Direct Sequence Spread Spectrum Visualizer

Background: Direct-Sequence Spread Spectrum (DSSS) multiplies a narrowband data signal by a much higher-rate pseudo-random chip sequence c(t) generated from a PN (Pseudo-Noise) code, spreading its bandwidth by the processing gain L_c = T_b/T_c (chips per bit, where T_b = bit duration and T_c = chip duration). At the receiver, correlating (despreading) with that same code collapses the desired signal back to its original narrow bandwidth, while any narrowband jammer or interferer — which was never spread at the transmitter — gets smeared across the full spread bandwidth by that same correlation, diluting its power spectral density by roughly the same factor L_c. This is why DSSS resists narrowband jamming: the achievable E_b/N₀ (energy per bit over noise power spectral density, in dB) improves by the processing gain (and any additional coding gain), and the jamming margin quantifies, in dB, how much stronger a jammer can be than the desired signal (J/S, jammer-to-signal ratio) before the link's bit error rate (BER) exceeds its target.

Description of This Web Application: Configure the DSSS processing gain (chips per bit), bit rate, coding gain, and target bit error rate, then attack the link with a narrowband jammer whose power relative to the signal (J/S) you control directly. Watch the transmit/despread waveforms and spectra, a live BER-vs-J/S curve with the jamming margin marked, and a real-time link status that flips from OK to jammed once J/S is pushed past the margin. A third tab lets you generate your own maximal-length (m-sequence) PN code from an LFSR (Linear Feedback Shift Register) and inspect its autocorrelation, showing why pseudo-random codes look like noise to everyone except the intended receiver. You will come away understanding how processing gain trades bandwidth for jamming resistance, and why increasing L_c (or adding coding gain) directly increases the jamming margin.