Which spread spectrum technique multiplies the original data signal with a pseudo-random noise spreading code to protect against interference?

Which spread spectrum technique multiplies the original data signal with a pseudo-random noise spreading code to protect against interference?

• A. Direct-Sequence Spread Spectrum (DSSS)
• B. FH-CDMA
• C. 802.11e
• D. 802.11g

Answer: (A)

Direct-Sequence Spread Spectrum multiplies the data by a pseudo-random noise spreading code to spread the signal over a wider bandwidth. This PN code lookup at the transmitter creates a signal that looks like noise unless the same code is used to despread at the receiver, which concentrates the energy back to the original data and makes the transmission more resistant to interference and narrowband noise. The idea is to hide the signal in a wider spectrum and recover it by matching the spreading code, improving interference tolerance and potentially enabling multiple users to share the channel through code division. The other options don’t use this multiplication-with-a-PN-code approach: frequency-hopping CDMA spreads the signal by hopping across frequencies rather than spreading with a PN code; 802.11e and 802.11g are standards (QoS features and OFDM-based signaling, respectively) rather than spread-spectrum techniques.

Direct-Sequence Spread Spectrum multiplies the data by a pseudo-random noise spreading code to spread the signal over a wider bandwidth. This PN code lookup at the transmitter creates a signal that looks like noise unless the same code is used to despread at the receiver, which concentrates the energy back to the original data and makes the transmission more resistant to interference and narrowband noise. The idea is to hide the signal in a wider spectrum and recover it by matching the spreading code, improving interference tolerance and potentially enabling multiple users to share the channel through code division.

The other options don’t use this multiplication-with-a-PN-code approach: frequency-hopping CDMA spreads the signal by hopping across frequencies rather than spreading with a PN code; 802.11e and 802.11g are standards (QoS features and OFDM-based signaling, respectively) rather than spread-spectrum techniques.