Channel Quality Indicator Estimation for OFDMA Systems in the Downlink

This paper investigates the problem of channel quality indicator (CQI) estimation in the context of OFDMA systems in the downlink. The problem of CQI estimation is addressed for SINR-based CQI forms. In this paper, we present a technique for instantaneous SINR estimation which consists in using the channel estimator already present at the receiver to obtain the useful signal levels and signal regeneration (SR) estimator to get the level of interference plus noise. We show that SR estimator has an error floor caused by channel estimation errors, and then we introduce a compensation factor rho in order to remove this error floor. The compensation factor rho is defined as the ratio between the variance of channel estimation errors and the level of interference plus noise at the input of the channel estimator. Thanks to the compensation factor rho we achieve a gain of about 1 dB in term of RMSE for CQI estimation over a wide range of CQI values.