TABLE OF CONTENTS Spread spectrum signals are subject to the same jamming equations as any other signals, but the ability of the cooperative receiver to collapse the spectrum gives it a "processing gain" that reduces the effectiveness of the jamming. In general, the processing gain advantage is the same as the spreading ratio (i.e., the transmission bandwidth/the information bandwidth). It is also defined (in DSSS signals) as the code rate (used for spreading) divided by the data rate. Another applicable term is "jamming margin," which is defined by the following formula.
M J = G p L SYS SNR OUT
where
M J= the jamming margin (in decibels);
G P = the processing gain (in decibels);
L SYS = the system losses (in decibels);
SNR OUT= the required output SNR.
It is important to remember that spread spectrum signals almost always carry their information in digital form. Thus, the considerations presented in Section 5.8.4 apply to any effort to jam spread spectrum signals of any kind. This enables some techniques which help overcome the jamming protection afforded by spectrum spreading.
If a narrow-bandwidth jamming signal is applied to a frequency-hopping receiver, it will be received only when the receiver happens to hop to that frequency. This will cause the jamming effectiveness to be significantly reduced. For example, if a CW jamming signal is applied to a Jaguar V receiver (which hops randomly over a maximum of...
