Coherent frequency/phase modulation scheme

An L-phase-levelled coherent frequency/phase modulation (LCFPM) scheme is proposed and analysed for additive white Gaussian noise channels. The optimised LCFPM scheme with L>2 is found to have superior bandwidth efficiency to the conventional dual-frequency quadrature frequency/phase modulation scheme     

Optimal operation of coreless PCB transformer-isolated gate drivecircuits with wide switching frequency range

Gate drive circuits for power MOSFETs and insulated gate bipolar transistors (IGBTs) often require electrical isolation. Coreless printed circuit board (PCB) transformers have been shown to have desirable characteristics from a few hundreds of hertz to a few megahertz and can be used for both power and signal transfer at low-power level. At low operating frequency, the magnetizing inductance has such low impedance that the driving power requirement could become excessive. This paper describes the use of a coreless PCB transformer for isolated gate drive circuits over a wide-frequency range. Based on a resonance concept, the optimal operating condition that minimizes the power consumption of the gate drive circuits is developed and verified with experiments. The coreless PCB transformer demonstrated here confirms a fundamental concept that the size and volume of a magnetic core could approach zero and become zero if the operating frequency is sufficiently high. Coreless PCB transformers do not require the manual winding procedure and thus simplify the manufacturing process of transformer-isolated gate drive circuits and low-power converters. Their sizes can be much smaller than those of typical core-based pulse transformers. The electrical isolation of a PCB is much higher than that of an optocoupler     

Adaptive Bit-Interleaved Coded OFDM With Reduced Feedback Information

If the channel is static and is perfectly known to both the transmitter and the receiver, the water-filling technique with adaptive modulation is known to be optimal (Gallager, 1968). However, for orthogonal frequency-division multiplexing (OFDM) systems, this requires intensive traffic overheads for reporting channel state information on all subcarriers to the transmitter. In this paper, we consider an adaptive modulation and coding scheme for bit-interleaved coded OFDM with reduced feedback information satisfying a specified quality of service level. We propose a rate adaptation scheme, which utilizes the estimated bit error rate for supportable transmission rates. In this scheme, a user equipment chooses a modulation and coding scheme (MCS) level, which can provide the maximum spectral efficiency based on one OFDM symbol rather than on all subchannels. Then the user needs to send back only the selected MCS level index. The proposed scheme does not require the water-filling procedure, and the amount of the feedback information reduces to a single integer value irrespective of the number of subcarriers. Simulation results show that the proposed scheme can significantly reduce the system complexity while minimizing the performance loss compared to the optimum water-filling scheme.     

A novel search method to reduce PAPR of an OFDM signal using partial transmit sequences

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak‐to‐average power ratio (PAPR) of the transmitted OFDM signal. Partial transmit sequence (PTS) technique can improve the PAPR statistics of an OFDM signal. As ordinary PTS technique requires an exhaustive search over all combinations of allowed phase factors, the search complexity increases exponentially with the number of sub‐blocks. In this paper, we propose a novel PTS technique with reduced complexity that each level inverts twice of phase factor bits from previous level. Then we also use initial random phase sequence to find the better search way of PAPR reduction. Numerical results show that the proposed method can achieve significant reduction in search complexity with little performance degradation. Copyright © 2006 John Wiley & Sons, Ltd.     

Electrotunable Non‐reciprocal Laser Emission from a Liquid‐Crystal Photonic Device

A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase‐retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right‐handed helices of different pitches. Electrotunable non‐reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non‐reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage.     

Resource Allocation with Partitioning Criterion for Macro-Femto Overlay Cellular Networks with Fractional Frequency Reuse

The interference mitigation technique based on fractional frequency reuse (FFR) provides improved cell-edge performance with similar overall cell capacity as that of systems with the frequency reuse factor of one. Furthermore, frequency sub-band allocation by FFR has the benefit of allowing flexibility for the deployment of femto-cells through frequency partitioning. Determination of a proper frequency partitioning criterion between the cell-center and the cell-edge, and between the cells with femto-cells is an important issue. In addition, time resource partitioning introduces another degree of freedom to the design of time-frequency resource allocation. In this paper, we propose a novel time-frequency resource allocation mechanism using FFR for a macro-femto overlay cellular network. Feasible frequency sub-band and time resource is allocated to the cell-center and the cell-edge region in a cell by the proposed partitioning criterion and the time partitioning ratio. We provide a guideline for how to determine the partitioning criterion for the regions and how to design the amount of time resource. We derive the average capacity of macro-cells and femto-cells, and introduce a new harmonic mean metric to maximize the average capacity of the regions while achieving the fairness among users in a cell.     

