In this paper, we propose a new type of hybrid ARQ protocol, in which a channel-adaptive variable rate channel coding scheme is combined with a multi-copy retransmission strategy so as to enhance the system performance under the delay constraint of real-time ATM services in broadband radio access networks. The main feature of a multi-copy retransmission strategy in this scheme is to improve the average throughput for a given Forward Error Correction (FEC) rate, subject to the prescribed cell loss requirement of the real-time wireless ATM services, while augmenting the reliability of channel state information required for a channel-adaptive FEC scheme. Our analysis shows that under a harsh fading channel, the proposed approach is useful for achieving the prescribed cell loss performance without significantly degrading the average throughput performance.

A method is described that can allocate bandwidth to each user flow fairly in a scalable network architecture such as differentiated services architecture. As promising queueing techniques for providing differentiated services, class-based packet scheduling and selective packet discarding have been attracting attention. However, if we consider that bandwidth should be allocated to each flow in a weighted manner, the parameters used in these methods such as the weight assigned to each class queue should be pre-determined appropriately based on an assumption about the number of flows in each class. Thus, when the actual traffic pattern differs from the assumed one, they may not work well. Instead of assuming the traffic conditions, our method estimates the number of active flows in each class by simple traffic measurement and dynamically changes the weight assigned to each class queue based on the estimated number. Our method does not need to maintain the per-flow state, which gives it scalability. Simulation showed that this method is effective under various patterns of the number of active flows.

Autonomous Information Service System is a proposition made to cope with the continuously changing conditions of service provision and utilization in current information systems. The faded information field (FIF), sustained by push/pull mobile agent technology, is such a distributed architecture that brings high-assurance of the system through a balanced selective replication of the information. When the demand changes, the information environment is restructured so that the same response time to services for all unspecified users can be achieved whatever the demand volume. However, once the structure is fixed, dispatching the randomly incoming requests on the FIF is still required to guarantee the same quality of service. Our goal is to warrant the autonomous dispatching of the pull mobile agents to adjust the continuously evolving arrival distribution of the demand to the current information environment. In this paper, we explain the concepts and realization of autonomous navigation under the goal of an autonomous load balancing of the pull mobile agent volume in the FIF structure. The appropriateness of this method for FIF environments has been shown by simulation.

In this paper, we propose an approach to solve the power control issue in a DS-CDMA cellular system using genetic algorithms (GAs). The transmitter power control developed in this paper has been proven to be efficient to control co-channel interference, to increase bandwidth utilization and to balance the comprehensive services that are sharing among all the mobiles with attaining a common signal-to-interference ratio(SIR). Most of the previous studies have assumed that the transmitter power level is controlled in a constant domain under the assumption of uniform distribution of users in the coverage area or in a continuous domain. In this paper, the optimal centralized power control (CPC) vector is characterized and its optimal solution for CPC is presented using GAs in a large-scale DS-CDMA cellular system under the realistic context that means random allocation of active users in the entire coverage area. Emphasis is put on the balance of services and convergence rate by using GAs.

We propose a software architecture for one-stop services of electronic commerce (EC). Users currently have trouble using multiple EC services because they are provided independently. Therefore a mediator that combines EC services and provides one-stop services to users would be useful. Service matching and service collaboration are important issues in the mediator because they are the main difficulties for users. The proposed architecture provides solutions to these issues. Multiple service assignment provides suitable combinations of EC services, flow division enables efficient execution of the combined EC services, and dynamic alternative service assignment enables flexible failure avoidance during the execution of combined services. These features make the proposed architecture a suitable mediator for EC services.

