The transmission rate in current passive optical networks can be increased by employing Orthogonal Frequency Division Multiplexing (OFDM) modulation. The computational kernel of this modulation is the fast Fourier transform (FFT) operator, which has to achieve a very high throughput in order to be used in optical networks. This paper presents the implementation in an FPGA device of a variable-length FFT that can be configured in run-time to compute different FFT lengths between 16 and 1024 points. The FFT reaches a throughput of 10 GS/s in a Virtex-7 485T-3 FPGA device and was used to implement a 20 Gb/s optical OFDM receiver.

The precise measurement of QT interval and QRS complex duration is important to characterize the electrical cardiac activity of the surface ECG. Variations of these intervals were evaluated when ECG sampling rate changes. The ECG recordings used in this study (n = 78) were obtained from a combination of pharmacological blockage and postural changes. The ECG recordings were originally sampled at 500 Hz, and then were downsampled by intervals of 25 Hz until the minimum sampling rate of 75 Hz. In all cases the down-sampling was implemented using cubic spline interpolation. The QRS complex duration, RR and QT intervals for each subject, condition and sampling rate were measured. The QT interval was corrected using two different techniques: Bazzett and individualized QT corrections. The effect of the sampling rate was modeled with an exponential decay function, which was used later to measure where the exponential reaches an asymptotic value (at 5τ ). The 5τ value for uncorrected QT was at 290 Hz, corrected QT with Bazzett was at 303 Hz, and corrected QT with Individual method was at 253 Hz, finally QRS complex duration was at 297Hz. An overestimation of the QT interval and QRS complex duration was observed when decreasing the sampling rate below 300 Hz. IntroductionThe surface ECG analysis is widely used for the diagnostic of cardiac diseases. The ECG is a noninvasive technique that allows the visualization of the heart's electrical activity. The changes in duration of the QT interval are related to certain pathologies, and with the effects of diverse drugs. On the other hand, the duration of QRS complex also gives information about the status of the myocardial conduction system. All this rise the necessity of making precise measurements of these intervals of theThe measurements on the ECG are mostly defined by the characteristic extrema, amplitudes, wave morphologies and intervals of time between extrema points (Figure 1). Figure 1. Definition of RR, QT and QRS complex in an ECG beat.In the present study the QT interval and duration of the QRS complex were measured when the autonomic nervous system was blocked with a combination of drugs and postural changes.Administration of atropine and propranolol was used to block sympathetic and vagal systems respectively, while subjects were in standing and supine position. This pharmacological and postural combination is useful to explore the QT interval correction techniques within a wide range of HR variations [3].An incorrect choice of the sampling rate (F s ) may introduce errors when the fiducial points of the ECG are measured, and therefore the intervals or segments between

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This paper presents the hardware architecture of an OFDM receiver suitable for optical communications. The receiver has been implemented in an FPGA device and used to demonstrate experimentally an optical OFDM transmission in a passive optical link with a directly modulated DFB laser and DAC/ADC at 5 GS/s. A bit rate of 20.37 Gb/s is achieved using an OFDM signal with subcarrier modulation format up to 512-QAM, it has been successfully transmitted over 10 km SSMF with a spectral efficiency of 8.38 bit/s/Hz.