A dynamic ID management protocol for CSMA/IC in ad hoc networks

Contention based MAC protocols are widely used in ad hoc networks because they are suitable, where no central control node exists. However, contention based MAC protocols waste much time because of frequent collisions and long contention times. Moreover, it is hard for them to fairly distribute medium access opportunities. As a result, the problem of unfair medium access may arise under normal network conditions. Recently, another contention based MAC protocol, named the Carrier Sense Multiple Access/ID Countdown (CSMA/IC) was proposed. CSMA/IC resolves medium access contention by comparing the IDs of contending nodes with a simple signaling process. Therefore, medium access collisions never happen as long as each node possesses a unique ID, and the time cost for contention may be smaller than any other contention based MAC protocols if the number of IDs is managed so as to be as small as possible. Furthermore, CSMA/IC may support fair medium access by manipulating the ID of each node properly. In this paper, we propose a novel dynamic ID management protocol which enables a node to acquire a unique ID without any message exchanges and fairly distributed the number of medium access opportunities to all contending nodes. The proposed protocol also makes the contention process of CSMA/IC efficient by dynamically managing the length of the ID field according to the network traffic. The simulation results show that the proposed ID management protocol significantly improves the aforementioned aspects of CSMA/IC MAC protocol compared to previous ID management schemes.     

Growth of tin whiskers for lead-free plated leadframe packages in high humid environments and during thermal cycling

Growth behavior of tin whiskers from pure tin and tin–bismuth plated leadframe (LF) packages for elevated temperature and high humidity storages and during thermal cycling was observed. In the storage at 60 °C/93% relative humidity (RH) and 85 °C/85%RH the galvanic corrosion occurred at the outer lead toes and shoulders where the base LF material is exposed, forming tin oxide layers of SnO₂. The corroded layers spread inside the film and formed whiskers around the corroded islands. Many whiskers were observed to grow from grain boundaries for the Fe–42Ni alloy (alloy42) LF packages. It was confirmed that the corrosion tends to occur on the side surfaces of outer leads adjacent to the mold flash. The contribution of ionic contaminants in epoxy mold compound (EMC) to the corrosion was not identified. During thermal cycling between −65 °C and +150 °C whiskers grew out of as-deposited grains for pure tin-plated alloy42 LF packages and they grew linearly with an increase of number of cycle. Growth mechanisms of the whiskers from grain boundaries and as-deposited grains were discussed from the deformation mechanism map for tin and mathematical calculation with a steady-state diffusion model.     

Statistical Characterization of Open Failures in the Fine-Pitch COG Interconnection

Chip-on-glass (COG) interconnection using anisotropic conductive film (ACF) is susceptible to open failures. Open failures can be induced by the absence of conductive particles or an insufficient contact. Experimental results as well as statistical approaches were used to understand the conditions for open failures in COG bonding. The binomial distribution was used to predict the probability of the open failure due to the deficiency of conductive particles. The probability of an open failure decreased with increasing bump area and decreasing particle size. The bump height variation was also an important factor that affected the probability of the open failure together with the bump-to-electrode gap and the particle size. The variation in bump height should be minimized to avoid open failures in fine-pitch applications where a smaller particle size is required.     

A 20-Gb/s 0.13-/spl mu/m CMOS serial link transmitter using an LC-PLL to directly drive the output multiplexer

A 20-Gb/s transmitter is implemented in 0.13-/spl mu/m CMOS technology. An on-die 10-GHz LC oscillator phase-locked loop (PLL) creates two sinusoidal 10-GHz complementary clock phases as well as eight 2.5-GHz interleaved feedback divider clock phases. After a 2/sup 20/-1 pseudorandom bit sequence generator (PRBS) creates eight 2.5-Gb/s data streams, the eight 2.5-GHz interleaved clocks 4:1 multiplex the eight 2.5-Gb/s data streams to two 10-Gb/s data streams. 10-GHz analog sample-and-hold circuits retime the two 10-Gb/s data streams to be in phase with the 10-GHz complementary clocks. Two-tap equalization of the 10-Gb/s data streams compensate for bandwidth rolloff of the 10-Gb/s data outputs at the 10-GHz analog latches. A final 20-Gb/s 2:1 output multiplexer, clocked by the complementary 10-GHz clock phases, creates 20-Gb/s data from the two retimed 10-Gb/s data streams. The LC-VCO is integrated with the output multiplexer and analog latches, resonating the load and eliminating the need for clock buffers, reducing power supply induced jitter and static phase mismatch. Power, active die area, and jitter (rms/pk-pk) are 165 mW, 650 /spl mu/m/spl times/350 /spl mu/m, and 2.37 ps/15 ps, respectively.     

