This paper proposes an opportunistic feedback and user selection method for a multiuser two-way relay channel (MU-TWRC) in a time-varying environments where a base station (BS) and a selected mobile station (MS), one of K moving MSs, exchange messages during two time slots via an amplify-and-forward relay station. Specifically, under the assumption of perfect channel reciprocity, we analyze the outage probabilities of several channel feedback scenarios, including the proposed scheme. Based on the analysis, the transmission rates are optimized and the optimal user selection method is proposed to maximize the expected sum throughput. The simulation results indicate that, with opportunistic feedback, the performance can be significantly improved compared to that without feedback. Moreover, the performance is nearly identical to that with full feedback, and close to the case of perfect channel state information at BS for low mobility MSs.

The underlaying architecture of Device-to-device (D2D) communication supports direct communication between users by reusing the radio resources of the LTE-A system. Despite the co-channel interference between the conventional cellular user equipment (CUE) and the D2D communication user equipment (DUE), LTE-A system can improve the combined data rate of CUEs and DUEs through effective transmit power control and resource allocation schemes. In this paper, we propose a novel mechanism, which combines the resource allocation scheme with the transmit power control scheme to maximize the overall data rate (defined as the sum-rate in the paper). We perform system-level simulations to determine the effectiveness of the proposed mechanism in terms of increasing the sum-rate. The simulation result shows that the proposed mechanism can improve the sum-rate in an underlaying LTE-A system that supports D2D communication.

To develop an envelope-tracking (ET) amplifier for next-generation cellular base stations, we propose a wideband envelope modulator, consisting of a linear-mode class-B amplifier and a switch-mode class-D amplifier. The function of the modulator is to track the envelope signal and supply voltage to an RF amplifier. To meet the requirements of a large-current and high-voltage supply that can handle a wideband signal, an “Alexander current-feedback amplifier topology” is applied to the linear-mode class-B amplifier. The Alexander topology not only boosts the voltage but also enhances the current capacity of a commercial high-speed operational amplifier (op-amp) by means of a push-pull stage with current mirrors and a buffer amplifier at the output of the op-amp. With this topology, a linear-mode amplifier can provide several-ampere-level current to a 11-Ω load. A prototype of the wideband envelope modulator is shown to achieve the efficiency of 71% with a 20-MHz WiMAX envelope signal at output power of 72W.

This paper investigates space and polarization multiplexing for multichannel transmission in a 120-GHz band wireless link system. The 120-GHz-band wireless equipment employs Cassegrain antennas with a gain of about 49dBi and cross-polar discrimination of 23dB. When each of two 120-GHz wireless links transmits a 10-Gbit/s data signal in the same direction over a distance of 800m, a bit error rate (BER) of below 10-12 is obtained when the receivers are set 30m apart. When forward error correction and polarization multiplexing are used for each wireless link, we can set two wireless links within 1m of each other and obtain a BER below 10-12. Moreover, we have experimentally shown that the rain attenuation of V- and H-polarization 120-GHz-band signal is almost the same.

Microwaves have typically been used for communications and radar, but nowadays are given much attention to energy transfer applications. This paper describes microwave power transfer from a satellite to Earth that is visualized as a solar power satellite system (SPSS). After the system configuration is explained, unique engineering features are presented. Then, some contributions made by Japanese community are introduced, focusing on microwave and antenna engineering. As SPSS will handle high power levels at microwave frequency, and so components should be mass-produced to reduce the cost, then we need to shift our paradigm on the technology involved. Finally, the roadmap to a commercial SPSS is discussed.

On-chip transmission lines are widely used in ultrahigh-frequency integrated circuits. One of the issues in modeling such transmission lines is that no reference impedance can be established on a chip. Conventionally, the parallel admittance Yp has been adopted as a reference parameter for on-chip transmission lines instead of a reference characteristic impedance of 50Ω. In the case of CMOS processes, however, Yp can have complicated characteristics in the short-millimeter-wave band owing to the frequency characteristics of the electric permittivity of low-k materials, which cannot be expressed using a simple circuit. To solve this problem, we propose the use of the series impedance Zs as a reference parameter for transmission-line modeling since it basically can be determined from the geometrical dimensions and the frequency-stable permeability and resistivity. The parameters of transmission lines obtained by the proposed method were compared with those obtained by conventional methods using a 40nm CMOS process. By using the equivalent circuit model of Yp along with RLC resonators, it is shown that the peaks of the frequency characteristics of Yp can be used to explain the absorption spectrum of the dielectric. This suggests that the proposed method is suitable for CMOS short-millimeter-wave transmission lines.