The IETF Differentiated Services (DiffServ) framework achieves scalability by (1) aggregating traffic flows with coarse grain QoS on the data plane, and (2) allocating network resources with a bandwidth broker (BB) on the control plane. However, there are many issues that need to be addressed under such framework. First, it has been shown that the concatenation of strict priority (SP) scheduler of class-based queues (CBQ) can cause delay jitter unbounded under certain utilization, which is not acceptable to support the premium service (PS). Furthermore, it is not clear how such a DiffServ network can support traffic flows requiring the guaranteed service (GS), which is a desirable feature of the future Internet. This paper presents architecture and mechanisms to support multiple QoS under the DiffServ paradigm. On the data plane, we present a node architecture based on the virtual time reference system (VTRS). The key building block of our node architecture is the core-stateless virtual clock (CSVC) scheduling algorithm, which, in terms of providing delay guarantee, has the same expressive power as a stateful weighted fair queueing (WFQ) scheduler. With the CSVC scheduler as our building block, we design a node architecture that is capable of supporting integrated transport of the GS, the PS, the assured service (AS), and the traditional best effort (BE) service. On the control plane, we present a BB architecture to provide flexible resource allocation and QoS provisioning. Simulation results demonstrate that our architecture and mechanisms can provide scalable and flexible transport of integrated traffic of the GS, the PS, the AS, and the BE services.

Characteristics of the optical feedback noise in semiconductor lasers under superposition of the HF (High Frequency) current were experimentally examined and theoretically analyzed. The feedback noise was mostly suppressed by superposition of HF current, but still remained when frequency of the HF current coincided with a rational number of the round trip time period for the optical feedback in experimental measurement. Theoretical analysis was also given to explain these characteristic based on the mode competition theory of the semiconductor laser.

This paper presents methods of combining buffer insertion and transistor sizing into a single post-layout optimization. The proposed method considers the tradeoff between upsizing transistors and inserting buffers then chooses the solution with the lowest possible power and area cost. The proposed method is efficient and tunable in that optimality can be traded for compute time.

This study investigates the problem of unfairness when QoS routing does not consider the mix of traffic classes. Unfairness is mainly caused by routing different traffic flows of the same class through paths with extremely different traffic mixtures, involving various service classes. Next, a new routing scheme--Service-sensitive Routing (SSR), which takes the state of traffic mixture of the various service classes into account, is proposed. To determine the QoS route for a flow request, SSR not only considers the available bandwidth and delay of the candidate paths, but also considers the mix of traffic classes on the paths. Additionally, the hybrid granularity routing decision in SSR scheme is scalable and suitable for the Differentiated Services and MPLS networks. Extensive simulations show that SSR can effectively reduce the variance of the average of queuing delays, for example by approximately 20% to 35% for a moderate offered load, compared to the shortest path routing. Furthermore, this routing scheme reduces the fractional reward loss and bandwidth blocking probability.

A nonlinear Volterra-series analysis of multiple ion-implanted GaAs FETs is given that relates carrier profile parameters of ion-implantation to nonlinear rf characteristics of a FET. Expressions for nonlinear coefficients of transconductance are derived from drain current-voltage characteristics of a multiple ion-implanted FET. Nonlinear transfer functions (NLTFs) are then obtained using Volterra series approach. Using these NLTFs third-order intermodulation distortion and power gain are explicitly given. A good agreement has been found between the calculation and the measurement for a medium power GaAs FET with a total gate width of 800 µm operated at 10-dB back off, verifying the usefulness of the present analysis.

In this paper, we present a numerical method with guaranteed accuracy to solve initial value problems (IVPs) of normal form simultaneous first order ordinary differential equations (ODEs) which have wide domain. Our method is based on the algorithm proposed by Kashiwagi, by which we can obtain inclusions of exact values at several discrete points of the solution curve of ODEs. The method can be regarded as an extension of the Lohner's method. But the algorithm is not efficient for equations which have wide domain, because the error bounds become too wide from a practical point of view. Our purpose is to produce tight bounds even for such equations. We realize it by combining Kashiwagi's algorithm with the mean value form. We also consider the wrapping effects to obtain tighter bounds.

