We have already proposed a carrier power control scheme of OFDM that makes it possible to improve the bit error rate characteristic. However, the data on the lost carriers by the severe fading or large additive noise can't be recovered by only this power control scheme. In this paper, a method of transmission power control of OFDM carriers combined with data spreading scheme in the frequency domain is proposed. In the proposed system, transmission power of each carrier is controlled so as to maximize the average signal to noise ratio of the data symbols after de-spreading the signals from DFT. As the results of computer simulations, it is confirmed that the proposed system can improve the bit error rate characteristics under multi-path channel.

A novel periodic element for the sandwich photonic bandgap (PBG) structure named as H-shape element is presented in this paper. Sandwich PBG structure is a kind of PBG structure whose periodic lattice is buried in the midmost of the substrate. There's no requirement to drill or suspend the substrate. The new H-shape element is made of a central block connected with a long and narrow block on either side, and possesses a quite deep forbidden gap, whose width and depth can be tuned by varying the dimension of the central block. Theoretical results, as confirmed experimentally, indicate that the maximum insertion loss in the stopband is up to 80 dB. This sandwich microstrip structure can be constructed using conventional printed-circuit-board fabrication processes and integrated with other microwave components in a multilayered circuit. An improved notch filter with chirped central blocks is presented. The length of the filter is reduced by 16.7%, and the fractional bandwidth is increased by 8.1% compared with that of a conventional sandwich microstrip notch filter on the same substrate. The experimental results agree well with the finite difference time domain (FDTD) simulations.

10-Gbit/s wireless data transmission using 120-GHz millimeter-wave (MMW) photonic technologies is presented. For such high-data-rate transmission, we have newly developed a planar broadband receiver that employs a > 200-GHz Schottky diode and a slot-ring antenna with a 10-dB bandwidth of 30 GHz. The receiver achieves a high video sensitivity of 190 mV/mW at 120 GHz due to its optimized data output circuit. The MMW wireless link using the receiver and photonic transmitter has data transmission bandwidth of 8.5 GHz, and succeeded in 10-Gbit/s data transmission, which is the fastest ever achieved through a MMW wireless link.

Recently, diverse multimedia applications with stringent multiple Quality of Service (QoS) requirements have been increasing. In particular, multicast communication has become more popular because of its availability and for efficient use of network resources. Most multicasts are point-to-multipoint, in which a source delivers data to multiple designated recipients, such as for video or audio distribution. In the near future, multipoint-to-multipoint communication services, including multimedia collaborations such as video conferencing and distant-learning, will be developed. However, when a conventional multicast routing algorithm is applied to a multipoint-to-multipoint communication service, it might result in excessive traffic concentration on some links. Therefore, we propose a new multipoint-to-multipoint routing method. It utilizes the Fallback+ algorithm to perform multicast routing for the purpose of satisfying multiple QoS requirements and alleviating traffic concentrations. Simulation experiments show that our method improves traffic load balance and achieves efficient use of network resources.

This Letter proposes a way of resolving spreading code mismatch in blind multiuser detection with subspace-based technique. It has been shown that subspace-based (SSB) blind multiuser detectors demonstrate the advantages of fast convergence speed and less sensitivity to spreading code mismatch over constrained mean output energy (CMOE) detectors. With a corrected scheme of the desired user code, the proposed method offers more robust capabilities over existing SSB techniques. Numerical results show that the effectiveness of the proposed technique.

In this paper, a predistorter using low frequency intermodulation (IM) signals is proposed. The harmonic generator of the proposed predistorter that consists of a hybrid coupler and four diodes biased separately extracts a second order low frequency IM signal. And with multiplication of second order IM signals, fourth order IM signal is obtained. A vector modulator, modulate fundamental signal with low frequency IM signals, generates predistortion IM signals and controls amplitude/phase of them with modulation factors. As a result, this predistorter is suppressed individual order intermodulation distortion signals of power amplifier effectively. The suggested predistorter has been manufactured to operate in Korea PCS base-station transmitting band (1840-1870 MHz). The test results show that the third order IM is cancelled more than 20 dB and the fifth order IM is cancelled about 10 dB for CW two-tone signals. Also, it's improved the adjacent channel power ratio (ACPR) more than 10 dB for CDMA (IS-95) signals.

