Improved receiver of ICI compensation for a spectral efficient frequency division multiplexing IM/DD system

Spectral efficient frequency division multiplexing (SEFDM) can greatly increase the spectral efficiency for intensity modulation/direct detection (IM/DD) optical communication systems. The sphere detection algorithm (SD) is the most efficient way to get the maximum likelihood (ML) solution to solve the inter-carrier interference (ICI) induced by the bandwidth compression of SEFDM system. However, SD algorithm is restricted by the numbers of subcarriers for SEFDM system, especially for larger numbers. Therefore, a sorted Gram-Schmidt (SGS) orthogonal decomposition algorithm, which can be applied to any subcarrier numbers, is proposed to overcome this restriction. To the best of our knowledge, the searched paths of FSD are researched for the first time to balance performance and complexity. Based on the analysis, a soft-tree-width sphere detection algorithm (SSD) is proposed and demonstrated by simulation and experiment. The results show that the proposed algorithm can greatly reduce the computational complexity (at least 40%) with the same system performance. The proposed algorithms are a promising candidate for flexible and efficient SEFDM systems. The SEFDM with the proposed detector is significant for the IM/DD optical systems.