TURKISH JOURNAL OF ELECTRICAL ENGINEERING AND COMPUTER SCIENCES, cilt.19, sa.2, ss.275-289, 2011 (SCI-Expanded)
Brain-computer interfaces (BCIs) provide a way to monitor and treat neurological diseases. An important
application of BCIs is the monitoring and treatment of epilepsy, a neurological disorder characterized by
recurrent unprovoked seizures, symptomatic of abnormal, excessive or synchronous neuronal activity in the
brain. BCIs contain an array of sensors that gather and transmit data under the constrains of low-power and
minimal data transmission. Asynchronous sigma delta modulators (ASDMs) are considered an alternative to
synchronous analog to digital conversion. ASDMs are non-linear feedback systems that enable time-encoding
of analog signals, from which the signal can be reconstructed. An efficient reconstruction of time-encoded
signals can be achieved using a prolate spheroidal waveform (PSW) projection. PSWs have finite time support
and maximum energy concentration within a given bandwidth. The ASDM time-encoding is related to the
duty-cycle modulation and demodulation, which shows that sampling is non-uniform. For transmission of
data from BCI, we propose a modified orthogonal frequency division multiplexing (OFDM) technique using
chirp modulation. Our method generalizes the chirp modulation of binary streams with non-uniform symbol
duration. Our theoretical results relate to recent continuous-time digital signal processing and compressive
sampling theories.