A Fast Automatic Gain Control Scheme for Initial Cell Search in TD-LTE Advanced

In this paper, we propose a fast automatic gain control (AGC) scheme for initial cell search in time division duplex (TD) long term evolution (LTE) advanced system. Since the received signal has a large signal power difference between uplink and downlink in TDD systems, conventional AGC scheme can not sufficiently adjust the AGC gain because the AGC gain does not converge fast enough to properly respond. Moreover, before UE is synchronized to eNodeB, UE is blind for the timing of eNodeB. So it´s impossible for UE to distinguish between own power and interfering powers. The initial AGC acquisition cannot be achieved within one time power measurement period. 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 a fast AGC scheme based on analogue output gain and fast unsynchronized AGC mode, which can not only effectively increase convergence speed of the AGC gain but also maintain the stability of AGC operation in TD-LTE advanced system. Simulation in variance channel environments showed that the proposed scheme can obtain a good behavior in terms of convergence speed for TD-LTE advanced system and verify that it is attractive and suitable for implementation with stable operation. So that the proposed scheme can achieve the requirement of TD-LTE advanced system and the purpose of rapid initial cell search.