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.

Radio on fiber transmission technique using a conventional intermediate frequency (IF)-band Surface Acoustic Wave (SAW) filter has been proposed in order to satisfy the 3rd Generation Partnership Project (3GPP) specification for International Mobile Telecommunications-2000 (IMT-2000) cellular systems. For the 3GPP specification, a key issue is to expand the dynamic range limited by clipping distortion of laser diode. In order to expand the dynamic range, for the down link, a narrow bandpass SAW filter is introduced after optical transmission, because the SAW filter can suppress the distortion caused by clipping of laser diode and improve the performance of adjacent channel leakage power ratio. For the up link, an optical modulation index (OMI) of a laser diode is optimized to improve the noise figure (NF) performance by controlling the gain of an amplifier between the antenna and the laser diode. As a result, both power control dynamic range of more than 44 dB in the down link and dynamic range of more than 97 dB in the up link were achieved in 6 km optical transmission. Other important parameters, such as Error Vector Magnitude, Reference Sensitivity Level, and so on in the 3GPP specification, were also satisfied.

A decentralized estimation system usually contains a number of remotely located local sensors that can pre-process observed signal and convey the processed data to a fusion center that makes a final estimation. The local sensors are linked to the data fusion center by transmission channels. When the observation (or estimate of parameter) is quantized at the peripheral sensors and an assumption of conditionally independent sensor data is made, due to potential communication constraints on the channels, the problem of quantization design and bandwidth allocation among the channels linking local sensors to the fusion center is studied in this letter.

The authors propose a circular polarization generator using a square waveguide with L-type probe located on a side wall of waveguide. The sides of the L-probe forming the right angle are placed perpendicular to the direction of propagation. The position of the right angle is kept at a distance of a quarter-wave length from the side wall. The device provides 27% bandwidth for 3 dB axial ratio at 8.4 GHz on azimuth interval of 160.

The fiber-optic sectorized remote antenna system by using the radio frequency (RF) optical transmission technique was promising for increasing the number of subscribers in the millimeter-wave broadband wireless access (MMW BWA) networks. To realize the cost-effectiveness of the fiber-optic sectorized remote antenna system covering four areas, we reached the conclusion that the best multiplexing schemes were the sub-carrier division multiplexing (SCM) of the intermediate frequency (IF) signals of 2 GHz for the down link, the coarse wavelength division multiplexing (CWDM) with the IF signals optical transmission for the up link and 1.3/1.55 µm-WDM for multiplexing the down link and the up link. In addition, the target specifications of this SCM-CWDM system were described, and the designs of the carrier to noise ratio (CNR) and the third order intermodulation distortion (IM3) were examined.

We investigated a tunable delay-line using an optical single-sideband modulator and an optical fiber loop. The single-sideband modulator consists of four optical modulators and an RF electric signal source. The fiber loop has a fiber Bragg grating and a couple of optical circulators. The number of times light circulates in the loop depends on the frequency of the rf-signal fed to the modulators. By using numerical simulations, we discussed the deformation of the waveform in the delay-line due to the fiber Bragg gratings, the modulators and the optical amplifiers put in the loop.

The paper presents a dual-band switchable low noise amplifier implemented in 0.25-µm CMOS technology for 5-GHz wireless multimedia applications. The high-speed wireless multimedia applications call for broadband design techniques for RF circuits. Instead of using conventional broadband techniques not well suitable for CMOS implementation, a dual-band switchable load is proposed for broadband LNA design. The dual-band switchable load enables the LNA operate at the lower or the upper band at 5-GHz band by a 1-bit control signal. The LNA exhibits over 17 dB power gain, 3.5 dB noise figure and input 1-dB compression point -23 dBm in both frequency bands. It draws 9.5 mA from 2.5 V supply. The power gain remains larger than 16 dB as temperature varies from -5 to 65.

High-speed streaming services are considered to be among the most promising services for the broadband Internet of the next generation. A contents delivery network (CDN) that allows effective and scalable content delivery will be required in this role. However, the actual requirements for the CDN, such as quality of service (QoS), the service deployment strategy and technical issues are not yet to be defined. In this paper, the bandwidth requirement of the CDN is derived through QoS evaluation. On the basis of this requirement, we propose two feasible CDN configurations: an IP technology based configuration and an optical video distribution technology based configuration. Finally, we make lists of technical issues for the configurations and discuss some of the possible solutions.

