In this paper, we discuss on the realization of reduced peak power transmission for the multicarrier systems. Since the signals have large amplitude fluctuations in conventional multicarrier systems, signals amplified by a nonlinear amplifier are greatly distorted, resulting in severe performance degradation. In order to avoid this large amplitude fluctuation, we propose a scheme for reducing the nonlinear distortion by using the set of the signal point series which show low peak to mean envelope power ratio (PMEPR) value. In this system, one symbol is transmitted with multicarriers and the received signal is detected with maximum likelihood sequence detection.

The gate oxide of sub-0.1 µm MOSFETs channel length is expected to be reduced beyond 3 nm in spite of an increasing direct tunneling gate current. As tunnel injection modeling into SiO2 is expected to depend on the electron transport model adopted for the device description, a critical comparison is made in this paper between gate currents obtained from simulators based on Drift-Diffusion, Energy-Balance, and Monte Carlo models. The studied device is a 0.07 µm channel length n-MOSFET with 1.5 nm thick gate oxide. It is shown that positive drain voltage is responsible for two opposite effects on DT leakage: a carrier heating and a potential barrier hardening along the channel. It is proved by a careful study of Monte Carlo microscopic quantities that, contrary to what holds for thicker gate oxide transistors, the balance is favorable to the potential barrier effect. Injection into SiO2 is then dominated by near-thermal carriers injected at the channel beginning. For this reason, the gate current decreases when increasing the drain bias, with the maximum leakage obtained for (Vgs=Vdd, Vds=0), and a correct agreement is obtained between the Drift-Diffusion, Energy-Balance, and Monte Carlo approaches of gate current calculation, in spite of very different physical descriptions of transport at the microscopic level.

Photocarrier transport of regiorandom poly(3-hexylthiophene) P3HT in ITO/P3HT/Al sandwich cell configuration has been investigated by means of Time-of-Flight technique. Characteristics of Schottky diode and the magnitude of hole mobility have been found to be affected by impurities involved during the synthesis. The hole mobility in regiorandom P3HT at room temperature has been estimated to be 2.4 10-5 and 2.6 10-4 cm2/V. s before and after the removal of ferric ions, respectively, at a field of 5.0105 V/cm. Field dependencies of mobility before and after purification show unique feature and have been discussed in terms of the disorder model.

An analytical error characteristics of GPS compass which determines heading and elevation of the vehicle using carrier phase measurements from 2 antennae is given. It is also shown that to obtain more precise heading, longer baseline along the vehicle is preferred and the accuracy of heading is always better than that of elevation since the vertical measurement uncertainty caused by geometry of satellites affects only on that of elevation. These results can be applied as basic directions for attitude determination: to what direction should the baseline be located to minimize the error, which satellites should be selected to minimize the error.

This paper presents the effect of stress on device degradation in metal-oxide-semiconductor field-effect transistors (MOSFETs) due to stud bumping. Stud bumping above the MOSFET region generates interface traps at the Si/SiO2 interface and results in the degradation of transconductance in N-channel MOSFETs. The interface traps are apparently eliminated by both nitrogen and hydrogen annealing. However, the hot-carrier immunity after hydrogen annealing is one order of magnitude stronger than that after nitrogen annealing. This effect is explained by the termination of dangling bonds with hydrogen atoms.

Closed-loop power control providing maximum capacity of the multicarrier channel with frequency selective Nakagami fading is investigated. Use of the famous Gallager channel capacity (water-filling) theorem with the assumption of limited transmitter power and independent fading in partial channels leads to the algorithm for their optimal power loading. Analytical expressions for the capacity of the multicarrier channel as a function of the number of its subchannels and the fading parameters are derived for the cases of Optimal Power Distribution (OPD) and Equal Power Distribution (EPD). The dependence of the capacity gain on the OPD system order, the fading depth and the average SNR due the optimal power control is obtained. Comparison of the power efficiencies of the systems with OPD and EPD is presented.

