Public telephone network have been dramatically changing to IP (Internet Protocol) based network. This paper starts with an overview of the present status of the telecommunications network and the rapid evolution of iDCs (internet Data Centers) now underway. Next, we focus on the existing configurations and the characteristics of power systems for IP equipment and iDCs, and then clarify the cutting-edge technologies for highly reliable powering systems and the advantages of DC power systems. Finally, the paper demonstrates energy-saving activities, and the prospected issues to be solved in the field of power systems for the coming full-fledged IT Age.

Next generation advanced power devices show remarkable progress in wide band-gap power devices such as silicon carbide and gallium nitride devices, as well as novel silicon devices called as super junction FETs and so on. The future direction of power electronics applications is surveyed in terms of output power density as an index of future power electronics development, instead of the power conversion efficiency, taking the device progress in sight. Over the last 30 years, the output power density of power electronics apparatuses has increased by a factor of two figures. New markets, such as a power supply for future generation CPU, a compact unit inverter and a electric vehicle-driving inverter unit, are expected to grow rapidly from 2010 to 2015 with the advance in the out power density of power converter. The possibility of power electronics innovation with progress in the output power density will be discussed in conjunction with development of next generation advanced power devices and related technologies.

The power system and the battery management of mobile phones used by NTT DoCoMo subscribers will be described. The energy requirements of the phones' AC-adaptors (chargers), their power-management systems, and trends in energy consumption will be focused on. The results of the new Li-ion batteries' safety tests, quick tests assessing battery capacity deterioration, and battery lifetime predictions will be also discussed.

A digitally controlled dc-dc power converter is useful to dc power supply systems for telecommunications and data communications systems that require high reliability and high performance. This paper presents a design criterion and output characteristics of 1 MHz high-speed digitally controlled dc-dc converter using a voltage controlled oscillator (VCO) as an analog to digital signal converter in the digital control circuit. As a result, it is revealed theoretically and experimentally that the proposed 1 MHz high-speed digitally controlled dc-dc converter has excellent static and dynamic characteristics. The adjustability of output voltage is less than 10 mV and there is no steady-state error within the integral controlled regulation range. Also, the overshoot is suppressed enough within 0.1 V and the transient time is very short.

This development proposes a highly efficient air-conditioning airflow system for a computer-machine room having high-heat-generating equipment using forced-air cooling. The proposed system recirculates room air in the area surrounding equipment back to the cooling supply air supplied from a double floor. The recirculated air is therefore used as cooling air for computers. This system enables the blowing temperature difference of air-conditioner units to be increased, blower capacity to be decreased, and overall efficiency of air-conditioner units to be increased. Here, we have proposed an air-conditioning airflow system that decreases the amount of cooling supply air while ensuring adequate air ventilation for equipment using forced-air cooling, and a design method for achieving this system.

We describe a simulation method and design for a stand-alone hybrid power supply system composed of a wind turbine generator and photovoltaic modules. The system has been developed to supply power for telecommunications equipment in areas with no commercial power sources. We also report a comparison of the simulation results with actual measured data. The results show that the hybrid system can function effectively as a power supply for telecommunications equipment.

Wind power generation occupies an important position as a new non-fossil energy in recent years, and the plant scale has been rapidly expanding as wind-farm. Since they are often built in topographically inconvenient places, the remote monitoring system has been required. Ethernet had been said to be unsuitable to the industrial network, it is one of the strong options because of its low cost and easiness to apply. In this case, it is important to secure the throughput enough for updating the data of numerous wind turbines within a fixed time. In order to achieve this, we adopted User Datagram Protocol/Internet Protocol (UDP/IP) and the multi-thread method to make the overhead of software small as possible. This paper presents the scheme of powerful network using Ethernet with multi-thread and multi-cast. The relation between the number of threads and total throughputs of network is clarified. The design procedure to derive the optimum number of threads is shown. And it is demonstrated that this scheme provide the local network of wind-farm with sufficient performance.

This paper describes the effect of power line inductance and smoothing capacitance on a single-phase AC power supply system. Voltage fluctuations were calculated when the three main types of smoothing circuit (capacitor input, choke input, and power factor correction types) were used and the magnitude of power line inductance and smoothing capacitance were changed. First, we show the difference in voltage fluctuation in the case of constant resistance and negative resistance in a DC-DC converter. Second, we show the waveforms for which the power line inductance affects the voltage fluctuation of the AC power supply system. Finally, we propose the boundary condition for the power line inductance affecting the voltage fluctuation of the AC power supply system and estimate AC power supply system stability.

This paper presents a novel current driving method for the synchronous rectifier (SR) in a Flyback topology. Compared to the previous proposed Current Driven Synchronous Rectifier (CDSR), the proposed CDSR features simple structure, low power loss and good performance. The proposed SR driving method is implemented in a 64 W Flyback converter with universal input, and efficiency as high as 92.5% is achieved at low input (90 V ac) and full load condition.

