In this paper, we propose a new coded orthogonal frequency division multiplex (COFDM)-based ubiquitous antenna system, which is composed of multiple radio base stations (RBSs) deployed over the service area and Radio-on-Fiber (RoF) link that connects RBSs to the central control station (CCS). The proposed system is capable of receiving multiple mobile terminals simultaneously operating at the same frequency by making effective use of joint detection. However, the propagation delay due to the RoF link could be a major problem for realizing the ubiquitous antenna system. In order to overcome this delay problem, we assume that the guard interval of COFDM is longer than the delay difference. Furthermore, in order to improve BER performance in a multipath Rayleigh fading channel, we also propose the MSE normalization scheme followed by the use of an MMSE-based joint detector. Computer simulation results show that the proposed system can improve the frequency utilization efficiency of the broadband wireless access system.

Transmitter power control is an effective scheme to improve the performance of cellular DS/CDMA systems. In the reverse link, pilot symbols are used to assist the estimation of received signal power in order to improve the performance of power control. In this paper, we propose a model for the evaluation of the performance of a power-controlled reverse link CDMA system in the presence of Rayleigh flat fading. The model allows analysis of design parameters such as the number of pilot symbols, the power control updating frequency and the maximum allowable transmitted power. Analysis result shows that when transmitter power control is used, system capacity can be increased by more than 40% for typical normalised Doppler frequency in cellular communications.

An L-band low quiescent current and low distortion SiGe heterojunction bipolar transistor (HBT) driver amplifier having a self base bias control circuit is described. Since the size of this bias circuit is small and it does not need an external control circuit, it is easy to be integrated with the driver amplifier on a single chip. According to the output power level, the self base bias control circuit, which is the combination of a constant base voltage circuit and p-metal oxide semiconductor (MOS) FET current mirror with a constant current source, automatically controls the base voltage, and allows low quiescent current at low output power level and low distortion at high output power level. The simulated results show that the driver amplifier having the self base bias control circuit achieves 1 dB power compression point (P1 dB) improvement of 2.4 dB compared with the driver amplifier having a conventional constant base voltage under the same quiescent current condition. The fabricated driver amplifier with the proposed bias circuit shows high P1 dB of 15.0 dBm with low quiescent current of 15.3 mA.

A Multiwavelength Brillouin/Erbium fibre laser which operates in long-wavelength band (L-band) is demonstrated with an approximate comb spacing of 10 GHz. The laser configuration consists of a long EDF to enable the L-band amplification and two 3-dB couplers to take a portion of the generated BEFL signal and re-inject it into the SMF to seed a cascaded BEFL line in the same direction as the first BEFL line. 20 lines including the anti-Stokes are obtained with the maximum Brillouin pump and 980 nm-pump power of 8.9 mW and 92 mW, respectively.

We have recently developed a programmable composite noise generator (P-CNG) which can easily control noise parameters such as average power, time-based amplitude probability distribution (APD), crossing rate distribution, occurrence frequency distribution and burst duration. Two applications of the P-CNG are demonstrated to show its usefulness. For the first application, Middleton's Class A noise is simulated. A method of setting parameters for Class A noise is demonstrated. The APD of P-CNG output is in good agreement with that of true Class A noise. In the second application, the P-CNG is used for subjective evaluation test (opinion test) of TV picture degradation. Five simple composite noise models with two kinds of APD are used. Other parameters such as average power are kept constant. Experimental results show that the envelope and APD of composite noises do not greatly influence the subjective evaluation. Finally the capabilities of the P-CNG are shown.

In general, the attenuation characteristics of band-pass filters can be improved by generating attenuation poles in the stop band. In this paper, a design method for a planar band-pass filter with attenuation poles based on a half-wavelength resonator is proposed. According to this design, the attenuation poles can be obtained at any desired frequency by means of coupling structures. Two kinds of filter with the characteristics of steep skirt and wide stop-band were designed and fabricated with the result that the validity of the design method was demonstrated. Therefore, a filter with excellent attenuation characteristics for various applications can be achieved.

We examine a concatenated code which consists of a rate 1/2, 4-state turbo code (an inner code) and a single-parity-check product code (an outer code), and discuss the decoding structure called a double concatenated decoding scheme. From our Monte Carlo simulation trials, we show the advantage of the concatenated codes over turbo codes alone. Specifically, when we use an interleaver of 4096 bits, the Eb/No to obtain a BER of 10-6 is about 1.45 dB for the concatenated code. On the other hand, it is more than 2.5 dB for the turbo code alone. So, the Eb/No improvement can be achieved by about 1 dB. This improvement in Eb/No was also obtained for the interleavers of 8192 and 2048 bits. Therefore, the concatenated codes using a double concatenated decoding scheme can solve the problem of the BER flattening in decoding of turbo codes.

