Recently, layer-4 (L4) switches have been widely used as load balancing front-end routers for Web server clusters. The typical L4 switch attempts to balance load among the servers by estimating load using the load metrics measured in the front-end and/or the servers. However, insufficient load metrics, measurement overhead, and feedback delay often cause misestimate of server load. This may incur significant dynamic load imbalance among the servers particularly when the variation of requested content is high. In this paper, we propose a new content sniffer based load distribution strategy. By sniffing the requests being forwarded to the servers and by extracting load metrics from them, the L4 switch with our strategy more timely and accurately estimates server load without the help of back-end servers. Thus it can properly react to dynamic load imbalance among the servers under various workloads. Our experimental results demonstrate substantial performance improvements over other load balancing strategies used in the typical L4 switch.

An optical FM system using an optical FM LD (laser diode) and an optical frequency discriminator (OFD), in which a nonlinear compensation scheme based on the interaction between its nonlinearities can minimize intermodulation distortion. This paper theoretically investigates the minimization influence for 3rd plus 5th order intermodulation distortion power for an optical FM radio-on-fiber system. The carrier to noise-plus-distortion power ratio (CNDR) is theoretically analyzed in employing the OFD whose transmission characteristic is controlled by a phase shifter. The results show that the designed receiver can achieve higher CNDR in the application of multicarrier transmission.

This paper investigates based on laboratory experiments the multiuser interference suppression effect of the coherent adaptive antenna array diversity (CAAAD) receiver employing an optical fiber feeder in the intermediate frequency (IF) stage, aiming at the practical use of adaptive antenna array beam forming techniques based on the W-CDMA air interface. We employed a configuration in which the optical fiber conversion, i.e., electrical-to-optical (E/O) conversion (vice versa (O/E)), is performed on a received signal amplified by an automatic gain control (AGC) amplifier in the IF stage, to abate the impact of the noise component generated by the E/O (O/E) converters. We first show by computer simulation the superiority of the optical fiber conversion in the IF stage to that in the radio frequency (RF) stage based on the achievable bit error rate (BER) performance. Furthermore, experimental results elucidate that the loss in the required transmit signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) of the implemented CAAAD receiver at the average BER of 10-3 employing the optical fiber feeders in the IF stage compared to that with coaxial cables is within a mere 0.2 dB (six antennas, three users, two-path Rayleigh fading channel model, and the ratio of the target signal energy per bit-to-interference power spectrum density ratio (Eb/I0) of the desired user to that of the interfering users for fast transmission power control (TPC) is ΔEb/I0=-15 dB).

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.

Recently, we have discovered wave propagation phenomena which are continuously existing waves of changing phase states between two adjacent oscillators from in-phase to anti-phase or from anti-phase to in-phase in van der Pol oscillators coupled by inductors as a ladder. We named the phenomena as "phase-inversion waves." In this study, phase-inversion waves which exist in the state of in-and-anti-phase synchronization have been found. We observe the phenomena by circuit experiments and computer calculations, and investigate them.

This paper proposes an efficient random access channel (RACH) transmission method that utilizes soft-combined consecutively retransmitted message data packets according to the Quality of Service (QoS) requirements for broadband multi-carrier/DS-CDMA (MC/DS-CDMA) in the reverse link. In the proposed scheme, the relative transmission power of a message from that of a successfully detected preamble for non-real time (NRT) type traffic data is significantly reduced by soft-combining several retransmitted message data packets thanks to time diversity since the delay requirement is relaxed. Meanwhile, for real time (RT) type traffic data, the relative transmission power of the message from that of the detected preamble is increased in order to reduce the packet error rate with a limited number of retransmissions. Simulation results elucidate that the total required average received signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) for error-free transmission with time diversity for NRT type traffic data is reduced by more than 2 dB compared to that for conventional RACH without the relative transmission power control for a wide rage of fading maximum Doppler frequencies.