In this paper a new method for the determination of the double layer capacitance and the internal inductance of a cell or battery is described. The resonance frequency of the double layer capacity with the internal inductance is determined by means of a phase measurement. The method can be used during operation of the battery. During a constant current discharge it is possible to predict the available discharge time from the resonance frequency at the start of the discharge and the actual resonance frequency. The method is tested with success on lead-acid batteries (VRLA, Plante) and nickel-cadmium batteries and it shows that the active surface is proportional to the state-of-charge (SOC). For primary zinc-MnO₂ cells the measured electrical capacitance is not simply related to SOC.

We have developed manganese-based lithium secondary battery technology as a part of a 10-year national project in Japan for The Development of Dispersed-Type Battery Energy Storage Technology. The cell chemistry we developed consisted of a modified graphite anode material containing dispersed Ag particles, and a partially substituted LiMn₂O₄ cathode with Li in the Mn sites. These materials showed a significant improvement in a cell's cycle life performance. The 250 Wh class single cell with the cell chemistry mentioned above showed energy densities of 131 Wh/kg and 295 Wh/dm³. The 2 kWh class module battery including 8 cells connected in series and a battery management system delivered energy densities of 122 Wh/kg and 255 Wh/dm³ that exceeded the final target of 120 Wh/kg and 240 Wh/dm³ for the project. Most of the target items for the battery performance were accomplished and proved. Thus the basis for practical application was developed, however, some areas concerning the further durability under various circumstances and conditions still remain to be accomplished. Continuous development for mass production and cost reduction is also expected for this technology in order to contribute to industry and society.

This paper proposes an independent control for parallel-connected multiple uninterruptible power supply (UPS) systems based upon a very simple control scheme. Here, the amplitude and phase angle of the output voltage are the controllable variables. With the only measurement of the output current, the active and reactive components are calculated to define the control variables. The entire system including the equations for the circuit, control and voltage limiters is well represented by a small-signal model, in which the computation of its eigenvalues constitutes the stability proof of the system. The root locus diagram gives an overall panorama of the system performance as a function of a certain gain and it aims to aid the further understanding and the design of the control. The experimental verification is carried out using a mere proportional-integral control scheme, which is a special case of the general control equation used in the theoretical analysis. For some situations, experiments show a flow of lateral current between UPS's, which causes an unbalanced current distribution. By increasing the proportional gain of the control equation for the output voltage amplitude, the lateral current can be substantially suppressed with a consequent improvement of the load sharing. Experimental results under various conditions show excellent results in terms of synchronization, load sharing and stability for three distinct output rating UPS's connected in parallel.

A UPS with an energy storage function using long-cycle-life VRLA batteries has been developed. Combining the functions of UPS and energy storage is effective to enhance the cost-effectiveness of the UPS. New long-cycle-life VRLA batteries, with capacities of 1000 or 1500 Ah at 2 V, have been developed for the UPS. A cycle life of 3000 or more cycles was estimated from our cycle test. The UPS has been installed in a telecommunications building for field-testing. This paper describes the system configuration, electrical characteristics of the UPS and its components, and result of our field test.

A stability of the cascade two-stage Power-Factor-Correction converter is investigated. The first stage is boost PFC converter to achieve a near unity power factor and the second stage is forward converter to regulate the output voltage. Previous researches studied the system using linear analysis. However, PFC boost converter is a nonlinear circuit due to the existence of the multiplier and the large variation of the duty cycle. Moreover, the effect of the second stage DC/DC converter on the first stage PFC converter adds more complexity to the nonlinear circuit. In this issue, low-frequency instability has been detected in the two-stage PFC converter assuring the limitation of the prior linear models. Therefore, nonlinear model is proposed to detected and explain these instabilities. The borderlines between stable and unstable operation has been made clear. It is cleared that feedback gains of the first stage PFC and the second stage DC/DC converters are the main affected parts to the total system stability. Then, a simplified nonlinear model is provided. Experiment confirm the two models with a good agreement. These nonlinear models have introduced new PFC design scheme by choosing the minimum required output capacitor and the feedback loop design.

This paper proposes a simple control method to improve the ignition behavior of cold cathode fluorescent lamp (CCFL) in digital-dimming control. Due to restriking manipulation in digital-dimming mode, the lamp life of CCFL is reduced substantially. To extend the lamp life, we realize a digital-dimming controller with soft-starting technique (DDC-SST) to reduce the high ignition voltage and to eliminate the ignition current spike. The half-bridge resonant inverter is employed in the presented backlight system. Complete analysis and design considerations are discussed in detail in this paper. Simulation and experimental results are close to the theoretical prediction. The overall efficiency of the system achieved at the rated power is over 91%. The ignition voltage is reduced about 30% without any lamp current spike occurred under digital-dimming operation.

