What is A-CSI (aperiodic-CSI)?

CSI is Channel State Information is a kind of indicator of how good or bad the channel is at a specific time. The CSI has three major components as CQI (Channel Quality Index), PMI (Precoding Matrix Indicator), and RI (Rank Indicator). Channel State Information is a mechanism that a UE measures various radio channel quality and reports the result to the network. CSI report types are of two types: Periodic and Aperiodic. Aperiodic CSI has PUSCH (Physical Uplink Shared Channel) only.