12-06-2014, 04:27 PM
Time-hopping seminar
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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