc networking and shows that the network performance can be increased even with relatively small range of relaying capability of terminals. This paper also shows by simulation that multihop relaying does not give significantly greater performance improvement than that by two-hop relaying. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(11): 1–10, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10135 [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]

With the development of mobile communication, active research is being done on the small-sized antennas such as microstrip antennas (MSAs). Moreover, MSAs normally are placed on spherical or cylindrical surfaces as a conformal antenna. Conformal MSAs are expected to have different characteristics compared to planar structure. In this case, numerical analysis is needed before the actual experiment. The method of analysis which has wide applications may be considered as efficient for this purpose. One such method is the conformal grids finite-different time-domain method (FD-TD method). In this paper, an MSA on a curved surface is analyzed using the conformal grids FD-TD method. Moreover, comparison with the experimental values also is performed. The experimental results and the analytical results ate in close agreement which shows the validity of the method of analysis. As a result, it is confirmed that in the range of this paper, the input impedance and radiation pattern varies from their values for the planar patch when the patch surface is curved. [ABSTRACT FROM AUTHOR]

Transmission channels in mobile communication are extremely unstable due to the effect of multipath fading. Therefore the realization of high-reliability communication necessitates the introduction of error control in the form of error-correction coding. This paper considers the decoding of error-correcting codes that are adapted to digital mobile communication operating under Rayleigh fading conditions. A soft decision Viterbi decoding using the received carrier level is studied for the case of convolutional codes. This soft decision method is based on the level of the received carrier by adaptively determining the metric used in the decoding. In this way a metric is obtained for digital mobile communication. This paper also presents an estimation method using error exponent which provides effective means to realize such a soft decision method. If the channel can be considered memory less due for example to interleaving, then this method provides an easy way to estimate: (1) the figure of merit for quantizing thresholds, and (2) the gains of the soft decision. First, it is shown that using this kind of estimation in the case of channels which can be considered sufficiently memoryless due to interleaving, extremely large gain is obtained by the soft decision method discussed in this paper. Next, simulations are performed and the efficiency of the estimation method is demonstrated. Finally, the bit error rate characteristics are shown for the case when the channel is not made sufficiently memoryless by interleaving. [ABSTRACT FROM AUTHOR]

This paper considers a multicarrier system performing burst transmission and discusses the channel estimation method, together with the estimation accuracy. In a multicarrier system such as OFDM, the channel state information of each subcarrier is estimated using a known signal, and then the signal is detected. Consequently, the accuracy of channel estimation has a large effect on transmission performance. Furthermore, in an MC-CDMA system in which OFDM is combined with code spreading in the frequency domain, the signal is also synthesized by using subcarriers in the receiver on the basis of the subchannel information. Thus, the signal quality after despreading depends greatly on the accuracy of channel estimation, and it is an important issue to establish a channel estimation method suited to a multicarrier system and to evaluate its accuracy. This paper considers channel estimation in the time domain based on correlation calculation for the known signal and channel estimation in the frequency domain using the FFT of the known signal. The accuracy of estimation is derived analytically, and a method of reducing the computational complexity is proposed. Finally, the receiver performance is derived quantitatively by computer simulation, assuming that these channel estimation procedures are applied, and the effects of these methods on the quality of the received signal are analyzed. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(4): 10–21, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20261 [ABSTRACT FROM AUTHOR]

The application of adaptive array antennas in wireless base stations in cellular mobile communication systems is studied to improve frequency utilization. Since the propagation path information differs in the uplink and the downlink in Frequency Division Duplex (FDD) where the carrier frequencies in the downlink and uplink differ, the method for generating the antenna weights for the downlink is an important topic of study. In this paper, we propose a method that measures the location of the mobile station via the uplink (direction and distance from the base station) and controls the antenna weights of the downlink based on that information. Then we clearly show the improvement in the receive CINR performance in the mobile station when the proposed method was applied to a DS-CDMA cellular system. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(2): 57–68, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20199 [ABSTRACT FROM AUTHOR]

Channel efficiency can be improved by transmission that integrates voice and the data. When this idea is applied to multicellular systems, channels must be assigned so that the intercellular interference power is minimized. Furthermore, channels must be provided with priority for voice calls, since real-time transmission is required. As a system that considers these requirements, this paper investigates a method of reducing intercellular interference in a circuit switching system with channel segregation in which data are transmitted with priority, using the silent period of voice calls. It is shown by computer simulation that the proposed method can improve performance characteristics such as the interference rate, blocking rate, forced termination rate, and hand-off rate. [ABSTRACT FROM AUTHOR]

