Impact of macrodiversity on capacity and coverage of cellular network

This paper proposes an analytical study of downlink macrodiversity. Considering a mobile in macrodiversity with two base stations, we first characterize and compute explicitely the load induced in a cell by downlink macrodiversity. We show that in most cases this load is positive, increasing the total cell load. We moreover show that the contribution of the macrodiversity to the cell load can be negative in the sense that the macrodiversity can increase the cell’s capacity. Afterward, we propose a new framework for the study of cellular networks called the fluid model which allows to calculate analytically that load. The key idea of the fluid model is to approximate the discrete base stations (BS) entities by a continuum of transmitters which are spatially distributed in the network. This allows us to obtain simple analytical expressions of the main characteristics of the network. In this paper, we focus on the downlink other-cell interference factor f, which we define here as the ratio of outer cell received power (i.e. the power received from other cells) to the inner cell received power. This fluid model allows calculating the influence of interference on any mobile in a cell, whatever its position. The fluid analysis we develop enables to calculate the load of a cell analytically, and to quantify the macrodiversity impact. We generalize our analysis, considering a macrodiversity with a great number of base stations of the network.     

Ferroelectric random access memory based on one-transistor–one-capacitor structure for flexible electronics

We have demonstrated a low temperature process for a ferroelectric non-volatile random access memory cell based on a one-transistor–one-capacitor (1T1C) structure for application in flexible electronics. The n-channel thin film transistors (TFTs) and ferroelectric capacitors (FeCaps) are fabricated using cadmium sulfide (CdS) as the semiconductor and poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer as the ferroelectric material, respectively. The maximum processing temperature for the TFTs is 100 °C and 120 °C for the FeCaps. The TFT shows excellent access control of the FeCap in the 1T1C memory cell, and the stored polarization signals are undisturbed when the TFT is off. The fabricated 1T1C memory cell was also evaluated in a FRAM circuit. The memory window on the bit line was demonstrated as 2.3 V, based on the 1T1C memory cell with a TFT having dimensions of 80 μm/5 μm (W/L) and a FeCap with an area of 0.2 × 10^?3 cm² using a bit line capacitor of 1 nF pre-charged at 17.2 V. The 1T1C memory cell is fabricated using photolithographic processes, allowing the integration with other circuit components for flexible electronics systems.     

Adaptive transmission scheduling over fading channels for energy-efficient cognitive radio networks by reinforcement learning

In this paper, we address a cross-layer issue of long-term average utility maximization in energy-efficient cognitive radio networks supporting packetized data traffic under the constraint of collision rate with licensed users. Utility is determined by the number of packets transmitted successfully per consumed power and buffer occupancy. We formulate the problem by dynamic programming method namely constrained Markov decision process (CMDP). Reinforcement learning (RL) approach is employed to finding a near-optimal policy under undiscovered environment. The policy learned by RL can guide transmitter to access available channels and select proper transmission rate at the beginning of each frame for its long-term optimal goals. Some implement problems of the RL approach are discussed. Firstly, state space compaction is utilized to cope with so-called curse of dimensionality due to large state space of formulated CMDP. Secondly, action set reduction is presented to reduce the number of actions for some system states. Finally, the CMDP is converted to a corresponding unconstrained Markov decision process (UMDP) by Lagrangian multiplier approach and a golden section search method is proposed to find the proper multiplier. In order to evaluate the performance of the policy learned by RL, we present two naive policies and compare them by simulations.     

A spread‐slotted random‐access protocol with multi‐priority for personal and mobile communication networks carrying integrated traffic

This paper describes and analyzes a medium access protocol for wireless personal communication networks serving integrated traffic. A multipriority mechanism, which is implemented and controlled explicitly by the users and without any involvement from the network is incorporated into the protocol. We examine the proposed protocol under reservation and nonreservation policies and evaluate its performance when handling integrated voice and data traffic. The proposed protocol is suitable to be used in Personal Communication Systems aiming to provide integrated (voice/data) services.     

