The file sizes of on going flows are fairly disparate on the current network. In this letter, we propose an "age-based" packet discard scheme in the Traffic Conditioner (TC) of a gateway to improve the performance of file transmission. The on going flows will be grouped to three classes of priority according to their "age" as network congestion occurs and the simulation results show that the proposed model can work efficiently in most of the congestion conditions.

The emerging multimedia applications for future mobile communication systems typically require highly diversified Quality of Service (QoS). However, due to the time and location dependent fluctuating nature of radio resources in the radio link, it is very difficult to maintain a constant level of QoS with the current end-to-end QoS control only. Therefore, wireless-aware QoS is the key issue for achieving better end-end QoS. In this paper, a new wireless QoS scheme for a joint CDMA/NC-PRMA cellular system are proposed considering QoS prioritization mechanism, users' diversified requirements and the harmonization with IP-QoS. Two wireless QoS-aware resource allocation algorithms are proposed to support QoS prioritization while achieving high radio resource utilization. By introducing a set of new QoS resource request parameters (minimum, average and maximum requirements), the algorithms can assign radio resource in a more flexible way than the conventional fixed resource allocation. Computer simulations indicate that the proposed QoS algorithms exhibit superior performance with respect to packet dropping probability for realtime application users, and improve transmission rate for non-realtime application users, which evince the effectiveness of the proposed wireless QoS algorithms.

This paper proposes a real-time scheduling mechanism for web server that finds a way to solve so-called priority inversion problem between tasks handling real-time web requests with higher priorities and tasks with lower priorities like HTML requests. The priority inversion problem of web server stems from operating two independent schedulers, web scheduler and kernel scheduler, without exchanging scheduling information or considering the requirement of each other. In the proposed mechanism, two schedulers are integrated in a kernel and the integrated scheduler schedules real-time web tasks and other application tasks together based on their priorities. Since the unified scheduler sees all tasks simultaneously in system, it can schedule the tasks with their absolute priorities and reduce the execution delay caused by the priority inversion. The proposed mechanism provides web server with a better chance to efficiently serve real-time web requests. The feasibility and performance of the proposed mechanism are empirically shown on an embedded system.

A new technique for optical generation of high-purity millimeter-wave (mm-wave) signals--namely, by synthesizing the outputs from cascadingly phase-locked multiple semiconductor lasers--was developed. Firstly, a high-spectral-purity mm-wave signal was optically generated by heterodyning the outputs from two phase-locked external-cavity semiconductor lasers. The beat signal was detected by a p-i-n photodiode whose output was directly coupled to a coax-waveguide converter followed by a W-band harmonic mixer. By constructing an optical phase-locked loop (OPLL), a high-spectral-purity mm-wave signal with an electrical power of 2.3 µW was successfully generated at 110 GHz with an rms phase fluctuation of 57 mrad. Secondly, the frequency of the mm-wave signal was extended by use of three cascadingly phase-locked semiconductor lasers. This technique uses a semiconductor optical amplifier (SOA) to generate four-wave-mixing (FWM) signals as well as to amplify the input signals. When the three lasers were appropriately tuned, two pairs of FWM signals were nearly degenerated. By phase-locking the offset frequency in one of the nearly degenerated pairs, the frequency separations among the three lasers were kept at a ratio of 1:2. Thus, we successfully generated high-purity millimeter-wave optical-beat signals at frequencies at 330.566 GHz with an rms phase fluctuation of 0.38 rad. A detailed analysis of the phase fluctuations was carried out on the basis of measured power spectral densities. The possibility of extending the mm-wave frequency up to 1 THz by using four cascadingly phase-locked lasers was also discussed.

We present theoretical and experimental results for a microwave photonic oscillator (MPO) that provides a microwave signal and a modulated optical wave simultaneously. Among the different techniques currently in use for optically generating a microwave signal, we have chosen a ring configuration based on an electro-optical Mach-Zehnder modulator (EOM) driven by a 1.55 µm DFB laser diode. An accurate modelling of EOM and the contributions from all noise sources in the oscillation loop allows us to predict performances of our designated MPO in a very good agreement with the measured oscillation power (up to 22 dBm, depending on the DC bias voltage) and phase noise spectral density (-130 dBc/Hz @ 10 kHz away from the carrier). We propose this hybrid microwave photonic source to be used as a local oscillator for a coherent laser radar operating at 1550 nm. A good compromise between a very high tunability range (1-8 GHz) and a high spectral purity (> -120 dBc/Hz @ 10 kHz) is obtained through a dual-loop configuration for the MPO.