We have experimentally observed chaotic oscillation of outputs in a diode-pumped Nd:YAG microchip laser array with an external Talbot mirror. The oscillation of chaotic output is observed at frequencies of sub MHz corresponding to the relaxation oscillation frequencies when the Talbot mirror is slightly tilted from the perfect alignment position with the internal cavity. Chaotic intermittent bursts also appear at frequencies of sub kHz due to longitudinal mode hopping. Synchronization of chaos is observed at these two different time scales. The generation of chaotic oscillations at sub MHz is confirmed by using numerical simulations. It is found that synchronized chaotic oscillations can be observed in the vicinity of the boundary of the injection locking range.

There are so many methods of calculating the cylindrical function Zν(x), but it seems that there is no method of calculating Zν(x) in the region of νx and |ν|»1 with high accuracy. The asymptotic series presented by Watson, et al. are frequently used for the numerical calculation of cylindrical function Zν(x) where νx and |ν|»1. However, the function Bm(εx) included in the m'th term of the asymptotic series is known only for m5. Hence, the asymptotic series can not give sufficiently accurate values of the cylindrical functions. The authors attempt to develop programs for the numerical calculation of the cylindrical functions using this asymptotic series. For this purpose, we must know the function Bm(εx) of arbitrary m. We developed a method of calculating Bm(εx) for arbitrary m, and then succeeded in calculating the cylindrical functions in the region νx with high precision.

The linearity of the GaAs Field Effect Transistor (FET) power amplifier is greatly influenced by the nonlinear characteristics of gate-source capacitance (Cgs) and drain-source current (Ids) for the FETs. However, previously suggested analysis methods of GaAs FET non-linearity are mainly focused on the investigations by each individual non-linear component (Cgs or Ids) without considering both non-linear effects. We analyze more accurately the non-linearity of GaAs FETs by considering non-linear effects of Cgs and Ids simultaneously. We also investigate the third-order intermodulation distortion (IMD3) of the GaAs FET in relation to source and load impedances that minimize FET non-linearities. From the simulation results by Volterra-series technique, we show that the least IMD3 is found at the minimum source resistance (RS) and maximum load resistance (RL) in the equivalent output power (Pout) contour. Simulated results are compared with the load and source pull data, with good agreement.

The capacity analysis of CDMA forward link is required to allocate high data-rate users. To solve this problem, we analyze the capacity of the CDMA forward link based on optimum power control. In a multi-cell environment, the intracell interference and intercell interference are derived. To show the capacity impact of high data-rate users, we introduce a location dependent factor, which is the ratio of intercell interference to intracell interference. Considering the location dependent factor, we propose a coordinated allocation scheme that can be used to allocate high data-rate users in sectorized cells. As a result, we show the capacity impact of high data-rate users according to location variations. The outage probability can be decreased when the coordinated allocation scheme is applied.

Improvements of Internet technology during the last decade have shifted the technical focus from reachability to the quality of communication. There are many technical frameworks, such as Integrated Service and Differentiated Services, which have been standardized to assure the quality of communication. QoS routing is also one of such frameworks. It changes or fixes a route that IP datagrams take, and is also indispensable to put a variety of services into practice. Nevertheless, experiment reports of QoS routing on operational network are quite few, especially with dynamic SLA. Therefore, we still do not know much about the important factors for QoS-enabled network to be realized, such as users' behavior, suitable services to offer, and configuration parameters. In this paper, we carried out field-trial with pseudo QoS routing and dynamic SLA in an actual network built at the WIDE retreat in autumn 2000. In this field-trial, we provided two different types of links to attendees. Attendees chose one of the links, through which their flows go, with our dynamic SLA. We describe the details and the results of this experiment. Our results could help to understand the customers' behavior for differentiated services, and therefore be useful for designing and deploying various QoS technologies.

