Spread-Spectrum Processing Gain & Jamming Margin

A direct-sequence spread-spectrum receiver despreads the wanted signal while spreading interference, giving a processing gain equal to the ratio of chip rate (spread bandwidth) to data rate. The jamming margin is how much stronger than the signal an interferer can be before the link fails, after allowing for the required Eb/N0 and implementation losses.

Equations & Parameters ▸

\(G_p = 10\log_{10}\dfrac{R_{\text{chip}}}{R_{\text{data}}} \qquad M_j = G_p - \left(\dfrac{E_b}{N_0}\right)_{\!\text{req}} - L_{\text{sys}}\)

R_chip	Chip rate (chip/s) — equal to the spread (RF) bandwidth for DSSS.
R_data	Information bit rate (bit/s).
(E_b/N₀)_req	Eb/N0 the demodulator needs for the target BER (dB).
L_sys	Implementation / system loss (dB), optional.
M_j	Jamming margin: how far above the signal a jammer can be while the link still closes.

References: R. L. Peterson, R. E. Ziemer & D. E. Borth, Introduction to Spread Spectrum Communications, Prentice Hall, 1995. · B. Sklar, Digital Communications, 2nd ed., Prentice Hall, 2001.

Inputs

Chip rate, R_chip

chip/s

Spread bandwidth

Data rate, R_data

bit/s

Information rate

Required Eb/N0 (optional)

Demod threshold

System loss, L_sys (optional)

Implementation loss

Results

Processing gain

G_p—

Spread factor—

Jamming

Jamming margin M_j—

Diagram

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