Search

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]

In applying satellite circuits to a large domestic telephone network, it is necessary to study channel assignment and dimensioning methods that take advantage of broadcast communication features. This paper shows that for a large-scale telephone transit network which has hierarchical structure, in order to absorb traffic fluctuation, it is attractive to apply satellite circuits to high-usage trunks in combination with terrestrial final trunks, by taking the Japanese telephone toll network as an example. Assuming this network construction, this paper considers three different satellite channel assignment schemes-Pre-Assignment, Timed Pre-Assignment, and Demand Assignment-and introduces a circuit capacity dimensionsing method to minimize the total network cost for each assignment. Finally, a comparison of channel capacity and network cost is made among these assignments under some traffic variation patterns. It was found that Timed Pre-Assignment is the most effective and economical scheme. Demand Assignment is a future technology and its application field is clarified in comparison with other schemes, with the cost increase for realizing Demand Assignment as a parameter. [ABSTRACT FROM AUTHOR]

Recently a few studies have been made of distributed coupled-line type digital frequency multipliers which multiply the repetition frequency of a square input wave. The transfer functions of an n-section distributed coupled-line constant-resistance network and an n-section distributed-constant bridged-T network have the form of a rational function of order n with respect to delay operator Z-1. We develop our discussion on the basis of this transfer function. The theory is developed for the coefficients of the rational function and the output response in a stationary state can be determined by the coefficients of both the denominator and numerator. The obtained results can be applied to all networks having the transfer functions treated in this paper, but the detailed realization condition for each individual network is not discussed. The experiments and calculations shown in Figs. 4 - 7 are conducted using the distributed coupled-line constant-resistance network as an application example. The network described here can be a digital frequency multiplier for two incident impulse trains, 1111 and 1-11-1. The behaviors of the multiplier in the frequency domain as well as in the time domain are investigated and it is shown that a faster impulse train can be obtained at the output in the time domain by adequately thinning out the discrete frequency components of the incident impulse train. [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]

The tree-type algorithm has been proposed and investigated widely as a random multiple-access communication protocol. It is a distributed algorithm but shows a stable throughput performance. Several proposals have been made, including Tsybakov's, for the tree-type algorithm with a reservation mechanism to improve farther the throughput performance. This paper proposes new TREE-DTA with reservation mechanism, which is based on the block access method and employs the deterministic Q-ary tree-type algorithm operating on the terminal addresses as the retransmission algorithm. The feature of the reservation mechanism proposed in this paper is that the realization is easy, compared to various other methods that have been proposed. To evaluate the performance of TREE-DTA with reservation mechanism, a mathematical model is used to derive the approximate expression for the relation between the throughput and the average delay. Furthermore, the performances of TREE-DTA with reservation mechanism are examined by a simulation experiment. The robustness to the system error and the application of the priority scheme are discussed. [ABSTRACT FROM AUTHOR]

This paper proposes an application method of the cooperative distributed multiagent model in multipath allocation algorithm and confirms its valid calculation results by realizing this model in a distributed computer environment. The multiagent model in this paper is an environment where each agent has the same function of asynchronous and parallel calculation and no globally controlling agents exist. To realize this model, this paper proposes an appropriate dividing method of the multipath allocation problem for asynchronous and parallel calculation, a unifying method of each agent's answers end interagent communication protocols. It also compares the required calculation time and the number of allocated paths of a single agent with that of the multiagents end shows the practical calculation ability of the multiagent model. [ABSTRACT FROM AUTHOR]

The control of the cell contention is a technical problem in the input queueing ATM cross-connect switch. This paper considers this problem and proposes a scheduling control method which dynamically assigns the cell transmission time. A construction of the distributed scheduling circuit also is proposed based on Batcher's sorting network. The proposed method processes the cells in the order of their arrivals, as in the conventional three-phase algorithm but has an advantage in that the throughput can he increased by approximately 26 percent without increasing the number of control processes per cell. Mother merit is that multirate ports can directly be contained in the switch. In this paper, the approximate model for the proposed method is constructed, and the mean delay and the cell loss probability are calculated theoretically. The actual operating performance is evaluated by a computer simulation. By combining the proposed method with the conventional self-routing spatial switch, a distributed switching circuit can he constructed as a whole, which is useful in developing an economical large- capacity ATM cross-connect switch. [ABSTRACT FROM AUTHOR]

