CQI: Estimation Over The Dowlink of OFDMA

Abstract

In this work, we analyze the problem of CQI measurements in the context of OFDMA which is the most probable candidate for DL of 3GPP-LTE. OFDMA will be employing link adaptation (adaptive coding and modulation, HARQ etc.) and frequency scheduling to mitigate the effects of inter-cell interference. These operations of AMC (Adaptive Modulation and Coding) and frequency scheduling will be performed on the basis of some feedback provided by the user to the base station. So our objective is to find some metric we can use as CQI feedback, measurement or estimation of this metric and proper schemes of feedback, over UL avoiding degradation of UL throughput. We establish the fact that effective SINR, which is geometric mean of the SINR over symbols of sub-frame, can work well as CQI. Now the problem comes out to be the estimation of SINR over OFDM symbols. So in this thesis, we analyze different SINR estimation algorithms and discuss their suitability for our particular case of DL OFDMA. In the end, we come up with the most suitable algorithm for estimating SINR. The performance of this algorithm is analyzed with DL OFDMA system.