Murata Electronics North America 910M Manual Do Utilizador

© 2000- 2004 Cirronet™ Inc 

Spread spectrum reduces the vulnerability of a radio system to interference from both 
jammers and multipath fading by distributing the transmitted signal over a larger region 
of the frequency band than would otherwise be necessary to send the information.  This 
allows the signal to be reconstructed even though part of it may be lost or corrupted in 
transit. 

 

 

 

 

 

Figure 1

Narrowband vs. spread spectrum in the presence of interference

 

 

The two primary approaches to spread spectrum are direct sequence (DS) and 
frequency hopping (FH), either of which can generally 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 pattern.  The ratio by 
which this modulating pattern exceeds the bit rate of the baseband 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.