With the development of such communication networks as INS in recent years, the communication protocol has become more complicated, and efficient description and validation are becoming more important. This paper proposes a new method of description and validation for the communication protocol, which realizes the merits of both the composite state-transition diagram and the high-level language. The method describes the communication protocol using the SL diagram, which is the complete state-transition diagram with built-in logical expressions. Using the SL diagram, it is easy to verify the existence of the deadlock by utilizing its graph-theoretic features. On the other hand, by regarding the SL diagram as a flowchart, the inductive assertion (technique used in proving the validity of the program) can be applied to validate the parameter functions. A method is also shown which can efficiently locate the invalid loop using the SL diagram. In this paper, the loop is defined as invalid if the transfer of a packet is continued without progressing the communication. Furthermore, it is pointed out by applying the proposed method that there exists in invalid loop in the standard protocol HDLC. An improvement of HDLC is proposed to eliminate such an invalid loop. [ABSTRACT FROM AUTHOR]

In a coherent optical fiber communication with a single-mode fiber and an optical heterodyne detection for improved receiver sensitivity, degradations of the receiving sensitivity due to fluctuation of the polarization condition of the received light are a problem. As a possible solution to this problem, this paper proposes a polarization diversity system with an error-detecting code or an error-correcting code. Its characteristics are analyzed and optimum design values are obtained. [ABSTRACT FROM AUTHOR]

Over the past few years, content delivery services using the Internet have been noted as a new business. In this type of data delivery, we consider services providing multiple classes having different data waiting times based on priority control. The utility to all users is thought to change with the number of classes under priority control and the traffic load ratio per class. Therefore, in this paper, we quantify the relationship between the waiting time and user utility in data transfers with priority control by employing a utility measurement function, and study the traffic load ratio of each class when provided with priority classes and maximizing the utility for all users. Then we analyze the conditions for maximizing utility for each data transfer method and the user utility measurement function, and demonstrate the optimum network efficiency through numerical examples. The results clearly show that a method providing multiple classes rather than a single class and using priority control increases the utility for all users. With priority control, the maximum utility is not reached at 100% network efficiency, but the maximum utility results when a few lines are free. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(7): 49–61, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10225 [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]

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]

Optical antennas used for point-to-point communication in optical intersatellite communication must have high aperture efficiency. By means of the reflector surface shaping method, it is possible to design an antenna with high aperture efficiency and low side lobes. However, the reflector surface becomes a nonspherical surface described by a higher-order polynomial and is very susceptible to errors in the manufacturing process. This paper proposes a shaped optical antenna whose shaped surface is described without a higher-order polynomial but with a nonspherical surface of the lowest order. The error characteristics are compared with those of the conventional shaped antenna. It is demonstrated that the proposed shaped optical antenna not only is more easily fabricated but also possesses almost identical error robustness to a nonshaped antenna. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(5): 62–74, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10145 [ABSTRACT FROM AUTHOR]