This paper considers the application of optical wireless communications to mobile communications. We consider an optical mobile communications system using cycle emission cells and allowing a reduction of the shadowing effect, which is a problem in optical wireless communications. The proposed system uses multiple transmitters with cycle emissions (DTCE). By varying the number of transmitters, the error rate performance is compared via computer simulation. It is anticipated in particular that when the proposed method is applied to mobile communications, multiple transmitters will be placed in the service area, and the distance between the transmitters and the synchronization among the transmitters will greatly affect the error rate performance. The performance is calculated by varying these parameters via computer simulation, and the results are evaluated. Furthermore, the result is compared to other models which have been proposed in order to reduce the shadowing effect, and the effectiveness of the DTCE system regarding optical wireless mobile communications is demonstrated. [ABSTRACT FROM AUTHOR]

This paper analyzes the down-link of a DS-CDMA system and clarifies the relationship between the system capacity and base station transmitter power, while taking handover and transmission quality into account, when the base station transmitter power control is suitably controlled so that the instantaneous SIR of mobile stations will be uniform in relation to traffic channels in a model that simultaneously considers the traffic channels and common control channel. This paper also shows that system parameters can be easily optimized if the derived equations are used. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(6): 84–103, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1167 [ABSTRACT FROM AUTHOR]

This paper discusses the method for direction-of-arrival estimation by an application of 2D-ESPRIT to a triangular planar array with an equilateral triangular lattice arrangement often used as a phased array for direction finding. It is difficult to apply the 2D-Unitary ESPRIT to the triangular array due to its element arrangement. Instead, the 2D-ESPRIT based on the standard ESPRIT is used. As the paring method for a multidimensional ESPRIT, the complex pairing (CP) method, simultaneous Schur decomposition (SSD), and mean eigenvalue decomposition (MEVD) have been proposed. In the case of 2D-Unitary ESPRIT, the simple CP method can be used for an extremely accurate estimation. Since CP cannot be used for the standard ESPRIT, SSD with a high computational load and MEVD requiring introduction of a reliability test need to be used. In this paper, as a pairing method of the signal parameters, a complex mean eigenvalue expansion method is proposed that does not require a reliability test and has a low computational cost. Through computer simulation, the azimuth angle and the elevation angle of multiple waves are estimated simultaneously so that the method's effectiveness is verified. A radiation pattern synthesis for separate reception of multiple waves is attempted with multiple beam forming weights obtained in the process of 2D-ESPRIT. The effectiveness of the synthesis method is confirmed. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(6): 59–68, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10016 [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]

Car antennas for road vehicle communications systems should be able to receive constantly the signals of beacon antennas at positions from just below the beacon antenna to a great distance along the road. In this paper, we restrict the discussion to the case of microstrip antennas and investigate what kind of patch shape is suitable for car antennas used in road vehicle communications systems. As a measure for evaluating the receiving power level, we define and use the “effective directivity,” which takes account of the distance between the beacon antenna and car antenna and the relative arrangement of both antennas. This effective directivity represents the effective received electric field intensity. We examine various patch shapes from the viewpoint that the desirable ones have constant effective directivity irrespective of car position. As a result, three types of simple-structure higher-order-mode microstrip antennas are proposed. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(11): 54–60, 2001 [ABSTRACT FROM AUTHOR]

CMA adaptive arrays operate well and have an excellent unwanted wave suppression capability if the desired signal has a constant envelope characteristic. Therefore, their application to mobile communication is expected. However, although no prior knowledge of the reference signal is required in CMA, it is not possible to predict which signal is acquired if other arriving waves have constant envelope characteristics. Therefore, there is a possibility that an interference wave arriving from a completely separate source may be acquired in error. Therefore, in order to constantly guarantee the communication quality, the acquisition characteristic for the desired wave needs to be improved. As a plan for improvement, this paper sets a constraint to protect the desired wave by means of the cyclostationary properties of the modulated signal and proposes a correlation constrained CMA adaptive array based on incorporation of this constraint into CMA. The acquisition characteristics of the desired wave and the unwanted wave suppression capability are studied by means of a computer simulation, and the effectiveness of the proposed system is confirmed. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 84(4): 48–56, 2001 [ABSTRACT FROM AUTHOR]

