Channel quality information

Channel quality information (CQI) is a part of channel status information (CSI). If the channel information is a scalar value such as $h$, general CQI is the power of $h$ divided by the power spectral density of the noise, i.e., $|h|^2/N_0$ when the noise spectral density is assumed to be $N_0$. On the other hand, if the channel information is represented by a vector such as $\mathbf{h}$, CQI is the norm of the channel vector divided by $N_0/\alpha$, i.e., $\alpha ||h||^2/N_0$, especially when open-loop transmit diversity transmission schemes are used where $\alpha$ the performance loss factor of the transmit diversity system.