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In this paper, we propose a fast AGC (Automatic Gain Control) scheme for 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) TDD (Time Division Duplex) system. Since the received signal has a large signal power difference between uplink and downlink subframe in wireless communication systems using a TDD scheme, conventional AGC scheme cannot sufficiently adjust the AGC gain because the AGC gain cannot converge fast enough to properly respond. Therefore, conventional AGC scheme leads to increased AGC gain variation, and the received signal will be attenuated by large AGC gain variation. To overcome this limitation, we propose an AGC scheme based on the average amplitude ratio calculation which can not only effectively increase convergence speed of the AGC gain but also maintain the stability of AGC operation in LTE TDD system. By using extensive computer simulation in various channel environments, we show that the proposed method can obtain a good behavior in terms of convergence speed for LTE TDD system and verify that the proposed method is attractive and suitable for implementation with stable operation.