This paper describes the architecture to implement an application in network environments, which adapts to unexpected change in the development phase. In this architecture, an application is expressed as an agent which consists of two layers: base level and meta level. The base level program is an application program and the meta level program is the program that controls the execution of the base level and changes the base level program. Virtual places are also provided in the network. They are used for the release of programs and information which agents retrieve to change their own base level program. An application (or an agent), when a change is required, moves from places to places for the retrieval of programs to adapt to the change. A program search strategy is introduced to adapt to changes by using distributed thesauri of released programs, which realizes an agent's program retrieval method in network environments.

The proliferation and development of cellular voice systems over the past several years has exposed the capabilities and the effectiveness of wireless communications and, thus, has paved the way for wide-area wireless data applications as well. The demand for such applications is currently experiencing a significant increase and, therefore, there is a strong call for advanced and efficient mobile data technologies. This article deals with these mobile data technologies and aims to exhibit their potential. It provides a thorough survey of the most important mobile packet data services and technologies, including MOBITEX, CDPD, ARDIS, and the emerging GPRS. For each technology, the article outlines its main technical characteristics, discusses its architectural aspects, and explains the medium access protocol, the services provided, and the mobile routing scheme.

A novel algorithm for an adaptive array that is suitable for a multi-carrier transmission will be proposed in this paper. In an adaptive array, signals received by antenna elements are weighted and combined together. In the proposed algorithm, distortion of a spectrum of the combined signal is detected and weight coefficients for each antenna element are controlled so that the spectrum of the combined signal becomes flat. Concept of the proposed algorithm can be interpreted as the CMA which is applied to signals sampled in the frequency domain. Furthermore, a configuration of the adaptive array will be shown. Signals separated in a receiver of the multi-carrier transmission are utilized to detect the distortion of the signal spectrum. By adopting the proposed configuration, the spectrum of the multi-carrier signal can be easily detected. In order to investigate the performance of the proposed adaptive array, computer simulation has been carried out. Numerical results show that; 1) A desired wave is captured well even if an interference wave is narrow band signal and is stronger than the desired wave. 2) Suppression performance for a co-channel interference wave depends on both a symbol timing and SIR of arrival waves. If the symbol timing of the interference wave greatly differs from the timing of FFT window of the receiver, the desired wave can be captured even if the co-channel interference wave is stronger more than 10 dB compared with the desired wave. The conventional CMA adaptive array has a serious problem that the narrow band interference wave is captured when it is stronger than the desired wave. On the other hand, it is extremely rare that the proposed adaptive array captures the narrow band interference wave. Therefore, it can be said that the proposed adaptive array is a robust system compared with the conventional system.

This paper proposes applying fast transmit power control (TPC) to the forward link of a direct sequence-code division multi-access (DS-CDMA) cellular system. Orthogonal spreading is assumed at a base station transmitter and coherent RAKE combining is assumed at a mobile station receiver. In DS-CDMA cellular mobile radio, the multiple access interference (MAI) from other cells and background noise limit the forward link capacity. Therefore, to increase the link capacity, fast transmit power control (TPC) can be introduced, which is similar to that developed for the reverse link, i. e. , the transmit powers of forward link channels are independently raised or lowered according to the instantaneous signal-to-background noise plus interference ratios (SIR's) measured at mobile stations. Fast TPC is fast enough to track the multipath fading as well as slow variations in the distance-dependence path loss and shadowing. On the average, the transmit power is increased to a user closer to the cell edge so that the effects of both other-cell MAI and background noise can be reduced while it is decreased to a user closer to the cell center. The effect of the TPC parameters (TPC interval, TPC target value, TPC step size, etc) on the forward link capacity in single- and multi-cell environments is evaluated by computer simulation. It is shown that fast TPC can almost double the forward link capacity in a multi-cell environment.

