Abstract: The current 3rd generation (3G) cellular wireless systems are evolving into 4th generation (4G).As a pathway to 4G, 3GPP developed Long Term Evolution (LTE).In terms of air interface techniques, LTE system uses OFDMA-based multicarrier modulation, MIMO techniques, and other advanced features to greatly improve the mobile wireless services.In this tutorial, we first survey the underlying techniques of the 4G systems such as OFDMA, SC-FDMA, MIMO, and fast multi-carrier resource scheduling.Then, we give technical overview of LTE and LTE-Advanced in detail.