Analytical Approximations of EESM Effective SNR Distribution Using Pearson System

Link adaptation is an important technique in achieving good system spectral efficiency. However, due to the effect of frequency selective fading, the SNRs of adjacent sub-carriers in an OFDMA system can potentially be different. To provide a reasonable signalling overhead, the smallest unit of channel quality feedback is represented in terms of a group of sub-carrier SNRs, or effective SNR for short. The knowledge of the PDF or CDF of the effective SNR can be very useful in performance analysis of systems involving frequency selective feedback. However, closed-form expressions of these statistical quantities are very difficult to obtained. In this paper, we propose to approximate these quantities using the method of Pearson system. Numerical results show that the proposed approximation is very accurate.