Multiple-Aperture Direct-Detection Receiver Based on Maximal Ratio Combining for FSO Communication

Collecting light using multiple small apertures offers a lot of advantages over doing so using a single large aperture, including the effective mitigation of scintillation under strong turbulence, low implementation cost, and ease of scalability. In this work, we experimentally demonstrate a free-space optical communication system utilizing a 7-aperture direct-detection receiver based on the maximal ratio combining (MRC) scheme. For the implementation of MRC scheme blindly by using AC-coupled photo-receivers, we estimate the instantaneous signal-to-noise ratio (SNR) from the received signals time-averaged optimally for bit-error ratio performance. The experiment results show that the proposed blind scheme estimates the SNR accurately, and thus performs similarly to the pilot-symbol-aided scheme.