Time-frequency-selective, equivalently time-variant multipath, fading channels in orthogonal frequency division multiplexing (OFDM) systems introduce intercarrier interference (ICI), resulting in severe performance degradation. To suppress the effect of ICI, several symbol detection methods have been proposed, all of which are based on the observation that most of the ICI's power is distributed near the desired subcarrier. However, these methods usually ignore the channel variation in a OFDM symbol block by fixing the number of considered ICI terms. Therefore, we propose a novel frequency-domain symbol detection method with moderate complexity, which adaptively determines the number of ICI terms within each OFDM symbol block.

Recently, we proposed space-time block coded-joint transmit/receive antenna diversity (STBC-JTRD) for narrow band transmission in a frequency-nonselective fading channel; it allows an arbitrary number of transmit antennas while limiting the number of receive antennas to 4. In this paper, we extend STBC-JTRD to the case of frequency-selective fading channels and propose frequency-domain STBC-JTRD for broadband direct sequence-spread spectrum (DSSS) signal transmission. A conditional bit error rate (BER) analysis is presented. The average BER performance in a frequency-selective Rayleigh fading is evaluated by Monte-Carlo numerical computation method using the derived conditional BER and is confirmed by computer simulation of the signal transmission. Performance comparison between frequency-domain STBC-JTRD transmission and joint space-time transmit diversity (STTD) and frequency-domain equalization (FDE) reception is also presented.

We analytically evaluated the effects of the analog components on a high-speed downlink packet access (HSDPA) system standardized by 3GPP. We considered the phase noise of synthesizers, the imbalance of demodulators between in-phase and quadrature channels, and the filters. The components are represented by the appropriate equations. We applied adaptive modulation and coding methods for HSDPA systems and base station transmission of adequate data rate signals complying with quality estimated by mobile stations (MSs). The quality represents a data rate indicating that MSs can receive the signals. We estimated the quality using a conventional signal-to-interference measurement of the common pilot channel (CPICH) and found that the phase noise creates a mismatch relationship between the quality and the data rate, while the demodulator imbalance and filters create a suitable relationship. We confirmed this using analytic methods and computer simulation.

This paper proposes an iterative maximum a posteriori probability (MAP) receiver for multiple-input-multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) mobile communications. For exploiting the space, time, and frequency diversity, the low-density parity-check code (LDPC) is used as a channel coding with a built-in interleaver. The receiver employs the expectation maximization (EM) algorithm so as to perform the MAP symbol detection with reasonable computational complexity. The minimum mean square error (MMSE), recursive least squares (RLS), and least mean square (LMS) algorithms are theoretically derived for the channel estimation within this framework. Furthermore, the proposed receiver performs a new scheme called backward symbol detection (BSD), in which the signal detection uses the channel impulse response that is estimated one OFDM symbol later. The advantage of BSD, which is explained from the viewpoint of the message passing algorithm, is that BSD can exploit information on the both precedent and subsequent OFDM symbols, similarly to RLS with smoothing and removing (SR-RLS) [25]. In comparison with SR-RLS, BSD reduces the complexity at the cost of packet error rate (PER) performance. Computer simulations show that the receiver employing RLS for the channel estimation outperforms the ones employing MMSE or LMS, and that BSD can improve the PER performance of the ones employing RLS or LMS.

This paper proposes a new channel estimation method and a new interference cancellation scheme for multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems in the presence of intersymbol interference (ISI). The proposed channel estimation method uses special training sequences (TSs) to have a desirable crest-factor of the transmitted training signal, and to prevent the influence of ISI on the channel estimation performance. By using the recommended training sequences, the ill-conditioned problem of the least square (LS) filter integrated in the proposed channel estimator can be avoided. The proposed interference cancellation scheme uses the estimated channel coefficients and the channel state information (CSI) to reproduce the interference components, which are then iteratively cancelled from the received signals. To reduced the error-floor of the demodulated symbols using for the calculations of the interference components, the so-called remodulation technique is also included in the proposed interference cancellation scheme. Simulation results show that the proposed channel estimation method outperforms conventional channel estimation methods, especially in the presence of ISI and if the signal-to-noise ratio (SNR) is larger than 15 dB. The combination of the proposed method with a space-time block code (STBC) to combat the interference influences results in an excellent system performance in terms of symbol error ratio (SER). In comparison with a STBC MIMO-OFDM system with sufficient guard interval (GI), this combination gains 1.52 dB of SNR at the same SER of 1.110-6 even after performing only one iteration of interference cancellation.

