SYSTEM AND METHOD FOR DEMODULATING DIGITAL COHERENT ENVELOPE OF FDMA SIGNAL

摘要

PROBLEM TO BE SOLVED: To provide a method for performing coherent detection and demodulation of an FDMA signal being the superimposition of a carrier that is subjected to amplitude modulation. SOLUTION: A digital signal processor is provided with an array of a special digital phase-locked loop (PLL), processes a received signal and extracts an envelope corresponding to each carrier. Each PLL responds to an error signal slowly and the loop maintains a phase even if the code of the amplitude value of the envelope suddenly changes. A down decimation technique is used to reduce a calculation load, which is achieved by applying a finite impulse response filter (FIR) about each frame only one time, and the vector of the tap value of the filter is multiplied by the frame only one time. Sine and cosine waveforms are digitally generated by solving a difference equation in the PLL in real time. It is possible to offer the automatic control of sine and cosine phases by generating a sine and a cosine in the PLL.