Performance Enhancement of W-Band RoF System Using 4D Trellis Coded Modulation OFDM With Precoding

In the paper, a four-dimensional trellis-coded modulation 16-quadrature amplitude modulation-orthogonal frequency division multiplexing (4D TCM 16QAM-OFDM) combined with precoding scheme is proposed and experimentally demonstrated in W-band radio-over-fiber (RoF) system. In W-band RoF system, frequency selective fading can cause unbalanced signal-to-noise ratio (SNR) distribution on the sub-carriers of the 4D TCM 16QAM-OFDM signals. Orthogonal circulant matrix transform (OCT) precoding, discrete Fourier transform (DFT) precoding, and constant amplitude zero autocorrelation sequence (CAZAC) precoding can be used to balance the SNR over the data subcarriers of 4D TCM 16QAM-OFDM signals. Moreover, DFT precoding and CAZAC precoding can reduce the peak-to-average power ratio (PAPR) of 4D TCM 16QAM-OFDM signals. After 50km single-mode fiber (SMF) and 5m free space transmission, the experimental results show that, at the bit error rate (BER) of 3.8×10
⁻³
, compared with 4D TCM 16QAM-OFDM using OCT precoding and DFT precoding, 4D TCM 16QAM-OFDM using CAZAC precoding can achieve the receiver sensitivity improvement of 2.33 dB and 0.48 dB respectively. In addition, compared with 4D TCM 16QAM-OFDM without precoding, it can achieve the receiver sensitivity improvement of 3 dB by using CAZAC precoding. Furthermore, 4D TCM 16QAM-OFDM has higher spectral efficiency than 8QAM-OFDM at the same symbol rate. The receiver sensitivity for 4D TCM 16QAM-OFDM using CAZAC precoding is enhanced about 1.1 dB, compared with 8QAM-OFDM using CAZAC precoding.