In this paper, we present an access scheme for packet-typed wireless networks, called DQRUMA/PAR (Distributed-Queueing Request Update Multiple Access with Periodically Automatic Reservation), which can transmit multimedia traffic efficiently. Here, we deal with three kinds of traffic i. e. voice, data and still picture. DQRUMA/PAR introduces the transmission scheme that mobile stations for voice communications reserve the transmission capacity periodically during their talkspurts. The transmission control process of DQRUMA/PAR will become easier than the one of DQRUMA, and the delay characteristic of voice is improved. Furthermore, we study two enforced protocols on DQRUMA/PAR. One is the more enforced protocol for voice communications. We call this as Voice Enforced mode (VE mode) on DQRUMA/PAR. The other is the more enforced protocol for data communications. We call this as Data Enforced mode (DE mode) on DQRUMA/PAR. The transmission delay of voice will become reduced significantly by introducing VE mode. On the other hand, the transmission delay characteristic of data will be improved by introducing DE mode. We carry out the performance comparisons of pure DQRUMA/PAR with PRMA and DQRUMA and show the considerable improvement of the protocol numerically. Next we make the performance comparisons between pure DQRUMA/PAR and two enforced modes on DQRUMA/PAR and show the considerable improvements of these enforced protocols, respectively.

This paper addresses an important issue on the spreading bandwidth of direct sequence code division multiple access (DS-CDMA) cellular mobile radio systems: does wider spreading bandwidth provide larger capacity? And if so, to what extent? The capacity of the perfect power controlled reverse link is evaluated by computer simulation for 1.25 MHz and 5 MHz spreading bandwidths under various sets of propagation channel parameters (path loss decay factor, shadowing standard deviation, shadowing correlation, number of resolved propagation paths) and antenna diversity reception.

In future multimedia mobile communication systems, heterogeneous users will require very different and time-varying transmission rates. Thus, they should be supported with a novel approach that can accommodate the fluctuating data rates in wireless channels. In this paper, a simple method that is used to admit the rates successfully is proposed. The method is also distributed in a sense that it can be implemented at each mobile without any interaction with other mobiles. The method consists of power control with a higher SIR (signal to interference ratio) target and periodic adjustment of the data rate. We prove a good rate admission property of the proposed method and verify its performance with numerical investigation.

Multi-path propagation structure in the urban mobile communication environment of 25 GHz band has been measured by means of newly developed "multi-path propagation parameter measurement equipment," which is capable of estimating coupled DOA (Direction Of Arrival), TOA (Time Of Arrival) and relative field strength by super resolution techniques. Before measurement, basic performance of the equipment has been evaluated in the anechoic chamber in order to ascertain limitation on measurement. For practice and verification of outdoor propagation characteristics, basic data have been collected in a works where accurate buildings and road layout is known. Sub-sequently, data have been collected in the urban mobile communication environment and following characteristics have been confirmed. 1) DOA and TOA of wave reflected by the side of building almost follow the ray-trace. 2) Street trees make 25 GHz band wave attenuate. 3) There are such unusual cases that it is possible to communicate in spite of out of line-of-sight by multi-path propagation. 4) Narrow streets have very complicated propagation structures. Finally, technologies that should be developed for the high-speed digital mobile communication are proposed based on the measurement results.

This paper describes a method of predicting transmission performance to be obtained by applying RAKE reception and parallel transmission in realistic urban multipath environments. Delay profiles measured in metropolitan Tokyo at microwave frequencies were used to obtain the impulse responses of radio channels, and the closed-form equations corresponding to the performance of these anti-multipath techniques were derived, by means of the characteristic function method, under the assumption that the phases of the impulse responses are uniformly distributed. Results show that RAKE reception provides bit error rates 100 times lower than bare transmission does, whereas the improvement obtained by using parallel transmission should be especially valuable in broadband communication systems, such as those operating at data rates above 10 Mb/s.

Measurements of delay spread were performed at microwave frequencies of 3.35, 8.45 and 15.75 GHz along quasi line-of-sight streets in metropolitan Tokyo. It is found that the delay spreads increase with the measurement distance and reach around 600 ns up to 1 km. It is also confirmed that a cumulative probability of the delay spreads follows a log-normal distribution. The gradients of delay spreads against the distance are greater for a lower mobile antenna height hm = 1.6 m than for hm = 2.7 m in these measurements because of blocking effect by the traffic of vehicles and pedestrians on the road. When the mobile antenna height is 2.7 m, the delay spreads within the range before the break points are observed relatively small: 90 ns (3.35 GHz), 140 ns (8.45 GHz) and 150 ns (15.75 GHz) at the cumulative probability of 90%. The gradients of delay spreads against the distance are greater for wider streets in our measurements.