Concerning information access for portable terminals, various methods of managing positional information as well as access methods are considered. Which is the optimum of those methods depends on network conditions, such as the speed of movement of the mobile host and the number of access requests to the mobile host. This paper is concerned with data queries in a mobile computing environment. The performance is evaluated for a system which can select the movement notification method in order to manage the position of the mobile host when the movement of the mobile host is detected, and the query processing method to process the query to the mobile host, from several alternatives. This paper presents a system in which these methods are dynamically switched in order to reduce the traffic over the whole network, and presents analytically the selection principle based on network conditions. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 83(4): 34–43, 2000 [ABSTRACT FROM AUTHOR]

In a low-antenna-height line-of-sight (LOS) microcell, the delay spread characteristic strongly depends on the road shape, the location of the transmitting and receiving points, and so on. To analyze this propagation mechanism, it is necessary to deal with location-specific properties. This paper describes analyzed results for the multipath delay mechanism in a rectilinear street with intersections where both transmitting and receiving stations exist. Special focus is placed on reflection at LOS building walls and on diffraction at building corners at street intersections, and their effect as a factor creating multipath delay is investigated numerically. We show that waves created by their reflection and/or diffraction are significant multipath delays making a major contribution to delay spread in microcells. This paper also presents a comparison between the calculated and measured delay spread, and discusses the effectiveness of the propagation mechanism described. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 82(4): 56–70, 1999 [ABSTRACT FROM AUTHOR]

This paper proposes a new loop antenna for circular polarization with a single feed. It is an unloaded loop antenna with a peripheral length of one wavelength and uses a compound-wire loop in which adjacent wires have different cross-sectional structures. This antenna is considered as a transmission line above a ground plane and analyzed as an equivalent circuit in which the different cross-sections of the wires are represented by different characteristic impedances. Using the transmission-line model, the condition for circular polarization is derived in terms of the characteristic impedances and the antenna height. Then, as a simple example, a loop antenna with composite radius and a circular cross-section is designed, and the relations among the antenna height, radius ratio, and the input impedance are investigated. The results are discussed and compared to the results of numerical analysis by the method of moments. Then, providing a proof of the effectiveness of the proposed method, an experiment considering the feeding structure is also described; the results agree well with the theory. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(5): 42–50, 1999 [ABSTRACT FROM AUTHOR]

In the signal transmission of land mobile communication, the received electric field is affected by multipath fading due to multipath propagation, and the transmission quality is degraded. A diversity reception of some type can be an effective technique against this fading. This paper analyzes theoretically the improvement possible using two-branch switched diversity against the cochannel interference and thermal noise when voice signals are processed by compander and are transmitted by PM. When the baseband SNR (signal-to-noise ratio) under fading is 15 dB, the improvement effects against thermal noise and cochannel interference are 9 dB and 4.5 dB, respectively. When the SNR is 10 dB, they are 7dB and 3 dB. Furthermore, we show that the optimum switching level maximizing the baseband SNR exists and depends on CNR (average carrier-to-noise ratio), and CIR (average carrier-to-interference ratio), and the modulation level. [ABSTRACT FROM AUTHOR]

This paper discusses the communication traffic characteristics of Dynamic Channel Assignment (DCA) in cellular mobile communication systems. In general, it is difficult theoretically to analyze the communication traffic characteristics of DCA. This paper proposes an approximate method called clique packing, for analyzing the blocking probability performance of an idealized DCA. For calculating the blocking probability of clique packing, an approximate formula is derived which is based on the Erlang B formula and is in a simple form. It is shown that the numerical results of the approximate method agree with computer simulation results. An approximate analytical method for calculation of the blocking rate el practical DCA methods such as the first-available method also is proposed. To calculate the blocking rate of the practical DCA methods, the simple formula for clique packing is used after modeling the practical DCA methods as clique packing. It is shown that the modeling is appropriate. This modeling enables the blocking rate of the practical DCA methods to be calculated by using the approximate formula for clique packing. [ABSTRACT FROM AUTHOR]

In a cellular mobile communication system, a service area is divided into many cells for efficient use of channels. It is necessary to take into consideration intercell vehicle movement for teletraffic performance evaluation of such cellular mobile communication systems. Its performance evaluation has been done for a one-dimensional band-shaped area, e.g., a highway, assuming that vehicle movement is one way. This paper presents a theoretical performance evaluation of a one-dimensional band-shaped area, assuming two-way vehicle movement. First, whether steady-state performance for the traffic offered to each cell is constant is analyzed and then the transient characteristic for the case in which traffic varies with time is analyzed. Through a comparison of theoretical and simulation results, the validity of the theoretical result is demonstrated. [ABSTRACT FROM AUTHOR]

