  This paper study the effect of interference management arising due to
millimeter wave (mmWave) communication on the performance of multiple input
multiple output (MIMO) based spectrum sharing cognitive systems. The highly
directed mmWave signals have short wavelength property which enables to
fabricate an increased number of antennas in a small confined space of the
communication system. The large antenna elements are utilized to harvest high
beamforming gains and to improve the signal to noise ratio (SNR) by analog
processing at the cognitive base station (CBS) and secondary users. Analog
processing at the CBS and at secondary user have hardware and computation
restrictions. These restrictions are solved by designing radio frequency (RF)
precoding and RF combining. In the digital domain, it is shown that
interference between secondary users can be canceled by baseband block
diagonalization technique. Towards this end, the underlay mode of operation is
considered to control interference on the primary user and to derive the
expression for optimal power allocation. The derived power allocation is a
solution to the rate maximization problem of mmWave MIMO cognitive radio (CR)
systems. Finally, numerical simulations are performed to yield various
significant insights into for different mmWave CR system conditions and also
validate the improvement in performance in comparison to the only digital
communication systems.
