Ergodic capacity of multi-antenna spectrum sharing cognitive radio with outdated CSI

The multi-antenna spectrum sharing cognitive radio system in Nakagami-m fading environment is analyzed in this paper. Both cases when secondary user is provided with perfect and outdated channel state information (CSI) of the channel from the secondary user´s transmitter to the primary user´s receiver are considered. Ergodic capacity of spectrum sharing system is studied for different transmission techniques using multiple antennas. It has been shown that the selection of optimal technique is complex and it depends on various factors such as the system dimensions, the fading characteristics of the propagation environment and the delay of provided CSI.