In this paper, we propose a multichannel Medium Access Control (MAC) protocol based on the Point Coordination Function (PCF) stipulated in the IEEE 802.11 standard in order to guarantee the end-to-end bandwidth in a multihop wireless network. In the proposed protocol, each wireless terminal is equipped with multiple wireless interfaces and assigns a wireless channel to each wireless interface. Each wireless interface autonomously determines whether to operate in the master mode as the parent terminal, in the slave mode as a child terminal, or in the silent mode as a transmission disabled terminal, and builds a parent-child relationship with each wireless link. Since this enables the use of the PCF at each wireless link and guarantees the bandwidth, the end-to-end bandwidth can be guaranteed in a multihop wireless network. We evaluate the performance of the proposed protocol in computer simulations and demonstrate improved throughput, delay, and packet loss rate compared to the conventional Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. We also demonstrate that the bandwidths for bandwidth-guaranteed packets are guaranteed even when traffic mixing conventional bandwidth-guaranteed packets and best-effort packets are present on the network. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(4): 16–25, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10139 [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 spread of multicast communication is expected from the perspective of the efficient utilization of the network. Since the connection state of multicast communication clearly differs from that of conventional unicast communication, the optimum network topology is believed to change if multicast communication spreads in the future. The authors studied the network topology used when unicast communication and multicast communication are mixed. It was found that the Delta-Star topology was optimal compared to the Star topology currently used in the lowest level of the network. In this paper, we studied the performance of each topology from the perspective of the required capacity of the equipment and the costs required to construct the network when a circuit switching or a connection service was assumed and the multicast traffic increased. Furthermore, we proposed a network extension method that changed the topology from the Star to the Delta-Star topology and evaluated the performance. We found that by using a relatively simple extension method to set the locations of the transmission route link extensions, adequate cost performance was obtained. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(6): 69–83, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1166 [ABSTRACT FROM AUTHOR]

Recently, on the Internet, only best-effort service has been provided, in which communication quality (QoS) aspects such as throughput and delay are not guaranteed. There is an increasing demand, however, for real-time transfer of voice and video data, and reservation-based service is being considered in which the communication quality is guaranteed by reserving network resources. Reservation-based service, however, has problems such as the overhead of packet processing, as well as scalability. There is an ongoing basic discussion as to whether best-effort service is sufficient or reservation-based service is necessary. This paper defines the communication quality which is obtained when the user uses a network application as the utility for the user. The user utility for the real-time application is derived and comparatively evaluated for the two service models, that is, best-effort service and reservation-based service. The following results are obtained quantitatively. Best-effort service can provide sufficient utility if a sufficient channel capacity is available, for which, however, sufficient channels must be provided by adequate network design. If not, reservation-based service is necessary. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(1): 11–21, 2002 [ABSTRACT FROM AUTHOR]

In reservation radio packet transmission protocols, non-collision packet reservation multiple access (NC-PRMA) is known to be able to transmit packets without any collision and to attain higher throughput than packet reservation multiple access (PRMA). However, so far only NC-PRMA in voice-only traffic has been studied. In this paper we evaluate NC-PRMA in integrated voice and data traffic. First, considering data terminals, we formulate an equilibrium point analysis by guaranteeing the number of slots for data packet transmission in one frame. The number is decided according to the number of terminals. Next, we evaluate the throughput and the voice packet dropping probability by theoretical analysis and computer simulation. It is shown that in integrated voice and data traffic NC-PRMA attains better throughput and voice packet dropping probability than PRMA. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 84(12): 13–21, 2001 [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]

The main problem of an indoor infrared (IR) wireless system via diffuse infrared link is bit error rate (BER) performance degradation due to intersymbol interference (ISI) induced by multipath distortion. In the previous study, only a rectangular pulse was employed as a transmitted pulse. However, multipath distortion tends to make the nondirected diffuse indoor IR channel have a low-pass frequency characteristic, and thus a rectangular pulse, whose spectrum has a form of sinc function, induces much ISI. In this paper, we analyze the BER performance of indoor IR wireless system via diffuse link employing different kinds of pulse waveforms, such as a Gaussian pulse and a raised cosine pulse, and consider the effect of ISI. Moreover, we analyze the BER performance employing a return-to-zero (RZ) pulse which has a guard interval in a slot. It is shown that the RZ Gaussian pulse is effective in mitigating the effect of ISI. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(9): 33–43, 2000 [ABSTRACT FROM AUTHOR]

