Study Of High-speed Digital Coherent Demodulation

The topic of this paper comes from the demand for high-speed data transferring and equipment digitalization in project practice. It aims at verifying the feasibility of digital coherent demodulation in real project environment, that is, whether the DSP chips and digital techniques available can satisfy its complexity. And, by comparing the error rate performance under the ideal condition of known carrier frequency, and phase, the performance of digital coherent demodulation with Doppler frequency shift is checked.In the paper, the digital technique of frequency and phase shift estimation and elimination is provided. By integrating the both parts of circuit together, digital coherent demodulation of base data with frequency and phase shift is implemented. Employed in project, the dependence on the analog carrier extraction circuit in coherent communication is removed; a frequency-constant local oscillator is used instead. Therefore, the demand for high frequency stability of transmitter and receiver is decreased.Applying the theory of detection and estimation and the theory of multi-level PSK (QDPSK), modeling and simulation of digital coherent demodulation was carried out. The result of simulation in MATLAB indicates that the model satisfies the demand for digital coherent demodulation in real world and is realizable by high-speed EPLD and DSP chips.