Modulation bandwidth limitation is one of the major drawbacks in light-emitting diode (LED)-based visible light communication (VLC) systems. Various advanced physical-layer modulation formats with digital/analog pre-equalization or adaptive modulation techniques are usually employed to improve the transmission rate of VLC systems. In this Letter, we use a radio frequency (RF) digital-to-analog converter (DAC) to directly realize signal pre-equalization without additional digital or analog signal processing. In addition, low-complexity real-valued precoding techniques are applied to reduce the peak-to-average power ratio (PAPR) and equalize the subcarrier signal-to-noise ratio (SNR). The proposed hybrid scheme is experimentally investigated in a spectral-efficient filter bank multi-carrier (FBMC)-based VLC transmission system. The results exhibit that the PAPR can be reduced by more than 3 dB at the complementary cumulative distribution function of 1 × 10−4 with the real-valued precoding techniques. By using the proposed hybrid scheme, the modulation bandwidth can be increased to 515 MHz for 16QAM-FBMC with a bit error rate below 3.8 × 10−3 after 2.3-m free-space transmission. The net bit rate is improved by more than 45% compared with the conventional FBMC-VLC.
In this Letter, we use radio-frequency digital-to-analog converters (DACs) operating in different frequency response modes to generate a high spectral-efficiency multi-band (MB) filter bank multicarrier (FBMC) signal. In the receiver, the undersampling technique is employed to realize down-conversions. No electrical mixers are required. Besides, discrete Fourier transform and orthogonal circulant matrix transform precoding techniques combined with channel-independent digital pre-equalization are enabled to enhance transmission performance. Both numerical simulations and offline experiments are performed. The relevant results show that the MB-FBMC without a cyclic prefix (CP) is robust against inter-symbol interference induced by the band-pass filtering. By using precoding and pre-equalization techniques, the bit error rate can be improved by more than one order of magnitude. In contrast, an additional 12.5% CP overhead is required for the MB orthogonal frequency division multiplexing system to achieve such an improvement.
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