In this paper, we propose a novel baseband (BB) phase shifter (PS) using a fixed-gain-amplifier (FGA) matrix. The proposed BB PS consists of 5 stages of a vector synthesis type FGA matrix with in-phase/quadrature-phase (I/Q) input/output interfaces. In order to achieve low gain variation between phase shift states, 3rd to 5th stages are designed to have a phase shift of +φi and -φi (i=3,4,5). To change between +φi and -φi phase shift states, two FGAs with DC bias in-phase/out-phase switches are used. The two FGAs have the same gain, therefore ideally no gain variation can be achieved. Using this configuration, phase shift error and gain variation caused by process mismatch and temperature variation can be reduced. Fabricated 5-bit BB PS has 3-dB bandwidth of 1.05GHz, root-mean-square (rms) phase errors lower than 2.2°, rms gain variations lower than 0.42dB. Power consumption of the PS core and output buffer are 4.9mW and 14.3mW, respectively. 1-dB compression output power is -12.5dBm. The fabricated PS shows that the total phase shift error and gain variation are within the required accuracy of a 5-bit PS with no requirement of calibration.

In this paper, a 24GHz transformer-coupled VCO is presented for a wide linear tuning range in the 0.13-µm CMOS process. The measured results of the proposed VCO show that the center frequency is 23.5GHz with 7.4% frequency tuning range. The output frequency curve has wide linear tuning region (5.5%) at the middle of the curve. Also, the VCO exhibits good phase noise of -110.23dBc/Hz at an offset frequency of 1 MHz. It has a compact chip size of 430 × 500µm2. The VCO core DC power consumption is 5.4mW at 1.35V VDD.

This paper proposes a new double-edge-triggered implicitly level-converting flip-flop, suitable for a low-power and low-voltage design. The design employs a sense amplifier architecture to reduce the delay and power consumption. Experimentally, when implemented with a 130-nm, single-Vt and 0.84V VDD process, it achieves 64% power-delay product (PDP) improvement, and moreover, 78% PDP improvement when implemented with a mixed-Vt technology, as compared to that of the classic double-edge-triggered flip-flop design.

Phase-nonreciprocal ε-negative and CRLH metamaterials are analyzed using a new approach in which field analysis and transmission line model are combined. The examined one-dimensional nonreciprocal metamaterials are composed of a ferrite-embedded microstrip line periodically loaded with shunt stubs. In the present approach, the phase constant nonreciprocity is analytically estimated and formulated under the assumption of operating frequency far above the ferromagnetic resonant frequency. The present approach gives a good explanation to the phenomenon in terms of ferromagnetic properties of the ferrite and asymmetric geometry of the metamaterial structure, showing a good agreement with numerical simulations and experiment.

This paper presents a voice conversion (VC) technique for noisy environments, where parallel exemplars are introduced to encode the source speech signal and synthesize the target speech signal. The parallel exemplars (dictionary) consist of the source exemplars and target exemplars, having the same texts uttered by the source and target speakers. The input source signal is decomposed into the source exemplars, noise exemplars and their weights (activities). Then, by using the weights of the source exemplars, the converted signal is constructed from the target exemplars. We carried out speaker conversion tasks using clean speech data and noise-added speech data. The effectiveness of this method was confirmed by comparing its effectiveness with that of a conventional Gaussian Mixture Model (GMM)-based method.

Variable-rate linear network codes are investigated in this paper, which are referred to as linear network codes that can support a demanded range of transmission rates on a common netowrk. A new kind of linear network code, called as strict linear broadcast, is defined. Compared with general linear broadcast, it imposes more rigid constraints on the global encoding kernels, but does not require larger finite field size for construction. Then, an efficient scheme is proposed to construct variable-rate linear broadcasts based on the strict linear broadcast. Instead of construcing a fix-rate linear broadcast for each demanded transmission rate, this scheme implements variable-rate linear broadcasts with a single-rate strict linear broadcast. Every node in the network, including the source node, needs to store only one local encoding kernel. When transmission rate varies, the coding operations performed on every network node remain unchanged. Thus, small storage space and no kernel-swithching operations are required on any network code. Furthermore, by combining the strict linear broadcast with a special source-data packetization strategy, a hierarchical broadcast scheme is proposed. With this scheme, multi-rate service can be provided by a single-rate strict linear broadcast to heterogeneous receivers, even at variable transmission rate. Thus, the variable-rate linear broadcasts constructed in this paper are also applicable to the network with heterogeneous receivers.

Genetic algorithm (GA) is now an important tool in the field of wireless communications. For multiple-input/multiple-output (MIMO) wireless communications system employing spatial multiplexing transmission, we evaluate the effects of GA parameters value on channel parameters in fading channels. We assume transmit-correlated Rayleigh and Rician fading with realistic Laplacian power azimuth spectrum. Azimuth spread (AS) and Rician K-factor are selected according to the measurement-based WINNER II channel model for several scenarios. Herein we have shown the effects of GA parameters and channel parameters in different WINNER II scenarios (i.e., AS and K values) and rank of the deterministic components. We employ meta GA that suitably selects the population (P), generation (G) and mutation probability (pm) for the inner GA. Then we show the cumulative distribution function (CDF) obtain experimentally for the condition number C of the channel matrix H. It is found that, GA parameters depend on the channel parameters, i.e., GA parameters are the functions of the channel parameters. It is also found that for the poorer channel conditions smaller GA parameter values are required for MIMO detection. This approach will help to achieve maximum performance in practical condition for the lower numerical complexity.

