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Spread spectrum security; pros and cons

Short answer

Spreading over a wide band forces a jammer to either disperse power or hit a small part that despreading corrects. The low power density hides the signal below noise, and without the code it cannot be intercepted. Advantages: jamming resistance, low detection probability, multipath tolerance, CDMA. Disadvantages: large bandwidth, complex synchronisation, near-far problem.

How can the use of spread spectrum technique provide security against jamming and interception? List the advantages and disadvantages of spread spectrum.

Security against jamming and interception

  • Jamming: a jammer puts strong noise in a narrow band to block communication. In spread spectrum the signal is spread over a very wide band, so a jammer must either spread its power over the whole band (so little power in each part, which is harmless) or hit only a small part of the band (which damages only a small fraction of the signal, repaired by despreading and error correction). The jammer would need a huge power. Processing gain also suppresses any narrow-band noise at the receiver after despreading.
  • Interception: the power of the spread signal is spread so thinly (power density below the noise floor) that it is hard to detect. Without knowing the secret PN code (hop sequence or chip sequence), an eavesdropper cannot despread it and sees only noise-like data. FHSS also hops so an interceptor hears only short random bursts.

Advantages

  • Resistance to jamming and interference.
  • Low probability of detection and interception.
  • Resistance to multipath fading.
  • Multiple users in one band (CDMA).
  • Privacy and precise ranging (GPS).

Disadvantages

  • Requires much larger bandwidth.
  • Complex hardware and exact code synchronisation.
  • Self-interference and near-far problem in multi-user systems.
  • Lower data rate for the bandwidth used.

✓ Answer checked by Claude Sonnet 5.5

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