A novel algorithm for an adaptive array that is suitable for a multi-carrier transmission will be proposed in this paper. In an adaptive array, signals received by antenna elements are weighted and combined together. In the proposed algorithm, distortion of a spectrum of the combined signal is detected and weight coefficients for each antenna element are controlled so that the spectrum of the combined signal becomes flat. Concept of the proposed algorithm can be interpreted as the CMA which is applied to signals sampled in the frequency domain. Furthermore, a configuration of the adaptive array will be shown. Signals separated in a receiver of the multi-carrier transmission are utilized to detect the distortion of the signal spectrum. By adopting the proposed configuration, the spectrum of the multi-carrier signal can be easily detected. In order to investigate the performance of the proposed adaptive array, computer simulation has been carried out. Numerical results show that; 1) A desired wave is captured well even if an interference wave is narrow band signal and is stronger than the desired wave. 2) Suppression performance for a co-channel interference wave depends on both a symbol timing and SIR of arrival waves. If the symbol timing of the interference wave greatly differs from the timing of FFT window of the receiver, the desired wave can be captured even if the co-channel interference wave is stronger more than 10 dB compared with the desired wave. The conventional CMA adaptive array has a serious problem that the narrow band interference wave is captured when it is stronger than the desired wave. On the other hand, it is extremely rare that the proposed adaptive array captures the narrow band interference wave. Therefore, it can be said that the proposed adaptive array is a robust system compared with the conventional system.

We propose a coherent automatic gain control (AGC) scheme with low complexity for high-speed satellite communications. A mathematical model for the gain detector and a stochastic difference equation are established to investigate the characteristics of the scheme. Based on the random process theory with the equation, we analyze the acquisition and tracking performance of the AGC loop. It has been verified that the results by the analytical method agree with the simulation results obtained in the presence of small amount of phase offsets in the carrier recovery circuits for the QPSK system. Though the analytical results deviate from the simulation results slightly in the presence of maximum phase offset, they give us the insight in analyzing the characteristics of the proposed scheme.

Multi-carrier (MC) signal has a large peak to mean envelope power ratio, so that the MC signal suffers from a high level of inter-modulation distortion due to the nonlinearity of the power amplifier stage. For portable terminals, it is undesirable to use linear amplifiers because high power efficiency is needed. To solve this problem, we propose a time division duplex (TDD)-code division multiple access (CDMA) communication system which uses an asymmetric modulation scheme between the forward and reverse links. The system consists of multicarrier modulation for the forward link and single carrier modulation for the reverse link. A pre-equalization method for the forward link transmission is also presented in this paper. In frequency selective fading, the system achieves a path diversity effect without any channel estimation unit at the mobile station by using the pre-phase equalizer. From the simulation results, it it found that the proposed system achieves better BER performance than the conventional MC-CDMA system and the single carrier RAKE system equipped at the mobile unit since the proposed system has the ability to suppress other user interfering signals.

In this paper, a type of multi-carrier direct sequence code division multiple access (MC-DS-CDMA) system which uses frequency spread coding is proposed and investigated for the down-link. An MC-DS-CDMA system is a combined system of CDMA and multi-carrier modulation. This system is often categorized as a "serial to parallel (S/P) type" system because serial to parallel converted data symbols are transmitted. They use different sub-carriers which are narrow-band DS waveforms. In this system, benefits of path or frequency diversity can not be obtained because of the narrow-band transmission of each data symbol. In order to benefit from the diversity, we propose to adopt frequency spread coding in an MC-DS-CDMA system. The proposed system exploits frequency diversity without additional redundancy, i. e. , no frequency or time redundancy is required to improve the performance. Computer simulation is carried out in a frequency selective fading channel and the results show its effectiveness in terms of average bit error rate (BER). Furthermore, the proposed system is compared with a multi-carrier (MC-) CDMA system which is often categorized as a "copy type" system and a single-carrier (SC-) DS-CDMA system using a RAKE receiver.

One of the problems in multi-carrier modulation is nonlinear distortion due to nonlinearity of channels, such as in HPA (High Power Amplifier). This problem is also true of multi-carrier SS (Spread Spectrum) systems. In this paper, an inter-modulation compensation scheme for multi-carrier M-ary/SS system is proposed. We propose two methods to control the sequences transmitted in parallel to avoid the occurrence of severe inter-modulation distortion. One is the "package sequence selection" method, which requires slight redundancy. The other method is based on error correction code, which requires no additional frequency or power except the redundancy for error correction. We confirm the validity of our proposed scheme by computer simulation, and the BER (Bit Error Rate) performance in an AWGN (Additive White Gaussian Noise) channel is presented.

