Comparison of interpolation-based sampling frequency offset compensation schemes for practical OFDM-VLC systems.

Sampling frequency offset (SFO) is an important issue in the orthogonal frequency-division multiplexing (OFDM)-based visible light communication (VLC) systems with low-cost analog-to-digital or digital-to-analog converters (ADCs/DACs). A digital interpolation or resampling filter can be used to effectively compensate the SFO. In such case, oversampling at the receiver ADC is required to mitigate the aliasing effect due to imperfect DACs and nonlinearity of visible light sources that cause extra frequency components inside/outside the OFDM signal spectrum. The oversampling factor (rate) is mainly determined by the order of the digital interpolation filter and nonlinear VLC links. The design of the OFDM-VLC receiver incorporating the digital interpolation filter is vital as it affects not only the transmission performance but also the complexity of digital signal processing (DSP). To evaluate the feasibility of the digital interpolation-based SFO compensation schemes for cost-sensitive VLC applications, in this paper, a real-time OFDM-VLC receiver incorporating the 2/3/4 order interpolation filters is experimentally demonstrated. An OFDM frame structure is designed for the synchronization including SFO estimation and compensation, in which the precision and latency of DSP are considered. On the basis of the real-time OFDM-VLC receiver, the comparison in the VLC transmission performance and DSP complexity between different interpolation-based SFO compensation schemes is discussed.