Spread Spectrum Communication Modulation And Demodulation Based On FPGA

Spread spectrum communication technology beginning in the1950s, with a stronganti-interference, confidentiality, higher band utilization and good capability of resistance tomultipath interference, so far is mainly used in mobile communication and military fields.QPSK (Quadrature Phase Shift Keying) digital modulation technology, has high spectrumefficiency, strong anti-interference ability, etc. FPGA (Field Programmable Gate Array)beginning in the1980s, has repeatedly programming modification, development tools,intelligent, good secrecy performance, powerful, short development cycle, small investment,can realize various complex logic operations, etc. High speed digital processing capacity ofFPGA combined with spread spectrum communication technique and technology of QPSK,toimprove the transmission reliability of communication system validity, confidentiality, andwill have a better protection.This paper studied the QPSK demodulation technology of channel and baseband PN code(spread spectrum code) tracking capture technology based on FPGA. In QPSK modulation thedigital frequency conversion technology are introduced. In QPSK demodulation the digitaldown conversion and carrier synchronization technology based on Costas loop are introduced.In PN code demodulation, introducing the serial and parallel hybrid acquisition scheme andtracking scheme based on door sooner or later.This design by QuartusII as a platform and matlab as an auxiliary design software, usingVerilog HDL hardware description language to carry on the design, Completed the CICextraction/interpolation filter, FIR low-pass filter, NCO digital-controlled oscillator, QPSKmodulation and demodulation, PN code modulation and demodulation of the FPGAdesign.And has carried on the Modelsim simulation test,finally downloaded to the FPGAdevice specific self-loop transmission test.