This paper proposes a coherent detection scheme that can reduce the estimation errors of the carrier phase due to Gaussian noise in communication systems where pilot symbol assisted modulation is employed to compensate for Rician fading distortion. This paper introduces two functions in addition to conventional fading estimation methods using Wiener interpolation, etc. The first is the weighted average function for reducing the estimation errors of the fading distortion detected by pilot symbols. The second is the moving average function for estimating the phase errors that are residual after being compensated for by the estimated fading distortion. This paper evaluates the bit error rate (BER) performance for the proposed method in both Rician fading channel and additive white Gaussian noise (AWGN) channel by computer simulation. Simulation results verify that the BER performance of the proposed method is superior to that of a conventional method in both Rician fading channel and AWGN channel. Simulation results also confirm that the degradation of the BER performance of the proposed method is only 0.1 dB in AWGN channel and only 0.3 dB in Rician fading channel compared with the theoretical curves even if we reduce the number of computations by simplifying the calculation of interpolation coefficients optimized for Wiener interpolation.

This paper proposes a short delay, error-resilient video transmission scheme for mobile radio channels. Compressed video data are sensitive to channel error. Video coding schemes such as H. 263 use variable length coding so channel error can cause synchronization failure in the decoder and fatally degrade the reconstructed video sequence by triggering intra- and inter-frame error propagation. ARQ prevents all forms of error propagation but significantly increases the transmission delay of the video frame. We propose a new error control scheme to reduces the delay incurred by ARQ; the receiving buffer can transmits the video frame data to the video decoder even if not all ARQ frames containing the video frame are received. The encoder transmits additional information, the Macro Block (MB) size, in the video frame header. Upon receiving this information, the receiving buffer can determine MB length which allows MB de-synchronization to be prevented. For example, if an ARQ frame is lost, the decoder determines the position of the missing MB and replace this MB with the equivalent block in the previous video frame; this prevents intra-frame error propagation. When all ARQ frames are received and decoded correctly, the video frame in the reference video memory is replaced with the correctly decoded one. Simulation results show that the proposed scheme can minimize the delay and the reduction in frame rate caused by retransmission control without intra- and inter-error propagation.

At the Information-technology Promotion Agency (IPA), we have been developing a network intrusion detection system called IDA (Intrusion Detection Agent system). IDA system has two distinctive features that most conventional intrusion detection systems lack. First, it has a mechanism for tracing the origin of a break-in by means of mobile agents. Second, it has a new and efficient method of detecting intrusions: rather than continuously monitoring the user's activities, it watches for an event that meets the criteria of an MLSI (Mark Left by Suspected Intruders) and may relate to an intrusion. By this method, IDA described herein can reduce the processing overhead of systems and networks. At present, IDA can detect local attacks that are initiated against a machine to which the attacker already has access and he or she attempts to exceed his or her authority. This paper mainly describes how IDA detects local attacks and traces intrusions.

The constant modulus algorithm (CMA) of the adaptive array has been developed for suppressing the co-channel interference and the intersymbol interference in mobile communications. In this paper a novel CMA for the hybrid of the adaptive array and equalizer (HAE) is proposed to combat the problems of insufficient degrees of freedom and mainbeam multipath interferers. The HAE with CMA utilizes the constant modulus property for the output signal of the HAE to adjust the weight vectors of the array and equalizer simultaneously. The co-channel interferers can be canceled by the array and the multipath interferers can be removed by the array or the equalizer following the array in the HAE. Therefore, the array in the HAE with CMA may need less number of elements than that required by the CMA array which cancels both the co-channel interferers and multipath interferers. Besides, the presence of the mainbeam multipath interferers, which may seriously degrade the performance of the CMA array, has much less effect on the HAE with CMA since it can be suppressed by the equalizer instead of the array. Simulation results are presented to demonstrate the merits of the CMA for the HAE.

In this paper we present a Quality of Service (QoS) management architecture for distributed multimedia applications in heterogeneous communication environments of wired and wireless networks. Gaps in network performance such as bandwidths and error rates between wired and wireless networks, as well as gaps in terminal performance in media handling between desktop computers and handheld computers, bring about heterogeneities. Furthermore, even performance gaps among various desktop computers cause heterogeneities. As a result of these heterogeneities in network and terminal performances and various user preferences, the QoS requirement from each receiver is different. Therefore, mechanisms that adjust and satisfy each QoS requirement are needed. We propose a proxy server called Communication Coordination Server (CCS), which intermediates a video server and a receiver and manages the QoS coordination. The CCS performs QoS admission, adjustment, and allocation mechanisms to satisfy the user's QoS requirement. Then transcoding is used to realize the allocated QoS, and it decodes the input video stream from the video server and encodes it within the CCS. A QoS mapping mechanism that translates application-level QoS into resource-level QoS is needed for the QoS admission. We also propose a new QoS mapping mechanism using spline functions that enables a continuous QoS translation. We have built a CCS prototype in our laboratory testbed, and have verified that the CCS can resolve the heterogeneities between the server and receiver by the QoS adjustment mechanism of the transcoding and the QoS admission.

