Design And Implementation Of The If Digital Spread Spectrum Receiver

The traditional radio receiver depends on hardware greatly and the compatibility of signal is not good,the appearance of Soft Radio technology brings on the reformation of receiver.One of the conceptions is making the A/D conversion(ADC) closer to antenna the whole way, namely laying the ADC on the intermediate frequency(IF) or radio frequency(RF) signal processing block,converting IF analog signal even RF analog signal into digital signal. However, it is difficult to realize RF signal sampling becausing of the current technology level of the chip, the IF singnal sampling method is adopted at present.The primary content in this paper is the design and simulation of IF signal sampling DSSS receiver. At the beginning, the theory of DSSS and Soft Radio is introduced, and the receiver architecture according to the system characteristic is gave. The research focus on The receiver key technique: DDC, matched filter and frequency offset emendation. Firstly, choosing the sampling rate, NCO architecture and the design of FIR filter are introduced. Secondly, because the data format and the de-spread spectrum method are unique, synchronization signal check circuit is designed and de-spreading the signal. Lastly, the issue of carrier frequency offset emendation is discussed. In this part, the carrier frequency synchronous feedforward structure and feedback structure are introduced, on the basis of method, detailedly studying the frequency offset arithmetic which is based upon FFT. It analyse the correlation result on frequency field, improving the capture of PN code and working out the frequency offset emendation. It not only corrects defects of costas loop but also corrects defects of feedforward structure, because the synchronization time of the former is long and the latter is baroque. The arithmetic suits burst digital transmission.The whole system is simulated in MATLAB/SINLINK,including the functional simulation of every part and the performance analysis of algorithmic.The sinulation have validated the validity of system. Finally, the FPGA platform is designed, including choosing the FPGA chip, designing the circuit and turning the receiver into reality.