Performance analysis of channel estimation for OFDM systems with residual timing offset

The authors present an analysis of the effect of timing offset on channel estimation for comb-type pilot-aided orthogonal frequency division multiplexing (OFDM) systems. Residual timing offset does not negatively affect the channel estimation of the pilot subcarrier, but does corrupt the channel information obtained via interpolation. This paper provides the mean square error (MSE) channel estimation performance when a linear interpolation technique is used in a comb-type pilot-aided OFDM system. Analysis shows that the performance degradation of the channel estimator due to imperfect frame synchronization is dependent on the frequency correlation of the channels and the amount of timing offset     

Novel Detection Scheme for LSAS Using Power Allocation in Multi User Scenario with LTE-A and MMB Channels

Massive MIMO (also known as the “Large-Scale Antenna System”) enables a significant reduction of latency on the air interface with the use of a large excess of service-antennas over active terminals and time division duplex operation. For large-scale MIMO, several technical issues need to be addressed (e.g., pilot pattern design and low-antenna power transmission design) and theoretically addressed (e.g., channel estimation and power allocation schemes). In this paper, we analyze the ergodic spectral efficiency upper bound of a large-scale MIMO, and the key technologies including channel uplink detection. We also present new approaches for detection and power allocation. Assuming arbitrary antenna correlation and user distributions, we derive approximations of achievable rates with linear detection techniques, namely zero forcing, maximum ratio combining, minimum mean squared error (MMSE) and eigen-value decomposition power allocation (EVD-PA). While the approximations are tight in the large system limit with an infinitely large number of antennas and user terminals, they also match our simulations for realistic system dimensions. We further show that a simple EVD-PA detection scheme can achieve the same performance as MMSE with one order of magnitude fewer antennas in both uncorrelated and correlated fading channels. Our simulation results show that our proposal is a better detection scheme than the conventional scheme for LSAS. Also, we used two channel environment channels for further analysis of our algorithm: the Long Term Evolution Advanced channel and the Millimeter wave Mobile Broadband channel.

     

An intelligent operations scheduling system in a job shop

Scheduling jobs effectively under the consideration of actual loads on machines is one of the most complicated tasks in production control. The conventional scheduling methods fail because of the complexity of the tasks. To deal with the complexity, knowledge-based approaches to job shop scheduling have been attempted. This paper presents an interactive scheduling expert system, IOSS (Intelligent Operations Scheduling System), which performs both predictive and reactive scheduling. IOSS combines the knowledge-based scheduling method with the interactive scheduling method to generate a feasible schedule and to revise the existing schedule. It is based on opportunistic and interactive repair based problem solving within a blackboard architecture. To handle conflicting events, heuristics are applied from the order point of view. Flexible reaction management is possible while keeping the changes in the generated schedule to a minimum by adjusting the schedule for tardy operations or changes in job shop status. The effectiveness of the proposed concept is demonstrated by applying the developed system to an example case.     

An Experimental and Theoretical Approach to Optimize a Three-Dimensional Clinostat for Life Science Experiments

Gravity affects all biological systems, and various types of platforms have been developed to mimic microgravity on the Earth’;s surface. A three-dimensional clinostat (3D clinostat) has been constructed to reduce the directionality of gravitation. In this report, we attempted to optimize a 3D clinostat for a life science experiment. Since a 3D clinostat is equipped with two motors, we fixed the angular velocity of one (primary) motor and varied it for the other (secondary) motor. In this condition, each motor ran constantly and continuously in one direction during the experiment. We monitored the direction of the normal vector using a 3D acceleration sensor, and also performed a computer simulation for comparison with the experimental data. To determine the optimal revolution for our life science experiment (i.e., a revolution yielding the strongest effects), we examined the promoter activity of two genes that were reported to be affected by microgravity. We found that the ratio of velocity of 4:1.8 (0.55) was optimal for our biological system. Our results indicate that changes of the revolutions of a 3D clinostat have a direct impact on the result and furthermore that the revolutions of the two motors have to be separately adjusted in order to guarantee an optimal simulation of microgravity.     

