Experimental full duplex simultaneous transmission of LTE over a DWDM directly modulated RoF system

In this paper, we are experimentally demonstrating the seamless integration of full duplex system frequency division duplex (FDD) long term evolution (LTE) technology with radio-over-fibre (RoF) for eNodeB (eNB) coverage extension. LTE is composed of quadrature phase shift keying (QPSK), 16-quadrature amplitude modulation (QAM) and 64-QAM, modulated onto orthogonal frequency division multiplexing (OFDM) and single carrier-frequency division multiplexing for downlink (DL) and uplink (UL) transmissions, respectively. The RoF system is composed of dedicated directly modulated lasers for DL and UL with dense wavelength division multiplexing (DWDM) for instantaneous connections, and Rayleigh backscattering and nonlinear interference mitigations. DL and UL signals have varying carrier frequencies and are categorized as broad frequency spacing (BFS), intermediate frequency spacing (IFS) and narrow frequency spacing (NFS). The adjacent channel leakage ratio (ACLR) for DL and UL with 64-QAM are similar for all frequency spacing while the crosstalk is observed for NFS. For the best case scenario for DL and UL transmissions we achieve error vector magnitude (EVM) values of ~2.30%, ~2.33%, and ~2.39% for QPSK, 16-QAM and 64-QAM, respectively while for the worst case scenario with NFS EVM is increased by 0.40% for all schemes.