A Novel Data Transmission Scheme for ATSC Terrestrial DTV Systems

In Advanced Television Systems Committee (ATSC) terrestrial digital television (DTV) systems, additional very low‐rate data can be transmitted by modulating the amplitude and polarity of the transmitter identification (TxID) signal. Although the additional data transmission scheme offers reliable transmission and has a very large coverage area, it has a limitation on the data rate. In this paper, we propose a novel additional data transmission scheme based on the TxID sequences of the ATSC DTV system and Walsh modulation. The proposed scheme not only increases the data rate significantly, but also offers a virtually identical coverage area compared to a conventional scheme.     

Dynamic Bandwidth and Carrier Allocation for Video Broadcast/Multicast Over Multi-Cell Environments

Recently, broadcast/multicast over cellular networks has been actively discussed over commercial wireless mobile terminals. Compared to conventional terrestrial or satellite broadcasting systems, the quality-of-service (QoS) for edge users is an important issue due to inter-cell interference over multi-cell environments. In this paper, we introduce a dynamic bandwidth and carrier allocation (DBCA) technique by fully utilizing different visual importance of each layer in multi-layer video for broadcast/multicast services when the number of users is limited over macro/micro/femto cell environments. To ensure an acceptable video quality for edge users, the bandwidth and the loading ratio are dynamically controlled to enhance the utility through the radio resource control in accordance with the visual importance. The simulation results show that DBCA exhibits much better QoS by sending visually more important data with high priority in the cell border region.     

Fabrication of wavelength-tunable butt-coupled sampled grating DBR lasers using planar buried heterostructure

Planar buried heterostructure (PBH) was adopted to fabricate a sampled grating distributed Bragg reflector laser diode (SGDBR-LD) having a low threshold current and a stable fundamental transverse mode. The etching process for butt-coupling was optimized to improve the reproducibility and the uniformity of the butt-coupled waveguide. The maximum output power of the fabricated SGDBR-LD was 20 mW at 200-mA continuous-wave operation at 25/spl deg/C. The output power was measured 10 and 9 mW higher than those of ridged waveguide (RWG) structure and buried ridge stripe (BRS), and the threshold current was slightly higher than those of RWG and BRS. The spectra of 25 channels spaced 50 GHz within the tuning range of 44.4 nm was obtained by a precise control of SG and phase control currents. The side-mode suppression ratio of more than 35 dB was obtained in the whole tuning range. The output power variation was less than 5 dB, which is 4 dB smaller than that of RWG structure.     

Chiral Stereoisomer Engineering of Electron Transporting Materials for Efficient and Stable Perovskite Solar Cells

A series of chiral stereoisomers of electron transporting materials with two chiral substituents is rationally designed and synthesized, and the influence of stereoisomerism on their physical and electronic properties is investigated to demonstrate highly efficient and stable perovskite solar cells (PSCs). Compared to mesomeric naphthalene diimide (NDI) derivatives, which have heterochiral side groups with centrosymmetric molecular packing of symmetric‐shaped conformers in the crystalline state, enantiomeric NDI derivatives have homochiral side groups that exhibit non‐centrosymmetric molecular packing of asymmetric‐shaped conformers in the crystalline state and exhibit better solution processability based on one order of magnitude higher solubility. A similar trend is observed in different rylene diimide stereoisomers based on larger semiconducting core perylene diimide. The PSCs based on NDI enantiomers with good film‐forming ability and a very high lowest phase transition temperature (T_lowest) of 321 °C exhibit a high and uniform average power conversion efficiency (PCE) of 19.067 ± 0.654%. These PSCs also have a high temporal device stability, with less than 10% degradation of the PCE at 100 °C for 1000 h without encapsulation. Therefore, chiral stereoisomer engineering of charge transporting materials is a potential approach to achieve high solution processability, excellent performance, and significant temporal stability in organic electronic devices.     

Correlated Quantum Phenomena of Spin–Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3 Based Artificial Superlattices

Unexpected, yet useful functionalities emerge when two or more materials merge coherently. Artificial oxide superlattices realize atomic and crystal structures that are not available in nature, thus providing controllable correlated quantum phenomena. This review focuses on 4d and 5d perovskite oxide superlattices, in which the spin–orbit coupling plays a significant role compared with conventional 3d oxide superlattices. Modulations in crystal structures with octahedral distortion, phonon engineering, electronic structures, spin orderings, and dimensionality control are discussed for 4d oxide superlattices. Atomic and magnetic structures, J_eff = 1/2 pseudospin and charge fluctuations, and the integration of topology and correlation are discussed for 5d oxide superlattices. This review provides insights into how correlated quantum phenomena arise from the deliberate design of superlattice structures that give birth to novel functionalities.