New Recommendation and Future Standards highlight the Power Factor Correction (PFC) converter as a basic requirement for switching power supplies. Most high-frequency power factor correctors use resistor emulation to achieve a near-unity power factor and a small line current distortion. This technique requires forcing the input current with an average-current-mode control to follow the input voltage. Stability of this system was discussed previously by using some linear models. However, in this paper, two nonlinear phenomena have been encountered in the PFC circuit, period doubling bifurcation and chaos. Detection of these new instability phenomena in the stable regions predicted by the prior linear PFC models makes us more susceptible towards them, and reveals the need to consider a nonlinear models. A nonlinear model performing the practical operation of a boost PFC converter has been developed. Then, a simplified and accurate nonlinear model has been proposed and verified experimentally. As a result from this model, instability maps have been introduced to determine the boundary between stable and unstable operating ranges. Then, the period doubling bifurcation has been studied through a new proposed technique based on the capacitor storage energy. It is cleared that, As the load lessens, a required extra storage power is needed to achieve the significant increase in the output voltage. Then, if the PFC system can provide this extra energy, the operation can reach stability with new zero-storage energy else the system will have double-line zero energy that is period doubling bifurcation.

This paper presents a novel self-excited ZVS half-bridge converter. This converter including a self-oscillating control circuit is very simply constructed. The converter achieves excellent efficiency, low voltage stress across the switches and low EMI noise by using zero-voltage-switching technique. This converter stores not only magnetic energy in the primary winding of the transformer but also electrostatic energy on the resonant capacitor during the on-periods, so that the converter realizes the miniaturization of the transformer, the reduced conduction losses and the low current stress in the switch. This paper analyzes the behavior of static characteristics by using an extending state-space-averaging method and presents design equations. Based on the analysis, two prototype converters are designed for a 120 W output and a 350 W output. Experimental results are given for two converters and they confirm the validity of the theory. The proposed converters have displayed excellent performance.

In recent years the size of transformer in a DC-DC converter becomes smaller and thinner for power module type application. It results in the increase of the leakage inductances because the number of turns of the secondary winding becomes smaller. This paper presents the analysis of static and dynamic characteristics of the novel flyback converter proposed before, and clarifies that the transformer's leakage inductances deteriorate the static load regulation, but improve the dynamic stability by increasing the dumping factor.

We propose a unique synchronous rectification method in the rectification circuit of a DC-DC converter. This paper describes a novel synchronous rectification circuit that uses a saturable current transformer. We explain operations of this circuit, and analyzed them in this work. In addition, we verified operations of this method applied in boost converter and demonstrated its effectiveness when two or more converters operate in parallel through simulations and experiments.

This paper presents a novel ZVS bidirectional 1 kW class DC-DC converter used for a photovoltaic (PV) system. The proposed circuit is based on a boost&buckboost converter, which consists of a boost converter and a buckboost converter. Bidirectional soft switching is realized by using of coupled inductors and auxiliary switches in the circuit. From the analysis of the circuit operation, ZVS conditions of the switches are derived. In the experiment, the maximum efficiency of the proposed converter during forward power flow was 97.1% on output power of 320 W.

In this paper, a novel type of the step-up high frequency transformer linked full-bridge soft-switching phase-shift PWM DC-DC power converter with ZVS and ZCS bridge legs is proposed for small scale fuel cell power generation systems, automotive AC power supplies. A tapped inductor filter with a freewheeling diode is implemented in the proposed soft-switching DC-DC power converter to minimize the circulating current in the high-frequency step-up transformer primary side and high-frequency inverter stage. Using a tapped inductor filter with a freewheeling diode makes possible to reduce the circulating current without any active switches and theirs gate-drive circuits. The operating principle of the proposed DC-DC power converter with each operation mode during a half cycle of the steady state operation is explained. The optimum design of the tapped inductor turns ratio is described on the basis of the circuit simulation results. Developing 1 kW 100 kHz prototype with power MOSFETs and 36 V DC source verifies the practical effectiveness of the proposed soft-switching DC-DC power converter. The actual efficiency of the proposed DC-DC power converter is obtained 94% for the wide load and output voltage variation ranges.

The effects of air-intake format of forced-air-cooled equipment on the efficiency of air conditioning systems are studied. A modern data center features a large number of information-processing devices to provide telecommunication services. These devices generate considerable heat, and the equipment that houses these devices often employs "forced air cooling" in which a cooling effect is achieved by sucking in large amounts of room air. An air conditioning system used for a machine room filled with such equipment therefore requires high fan driving power resulting in significantly low air conditioning efficiency. In this study, we first performed mockup-based experiments to obtain a quantitative understanding of how different air-intake formats for equipment affect the temperature at various room locations such as equipment intake. We then created a model for predicting the temperature at various locations, and on the basis of this model, we analyzed the factors affecting intake temperature and examined how intake temperature affects air conditioning efficiency. It was found that placing air inlets in the lower 1/3 portion of forced-air-cooled equipment could prevent the equipment from reabsorbing the hot air that it blows out and therefore improve air conditioning efficiency.

Discrete-time queueing models have been studied for many years because of their direct applicability in the performance evaluation of digital communication system and networks, where buffers are used to temporarily store information packets which cannot be transmitted instantaneously. In this paper, we investigate the behavior of a discrete-time multiserver buffer system with infinite buffer size. Packets arrive in the system according to a two-state correlated arrival process. The service times of the packets are assumed to be independent and identically distributed according to a geometric distribution. We present an analytical technique, based on the use of generating functions, for the analysis of the system. Explicit expressions are obtained for the mean values, the variances and the tail distributions of the system contents and the packet delay. The influence of the various model parameters on the behavior of the system is shown by means of some numerical examples.

