Automatic gain control for multi carrier in OFDM systems

This paper presents automatic gain control (AGC) algorithm in wireless orthogonal frequency division multiplexing (OFDM) system using carrier aggregation such as 3G-LTE. When analog signal of multiple frequency bands is converted to digital signal by analog to digital converter (ADC), proposed algorithm controls each band gain effectively. We first analyze the method of AGC using carrier aggregation in general OFDM system such as 3G-LTE. The analysis will show that the gain value is unstable because of wireless channel status or presence of packet or difference with losses for radio frequency (RF) front end in each band. This unstable fluctuation of gain is generated by the variation of received signal power that varies with channel status or quantity of received packet. We show how proposed algorithm can effectively control the gain value in carrier aggregation environments. Results of simulation show that the utilization of proposed algorithm can calculate the optimal gain value. As a result, proposed AGC algorithm can increase bit resolution of received signal because optimal gain values are calculated in each aggregation band. Especially, received signal can be easily saturated in ADC input because OFDM system or 16-QAM and 64-QAM modulation schemes for high data rate transmission have the characteristic of high peak to average power ratio (PAPR), therefore proposed AGC algorithm supports to keep system performance stable in carrier aggregation environments.