We propose an approach to obtain the relation between the number of voice call users and the number of data call users in the reverse link of a DS-CDMA cellular system with mixed rate traffic. The analyzed results show that as the number of data call users with high bit rate increases, the number of allowable voice call users decreases rapidly and linearly.

It is important to know phase offsets of a binary code in the field of mobile communications because different phase offsets of the same code are used to distinguish signals received at a mobile station from those of different base stations. When the period of the code is not very long, the relative phase offset between the code and its shifted code can be found by counting the number of bits delayed from the code of the same bit streams. But as the period of the code increases, it becomes difficult to find the phase offset. This paper proposes a new method to calculate the phase offset of a binary code. We define an accumulator function, which is used to calculate the phase offsets between the code and its shifted code. Also the properties of the accumulator function are investigated. This number theoretical approach and its results show that this method is very easy for the phase offset calculation. Its application to the code division multiple access (CDMA) system to define a reference code is given. The simple circuit realization of the accumulator function to calculate the phase offset between the received code and receiver stored replica code is described.

Access control is a key technology for providing data security in database management systems (DBMSs). Recently, various authorization models for object-oriented databases (OODBs) have been proposed since authorization models for relational databases are insufficient for OODBs because of the characteristics of OODBs, such as class hierarchies, inheritance, and encapsulation. Generally, an authorization is modeled as a set of rights, where a right consists of at least three components s, o, t and means that subject s is authorized to perform operation t on object o. In specifying authorizations implicitly, inference rules are useful for deriving rights along the class hierarchies on subjects, objects, and operations. An access request req=(s,o,t) is permitted if a right corresponding to req is given explicitly or implicitly. In this paper, we define an authorization model independent of any specific database schemas and authorization policies, and also define an authorization specification language which is powerful enough to specify authorization policies proposed in the literature. Furthermore, we propose an efficient access control method for an authorization specified by the proposed language, and evaluate the proposed method by simulation.

We demonstrate that the frequency modulated video signals in the subcarrier multiple access optical network can be satisfactorily transmitted using our proposed method, that broadens an optical spectrum by multiplying the subcarrier signals by an additional signal and that reduces optical beat interference, even if the wavelengths of four Fabry-Perot laser diodes are very close each other.

Error performance as well as ATM cell transfer characteristics in a new category of wireless access systems is discussed. Relocatable wireless access with neutral feature between the fixed and mobile systems can convey Mbit/s-order capacity with fairly high quality under line-of-sight propagation. It is an important question for such wireless access systems whether they are able to form a part of wired networks satisfying performance objectives specified in ITU-T Recommendations. This paper analyzes the characteristics of relocatable systems under Gamma-distribution fading environments, and clarifies quantitative relations between Bit Error Rate (BER), Severely Errored Second (SES), Errored Second (ES) and Cell Loss Ratio (CLR) in a calculation model employing QPSK and typical HEC (Header Error Control). Thus it is demonstrated for the first time that in most cases the dominant parameter is the SES objective. Also it will be possible for a relocatable system with appropriate fade margin to meet the ITU-T performance specifications.

This paper proposes a new MAC protocol and physical channel control schemes for TDMA-TDD multi-slot packet channel. The goal of this study is to support both circuit-switched and packet-switched communications on the same resources and to enable high-speed packet transmission using a multi-slot packet channel. In the proposed channel control schemes, three points are taken into account; 1) effective sharing of time slots and frequencies with minimum impact on circuit communications, 2) compatibility with the existing access protocol and equipment, and 3) dynamic allocation of uplink and downlink slots. As for the MAC protocol, we adopt BRS (Block Reservation Scheme) and adaptive access control scheme to the proposed MAC protocol. In addition, to overcome the inherent disadvantage of TDD channels, packet scheduling and access randomizing control are newly proposed in this paper. The results of throughput and delay evaluations confirm that downlink capacity can be drastically enhanced by the dynamic allocation of uplink and downlink slots while corruption under heavy traffic loads is prevented by applying the adaptive traffic load control scheme.

This paper introduces an error controlled decision feedback (ECDF) multiuser receiver, which integrates a successive canceller with linear block channel coding to mitigate decision error propagation. In particular, it uses a switching successive cancellation feedback loop, which can be open if excessive bit errors occur to prevent decision error propagation. The results of computer simulation show that the ECDF receiver possesses advantages in terms of near-far resistance and BER over many reported schemes.

