Calculation of the spatial preprocessing and link adaption feedback for 3GPP UMTS/LTE

This paper presents an efficient method for calculating the Precoding Matrix Indicator (PMI), Rank Indicator (RI) and Channel Quality Indicator (CQI) at a Long Term Evolution (LTE) User Equipment (UE). The indicators are required for spatial preprocessing and link adaption in the downlink of a 3GPP UMTS/LTE system. To reduce the computational burden for the UE, our method decomposes the problem into two separate steps, one of jointly evaluating the PMI and RI based on a mutual information metric and one of choosing the CQI value to achieve a given target Block Error Ratio (BLER) constraint. The performance of the method is evaluated utilizing an LTE downlink physical layer simulator. The influence of estimated channel knowledge on the feedback choice is investigated for Least Squares (LS) and Linear Minimum Mean Squared Error (LMMSE) channel estimators.