Transmit diversity schemes are an effective capacity improvement method for down link of wideband code division multiple access (W-CDMA) systems. In this paper, we propose to use transmit antenna subset selection scheme in conjunction with closed loop transmit adaptive array (TxAA). The proposed scheme selects NS optimum antennas among NT (>NS) transmit antennas in order to maximize diversity gain from the selected antennas, and also reduces the cost of RF chains by employing two different types of RF modules for the selected and the unselected antenna group, respectively. Computer simulation results show performance improvement by the proposed scheme over the conventional TxAA when considering up link control information feedback.

We describe a low-cost and extremely stable millimeter-wave transmission system that uses a double-side-band (DSB) millimeter-wave self-heterodyne transmission technique. This technique allows us to use a comparatively low-cost and unstable millimeter-wave oscillator regardless of the modulation format. Furthermore, a transmission band-pass-filter (BPF) is not needed in the millimeter-wave band. The system cost can therefore be substantially reduced. We have theoretically and experimentally evaluated the carrier-to-noise power ratio (CNR) performance that can be obtained when using this technique relative to that attainable through a conventional millimeter-wave self-heterodyne technique where a single-side-band signal is transmitted. Our results show that the DSB self-heterodyne transmission technique can improve CNR by more than 3 dB.

The banyan network is a popular and basic structure of the multi-stage ATM switches. This paper presents a novel approach to resolve the internal blocking of the banyan network by using a Non-Blocking Permutation Generator (NBPG). The NBPG performs two functions, i.e., the first is to extract the conflict cells from the incoming cells and the second is to re-assign new input port addresses to the conflict cells. As a result, NBPG generates non-blocking I/O permutations. To estimate the performance of the NBPG, we provide the results of several simulations.

A simple configuration for millimeter-wave fiber-wireless transmission, with remote local-oscillator (LO) delivery from the central office, both for the uplink and for the downlink, and a simple, cost-effective, base-station solution is proposed. Under the assumption of using commercially available components and a conventional single-mode fiber (with dispersion of 17 ps/nm/km at 1.55 µm), our numerical results show that, with a laser linewidth of 150 MHz, a laser power of 0 dBm and an optical gain of only 6 dB, it is possible to transmit, without repeaters, data rates of 622 Mbit/s across about 18 km at a bit-error-rate of 10-9. By increasing the optical gain to 24 dB, the link length can be increased to approximately 67 km for a laser linewidth of 75 MHz and to 78 km for a laser linewidth 1 MHz.

In this letter, we evaluate the performance of several adaptive and non-adaptive AQM schemes for congestion control in a dynamic network environment with variable bandwidth links. The AQM schemes examined are RED, BLUE, Adaptive RED, REM, AVQ and PI controller. We compare their queueing performance and show that none of them can derive stable queue length and low packet drop rate simultaneously in networks where both input traffic and available output bandwidth are time varying. Adaptive and efficient algorithms should be designed and applied in order to improve the adaptiveness and robustness of congestion control in dynamic networks such as Internet.

An optical fiber line testing system is essential for reducing maintenance costs and improving service reliability in optical access networks. NTT has already developed such a system called AURORA (AUtomatic optical fibeR opeRAtions support system). As we already use the 1310 and 1550nm wavelengths for communication, we use the 1650nm wavelength for maintenance testing in accordance with ITU-T recommendation L.41. Recently, a long wavelength band (L-band) that extends to 1625nm has begun to be used for WDM transmission. With a view to monitoring optical fiber cables transmitting L-band communication light, an attractive way of separating the U-band wavelength of the test lights from the L-band wavelength of the communication light is to use a chirped fiber Bragg grating (FBG) filter because of its steep optical spectrum. However, it is difficult to measure fiber characteristics with an optical time-domain reflectometer (OTDR), because multi-reflections appear in the OTDR trace when FBG filters are installed at both ends of an optical fiber line. In this paper, we consider this problem and show that the reflection loss at the port of a test access module (TAM) must be more than 36.6dB. We also describe the system design for an extended optical fiber line testing system using an L/U-band optical coupler, which has two chirped FBGs between two 4-port circulators for L-band WDM transmission. In this system, the reflection loss at a TAM port was 38.1dB, and we confirmed that there was no degradation in the OTDR trace caused by multi-reflections at the optical filters.

