Benefits of Spread Spectrum

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Benefits of Spread Spectrum [Copy link]

Anti-interference and anti-blocking performance

Spread spectrum technology brings many benefits, and anti-interference characteristics are the most important advantages. Because interfering and blocking signals do not contain the spreading factor, they are suppressed. After despreading, only the desired signal containing the spreading factor will appear in the receiver. As shown in Figure 5.



If the interfering signal (narrowband or wideband) does not include the spreading factor, its effect can be ignored after despreading. This suppression capability also works on other spread spectrum signals that do not have the correct spreading factor. It is precisely because of this that spread spectrum communication allows different users to share the same frequency band (such as CDMA). Note that spread spectrum is a wideband technology, but wideband technology is not spread spectrum, and wideband technology does not necessarily include spread spectrum technology.

Signal interception prevention

Signal interception prevention is the second advantage obtained by spread spectrum. Because unauthorized users do not know the spreading factor that spreads the original signal, they cannot decode it. Without the correct spreading factor, the spread spectrum signal is equivalent to noise or interference (of course, if the spreading factor is very short, it can be cracked using scanning methods). Fortunately, spread spectrum communications allow the signal power to be below the noise floor because the spreading process reduces the spectral density, see Figure 6 (same total energy but spread across the entire frequency domain). This allows the information to be hidden, an effect that is a hallmark of Direct Sequence Spread Spectrum (DSSS) (DSSS is described in more detail later). Other receivers cannot resolve this transmission, and the only effect on them is a slight increase in total noise power!



Wireless channels often have multipath propagation effects, where there is more than one path from the transmitter to the receiver (Figure 7). These paths are caused by reflections or refractions through the air and reflections from the ground or objects such as buildings.