A novel channel assignment scheme in DS-CDMA cellular systems is proposed, which overcomes the handoff interruptions of delay sensitive services by increasing the probability that soft handoff occurs in handoff for them. For that purpose, the priority of using the frequency channels served by all of cells is given to delay sensitive services over delay insensitive ones.

In this paper, Wavelength Division Multiple access (WDM) ring is proposed for interconnection in workstation clusters or parallel machines. This network consists of ring connected routers each of which selectively passes signals addressed in some particular wavelengths. Other wavelengths are once converted to electric signals, and re-transmitted being addressed in different wavelengths. Wavelengths are assigned to divisors of the number of nodes in the system. Using the regular WDM ring with imaginary nodes, the diameter and average distance are reduced even if the number of nodes has few divisors. It provides better diameter and average distance than that of the uni-directional torus. Although the diameter and average distance is worse than that of ShuffleNet, the physical structure of the WDM ring is simple and the available number of nodes is flexible.

The location of stations on the buses can not be ignored in the analysis of the DQDB protocol, especially when traffic load is heavy. In this paper, we propose a new method to model the DQDB (Distributed Queue Dual Bus) protocol by assuming that the request arrival process depends on both the value of the request counter and the location of a station on the buses. By taking these dependences, we can catch the real behavior of the DQDB stations, which is locationally dependent and unfair under heavy load traffic. Based on this model, we analyze the DQDB system with finite buffer by considering the request counter states and buffer states separately and obtain the throughput, mean packet delay and packet reject probability of individual stations. The throughput in individual stations matches that of simulation very well within the range of traffic up to the channel capacity. Also the delay and packet reject rate performance is good up to moderate traffic load. These numerical results reveal the properties of the location dependence and the unfairness of DQDB system under heavy load condition. The analytic results under heavy load traffic for a general DQDB system has not been reported till now. Therefore we conclude that our model and analysis are valid and effective.

This paper introduces a new analytic method that uses modified state equations to evaluate the performance of PCSD (Packet Channel Sharing protocol for DCA systems) with the goal of increasing the spectrum efficiency of DCA systems by realizing channel sharing between circuit-switched calls and packets. The results of this analysis show that PCSD is more suitable for microcellular systems than cellular systems, and that PCSD system performance improves as the average holding time of circuit-switched calls increases. Moreover, this paper proposes a novel scheme to determine the optimum release delay time of packet channels in order to achieve high throughput for packets as well as high channel capacity for circuit-switched calls. The proposed scheme shows that the optimum release delay time for PHS (Personal Handy-phone System) is greater than 60 frames and less than 100 frames.

Recently there has been an enormous growth in the popularity of the Internet. The provisions of access to the Internet will be one of the principal services of the next generation of access networks. In order to provide cost-effective Internet access over ATM-based broadband access networks, the introduction of an available bit rate (ABR) service class is a promising solution. This paper describes our analysis of ABR behavior over ATM-based access networks focusing on explicit-rate-based rate controls and their round-trip time effects. We also describe the hardware implementation of the ABR-based rate controls.

This paper discusses an ATM based access system for a broadband access network that provides flexible and cost effective multimedia services for mass consumption including households. The access system proposed herein uses ATM-PDS subscriber transmission technologies, thus enabling multiple users to share a single fiber resource while transmitting or receiving multimedia information within the broadband network. The system also has virtual channel concentration function by using the bearer connection control protocol being studied for VB5. 2 interface in the ITU-T. We show that the virtual channel concentration function reduces the access cost per user. We also discuss multiple QoS control methods in the system to provide multiple services efficiently. This paper evaluates two methods to handle ABR class and UBR class traffic: shared bandwidth with preferred ABR method, and guaranteed bandwidth with overriding method. The result indicates that when using the shared bandwidth with preferred ABR method for the access system, ABR throughput and UBR throughput per VC depend on the proportion of the number of ABR-VC connections to the total active VCs and on the each buffer size in the access system. And it is difficult to control ABR-VC and UBR-VC throughputs in the access network by using the shared bandwidth with preferred ABR method, which simple mechanism. With the guaranteed bandwidth with overriding method, while ABR-VC throughput and UBR-VC throughput also depend on the proportion of ABR-VCs to the total VCs and on the buffer size, it can offer the minimum guaranteed throughput to the UBR traffic. The result shows the method is effective for easy service provisioning.

