The Design And Realization Of Muti-rate Modem Based On FPGA

Modem plays a very important role in communication system. With the development of Grand Scale Integration and digital signal processor the demand for multi-rate communications is increasing greatly. The key technology of variable spreading gain, used to make multi-rate compatible, is studied in this thesis, and a multi-rate modem based on low spreading factor is realized in FPGA. Currently, the modem has been successfully applied in the practical engineering.In the thesis, the techniques of multi-rate research status and research focus at home and abroad are firstly introduced. The difficulties in realizing the modem are analyzed, and the rudiments and development platform of SDR are summarized. The technical details of the multi-rate modem are also given. In order to capture the low spreading factor code and recover the carrier, a synchronization method, flywheel, is presented. Meanwhile, the parameters and stability of the carrier recovery loop are discussed. Then the flatform of system hardware based on the FPGA is introduced. Some key parts of the hardware and heir initialization are described. The performance test of the multi-rate modem was carried out, and the test results meet the design requirements.