A novel optical packet switch architecture is proposed that can support simultaneous processing and routing of packets in bands, without disturbing the granularity of the system. The packet router consists of a waveband converter and an AWG, combined in such a way that processing and switching of packets within and between the wavebands is allowed. The waveband converter is based on four-wave mixing in semiconductor optical amplifiers. Experimental results of the waveband conversion technique are presented to prove the feasibility of such a scheme. Simulation results of an 12 packet router are used to explain the operation of such a subsystem for a synchronous optical packet switched network.

To sample a band-limited analog signal directly from the high frequency down to the baseband for the digital signal processing with significantly reduced computation, several concepts of the bandpass sampling are introduced. In this paper, a robust bandpass sampling scheme when there exist frequency deviations due to the channel effect and hardware instability is proposed for practical use, and the effects of the frequency deviations are discussed to select a proper sampling frequency.

A broadband access network is required for supporting the increased Internet data traffic. One of the most cost-effective solutions is the Ethernet Passive Optical Networks (E-PONs) with the efficient bandwidth assignment function by which the upstream bandwidth can be shared among access users. To satisfy the services with heterogeneous QoS characteristics, it is very important to provide QoS guaranteed network access while utilize the bandwidth efficiently. In this paper, a dual DEB-GPS scheduler in E-PON is presented to provide delay-constraint and lossless QoS guarantee to QoS service and maximize the bandwidth to best-effort service. Simulation results show our scheme outperforms the conventional bandwidth allocation scheme in E-PON system.

We will present a novel core mode blocker fabricated with hydrogen loaded Ge-B co-doped fiber exposed to the electric arc discharge using local heat exposure. Tunable bandpass filter based on cascaded LPFGs with a core mode blocker inserted between the LPFGs will be also described. The characteristics are: 6.5-nm bandwidth, 30-nm tuning range, and 15-dB dynamic range, respectively. It can be very useful for application to wavelength stabilization and physical sensors.

A virtual private network (VPN) service is likely to be used by customers as a replacement for networks constructed using private lines, and thus its functionality should include the performance guarantee provided to those customers. To provide guaranteed services, the network provider allocates appropriate capacities to multiple virtual backbone networks such that the underlying network can be shared among them. As VPN users are demanding reliable and dynamic allocation of capacities, recently the capacity resizing approach has been considered as a cost efficient way of providing virtual network services. We propose a new scheme for dynamic allocation of virtual link capacities. The allocated capacities are adjusted dynamically according to the users' requests such that their capacities are increased in a fair manner and the total reservation does not overwhelm the underlying network. Depending on the network's status and allocation policy, a virtual link may increase or decrease its capacity, for example, for a monetary incentive. VPN users send control packets whenever they want to resize their capacities, and the network handles them in an efficient and fair way. The simulation and analytic results in this paper show that our scheme is simple and robust such that the users and the network communicate using simple control packets and the link capacities are allocated efficiently.

GPS receivers are susceptible to jamming by interference. This paper proposes a recurrent neural network (RNN) predictor for new application in GPS anti-jamming systems. Five types of narrowband jammers, i. e. AR process, continuous wave interference (CWI), multi-tone CWI, swept CWI, and pulsed CWI, are considered in order to emulate realistic conditions. As the observation noise of received signals is highly non-Gaussian, an RNN estimator with a nonlinear structure is employed to accurately predict the narrowband signals based on a real-time learning method. The node decoupled extended Kalman filter (NDEKF) algorithm is adopted to achieve better performance in terms of convergence rate and quality of solution while requiring less computation time and memory. We analyze the computational complexity and memory requirements of the NDEKF approach and compare them to the global extended Kalman filter (GEKF) training paradigm. Simulation results show that our proposed scheme achieves a superior performance to conventional linear/nonlinear predictors in terms of SNR improvement and mean squared prediction error (MSPE) while providing inherent protection against a broad class of interference environments.