Circular MIMO FSO Nodes With Transmit Selection and Receive Generalized Selection Diversity

Mobile free space optical (FSO) nodes have been characterized as a way to resolve movement and misalignment incompatibilities that are inherent in optical nodes. By introducing multibranch angular diversity mobility to FSO nodes, connection reliability is enhanced. In this paper, receiving branches are assumed to be circularly placed on a single plane, and transmitting branches are positioned on a different platform. A coverage of 360 in this unbalanced branch configuration is achieved with the deployment of diversity combining, wherein the transmitter follows a transmit selection diversity rule. Channel turbulence is modeled as weak lognormal with spatially correlated fading samples. On the receiver side, selection combining (SC), equal gain combining (EGC), maximum ratio combining (MRC), and threshold generalized SC (T-GSC) schemes serve as candidates for combining purposes. Statistical discussion relative to branch signals and combiner output is presented, and bit error performance and outage probability are numerically evaluated. When compared with MRC, T-GSC was found to have lower estimation error. The T-GSC scheme additionally demonstrated overall superior performance over SC and EGC for mobile FSO.