A test structure to separately analyze the location where the hot-carrier-induced CMOSFET reliability is determined around the center or the isolation-edge along the channel-width was proposed and fabricated. The test structure has four kinds of MOSFETs; [A] and [D] MOSFETs with a short and a long channel-length all over the channel width, respectively, [B] MOSFET with the short and the long channel-length around the center and the both isolation-edges, respectively, and [C] MOSFET with the channel-length regions vice versa to the [B] MOSFET. The time dependent changes of the threshold voltages VT, the saturation currents IS, the linear currents IL and the maximum transconductances β up to 50,000 s were measured. All data for the wide channel-width MOSFETs were almost categorized into three; [A], [B]/[C] and [D]. The [B]/[C] data were well estimated from simple theoretical discussions by the combination of [A] and [D] data, which mean that the reliabilities are nearly the same around the center or the isolation-edge for the CMOSFETs.

In this paper, it is shown that the bit erasure probability of turbo codes with iterative decoding in the waterfall region is nonlinearly scaled by the information blocklength. This result can be used to predict efficiently the bit erasure probability of the finite-length turbo codes over the binary erasure channel.

In OFDM based mobile communication systems, channel variation during one symbol period introduces intercarrier interference (ICI). Conventional pilot-aided equalization mitigates the ICI at the price of band inefficiency. On the other hand, the blind or semi-blind equalization method, which utilizes the known statistic properties of the transmitted data, will raise system complexity. In this letter, without bandwidth-consuming pilots, a novel channel estimation and tracking method based on an iterative equalization technique (IET) is proposed. The proposed approach successfully achieves a good compromise between bandwidth efficiency and system complexity, and its validity is demonstrated by numerical simulations, especially for fast fading channel.

We report on a channel drop filter with a mode gap in the propagating mode of a photonic crystal slab that was fabricated on silicon on an insulator wafer. The results, simulated with the 3-dimensional finite-difference time-domain and plane-wave methods, demonstrated that an index-guiding mode for the line defect waveguide of a photonic crystal slab has a band gap at wave vector k = 0.5 for a mainly TM-like light-wave. The mode gap works as a distributed Bragg grating reflector that propagates the light-wave through the line defect waveguide, and can be used as an optical filter. The filter bandwidth was varied from 1-8 nm with an r/a (r: hole radius, a: lattice constant) variation around the wavelength range of 1550-1600 nm. We fabricated a Bragg reflector with a photonic crystal line-defect waveguide and Si-channel waveguides and by measuring the transmittance spectrum found that the Bragg reflector caused abrupt dips in transmittance. These experimental results are consistent with the results of the theoretical analysis described above. Utilizing the Bragg reflector, we fabricated channel dropping filters with photonic crystal slabs connected between channel waveguides and demonstrated their transmittance characteristics. They were highly drop efficient, with a flat-top drop-out spectrum at a wavelength of 1.56 µm and a drop bandwidth of 5.8 nm. Results showed that an optical add-drop multiplexer with a 2-D photonic crystal will be available for application in WDM devices for photonic networks and for LSIs in the near future.

Multimedia Wavelength Division Multiple Access (M-WDMA) specially designed to accommodate multimedia traffic is a well-known media access control (MAC) protocol. This paper extensively analyzes the throughput of M-WDMA. Specifically, this analysis considers a wide range of network conditions including varying traffic loads, probabilistic occupancy of time segment, various traffic distribution patterns (TDPs) and channel sharing methods (CSMs) under both symmetric and asymmetric traffic load patterns (TLPs). Thus, the analytic behavior of M-WDMA can be investigated for designing a WDMA network managing multimedia traffic under practical environments.

A Non-Uniform Discrete Multitone (DMT) transceiver employing an octave spaced quadrature mirror filter (QMF) bank, can be used to overcome the problem of channel noise enhancement in the zero-forcing (ZF) equalization technique. In this letter, performance of the Non-Uniform DMT system is analyzed. A study of the crosstalk between sub-channels due to non-ideal filter banks is also presented. Crosstalk analysis is based upon the bit error rate (BER) performance versus the QMF order in a standadard ADSL channel. Performance comparison of the Non-Uniform DMT transceiver and a conventional DMT system is given, and it is shown that the Non-Uniform DMT transceiver displays slight improvement over the conventional DMT system for the filters of higher order.

