Design And Implementation Of Universal Modem

Modem is one of the most critical part of the communication system,the quality of the demodulation directly affects the quality of the communication system.With the development of communication technology,various modulation methods are emerging constantly.Modems gradually shift from traditional analog communication to digital communication.With the development of software radio technology in recent decades,the hardware platform can be controlled through software programming.Therefore,it is very necessary to design a digital modem capable of demodulating a variety of modulation schemes by using software radio technology.The purpose of this project is to study and implement various modulation schemes(QPSK,8PSK,16 APSK,16QAM,32 APSK,64APSK,64QAM)digital modems.1.The four common frequency estimation algorithm(Kay algorithm,Fitz algorithm,L & R algorithm,M&M algorithm)are simulated and analyzed.And the complexity of the algorithms is compared.According to the performance and complexity of the algorithms,the paper choose the algorithms which are suitable for the implementation of system.At the same time,the phase estimation algorithm(ML algorithm)based on the assist by the pilot is simulated and analyzed.2.The fine carrier phase synchronization of various modulation methods is studied.The structure of fine carrier phase synchronization and the phase error detector expressions of various modulation methods are given.The performance of fine carrier phase synchronization algorithm is simulated and analyzed for the 32 APSK and64APSK modulation.3.The paper carries on the realization and emulation verification to the modem.Firstly,the paper introduces the overall structure of modem,then using the hardware programming language of Verilog to design the realization of every module according to the characteristics of algorithms.And the modelsim simulations are performed on each module of modem.Finally,the platform of simulations and verifications for the entire modem is build.The paper compares the data of maltab fixed-point simulation and modelsim simulation,explain the correctness of the scheme.