DNT500
2008 by RF Monolithics,
Inc.
2
M-0500-0000 Rev D
Figure1
Narrowband vs. spread spectrum in the presence of interference
1.2 Frequency Hopping versus Direct Sequence
The two primary approaches to spread spectrum are direct sequence spread spectrum
(DSSS) and frequency hopping spread spectrum (FHSS), either of which can gener-
ally be adapted to a given application. Direct sequence spread spectrum is produced
by multiplying the transmitted data stream by a much faster, noise-like repeating pat-
tern. The ratio by which this modulating pattern exceeds the bit rate of the base-band
data is called the processing gain, and is equal to the amount of rejection the system
affords against narrowband interference from multipath and jammers. Transmitting
the data signal as usual, but varying the carrier frequency rapidly according to a
pseudo-random pattern over a broad range of channels produces a frequency hopping
spectrum system.
Figure 2
Forms of spread spectrum
