Automatic gain control scheme for M-PAM receiver with precision-limited ADC

Abstract

In this paper, we study on the automatic gain control (AGC) scheme for pulse amplitude modulation (PAM) with low-precision analog-to-digital converters (ADCs). For M-PAM communication systems, we investigate the problem of AGC schemes under the assumption that low precision ADCs (e.g., 1–4 bits) are used at the receiver end. We adopt blind approach to estimate the amplitude of an unknown sequence by analyzing the distribution characteristics of corresponding quantized samples. For the fixed thresholds ADCs, and altering the gain to ADC input, we propose an algorithm based on ADC output's distribution-function to adjust the gain of the amplifier in front of the ADC. The sequence used in the proposed algorithm can be training sequence or the transmitted data symbols. Different from the existing solutions, our method doesn't use the dither signal for SNR increasing to achieve acceptable estimation performance. Thus, the complexity of the receiver can be reduced. Moreover we find that the NMSE performance of our algorithm can be better when SNR is larger. As a result, the proposed scheme can obtain better BER performance than the dither signal based schemes. Meanwhile we apply our AGC scheme to track the time-varying signal and achieve a good result as well.