This paper compares the radio link capacity between multi-carrier/DS-CDMA (MC/DS-CDMA) and multi-carrier CDMA (MC-CDMA) for reverse-link broadband packet wireless access taking into consideration: the asynchronous signal reception at the receiver; the path timing or symbol timing detection of all major subject factors; and the channel estimation error. Simulation results show that although the influence of the asynchronous signal reception on the packet error rate (PER) performance in MC-CDMA is slight, the degradation caused by the channel estimation error in MC-CDMA is severe compared to that caused by the path timing detection error in MC/DS-CDMA. Consequently, the required average received signal energy per bit-to-background noise spectrum density ratio (Eb/N0) at the average PER of 10-2 in MC/DS-CDMA is reduced by approximately 4.5 dB compared to that in MC-CDMA assuming a 12-path exponential decayed Rayleigh fading channel. Furthermore, the number of accommodated users in MC/DS-CDMA is 2.5 fold greater than that in MC-CDMA employing two-branch antenna diversity reception. Therefore, we conclude that MC/DS-CDMA is more appropriate than MC-CDMA for the reverse link broadband packet wireless access, and that it has advantageous features such as an inherently much lower peak-to-average power ratio compared to MC-CDMA, which accompanies a high peak-to-average power ratio causing an increase in the back-off of the power amplifier.

Frequency channel allocation according to the interference among links is important in autonomous distributed control wireless base station networks from the viewpoint of efficient frequency utilization. It is generally difficult to estimate the interference imposed on other links in a distributed control scheme. This paper proposes a novel frequency channel allocation scheme employing distributed control utilizing broadcast signals to estimate the intensities and frequencies of the interference to other links. The frequency channel, which can be allocated to a link from the viewpoint of the degree of the interference imposed on other links, can be found by receiving broadcast signals. Simulation results show that the proposed scheme efficiently allocates frequency channels to each link to avoid the interference.

This paper proposes an ROF ubiquitous antenna architecture for the wireless CDMA system. The proposed system separates each component of independent signals passing through the multipath in radio and optical links, which are gathered at passive double star link, by using RAKE reception and the macrodiversity effect is obtained. Theoretical analysis shows that the proposed system improves BER performance by 22 dB and reduces the transmission power and its control range by 19 dB.

A novel interference reduction method, transmit power and window control (TPWC), is proposed to enhance the system capacity in the downlink of code division multiple access (CDMA) cellular packet systems. TPWC measures the propagation conditions and calculates the required instantaneous transmit power between a base station (BS) and a mobile station (MS). Then, TPWC sends packets only during a transmit time-window, in which the packets can be sent with less power than a predetermined threshold. TPWC reduces the average transmit power at the cost of an extra transmission delay at the BS. Computer simulations show that TPWC enhances the system capacity by two-fold in a CDMA cellular packet system when each MS has a loading ratio of 0.5 and an average delay allowance of 5 ms for the unit packet length of 1 ms. Furthermore, this paper proposes a multi-link packet transmission (MLPT) scheme in order to reduce the delay caused by TPWC. When an MS is at the cell edge, packets are distributed by MLPT to multiple BSs, from which packets are sent to the MS; thus, the transmission delay can be reduced by utilizing the transmit windows of each BS.

In the paper, we propose a new method for chromatic dispersion measurement of WDM components in both transmission and reflection, employing photonic microwave technology. The dispersion can be determined by measuring the frequency spectrum range change of the microwave notch filter. The method features the advantages of low-cost and simplicity. Experimental results demonstrate that our setup is capable of measuring relative group delay with better than 1 ps time resolution and the measurement results show a good agreement with that measured by the conventional phase-shift technique.

A mobile station (MS) positioning method using signal strength is an algorithm to estimate the geographical position of a target MS based on measured strength of signals transmitted to/from the MS from/to multiple base stations (BSs) at known geographical positions. This paper proposes a novel MS positioning method using signal strength in cellular systems. The primary sources of position location error for positioning methods using signal strength are multipath fading and shadowing. Although signal strength averaging can help to reduce the effect of multipath fading, the effect of shadowing still remains. In order to eliminate the error caused by shadowing, the proposed method applies a statistical approach and a minimum mean squared error (MMSE) criterion to determine a position estimate. The performance of the proposed method is compared to that of a maximum likelihood (ML) positioning method and a cell-site positioning method. The performance is obtained by computer simulations and field experiments. A computer simulation result shows that the proposed method can determine position estimates in higher probability than the ML method. Also, it is shown that the proposed method provides higher accuracy than the ML method and the cell-site method.