An adaptive interpolated FIR (IFIR) echo canceller was recently proposed for xDSL applications. This canceller consists of an FIR filter, an IFIR filter, and a tap-weight overlapping and nulling scheme. The FIR filter is used to cancel the short and rapidly changing head echo while the IFIR filter is used to cancel the long and slowly decaying tail echo. This echo canceller, which inherits the stable characteristics of the conventional FIR filter, requires low computational complexity. It is well known that the interpolation filter for an IFIR filter has great influence on the interpolated result. In this paper, a least-squares method is proposed to obtain optimal interpolation filters such that the performance of the IFIR echo canceller can be further improved. Simulations with a wide variety of loop topologies show that the optimal IFIR echo canceller can effectively cancel the echo up to 73.0 dB (for an SHDSL system). About 57% complexity reduction can be achieved compared to a conventional FIR filter.

With the need and adoption of link aggregation where multiple links exist between two adjacent nodes in order to increase transmission capacity between them, there arise the problems of service guarantee and fair sharing of multiple servers. Although a lot of significant work has been done for single-server scheduling disciplines in the past years, not much work is available for multi-server scheduling disciplines. In this paper, we present and investigate two round robin based multi-server scheduling disciplines, which are Multi-Server Uniform Round Robin (MS-URR) and Multi-Server Deficit Round Robin (MS-DRR). In particular, we analyze their service guarantees and fairness bounds. In addition, we discuss the misordering problem with MS-DRR and present a bound for its misordering probability.

Personal communication service (PCS) networks support the delivery of communication services as the mobile user moves from one region to another. When a mobile user receives a call, the network has to quickly determine its current location. The existing approach suffers from high delay in locating the mobile since the mobile's current location has to be always consulted on the location databases. Caching the location of the remote mobile is useful to reduce this delay. However, the longer the useless record caused by the movement of the mobile remains in a cache, the higher the degradation of cache memory utilization is imposed on a system. In this paper, we propose an efficient caching scheme that a cached record is not allowed to remain over the predefined time, called a time-threshold, in a cache. A long time-threshold may cause to increase the obsoleteness of the cached record. In contrast, a short time-threshold may cause to degrade memory utilization. This paper finds the optimal time-threshold to enlarge cache memory utilization. Also, we provide a unique solution for determining the optimal time-threshold, and study the effects of changing the important parameters of mobility, calling patterns, and network conditions on the optimal time-threshold. Furthermore, we compare the performance of the proposed caching call delivery scheme and the existing call delivery schemes.

We consider a rate control algorithm for elastic services to allocate bandwidth in a network subject to throughput and fairness constraints. Our algorithm achieves a max-min fair bandwidth allocation among contending elastic connections, and has desirable properties in that it can operate in a decentralized and asynchronous manner accounting in part for heterogeneity in round trip delays. The algorithm is simple and scalable in that, 1) the network links make local measurements of capacity and calculate local 'explicit rates' which are fed back to sources without requiring knowledge of the number of on-going connections, while 2) sources adjust their transmission rates so as not to exceed the received explicit rate indication. The algorithm is designed to track a "dynamic" network environment. We discuss its stability, convergence, and feasibility issues related to fair allocation and rate-based flow control. We also consider the role of sessions with priorities to differentiate among users with elastic services. Through rigorous analysis and simulations, we have shown that it has indeed desirable characteristics for networks with elastic services as well as other service types, which are expected to be common in future network environment.

This paper proposes a scalable video delivery scheme, named P2PVD, for large-scale video-on-demand applications based on the emerging peer-to-peer structure and characteristic user behaviors. Two types of orders are permitted in P2PVD: reserved and urgent. Reserved orders are encouraged with a lower price policy, which smoothes the network traffic and reduces the server load. The requesting peers use delay-aware dynamic parallel transmission to serve the reserved and urgent orders, and supplying peers employ three priority rules to increase the capacity of P2PVD. Experimental results indicate that P2PVD is scalable.

The notion of effective bandwidth provides an elegant and powerful mathematical basis for the provision of QoS-assured services over IP networks. In this paper, we propose a semi-parametric estimator of effective bandwidth, called Gaussian estimator using buffer masurement, for superposition of sources in IP networks. In contrast to most existing proposals concerning the effective bandwidth estimator, our proposal works based on a small set of measurements of the workload in the buffer of a router. We analytically show the property of the proposed estimator with respect to the dependence on the service rate. We provide numerical results to show that our proposed estimator is more accurate than estimators that rely only on the amount of traffic from sources.