This paper proposes a method that calculates the approximate cross-correlation between two discrete sequences with high speed. The method is evaluated by applying the idea to range compression in the SAR image reconstruction process. When the sequences are very long, tremendous computation time is required, even if the cross-correlation function is calculated through the frequency domain. This is a problem when real-time processing is required. In such a case, however, it is often more important to determine the approximate value with high speed than to determine precisely the value of the cross-correlation function. From this viewpoint, this paper proposes a method in which the wavelet transform is applied to the two sequences, and the correlation function for the obtained short sequences is defined as an approximation to the original correlation function. By forming a hierarchy of wavelet functions, a hierarchy of approximate values is formed according to their accuracy. It is also possible, by successively improving the accuracy starting from a coarse approximation, to finally obtain the accurate value. The algorithm for such an idea is presented. Then, by applying the idea to the SAR range compression, the proposed method is experimentally evaluated. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(6): 10–20, 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]

The M-sequence (maximum length sequence) is often used as a ranging signal in radar and other systems. This paper considers the case where an M sequence ranging signal is detected by an MPD (matched pulse detector), which is a digital correlator, and analyzes the probabilities for miss detection and for false detection due to bit error. Previously, this correlation function has not been derived analytically. In this paper, a procedure is presented where the threshold for the miss detection and false detection probabilities is determined by a simulation result for the correlator. An experiment is attempted in which a single M-sequence is detected in satellite communication using VSAT (very small aperture terminal). It is shown that the experimental results and analysis almost agree for a single M-sequence with a 31-bit code length. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 82(2): 82–89, 1999 [ABSTRACT FROM AUTHOR]

This paper proposes a new network architecture, ALPEN (ATM multi-protocol emulation network), based on a new concept for realizing full-scale multimedia communication networks. In ALPEN, various communication protocols, such as ABR (available bit rate), FRM (fast resource management), or SHM (short hold mode), can be handled using a single, simple transit network. Each protocol is emulated at the edge node of the WAN (wide area network), and the status of the transit network is checked by periodically examining the residual bandwidth information of each route. ALPEN is a cost-effective and flexible network architecture because it enables us to implement new services or protocols easily by modifying only the edge nodes. In ALPEN, since individual edge nodes periodically obtain the bandwidth information, it is possible to respond promptly to a user's request to change his bandwidth. In particular, when the network's RTT (round trip time) is long, as in a WAN, ALPEN is a promising way to resolve the problem of performance responsibility. Although each edge node periodically checks the disperse information to all destination edge nodes on a residual bandwidth, the information might be old, or it might be necessary to process it independently at the multiple edge nodes. Therefore, the parameter of “effective residual bandwidth” is estimated by a statistical method; the estimation also considers that bandwidth resources may be overbooked by multiple edge nodes. The statistical method is described in this paper. The ALPEN introduced in this paper is an effective architecture that makes it possible to implement new or various unforeseeable network services in the future multimedia era, in which various services and protocols may exist simultaneously. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(8): 19–31, 1998 [ABSTRACT FROM AUTHOR]

Recently, for the improvement of reliability of digital communication systems, various kinds of error-correcting codes are being used. To improve system reliability through the use of more capable error-correcting codes it is extremely important to simplify the decoder construction and to reduce the decoding delay. This paper studies a decoding algorithm for a class of simple iterated codes (SI codes) constructed by simply repeating I times a codeword (called block) in a given code (called subcode). Moreover, this paper discusses the decoding delay when this decoding algorithm is applied to decoding the Reed-Muller codes constructed by the superimposing method. [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]

Reconfigurable beam antennas are suitable for onboard antennas from the point of view of frequency reuse, satellite power utilization, and flexibility for traffic demand variation. In this paper, an efficient design method of the feed-array excitation coefficients for arrayfed reflector-type reconfigurable beam antennas is proposed. The feed-array is composed of several subarrays, and only amplitude between subarrays is controlled to achieve reconfigurability. Excitation coefficients of subarrays and amplitude between subarrays are determined efficiently by the proposed design method. The method is verified by a design example for an international communications satellite application. [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]

This paper discusses capacity expansion problems for telecommunication network facilities, based on fuzzy dynamic programming. Although cost functions, discount rates, demand functions, and so on should be given, they usually cannot be defined clearly because of technical developments or business fluctuations. This paper represents undefined factors by fuzzy numbers with triangular membership functions (TFN). Multiplication of division of TFN does not give rigid TFN, but we approximate them to TFN for ease of calculation. Three methods based on this approximation are compared, using numerical examples. Approximation accuracies are confirmed by strict calculation using removal of defining orders of fuzzy numbers. [ABSTRACT FROM AUTHOR]