Land mobile communications systems that implement spread spectrum are being actively researched. With direct-sequence spread spectrum, performance is predicted to improve by dividing a multipath delay wave into separte paths, using path diversity combining, and so-called path diversity receiver. Generally, although performance improves with an increase in the number of branches in a diversity system, a small number of branches is preferred with the implementation of a receiver. Hence, this paper analyzes the performance when n = 2 for a model of a path diversity receiver where n = paths are selected from M candidate paths in order of the largest instantaneous signal-to-noise (S/N) ratio, and bearing in mind the receiver that produces the maximal ratio combining. The results show that there is no significant differences between n = 4 and n = 2 when M = 4. The average power delay profile shows the number of effective branches when applying a system of n = 2 branches to path diversity for both the exponential and rectangular models. Also, the theoretical value for the BPSK and FSK average bit error rate performance is determined for a primary modulation system with the rectangular model. [ABSTRACT FROM AUTHOR]

This paper proposes the differential detection type direct sequence/code-division multiple-access (DS/CDMA) adaptive interference canceller (AIC) that can track the fast fading. The proposed AIC is composed of the fractionally chip-spaced code-orthogonalizing filter (COF) with tap length corresponding to several bit periods and the differential detector. The COF makes adaptively the tap weight orthogonal to all spreading codes of other users as a despreading code of the desired user so that the interferences from other users are cancelled and the signal component of the desired user is extracted. The differential detector compensation the carrier phase variation due to finding in the desired user's signal at the COF output. By such a structure, the tracking performance of AIC to the channel variation can be improved to the limit of the tracking performance of the differential detector. This paper evaluates the basic ability of the proposed AIC in the fast-fading channel. The AIC is especially expected to be utilized in the DS/CDMA mobile communications since the receiver is of the signle-user type, where no information concerning other users is needed. [ABSTRACT FROM AUTHOR]

Efficient handover during both mobile telephone and portable telephone communication is a technology essential m implementing ideal mobile communications. However, there exists the possibility of a transmission data slip during the process of circuit switching, which has become a problem in communication using terminal machines such as data modems and FAX machines connected to mobile telephones and portable telephones. In this paper, a transmission data slip accompanying route changes reside digital exchanges in a handover during telephone communications is assumed; it is shown on the basis of this assumption that a lag in synchronism occurs m the receiver terminal equipment. Then a sync lag of the receiver terminal modem during handover has been confirmed by tests using actual analog cellular phones and a transmission data slip has been shown on the basis of the results of the tests. In this paper, a synchronism control method minimizing the sync lag has been studied. The efficacy of this method has been confirmed as a result of applying the method to a mobile telephone FAX modem. [ABSTRACT FROM AUTHOR]

The dual-frequency antenna with the same beam- width is well suited to the mobile communication base station antenna. One candidate is a corner reflector antenna whose elements are connected to a parallel feed line. However, no design equations or analysis have been published. This paper corrects this deficiency through analysis of the characteristics after integration of the two factors, spatial coupling and transmission line, for this antenna. A two dual-frequency corner reflector antenna is designed. One uses co-phase feedlines and is a wide band sector-beam antenna with a 3 dB beamwidth difference of 300 in the field pattern of horizontal plane and a return loss of less than -15 dB over a wide frequency range (from 900 MHz to 1.5 GHz). The other uses antiphase feed lines and its beamwidths can be varied by changing the corner angle while the beamwidths are coincident at two frequencies. [ABSTRACT FROM AUTHOR]

This paper proposes a high-accuracy positioning service for terrestrial mobile communication systems which employs the global positioning system (GPS) with the differential method (DGPS). The proposed system provides a high-accuracy navigation service to land-based mobile communication users. The proposed system also provides a comprehensive vehicle control service to the transportation companies when both forward and return links are available in the terrestrial-based mobile communication systems. This paper also assesses the performance of the DGPS method by computer simulations and a field experiment in an urban area to identify the viability of the proposed system under an actual environment. The relationship between average hinging time rate and the average visible number of satellites in various operating environments also is investigated. [ABSTRACT FROM AUTHOR]

This paper studies the system performance of a zone-structured packet radio network with mobile terminals to which the slotted ALOHA protocol is applied. Conventional performance analyses of the zone-structured packet radio network have not considered the effect of terminal mobile speed. Here, a model is developed for such a zone-structured network where a Markov model is used as the mobility model of a terminal and analytical techniques to evaluate static and dynamic performance of the system are presented. Numerical results and their intuitive interpretations are discussed to examine the effect of zone overlapping, mobile speed, etc. [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]

