A Two-stage Digital AGC Scheme with Diversity Selection for Frame-based OFDM Systems

Abstract

This paper addresses a digital automatic gain control (AGC) strategy for frame-based orthogonal frequency-division multiplexing (OFDM) systems. Two stages of gain adjustment are adopted to adjust gain accurately and rapidly. Magnitude level of received signal is calculated over short and long period in two stages, respectively. Appropriate volumes of gain adjustment are then obtained by subtracting the estimated levels from the desired level of ADC. Next, digital volumes of gain adjustment are converted into analog control signals for variable gain amplifiers. Short stage deals with various situations as well as coarse gain adjustment. Long stage adjusts gain accurately with no more than 4 % inaccuracy of the desired level. The proposed digital AGC approach help raise SNR of received signals, enable subsequent receiver algorithms to operate efficiently with the robust signals. Additionally, the proposed approach can be easily implemented in conventional CMOS technology