An IP (Internet Protocol) over WDM network is expected to be an infrastructure for the next-generation Internet by directly carrying IP packets on the WDM-based network. Among several architectures for IP over WDM networks, one promising way is to overlay a logical topology consisting of lightpaths over the physical WDM network so that IP packets are carried on the lightpaths. The conventional methods for designing the logical topology have been focusing on maximizing throughput of the traffic. However, when the WDM network is applied to IP, the end-to-end path provided by the logical topology of the WDM network is not suitable to IP since IP has its own metrics for route selection. In this paper, we propose a new heuristic algorithm to design a logical topology by considering the delay between nodes as an objective metric. This algorithm uses a non-bifurcated flow deviation to obtain a set of routes that IP packets are expected to traverse. Our proposal is then compared with conventional methods in terms of the average packet delays and throughput. It is shown that our method becomes effective when the number of wavelengths is a limited resource.

In this paper, we first address the current state of broadband services in Korea. Here, we introduce relevant statistics, current access network architectures, and activities of some major carriers. We also briefly introduce Korean government's policies on research and development projects and plans for promoting the country toward an advanced information society. We then introduce a large-scale, collaborative project named "Photonic Access To the Home (PATH)" with five-year period of performance, started in year 2002. The project is under leadership of the government and ETRI in collaboration with universities and industry. We finally provide a rather detailed description of the FTTH (Fiber To The Home) technology based on the wavelength division multiplexing technology, which has been under research in our laboratory as a part of the PATH project. We show some of our achievement including new architectures and networking principles for the FTTH network, analysis of the dynamic allocation of user bandwidth, and the experiment for a low-cost WDM optical source.

Implementation issues on generalized multi-protocol label switching (GMPLS) -based photonic switching networks are experimentally analyzed. A resilient control plane architecture using in-fiber and out-of-fiber control channels is proposed to resolve issues of establishing the control plane in out-of-band networks. The resilient control plane is demonstrated in a photonic cross-connect (PXC) -based GMPLS network involving a 1,000 km transmission line. Fast signaling for provisioning and restoration operation is accomplished by implementing in-fiber control channels as primary, and the out-of-fiber control channels effectively operate as secondary and restore messaging of the control information between neighbors. The control channel protection is initiated by the link management protocol (LMP). Using the test bed, optical layer routing operation is investigated to assess the effects on the signal quality of wavelength paths, and transparent routing of the wavelength paths over one-hop and two-hops route is demonstrated within 1 dB difference regarding the Q factor. Stable operation of loss of light (LOL) -triggered restoration is demonstrated by setting the optical level threshold 5 dB higher than the amplified spontaneous emission (ASE) noise level.

European research Framework Programs and in particular their impact on international standardization for the development of third generation mobile communication systems are reviewed, which are currently being deployed. In 2002 the European Commission launched the 6th Framework Program. In parallel, research on systems beyond third generation started already. Therefore, international organizations such as the Wireless World Research Forum (WWRF) were established. WWRF and other international activities are presented. The vision of the Wireless World is developed from the user perspective, where already a high degree of international harmonization was achieved. The building blocks of the Wireless World and the resulting necessary major research areas are summarized. Future research projects on systems beyond third generation will focus on these topics. Global cooperation will be an important prerequisite to achieve harmonized future standards. Therefore, the 6th Framework Program of the European Commission will provide an important platform for international cooperation. The 6th Framework Program is described in detail.

