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With the maturation of wireless charging technology, Wireless Rechargeable Sensor Networks (WRSNs) has become a promising solution for prolong network lifetimes. Recently studies propose to employ a mobile charger (MC) to simultaneously charge multiple sensors within the same charging range, such that the charging performance can be improved. In this paper, we aim to jointly optimize the number of dead sensors and the energy usage effectiveness in such multi-node charging scenarios. We achieve this by introducing the partial charging mechanism, meaning that instead of following the conventional way that each sensor gets fully charged in one time step, our work allows MC to fully charge a sensor by multiple times. We show that the partial charging mechanism causes minimizing the number of dead sensors and maximizing the energy usage effectiveness to conflict with each other. We formulate this problem and develop a multi-node temporal spatial partial-charging algorithm (MTSPC) to solve it. The optimality of MTSPC is proved, and extensive simulations are carried out to demonstrate the effectiveness of MTSPC.

We present dual-polarization OFDM/OQAM transmission for passive optical network. The ISFA and MMSE with the full loaded and half loaded preamble structures are used to mitigate the intrinsic imaginary interference.

We propose a modified OFDM/OQAM scheme for VLC, which can efficiently boost the data rate and combat multipath induced distortions. To combat the effect of IMI, ISFA and MMSE combined with IAM are proposed.

We propose a modified orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) scheme for visible light communications (VLC). The OFDM/OQAM VLC system can efficiently boost the data rate, and combat multipath induced the inter symbol interference (ISI) and inter carrier interference (ICI). To combat the effect of intrinsic imaginary interference, intrasymbol frequency-domain averaging and minimum mean squared error (MMSE), combined with interference approximation method, are proposed. The experiment results show that the proposed system offers similar bit error rate performance to that of OFDM, while the bit rate is increased by 9% for the elimination of cyclic-prefix and guard band.

We propose an efficient time-domain channel estimation method for polarization interleaving orthogonal frequency division multiplexing passive optical network (OFDM-PON) with direct detection. Compared with the frequency-domain least square channel estimator (FLSE) and intra-symbol frequency-domain averaging (ISFA), the time-domain channel estimator (TD-CE) with overhead reduction demonstrates better system robustness against transmission impairments, such as optical noise, chromatic dispersion, and polarization mode dispersion.

We propose an uplink visible light communication (VLC) scheme based on interleaved frequency division multiple access (IFDMA), which provides some highly desirable features such as high spectral efficiency and high tolerance against multipath distortion. Compared with OFDMA, the IFDMA has lower PAPR and lower computation complexity at the transmitter. The experiment results show that the increased transmission span is about 7.5-cm at a BER of 10−5 for IFDMA compared with the OFDMA.

Recently, nonlinear optical responses of the graphene have attracted much attention [1]. In this work, we theoretically investigate second harmonic generation (SHG) from bilayer-graphene (BLG) embedded in photonic crystals (PCs) using the transfer-matrix method [2]. Two kinds of cases are considered. One is a single BLG layer embedded in the defective PC (Fig. 1(a)), the other is a stack of BLG layers in the dielectric multilayer structure (Fig. 1(b)). It is found that the improved field localization within the defective PC enhances SHG by three orders of magnitude compared with the bare BLG (Fig. 2(f)). Although the SHG efficiency from the stack of BLG layers in the dielectric multilayer structure is lower than that from the defective PC due to the effect of absorption, there are some advantages in controlling the polarization dependence of the SHG for such a case. For example, various intensity ratios of p-polarized and s-polarized second harmonic outputs can be realized by adjusting the azimuthal rotational angles of the BLG layers for the incident wave with a certain polarization (Fig. 3). We believe that these phenomena are very beneficial for the design of optical devices.