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.     

Optoelectronic and microwave transmission characteristics of indium solder bumps for low-temperature flip-chip applications

This paper describes low-temperature flip-chip bonding for both optical interconnect and microwave applications. Vertical-cavity surface-emitting laser (VCSEL) arrays were flip-chip bonded onto a fused silica substrate to investigate the optoelectronic characteristics. To achieve low-temperature flip-chip bonding, indium solder bumps were used, which had a low melting temperature of 156.7/spl deg/C. The current-voltage (I-V) and light-current (L-I) characteristics of the flip-chip bonded VCSEL arrays were improved by Ag coating on the indium bump. The I-V and L-I curves indicate that optical and electrical performances of Ag-coated indium bumps are superior to those of uncoated indium solder bumps. The microwave characteristics of the solder bumps were investigated by using a flip-chip-bonded coplanar waveguide (CPW) structure and by measuring the scattering parameter with an on-wafer probe station for the frequency range up to 40 GHz. The indium solder bumps, either with or without the Ag coating, provided good microwave characteristics and retained the original characteristic of the CPW signal lines without degradation of the insertion and return losses by the solder bumps.     

Systematic Study of Widely Applicable N‐Doping Strategy for High‐Performance Solution‐Processed Field‐Effect Transistors

A specific design for solution‐processed doping of active semiconducting materials would be a powerful strategy in order to improve device performance in flexible and/or printed electronics. Tetrabutylammonium fluoride and tetrabutylammonium hydroxide contain Lewis base anions, F^? and OH^?, respectively, which are considered as organic dopants for efficient and cost‐effective n‐doping processes both in n‐type organic and nanocarbon‐based semiconductors, such as poly[[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)] (P(NDI2OD‐T2)) and selectively dispersed semiconducting single‐walled carbon nanotubes by π‐conjugated polymers. The dramatic enhancement of electron transport properties in field‐effect transistors is confirmed by the effective electron transfer from the dopants to the semiconductors as well as controllable onset and threshold voltages, convertible charge‐transport polarity, and simultaneously showing excellent device stabilities under ambient air and bias stress conditions. This simple solution‐processed chemical doping approach could facilitate the understanding of both intrinsic and extrinsic charge transport characteristics in organic semiconductors and nanocarbon‐based materials, and is thus widely applicable for developing high‐performance organic and printed electronics and optoelectronics devices.     

Relationship between HOMO energy level and open circuit voltage of polymer solar cells

A series of π-conjugated polymers (PDHF-BT and PDHF-TBT) with 4-(3,4-ethylenedioxythienyl)-2,1,3-benzothiadiazole (BT), 4,7-bis(3,4-ethylenedioxythienyl)-2,1,3-benzothiadiazole (TBT), and 9,9′-dihexylfluorene were synthesized by the Suzuki coupling reaction. The HOMO energy level of PDHF-BT was −5.47 eV, which was lower than that of PDHF-TBT (−5.22 eV), while the LUMO energy level of PDHF-BT (−3.45 eV) was very similar to that of PDHF-TBT (−3.42 eV). These energy levels of PDHF-BT and PDHF-TBT were also supported by a DFT calculation. The power conversion efficiency (PCE) of the polymer solar cell (PSC) with a structure of ITO/PEDOT:PSS/PDHF-BT:PCBM (1:1)/Al was determined as 0.34% and it was larger than that of the device based on PDHF-TBT (0.22%). Correspondingly, the V_oc of the PSC based on PDHF-BT (0.71 V) was much larger than that of the device based on PDHF-TBT (0.40 V). The results support that the V_oc of polymer based PSCs is strongly related to the HOMO energy level of the active polymers.     

A high performance and low complexity sampling-based intra coding method for H.264/AVC

The H.264/AVC video coding standard can achieves higher compression performance than previous video coding standards, such as MPEG-2, MPEG-4, and H.263. Especially, in order to obtain the high coding performance in intra pictures, the H.264/AVC encoder employs various directional spatial prediction modes and the rate-distortion (RD) optimization technique inducing high computational complexity. For further improvement in the coding performance with the low computational complexity, we introduce a sampling-based intra coding method. The proposed method generates two sub-images, which are defined as a sampled sub-image and a prediction error sub-image in this paper, from an original image through horizontal or vertical sampling and prediction processes, and then each sub-image is encoded with different intra prediction modes, quantization parameters, and scanning patterns. Experimental results demonstrate that the proposed method significantly improves the intra coding performance and reduces the encoding complexity with the smaller number of the RD cost calculation process.     

