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 2k
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).
*Frequency-hopping spread spectrum
*Direct-sequence spread spectrum
"Time hopping and frequency hopping in ultrawideband systems"
Category:Channel access methods