NOMA MIMO Downlink in LEO Satellites

We consider two Low Earth Orbit (LEO) satellites that transmit with minimal cooperation at the same time and frequency to multi antennas land-terminal (LT). The satellites transmit in a non-orthogonal manner, and the LT employs a QR decomposition to gradually decode the two data streams. In comparison to a single transmit satellite, this scheme can increase the achievable terminal throughput significantly due to spatial multiplexing. However, since the satellite channel is characterized by Line-of-Sight (LOS) propagation, obtaining spatial multiplexing-gain depends on the system instantaneous configuration, i.e., the relative location of the satellites and the LT antennas. In this work, we characterize the performance of Non-orthogonal multiple access (NOMA) multiple input multiple output (MIMO) in LEO satellites. We use our recently introduced statistical model and define an outage event for the NOMA MIMO scheme. We then calculate upper and lower bounds on the outage probability (OP), which successively depicts its behavior where the satellite or receive antennas spatial separation is small. In the other case, where the spatial separation is high, we present a simple approximation for the OP which is shown to be quite accurate. The derived expressions indicate that dual satellite transmission can increase the downlink throughput with high probability.