The dense wavelength division multiplexing (DWDM) technique is very attractive for effectively increasing the channel capability, even for access networks. Some DWDM radio-on-fiber (ROF) systems have been studied recently. In those systems, fiber Bragg gratings (FBG) or arrayed waveguide gratings (AWG) were used to demultiplex DWDM ROF signals. In this report, an alternative channel-selection scheme of DWDM millimeter-wave-band ROF signals by optical heterodyne detection with dual-mode local light is newly proposed. Error-free demultiplexing and transmission over a 25-km-long SMF of the DWDM signal, which consists of two 60-GHz-band, 155-Mb/s-DPSK ROF signals, are demonstrated.

We propose an extended one-shot decorrelating detector (EOS-DD) which may be viewed as a generalized double window multiuser detector (DW-MD) for asynchronous direct-sequence code-division multiple-access (DS/CDMA) systems in frequency selective fading environments. The EOS-DD extends a processing window and the received signal over an extended window is utilized for decorrelating. The effects of the window size on BER performance are investigated by numerical analysis. Analysis and simulation show that the EOS-DD is superior to the one-shot decorrelating detector (OS-DD) and finite memory length truncated decorrelating detector (FIR-DD) in terms of noise enhancement and near-far resistance. It is also shown that the EOS-DD with window size 4 can provide significantly improved performance compared to the EOS-DD with window size 2.

This paper proposes an IPv6-based network service control architecture for providing a variety of customized services to both stationary and mobile users in a unified manner. Recent trends in the Internet indicate its evolution into a combination of broadband and mobile-aware networks. One means of providing users with cost-efficient customized services in such large-scale IP networks is to introduce flexible network intelligence capabilities for managing network resources and services. The purpose of the proposed network architecture is to upgrade the Internet so that it functions more intelligently by using service profiles (data sets containing the service specifications of individual users) and mechanisms for their distribution. It is possible to make network services intelligent by using network application programming interfaces (APIs), which have been under study in international standardization groups. We apply the open API concept to our proposed architecture to produce a wide variety of services. We also propose a new open API to support Web content adaptation services, which add value to Web access.

Load balancing among multiple mirror servers located at distributed positions in the network is a key technique for content delivery services. For bandwidth allocated services, we consider how to select a suitable server from several candidates containing the same content at the time of a request. We propose limiting the candidates in advance and selecting a server from the limited set of servers in a round-robin fashion. The server sets that minimize the variance of the link load are derived using a greedy method for a given network topology and service demand. Through numerical evaluation, we demonstrate that the proposed method is superior to previous methods.

In content distribution networks (CDNs), the content routing which directs user requests to an adequate server from the viewpoint of improvement of latency for obtaining contents is one of the most important technical issues. Several information, e.g. server load or network delay, can be used for content routing. Network support, e.g. active network, enables a router to select an adequate server by using these information. In the paper, we investigate a server selection policy of a network support approach from the viewpoint of which information to be used for effective server selection. We propose a server selection policy using RTT information measured at a router. Simulation results show that our proposed server selection policy in content routing selects a good server under both conditions where server latency and network delay is a dominant element of user response time. Furthermore, we also investigate about location of routers with network support bringing good performance for our proposed scheme.

Adaptive Battery Conservation Management (ABCM), an effective form of power conservation for mobile terminals in an always-connected environment, was proposed and evaluated in a previous published work. The ABCM method employs three states: active, dormant, and the Battery Saving Mode (BSM). The BSM is defined as a battery-saving state; in the BSM, the mobile terminal saves power by intermittently receiving paging notifications via a paging channel between the packet bursts of a session. Two control parameters, the sleep-timer and paging interval, are set up according to packet class and are the keys to the performance of a system with this method. In real-time communications, a long sleep-timer and short paging interval are selected to minimize buffering delay. In non-real-time communications, on the other hand, a short sleep-timer and long paging interval are chosen to reduce power consumption by the mobile terminal. Our previous evaluation showed that the method is effective as a means for power conservation in non-real-time communications. In real-time communications, on the other hand, the ABCM method provides shorter buffering delays and the same battery-conservation performance as the conventional method. To further improve the ABCM method's performance, we now propose an enhanced ABCM method that employs multiple BSM sub-modes, each of which has a different paging interval. As dormant periods become longer, the mobile terminal makes transition to successive sub-modes, each of which has a longer interval than the previous one. In this paper, we evaluate the battery conservation effect of the ABCM method through theoretical analysis and computer simulation. Numerical evaluation indicates that the ABCM method will be suitable for the broadband multimedia packet-radio systems of the future.

This letter addresses the QoS issue of a RSVP flow during handoff events. For the QoS guarantee of real-time applications with RSVP reservation in All-IP wireless networks, mechanisms are required to minimize the resource reservation path changes and the packet loss resulting from handoff events. If the new RSVP reservation is made along the path via a new base station (BS) in advance for soft handoff, on-going RSVP flow session can be kept with the guaranteed QoS. Therefore, we propose a seamless switching scheme of RSVP branch path for soft handoff. We also show that this scheme could provide the QoS guarantee by adaptively adjusting the pilot signal threshold values for soft handoff.

