Wideband RF Front-End Design And Realization Based OFDM Wireless Communication

With the rapid development of the information age,communication technology is particularly important in the contemporary,especially with the increasing demand for wireless communications.Wireless communication technology has become an indispensable part of the communication field.The development of OFDM technology has further improved the performance of data transmission rate,band utilization and anti-multipath effect in wireless communication.OFDM technology is mainly used in DVB,WLAN,mobile communications,ADSL,etc.There is no mature communication platform and RF front-end of the OFDM modulation system in the lower frequency 400 MHz ~ 500 MHz band.These signals have some characteristics such as longer wavelengths,easier to diffuse.It is suitable for communication in the jungle,mountains,blocking environment,and military communications.In order to make full use of the spectrum resources efficiently and solve the problem of longer wavelength,non-line-of-sight transmission and multi-path effect in this frequency band,this paper studies the RF front-end of OFDM-based broadband wireless communication system.The main results are as follows:1.Aiming at the problems of gain jitter and frequent adjustment gain in the control of peak-to-average ratio signal,a novel AGC algorithm and circuit for high peak-to-average ratio signal is proposed.First of all,according to the size of the gain per level of the amplifier circuit,and then the gain can be controlled for each power segmentation of the input signal.The circuit is mainly composed of fixed gain amplifier,variable attenuator and power detection chip.The measured results show that the AGC circuit can realize fast and accurate adjustment of the gain of each frame,and the input dynamic range is up to 90 dB,which can meet the fast adjustment of the PAPR.2.Considering the work of the circuit in the TDD mode,in order to reduce power consumption,it needs to load and unload the power circuit board for short-distance communication and long-distance communication.Two-stage switching circuits are designed for low-power signal and high-power signal.It achieves the function of low-power signal transceiver switching by using RF board alone.It also achieves the function of high-power signal transceiver by switching using both RF board and power amplifier board.3.The nonlinearity and stability of the power amplifier are analyzed.Aiming at the problem that the average power of the output signal is small and the efficiency is low when the PAPR signal is output,a design and implementation method of OFDM signal linear power amplifier in UHF band is proposed.By ADS simulation software,using the method of load pull and source pull,we simulate the best input impedance and output impedance,and get the best static DC operating point.The input and output matching circuits of the power amplifier are designed by using coaxial line balun.Based on the efficiency and linearity,an UHF band linear power amplifier is designed for high peak-to-average signal.Simulation and test results show that the transmit circuit can support OFDM signal transmission with peak-to-average power ratio of 7 ~ 8dB in the 400 MHz ~ 500 MHz frequency band,and the peak power can reach 42 dBm.