In this paper, A Parallel Combinatory-Orthogonal Frequency Division Multiplexing (PC-OFDM) system is proposed and analyzed. The proposed system selects at each symbol interval a subset of the available sub-carriers, and the selected sub-carriers are modulated by points from an M-PSK signal constellation. PC-OFDM systems can be designed to have lower Peak to Average Power Ratio (PAPR), higher bandwidth e ciency, and lower bit error probability on Gaussian channels compared to ordinary OFDM systems. A bit mapping procedure using the Johnson association together with a position algorithm for the PSK symbols is proposed. Good analytical approximations of the BER for PC-OFDM systems are derived for AWGN and Ricean fading channels, and extensive simulation results are presented.

Autofluorescence is a nuisance in the field of fluorescence imaging and tomography of exogenous molecular markers in tissue, degrading the quality of the collected data. In this letter, we report autofluorescence insensitive imaging using highly efficient upconverting nanocrystals (NaYF4:Yb3+∕Tm3+) in a tissue phantom illuminated with near-infrared radiation of 85mW∕cm2. It was found that imaging with such nanocrystals leads to an exceptionally high contrast compared to traditional downconverting fluorophores due to the absence of autofluorescence. Upconverting nanocrystals may be envisaged as important biological markers for tissue imaging purposes.

No abstract

No abstract

No abstract