A Time Hopping Pulse Spacing Modulation (TH-PSM) system, which combines the pulse position modulation system with code shift keying, is proposed. The following performances are analyzed; (1) data transmission rate, (2) error rate in a single-user case, (3) error rate in a multi-user case, and (4) spectral efficiency. Consequently, the data transmission rate of the proposed system is higher than that of the conventional Spread Spectrum Pulse Position Modulation (SS-PPM) system. The proposed system can improve the probability of block error by increasing the number of information bits per spreading code. Moreover, the spectral efficiency of the proposed system is higher than that of the conventional system. The proposed system is more attractive than the conventional SS-PPM system for optical communications, power-line communications, and UWB communications.

In this paper, a quasi-synchronous code-division multiple-access (QS-CDMA) is investigated for application in the reverse link of a microcellular or indoor mobile communication environment. In a QS-CDMA system, the relative time delay between the signals of different users is normally restricted within a few chips. Generalized orthogonal (GO) codes added with guard chips are employed as the spreading sequences in this paper and the strict timing error restrictions for BPSK and M-QAM modulation schemes are derived based on the correlation properties of GO code set which determines the multiple access interference (MAI). The results reveal that the system employing GO code set with bigger GO zone can tolerate more serious timing error, and higher order modulation schemes require stricter synchronization. Based on the system model presented, the BER performance for BPSK and M-QAM is evaluated by Gaussian Approximation (GA) and Monte Carlo simulation. The system capacity in terms of acquirable total bit rates are also evaluated, revealing that if system synchronization error is limited within the GO zone, M-QAM scheme can be utilized to improve the system capacity.

Although there has been a great deal of research on automatic summarization, most methods rely on statistical methods, disregarding relationships between extracted textual segments. We propose a novel method to extract a set of comprehensible sentences which centers on several key points to ensure sentence connectivity. It features a similarity network from documents with a lexical dictionary, and spreading activation to rank sentences. We show evaluation results of a multi-document summarization system based on the method participating in a competition of summarization, TSC (Text Summarization Challenge) task, organized by the third NTCIR project.

A new beamforming technique based on the power method is proposed in this paper. We show that the new technique is quite robust to the angular spread in the received signals making it particularly useful for smart antennas in WCDMA systems. The proposed technique utilizes two primary eigenvectors of the autocovariance matrix of the received data to form the weight vector of a smart antenna. An efficient adaptive procedure combining the power method and deflation method is given to compute the first and second largest eigenvalues with a reasonable complexity and accuracy. To demonstrate the proposed technique, it has been applied to WCDMA signal environment showing its robust and improved performance.

With the progress of the electronics industry and radio communication technology, humans enjoy greater freedom in communicating. On the other hand, certain problems, such as electromagnetic interference (EMI), have arisen due to the increased use of electromagnetic (EM) waves. EM wave absorbers are used for constructing an anechoic chamber to test and measure EMI and electromagnetic susceptibility (EMS). Prior to 1998, international standards for anechoic chambers required that EM wave absorbers should absorb more 20 dB in the bandwidth from 30 MHz to 1,000 MHz. Since November 1998, however, the Comit International Special des Perturbations Radioelectrigne (CISPR) has required that the frequency bandwidth be extended from 1 GHz to 18 GHz for EMI measurement by the CISPR11. In this work, wide-band EM wave absorbers were designed by a theoretical model using the equivalent material constants method (EMCM). We designed a cross-shaped absorber which has a bandwidth from 30 MHz to above 2 GHz under the tolerance limit of -20 dB in reflection, the results of which were compared with the results analyzed using the finite-difference time-domain method (FDTD). The tapered cross-shaped absorber was also designed, which has a bandwidth from 30 MHz to 26 GHz under the same tolerance limit.