Telecommunications networks are designed and managed based on statistical traffic data including basic traffic obtained at peak traffic hours. Network links are also designed based on the basis traffic. The network is designed so that the quality of services (network blocking) is at a certain level when basic traffic is applied to the network and the network is managed so that quality of services is maintained for the basic traffic. This conventional method is universal and simple because the required data for design and management are very small. On the other hand, recent telecommunication systems have the ability to measure and collect detailed traffic data. This paper proposes a new network design method in which time-series traffic data rather than statistical traffic data is used for network design. Combining the time-series traffic data and the tariff data for each hour, we can design a network based on total revenue. Unlike the conventional method, the proposed method makes it possible to estimate revenues, costs, and damages. Using time-series traffic data obtained for every hour of the year, a method is devised that optimizes the number of circuits (i.e., for optimizing network blocking) and thus maximizes profits. This paper also presents a new methodology for traffic data and a new network structure that effectively uses the proposed method.

This paper consider the performance of traffic capacity and handover frequency in a DS/CDMA system under imperfect handover. The effect experienced when the number of base stations observed by the personal station is restricted is estimated. Furthermore, the effect of handover hysteresis also is considered. Simulation models are presented which can evaluate the traffic capacity and the handover frequency under these imperfections. System performance is evaluated by computer simulations using these models. It is found that if the number of observed base stations is 3 and the standard deviation of short-distance medium value variance is 6 dB, the reverse-link traffic capacity is reduced to about 90 percent and the forward-link traffic capacity is reduced to about 85 percent, while the handover frequency is about 90 percent of the frequency of the short-distance medium value variance. It is found also that if the handover hysteresis is 4 dB and σ is 6 dB, the reverse-link traffic capacity is reduced by about 10 percent while the handover frequency is about 10 percent of the frequency of the short distance medium value variance. [ABSTRACT FROM AUTHOR]

This paper proposes differential parallel combinatory spread spectrum (DPC/SS) communication systems; one of the parallel combinatory spread spectrum (SS) communication systems the authors have been studying so far. The parallel combinatory SS system is a spectral efficient SS system in which the system transforms several bits of data into a combination of pseudonoise (PN) sequence with modulation of positive and negative signs and transmits them. The proposed DPC/SS system applies differential encoding to the positive or negative sign modulation of the PN sequences, and then they are transmitted. In the receiver, the combination of a transmitted sequence set is estimated by noncoherent detection and the coded sign is demodulated by differential detection. Thus, the receiver does not need to regenerate the phase of the carrier frequency. The proposed systems will be applicable to a mobile cellular system in which a large phase variation interferes with the communications. This paper evaluates the error performances of the DPC/SS systems in additive white Gaussian noise (AWGN) channels and frequency-nonselective, slowly Rayleigh fading channels. It also evaluates the effect of diversity in the Rayleigh fading channels. In the AWGN channel, the DPC/SS system is superior by 1 dB to the differential phase-shift keying (DPSK) system and to the BPSK system in terms of required signal-to-noise ratio at 10 bit error rate (BER) at the same spectral efficiency. In the Rayleigh fading channel, diversity reception in the DPC/SS system gains more improvement in the BER performance, as the number of branches increases, than that obtained in a direct-sequence spread spectrum system with DPSK. [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 aims at improvement of the interbeam connectivity of the multibeam satellite for fixed satellite communications under frequency division multiple access (FDMA) operation and proposes the subchannel switched FDMA (SS/FDMA) system, which is realized by installing the filter matrix on-board the satellite. In the proposed system, each transponder is used to realize multiple interbeam connections and the interbeam connectivity is improved greatly compared to the traditional system. A satellite network among multiple beams can be constructed efficiently. A method is shown in this paper to determine the transmission parameters which maximize the system capacity of the multibeam satellite network and minimize the average transmission equivalent isotopically radiated power (e.i.r.p.) for one career. Example calculations me shown for the power-limited and band-limited systems. In the band-limited system, the number of subchannels and the ratio of bandwidths of the subchannels are important parameters. From such a viewpoint, a method is shown which determines the number of subchannels when the bandwidth ratio of the subchannels is specified. An example calculation is shown taking into account uniform and nonuniform traffic distribution patterns. [ABSTRACT FROM AUTHOR]

