| Frequency hopping communication has been widely applied in every field of communication, because of its outstanding anti-interference and low interception. Combined with M-ary soft spread spectrum, the anti-interference and concealment are improved. With the development of jamming technique, frequency hopping needs wider bandwidth and faster hopping rate. A point-to-point burst wideband communication system based on high speed baseband frequency hopping and high order M-ary soft spread spectrum is studied in this paper, the system has characteristics of concealment, wide band, anti-interference and high gain. The work in the paper includes:1. The overall scheme design of the transmitter and receiver is given. Emphasis is focus on the design and Implementation of corresponding modules, the chip selection of FPGA, AD and DA is completed.2. The FPGA design and implementation of baseband processing modules of the transmitter are completed, including the module of synchronous head, M-ary soft spread spectrum, scrambling, high speed waveform shaping and frequency hopping. The coordinate DDS technique is applied for high speed frequency hopping over a wide range of frequency, the bandwidth is 300 MHz and hopping rate is 19.5k hop/s.3. The FPGA design and implementation of the long code(the length is 16376 and the chip rate is 40Mbps) real-time capture is completed. The PMF-FFT algorithm is used in the capture. An improved PMF structure is designed to reduce resources consumption, and the parallel pipeline structure is applied to 64-points FFT.4. The FPGA design and implementation of the rest modules of the receiver is completed, including high speed de-hopping, 256-ary soft de-spread spectrum, tracking and interface module. According to the complexity problem of using correlators, cyclic correlation algorithm is applied to de-spread, and the synchronization tracking is realized by early-late loop to adjust the sample time of data. |
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