We report on the first demonstration of single sideband (SSB) modulated time stretch system. In addition, we present an analytical model relating the system performance to the phase and amplitude mismatches in the SSB modulator. The results show that, fortuitously, the system is tolerant to such mismatches. In particular, using commercially available components,the dispersion induced power penalty can be kept below 2.5 dB over 4-20 GHz bandwidth for any stretch factor. The experiments demonstrate 120 Gsample/s real-time capture of a 20 GHz SSB-modulated microwave signal.

This paper focuses on a global ultrasonic system for self-localization of a mobile robot. The global ultrasonic system consists of some ultrasonic generators fixed at some arbitrary position in the global coordinates and two receivers in the moving coordinates of the mobile robot. This system is used to obtain the state vector of the mobile robot in the global coordinates from the distance measurement between the ultrasonic generator and the receiver. In order to avoid the cross-talk and to synchronize the ultrasonic sensors, the sequential cuing technique using small-sized radio frequency module is adopted. An extended Kalman filter algorithm is used to process the noisy ultrasonic signal and to estimate the state vector. Computer simulations and experiments are conducted to verify the effectiveness of the proposed global ultrasonic system.

Without transmit power control (TPC) and Rake combining, the uplink capacity of a direct sequence code division multiple access (DS-CDMA) packet mobile communication system significantly degrades due to the near-far problem and multipath fading. In this letter, assuming a single cell system with an interference-limited channel, the impact of the joint use of Rake combining and TPC on the uplink capacity is evaluated by computer simulation. Slow TPC is found to give a link capacity larger than fast TPC. This is because, with slow TPC, the received signal power variations due to fading remain intact and this results in a larger capture effect.

We present a new method called the slope nucleation method (SNM) for the growth of high-quality organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystals. The SNM features the ability to control the nucleation position and the growth orientation of DAST crystals in spontaneous nucleated growth. X-ray diffraction (XRD) rocking curve measurements indicate that the SNM is effective for obtaining high-quality DAST crystals as compared to conventional spontaneous nucleation methods. We evaluated the electro-optic (EO) properties of DAST crystals by an external EO probing technique because DAST crystals are expected to be used in transverse-field probing. DAST crystals exhibits nearly five-times EO sensitivity enhancement as compared to inorganic KTiOPO4 (KTP) crystals at 90 kHz. The larger EO signal power obtained from the DAST crystal was almost constant at low frequencies (30 Hz to 90 kHz), whereas the KTP crystal could not respond below 180 Hz. We also observed excellent signals at all measured points due to the improved crystallinity of the crystal grown by the SNM.

We present low-cost millimeter-wave (MMW) photonic techniques for implementing gigabit/s wireless links. A passive mode-locked laser consisting of a Fabry-Perot laser and a single-mode fiber is used to generate 120-GHz optical MMW signals. We modulated these MMW signals by controlling the bias voltage of the photodiode. The MMW generation and modulation methods do not need expensive photonic components or high-power drivers. A link employing these low-cost photonic techniques achieved 1.25-Gbit/s wireless data transmission.

We developed compact high-power photonic millimeter-wave emitter (PME) modules for 60-GHz fiber radio links. The PME chip is a monolithic integration of a uni-traveling-carrier photodiode (UTC-PD) and an antenna. One module was fabricated by attaching the chip and a plastic housing to a metal substrate, and the equivalent-isotropic radiated power (EIRP) of over 8 dBm was obtained with weak directivity of the radiated pattern. This module is suitable for point-to-multi-point communication. It is very compact, 29 24 6 mm. A module whose antenna gain was increased by attaching a dielectric lens to it was also fabricated, and the estimated EIRP of 18 dBm was obtained. This type of module is suitable for point-to-point communication and it too is compact, 29 24 17.5 mm. We achieved high-speed error-free data transmission of 1.25- and 2.5-Gbit/s phase-shift keyed (PSK) signal. The maximum distances of free-space propagation were estimated to be 18.2 and 8.9 m at bit rates of 1.25 and 2.5 Gbit/s, respectively.