Phase Engineering of Transition Metal Dichalcogenides with Unprecedentedly High Phase Purity,Stability, and Scalability via Molten-Metal-Assisted Intercalation

The crystalline phase of layered transition metal dichalcogenides (TMDs) directly determines their material property. The most thermodynamically stable phase structures in TMDs are the semiconducting 2H and metastable metallic 1T phases. To overcome the low phase purity and instability of 1T-TMDs, which limits the utilization of their intrinsic properties, various synthesis strategies for 1T-TMDs have been proposed in phase-engineering studies. Herein, a facile and scalable synthesis of 1T-phase molybdenum disulfide (MoS₂) via the molten-metal-assisted intercalation (MMI) approach is introduced, which exploits the capillary action of molten potassium and the difference between the electron affinity of MoS₂ and the ionization potential of potassium. Highly reactive molten potassium metal can readily intercalate into the MoS₂ interlayers, inducing an efficient phase transition from the 2H to 1T crystal structure. The ionic bonding between the intercalated potassium and sulfur lowers the energy barrier of the 1T-phase transition, enhancing the phase stability of the 1T crystals. Owing to the high purity and stability of the 1T phase, the electrocatalytic performance for the hydrogen evolution reaction is significantly higher in 1T-MoS₂ (MMI) than in 2H-MoS₂ and even in 1T-MoS₂ synthesized using n-butyllithium.     

Design and Performance Analysis of Soft Decision-Based Network-Assisted Interference Cancellation and Suppression Scheme

Recently, 3rd Generation Partnership Project (3GPP) has developed a network-assisted interference cancellation and suppression scheme to reduce the effect of interference. In this paper, we propose an advanced receiver based on soft decision to reduce the interference from the neighbor cells. The proposed receiver can suppress and cancel the interference by calculating the unbiased estimation value of the interference signal using the minimum mean square error or the interference rejection combining receiver. The interference signal is updated using soft information expressed by the log-likelihood ratio. We perform the system-level simulation based on 20 MHz bandwidth of a 3GPP LTE-Advanced sidelink system. The simulation results show that the proposed receiver can improve the signal-to-noise-plus-interference ratio, throughput, and spectral efficiency of a conventional system.

     

Zwitterionic Conjugated Surfactant Functionalization of Graphene with pH‐Independent Dispersibility: An Efficient Electron Mediator for the Oxygen Evolution Reaction in Acidic Media

The functionalization of graphene has been extensively used as an effective route for modulating the surface property of graphene, and enhancing the dispersion stability of graphene in aqueous solutions via functionalization has been widely investigated to expand its use for various applications across a range of fields. Herein, an effective approach is described for enhancing the dispersibility of graphene in aqueous solutions at different pH levels via non‐covalent zwitterion functionalization. The results show that a surfactant with electron‐deficient carbon atoms in its backbone structure and large π–π interactive area enables strong interactions with graphene, and the zwitterionic side terminal groups of the molecule support the dispersibility of graphene in various pH conditions. Experimental and computational studies confirm that perylene diimide amino N‐oxide (PDI–NO) allows efficient functionalization and pH‐independent dispersion of graphene enabled by hydration repulsion effects induced by PDI–NO. The PDI–NO functionalized graphene is successfully used in the oxygen evolution reaction as an electron mediator for boosting the electrocatalytic activity of a Ru‐based polyoxometalate catalyst in an acidic medium. The proposed strategy is expected to bring significant advances in producing highly dispersible graphene in aqueous medium with pH‐independent stability, thus broadening the application range of graphene.     

Effects of surface treatments using PECVD-grown hexamethyldisiloxane on the performance of organic thin-film transistor

Hexamethyldisiloxane (HMDSO) was deposited on a gate dielectric surface by plasma enhanced chemical vapor deposition for surface treatment, and its effects on the microstructure of pentacene and the transistor characteristics were examined. HMDSO films were deposited at room temperature at various RF powers (10 W to 120 W). Atomic force microscopy analysis of the pentacene films showed a significant increase in the grain size of the samples treated under the optimum RF power (10 W), which in turn led to a significant improvement in the electrical mobility. These results show that PECVD-grown HMDSO can be used as an effective surface treatment and warrants further investigation for process optimization.