Time-hopping

Time-hopping (TH) is a communications signal technique which can be used to achieve anti-jamming (AJ) or low probability of intercept (LPI). It can also refer to pulse-position modulation, which in its simplest form employs 2^k discrete pulses (referring to the unique positions of the pulse within the transmission window) to transmit k bit(s) per pulse.

To achieve LPI, the transmission time is changed randomly by varying the period and duty cycle of the pulse (carrier) using a pseudo-random sequence. The transmitted signal will then have intermittent start and stop times. Although often used to form hybrid spread-spectrum (SS) systems, TH is strictly speaking a non-SS technique. Spreading of the spectrum is caused by other factors associated with TH, such as using pulses with low duty cycle having a wide frequency response. An example of hybrid SS is TH-FHSS or hybrid TDMA (time division multiple access).

• Spread spectrum
• Frequency-hopping spread spectrum
• Direct-sequence spread spectrum
• Ultra-wideband

• Frenzel, Louis E. (2001). Communication Electronics (3rd ed.). New York: McGraw Hill. ISBN 0-02-804837-7.

• "Time hopping and frequency hopping in ultrawideband systems"

• Channel access methods
• Wireless locating
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