This paper investigates an adaptive equalizer with career frequency offset compensation for digital mobile radio transmission over several tens kbit/s. The performance of conventional adaptive equalizers for mobile radio severely degrades for receiving signals having carrier frequency offset which is mused by local oscillator frequency offset due to misadjustment, temperature dependence, and aging. Carrier frequency offset compensation for TDMA burst signaling requires both accurate and short-time measurements. However, both requirements have a trade-off relationship and must be optimized. This paper proposes the carrier-acquisition-during-training (CAT) algorithm for transmissions allowing a training signal. First, two basic configurations and their equivalence are discussed. Next, computer simulations and real-time experiments with one-chip DSP show the effectiveness of CAT by demonstrating training convergence, optimum parameter characteristics, and average BER performance under two-path selective fading with one-symbol delay difference and independent Rayleigh components. [ABSTRACT FROM AUTHOR]

This paper reviews recent worldwide activities concerning research and development for spread spectrum communication technologies. Included are various novel proposals, remits of analysis, and experimental results concerning spreading code, synchronization, device, system construction, and applications to consumer and mobile communications. For the spreading code, however, two invited papers are presented in this special issue and hence only a brief explanation is made hole. Instead, considerable space is devoted to the recent progress toward development of CDMA public land mobile telecommunication systems in the United States. [ABSTRACT FROM AUTHOR]

Most of the past studies concerning the decoding performance of trellis coded modulation (TCM) in a fading channel have been based on time diversity using interleaving/deinterleaving. One problem with time diversity is that a large decoding delay is produced due to the interleaving/deinterleaving which depends on the fading interval. This paper considers TCM signals using space diversity which can drastically improve the decoding relay and analyzes the decoding characteristics in Rice fading channels. An analysis is also made of the effect of the Euclidean distance (ED) and the Hamming distance (HD) of the trellis code on the average bit error rate (BER), and it is shown that a code design considering those two distance structures is needed in a channel with severe fading. This paper considers the major application of the proposed method to be digital voice transmission in mobile communication via satellite. Consequently, a simulation is made for the second-order space diversity decoding performance for the trellis coded 8-PSK signal. The optimal trellis coding at the transmitter is discussed for BER = 10-4. [ABSTRACT FROM AUTHOR]

Methods for evaluating the cross-polarization power ration (XPR) in mobile communication include the one using a crossed dipole, the one using a dipole antenna and a turnstile antenna, and that using a dipole antenna and a loop antenna. However, measurement errors in these methods have not been investigated. In this paper, the measurement error characteristics of various XPR measurement methods are analyzed theoretically. By finding the factors causing degradation of measurement accuracy, this paper proposes a method with more accuracy and clarifies its measurement error characteristics. it is found that the measurement error depends on the XPR and the measurement accuracy id degraded significantly because the measuring antenna does not have isotropic characteristic and the antenna for horizontal polarization has a vertical polarization pattern. To improve this deficiency, a method is proposed in which a cylindrical slot antenna is used for the horizontal polarization because the sensitivity of this antenna to the vertical polarization can be made sufficiently low. it is pointed out that the measurement error with this antenna can be improved significantly. [ABSTRACT FROM AUTHOR]

This paper presents a method of traffic analysis for the control channel access protocol in the mobile communication system. The control channel is for the transfer of the control signals such as the mobile-originated call setup signal for the communication channel, the land-originated call setup signal, and the response signal for the land-originated call setup signal. As the transmission scheme for the mobile-originated call setup signal in the control channel access protocol, various access schemes used in the radio packet communication and LAN can be employed according to how the system is used. The following two points are the features of the control channel access protocol: (1) To avoid the collision between the mobile-originated call setup signal and the response signal, and to improve the efficiency of the channel, the access inhibit control is affected for the up-link control channel from the down-link control channel; (2) to reduce the connection delay, the retransmission interval must be set as short compared with the signal generation interval, and the number of re- transmissions is limited. This paper presents a method of traffic analysis, which is a combination of Se-C analysis and the diffusion approximation analysis, which can cope with various transmission schemes for the mobile-originated call setup signal with the foregoing features. The proposed method of analysis is applied to two kinds of control channel access protocols employing the ALOHA and EGMA system, respectively, for the transmission of the mobile-originated call setup signal. The effectiveness of the method of analysis is verified. The effects of the retransmission interval and the limit of the number of retransmissions on the throughput and the average number of retransmissions are clarified. [ABSTRACT FROM AUTHOR]

