ABSTRACT
Non-orthogonal multiple access (NOMA) via power domain multiplexing is widely deployed in bandwidth-limited light-emitting-diode-based visible-light-communication (VLC) systems due to its excellent spectral efficiency. However, quadrature phase-shift keying (QPSK) or even lower-order modulation formats are dominant; therefore, the spectral efficiency can be further improved with the higher-order quadrature amplitude modulation (QAM) modulation. Besides, error propagation (EP) deteriorates the system performance of lower power users during demodulation with imperfect successive interference cancellation. In this paper, we experimentally demonstrate a low-density parity-check (LDPC) codes-enabled 16QAM/QPSK modulation scheme for the orthogonal frequency-division multiplexing-based NOMA-VLC transmission system. Moreover, the analog pre-equalization technique is employed to enhance the modulation bandwidth. The experimental results exhibit that the EP can be significantly mitigated, and the bit error rate performance of lower power users can be improved by up to about 2 orders of magnitude by using LDPC codes and an analog pre-equalization technique.
ABSTRACT
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.
