Explanation: Spread-spectrum communication intentionally spreads a signal's energy over a much wider bandwidth than necessary for the information content alone. This is achieved by modulating the carrier with a pseudo-random noise (PN) code (Direct Sequence Spread Spectrum - DSSS) or by rapidly changing the carrier's frequency in a pre-determined hopping pattern (Frequency Hopping Spread Spectrum - FHSS). Both methods utilize a specific, pre-determined sequence to vary the RF carrier, making the signal robust against interference and difficult to detect or jam, fulfilling the description perfectly. AMTOR and SITOR are specific, relatively narrow-band digital communication modes, primarily for text, utilizing error correction, not wide-bandwidth spreading techniques. "Time-domain frequency modulation" is not a standard or meaningful term in radio theory; frequency modulation naturally occurs in the time domain.