Since the TCP is the transport protocol for most Internet applications, evaluation of TCP throughput is important. In this paper, we establish a framework of evaluating TCP throughput by simple measurement. TCP throughput is generally measured by sending TCP traffic and monitoring its arrival or using data from captured packets, neither of which suits our proposal because of heavy loads and lack of scalability. While there has been much research into the analytical modeling of TCP behavior, this has not been concerned with the relationship between modeling and measurement. We thus propose a lightweight method for the evaluation of TCP throughput by associating measurement with TCP modeling. Our proposal is free from the defects of conventional methods, since measurement is performed to obtain the input parameters required to calculate TCP throughput. Numerical examples show the proposed framework's effectiveness.

FEC (Forward Error Correction) is widely used to recover packet loss over the Internet since it does not involve additional network delay. However, FEC still needs much additional network bandwidth for redundancy, and does not consider the priority or the importance of video frames to generate redundant data. In this paper, we present Periodic FEC (PFEC) to make up for the shortcomings of FEC. PFEC divides frames into high-priority frames and low-priority frames, and gives redundancy only to high-priority frames. As specific examples, we describe two types of PFEC: Media-Independent PFEC and Media-Dependant PFEC. Moreover, based on the two-state continuous time Markov chain, we propose redundancy control algorithms of the PFEC schemes that can adjust the amount of redundancy to optimal levels depending on network loss conditions. For better performance, we also consider UEP (Unequal Error Protection) based on PFEC that gives redundancy to low-priority frames as well as high-priority frames. Experimental results show that compared with FEC, PFEC reduces the amount of redundancy considerably but degrades PSNR slightly, and UEP based on PFEC economizes redundancy without the degradation of the PSNR.

In this paper, the bit error rate (BER) and the outage probability are presented for a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver operating in a correlated frequency-selective Nakagami-m fading environment with multiple access interference. A simple approximated probability distribution function of the signal-to-interference-plus-noise ratio (SINR) is derived for the receiver with multiple correlated antennas and RAKE branches in arbitrary fading environments. The combined effects of spatial and temporal diversity order, average received signal-to-noise ratio, the number of multiple access interference, angular spread, antennae spacing and multi-path Nakagami-m fading environment on the system performance are illustrated. Numerical results indicate that the performance of the 2D-RAKE receiver depends highly on the operating environment and antenna array configuration. The performance can be improved by increasing the spatio-temporal diversity gains and antenna spacing.

This paper introduces an efficient affine projection algorithm (APA) using iterative hyperplane projection. The inherent effectiveness against the rank deficient problem has led APA to be the preferred algorithm to be employed for various applications over other variety of fast converging adaptation algorithms. However, the amount of complexity of the conventional APA could not be negligible because of the accomplishment of sample matrix inversion (SMI). Another issue is that the "shifting invariance property," which is typically exploited for single channel case, does not hold ground for space-time decision-directed equalizer (STDE) application deployed in single-input-multi-output (SIMO) systems. Therefore, fast adaptation schemes, such as fast traversal filter based APA (FTF-APA), becomes impossible to utilize. The motivation of this paper deliberates on finding an effective algorithm on the basis of APA, which yields low complexity while sustaining fast convergence as well as excellent tracking ability. The performance of the proposed method is evaluated under wireless SIMO channel in respect to bit error rate (BER) behavior and computational complexity, and upon completion, the validity is confirmed. The performance of the proposed method is evaluated under wireless SIMO channel in respect to bit error rate (BER) behavior and computational complexity, and upon completion, the validity is confirmed.

The IEEE 802.11 protocol is one of the most important standards for Wireless Local Area Networks. The primary MAC protocol of 802.11 is the distributed coordination function (DCF), which is Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with binary slotted exponential backoff scheme. The basic access and the RTS/CTS access mechanisms are the two channel access methods defined in DCF. In real work environments, the common channel access method of 802.11 is the coexistence of the above two mechanisms, i.e., packets longer than a given threshold RTS_threshold are transmitted according to the RTS/CTS mechanism, otherwise, they are transmitted by means of basic mechanism. The common mechanism is called as hybrid access mechanism in this paper. Few analytical models have been proposed to evaluate the hybrid access mechanism up to now. The necessary condition which enables the hybrid mechanism to work is that the packets must be variable. But, almost all analytical models proposed for 802.11 DCF assume that the packet size is fix, so they can not study the hybrid access method. In this paper, we propose a detailed analytical model to evaluate the saturation performance of the hybrid access mechanism, in the assumption that the packet lengthes are sampled from a general distribution function f(x). Both the throughput and the delay performances are concerned. Our model is validated by extensive simulations. By means of the proposed model, we compare the performances of the above three mechanisms, i.e., basic, RTS/CTS and hybrid, under different network scenarios. Numerical results show that the hybrid access mechanism is the best choice in almost all scenarios.