In this paper, we focus on an OFDM peak power reduction method that uses clipping and filtering. This method can reduce the peak power of OFDM via clipping, and can also reduce the out-band emission via filtering, even if a nonlinear amplifier is used. However, the filtering causes peak power regeneration. For purposes of reducing the effect of peak power regeneration, we propose an adaptive clipping level control method for OFDM peak power reduction, as part of a technique using clipping and filtering. In this method, the clipping level is optimized by checking the peak power regrowth which is caused by inserting a filter, by using a multi-stage filtering simulator. Thus the peak power is adjusted to the target PAPR. If the target PAPR is decided to be the saturation power of an amplifier, the bit error rate performance is improved without increasing the out-band emission. In order to confirm the effectiveness of the proposed system, we evaluate its performance by using computer simulation.

This paper proposes a pilot channel assisted minimum mean square error (MMSE) combining scheme in orthogonal frequency and code division multiplexing (OFCDM) based on actual signal-to-interference power ratio (SIR) estimation, and investigates the throughput performance in a broadband channel with a near 100-MHz bandwidth. In the proposed MMSE combining scheme, the combining weight of each sub-carrier component is accurately estimated from the channel gain, noise power, and transmission power ratio of all the code-multiplexed channels to the desired one, by exploiting the time-multiplexed common pilot channel in addition to the coded data channel. Simulation results elucidate that the required average received signal energy per bit-to-noise spectrum density ratio (Eb/N0) for the average packet error rate (PER) = 10-2 is improved by 0.6 and 1.2 dB by using the proposed MMSE combining instead of the conventional equal gain combining (EGC) in a 24-path Rayleigh fading channel (exponential decay path model, maximum delay time is approximately 1 µsec) in an isolated cell environment, when the number of multiplexed codes = 8 and 32, respectively, with the spreading factor of 32. Furthermore, when the average received Eb/N0 = 10 dB, the achievable throughput, i.e., the number of simultaneously multiplexed codes for the average PER = 10-2 in the proposed MMSE combining, is increased by approximately 1.3 fold that of the conventional EGC.

Upper bounds on the bit error rate (BER) for maximum likelihood (ML) decoding are derived in convolutional coded parallel combinatorial spread spectrum (PC/SS) systems over additive white Gaussian noise (AWGN) channels. PC/SS systems can achieve higher data transmission than conventional multicode SS systems. To make the derivation tractable, we put a uniform interleaver between a convolutional encoder and a PC/SS transmitter. Since the PC/SS transmitter is employed as the "inner encoder," the bounds are obtained in a similar manner of the derivation in serially concatenated codes through a uniform interleaver. Two different error patterns in the PC/SS system are considered in the performance analysis. Numerical results show that the derived BER bounds are sufficiently accurate. It is found that the coded PC/SS systems outperform coded all-code-parallel DS/SS systems under the same data rate conditions if the number of pre-assigned PN codes increases.

Software with design flaws increases maintenance costs, decreases component reuse, and reduces software life. Even well-designed software tends to deteriorate with time as it undergoes maintenance. Work on restructuring object-oriented designs involves estimating the quality of the designs using metrics, and automating transformations that preserve the behavior of the designs. However, these factors have been treated almost independently of each other. A long-term goal is to define transformations preserving the behavior of object-oriented designs, and automate the transformations using metrics. In this paper, we describe a genetic algorithm based restructuring approach using metrics to automatically modify object-oriented designs. Cohesion and coupling metrics based on abstract models are defined to quantify designs and provide criteria for comparing alternative designs. The abstract models include a call-use graph and a class-association graph that represent methods, attributes, classes, and their relationships. The metrics include cohesion, inheritance coupling, and interaction coupling based on the behavioral similarity between methods extracted from the models. We define restructuring operations, and show that the operations preserve the behavior of object-oriented designs. We also devise a fitness function using cohesion and coupling metrics, and automatically restructure object-oriented designs by applying a genetic algorithm using the fitness function.

In evaluating the teletraffic of mobile communication networks, it is important to model the motion of terminals. In the previous migration model, mobility characteristics of terminals, such as cell dwell time, have been expressed by a single probability distribution. In this paper, we discuss the modeling of the cell dwell time of terminals in each cell. Using measured data we show that cell dwell time differs from cell to cell and follows log-normal distributions rather than conventional exponential distributions.

