Precoding for Orthogonal Space–Time Block-Coded OFDM Downlink: Mean or Covariance Feedback?

This paper presents linear and nonlinear precoding design for error-rate improvement in orthogonal space–time block-coded (OSTBC) multiple-input–multiple-output (MIMO) orthogonal frequency-division-multiplexed (OFDM) downlink, where both the conditional mean of the channel gain matrix and the channel gain covariance matrix may be available at the transmitter. The conditional means of the channel matrix are derived for a general transmit-antenna-correlated frequency-selective fading MIMO channel with estimation errors and feedback delay. Mean-feedback linear precoding and nonlinear Tomlinson–Harashima precoding (THP) are developed to maximize the signal-to-noise power ratio (SNR). The intuition that when the mean feedback becomes accurate the mean-feedback precoding outperforms covariance precoding is confirmed. Dual-mode precoding is also proposed, in which the novel mean-feedback precoding or covariance precoding is adaptively chosen at the receiver. The precoding-mode switching metric is the maximized SNR, which is an indicator of the error rate. The receiver calculates its metric, selects the mode that achieves a higher SNR, and decides whether mean feedback is necessary. Our proposed precoders (both mean feedback and adaptive) significantly reduce the system error rate. Nonlinear precoding is shown to outperform linear precoding. Adaptive precoding outperforms both mean-feedback precoding and covariance precoding if individually applied in OSTBC OFDM.      

Advanced AAO Templating of Nanostructured Stimuli‐Responsive Polymers: Hype or Hope?

Nanostructures play a significant role in introducing distinctive functionality to materials. A synergistic combination of nanofabrication techniques with material properties holds great promise in creating smart biomimetic structures. An advanced preparation technique to fabricate complex and sophisticated hierarchical polymeric nanostructure templates via anodized alumina oxide membranes is highlighted. Moreover, nanostructures made of responsive polymers activated by environmental stimuli offer a huge potential in a wide range of applications by enhancing their responsiveness. The current state of research on novel nanostructures fabrication by integrating anodic aluminum oxide with stimuli‐responsive polymers is presented, with an emphasis on the underlying actuation mechanism in terms of application. Furthermore, the potential direction for future research is discussed.     

Plasmonic Enhancement or Energy Transfer? On the Luminescence of Gold‐, Silver‐, and Lanthanide‐Doped Silicate Glasses and Its Potential for Light‐Emitting Devices

With the technique of synchrotron X‐ray activation, molecule‐like, non‐plasmonic gold and silver particles in soda‐lime silicate glasses can be generated. The luminescence energy transfer between these species and lanthanide(III) ions is studied. As a result, a significant lanthanide luminescence enhancement by a factor of up to 250 under non‐resonant UV excitation is observed. The absence of a distinct gold and silver plasmon resonance absorption, respectively, the missing nanoparticle signals in previous SAXS and TEM experiments, the unaltered luminescence lifetime of the lanthanide ions compared to the non‐enhanced case, and an excitation maximum at 300–350 nm (equivalent to the absorption range of small noble metal particles) indicate unambiguously that the observed enhancement is due to a classical energy transfer between small noble metal particles and lanthanide ions, and not to a plasmonic field enhancement effect. It is proposed that very small, molecule‐like noble metal particles (such as dimers, trimers, and tetramers) first absorb the excitation light, undergo a singlet‐triplet intersystem crossing, and finally transfer the energy to an excited multiplet state of adjacent lanthanide(III) ions. X‐ray lithographic microstructuring and excitation with a commercial UV LED show the potential of the activated glass samples as bright light‐emitting devices with tunable emission colors.