The following is a method to eliminate an interference signal. The interference signal is obtained from the source, and the amplitude and the phase of the interference signal is adjusted to the same amplitude and the opposite phase of the interference component, and is added to the received signal. One important problem is how to control automatically the amplitude and the phase of the interference signal. This paper proposes a vector correlation detection-type interference canceller for the digital system. A orthogonal error signal detector is employed which produces the in-phase and quadrature error signals. Combining the circuit and the given interference signal, the correlation detection is performed between the two to perform the automatic control of the amplitude and the phase of the interfering signal. In the first part of this paper, the operation principle is described theoretically. Then, the configuration is shown. An experiment was carried out where the desired signal is 16 QAM or 256 QAM, and the interference signal is an FM signal (telephone 3600 ch.). the improvement factor was 26 dB for 16 QAM and 21 dB to 140 ms. The result indicated the validity of the theory and the effectiveness of the proposed canceller. [ABSTRACT FROM AUTHOR]

This paper discusses the design of the IF filter for the mobile communication receiver, realizing narrowband and low-distortion FM transmission characteristics. In the traditional mobile communication system with 25-kHz channel spacing, a Caebyshev IF filter with a steep stop-band roll-off has been employed to prevent interference from adjacent channels. If the same design is applied to the narrowband mobile communication system with 12.5-kHz channel spacing, the linear distortion due to the IF filter increases the demodulation distortion. First, this paper derives the expressions for the demodulation distortion and the adjacent channel selectivity in the narrowband FM transmission system, using the TBT filter as the model for the receiver. Then, based on the result, the condition for the narrow-band IF receiver filter is derived to realize the low distortion and the required adjacent channel selectivity. Finally, a receiver was constructed experimentally on the breadboard, and it was verified that the theory and measurement are in good agreement. [ABSTRACT FROM AUTHOR]

In this paper, we improve On-Demand Multicast Routing Protocol (ODMRP), which is a multicast routing protocol for Mobile Ad hoc Network (MANET), and propose a new protocol decreasing the number of data forwarding without deteriorating communication reliability. The proposed protocol avoids unnecessary data forwarding by distinguishing each multicast source at every Forwarding Group (FG) Node used in ODMRP. Moreover, the proposed protocol utilizes Support Group (SG), which also distinguishes each multicast source, in order to retain substitute routes without any redundant data forwarding. Therefore, the proposed protocol can avoid deteriorating communication reliability. We evaluate the performance of ODMRP, ODMRP with SG, and the proposed protocol, and we show that the proposed protocol can decrease the number of data forwarding compared with the conventional protocols. We also show that the proposed protocol can restrain the deterioration of packet delivery ratio within allowable range except the case where the number of multicast sources and receivers is extremely large. Furthermore, we show that the proposed protocol can mitigate the deterioration of packet delivery ratio caused by traffic congestion in the case where the number of multicast sources is large. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(11): 36–47, 2007; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/ecja.20382 [ABSTRACT FROM AUTHOR]

The expansion of a communication area and the provision of services to wide districts can be expected if ad hoc networks are connected to established networks. In this environment, two types of routes exist between mobile stations that compose ad hoc networks: routes using wireless links only and routes via base station and the established networks. However, most routing protocols decide a route simply by the minimum hop counts between mobile stations without taking the differences of communication performance between the established network and ad hoc networks into account. This paper presents a new routing protocol that uses simple formulas to decide which route is effective, a route using wireless links only, or a route via the established networks. The formulas are derived from the results of simulation on the communication performance of some routes that uses IEEE802.11b as wireless links and Ethernet of 100 Mb/s as wired links. The performance of our proposed routing protocol, which is realized as an extension of ad hoc on-demand distance vector (AODV), is evaluated by simulation. The results show that the proposed routing protocol is effective especially under a high data rate situation compared with AODV. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(10): 47– 56, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20363 [ABSTRACT FROM AUTHOR]

Recently, attention has focused on multihop wireless networks capable of expanding the communication area by employing wireless relays between nodes and access points. However, the problem in a multihop wireless network is differences arise in the throughput caused by the number of hops from the base station connected to wired networks. In this paper, we propose a scheduling algorithm which solves this problem. In this proposal, the uplink packets and downlink packets are queued separately, and the uplink packets are classified into packets originated within the node and forwarded packets from adjacent wireless nodes and queued. When the node transmits a packet, the fairness among the nodes is improved by scheduling based on the source identifiers of the queued packets. The results of a performance evaluation using a network simulator verified a maximum tenfold improvement in the fairness among the subscribers compared to typical schemes. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(4): 11–22, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20364 [ABSTRACT FROM AUTHOR]

