Research And Implementation Of Digital Down Converter Supporting Fast Frequency Hopping

In the face of increasingly complex communication environment,modern wireless communication requires communication systems to have better versatility and anti-jamming.Software radio technology makes communication systems have good versatility,so it plays an increasingly important role in modern wireless communications,and is often used in military cooperative operations and civil mobile communications.The communication system using fast frequency hopping technology has stronger anti-jamming ability,so fast frequency hopping technology is widely used in wireless communication.Digital down converter is an important part to ensure the universality of software radio hardware platform.This paper focuses on the research of digital down converter which can be used in RF direct sampling receiver and broadband IF receiver,and supports fast frequency hopping.The mixing module and decimation filter module in digital down converter are designed in detail.The flexibility of digital down converter is improved while supporting fast frequency hopping.The main contents and methods of this paper are as follows:Fast frequency hopping requires short frequency switching time,high precision and wide frequency hopping bandwidth of carrier signal source.In order to meet these requirements,an improved numerical control oscillator based on three-step rotation CORDIC algorithm is proposed in the design of mixing module.The frequency switching time of the numerical control oscillator is further shortened and the accuracy is improved by using the mode of parallel operation of multiple phase accumulators and the method of compensating the fractional part of the frequency control word.In addition,the multiplier is replaced by adder to optimize the mixer module of multiplier structure,which saves hardware resources..For the decimation filter module,FIR filters with configurable decimation coefficients are designed.Various working modes meet the needs of different users and improve the flexibility of digital down converter.Multiphase decomposition technology is used to reduce the pressure of the filter operation speed.Time-sharing multiplier and adder technology is used to realize the filter to reduce hardware resource consumption.Adder tree technology is used to improve the system clock working frequency.Finally,an improved digital down converter supporting fast frequency hopping is implemented with the hardware description language Verilog.Based on Modelsim and MATLAB tools,the correctness of its functions is verified.The resources and timing are evaluated with Design Compiler,a logic synthesis tool.The results show that the maximum operating frequency of the system clock is 1.176 GHz and the area is 87227 square microns.The digital down converter module designed and implemented in this paper has better flexibility and versatility,and can be widely used in frequency hopping system after expansion.It has certain research and application value.