There has been greatly increasing interest in orthogonal frequency division multiplexing (OFDM) for broadband wireless transmission due to its robustness against multipath fading. However, OFDM signals have high peak-to-average power ratio (PAPR), and thus, a power amplifier must be operated with a large input power backoff (IBO). Recently, OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error-frequency domain equalization (MMSE-FDE) has been presented to reduce the PAPR, while improving the bit error rate (BER) performance of conventional OFDM. In this article, by extensive computer simulation, we present a comprehensive performance comparison of OFDM-based schemes in a nonlinear and frequency-selective fading channel. We discuss about the transmission performance of OFDM-based schemes with respect to the transmit peak-power, the achievable capacity, the BER performance, and the signal bandwidth. Our results show that OFDM/TDM using MMSE-FDE achieves a lower peak-power and capacity than conventional OFDM, which means significant reduction of amplifier transmit-power backoff, but with a slight decrease in signal bandwidth occupancy.

INTRODUCTION/AIM In acute organophosphate poisoning the issue of special concern is the appearance of muscle fasciculations and convulsions that cannot be adequately antagonised by the use of atropine and oxime therapy. The aim of this study was to examine atidotal effect of obidoxime or HI-6 combinations with memantine in mice poisoned with soman, dichlorvos or heptenophos. METHODS Male Albino mice were pretreated intravenously (iv) with increasing doses of oximes and/or memantine (10 mg/kg) at various times before poisoning with 1.3 LD-50 of soman, dichlorvos or heptenophos, in order to determine the median effective dose and the efficacy half-time. In a separate experiment, cerebral extravasation of Evans blue dye (40 mg/kg iv) was examined after application of memantine (10 mg/kg iv), midazolam (2.5 mg/kg intraperitonealy--ip) and ketamine (20 mg/kg ip) 5 minutes before soman (1 LD-50 subcutaneously--sc). RESULTS Coadministration of memantine induced a significant decrease in median effective dose in null time of both HI-6 (7.96 vs 1.79 gmoL/kg in soman poisoning) and obidoxime (16.80 vs 2.75 micromoL/kg in dichlorvos poisoning; 21.56 vs 6.63 micromoL/kg in heptenophos poisoning). Memantine and midazolam succeded to counteract the soman-induced proconvulsive activity. CONCLUSION Memantine potentiated the antidotal effect of HI-6 against a lethal dose of soman, as well as the ability of obidoxime to antagonize the toxic effects of dichlorvos and heptenophos probably partly due to its anticonvulsive properties.