Mobile communication services have become popular due to the rapid popularization of cellular mobile telephones. In order to offer services to an increasing number of users and to upgrade services, the development of Third-Generation Mobile Telecommunication is required. Our proposed system utilizing W-CDMA enables high-speed variable data communications, uninterrupted hand-over between communication zones, doubling of subscriber capacity and reduction of operation costs. Various actions are being taken internationally toward the establishment of a global standard for the Third-Generation Mobile Telecommunication System, aiming at its practical application around AD 2000. The W-CDMA system has been adopted as the standard for Japan. We are developing experimental W-CDMA system equipment. For this development, many Field Programmable Gate Array (FPGA) devices and Digital Signal Processors (DSP) have been used to meet the changes of equipment specifications and system evaluation parameters. By developing customized Large-scale Integrated circuit (LSI) devices and high-speed DSP, a small-size portable phone and a compact visual phone have been realized. Also, high-density mounting of the signal processing parts has been done in the Base Transceiver Station (BTS). In the development of a Mobile Communication Controller Simulator (MCC-SIM), the developmental period has been shortened by using our ATM switching system (AD8700) and generic-use PBX (Pana EXA) in the proposed system. In this paper, the features of the W-CDMA system and the outline of the newly developed experimental equipment have been described.

Multimedia communications over mobile networks suffer from fluctuating channel degradation. Conventional error handling schemes consist of the first stage error correction decoding in wireless interface and the second stage error correction decoding in multimedia demultiplexer, where the second stage decoding result is not used to improve the first stage decoding performance. To meet the requirements of more powerful error protection, we propose iterative soft-input/soft-output error correction decoding in multimedia communications, where the likelihood output generated by the error correction decoding in multimedia demultiplexer is fed back to the decoding in wireless interface and the decoding procedure is iterated. The performances were evaluated by MPEG-4 video transmission simulation over mobile channels.

To realize S-band mobile satellite communications and broadcasting systems, the onboard mission system and equipment were designed for the Japanese Engineering Test Satellite VIII. The system performs voice communications using handheld terminals, high-speed data communications, and multimedia broadcasting through a geostationary satellite. To enhance system efficiency and flexibility, the onboard mission system features phased-array-fed reflector antennas with large antenna diameter and baseband switching through onboard processors. Configurations and performance of the subsystems and key onboard equipment, large deployable reflectors, feed arrays, beam forming networks and onboard processors, are presented. The S-band mobile systems and onboard equipment will be verified through in-orbit experiments scheduled for 2002.

In this paper, we propose a preemptive priority handoff scheme for integrated voice/data cellular mobile systems. In our scheme, calls are divided into three different classes: handoff voice calls, originating voice calls, and data calls. In each cell of the system there is a queue only for data calls. Priority is given to handoff voice calls over the other two kinds of calls. That is, the right to preempt the service of data is given to a handoff voice call if on arrival it finds no idle channels. The interrupted data call returns to the queue. The system is modeled by a two-dimensional Markov chain. We apply the Successive Over-Relaxation (SOR) method to obtain the equilibrium state probabilities. Blocking and forced termination probabilities for voice calls are obtained. Moreover, average queue length and average transmission delay of data calls are evaluated. The results are compared with another handoff scheme for integrated voice/data cellular mobile systems where some numbers of channels are reserved for voice handoff calls. It is shown that, when the data traffic is not very light, the new scheme can provide lower blocking probability for originating voice calls, lower forced termination probability for ongoing voice calls, and shorter average queue length and less average transmission delay for data calls.

We propose and analyze a traffic model of a cellular radio communication network with an arbitrary cell connection and arbitrary probabilistic movement of mobiles between the cells. Our analytic model consists of birth-and-death processes for individual cells connected by the numerical adjustment of hand-off rates. This approximation is validated by simulation. We evaluate the probabilities of the immediate loss, the completion, and the forced termination during hand-off for an arbitrary call in the network. Our numerical examples reveal the cases in which the increase in the generation rate of new calls results in the increase in the loss probability without affecting much the probability of forced termination in a limited service area.