Performance and Compensation of I/Q Imbalance in Differential STBC-OFDM

Differential space time block coding (STBC) achieves full spatial diversity and avoids channel estimation overhead. Over highly frequency-selective channels, STBC is integrated with orthogonal frequency division multiplexing (OFDM) to achieve high performance. However, low-cost implementation of differential STBC-OFDM using direct-conversion transceivers is sensitive to In-phase/Quadrature-phase imbalance (IQI). In this paper, we quantify the performance impact of IQI at the receiver front-end on differential STBC-OFDM systems and propose a compensation algorithm to mitigate its effect. The proposed receiver IQI compensation works in an adaptive decision-directed manner without using known pilots or training sequences, which reduces the rate loss due to training overhead. Our numerical results show that our proposed compensation algorithm can effectively mitigate receive IQI in differential STBC-OFDM.Comment: 7 pages, 2 figures, IEEE GLOBECOM 201

Ions-induced Epitaxial Growth of Perovskite Nanocomposites for Highly Efficient Light-Emitting Diodes with EQE Exceeding 30%

Cesium lead bromide (CsPbBr3) is a widely used emitter for perovskite light-emitting diodes (PeLEDs), benefiting from its large carrier mobility, high color purity and good thermal stability. However, the three-dimensional CsPbBr3 films encounter challenges due to their massive intrinsic defects and weak exciton binding effect, which limited their electroluminescence efficiency. To address this issue, the prevailing approach is to confine carriers by reducing dimensionality or size. Nonetheless, this method results in an increase in surface trap states due to the larger surface-to-volume ratio and presents difficulties in carrier injection and transport after reducing lattice splitting to smaller sizes. Here, we successfully achieved proper control over film crystallization by introducing sodium ions, which facilitate the epitaxial growth of zero-dimensional Cs4PbBr6 on the surface of CsPbBr3, forming large grain matrixes where CsPbBr3 is encapsulated by Cs4PbBr6. Notably, the ions-induced epitaxial growth enables the CsPbBr3 emitter with significantly reduced trap states, and generates coarsened nanocomposites of CsPbBr3&Cs4PbBr6 with grain size that surpass the average thickness of the thin perovskite film, resulting in a wavy surface conducive to light out-coupling. Additionally, another additive of formamidinium chloride was incorporated to assist the growth of nanocomposites with larger size and lower defects as well as better carrier injection and transportation. As a result, our demonstrated PeLEDs based on the coarsened nanocomposites exhibit low nonradiative recombination, enhanced light extraction and well-balanced carrier transportation, leading to high-performance devices. The champion device achieved an external quantum efficiency of 31.0% at the emission peak of 521 nm with a narrow full width at half-maximum (FWHM) of 18 nm

Enhanced Bayesian compressive sensing for ultra-wideband channel estimation

This paper addresses the application of the emerging compressive sensing (CS) technology to the detection of ultra-wideband (UWB) signals. Capitalizing on the sparseness of random UWB signals in the basis of eigen-functions, we develop a new CS dictionary called eigen- dictionary. Coupled with this eigen-dictionary, an enhanced Bayesian learning procedure is proposed to reconstruct the sparse UWB signal from a small collection of random projection measurements. Furthermore, by utilizing a common sparsity profile inherent in UWB signals, the proposed Bayesian algorithm naturally lends itself to multi-task CS for simultaneously recovering multiple UWB signals. Since the statistical inter-relationships between different CS tasks are exploited, the multi-task (MT) Bayesian CS can efficiently improve the reconstruction accuracy and thus the performance of UWB communications. Simulations based on real UWB data demonstrate the advantages of the proposed approach over its counterparts