In generating Frequency-Hopping (FH) sequences for Frequency Hopping Spread Spectrum Multiple Access (FH-SSMA) applications, binary maximal-length sequences (m-sequences) over GF(2m) have been preferred because of their characteristics of good Hamming correlation property, long period capability and high speed generation in association with simple hardware implementation based on Feedback Shift Registers (FSR). In practice, however, one difficulty of applying such sequences into the FH-SSMA communication systems with a wide bandwidth such as Military Satellite Communication (MilSatCom) is that the number of hopping frequency slots available may be far from a power of 2 in proportion to the spreading bandwidth. In that case, we can not make good use of the spreading bandwidth. In this paper, we propose a construction of some favorable FH sequences which deals effectively with the above difficulty using FSR and some nonlinear logic by introducing a re-mapping method. We show that the resulting sequences satisfy the (almost) uniform symbol distribution in one period and preserve a reasonably good Hamming correlation property so that they are appropriate for FH-SSMA applications.

Complete complementary codes have the property that the sum of correlation functions of several sequences satisfies both ideal autocorrelation and cross-correlation values. Modulatable complete complementary codes (MCC codes), which is a type of periodic complete complementary codes, are suitable for spreading sequences of M-ary CDMA systems. In the present paper, we propose a new method for constructing MCC codes. Using this method, we can easily generate various MCC codes.

Future electric lights will be comprised of white LEDs (Light Emitting Diodes). White LEDs with a high power output are expected to serve in the next generation of lamps. In this paper, an indoor visible data transmission system utilizing white LED lights is proposed. In the proposed system, these devices are used not only for illuminating rooms but also for an optical wireless communication system. This system is suitable for private networks such as consumer communication networks. However, it remains necessary to investigate the properties of white LEDs when they are used as optical transmitters. Based on numerical analyses and computer simulations, it was confirmed that the proposed system could be used for indoor optical transmission.

Adaptive arrays have been recognized as an attractive mean for overcoming multipath fading and interference rejection in the field of mobile communications. In, an adaptive array applicable to single-user spread spectrum (SS) systems has been proposed. In this system, any a priori information concerning incoming signal, even the spreading code and synchronization, is not necessary while it achieves equalizing, beamforming and despreading of a received signal, simultaneously. In this paper, we propose a multistage blind adaptive array antenna based on the above-mentioned adaptive algorithm in order to realize blind signal processing that is applicable to multi-user SS systems. Behavior and performance of the proposed multistage system are examined through computer simulations.

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 scheme of subband adaptive array for multicode Direct Sequence Code Division Multiple Access (DS-CDMA) is proposed in this paper. The proposed scheme has a flexible configuration which allows basestation to be able to dynamically adapt to multirate transmission requests from subscribers. It is shown that the novel scheme can effectively suppress multiple access interferences (MAI) by appropriately forming main beam toward the desired user while pointing beampattern nulls toward MAI sources. Moreover, the combination of the subband adaptive array with the so-called cyclic prefix spreading code CDMA is also proposed to mitigate multipath fading and maximize diversity gain in multipath fading environment.

We demonstrate polarization-independent and highly-efficient optical fiber wavelength converters in a 10 Gb/s NRZ transmission system. They are based on synchronous phase or frequency modulations of the two orthogonally polarized pump lights, and can suppress not only the stimulated Brillouin scattering (SBS) but also the spread of the converted spectrum without modulating the signal light.

This paper presents design of spreading codes for asynchronous DS-CDMA systems. We generate maximal-period sequences with negative auto-correlations based on one-dimensional maps with finite bits whose shapes are similar to piecewise linear chaotic maps. We propose an efficient search algorithm to find such maximal-period sequences. This algorithm makes it possible to find many kinds of maximal-period sequences with sufficiently long period for practical CDMA applications. We also report that maximal-period sequences can outperform conventional Gold sequences in terms of bit error rate (BER) in asynchronous DS-CDMA systems.