In this paper, we propose new models for directly evaluating DPA leakage from logic information in CMOS circuits. These models are based on the transition probability for each gate, and are naturally applicable to various actual devices for simulating power analysis. Furthermore, we demonstrate the weakness of previously known hardware countermeasures for both our model and FPGA and suggest secure conditions for the hardware countermeasure.

We propose reallocating the power resource among the code symbols in such a way to minimize the post decoding error probability of turbo code. We consider several power reallocation policies and investigate their performance in slowly-varying Rayleigh flat fading channel. We show that the proposed scheme can reduce the post decoding error probability by two orders of magnitude and provide a power gain of 0.86 dB at BER=10-6 over the traditional equal power allocation among all code symbols. We also propose applying different power levels and cut-off thresholds on systematic and parity check bits depending on the channel gain, and investigate the effect of channel gain estimation error.

We propose and demonstrate a new fabrication process of a microchannel using the Damascene process. This process aims to integrate photonic circuits with microchannels fabricated in a glass film. The microchannel is fabricated by the removal of the sacrificial layer after a sacrificial layer is formed by the Damascene process and the cover is formed by sputter deposition. A thin cover layer can be formed by the sacrificial method, because the cover layer is supported by the sacrificial layer during film formation. The cover layer is hermetically sealed, since it is formed by radio frequency (RF) sputtering deposition. The thickness is 1 µm and the width ranges from 3.5 to 8 µm. Using the proposed microchannel fabrication method, we prepared a microelectromechanical system (MEMS) optical switch using microfluidics, and we confirmed its functional operation. This optical switch actuates a minute droplet of liquid injected into the microchannel using Maxwell's stresses. Light propagates straight through the waveguide so that the light passes through the microchannel when the droplet is in the microchannel, but the light rays are completely reflected into a crossed waveguide when the droplet is not in the microchannel. Since this fabrication method uses techniques common to those in the formation of copper wiring in an IC chip, it can be used in the microchannel process.

This paper proposes a new countermeasure, Random Switching Logic (RSL), against DPA (Differential Power Analysis) and Second-Order DPA at the logic level. RSL makes a signal transition uniform at each gate and suppresses the propagation of glitch to allow power consumption to be independent of predictable data. Furthermore, we implement basic logic circuits on the FPGA (Field Programmable Gate Array) by using RSL, and evaluate the effectiveness. As a result, we confirm the fact that the secure circuit can be structured against DPA and Second-Order DPA.

This letter proposes a robust detection scheme of orthogonal space-time block codes that face very fast fading channels. The proposed detection scheme employs a QR decomposition on the channel matrix and minimizes noise enhancement and impact of channel estimation errors which occur in a conventional detection scheme. It is shown by simulations that the proposed detection scheme outperforms the conventional detection scheme when the channel fading is very fast.

This letter analyzes the degradation effect of null subcarriers in orthogonal frequency domain multiplexing (OFDM) systems on the time-domain maximum likelihood (ML) estimation performance. The analysis is used as the basis for a proposal for a channel estimation method that can overcome performance degradation caused by null subcarriers. The accuracy of the proposed method is confirmed by the numerical analysis.

Software defined radio, which uses reconfigurable signal processing devices, requires the determination of multiple unknown parameters to realize the potential capabilities of adaptive communication. Evolutional algorithms are optimal multi dimensional search techniques, and are well known to be effective for parameter determination. This letter proposes an evolutional algorithm for learning the mobile time-varying channel parameters without any specific assumption of scattering distribution. The proposed method is very simple to realize, but can provide precise channel estimation results. Simulations of an OFDM system show that for an example of OFDM communication under the time-varying fading channel, the proposed learning method can achieve the better BER performance.

We investigate selection transmit multi-input multi-output systems where only a single transmit antenna is selected for the transmission and multiple receive antennas are employed for maximal ratio combining. Antenna selection is performed by a generalized selection criterion based on the ordinal number of the strength of the received signal-to-noise ratio.

This letter presents an iterative decision feedback channel estimation scheme for burst mode COFDM transmission. The feature of the proposed scheme is that the channel estimation using metrics comparison is applied to the initial stage of the iterative mechanism, which makes it possible to provide a reliable data stream at the initial stage. Computer simulation results show that the proposed approach provides better BER than the traditional iterative decision feedback channel estimation scheme irrespective of the number of iterations.