Discrete Wavelet Multi-carrier Transceiver (DWMT) system, which can be viewed as a kind of OFDM, has many advantages because it uses wavelets as its base functions. In this paper we present a new sub-carrier frequency offset correction method for DWMT systems with little assistant information. The essential ideal of this algorithm is: when an orthogonal multi-carrier system is of perfect frequency synchronize, the demodulated signals of different sub-carriers are independent of each other. Whereas when frequency offset exists, intercarrier interference will distort the demodulated signal, i.e. every demodulated signal is the sum of several modulated signals' projects on the demodulating frequency. So the adjacent demodulated signals consist of the element of the same modulated signal, and these demodulated signals are correlated with each other. The degree that they correlated with each other depends on sub-carrier relative frequency offset. Since that little assistant information is used in this algorithm the spectrum efficiency can be largely increased. Simulation results shown that if the number of the sub-carrier of the DWMT system is bigger than 1000, the relative frequency offset can be limited in 2%.

Iterative multiuser detection and space-time coding are two promising techniques to increase the capacity and performance of coded multiuser systems in wireless channels. In this paper, a low-complexity iterative multiuser receiver is proposed using combined group multiuser detection and interference cancellation for space-time block coded MC-CDMA system. Turbo code is used for outer channel coding with log-MAP decoding. In each group, consisting of smaller number of users, multiuser likelihood ratios can be computed by employing MAP-based approach by taking into account of all possible transmitted symbols within each STBC time slot for these users. Moreover, once decoding information of all users are available after the first iteration, soft interference cancellation can be used instead of groupwise MAP-based detection for lower complexity, without sacrificing the performance significantly. Simulation results are presented in a Rayleigh multipath fading environment. The proposed receiver offers performance very close to that of single user system within a few iterations of joint detection and decoding.

As the number of mobile terminals (or users) keeps explosively increasing, the location management to track mobile terminals in cellular networks is becoming more important. However, the location management schemes presently adopted in cellular networks use static location information without considering the moving direction of a mobile terminal. This approach is insufficient in reflecting the different directional behaviors of mobile terminals. Thus, there is a need to develop a dynamic location management scheme more adaptive to the moving direction of a mobile terminal. This paper proposes a direction-based scheme (DBS) that can determine a location update and vary a paging area dynamically according to the moving direction. The direction vector was defined to represent the moving direction and to compute the distance from the cell where a location update occurs to the current cell. The offset operation of direction vectors represented the location of a mobile terminal in a paging area. This allowed the mobile terminal to determine whether a location update would be performed or not. In addition, simulations showed that DBS outperforms other location management schemes in most cases except in those with a low call-to-mobility ratio (CMR), particularly if a mobile terminal has directional behavior.

In wide-area wireless access systems such as satellite communications systems and stratospheric platform systems, electric power supplies for radio communications are realized using solar photovoltaic cells and/or fuel cells. However, the on-board weight limits restrict the number of cells that can be equipped. In addition, the transmission power of such systems is limited taking account of issues and regulations on sharing the same frequency band with other systems. Hence, both the frequency band and electric power is limited, which are crucial radio resources for those systems. Although radio channel allocation methods taking account of the frequency constraint only or the power constraint only have been proposed, radio channel allocation methods taking account of both constraints simultaneously have been insufficiently studied. This paper proposes a radio channel allocation method that provides global optimum allocation results by utilizing the linear programming method. The proposed method has features such that the method first allocates radio channels in proportion to the traffic demand distributed over the service coverage area and then maximizes the total radio channels allocated to systems. Numerical results are presented for a stratospheric platform system that covers an area of Japan, as an example, to demonstrate that the proposed method optimally allocates radio channels taking account of both constraints while efficiently allocating excess resources. In addition, whether a system reaches either the frequency or power limit can be estimated, by investigating the radio channel allocation results. Furthermore, enhanced linear programming models based on a method aiming at practical use of the radio channel allocation results in operation are also introduced. The enhanced model is demonstrated to work effectively to avoid unbalanced radio channel allocations over geographical areas. The proposed method and linear programming models are useful not only for making pre-plans but also for determining the amount of necessary frequency and power resources in designing systems.

In multicarrier code division multiple access (MC-CDMA) systems, the orthogonality among the spreading codes is destroyed because the channels exhibit frequency-selective fading and the despreading stage performs gain control; that is, inter-code interference (ICI) can significantly degrade system performance. This paper proposes an optimum spreading code assignment method that reflects our analysis of ICI for up and downlink MC-CDMA cellular systems over correlated frequency-selective Rayleigh fading channels. At first, we derive theoretical expressions for the desired-to-undesired signal power ratio (DUR) as a quantitative representation of ICI; computer simulation results demonstrate the validity of the analytical results. Next, based on the ICI imbalance among code pairs, we assign specific spreading codes to users to minimize ICI (in short, to maximize the multiplexing performance); our proposed method considers the quality of service (QoS) policy of users or operators. We show that the proposed method yields better performance, in terms of DUR, than the conventional methods. The proposed method can maximize the multiplexing performance of a MC-CDMA cellular system once the channel model, spreading sequence, and combining strategy have been set. Three combining strategies are examined at the despreading stage for the uplink, equal gain combining (EGC), orthogonality restoring combining (ORC), and maximum ratio combining (MRC), while two are considered for the downlink, EGC and MRC.

