Differentiate direct-sequence spread spectrum (DSSS) and frequency-hopping spread spectrum (FHSS) in SEW applications.

• A. DSSS spreads with a PN code; FHSS rapidly changes carrier frequency to avoid jamming
• B. DSSS and FHSS are identical in interference resistance
• C. FHSS uses PN code spreading; DSSS uses frequency hopping
• D. DSSS is slower and more jam-prone than FHSS

Answer: (A)

The key idea here is how each spread-spectrum method makes the signal look different to a potential jammer and how that helps it survive interference. In direct-sequence spread spectrum, the data are multiplied by a high-rate pseudo-random code, turning each data bit into a long sequence of chips. This spreads the signal’s energy across a wide bandwidth. The receiver that knows the same code can correlate to recover the data, and that correlation provides a processing gain that helps suppress interference and noise. In frequency-hopping spread spectrum, the transmitter rapidly changes its carrier frequency according to a hopping pattern and dwells briefly on each channel. The signal’s energy stays on the current frequency, but it hops across frequencies so a jammer has a harder time following and jamming every part of the spectrum.

In SEW contexts, this matters because narrowband jamming can be problematic, but DSSS resists it by spreading energy over a wide band, while FHSS resists it by moving away from jammed frequencies. The combination of PN-code spreading for DSSS and rapid frequency changes for FHSS is what makes the statement describing both mechanisms correct.

The other options mix up which technique uses PN code spreading versus frequency hopping, or make broad claims about interference resistance that don’t hold universally, so they don’t capture the fundamental distinction as clearly.