As it's a well-known fact that highly focused beams or the "pencil beams" shall be central to 5G mmWave cellular communication. MmWave don't only promise unchannelised high-bandwidth at the higher portion of EM spectrum but it also promise dense deployment with beamforming and multiplexing gains which means higher frequency reuse. In this connection what shall be the role of cognitive radio when plenty of spectrum shall be available for 5G cellular communication at mmWave bands?