To improve frequency efficiency or user capacity in multi-path fading environments, we introduce and investigate an orthogonal multi-carrier frequency hopping-code division multiple access (FH-CDMA). These improvements are achieved by combining the orthogonal frequency division multiplexing (OFDM) and FH-CDMA schemes. The basic idea has been previously proposed by the authors. The aim of study in this paper is to evaluate the performance of this scheme in various environments. The theoretical analysis of bit error rate (BER) performance in this paper includes the effects of frequency selective fading in land mobile communications and of nonlinear amplification in satellite communications. A modified scheme of controlling transmission power to be controlled according to the number of simultaneously accessing users is also discussed. This modified scheme improves BER performance for frequency selective fading when the number of simultaneously accessing users in a cellular zone is small. Furthermore, an error-correcting code and its erasure decoding are applied in order to reduce errors due to hits in asynchronous FH/CDMA for reverse link as well as errors due to fading and noise.

In this paper, a method of Transmission Power Control (TPC) for Orthogonal Frequency Division Multiplexing Direct Sequence Code Division Multiple Access (OFDM-DS-CDMA), in order to compensate for power attenuation at each subcarrier, is proposed. Instead of assigning same power levels for all-subcarriers, different transmission power levels are assigned to different subcarriers, according to the attenuation of the subcarriers. System performance, in terms of Bit Error Rate (BER), has been evaluated by Monte Carlo simulation. The simulation results presented significant improvement, the proposed system performed much better than the system without TPC. It is shown that the Each Carrier TPC performs better than All Carriers TPC, which all carriers are controlled uniformly, hence Each Carrier TPC is more suitable for OFDM-DS-CDMA system.

An ultra-fast optoelectronic decision circuit using resonant tunneling diodes (RTD's) and a uni-traveling-carrier photodiode (UTC-PD) is proposed. The circuit employs two cascaded RTD's for ultra-fast logic operation and one UTC-PD that offers a direct optical input interface. This novel configuration is suitable for ultra-fast decision operation. Two types of decision circuits are introduced: a positive-logic type and a negative-logic type. Operations of these circuits were simulated using SPICE with precisely investigated RTD and UTC-PD models. In terms of circuit speed, 40-Gbit/s decision and 80-Gbit/s demultiplexing were expected. Furthermore, the superiority of the negative-logic type in terms of the circuit operating margin and the relationship between input peak photocurrent and effective logic swing were clarified by SPICE simulations. In order to confirm the basic functions of the circuits and the accuracy of the simulations, circuits were fabricated by monolithically integrating InP-based RTD's and UTC-PD's. The circuits successfully exhibited 40-Gbit/s decision operation and 80-Gbit/s demultiplexing operation with less than 10-mW power dissipation. The superiority of the negative-logic type circuit for the circuit operation was confirmed, and the relationship between the input peak photocurrent and the effective logic swing was as predicted.

A clock recovery circuit is a key component in optical communication systems. In this paper, an optoelectronic clock recovery circuit is reported that monolithically integrates a resonant tunneling diode (RTD) and a uni-traveling-carrier photodiode (UTC-PD). The circuit is an injection-locked-type RTD oscillator that uses the photo-current generated by the UTC-PD. Fundamental and sub-harmonic clock extraction is confirmed for the first time with good clock recovery circuit characteristics. The IC extracts an electrical 11.55-GHz clock signal from 11.55-Gbit/s RZ optical data streams with the wide locking range of 450 MHz and low power dissipation of 1.3 mW. Furthermore, the extraction of a sub-harmonic clock from 23.1-Gbit/s and 46.2-Gbit/s input data streams is also confirmed in the wider locking range of 600 MHz. The RMS jitter as determined from a single sideband phase noise measurement is extremely low at less than 200 fs in both cases of clock and sub-harmonic clock extraction. To our knowledge, the product of the output power and operating frequency of the circuit is the highest ever reported for injection-locked-type RTD oscillators. These characteristics indicate the feasibility of the optoelectronic clock recovery circuit for use in future ultra-high-speed fully monolithic receivers.