Takine investigated the continuous time queueing system with single server and Markovian arrival streams (MAS) where service times of customers depend on the states of the underlying Markov chain immediately before and after arrivals and may differ from one another among streams. In this paper, we consider the discrete version of Takine's model. Since a MAS can be used to model the correlated traffics of several classes, we consider the discrete time queueing system with MAS as an input traffic. Moreover packets from different classes of traffic may require different service times. So service times of customers which are different from one another among streams and may depend on the states of the underlying Markov chain immediately before and after arrivals, are also considered. We obtain the distribution of the workload in the system using Neuts' matrix analytic method. Based on this result, we obtain the distributions of the actual waiting time and the sojourn time of a customer of each class and the joint distribution of the numbers of customers of each class. We also provide a recursion formula for computing the joint queue length distribution. We give an application to multimedia conference system and numerical example.

A minor component analysis approach based on the generalized sidelobe canceler is presented to realize the blind suppression of multiple-access interference in multicarrier code division multiple access systems. With a rough user-code and timing estimations, this proposed method of less computation performs the same as minimum mean square error detectors and outperforms existing blind detectors. Simulation results illustrate the effectiveness of the blind multiuser detection.

The energy conservation law and the optical theorem in the grating theory are discussed: the energy conservation law states that the incident energy is equal to the sum of diffracted energies and the optical theorem means that the diffraction takes place at the loss of the specularly reflection amplitude. A mathematical relation between the optical theorem and the energy conservation law is given. Some numerical examples are given for a TM plane wave diffraction by a sinusoidal surface.

In this paper, we propose a new multistage (iterative) structure where Kalman channel estimation and parallel interference cancellation multiuser detection are conducted in every stage (iteration). The proposed scheme avoids the complexity of the decorrelator in front of Kalman channel estimator, and has better performance than the previous scheme.

The proxy mechanism widely used in WWW systems offers low-delay data delivery by means of "proxy server." By applying proxy mechanisms to video streaming system, we expect that high-quality and low-delay video distribution can be accomplished without introducing extra load on the system. In addition, it is effective to adapt the quality of cached video data appropriately in the proxy if user requests are diverse due to heterogeneity in terms of the available bandwidth, end-system performance, and user's preferences on the perceived video quality. In this paper, we propose proxy caching mechanisms to accomplish high-quality and low-delay video streaming services. In our proposed system, a video stream is divided into blocks for efficient use of cache buffer. A proxy cache server is assumed to be able to adjust the quality of cached or retrieved video blocks to requests through video filters. We evaluate our proposed mechanisms in terms of the required buffer size, the play-out delay and the video quality through simulation experiments. Furthermore, to verify the practicality of our mechanisms, we implement our proposed mechanisms on a real system and conducted experiments. Through evaluations from several performance aspects, it is shown that our proposed mechanisms can provide users with a low-latency and high-quality video streaming service in a heterogeneous environment.

We can easily access a remote database as well as a local database with HTML forms. Although implementing a database application with HTML forms is much simpler than implementing it with a proprietary graphical user-interface system, HTML forms and CGI programs still must be coded. We implemented a software tool that automatically generates the SQL statements that create a database for an application, the forms that are used as a user interface, and the Java servlets that retrieve the data requested through the forms. The database tables to be created and the forms to be generated are determined by the class diagram for the application. Our software tool, which we call WebSiteGen, thus simplifies the implementation of a Web-based database application.

The authors have been interested in a Scanning Laser Microscope (SLM) and applied it to studies of contact phenomena. In particular, a digital SLM is being currently used, and confirmed to be a successful tool for investigating the contact phenomena. In this paper, the theory and mechanism of a digital SLM are briefly explained, and some actual data obtained with the digital SLM are presented for demonstrating its usefulness for studies of contact phenomena.

We fabricated 1.3µm AlGaInAs inner-stripe laser diodes (LDs), employing a GaInAsP waveguide layer and an n-InP current blocking layer. We compared the effects of the thickness of n-InP current blocking layer. A blocking layer with 500nm thick restricts the leakage current significantly. The inner-stripe LD was compared with the conventional ridge LD. I-L characteristics of both types of LDs were measured. Threshold currents of the inner-stripe LD and the ridge LD were 8.5 and 10.6mA, respectively. A threshold current of the inner-stripe LD is smaller than that of ridge LD. And the resistance of the inner-stripe LD was a few ohms lower than that of the ridge LD. Output power of 88mW was obtained at 200mA with 300µ m-long cavity. This was twice the power of a conventional ridge laser. The characteristic temperature of the inner-stripe LD was obtained 76 K from 20 to 85. We obtained a good linearity up to 100mA at 85. Therefore the inner-stripe LD has an advantage of high power devices.