4G Long Term Evolution (LTE) mobile system adopts Adaptive Modulation and Coding (AMC) as a link adaption mechanism that is based on the User Equipment (UE) periodically reporting channel condition summarised through Channel Quality Indicator (CQI) which, in turn, is based on Signal-to-Interference-plus-Noise Ratio (SINR) and Reference Signal Received Power (RSRP). Although CQI has a predominant role in accurately assignment of radio resources, standards do not define how to compute CQI from SINR and RSRP, so that each UE manufacturer operates according to proprietary policies. The paper focuses on the efficient evaluation of the relationship between SINR, RSRP and CQI and also to assess how AMC affects LTE performance. To operate in a realist environment, measurements are carried out with a smartphone-based procedure.