Signal extraction with frequency arrangement (SEFA) and superimposed subcarrier modulation (SSM) schemes in fiber-oriented wireless access systems

This paper describes technologies for the improvement of the noise and nonlinearity characteristics of wireless access systems based on subcarrier optical transmission. First, the superimposed subcarrier modulation (SSM) technique is proposed to reduce the reflection noise induced by fiber connectors. We experimentally confirmed that the proposed method reduces this noise, and we found the optimum frequency and power of the superimposed subcarrier, SSM design methodology is also presented, taking both noise and nonlinearity into account. Second, signal extraction with frequency arrangement (SEFA) is proposed for increasing the optical modulation index, because the third-order intermodulation distortion (IM3) produced by the optical devices can be ignored. Simulation results show that SEFA greatly improves the transmission performance in terms of both the ratio of desired-to-undesired signal and the receiver sensitivity under Rayleigh fading. Combining the SSM and SEFA is also considered, for use with FP-LDs or DFB-LDs. These technologies will enable cheaper FP-LD implementation in fiber-oriented wireless access systems.