Research And Implementation Of AGC Technology For QAM Modulation Receiving Signal In Wireless Communication

When the wireless communication receiver receives millimeter wave signal,due to the influence of the physical channel,the received signal often changes greatly,which is not conducive to the receiver to complete the demodulation of the signal.In fact,it has long been pointed out in the literature that in the QAM signal receiver,the input end of the demodulator must have an automatic gain control(AGC)system to keep the average power of the QAM signal constant,otherwise the demodulated I and Q signals may be unbalanced,resulting in an increase in the bit error rate of the communication system.This paper is based on the development project of a millimeter wave receiver to carry out the research of automatic gain control technology in wireless communication.This paper studies the automatic gain control technology in wireless communication QAM receiver,which is mainly divided into four parts: the principle and technical index of AGC,the modeling and analysis of AGC scheme,the simulation and implementation of AGC scheme,and the experimental verification of the implementation results.In the process of designing AGC scheme,a logarithmic AGC loop with double error factors is proposed by referring to a large number of previous researches on AGC technology in the field of communication.The loop model of the scheme is not designed too complex,so as to avoid taking up too much system resources,increasing the complexity of the system operation and leading to long adjustment time in the process of implementing the scheme.In the simulation part of the scheme,the ideal input signal,i.e.sinusoidal signal with different amplitude,is used first,and then the 64 QAM signal with Gaussian white noise is input,and good output results are obtained.In the board experiment and verification part of the scheme,the experimental platform mainly includes RF transceiver chip and FPGA processor,because the experimental platform is the existing millimeter wave receiver products.The RF transceiver chip is responsible for receiving and converting RF signal to baseband signal.The chip can be configured as external AGC,or not to enable its AGC function.The AGC algorithm is implemented by FPGA processor,that is,internal AGC.FPGA processor not only needs to realize internal AGC function,but also contains other signal processing modules,so internal AGC can be well connected with subsequent modules.After testing,the AGC designed in this paper can complete the automatic gain control when receiving 64 QAM signal,its response time is less than 5?s,and the output dynamic range of baseband signal is less than 5d B,which meets the pre design requirements.The design idea can be used as a reference for engineers with relevant needs.