The Virtual Path concept has several beneficial features to construct an economical and efficient Asynchronous Transfer Mode (ATM) network. The Virtual Path capacity control technique can increase network flexibility and improve transmission efficiency through statistical sharing of facilities. This paper presents an adaptive virtual path capacity control method which maximizes transmission efficiency under the condition of limited processing load. Evaluation shows that the proposed method successfully im- proves network transmission efficiency with a slight increase in processing load compared to the fixed virtual path capacity scheme. [ABSTRACT FROM AUTHOR]

This paper evaluates the performance of the two-way message transmission system on the meteor burst channel developed and tested by the authors. First, the usual channel model is simplified and then the system is analyzed. It is shown through simulations that the errors introduced by the new channel model and by the approximated analysis method are negligible and the proposed method can be used to design and evaluate the system. The performance of the system having packets with subblocks is compared to that of one with usual packets. It is shown that, by using packets with subblocks, robustness of the system performance against changes of channel parameters as well as a shorter time needed to transmit a message can be obtained. The method of performance evaluation shown in this paper has adequate generality and is also applicable to many other meteor burst communication (MBC) systems. [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 the multichannel frequency division multiplex (FDM) optical transmission, the intermodulation distortion generated by the nonlinearity of the LD is a problem. In this paper, it is analyzed that fin the number of transmission channel, N, and the optical modulation index per channel, m, the CSO and CTB are constant for a different value of N if the effective optical modulation index, m√N, is maintained. The results are compared with experiments. In the present analysis, two types of nonlinearity of the current-to-optical conversion characteristics are considered. One of them is the nonlinearity near the bias current of the LD and is predominant in the region of a small effective optical modulation index. Another is the nonlinearity at the threshold value of the LD and is dominant when the effective optical modulation index is large. It is shown by means of the probability density function that the CSO and CTB degrade suddenly if the effect of the nonlinearity of the threshold value appears. In the FM-FDM optical transmission. many distortions in the transmission bandwidth behave as the white noise due to frequency modulation when the carrier is frequency modulated by a video signal. Hence, the CN ratio is effectively degraded. In this paper, it is further presented that the CN ratio degraded by the distortions can be derived from the CSO and CTB by taking into consideration the frequency allocation of the FM signal. [ABSTRACT FROM AUTHOR]

There are two aspects to the region segmentation coding and the model-based coding which extract and encode the structure and features from image information. They are the “technique for compression of image reformation7rdquo; and the “technique for structural description of image information.” If me image information is described structurally, not only is the highly efficient coding realized but also a new image can be constructed by a local manipulation of the original image. This paper combines the region segmentation of the image based on Munsell color space and the region merge based on the hue difference between the regions. Then a new region segmentation coding based on the result of the formentioned region segmentation is proposed. It is assumed that an object consisting of the color image corresponds to a region of almost the same hue. The hue information within the region is course-quantized based on the memory colors, and the shape information is coded using the chain code. For the value information which contains the information for the shape, shade, etc., of the object, the adaptive cosine transform coding is applied. For the chrome information, the region is approximated by a polynomial function and its coefficients are encoded. The proposed coding method is applied to several standard images which are portraits of relatively simple structures with different face sizes. The color information is transtmitted with a relatively high efficiency, occupying approximately one-fourth of all the transmitted information; and the usefulness of the region segmentation proposed in this paper is demonstrated. Compared to the traditional waveform coding, the method has the advantage that the local manipulation of the image is easier, although the total trasmitted information is slightly larger. [ABSTRACT FROM AUTHOR]