We report on several photoconductive (PC) geometries for the generation of both guided-wave and free-space terahertz (THz) waveforms. It is found that guided-wave THz electrical waveforms can be produced through both PC self-switching and frozen wave generation--eliminating the need for an ultrashort carrier lifetime in the semiconductor substrate. The concept of PC switching is also applied to the generation of free-space THz waveforms, and various ZnSe detectors are investigated as potential electro-optic THz sensors.

This paper presents a novel mm-wave and THz device concept, with a detailed physical modeling and quantitative performance evaluation, called as CW HTS (high temperature superconductive) photomixer/antenna. Optical heterodyne photomixing in the DC-biased HTS strip has been employed to create mm-wave and THz signal, and the size of strip on the grounded dielectric substrate is designed to have an efficient broadside radiation. Incorporating the HTS microstrip configuration as both photomixing media and radiation element at the same time not only increases the CW photocurrent but also the radiation power, while it reduces the radiation loss associated with the patch antenna. Two possible configurations called as longitudinal and transversal will be introduced and their photomixing efficiency and output radiation power will be compared. The detailed analysis along with the optimum design of the geometrical parameters of the microstrip structure shows that the transversal scheme exhibits higher radiation power. The typical nW output power can be obtained by mW laser pump power for frequencies up to the gap frequency of the HTS material. The output power of the proposed device is theoretically higher than the experimentally available data from a Low-Temperature-Grown (LTG) GaAs photomixer integrated with dipole or bow-tie antenna reported in the literature.

This paper considers a wireless coherent system that enables high-speed-data transmission in the presence of carrier phase error over an additive white Gaussian noise (AWGN) channel. Carrier phase noise is caused by imperfect carrier tracking of the coherent demodulation. The channel characteristics of the system were modeled using phase noise whose stochastic process followed the Tikhonov distribution. For this model, we first propose an optimum detector that produces the most suitable decoding metric for a soft-input/soft-output (SISO) decoder, and then develop some simpler forms of the optimum detector to obtain efficient implementation at close to optimal performance. Those simple detectors that have a wide range of performance/complexity tradeoffs are promising in various applications. To evaluate the effectiveness of the proposed detectors, we have applied them to a bandwidth-efficient turbo-coded modulation scheme in which a component decoder based on SISO principles necessitates more exact channel measurement than is possible with a conventional decoder based on Viterbi decoding. Simulation results have demonstrated that the optimum detector enables excellent bit error rate (BER) performance that exceeds that with a normal detector designed for AWGN channels by more than 1 dB at a BER of 10-6 under a severe phase noise environment.

In our previous research, we proposed a nonlinear digital filter to Estimate the Smoothed and Differential values of the sensor inputs by using Sliding mode system (ESDS). This estimator is able to eliminate impulsive noise efficiently from time series data. We applied this filter to processing outputs of robot sensors, and it became possible to perform robust environment recognition. ESDS is designed using a theory of variable structure system (VSS) with sliding mode. In short, ESDS is a nonlinear filter. Therefore, it is very difficult to clarify the behavior of the system analytically. Consequentially, we deal with the step function with impulsive noise as an example, and we attempt to eliminate this impulsive noise by keeping the sudden shift of signals. In this case, there is a trade-off between the noise elimination ability and the tracking performance for an input signal. Although ESDS is a nonlinear filter, it has the same trade-off as linear filters such as a low-pass filter. In order to satisfy these two conditions simultaneously, we use two filters whose parameters are independent of each other. Furthermore, in order to repress the adverse affect of impulsive noise in the steady-state, we introduced the boundary layer. Generally, a boundary layer is used so as to inhibit the harmful effect of chattering. Chattering is caused in the sliding mode system when the state of the system vibrates on the switching line of a sliding mode system. By introducing the boundary layer to ESDS, we can repress the adverse effect of impulsive noise in the steady-state. According to these considerations, we clarify the relationship between these characteristics of ESDS and the arbitrary parameters.