High current conduction with high mobility by non-radiative charge recombination interfaces in organic semiconductor devices

We report a unique non-radiative p-n-p junction structure to provide high current conduction with high mobility in organic semiconductor devices. The current conduction was improved by increasing p-n junctions made with intrinsic p-type hole transport layer and n-type electron transport layer. The excellent hole mobility of 5.3 × 10^?1 cm²/V s in this p-n-p device configuration is measured by the space charge limited current method with an electric field of 0.3 MV/cm. Enhanced current conduction of 248% at 4.0 V was observed in fluorescent blue organic light-emitting diodes with introduction of non-radiative p-n-p-n-p junction interfaces. Thereupon, the power efficiency at 1000 cd/m² was improved by 22% and the driving voltage also was reduced by 17%, compared to that of no interface device. Such high current conduction with high mobility is attributed to the carrier recombination at p-n-p interfaces through coulombic interaction. This non-radiative p-n-p junction structure suggested in this report can be very useful for many practical organic semiconductor device applications.     

Base station location in a cellular CDMA system

We consider a cellular CDMA system in which blocking is enforced when the relative interference exceeds a certain threshold level. This paper addresses a radio network design problem in such a CDMA system. Given the data of call‐traffic distributed over the service area and potential sites of base stations, the objective of the problem is to locate base stations so as to minimize the associated cost for establishing base stations while keeping the probability of blocking under control. We develop an efficient algorithm for solving the design problem. Computational experiments with real‐world data are conducted to show both the efficiency and the practicality of the proposed design method. This revised version was published online in August 2006 with corrections to the Cover Date.     

A new on-chip interconnect crosstalk model and experimentalverification for CMOS VLSI circuit design

A new, simple closed-form crosstalk model is proposed. The model is based on a lumped configuration but effectively includes the distributed properties of interconnect capacitance and resistance. CMOS device nonlinearity is simply approximated as a linear device. That is, the CMOS gate is modeled as a resistance at the driving port and a capacitance at a driven port. Interconnects are modeled as effective resistances and capacitances to match the distributed transmission behavior. The new model shows excellent agreement with SPICE simulations. Further, while existing models do not support the multiple line crosstalk behaviors, our model can be generalized to multiple lines. That is, unlike previously published work, even if the geometrical structures are not identical, it can accurately predict crosstalk. The model is experimentally verified with 0.35-μm CMOS process-based interconnect test structures. The new model can be readily implemented in CAD analysis tools. This model can be used to predict the signal integrity for high-speed and high-density VLSI circuit design     

A novel approach to characterization of progressive breakdown in high-k/metal gate stacks

Dielectric breakdown (BD) of nFETs with TiN metal gates and HfO₂/interfacial layer with 1.09 nm EOT is studied. Occurrence of progressive BD at low current levels is demonstrated. A new measurement methodology for extraction of the PBD time and its dependence on gate voltage are reported.     

Restorable Type Conversion of Carbon Nanotube Transistor Using Pyrolytically Controlled Antioxidizing Photosynthesis Coenzyme

Here, a pyrolytically controlled antioxidizing photosynthesis coenzyme, β‐Nicotinamide adenine dinucleotide, reduced dipotassium salt (NADH) for a stable n‐type dopant for carbon nanotube (CNT) transistors is proposed. A strong electron transfer from NADH, mainly nicotinamide, to CNTs takes place during pyrolysis so that not only the type conversion from p‐type to n‐type is realized with 100% of reproducibility but also the on/off ratio of the transistor is significantly improved by increasing on‐current and/or decreasing off‐current. The device was stable up to a few months with negligible current changes under ambient conditions. The n‐type characteristics were completely recovered to an initial doping level after reheat treatment of the device.