Automatic Gain Control in High speed WCDMA Terminals

Abstract: In this study, it is investigated how different parameters influence 16QAM modulation. The focus is on how different parameters in the Automatic Gain Control algorithm influence raw bit error rates, but other parameters such as frequency error and misplaced decision levels are also investigated. The goal is not to develop optimal parameter configurations, but to gain some understanding on what parameters that are of great importance. The simulations are made with several types of fading multi path channels as well as Additive White Gaussian Noise (AWGN) channels. The investigations are carried out through simulations in a simulation environment implemented in Matlab. From the simulations the conclusion is drawn that 16QAM is more sensitive to frequency errors than QPSK and that an important parameter in the AGC is the DC blocker bandwidths. The optimal AGC design with repsect to bit error rate depends on the type of channel model used, but it seems that a slower AGC design is preferred when compared to a faster one. The step resonse simulations indicate that there is no problem with using a fast AGC. The AGC seems to be more important at high signal to noise ratios because the fading become more visible in that case.