Fast Beam Alignment for Millimeter Wave Time-Varying Channels Using Sparse Codes

In this paper, a novel beam alignment algorithmbased on the sparse graph coding theory is proposed for millimeterwave (mmWave) time-varying channels. Firstly, a pilotdesign method is introduced to transform the mmWave timevaryingbeam alignment into a sparse-graph design and detectionproblem. Inspired by Low-Density-Parity-Check (LDPC) codesand fountain codes, a multi-stage sparse coding method isproposed for the design of the measurement matrix and thetheoretical bound of the probability of success is derived to guidethe design of the sparse-graph. A beam alignment algorithm issubsequently proposed to detect the beam index and estimate thecarrier frequency offset (CFO). Then, the Carme´r-Rao LowerBound (CRLB) is derived. Simulation results demonstrate thatthe proposed beam alignment algorithm achieves significantperformance improvements over the conventional counterpartsin both the noiseless and noise cases

Beam Alignment for Millimeter Wave Multiuser MIMO Systems Using Sparse-Graph Codes

In order to achieve millimeter wave (mmWave) beam alignment , a class of beam scanning and searching schemes have been extensively studied [1–3]. Recently, to address the problems of the traditional algorithms have a high sample complexity, some adaptive beam scanning approaches utilize the hierarchical beamforming codebook to reduce the training time at the cost of frequent feedback [2]. Then, to eliminate the feedback link, a random beam alignment algorithm is proposed by utilizing the pseudo-random spreading codes [3]. However, it needs a Pseudo-Noise (PN) sequences with sufficient length to ensure the good correlation properties of different beams. Furthermore, in addition to the above disadvantages, most of the existing algorithms require either a separate pilot sequence per user or long beam scanning time when considering mmWave multiuser uplinking systems. To solve the above problems, a novel class of beam alignment algorithms based on the sparse graph coding theory are proposed in this paper. Firstly, we investigate the uplink mmWave beam training structure. Based on the analysis, the mmWave multiuser beam alignment problem is transformed into the sparse-graph design and detection problem. Secondly, a beam alignment algorithm framework based on sparse-graph coding and decoding is proposed. Furthermore , we derive the theoretical bound to chose the optimal parameters of the designed coding matrix. Finally, two beam alignment algorithms are proposed to detect the beam index in different settings. Simulation results confirm that our beam algorithms outperform the conventional beam training methods. Proposed Uplink Beam Training Scheme. This paper considers a typical uplink mmWave MU-MIMO system, where the BS communicates with K UEs simultaneously. Suppose that the BS is equipped with N R antennas and N RF RF chains, while the k-th UE has M T antennas and M RF RF chains. Then, the channel associated with the k-th UE can be given by [4

Design, Preparation and In Vitro Evaluation of Core–Shell Fused Deposition Modelling 3D-Printed Verapamil Hydrochloride Pulsatile Tablets

The aim of the study was to investigate core–shell pulsatile tablets by combining the advantages of FDM 3D printing and traditional pharmaceutical technology, which are suitable for a patient’s individual medication and chronopathology. The tablets were designed and prepared with the commercial verapamil hydrochloride tablets as core inside and the fused deposition modelling (FDM) 3D-printed shell outside. Filaments composed of hydroxypropylmethyl cellulose (HPMC) and polyethylenglycol (PEG) 400 were prepared by hot melt extrusion (HME) and used for fabrication of the shell. Seven types of printed shells were designed for the tablets by adjusting the filament composition, geometric structure and thickness of the shell. A series of evaluations were then performed on the 3D-printed core–shell tablets, including the morphology, weight, hardness, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), in vitro drug release and CT imaging. The results showed that the tablets prepared by FDM 3D printing appeared intact without any defects. All the excipients of the tablet shells were thermally stable during the extruding and printing process. The weight, hardness and in vitro drug release of the tablets were affected by the filament composition, geometric structure and thickness of the shell. The pulsatile tablets achieved personalized lag time ranging from 4 h to 8 h in the drug release test in phosphate-buffered solution (pH 6.8). Therefore, the 3D-printed core–shell pulsatile tablets in this study presented good potential in personalized administration, thereby improving the therapeutic effects of the drug for circadian rhythm disease