| Spread Spectrum (SS) communication is a kind of communication system with excellent performance, and has attracted wide attention and interest of researchers since it was born. This dissertation discusses the de-spreading and demodulation of the digital Direct Sequence (DS) BPSK receiver, which will be used in aircraft telemeter, with focus on the techniques of digital down-convert (DDC), fast acquisition and tracking of pseudo noise (PN) sequence, carrier synchronization and data demodulation etc. This dissertation designs a scheme of de-spread and demodulation about DS-BPSK signal, analyzes its feasibility through simulation, and finally implements it on FPGA. The main contents of the dissertation are as follows:The scheme of all digital DS-BPSK receiver is proposed based on software defined radio. This scheme is applicable for SS information frame telemeter using PN code in high dynamic environment.Combining orthogonal DDC with the spectrum shifting by undersapling, the new DDC scheme is brought forward to realize the translation intermediate frequency (IF) to baseband.The synchronization method of PN sequence for the need of fast acquisition and tracking in telemeter is presented. Considering acquisition time and complexity of hardware, phase searching simultaneously in muti-channel, is used in PN acquisition. Then non-coherent delay lock loop aided with carrier tracking, which has good performance of high dynamic range, is chosen to realize the PN tracking.The carrier synchronization scheme for big frequency offset is discussed, which frequency range is shrunk step by step. First, do the frequency searching of time-frequency domain until the synchronization of PN code is accomplished. Second, use FLL to track the residual frequency bias. At last PLL is adopted for correcting phase offset and demodulation.The whole scheme is implemented on FPGA concretely and skillfully. And the practical knowledge about the design and development of FPGA are also introduced. |
PDF Full Text Request