Narrow-band versus spread spectrum transmission
Figure 1.1.1
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 generally be adapted to a given application. Direct sequence spread spec-
trum is produced by multiplying the transmitted data stream by a much faster, noise-like repeating pattern. 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 narrow-band 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.
Forms of spread spectrum - direct sequence and frequency hopping
Figure 1.1.2
One disadvantage of direct sequence systems is that due to design issues related to broadband transmitters and receiv-
ers, they generally employ only a minimal amount of spreading, often no more than the minimum required by the regulat-
ing agencies. For this reason, the ability of DSSS systems to overcome fading and in-band jammers is relatively weak. By
contrast, FHSS systems are capable of hopping throughout the entire band, statistically reducing the chances that a
transmission will be affected by fading or interference.
©2012 by Murata Electronics N.A., Inc.
DNT90M Integration Guide (2012/09/17)
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