Spread Spectrum Modulation and Demodulation

An explanation about DSSS Spread Spectrum Modulation and Demodulation. In this video, Gregory explains the full topology of a Spread Spectrum demodulator, showing how the bitstream is recovered, how the code sequence is acquired, synchronized and carrier phase/offset is compensated.

Spread Spectrum modulation spreads the data signal in a larger bandwidth, using a PRBS sequence, with statistical noise like characteristics.

The process of demodulation needs precise synchronization of the local code sequence. The code phase is first acquired, in the acquisition step, and then tracked, aligning the local PRBS/LFSR using an early/late correlation topology.

Carrier phase/offset is compensated using phasor rotation in a Costas Loop like topology. The carrier phase/offset NCO is controlled by a PI Controller fed from an error detector, that forces corrections to align the constellation to the correct position.

The continuous recovered bitstream/IQ constellation can now be sampled, to determine the data symbol. A NCO running at the baudrate and a Gardner Time Error Detector in conjunction with a PI controller corrects the sampling interval/point.

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Learn about FSK Modulation and Demodulation: https://youtu.be/KGP_x9930Tc

A related video about Clock Recovery PLL: https://youtu.be/HcYFFlsSLrg

Learn how a Costas Loop demodulator works for PSK modulations: https://youtu.be/Zwj63BWtRok

Article about how DFT works: https://gusbertianalog.com/understanding-the-fourier-series-a-statistical-point-of-view/

00:20 - Introduction 02:20 - Modulation details 03:30 - Theoretical Spread Spectrum receiver 05:38 - Real quadrature demodulator 06:20 - DSSS signal waveforms 08:28 - Code Acquisition 11:14 - How the correlator works 12:30 - Code Tracking 15:20 - Simulations 19:15 - Carrier phase/offset compensation 21:45 - Time recovery/synchronization

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