A field trial, within a suburban macro-cell environment, of a space-time (ST) equalizer for TDMA mobile communication systems is described. The ST equalizer was a cascade connection of two array processors for a four-antenna array and a two-branch-metric-combining maximum-likelihood sequence estimation (MLSE) that was designed to obtain full space- and path-diversity gains from first-arrival and one-symbol-delayed signals while suppressing excessively long-delayed inter-symbol interference (ISI). The radio frequency was 3.35 GHz, the transmission rate was 4.096 Mb/s, and the modulation was QPSK. The long-delayed ISI reduction and the space-path diversity effect of the ST equalizer was validated by Eb/N0 vs. bit-error-rate (BER) curves with respect to delay spread and antenna spacing as compared with the case of an array processor alone being used.

Though analysis of an indoor propagation channel has been conventionally used the ray-tracing method, in this paper using three dimension of finite difference time domain methods can easily and exactly be obtained three-dimensional complex structures. An excitation signal of FDTD made use of plane wave. An absorbing boundary condition used the most reflection less perfectly matched layer in the outset plane. An empty room surrounded a wall composed of brick, concrete and case that there are indoor furniture in the room were simulated. As simulation outcome, we could identify frequently rising reflection, refraction, scattering of objects and a fading effect of multipath at indoor propagation environment, calculate mean excess delay and rms delay spread for receiver design.

Polarimetric SAR interferometry has been successful and attractive for forest parameters (tree height and canopy extinction) estimation. In this paper, we propose to use the ESPRIT algorithm to extract the interferometric phase of local scatterers with polarimetric and interferometric SAR data. Two or three local scattering waves can be extracted at each image patch when a fully polarimetric data set (HH, HV, VV) is available. Furthermore, the ESPRIT can estimate two dominant local scattering centers when only a dual polarimetric data set (e.g., VV and VH) is provided. In order to demonstrate effectiveness the proposed technqiue, we examined the relation between local scattering centers extracted by this method and complex coherence of the coherent scattering model for vegetation cover. The results show that the three-wave estimation can be more accurate than the two-wave case. The extracted interferometric phases with full and dual polarization data sets correspond to effective ground and canopy scattering centers. In this investigation, SIR-C/X-SAR data of the Tien Shan flight-pass are used.

A new analog correlator circuit is proposed for direct sequence code division multiple access (DS-CDMA) demodulator. The circuit consists of only 16 switches, 4 capacitors and 2 level shifters. Control sequence requires only three clock phases. Simulation with code length of 127 reveals that the proposed circuit has a good ability to cancel off the charge error and dissipates 3.4mW at 128MHz. The circuit had been designed using a 0.6µm CMOS process. The area of 256µm 245µm is estimated to be 9 times smaller compared to other reported equivalent analog correlators.

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.

Time variations of the wireless channel cause Inter-Carrier Interference (ICI) between different subcarriers in an OFDM system. In a highly mobile environment this interference may become so high that it degrades up to unacceptable levels the communication channel. In this paper, firstly we obtain a simplified expression for the total ICI experienced by every subcarrier in an OFDMA system. Unlike other previous works, the result establishes an explicit and useful relation between the ICI on each subcarrier and the speed of the rest of the terminals in the system. Then, by means of a mathematical analysis we extend the scope of that expression to a hybrid system in which OFDMA and CDMA are combined. Using the good autocorrelation and cross-correlation properties provided by Gold-sequences we propose a Gold-Code-based CDMA-OFDMA transmission technique for the asynchronous uplink channel. We show that the proposed method can reduce the total ICI and potentially increase the capacity of the system in comparison to a conventional OFDMA system.

This paper proposes a low power consumption Analog Matched Filter (AMF) that utilizes capacitor multiply-and-accumulate operations. A high-speed, high-precision Analog-to-Digital (A/D) converter is unnecessary because the proposed circuit directly samples received analog signals. A code-shifting MF structure is used to prevent errors from accumulating. A 15-tap AMF circuit was fabricated using 0.35 µm CMOS technology. Power consumption for the 128-tap circuit is estimated to be 22.3 mW at 25 MHz and 3.3 V, and the area is estimated to be 0.33 mm2. The proposed circuit will thus be a useful LSI for mobile terminals.