The symbol basis side information generated by Viterbi's ratio threshold test technique is proposed to improve the performance of the asynchronous slow-frequency-hopped multiple access system with BFSK signaling in the frequency non-selective fading channel. By properly setting the ratio threshold to produce erasure decisions for the received symbols, the system performances are optimized. The relationship among the hit symbols in a hop duration is exploited by this symbol basis side information to greatly reduce the packet error probability. This packet error rate improvement can be as large as two order of magnitude, compared with perfect hop basis side information systems.

This paper proposes a novel synchronous acquisition method with an adaptive filter in asynchronous direct sequence/code division multiple access (DS/CDMA) communication systems. An adaptive filter is used in a single-user receiver, in complete synchronization of desired user's signal, the tap coefficients of the filter are controlled to orthogonalize to all other user's spreading sequences without knowledge of the sequences, amplitude and time delays of the signals. While, in the proposed system for synchronous acquisition, the tap coefficients are controlled to orthogonalize to all user's sequences including desired user's signal. The synchronous acquisition can be achieved by using the difference of cross-correlation function value between desired user's sequence of inphase and the tap coefficients for each phase. The principle and performance evaluation for the proposed method are shown. As a result, compared to an acquisition method of conventional sliding correlator, considerable improvement of the average acquisition time can be achieved in large power multiple access interference environment.

This paper is concerned with CDMA applied to personal and mobile communications on a global basis using multiple low earth orbital satellites (LEOS). We focus our attention on some unique aspects of LEOS systems and discuss their influences on the CDMA system performance as well as the techniques for coping with these aspects. We deal with three kinds of important items that are unique to LEOS systems; Doppler frequency shift due to satellite movement, propagation delay affecting packetized data transmission and geographical nonunifomity in traffic.

In this paper, three issues concerning the linear adaptive receiver using the LMS algorithm for single-user demodulation in direct-sequence/code-division multiple-access (DS/CDMA) systems are considered. First, the convergence rate of the LMS algorithm in DS/CDMA environment is considered theoretically. Both upper and lower bounds of the eigenvalue spread of the autocorrelation matrix of receiver input signals are derived. It is cleared from the results that the convergence rate of the LMS algorithm becomes slow when the signal power of interferer is large. Second, fast converging technique using a prefilter is considered. The LMS based adaptive receiver using an adaptive prefilter adjusted by a Hebbian learning algorithm to decorrelate the input signals is proposed. Computer simulation results show that the proposed receiver provides faster convergence than the LMS based receiver. Third, the complexity reduction of the proposed receiver by prefiltering is considered. As for the reduced complexity receiver, it is shown that the performance degradation is little as compared with the full complexity receiver.

The capture effect caused by some of power assignment, Rayleigh fading, and near-far effect, can improve the performance of random-access techniques in mobile radio environment. Moreover, if we consider the overall effect of them, the system performance can be noticeably improved. In this paper, the combined effect of fixed power assignment scheme, Rayleigh fading, and near-far effect on the performance of slotted ALOHA are studied. Plus, the performance degradation caused by AWGN is also investigated. The type of signal capture to be considered is the one that a signal involved in a collision survives if its power level exceeds the sum of the other signals participating in the same collision. Numerical calculations are used to demonstrate the degree of improvement and degradation.

This paper describes a mobile information access system based on a multi-agent architecture. With the rapid progress of wireless data communications, mobile Internet access will be more and more popular. In mobile environments, user location plays an important role for information filtering and flexible communication service. In this paper, we propose a mobile information service system where a user with a handy terminal accesses Internet in an open air to look up map information and related town information. Each user information is managed by an independent agent process. And the agent provides each user with a personal service collaborating with other applications. A map-based information service example based on this architecture is also described.

The introduction of networks providing Internet-like services such as the Open Computer Network (OCN) by NTT and others like it will lead to higher level demands by users. For example, users will be asking for higher quality, greater functionality, and lower charges for high-speed, high-throughput data transfer. To respond effectively to the wishes of sophisticated and varied users, technological development must be pursued from the user's point of view. For this reason, research and development is being performed on middleware to open up network functions and make it possible for the user and network to cooperate with each other. This paper discusses the development of major technologies for achieving an enhanced internetworking that should become a catalyst for the future multimedia network, and presents a future vision for the network.