In this paper, a simple subcarrier selection combining technique is proposed for orthogonal frequency-division multiplexing (OFDM) systems with multiple receive antennas. The subcarrier-based selection algorithm is developed in the frequency domain to achieve an optimal selection combining gain for OFDM systems, instead of the antenna-based selection algorithms in the time domain or frequency domain. The proposed technique selects an optimal subcarrier with a maximum channel gain among all the receive antennas with the same subcarrier position, based on the estimated channel frequency response during the training period. Hardware complexity for the proposed technique is minimal since it requires single front-end with multiple receive antennas and single baseband demodulator. It is shown by computer simulation that a significant gain can be achieved by the proposed technique over the conventional selection combining technique for OFDM systems in practical situations.

The coarse frequency offset estimation algorithm has to provide an initial frequency error estimate, which is sufficiently accurate in order to operate reliably for the subsequent fine frequency synchronization algorithm. In this letter, we deal with a coarse frequency offset estimation for digital audio broadcasting. We propose an improved frequency synchronization scheme which uses the minimum energy detection scheme. We compare the performance of proposed scheme with that of conventional schemes under AWGN and Rayleigh channel. It has been shown that the proposed algorithm has high robustness against a large range of symbol timing offset with a low complexity.

In this paper, we propose an efficient requantization method for transcoding of MPEG video. Transcoding is the process of converting a compressed video format to another different compressed video format. We propose an simple and efficient transcoding by requantization in which MPEG coded video at high bit-rate is converted into MPEG bitstream at lower bit-rate. To reduce a image quality degradation, we use HVS (Human Visual System). By using this effect, the part of image in high activity region is coarsely quantized without seriously degrading the image quality. Experimental results show that the proposed method can provide good performance.

A bi-directional and multi-channel wireless telemetry capsule, 11 mm in diameter, is presented that can transmit video images from inside the human body and receive a control signal from an external control unit. The proposed telemetry capsule includes transmitting and receiving antennas, a demodulator, decoder, four LEDs, and CMOS image sensor, along with their driving circuits. The receiver demodulates the received signal radiated from the external control unit. Next, the decoder receives the stream of control signals and interprets five of the binary digits as an address code. Thereafter, the remaining signal is interpreted as four bits of binary data. Consequently, the proposed telemetry module can demodulate external signals so as to control the behavior of the camera and four LEDs during the transmission of video images. The proposed telemetry capsule can simultaneously transmit a video signal and receive a control signal determining the behavior of the capsule itself. As a result, the total power consumption of the telemetry capsule can be reduced by turning off the camera power during dead time and separately controlling the LEDs for proper illumination of the intestine.

The electrical characteristics of biologically active points (BAPs) compared with those of the surrounding human skins are investigated. We confirm that BAPs have lower resistance and higher capacitance than the surrounding skins have. We find that BAPs have higher characteristic frequency than surrounding skins and sometimes the impedance spectra of BAPs have two semicircles on the complex impedance plane. Therefore, we propose the skin impedance model that is proper to the BAPs. This model describes our experimental results sufficiently.

A LiNbO3 piezoelectric actuator controls the Au-Au contact gap. The control accuracy of the actuator is within the sub-micron range. Contact voltage, contact current, displacement of electrodes and driving voltage of the actuator were continuously and synchronously recorded by an A/D converter and send to a computer. The measured oscillograph data for 1500 contact operation were processed by the computer. Factors of discharge and bridge phenomena were derived at a contact operation. The delay time between displacement and driving signal of the actuator increased when one side of electric contact were vibrated. The resonance was seen in the actuator, and the dependency to the current and the amplitude was seen.

This paper presents a modified microwave radio-thermometer (MRTM) with material characteristic estimator and multiple temperature conversion tables to measure subcutaneous temperature of a living body. This estimator provides a temperature retrieval unit with material characteristics such as permittivity, conductivity, thickness and geometry of the living body. The temperature retrieval unit with multiple temperature conversion tables can select one of the tables and compute temperature value corresponding to measured radiation power. In the experiments, it was shown that the radio-thermometer could reduce measurement errors of about 0.82 to 7.68 for the cases of distilled water and mixed liquid # 5 with thickness of 29.5 cm and 9.5 cm at the temperature of 37.

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.