This paper presents a dual-frequency microstrip antenna for both 2 GHz and 5 GHz for a dual-band receiver. For a simple structure and low cost design, the microstrip feed circuit is designed on the same substrate as the antenna elements. Each antenna element is directly fed by the microstrip line, and the open stubs are loaded on the feed line of 2 GHz to suppress the higher order mode resonances between 2 GHz and 5 GHz. The feed line length of each antenna is adjusted so as to change it to the open condition at the other element frequency at the feed point. In addition, we propose the antenna structure in which two antenna elements for 2 GHz are split and placed at either sides of the 5 GHz antenna to coincide with the center positions of each antenna element. We investigate the proposed antenna by calculations and measurements to show the combiner free design for the dual band antenna.

The design, manufacture, and test results are presented for a 90polarization-rotating Van Atta array reflector with suppressed scattered field for the 1.27-GHz band. The reflector consists of 48 element antennas, half for horizontal polarization and half for vertical polarization. It receives a horizontally or vertically polarized wave and retransmits a vertically or horizontally polarized wave, respectively. The measured cross-polarized radar cross section of the reflector was 15.8 dBm² on average, which agreed well with a theoretical prediction. Although the suppression of the scattered field was limited to about -20 dB relative to the retransmitted field, we could suppress more the scattered field by accurate positioning and careful characteristics adjustment of element antennas. Theoretical calculations showed that total phase errors of the element antennas including positioning errors and impedance characteristics errors have to be within 7.5to suppress the scattered field by less than -30 dB.

JERS-1 L-band SAR data can be, especially over urban areas affected by ground radar interferences. For most of the applications of the data the interferences should be suppressed. Notch filtering during image correlation process is one of the straightforward ways to do this. However, lower the threshold is, more signals from earth surface is eliminated. In this paper, a probability density function (PDF's) model of the ground radar interference signal is worked out from experimental data, and used for the suppression of interferences and the preservation of backscattered signals. The validity of the model is confirmed against real SAR data, and a general filter threshold--applicable to all JERS-1 SAR data--without any conditions is proposed.

In this paper, we propose an autonomously distributed QoS control method for MPEG video streaming in a wide area network. The capacity of the links and the characteristics of video streams change dynamically. However, managing the condition of all the links and streams in the network is difficult. In the proposed method, the routers in the network monitor the conditions of the links and streams locally and control the transmission rate of the stream server. Picture-quality oriented fairness is achieved by reducing the transmission rate of the streams with the higher PSNR in the bottleneck link. The computer simulation results show that the proposed method can be applied to a wide area network.

We have demonstrated radio-over-fiber transmission of wireless signals at millimeter-wave bands. The system incorporated 25 km of an optical intermediate frequency feeder and 60 GHz OFDM signal transmission at 155 Mbps with a BER of less than 10^-6 was achieved within the system cell of a radius of 2.6 m under the channel condition of Line-of-Sight.

This letter describes the current mechanism for IP address configuration in the wireless Internet and examines its drawbacks, and suggests a new mechanism of address configuration which provides a reduced message exchange for address configuration in the wireless Internet over the current 4-way message exchange when performing address configuration through DHCP. Analytic performance evaluation and comparison have shown that the proposed mechanism is faster in terms of delay than the existing mechanism including reduced packet loss when in motion.

This paper proposes a Real-Time Compression Architecture (RTCA), which maximizes the efficiency of web services, while reducing the response time at the same time. The developed architecture not only guarantees the freshness of compressed contents but also minimizes the time needed to compress the message, especially when the traffic is heavy.

This letter presents an alternative analytical expression for the symbol error probability (SEP) of the coherent M-ary phase shift keying (M-PSK) system when an arbitrary phase error exists in an additive white Gaussian noise (AWGN) channel. Unlike the previous work, it is shown that the SEP performance of the M-PSK system can be completely characterized by the one- and two-dimensional Gaussian Q-functions. The new expression is numerically more convenient to manipulate than the previous results by replacing the integral operations with the built-in functions commonly available in various mathematical software tool libraries.

The multiple space-time trellis codes (M-STTC) structure is one of the Multiple Input Multiple output (MIMO) schemes providing high transmission rate and diversity and coding gain without bandwidth expansion. In this paper, an M-STTC system is proposed wherein the transmitter employs a multiple space-time TCM for the fast fading channel and the receiver has a decoding order block, several whitening processors, STTC decoders, and interference cancellers. The proposed layered receiver adopts a whitening process instead of a minimum mean squared error (MMSE) estimator, which is widely used in the BLAST type receiver. An optimum decoding order scheme is also planned since it gives at least a 2 dB gain in the proposed system in the fast flat Rayleigh fading channel of f_d T_c = 1/3 at the FER of 10^-2. For an M-STTC system employing two STTCs with four transmit and receive antennas, the layered receiver with whitening process obtains a 5 dB gain over the coded layered space-time processing in the fast flat Rayleigh fading channel at the FER of 10^-2.

A simple Minimum Rate Supporting Scheduler (MRSS) is proposed for HSDPA (High Speed Downlink Packet Access). MRSS guides the user selection in order to provide, if any, a prespecified minimum rate for each user. The simulation results show that MRSS successfully supports to keep the minimum rate up to fairly high traffic load, where existing methods fail, with tolerable degradation in throughput.