A clock recovery circuit is a key component in optical communication systems. In this paper, an optoelectronic clock recovery circuit is reported that monolithically integrates a resonant tunneling diode (RTD) and a uni-traveling-carrier photodiode (UTC-PD). The circuit is an injection-locked-type RTD oscillator that uses the photo-current generated by the UTC-PD. Fundamental and sub-harmonic clock extraction is confirmed for the first time with good clock recovery circuit characteristics. The IC extracts an electrical 11.55-GHz clock signal from 11.55-Gbit/s RZ optical data streams with the wide locking range of 450 MHz and low power dissipation of 1.3 mW. Furthermore, the extraction of a sub-harmonic clock from 23.1-Gbit/s and 46.2-Gbit/s input data streams is also confirmed in the wider locking range of 600 MHz. The RMS jitter as determined from a single sideband phase noise measurement is extremely low at less than 200 fs in both cases of clock and sub-harmonic clock extraction. To our knowledge, the product of the output power and operating frequency of the circuit is the highest ever reported for injection-locked-type RTD oscillators. These characteristics indicate the feasibility of the optoelectronic clock recovery circuit for use in future ultra-high-speed fully monolithic receivers.

This paper describes a forward subchannel control of multi-carrier scheme intended to compensate for phase/amplitude distortions under frequency selective fading. The forward subchannel control scheme is used for a Time Division Duplex (TDD) multi-carrier system on up-link. The forward subchannel control scheme provides forward subchannel control of phase/amplitude variation and subchannel assignment control. These controls are applied before transmission of an up-link signal. The forward control parameters are estimated by a preamble down-link signal. Simulation results clarify that the BER performance with the forward subchannel control scheme shows a superiority of more than one order at the condition of 22 dB of Eb/N0 and 400 Hz of fading frequency.

By integrating three networks, namely, Public Switched Telephone Network (PSTN), Personal Handy-Phone System (PHS) and Intelligent Network (IN) to work together as a Personal Communication Telephone (PCT) service to be offered in the Bangkok metropolis area, the PCT service enables the advent of three new concepts, first, using the same telephone number as that of the fixed line to become a "Personal Number," second, a cell coverage designed to cover larger areas than that of the PHS (by changing hand-out threshold level from 33 dBµV to 30 dBµV and hand-in threshold level from 30 dBµV to 25 dBµV) in order to reduce the muting time during the handover process and provide higher mobility at up to 60 kilometers per hour, and third, a technique of "2 carriers per area" to reduce "call drop." All these techniques will be described in this paper.

The characteristics of the decision feedback carrier recovery loop (DFL) for conventional QPSK signaling is evaluated experimentally through measurements of the carrier-to-noise ratio of the regenerated carrier, lock range, acquisition waveforms and bit error rates. The results show that the DFL hardly exhibits inferiority to the ideal synchronization by designing the loop natural frequency adequately small. The DFL is shown superb in carrier tracking.

An efficient ARQ scheme based on the packet combining technique is investigated for multi-carrier modulation systems. In multi-carrier modulation systems, several sub-carriers are used for high data rate transmission and their individual received signal quality becomes different from one sub-carrier to others in a frequency selective fading channel. Therefore by changing the assignment of data to the sub-carriers in the retransmission packets, the distortion between the previous transmitted packet and the newly retransmitted one will be different. This is the principle of the proposed adaptive data order rearrangement for a packet combining ARQ scheme, which can achieve more diversity gain in packet combining and improve the ARQ performance. From the results of the theoretical analysis and the computer simulation, it is confirmed that the proposed packet combining ARQ with the proposed operation can achieve the better performance in terms of the average packet transmission success probability. In addition, this proposed scheme is also compared with the conventional multi-carrier modulation ARQ scheme based on the partial retransmission of a packet. The computer simulation results demonstrate that the proposed scheme has also advantage against the latter one, and it is considered to be as a more efficient ARQ scheme for multi-carrier modulation systems.