← Back

Spread Spectrum

CDMA - spreading signal across bandwidth for security and multiple access

Data: 1

Code: 1100101

Original Data Bit

Spreading Code (PN Sequence)

Spread Signal = Data ⊕ Code (XOR)

Received Signal (with noise)

Despread = Received × Code (Correlation)

Spectrum Comparison

How Spread Spectrum Works

Spreading: Multiply narrowband data by wideband pseudo-random code. This spreads energy across bandwidth.

Despreading: Multiply by same code at receiver. Signal energy concentrates; interference stays spread.

Processing Gain: Ratio of spread bandwidth to original bandwidth. Higher gain = better noise immunity.

CDMA: Multiple users share same spectrum with different codes. Codes must be orthogonal or near-orthogonal.

Applications: GPS, 3G cellular (CDMA2000, WCDMA), military comms, Bluetooth, Wi-Fi.