In this paper, we propose a speech-presence uncertainty estimation to improve the global soft decision-based speech enhancement technique by using the spectral gradient scheme. The conventional soft decision-based speech enhancement technique uses a fixed ratio (Q) of the a priori speech-presence and speech-absence probabilities to derive the speech-absence probability (SAP). However, we attempt to adaptively change Q according to the spectral gradient between the current and past frames as well as the status of the voice activity in the previous two frames. As a result, the distinct values of Q to each frequency in each frame are assigned in order to improve the performance of the SAP by tracking the robust a priori information of the speech-presence in time.

This letter deals with blind carrier frequency offset estimation by exploiting the minimum variance distortionless response (MVDR) criterion for interleaved uplink orthogonal frequency division multiple access (OFDMA). It has been shown that the complexity and estimation accuracy of MVDR strictly depend on the grid size used during the search. For the purpose of efficient estimation, we present an improved polynomial rooting estimator that is robust in low signal-to-noise ratio scenario. Simulation results are provided for illustrating the effectiveness of the proposed estimator.

In this letter, a fast transmit antenna selection algorithm is proposed for the spatial-temporal combining-based spatial multiplexing ultra-wideband systems on a log-normal multipath fading channel. The presented suboptimum algorithm selects the transmit antennas associated with the largest signal to noise ratio value computed by one QR decomposition operation of the full channel matrix spatially and temporally combined. It performs the iterative channel scaling operation about the channel matrix and singular value decomposition about the channel scaled matrix. It is shown that the proposed antenna selection algorithm leads to a substantial improvement in the error performance while keeping low-complexity, and obtains almost the same error performance as the exhaustive search-based optimal antenna selection algorithm.

MIMO transmission technologies have become an essential component of cellular systems such as Long Term Evolution (LTE) and LTE-Advanced. Recently, evaluating the communication performance of mobile users in cellular MIMO systems has become an urgent requirement. In this paper, we propose dynamic MIMO channel modeling for the urban environment. Our proposal is based on Geometry-based Stochastic Channel Modeling (GSCM). The cluster parameters such as the local scatterer locations around the measurement course are estimated by applying the particle filtering to measured data. We carried out radio propagation measurements in an urban environment at 3.35GHz band, and generated the dynamic channel from the measured data. The experiments showed that both the spreads and auto-correlation of Time of Arrival (ToA), Angle of Arrival (AoA) and Angle of Departure (AoD) were reconstructed within the acceptable error range in our dynamic channel model.

A predictive compact model of p-MOSFET negative bias temperature instability (NBTI) degradation for circuit simulation is reported with unified description of the interface-state-generation and hole-trapping mechanisms. It is found that the hole-trapping is responsible for the initial stage of the stress degradation, and the interface-state generation dominates the degradation afterwards, especially under high stress conditions. The predictive compact model with 8 parameters enables to reproduce the measurement results of the NBTI degradation under a wide range of stress bias conditions. Finally, the developed NBTI model is implemented into the compact MOSFET model HiSIM for circuit degradation simiulation.

Several broad bandwidth, electrically small, non-Foster element-augmented antennas have been designed, analyzed and measured. Both electric loop (protractor) and electric dipole (Egyptian axe) structures have been selected as the near-field resonant parasitic (NFRP) elements for these antenna designs. In order to increase their instantaneous 10dB bandwidth, negative impedance convertor (NIC)-based capacitor and inductor elements have been designed accordingly to be incorporated internally into those NFRP elements. Proper design and analysis procedures for these systems are introduced. The simulated performance characteristics of the resulting non-Foster element-augmented protractor and Egyptian axe dipole antennas are presented. Favorable comparisons with their experimentally measured values are demonstrated.

Folded dipole antenna with feed line (FDAFL) whose relative bandwidth is 65% (VSWR≤3) has been reported as a wideband planar antenna for a small terminal. However, this antenna is constructed outside of the ground plane (50×80mm2) by 12mm. In this study, we analyze the antenna configurations of FDAFL in 3D so that the antenna does not protrude from the ground plane as much as possible. Two different 3D antenna models derived from FDAFL are investigated. The first model is folded over the ground plane, and the second one is folded outside of the ground plane. The relative bandwidth, the VSWR characteristics and radiation patterns are studied. As a result, it is confirmed that antenna prominence could be reduced and broadband characteristics over 74% and 83% are obtained by the 3D models, respectively, which are wider than the bandwidth of conventional 2D model. Thus, FDAFL could be used in both 2D and 3D for a small terminal.