In wireless communications, channel state information (CSI) refers to known channel properties of a communication link. This information describes how a signal Multipath propagation|propagates from the transmitter to the receiver and represents the combined effect of, for example, scattering, fading, and power decay with distance. The CSI makes it possible to adapt transmissions to current channel conditions, which is crucial for achieving bit error rate|reliable communication with high Bit rate|data rates in MIMO|multiantenna systems.
CSI needs to be estimated at the receiver and usually quantization (signal processing)|quantized and feedback|fed back to the transmitter (although reverse-link estimation is possible in Time-division duplex|TDD systems). Therefore, the transmitter and receiver can have different CSI. The CSI at the transmitter and the CSI at the receiver are sometimes referred to as CSIT and CSIR, respectively.