In this letter, a generalized extension of the linear Z₄ space time (ST) code of [1] is conducted to obtain a linear Z_w structure that can be flexibly used for various numbers of transmitter antennas, number of states, and modulation types. Additionally, the corresponding recursive systematic (RS) code structure is presented. The optimal code of the quadrature phase shift keying (QPSK) and 8 phase shift keying (PSK) modulation with 2 transmit antenna case is obtained from a code search and analyzed in comparison to the codes of [5]. Additionally, the structure for the 8, 32, and other number of states that were not provided in are [1] presented in this paper.

The data throughput of wireless LAN of IEEE 802.11 g in mobile environment is measured according to the distance between AP and NIC, and the moving speed. It shows there is no degradation of the maximum data throughput of 20 Mbps due to the vehicle speed up to 160 km/h.

This paper presents a performance comparison between carrier interferometry coded OFDM (CI/COFDM) and typical coded OFDM (COFDM) using multiple receive antennas. The feature of CI/COFDM with diversity reception is to combine the time diversity benefit introduced by channel coding with the frequency and space diversity benefits created by frequency-domain equalization (FDE). Simulation results for QPSK showed that, at the perfect channel estimation, CI/COFDM outperforms COFDM under frequency and time selective fading channels because of the powerful time diversity benefit introduced by channel coding with time interleaving. However, at the imperfect channel estimation, this advantage of CI/COFDM over COFDM becomes very limited.

In order to exploit the benefits of soft handoff, finding good values of handoff control parameters is important. In cellular system specifications such as IS-95C and WCDMA, handoff decision algorithm includes signal strength averaging and drop timer in addition to hysteresis. This paper analyzes the effects of signal strength averaging and drop timer and their performance tradeoffs. Because averaging and drop timer are both based on time delay, one may expect that they have similar impact on soft handoff performance. The results show that the effects of averaging and drop timer are rather similar and closely connected in terms of reducing the signaling overhead. However, they have different impacts on resource usage and diversity gain of the system.

In this paper, iterative adaptive soft parallel interference canceller (ASPIC) is proposed for turbo coded multiple-input multiple-output (MIMO) multiplexing. ASPIC is applied to transform a MIMO channel into single-input multiple-output (SIMO) channels for maximum ratio diversity combining (MRC). In the ASPIC, replicas of the interference are generated and subtracted from the received signals. For the generation of replicas with higher reliability, iterative ASPIC is proposed. It performs the iterative interference cancellation by feedback of the log-likelihood ratio (LLR) sequence obtained as the turbo decoder output. For iterative ASPIC, at the transmitter, the information sequence and parity sequence are transmitted from different antennas. In this paper, the achievable bit error rate (BER) performance, in a Rayleigh fading channel, for the turbo coded MIMO multiplexing with the proposed iterative ASPIC system is evaluated by computer simulation.

In this paper, a compact and wideband printed monopole antenna is proposed. The proposed antenna is fed by CPW line and has two stubs for impedance matching. A simple monopole element has resonance frequency of 2.5 GHz (low resonance frequency). High resonance frequency of 5.5 GHz and wideband characteristic can be achieved by adjusting the position and size of stubs. The designed antenna has dimension of 0.125 λ₀ height and 0.16 λ₀ width where λ₀ is the free-space wavelength at 2.5 GHz. The measured bandwidth of the antenna is 3.56 GHz (2.47-6.03 GHz) for S₁₁ less than -10 dB. FDTD method is used to analyze the proposed antenna with wideband characteristic.

In this letter, we present a new triple-band planar antenna, a non-uniform meandered and fork-type grounded antenna (NMFGA), for mobile communication systems. The antenna is designed for triple-band operations at 900 MHz, 1800 MHz, and 2450 MHz bands. A prototype of the NMFGA was constructed and studied. Measured and simulated return loss and measured radiation patterns were obtained. The experimental results demonstrate the attractive bandwidth and radiation performance of the newly developed antenna for all the three bands.

The three main reasons why the new H.264 (MPEG-4 AVC) video coding standard has a significant performance better than the other standards are the adoption of variable block sizes, multiple reference frames, and the consideration of rate distortion optimization within the codec. However, these features incur a considerable increase in encoder complexity. As for the multiple reference frames motion estimation, the increased computation is in proportion to the number of searched reference frames. In this paper, a fast multi-frame selection method is proposed for H.264 video coding. The proposed scheme can efficiently determine the best reference frame from the allowed five reference frames. Simulation results show that the speed of the proposed method is over two times faster than that of the original scheme adopted in JVT reference software JM73 while keeping the similar video quality and bit-rate.

This paper introduces a new frame-based bit-rate control scheme for bandwidth-adaptive video coding. Proposed method can accurately adapt to the rapid varying scene characteristics by reducing the number of occurrences of the extrapolations while updating the rate-distortion model used for determine the appropriate quantization steps.