Effect of noise variance estimation on channel quality indicator in LTE systems

The channel quality indicator (CQI) is an important LTE parameter that is used to cope with the channel variations. The accuracy of the CQI calculation depends on the channel and the noise variance estimations. In this paper, we study the effect of the noise variance estimation on the CQI calculation. We assess the performance of a widely-used CQI algorithm, the mutual information effective SINR mapping (MIESM), using two different methods for the noise variance estimation. The first method is a cyclic-prefix (CP) (time) based estimation and the second one is a pilot (frequency) based estimation. It is shown that the CP-based method is more robust to the channel estimation error compared to the pilot-based one, and can provide more accurate results especially in the cases where the number of pilots are much less than the CP length (e.g. for small bandwidth). However, the pilot-based method is much more robust to the presence of interference signals in the LTE band, a common scenario that is a part of the LTE-standard conformance tests.