In this paper, the co-existence of TDMA and W-CDMA spectrum sharing system (TDMA/W-CDMA overlaid system) with cellular architecture is discussed. In this system, both systems share the same frequency band to improve the spectrum efficiency. Overall rate, bit error ratio (BER) and spectrum efficiency of the system are calculated for the forward link (down-link) in the presence of AWGN channel. Taking into account the path loss and shadow fading loss in this system with cellular architecture, W-CDMA applying interference cancellation (IC) shows a substantial difference in spectrum efficiency, the overlaid system can provide a greater overall rate and higher spectrum efficiency than a single multiple access-based system such as TDMA system or W-CDMA system. The interference cancellation can significantly improve BER of the spectrum overlaid system.

The conventional average model for a pulse width modulator employed in a voltage-mode-controlled pulse width modulated converter tends to be numerically unstable when the on-time duty ratio becomes sufficiently small. This paper presents a new average model for a voltage-mode control modulator that is not susceptible to such numerical problems. The validity of the proposed model is confirmed with cycle-by-cycle simulations using an exact discrete-time model.

This paper reviews the advantages of the silicon three-dimensional MMIC technology such as low loss transmission lines, high integration level, and high Q-factor on-chip inductors. Coupled to the masterslice concept, this technology also offers simple design procedure, short turn-around-time, low cost, and potential integration with LSI circuits. A K-band amplifier and an up-converter demonstrate the high frequency operation and low-power consumption benefits of the Si 3-D MMIC technology. A C-band Si-bipolar single-chip transceiver is proposed to illustrate the high integration level offered by the masterslice concept. Finally, the recent advances we achieved toward high Q-factor on-chip inductors provide the design of the S-band low noise amplifier presented in this paper.

This paper proposes a multi-host RAID-5 architecture in which multiple hosts can access disk array via storage area network. In this configuration, parity inconsistency occurs when different hosts try to write to the same stripe simultaneously. Parity consistency can be ensured by the serialization of the writes to the same stripe with locking method. While conventional locking methods can be used, the performance is degraded in the case of large number of hosts. When multiple-reader single-writer file consistency semantic is used, most of the stripes are written exclusively by a single host, so parity inconsistency problem does not occur. By removing locking of those stripes which amounts to 95% in practical workloads, the performance becomes more scalable and 50% faster than using the conventional stripe locking methods.

BiCMOS provides the benefits of both bipolar and CMOS technologies and enables the integration of RF SOCs.

In a wireless home network, shadowing is frequently caused by human bodies or furniture. Therefore, relay transmission function is considered for the hub station in Wireless Homelink when the direct communication of terminals is obstructed. However, in relaying high rate isochronous data such as video streams, the bandwidth resource of Wireless Homelink may be crammed with those data. In this paper, we propose an efficient relay scheme--"Pipeline Repeater" for Wireless Homelink. The proposed scheme spatially multiplexes the relay transfer of the isochronous data using antenna directivity. The Pipeline Repeater can relay the isochronous packets as an efficient use of the limited frequency band, and it can be achieved to repeat the high rate data with delay of only one frame. To verify the proposed scheme, we conduct measurements in some actual home environments, and perform the numerical analyses and computer simulations based on the measurements. Our results confirm the efficiency of the Pipeline Repeater scheme.

A novel common emitter common collector transistor pair (CECCTP) mixer is presented. A LO pumped CECCTP enables even harmonic mixing operation, and a balanced CECCTP mixer configuration enables the suppression of both 2fLO and fIM2 which are undesirable component for direct conversion mixer. A 2 GHz-band balanced CECCTP mixer is fabricated in SiGe HBT process, and the direct conversion characteristics are measured. It performs conversion gain of 8.8 dB, NF of 14.9 dB and IIP2 of 42.3 dBm when LO power is -6 dBm, supplied voltage is 3 V and current is 5 mA.

In this paper, we discuss the applicability of H filtering algorithm for a decision feedback equalizer (DFE) in mobile communications environments. A comparison of bit error rate (BER) performance between a H2 filtering (recursive least squares) algorithm-based and an a priori H filtering algorithm-based fractionally-tap-spaced DFEs in various fading channels is presented. Against, our results are rather pessimistic of the H equalizer, namely, as compared with the H2 equalizer, at most the same or a little better BER performance of the H equalizer is obtained only when the ratio of the average received energy per bit to the white noise power spectral density and the normalized fading rate are large enough, especially in Rician fading channels. Moreover, the H equalizer has the problems of how to choose an appropriate prescribed positive value and computational complexity, therefore it may not be considered as an attractive alternative to the H2 equalizer for wireless communications systems.