Home Health Gateway Based Healthcare Services Through U-Health Platform

The Ubiquitous Health, or u-Health, service is an IT health care service using the ubiquitous computing environment. U-Health provides customized medical services. As it is a service that has developed from the current hospital visiting medical system, the u-Health service provides a patient with healthcare anywhere and anytime. In this paper, we propose a home health gateway based healthcare services through the u-Health platform. Using home health gateway, u-Health can provide health monitoring, diet, and exercise services using the healthcare decision support module in the ubiquitous environment. This approach would offer specialized services using an external content provider of DB. In addition, a doctor can provide advice to patients using the monitoring service. The proposed u-Health platform provides effective services using home health gateway in ubiquitous environments to customers, which will improve the health of chronic patients.     

Unraveling the Significance of Li+/e−/O2 Phase Boundaries with a 3D-Patterned Cu Electrode for Li–O2 Batteries

The reaction kinetics at a triple-phase boundary (TPB) involving Li⁺, e⁻, and O₂ dominate their electrochemical performances in Li–O₂ batteries. Early studies on catalytic activities at Li⁺/e⁻/O₂ interfaces have enabled great progress in energy efficiency; however, localized TPBs within the cathode hamper innovations in battery performance toward commercialization. Here, the effects of homogenized TPBs on the reaction kinetics in air cathodes with structurally designed pore networks in terms of pore size, interconnectivity, and orderliness are explored. The diffusion fluxes of reactants are visualized by modeling, and the simulated map reveals evenly distributed reaction areas within the periodic open structure. The 3D air cathode provides highly active, homogeneous TPBs over a real electrode scale, thus simultaneously achieving large discharge capacity, unprecedented energy efficiency, and long cyclability via mechanical/electrochemical stress relaxation. Homogeneous TPBs by cathode structural engineering provide a new strategy for improving the reaction kinetics beyond controlling the intrinsic properties of the materials.     

A handover-aware seamless video streaming scheme in heterogeneous wireless networks

With the development of wireless technologies, video streaming services over heterogeneous wireless networks have become more popular in recent years. Video streaming schemes for heterogeneous networks should consider vertical handover in which the link capacity is varied significantly, because the quality experienced for a video streaming service is affected by the network status. When a vertical handover occurs, an abrupt bandwidth change and substantial handover latency lead to bursty packet loss and discontinuity of the video playback. In this paper, we propose a handover-aware video streaming scheme to provide seamless video streaming services over heterogeneous wireless networks. The proposed scheme adjusts its sending rate and the quality level of the transmitted video streams according to the significant bandwidth variation that occurs in a vertical handover. To expedite the response to the bandwidth variation due to a handover, our scheme uses an explicit notification message that informs the streaming server of a client's handover occurrence. In order to evaluate the performance, we use a simulation environment for a vertical handover between wireless local area networks and cellular networks. Through the simulation results, we prove that our scheme improves the experienced quality of video streaming in vertical handovers.     

Sphere-bound-achieving coset codes and multilevel coset codes

A simple sphere bound gives the best possible tradeoff between the volume per point of an infinite array L and its error probability on an additive white Gaussian noise (AWGN) channel. It is shown that the sphere bound can be approached by a large class of coset codes or multilevel coset codes with multistage decoding, including certain binary lattices. These codes have structure of the kind that has been found to be useful in practice. Capacity curves and design guidance for practical codes are given. Exponential error bounds for coset codes are developed, generalizing Poltyrev's (1994) bounds for lattices. These results are based on the channel coding theorems of information theory, rather than the Minkowski-Hlawka theorem of lattice theory