A Belief Propagation Based Framework for Soft Multiple-Symbol Differential Detection

Soft noncoherent detection, which relies on calculating the \textit{a posteriori} probabilities (APPs) of the bits transmitted with no channel estimation, is imperative for achieving excellent detection performance in high-dimensional wireless communications. In this paper, a high-performance belief propagation (BP)-based soft multiple-symbol differential detection (MSDD) framework, dubbed BP-MSDD, is proposed with its illustrative application in differential space-time block-code (DSTBC)-aided ultra-wideband impulse radio (UWB-IR) systems. Firstly, we revisit the signal sampling with the aid of a trellis structure and decompose the trellis into multiple subtrellises. Furthermore, we derive an APP calculation algorithm, in which the forward-and-backward message passing mechanism of BP operates on the subtrellises. The proposed BP-MSDD is capable of significantly outperforming the conventional hard-decision MSDDs. However, the computational complexity of the BP-MSDD increases exponentially with the number of MSDD trellis states. To circumvent this excessive complexity for practical implementations, we reformulate the BP-MSDD, and additionally propose a Viterbi algorithm (VA)-based hard-decision MSDD (VA-HMSDD) and a VA-based soft-decision MSDD (VA-SMSDD). Moreover, both the proposed BP-MSDD and VA-SMSDD can be exploited in conjunction with soft channel decoding to obtain powerful iterative detection and decoding based receivers. Simulation results demonstrate the effectiveness of the proposed algorithms in DSTBC-aided UWB-IR systems.Comment: 14 pages, 12 figures, 3 tables, accepted to appear on IEEE Transactions on Wireless Communications, Aug. 201

In-situ synthesis of gold nanoparticles in nitrogen-doped titania nanosheets via layer-by-layer assembly method

Self-assembled multilayer films of nitrogen-doped exfoliated titania nanosheets and Au nanoparticles (NP) were fabricated via layer-by-layer assembly method followed by solar irradiation treatment. Au NP were found to form by in-situ reduction and thus disperse homogeneously between nitrogen-doped titania nanosheet galleries and the composite films of disordered structure, as confirmed by transmission electron microscope and X-ray diffractometer. Ultraviolet–visible absorption spectra in the multilayer buildup process indicated that plasmon resonance of the multilayer films was enhanced and red-shifted due to the changes of surrounding medium. It is found that nearly equal amounts of nanosheets were assembled and golds were reduced in each deposition cycle. X-ray photoelectron spectroscopy observation revealed that the interaction between the two components affects the distribution of electrons of Au, which causes the negative shift of the binding energy of Au NP. Compared with pure nitrogen-doped (N-doped) titania nanosheets, the higher hydroxyl density on the surface of such multilayer films was confirmed to be beneficial to efficiently separating the photogenerated electrons and holes, and as a result enhancing their photocatalytic activities