Capacity Analysis of a MIMO Laser Link From Lunar Surface to Earth

Moon explorations are expected to develop over the next decades. The demand of data transfer from the Moon to Earth for scientific purposes will soon exceed the capacity of conventional communication systems. We propose the application of multiple input multiple output (MIMO) to free-space optical communication (FSO) to further increase the capacity of Moon-Earth connections. However, the MIMO capacity of FSO links depends on the geometrical arrangement of the lasers and optical receivers. This geometry and, thus, the capacity change over time due to the relative motion of the Moon and the Earth. We analyze these capacity variations and propose an adaptive array geometry on Earth to control the array orientation of the receiving telescopes. In particular, we show that the rotation of the uniform linear array (ULA) on Earth according to the passage of the Moon maintains the capacity gain over time. We analytically derive the optimal orientation of the ULA. In addition, we propose a system design comprised of multiple distributed optical ground stations (OGSs) across the globe to obtain a permanent coverage. Simulation results show that a constantly high capacity gain can be provided in most of the time.