Traffic generated by B-ISDN services is difficult to predict because the fluctuations in normal traffic patterns are large. As a result, it is difficult to provide network equipment to avoid traffic unbalance. The advantage of using asynchronous transfer mode (ATM) in BISDN networks is that path bandwidth control facilities can be used to dampen the unbalance in traffic. This paper proposes a new algorithm, based on the hatch modification method, for controlling traffic fluctuations. The batch modification method is used to control path bandwidth from a centralized control center. The virtual path bandwidth is calculated using optimization calculations based on information from the entire net-work. Hence, it is necessary to develop an algorithm to perform the optimization calculations. The algorithm uses the worst case blocking probability and the total amount of traffic. The algorithm is verified with numerical examples that compare traffic patterns in a model net work. [ABSTRACT FROM AUTHOR]

This paper discusses the Layered construction of the OSI second layer (data link layer) in the satellite packet communication network from the viewpoint of the system performance. The isolated-type system, where the media access control (MAC) sublayer and logical link control (LLC) sublayer are defined independently, and the combined-type system, where they are defined in a related way, are considered. The performances of those two systems are compared, using the throughput and the average response time as the evaluation criteria. The TDMA-Reservation and the slotted-ALOHA are considered as the MAC protocol. The connection-oriented type is considered as the LLC protocol. As to the TDMA-Reservation communication network, the isolated-type system is analyzed by the equilibrium point analysis. Then the performances of the isolated type and the combined type are compared by the analysis and simulation. It is shown quantitatively by comparison that the performance of the isolated type is always better than that of the combined type. As to the Slotted-ALOHA communication network, it is shown by simulation that little difference is observed in the performances of the isolated and the combined types. [ABSTRACT FROM AUTHOR]

An asynchronous transfer mode (ATM) switching network handles not only traffic of various bandwidths, but multirate bursty traffic including constant bit rate and variable bit rate traffic as well. Consequently, to simplify the design and operation of the facility, it is desirable for the ATM network to be nonblocking at the connection level. The nonblocking issue when the network must handle variable bit rate traffic is related closely to the connection admission control (CAC) method. While the non blocking feature for a linear CAC function has been studied in the past, the relation between the switching network cell-level quality and non-blocking characteristic for a specific CAC premising variable bit rate traffic has not been analyzed. This paper examines a nonlinear CAC, evaluates the cell loss probability and statistical multiplex gain when it is applied and proposes the definition for a non-blocking feature called "(ρ0, p, q) nonblocking." Next, a cell distribution-type, three-stage ATM switching network is shown that ensures (ρ0, p, q) nonblocking for traffic including multicast connections without expanding the internal link capacity either in terms of space or speed. [ABSTRACT FROM AUTHOR]

It is known that the bit error rate is deteriorated if them exist echoes on the transmission line. This paper presents a theoretical analysis on influences of an echo on the bit error rate in the optical DPSK communication system. In general, there exists a floor in the bit error rate due to the phase fluctuation of the laser light, which is not reduced by increasing the received optical power. It is shown that the floor value increases with the increase of the amplitude ratio of the echo to the principal wave, as well as the increase of the delay time. It also is shown that the effect of the echo is more remarkable when the hit rate is higher and the spectral Iinewidth of the laser light is narrower. [ABSTRACT FROM AUTHOR]

Intensive research and development efforts have been made on the intelligent network (IN) to realize diversified and advanced telecommunication services and the early introduction of new services under a multi-vendor environment. Earlier research and development, however, assume the conventional telephone service and narrowband ISDN services and gave little consideration to the broadband ISDN. The study of the IN from the viewpoint of the broadband ISDN is urgent considering the systematic realization of the services (i.e., multimedia services) that are not yet sufficient as well as the increase of the demand for the development of new services. This paper proposes the call model, which provides the basis for realizing the IN architecture incorporating the broadband ISDN. First, the basic concepts are defined clearly. Then the call model is proposed which can realize the general connection control for various connection types as well as the flexible control for the multiple virtual channels in the multimedia environment. The model also facilitates the control of the interactions among related services. Finally, the service control characteristics of the proposed call model are investigated. [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]