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Tactical Wireless Communications and Networks: Design Concepts and Challenges by George F. Elmasry

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2.6 Spread Spectrum Modulation

Spread spectrum modulation is an important area of interest when it comes to tactical wireless radios. This modulation technique was first used in tactical radios and later made available for commercial use. Generally, modulation techniques tend to minimize the bandwidth occupied by the modulated signal since the spectrum is probably the most important commodity in wireless communications. There are cases where a much wider spectrum is used (wider in comparison to the signal rate in symbol per second and can be in the order of hundreds or thousand time wider). With the use of a wider spectrum and proper modulation techniques, we can achieve a spectrum capacity close to that of orthogonal modulation. Multiple users share the spectrum in a given frequency range with no mutual interference using what is known as code division multiple access (CDMA). Spread spectrum is used for tactical radio and commercial wireless (3G air interface) for different reasons.

In tactical wireless communications, it has the following advantages:

1. Spreading the transmitter power means lower power spectral density and makes the signal less detectable by the enemy.
2. Spreading the signal makes it less vulnerable to enemy jamming.
3. A spread-spectrum signal is less sensitive to multipath interference.

Commercial wireless uses spread spectrum for reasons that include:

1. Lower power spectral density means less interference to narrow band signals using the same frequency ...

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