Receiver Sensitivity Improvement of Layered-ACO-OFDM System Enabled by Layered-DFT/OCT Precoding Technique

Layered asymmetrically clipped optical orthogonal frequency-division multiplexing (L-ACO-OFDM) is power and spectral efficient scheme for intensity-modulation and direct-detection systems. However, the non-flat signal-to-noise ratio (SNR) condition over OFDM subcarriers due to the non-perfect frequency responses of devices and optical fiber link will degrade the bit error ratio (BER) performance. Furthermore, the errors will propagate to the higher layers during the L-ACO-OFDM demodulation. As a result, the receiver sensitivity of L-ACO-OFDM systems will be reduced. In this paper, the layered precoding technique is applied to the L-ACO-OFDM system to average SNR over OFDM subcarriers separately in each layer. The numerical simulations show that both layered discrete Fourier transform (DFT) and layered orthogonal circulant matrix transform (OCT) precoded L-ACO-OFDM systems have a similar receiver sensitivity, but have better receiver sensitivity than the uncoded L-ACO-OFDM system at a BER of 1e-3.