Abstract
An optical wireless multiple-input multiple-output communication system employing intensity-modulation direct-detection is considered. The maximal diversity order of the channel is characterized by studying the outage probability. Then, spatial repetition coding is shown to be diversity-optimal as it achieves the channel's maximal diversity order. This diversity order is given by a simple expression which is suitable for any channel statistics of practical interest. The results are specialized to some practical channel statistics, and numerical results are provided to verify the results.