Cellular mobile communications require the detection of received levels at mobile stations so that the positions of the mobile stations can be detected. Given that paths can be isolated in the broadband DS-CDMA method, the technique generally used is RAKE reception, and improvements in detection accuracy due to the path diversity effect can be expected. This paper discusses the application to the DS-CDMA technique of a method in which the average reception power is estimated from N reception levels (the true value) obtained by sampling at a certain time interval ΔT in a mobile communication environment in which the reception voltage changes dynamically as the mobile unit runs. First, we perform a theoretical analysis of the detection accuracy of the received level in a general reception model that simultaneously takes both antenna diversity and path diversity into consideration, and then we demonstrate the plausibility of the theoretical analysis by means of computer simulations. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(2): 58–71, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20217 [ABSTRACT FROM AUTHOR]

The use of IP telephony is spreading rapidly. It was developed chiefly for general home use, and mainly supports calls to the PSTN. In such a service configuration, various problems of realizing telephone service, such as the network address translation (NAT) problem, have generally been solved by the use of a terminal specified by the service provider. On the other hand, the design of origination/destination services between VoIP in enterprise private networks and the PSTN involves various problems, including the solution of the NAT problem, and the requirements differ considerably from those of IP telephony for general home use. This paper presents a method of solution of the technical problems related to interconnection between VoIP and PSTN in enterprise IP networks. The solution is the result of investigations emphasizing the practical aspect and repeated verification experiments, and is applicable to real commercial services. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(4): 42–51, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20197 [ABSTRACT FROM AUTHOR]

With recent advances in IP-related technology, VoIP, which can provide cheaper communications than conventional telephone networks, is attracting interest. Communication within IP networks has already been established in practice. In the early stage of introduction of the technology into the public network, VoIP and conventional tele-phony coexist, and it is important in spreading the use of VoIP that interconnection to the existing network should be achieved. Furthermore, in order to promote the shift from telephone to VoIP, the existing telephone service should be available. These functions of interconnection and the existing service are resources of the PSTN exchange system, and it is inefficient if a new VoIP system is developed without utilizing these resources. Consequently, this paper proposes an architecture for the Call Agent system in which the above functions and the VoIP function are achieved by extending the PSTN switching software. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(4): 52–60, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10229 [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]

Wideband DS-CDMA (W-CDMA) has been used as the wireless access system for the IMT-2000 next-generation mobile communications system. Since this is an asynchronous inter-base-station system, spreading code (scrambling code) identification and timing synchronization detection must be performed during cell search. A three-step cell search method has been proposed for this purpose. In each step, the average value of the instantaneous received signal over a certain period (after despreading) is used for identification. Thus, the accuracy of identification is strongly dependent on the averaging period. This paper analyzes the basic relationship between the averaging period and identification accuracy, taking account of the SIR, the maximum Doppler frequency, and the number of samples used in averaging. The cell search characteristics are investigated for each step of the three-step cell search method. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(5): 67–78, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20105 [ABSTRACT FROM AUTHOR]

Wireless link systems have been investigated for use as base station networks in future mobile communication systems. They utilize a high-frequency band and multilevel modulation scheme to satisfy the system requirements for high capacity. An interference canceler (IC) is an effective method of enhancing the system frequency utilization efficiency. In such a system, however, performance of the IC is severely degraded by the frequency offset between the desired and interference signals since the frequency offset due to the inaccuracy of local oscillators in each base station becomes extremely large in a high-frequency band. Moreover, signal constellation ambiguity frequently occurs and this impairs the IC performance severely when multilevel modulation is employed. This paper proposes two methods to address the aforementioned problems. One method estimates and compensates for the frequency offset by adjusting the frequency of the desired signal to that of the interference signal. Another method controls the transmission power or the phase of the desired signal in order to avoid the signal constellation ambiguity. Simulation results show that the proposed methods effectively suppress the frequency offset and the signal constellation ambiguity and that the IC is effective when using the proposed methods even when employing a high-frequency signal and multilevel modulation. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(5): 39–49, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20161 [ABSTRACT FROM AUTHOR]