The hop count shift problem and its impacts on protocol design in wireless ad hoc networks

The hop count information has been exploited in the design of networking protocols in wireless ad hoc multi-hop networks. The hop count setup process normally assumes a perfect disk communication model and uses a simple controlled flooding approach. However, the practical communication model may not be such a disk communication model but time-varying and lossy. Sometimes transmissions can be successful beyond the nominal transmission range, i.e., the radius of such a disk model. The defacto hop count which are setup via time-varying and lossy radio channels may be different from the one based on the disk communication model. This paper introduces the hop count shift problem in realistic radio channels and investigates its impacts, via extensive simulations, on some representative hop count based protocols. Our simulation results suggest that these protocols’ performance generally suffers from the hop count shift problem, and the degradation is dependent on how the practical communication model deviates from the disk communication model. We also propose a strategy to combat the hop count shift problem and conduct simulations to show its effectiveness. The study of this paper necessitates reexaminations for the design of new hop count setup mechanism and the hop count based networking protocols.     

Electron cyclotron current drive on WT-III by a 56 GHz gyrotron

Electron cyclotron current drive (EC-CD) experiments have been carried out at the fundamental and the second harmonics on the WT-III tokamak using extraordinary mode radiation at 56GHz launched from the low field side. The EC driven current of 24 kA is attained at the power level of 100 kW and the plasma with the density of 2 × 10¹²cm^?3 and the electron temperature of several hundreds eV can be sustained during the EC pulse. The efficiency of EC-CD is 1·0 × 10^?2 (10¹⁹m^?2 A W^?1) at the fundamental and 3·5 × 10^?2 at the second harmonic. The unidirectional high energy electrons in the initial target plasma is necessary for EC-CD     

Thermal Conductivity Measurements on Challenging Samples by the 3 Omega Method

The 3 omega method is the best established method for measuring the thermal properties of thin films (>100 nm) and nanowires. Theoretically, the method could be applied to many more types of samples, leading to new knowledge, but to date little effort has been made to extend its applicability. An enabling set of technologies has been tested at the Fraunhofer-IPM. The technologies developed encompass a new design of microheater, the measurement of bulk samples with a prefabricated microheater on adhesive tapes and polymer sheets, the measurement of tiny bulk samples glued to the underside of polymer sheets, a fully automated experimental setup, and a new numerical tool adapted to the new type of heater. The new design of microheater and software were validated using float glass as a reference material. A microheater on adhesive tape was used to measure accurately the thermal properties of sintered thermoelectric materials. The thermal conductivity of a very small melt-spun nanocomposite sample glued to the underside of a Kapton™ sheet was measured. The potential of the new design of microheater to measure very thin (~nm) films is discussed.     

A 2.7–6.1 GHz CMOS local oscillator based on frequency multiplication by 3/2

Frequency multiplication by 3/2 is proposed as a means to expand the frequency generation capabilities of a single LC VCO. Fractional frequency multiplication is obtained by cascading a broadband injection locked modulo-two divider and a multiply-by-three circuit based on edge combining. The proposed solution is inductorless, thus very compact. It allows the generation of all frequencies from 2.7 to 6.1 GHz with a performance suitable for cellular standards. It shows a phase noise floor below ?150 dBc/Hz and a spurious level below ?35 dBc. The multiplier by 3/2 consumes 5 mA and the VCO draws 10 mA from a 1.2 V supply. The additional power consumption due to the multiplier trades with the small area penalty and the flexibility of this solution, compared to the use of multiple LC VCOs.     

Development of 3.7 % Efficient Cu2ZnSnSe4 Solar Cells by Selenizing Cu-Zn-Sn Films Deposited by DC Sputtering on TiN-Protected Mo/Glass Substrates

Cu₂ZnSnSe₄ (CZTSe) films for solar cell devices were fabricated by sputtering of a Cu-Zn-Sn target followed by post-selenization at 500–600 °C for 1 h in the presence of single or double compensation discs to supply Se vapor. The optimized selenization conditions avoided the Se deficiency and enhanced the grain growth of CZTSe films. The 600 °C-selenized CZTSe films adjacent with double discs obtained the large grains of 2–5 μm and had a [Cu]/([Zn]+[Sn]) ratio of 0.94 and a [Zn]/[Sn] ratio of 1.34. In order to fabricate the device on Mo-coated glass substrates, a TiN reaction barrier layer was coated before the Cu-Zn-Sn sputtering coating. The TiN-CZTSe device had 3.7 % efficiency (η), as compared to 0.58 % for the TiN-free one. The efficient device had the CZTSe layer with hole concentration (n _p) of 3.4 × 10¹⁷ cm^?3, Hall mobility (μ) of 54 cm² V^?1 s^?1, and electrical conductivity (σ) of 2.9 Ω^?1 cm^?1.