In this paper we study the scalability issue in the design of a centralized bandwidth broker model for dynamic control and management of QoS provisioning. We propose and develop a path-oriented, quota-based dynamic bandwidth allocation mechanism for efficient admission control operations under the centralized bandwidth broker model. We demonstrate that this dynamic bandwidth allocation mechanism can significantly reduce the overall number of QoS state accesses/updates, thereby increasing the overall call processing capability of the bandwidth broker. Based on the proposed dynamic bandwidth allocation mechanism, we also extend the centralized architecture with a single bandwidth broker to a hierarchically distributed architecture with multiple bandwidth brokers to further improve its scalability. Our study demonstrates that the bandwidth broker architecture can be designed in such a manner that it scales with the increase in the network capacity.

In the past, a number of scheduling algorithms that approximate GPS, such as WFQ, have been proposed and have received much attention. This class of algorithms provides per-flow QoS guarantees in terms of the bounded delay and minimum bandwidth guarantee. However, with O(log N) computational cost for each new arrival scheduling, where N is the number of backlogged flows, these algorithms are expensive to implement (e.g., in terms of scalability). Moreover, none of them addresses the issues of delay distribution and jitter. In this paper, we propose a new traffic scheduling discipline called Jitter Control Frame-based Queueing (JCFQ) that provides an upper bound for delay jitter in the case of rate-controlled connections, such as packet video streams and IP telephony, while guaranteeing bounded delay and worst-case fair weighted fairness, such as in the WF2Q algorithm, but with O(1) complexity in selecting the next packet to serve, assuming that the number of flows is fixed. Three different algorithms for slot or service order assignment between flows are proposed: Earliest Jitter Deadline First (EJDF), Rate Monotonic (RM) and Maximum Jitter First (MJF). In these algorithms, delay jitter is formulated into the virtual finish time calculation. We compare the fairness, delay and jitter performance of the JCFQ with that of the MJF algorithm with WF2Q via simulation. The results show that with proper choice of the slot size, JCFQ can achieve better flow isolation in delay distribution than can WF2Q.

We propose the Geographical Location Information (GLI) system that maps a mobile entity on the Internet to a geographical position. Users can look up the latest geographical location information of registered mobile entities (forward-lookup) and can also search for mobile entities within a specified area (reverse-lookup). The GLI system consists of home and area servers. The home server maintains latest geographical location information of the mobile entities and processes forward-lookup requests. The area server maintains the latest geographical location information of the mobile entities in the area that it manages and processes reverse-lookup requests. To provide a highly scalable system, home and area servers are managed in a distributed manner based on a hierarchical server structure and delegation of authority to servers that manage lower layers. To reduce the amount of traffic due to distributed management, the delegation information of authority is cached by the servers. In our performance evaluation of the GLI system, the prototype implementation can handle 4,500-8,000 requests/sec for location lookup and location registration. We found that 52 home servers and 33 area servers are enough to handle all cars in Japan under some assumed parameters through the performance evaluation.

ATM networks are connection-oriented. Making a call requires first sending a message to do an admission control to guarantee the connections' QoS (quality of service) in the network. In this paper, we focus on the problem of translating a global QoS requirement into a set of local QoS requirements in ATM networks. Usually, an end-user is only concerned with the QoS requirements on end-to-end basis and does not care about the local switching node QoS. Most of recent research efforts only focus on worst-case end-to-end delay bound but pay no attention to the problem of distributing the end-to-end delay bound to local switching node. After admission control, when the new connection is admitted to enter the network, they equally allocate the excess delay and reserve the same bandwidth at each switch along the path. But, this can not improve network utilization efficiently. It motivates us to design a novel local QoS requirement allocation scheme to get better performance. Using the number of maximum supportable connections as the performance index, we derive an optimal delay allocation (OPT) policy. In addition, we also proposed an analysis model to evaluate the proposed allocation scheme and equal allocation (EQ) scheme in a series of switching nodes with the Rate-controlled scheduling architecture, including a traffic shaper and a non-preemptive earliest-deadline-first scheduler. From the numerical results, we have shown the importance of allocation policy and explored the factors that affect the performance index.