dzoni_battery
Newbie level 1
Hi,
I'm trying to build pi/4 QPSK demodulator in software and I have some difficulties with timing recovery circuit . Inputs for my software are symbol rate, sampling rate and I/Q samples from quadrature demodulator ( A/D converter, Direct digital synthesizer and I/Q low pass FIR filter ) implemented in hardware. In software I’m using QPSK Costas loop for phase synchronization, modified for its new purpose. Modification consists of vector rotation for pi/4 angle for every second symbol, driven by timing circuitry, to achieve QPSK-like constellation. That is the reason why I need good timing recovery method, and, most of all, very good initial estimation of symbol timing before starting PLL. If someone can recommend me something that knows it’s going to do a very good job and maybe little explaines, please help.
I'm trying to build pi/4 QPSK demodulator in software and I have some difficulties with timing recovery circuit . Inputs for my software are symbol rate, sampling rate and I/Q samples from quadrature demodulator ( A/D converter, Direct digital synthesizer and I/Q low pass FIR filter ) implemented in hardware. In software I’m using QPSK Costas loop for phase synchronization, modified for its new purpose. Modification consists of vector rotation for pi/4 angle for every second symbol, driven by timing circuitry, to achieve QPSK-like constellation. That is the reason why I need good timing recovery method, and, most of all, very good initial estimation of symbol timing before starting PLL. If someone can recommend me something that knows it’s going to do a very good job and maybe little explaines, please help.