Study Of Direct Sequence Spread Spectrum Receiver Base On Software Radio

As the emergence of the multi-criterion and multi-mode in the radio communication, the increasing need for co-operation and the lack of radio spectrum resource, traditional radio communication can not satisfy the need of development. The software radio technology put forward a feasible way to solve it, and become a focus. This dissertation mainly studies the application of the software radio technology in the direct sequence spread spectrum (DSSS) receiver.Firstly, the concept of the software radio and its characteristic is introduced, and the way to realize it is analyzed. DSP is used to process the baseband signal, including demodulation, decode, the adaptive equilibrium, the frame adjustment etc. FPGA is used to design digital up/down converter and sampling filter for its flexibility and fast processing. The algorithm structure of FPGA and the way to solve the limitation of FPGA are discussed additionally.Secondly, the mathematic expression of DSSS receiver and its processing gain and the characteristic of the PN code are discussed. The spread spectrum communication has advantages of anti-noise, anti-interaction and nice secrecy for the noise characteristic of PN sequence. The ways based on the PN sequence's self-correlation and co-correlation to synchronize are compared. Digital matched filter (DMF) is chose because it can greatly reduce the time of acquisition; furthermore, the tapped parallel design can cut down the demand for hardware.Finally, the scheme of the spread spectrum receiver based on the software radio is proposed. After the character between the radio frequency (RF) sampling receiver and the intermediate frequency (IF) sampling receiver is compared, the later is selected. In this scheme, the super-heterodyne which get proper A/D sampling rate through choosing a proper frequency and bandwidth is used in the front analog pre-processing.The analog filter is replaced by digital filter after A/D converter to improve the filter's range and the system's flexibility. The baseband design is based on modularization and different functional circuit is implemented in different module.The whole system is simulated in Simulink. The functions include signal source designing, spread spectrum and de-spread spectrum designing, general demodulation designing and sampling and judging designing.' Through the experiment, the result is desirable.