Research And Digital Realization Of Shortwave Spread Spectrum Receiver

Spread spectrum technology has the great meanings on the military and public communication. At the same time, software radio develops so rapidly that it' s significant to study the digital realization of marine shortwave direct-spectrum system applying its concept and general hardware platform.in the paper it sets forth the spread spectrum' s theory, specifications, types, characteristics and m sequence' s properties, furthermore, the models of DS transmitter and receiver are given. The algorithms on the sampling, multi-velocity signal processing, digital orthogonal mixing frequency, demodulation of BPSK and synchronization of PN code are studied, in addition, it finishes the Kaiser and integral comb filters. The parameters of earth wave transmit, atmosphere noise, transmitter' s antenna efficiency is simulated, which provide the basis for the receiver' s technology specifications.Based on the specifications, DS-SS digital receiver is achieved including the front analog amplifier, A/D sampling, digital down converter (DDC), baseband signal processing and assistant circuits. Appling the software algorithms it achieves the mixing frequency, multi-order decimation and alias rejection filters. In the DSP it accomplishes the configuration of AD6620, data transmission and BPSK demodulation. Parallel boot mode of 16-bit is achieved so that the whole spread spectrum digital system is finished. CPLD completes the system' s clock control and coding. Communication interface with the computer is set in order to extend the application.