Beam pointing optimization for spatial diversity MIMO free space optical communications

초록

In this paper we propose a beam pointing algorithm to find optimal beam coordinates maximizing link performance in multiple-input multiple-output (MIMO) free space optical communications (FSOC) with spatial diversity. We first derive the received signal-to-noise ratio (SNR) with spatial diversity and analyze the convexity condition of SNR function with respect to transmit beam coordinates. Then we obtain the beam coordinates maximizing the received SNR through an alternating optimization (AO) algorithm and Newton's method. However the proposed algorithm requires instantaneous channel state information (CSI) which requires a high signaling overhead in MIMO FSOC. Thus instead of exploiting instantaneous CSI we utilize statistical CSI and propose a robust beam pointing algorithm with respect to atmospheric turbulence and pointing error. Numerical results show that our proposed algorithm outperforms conventional schemes in a dynamic FSOC network. Furthermore we confirm that the optimal coordinates which are robust to the channel conditions approach to the centroid of receiver lenses as the strength of turbulence and pointing error increases. © 2024 Elsevier B.V.

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