Since the base station antennas for mobile communications are installed on the same steel towers as the antennas of several communication systems, antenna installation space is very congested. Therefore, these antennas are often installed on the roofs of buildings. Reduction of the installation space and of the wind load is highly desirable. In order to reduce the wind load, it is necessary to make the area exposed to the wind (the antenna aperture width) smaller. In this paper, miniaturization of the base station antenna for a six-sector wireless zone configuration is discussed. The antenna consists of two-element dipole antennas with a planar reflector. The main reflector width is 0.5λ and the antenna aperture width is 0.62λ in the design. By making the size of the main reflector smaller, reduction of the antenna aperture width is attempted. By an appropriate configuration of the side reflector plate and the parasitic element, the increase of the beam width and the degradation of the front-to-back ratio are limited. Reduction of the main reflector width by 50% and of the antenna aperture width by 38% is found to be possible. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(11): 68–76, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10185 [ABSTRACT FROM AUTHOR]

The adaptive array antenna is an effective means of improving frequency efficiency in cellular mobile communication systems. In these systems, the frequency efficiency is generally improved by improving the CIR characteristic. This paper considers W-CDMA systems from such a viewpoint, assuming that an adaptive array antenna is used in the wireless base station. The relation between the array antenna structure (the number and directivity of antenna elements) and the frequency efficiency is analyzed by examining the improvement of the CIR characteristic in a cellular environment containing multiple cells. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(7): 31–42, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10176 [ABSTRACT FROM AUTHOR]

In this paper, we study server selection methods from the perspective of selecting the server having the shortest download time when a file is downloaded from a mirror Web site. Specifically, we focus on server selection methods on the client side and propose a dynamic server selection method based on Quality of Service (QoS) statistical data. This method features using past stored data in a more advanced manner than a conventional server selection method by collecting past QoS data according to the day of the week and the time period. We also study and evaluate the method based on experimental results using the Internet. First, we study the optimum values for the parameters of the proposed server selection method. Then we compare and evaluate this server selection method and an existing server selection method. As the evaluation metrics, in addition to objective evaluation indices such as the mean and maximum download time, we use the download give-up rate and the stress level which reflect the user's feelings. Based on these results, we demonstrate the superiority of this server selection method. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(7): 43–54, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10168 [ABSTRACT FROM AUTHOR]

Recently, with the advent of personal high-performance electronic devices such as computers and with proliferation of mobile communications such as cellular phones, reduction of the size and weight of the systems, enhancement of processing speed, and voltage reduction of the electronic devices have been pursued. As a result, the problems of interference by unwanted electromagnetic waves between various devices and within individual devices have appeared. Various approaches are conceivable. The author has been performing research on these problems from the standpoint that the electromagnetic elucidation of the generation and propagation mechanisms of the unwanted waves is essential. In the present paper, the voltage and current distributions on a parallel two-wire line with a bend, representing the basic configuration of a transmission line, are analyzed by the FDTD method. By using this analysis, the complex power near the bend is derived and the transmission/radiation characteristics at the bend are quantitatively elucidated. Next, the transmission/radiation characteristics of a microstrip line with a 90° bend are analyzed by the FDTD method in the case where an adjacent line exists. In this way, the effect of the adjacent line is elucidated. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(7): 11–22, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10190 [ABSTRACT FROM AUTHOR]

Broadband DS-CDMA (W-CDMA) has been adopted as the wireless access scheme for the next-generation mobile communication system IMT-2000. Since the scheme is asynchronous between base stations, there must be functions for discrimination and synchronization timing detection of the spreading code (scrambling code). The three-step cell search method is proposed as its realization. Various diversity methods have been used in mobile communication in order to improve communications quality. Performance improvement is also expected from the proposed scheme with the use of diversity. This paper considers the case in which (1) the transmit diversity (TSTD) and (2) the receiving antenna diversity are used in the three-step cell search method. The performance is analyzed and the effectiveness of each diversity is investigated. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(12): 91–104, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1182 [ABSTRACT FROM AUTHOR]

Recently, in order to improve channel use efficiency, the SDMA (Space Division Multiple Access) system has been proposed. In this paper, an adaptive array is applied to a cellular system and the SDMA system with MMSE-based weight control performed for fixed channel assignment and dynamic channel assignment is discussed. In addition to the conventional blocking rate and the forced call termination rate, the ISR (Incomplete Service Rate) is defined as a new QoS (Quality of Service) and its characteristics are evaluated. Further, the occupation rate within the home cell by the SDMA system is studied with random assignment. It is found that the capacity increases by a factor of 2.08 with a blocking rate of 3% when the SDMA system is combined with a fixed channel assignment of nine cell repetition. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(11): 75–83, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10069 [ABSTRACT FROM AUTHOR]