Study On Technologies Of π/4-DQPSK Modulation And Demodulation Realized By FPGA

π/4-DQPSK(π/4 offset Differentially Encoded Quadrature Phase Shift Keying)modulation has the feathure of high spectrum utilization ratio, good spectrum specification, strong anti-multipath performance and so on. Therefore, the modem is widely used in the mobile communication and satellite communication.As the software radio theory and digital communication technology become more sophisticated, the realization of digital wireless communication system has become more and more widely. The task of the paper is to study theπ/4-DQPSK modem and realize it in the form of all-digital using FPGA technology. The main contents and work of this paper are:Firstly, the paper introduces the basic principle and structure of theπ/4-DQPSK modem, reasearches the key modules of the modem including the phase mapping, shaping filter, the entire multiple interpolation filter, direct digital frequency synthesizer, digital upward frequency conversion, digital down conversion, baseband differential demodulation and so on. It also builts the system simulation platform of theπ/4-DQPSK modem in MATLAB, verifies the feasibility of the designed system.Secondly, the paper emphasized reasearches the frequency estimation algorithm under large Doppler frequency offset, including arc cotangent frequency estimation algorithm and its simplified algorithm, frequency estimation algorithm based on FFT and its improved algorithm. The arc cotangent frequency estimation algorithm has simple structure, a small amount of calculation and is easy to implementation. The estimation range and estimation accuracy of FFT frequency offset estimator was mutually contradictory. In order to solve the problem, the improved FFT frequency estimation algorithm was proposed by the paper, which has large estimated range (up to ? Rs/ 2~Rs/2) and high estimated accuracy (up to±Rs/ 2N2). The paper also emphasized studies the bit synchronization algorithm of the modem, including Gardner algorithm and its simplified algorithm. And it realizes the simplified Gardner algorithm using FPGA technology.Finally, the paper implementsπ/4-DQPSK modem system in Quartus II using VHDL (Very High Speed Integrated Circuit Hardware Description Language) programming language. Then it designes and produces the hardware circuit in Protel 99, downloades the program to it, and completes the downloading of the program and the output of the signal. The measured waveform shows thatπ/4-DQPSK modem system can fully satisfy the design requirements and achieve the modem of transceiver correctly.